JWST image of the spiral galaxy NGC 628

Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on BlueSky for more coverage. The usual posting schedule for AAS Nova will resume on January 16th.

Table of Contents:

Committee on Astronomy and Public Policy Plenary Lecture: Lia Epperson (American University – Washington College of Law) (by Briley Lewis)

The final day of AAS 243 began with a plenary on an important topic: what the recent Supreme Court decisions on the use of race in college admissions mean for us as educators. In these cases, a group called Students for Fair Admissions (SFFA) challenged Harvard University and University of North Carolina (UNC) on their race-based considerations in admissions.

Epperson began by saying, “In an era where sometimes the pursuit of knowledge is maybe less appreciated than we would have liked as educators, I think it’s important for all of us to really understand the history of how we got to this moment.” Before diving into the details of the current cases, she provided an overview of how race, education, and affirmative action have been intertwined in the history of US law.

Race is embedded in the US Constitution (with the three-fifths, importation, and fugitive slave clauses), clearly indicating that our country’s founding document cared about “embedding a racial hierarchy,” said Epperson. This initial founding law has had “ripple effects on education and access to education” throughout US history, she added.

The first landmark case on education and race was Sweatt vs. Painter in 1950, when a Black student challenged a Texas law school. The Supreme Court decided that denying admission denied the student “standing in the community, traditions, and prestige customarily accorded to white students.” This ruling made clear that diversity and inclusion were to be considered a fundamental part of higher education.

Soon after, in 1954, the famous Brown vs. Board of Education ruling was issued, establishing separate education as inherently unequal. The term “affirmative action” then appeared in 1961 — not as a Supreme Court ruling or law specific to education, but from an executive order from President Kennedy initially intended for employment and contracting. The order stated that “government contractors may take affirmative action” to ensure treatment is not racially divided.

Forty years of legal precedent thereafter solidified the importance of race in holistic admissions processes, citing the benefits to democracy and pathways to leadership provided by education. Three crucial cases in this precedent were Bakke vs. Regents of UC Davis (1978), Grutter v. Bollinger and Gratz v. Bollinger (2003), and Fisher v. Texas I and II (2003, 2006). Research on K-12 schools has also shown that diverse schools improve students’ critical thinking skills, increase their civic engagement, and lead to higher graduation rates.

The Harvard case was the first to challenge race-conscious admissions, at an institution that excluded people of color for 85% of its 400-year history. UNC was founded in 1789 to serve the children of slave owners and didn’t admit their first Black student until 1951 (and even then, it was only due to a federal court order).

The questions posed before the court in these two contemporary cases were the following: Does Harvard violate Title IX by discriminating against Asian Americans? Do these schools fail to use race-neutral alternatives? Do they use race as more than just a factor to boost applicants?

Lower court decisions upheld the precedent supporting race-conscious admissions, yet the Supreme Court changed tack. In a decision that Judge Ketanji Brown Jackson described as defying “law, history, logic, and justice,” the court cited that there was no compelling interest to continue affirmative action (considering diversity only a “commendable goal”), claimed that affirmative action relied on racial stereotypes, and that there was no clear end in time for affirmative action as described in the past.

Epperson clearly described what colleges may and may not do in the wake of this decision, and factors the court did not address. Colleges may design their missions as they see fit, and they may include qualities from student experiences based on race. The decision did not address scholarships, financial aid, recruitment, retention, pathway programs, employment, or DEIA programs — only admissions. It also does not affect employment, which is covered by Title VII of the Civil Rights Act.

Additionally, colleges are still allowed other forms of affirmative action that universities use to shape their student population. Legacy admissions are still legal, and often biased towards white students; for example, Princeton legacy applicants have nearly a 30% success rate in admissions, while everyone else has a less than 5% shot. Similarly, colleges are allowed to consider major donors, demographic/regional preferences, socioeconomic status, and athletes. Shockingly, only 11% of athletes would be admitted without this bonus factor in their favor.

In the wake of this decision, SFFA is instigating further litigation, including a challenge to a prestigious high school magnet program focused on diversity, to fellowship and grant programs aimed at increasing diversity, and to West Point (because the original court decision didn’t apply to military academies). Epperson also highlighted ongoing efforts to counter these efforts and increase diversity in university admissions: targeted recruitment and retention, a more holistic admissions process, elimination of other forms of affirmative action (e.g., legacy), elimination of college entrance exam requirements, and legislation to further diversity.

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Press Conference: High-Energy Universe (by Mark Popinchalk)

It’s the last day of AAS, and while attendees might have low energy, this press conference was full of high-energy (astrophysics)!

Evidence of a Relic Active Galactic Nucleus Eruption (Press release)

The press conference started with Kimberly Weaver (NASA Goddard SFC) telling us how XMM Newton found a relic of an eruption from an active galaxy! Active galactic nuclei (AGN) are the centers of galaxies with a supermassive black hole accreting a hot disk of material. This produces lots of energy, and it can even produce high-powered jets, such as the AGN in Messier 87.

The team wanted to understand how AGN may affect star formation and power galactic outflows. All this high energy and moving matter should have a significant effect on galaxy evolution, and it was expected that one could trace previous nuclear activity.

So the researchers used ESA’s XMM Newton to look at NGC 4945. NGC 4945 is a spiral galaxy, also classified as a starburst due to its recent star formation. XMM has high sensitivity and a wide field of view. With just one observation they could image the entire galaxy.

Using their data, they saw that high-energy X-rays were outlining a huge clump of cold gas, 32,000 light-years long! But there were clearly some things in the way of the gas, such as individual stars and the light from the AGN itself. So they took further images using NASA’s Chandra X-ray Observatory. Using these observations they could remove the intervening features and still see a huge amount of cold gas.

Slide depicting the relic signature. The bullet points read, jet drove into the galaxy disk, cold gas is a fossil of that activity, we detect the relic signature because high-energy X-rays travel through the disk.

A slide from the press conference of Kimberly Weaver showing cold gas in a distant galaxy.

The gas lined up with other observations suggesting a strong collimated outflow of material. The team thinks that 5 million years ago, jets from the AGN weren’t aimed out into space like they are in Messier 87, but instead smashed into the rest of the galaxy! Theory says that once they smash into the thing, the jets then disappear. So what we have leftover is a relic signature of how the jet drove in and left behind the cold gas clouds as a fossil of that activity.

Unveiling the Most Promising Formation Channel of Fast Radio Bursts Using Local Universe Bursts (Press release)

Next up were Aaron Pearlman (McGill University) and Mohit Bhardwaj (Carnegie Mellon University), who were presenting the evidence for a potential dominant formation channel of fast radio bursts (FRBs). FRBs are bright radio pulses of millisecond duration. What causes them is unknown, but the source must be very powerful, as the signals travel between galaxies. We know this because as radio waves move through intervening material, the signal disperses, and the amount of dispersion in FRB signals implies that they come from outside the galaxy.

But what causes them? And can there be multiple formation channels? The researchers used the CHIME radio telescope. Using it, they are able to find roughly 100 new FRBs per month. Using the telescope they can identify the location of the FRBs within 1 arcmin.

Using their previous database, they associated four of the FRBs to nearby spiral galaxies. Then they looked at other local-universe FRB sources that were associated with a galaxy, and saw that the sources are spiral galaxies.

Now that they had spiral galaxies as a clue, they could rule out many of the proposed formation methods. Globular clusters as a source was out, as we would see them from elliptical galaxies too. Certain stellar interactions? No way, otherwise it wouldn’t just be spirals either. Since they were all coming from spirals, they think this means it has to be one thing and one thing only: core collapse supernovae.

A slide outlining the potential FRB sources, including supernovae, super-luminous supernovae and long gamma-ray bursts, accretion induced collapse of white dwarfs, mergers of white dwarfs, and mergers of neutron stars.

A slide from the press conference of Aaron Pearlman and Mohit Bhardwaj showing potential origins of fast radio bursts.

The prevalence of spiral hosts in the local universe is a major clue for FRBs, but it doesn’t answer everything. For example, we know of repeating FRBs — how does a supernova happen twice!

Evidence for Large-Scale Anisotropy in the Gamma-ray Sky (Press release)

Next up was Alexander Kashlinsky (NASA Goddard SFC), who had a real mystery to share with us all, about the distribution of gamma-ray radiation in the universe.

To start, there is a well-documented and studied dipole distribution in the cosmic microwave background radiation. In other words, there seems to be a preferred direction to it. There shouldn’t really be, but one possible explanation is that it could be due to the motion of the solar system making it appear that way.

If the CMD dipole is simply due to the solar system’s motion, then it should be detectable in gamma-ray radiation, too. If it isn’t, then it could have a potential cosmological implication.

Kashlinsky intended to probe for the dipole moment of the gamma-ray sky using Fermi LAT observations. Gamma rays are not microwaves, and due to relativistic effects they expected any dipole to be a bit higher in amplitude than that of the CMB.

However, what they measured was a gamma-ray dipole 10 times greater in amplitude than the CMB! They checked to see if the same is true for ultra-high-energy cosmic rays and found a similar dipole. They thought that maybe the ultra-high-energy cosmic rays are causing the gamma-ray dipole when they cascade and decay, but after looking at how that energy would be dissipated, it doesn’t make sense.

The slide has a gamma-ray image of the plane of the Milky Way, with the dipole located below and slightly to the right of the plane. The text describes how pion decay of pions produced through proton decay or ultra-high-energy cosmic rays colliding with CMB photons cannot produce enough gamma rays to explain the observations. Instead, co-emission by an as-yet-unknown source is a likelier explanation.

A slide from the press conference of Alexander Kashlinsky showing the location of the bizarre gamma-ray dipole.

Instead, it may be possible that the ultra-high-energy cosmic rays and the gamma rays come from the same source. So this co-emission of both ultra-high-energy cosmic rays and gamma rays seems to be coming from a yet unknown source!

Astronomers Find Spark of Star Birth Across Billions of Years (Press release)

Finally, Michael Calzadilla (MIT) asked the room how we arrived at the galaxies that we see today. Galaxies that we see today are either elliptical, sometimes called “red and dead,” while others are star-forming spirals. How do galaxies acquire the gas needed for star formation? Gas comes in and out of galaxies, and when the thermodynamics is right, stars can form. This atmospheric cooling has been known for the last 2 billion years and shown to be important for modern galaxies, but what about the past?

Well, the past was different! The peak of cosmic star formation was in the past, as well as galaxy mergers and black hole accretion, all peaking in the last 7–11 billion years. The challenge has been to find distant clusters and get multiwavelength follow up to understand their star formation.

The team used a well studied SPT-Chandra sample, which consists of an unbiased sample of 95 galaxy clusters spanning 10 billion years in evolution and that already had multiwavelength follow up.

The text reads, "Was atmospheric cooling just as important in the past? Cosmic star formation, mergers, black hole accretion peaked between 7–11 years ago. Challenges: finding distant clusters and multiwavelength followup."

A screenshot of the press conference of Michael Calzadilla discussing the atmosphere needed for star formation in galaxies.

They showed that the necessary thermodynamic conditions to trigger star formation that exist in the most recent 2 billion years are also needed back to 10 billion years ago too. So, it seems like making stars is still pretty similar! However, they found that the black hole feedback that regulates star formation in the current universe might not be doing the same thing in the past.

Perhaps a topic for a press conference at a future AAS!

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Plenary Lecture: New Views of Dust and Star Formation in Nearby Galaxies with JWST, Karin Sandstrom (University of California, San Diego) (by William Lamb)

JWST is the gift that keeps on giving. It’s revolutionising astrophysics, cosmology, and our view of the universe. In this plenary, Karin Sandstrom offered attendees a snapshot of the incredible science that is being conducted with JWST after only 1.5 years of science operation.

Before JWST, there were some outlying questions regarding the baryon cycle: the flow of gas and dust from the interstellar medium onto galaxies that fuels star formation, which then causes the expulsion of material via outflows from the galaxy back into the interstellar medium. Those questions include what controls the gas reservoir for star formation and what controls the efficiency of star formation?

Previously, we had limited techniques to trace the interstellar medium and stellar formation, but with the telescope’s resolution and sensitivity to the near- and mid-infrared spectrum, this is no longer an issue. For example, Dr. Sandstrom attempted to get the audience excited about polycyclic aromatic hydrocarbons (PAHs), which are large carbonaceous molecules. The infrared emission from PAHs is strongly correlated with the presence of the interstellar medium. Thus, this makes PAHs a high-resolution tracer, which means by detecting PAHs, you detect where the interstellar medium is and where it is flowing. JWST’s light filters were designed to capture the emission from PAHs, hence JWST can create high-resolution maps of the interstellar medium in our Local Group. With this new map, we can compare simulations of galaxy formation to high-quality data to improve our models, and further refine our models of stellar formation.

And of course, Sandstrom just had to share some of the stunning images from JWST’s remarkable instrumentation…

Dr. Sandstrom standing on a stage in front of a photo of a galaxy.

Sandstrom presenting an image of NGC 628 as taken by JWST.

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Press Conference: Oddities in the Sky (by Isabella Trierweiler)

True to its name, this session included a variety of puzzling phenomena that challenge our current astronomical models!

A Big Ring on the Sky: Alexia Lopez (Jeremiah Horrocks Institute – University of Central Lancashire) (Press release)

The standard model describes our best understanding of cosmology in our universe, and it hinges on a critical assumption, that the structure of our universe is isotropic and homogeneous on the largest scales. Verifying the assumption of homogeneity is really important; we currently estimate that the scale of homogeneity is about 1.2 billion light-years. In other words, the universe should not have any overarching structures that are larger than this scale. However, two years ago Lopez presented one large-scale structure that challenges homogeneity (the “Giant Arc”), and today she presented a second such structure called the “Big Ring.” The two structures are 3.3 billion and 1.3 billion light-years across, respectively.

To find these structures, Lopez uses the light from distant quasars to identify clumps of intervening matter. From the quasar mapping, she can construct a 3D map of intervening large-scale structure, with locations based on the dimmed quasars and distances extrapolated from Mg II absorption. Both of the identified structures are curiously about 9.2 billion light-years away, and they are quite close together on the sky. However, it’s unclear if this is a sign of a larger trend in the distribution of large scale structures. If these structures are proof that our current standard model for cosmology is insufficient, some options for improving our model include invoking cosmic strings, which may construct large scale structures, or assuming a “conformal cyclic cosmology” in which we are living in an infinite cycle of universes, resulting in the creation of circular structures. Lopez plans to continue her quasar analysis to get a better idea of how common these homogeneity-breaking structures might be.

A Potentially Isolated Quiescent Dwarf Galaxy: Timothy Carleton (Arizona State University)

Carleton presented an odd galaxy that was fortuitously observed by the PEARLS project, an extragalactic survey using JWST. He noticed the galaxy (called PEARLSDG) in the PEARLS images due to its odd appearance relative to the other nearby galaxies, which were the original targets of the survey. PEARLSDG is a dwarf galaxy imaged in remarkable detail — JWST was actually able to resolve individual stars in the galaxy! While most dwarf galaxies imaged by PEARLS and other projects are either young and isolated or old with a massive companion, PEARLSDG sticks out as an old, isolated galaxy. How old and isolated galaxies form remains an open question, and Carleton says further spectroscopy of the galaxy will help characterize it and hopefully shed more light on how it formed.

Timothy Carleton presents JWST observations of a potential isolated dwarf galaxy

Timothy Carleton presents JWST observations of a potential isolated dwarf galaxy.

Close Encounters of the Supermassive Black Hole Kind: Tidal Disruption Events and What They Can Reveal About Black Holes and Stars in Distant Galaxies: Ananya Bandopadhyay (Syracuse University) (Press release)

Supermassive black holes (SMBHs) are intriguing objects that are generally very difficult to study as they do not emit light. Because of this, tidal disruption events (TDEs) are especially valuable events, providing some insight into the properties of the SMBH. TDEs occur when a star approaches a SMBH and is disrupted by the strong tidal forces around the black hole. The disruption and accretion of the star in turn spark a flare whose light curve we can measure. TDEs are relatively rare, and we know of about a hundred of these events so far. The typical pattern for a TDE light curve is a rise in brightness over a 30–50 day period, followed by a gradual tapering off period. The main question in this work is what determines the peak luminosity and the timescale of this light curve.

We typically use analytical approximations to recreate the shape of the light curves, but Bandopadhyay demonstrated that the generally accepted analytical model for TDEs results in a very different light curve relative to detailed hydrodynamical simulations, motivating the need for a new model. She presented an updated model for TDE light curves in which she demonstrated that the timing of the peak in the light curve is actually independent of the mass of the accreted star, remaining at ~50 days across the board, while the peak luminosity of the TDE scales with the stellar mass. One of the implications of this finding is that TDEs that are energetic enough to cause jets around the SMBH are likely related to the disruptions of high-mass stars.

Impressively, much of the work of the project was completed by high school students! Syracuse University hosts a summer research program, and their student interns worked on the numerical simulations for the TDEs and are co-authors for this work.

Zooniverse People-Powered Research Platform Reaches New Milestones: Laura Trouille (The Adler Planetarium; Zooniverse)

Zooniverse is the largest platform available for citizen science, with over 2.6 million participants around the world. It was started in 2007 through the founding of the GalaxyZoo project, in which members of the public helped classify different galaxy images. The platform grew rapidly, particularly after 2015 when a DIY project builder was added so that any researcher could easily create their own project. Laura shared that currently 40–50 new projects are added every year! Between the large user base and integrated machine learning algorithms, Zooniverse is a very powerful tool for analyzing large datasets and has led to over 400 scientific publications, often with citizen scientists included as co-authors.

Trouille noted a few recent results from Zooniverse projects. Having so many different eyes on the data makes Zooniverse especially good at identifying unusual features that would typically escape notice in simple coded pipelines. In the past few weeks, the project “Planet Hunters TESS” discovered a habitable-zone planet while the “Backyard Worlds” team identified an aurora on a brown dwarf! To date, citizen science users have contributed 1.6 million hours of work to Zooniverse projects, the equivalent of nearly 800 full-time workers.

If you’d like to contribute as a citizen scientist, getting involved is super easy! Consider joining the gamma-ray bursts team, or hunt for asteroids with the Daily Minor Planet group. And if you’re a scientist who would like to start your own project, definitely do reach out to Trouille and her team.

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Dannie Heineman Prize Lecture: Small Bodies: Primitive Witnesses to the Birth of a Habitable Solar System, Karen Meech (University of Hawaiʻi) (by Yoni Brande)

Karen Meech, the winner of the 2023 Dannie Heineman Prize for Astrophysics, has spent her career studying small bodies (like comets and asteroids) in the solar system. Her prize lecture today focused on how observations of these bodies can teach us about how both our own solar system evolved and how extrasolar planetary systems may be able to develop habitability.

Our current understanding of the development of life says that habitability needs liquid water, organic energy sources, and rocky planets. No currently known extrasolar planetary systems meet these criteria, so we need to know whether the conditions in our solar system are unique.

A common refrain in astrobiology is “follow the water” — that is, understand where water is in a system and how it moves around, and then we should be able to predict where life might arise. In order to study the water content of the early solar system, astrobiologists like Meech and collaborators use remote observations as well as direct analysis of samples of comets and asteroids, which are cosmic detritus left over from those early eras. Meech showed a short review of this history, showing that within a few hundred million years of Earth’s formation, it already had liquid water oceans. The main question, then, is how the water got here.

One theory says that icy bodies from the outer reaches of the solar system were gravitationally scattered to the inner solar system and eventually impacted Earth. This cometary water then became the main reservoir. To test this, we can look at the ratio of deuterium to hydrogen (D/H). The D/H ratio of the early solar system is low near the Sun and increases with distance from the Sun, making it a good tracer of formation location. Earth’s D/H value is significantly elevated for its current position, which is a point in favor of the icy body delivery theory. If high D/H comets swung by Earth and dropped off their water, that could increase Earth’s D/H ratio. However, the last few decades of observations have shown mixed D/H results for different small bodies, and Meech stressed that we really don’t fully understand these primordial isotopic ratios, or if they are even meaningful in studying these formation and evolution processes.

Ultimately, Meech says, water probably comes from multiple sources — we just need to figure out which sources and when. Planet formation is complex, with many chemical and dynamical processes jumbling up the possible tracers of this history. A newly observed kind of comet may finally untangle some of this historical web.

Long-period, tailless comets called “Manxes” (named after the cat) show spectra similar to inner-solar system rocky asteroids. Meech and collaborators’ studies of Manxes show they may have a complex history. They likely began their lives as normal main-belt asteroids (hence the similar spectra), but were dynamically scattered out to the Oort Cloud, and then scattered back into the inner solar system on comet-like orbits. They appear to have a range of surface colors, which could be evidence of diverse formation locations across the solar system.

Meech concluded with some final thoughts: the study of Earth’s water is interdisciplinary, merging expertise from astronomy, planetary science, geology, and more. We need a better understanding of the chemical and dynamical history of our solar system, and in order to obtain that we need in-situ explorations of solar system planets, small bodies, and even interstellar interlopers like ʻOumuamua. These topics have far-reaching implications for habitability and the origin of life. If the solar system is not representative of planetary systems in general, and if the conditions here are special, we can’t assume all other potentially habitable systems will have them as well.

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Berkeley Prize Lecture: Exploring Our Transient Universe In All Colors, Wen-fai Fong (Northwestern University) (by Pratik Gandhi)

Wen-fai Fong, while receiving the Berkeley Prize, remarked that the award is important to her because it recognizes not only her work but also that of her amazing research group. Throughout her plenary talk, she highlighted the work of her graduate students, postdocs, and external collaborators. Fong likes to study astronomical “transients,” or phenomena that are time-varying, using the technique of multi-messenger astronomy — probing these phenomena using observations across the entire electromagnetic spectrum from radio waves to gamma rays, and also using gravitational waves. As she remarked, “the universe varies on remarkably human timescales,” and she derives great joy from observing it in all its variety of colors.

Speaking of colors, Fong highlighted three key themes throughout her talk: (1) Teamwork, which she discussed as being crucial for the kind of fast-paced, time-sensitive research required in transient astronomy, (2) the importance of color, in terms of leveraging the entire electromagnetic spectrum, and (3) that timing is everything, especially in the discipline that she and her group specialize in.

In terms of why the study of transients is important, Fong mentioned that they are often the birthplaces of numerous heavy elements, laboratories for studying extreme physics, the sources of gravitational waves, and probes of otherwise invisible material that we wouldn’t have noticed otherwise. The sources of transients are often the formation of the three classes of compact objects: white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). These compact objects are all the end stages of the life cycles of stars of different masses, with NSs and BHs occurring as a result of massive stars going supernova (which happen to be the most common transients).

Gamma-ray bursts (GRBs)

Fong mentioned how GRBs were first discovered in the 1960s, after which NASA developed multiple gamma-ray observatories in space. Thousands of GRBs have been detected to date, and they are usually extragalactic in origin. GRBs come in two populations (long and short), with short GRBs occurring during NS-NS mergers and long GRBs happening during the collapse of massive stars. Her group focuses mainly on short GRBs; the first evidence for which was the 2017 discovery of gravitational waves from a NS-NS merger followed by a GRB. Short GRBs have been detected in galaxies out to redshifts of z ~ 2!

Fong highlighted how when GRBs are detected (by the Swift telescope, for example), her phone will ping with notifications. Time is of the essence, because they have to mobilize multiple telescopes across the spectrum immediately. Right before Thanksgiving 2023 there was a GRB that was detected, and it was only through the amazing teamwork of her group that they were able to mobilize multiple telescopes and get memos (“circulars”) out to the transients community!

Questions that the Fong group is trying to address concerning GRBs include the following: What do two NSs create? How and where are heavy elements created? What conditions are required to produce these rare transients? The afterglow radiation that produces the GRBs gives us a handle on burst energetics. The NS-NS merger itself tells us about the mass of heavy elements produced. Finally, her group is working on building the BRIGHT repository, a catalog of galaxies that host GRBs, to try to understand the conditions required for them to occur.

Fast radio bursts (FRBs)

Fong also highlighted a second kind of transient, which has only recently been discovered. In 2007, a serendipitous discovery sparked the fast radio burst (FRB) revolution. FRBs are milliseconds-long bright radio pulses similar to GRBs but on the radio side of the spectrum. Some FRBs repeat periodically while others do not, and the cause of this difference is still unknown! Leading hypotheses for the sources of FRBs include magnetars, or extremely magnetized neutron stars. The Fong group is part of the “Fast and Fortunate FRB Follow-up” (F4) collaboration, which mobilizes telescopes across the electromagnetic spectrum, from ALMA to Chandra, in order to also look at the host galaxies of the FRBs.

Fong concluded the talk by returning to the importance of teamwork, color, and timing, and saying, “There is incredible momentum behind this field and the era of 1,000+ hosts is not far away — we’re thrilled; we’re excited; we’re scared!”

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Illustration of the cold neutral clouds expelled from the center of the Milky Way by hot winds

Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on BlueSky for more coverage. The usual posting schedule for AAS Nova will resume on January 16th.

Table of Contents:

Henry Norris Russell Lectureship: Frank Shu’s Legacy in Unraveling Star Formation, Susana Lizano (Instituto De Radioastronomia Y Astrofisica) (by Ivey Davis)

Frank Shu was a titan of astrophysical fluid dynamics theory, with his work being seminal to our understanding of star and planet formation, protoplanetary (and planetary) disk structure, galactic spiral arm formation and stability, and nigh countless other topics across essentially all fields in astrophysics. He was awarded the Henry Norris Russell Lectureship before his passing in April of 2023. Upon being awarded the Lectureship, he not only requested that Susana Lizano give this lecture on his behalf, but also donated the associated money back to the AAS. In honor of Shu’s contribution to astrophysical fluid dynamics, and astronomy as a whole, Lizano gave an overview of Shu’s career, which in a way is an overview of the field of star formation theory.

Shu’s first work was addressing the spiral structure of galaxies by treating them as density waves propagating through a disk, rather than as fixed, physical structures as had originally been assumed. This new framework solved the winding problem that had arisen in the fixed-structure framework, as well as addressed other galactic features like color gradients and the locations of OB star associations. Similar density-wave treatments would later be applied to other places we see disks, such as in Saturn’s rings and in the material around young or forming stars.

In 1977, Shu published his work on the collapse of spheres of gas as a way to explain core formation and subsequent star formation. A decade later, he, along with Lizano and Fred Adams, would publish the review that is still used as the star formation paradigm, showing how pressure, temperature, and density evolve with time to eventually form young stellar objects from molecular gas clouds and also explains the onset of the Hayashi track. Expansions of this work to rigorously analyze the effects of magnetic fields and rotation on gaseous bodies, both by Shu and by others, would go on to explain or elaborate on evolutionary sequences from protostars to main-sequence stars, the scale height and aspect ratio of accretion disks, disk formation conditions, planetary migration, planetesimal formation, and so much more.

Shu was an active researcher and astronomical community member, serving as president of the AAS from 1994 to 1996, and most recently was investigating technologies to help combat the climate crisis. Questions following Lizano’s talk not only included questions about what the future of the field looked like, but also recountings of individuals’ personal experiences with Shu. This lecture was a truly heartfelt tribute to a dedicated astronomer and mentor.

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Press Conference: Supernovae and Stars (by Mark Popinchalk)

This press conference was all about stars going supernova! (Except for one result about galactic gas that was shuffled into the session due to a missed flight.)

A 12.4-Day Periodicity in a Close Binary System After a Supernova (Press release)

First, Ping Chen (Weizmann Institute of Science) shared a peculiar system with us. You can measure the kind of light a supernova gives off to see what elements are in it. It may have some hydrogen, or helium, or neither. This is often thought to be due to what the outer layers of the star were doing before the explosion. The dense core will stay put, but the outer layers of hydrogen or helium may or may not get stripped off. Whether this stripping always occurs, and how it happens, is hotly debated. 

The case of the supernova SN 2022jli is especially weird. Its brightness shows a periodic dimming and brightening on a 12.4-day period, which is already unique. It becomes even more interesting that the spectra of the supernova usually doesn’t show hydrogen, except for particular points in the 12.4-day period!

slide showing the orbital interactions of the compact supernova survivor and its binary companion

A six-panel slide from Ping Chen’s talk showing the orbital interactions of the compact supernova survivor and its binary companion.

The story appears to be that there were two stars in a binary system, one that went supernova and is now a compact object, and the other a star in an elliptical orbit around the remnant. When the outer star approaches the remnant on its orbit, the remnant strips some hydrogen from the outer star and the extra hydrogen is added to the remnant’s spectra. The outer star has to be on an elliptical orbit so that the stripping only occurs at certain points during the star’s orbit.


Rare Insight Into the Origins of Type Ia Supernovae Progenitors From a Double Detonation (Press release)

Estefania Padilla Gonzalez (UC Santa Barbara and Las Cumbres Observatory) introduced the audience to a great candidate for a double detonation Type Ia supernova. She started by introducing us all to Type Ia supernovae. They have predictive luminosity, which is to say that the light from their explosions are understood really well, and they have been used as “standard candles” to enable distance measurements to other galaxies.

Even though they are well understood, there are still some questions on how Type Ia supernovae explode. The common understanding is that to have a Type Ia supernova you need a white dwarf that is under 1.4 solar masses, the Chandrasekhar limit. Then you need another nearby star to feed mass onto the white dwarf until it crosses that limit, and boom! Supernova!

However, there may be sub-Chandrasekhar-mass explosions. Their occurrence is not currently supported by observations, but they are theoretically possible. How can we get the smaller stars to explode? The idea is that the helium layer surrounding the core of the star starts to ignite early, which causes a shock wave that travels around the star. When the shock waves meet each other, that provides even more force that could trigger the rest of the core to go full supernova.

photograph of a slide listing the conclusions of a presentation

Summary slide from Estefania Padilla Gonzalez’s talk.

And that’s where the team’s research comes in! SN 2022joj is a Type Ia supernova that has a few different characteristics, a non-standard candle. For example, there is suppression in the blue wavelengths of the light it emits, which might be due to helium ash absorption at those wavelengths. However, once the full explosion occurs, the end result looks like a regular Type I supernova.

It’s an exciting candidate for a double detonation of a thin helium shell!

Periodic Eruptions of a Supernova Impostor

Mojgan Aghakhanloo (University of Virginia) was next, and had an intriguing system, an impostor supernova! SN 2000ch is the impostor in question, and it’s thought to be an evolved massive star that has undergone non-terminal eruptions. What does that mean? It’s a big star that’s not dead yet. Eta Carinae is a great example that some might be familiar with — huge outer layers barely contained in its gravity influence, a star that is just clinging to life. It went through a “Great Eruption” in the past.

SN 2000ch is having an even worse time. Since 2000, it’s had 23 different eruptions, and the team has shown that there is an interesting periodicity to it, that the eruptions occur approximately every 200.7 ± 2 days. What’s the cause? It’s probably another binary system! 

Slide titled "interacting binary system" with bullet points reading "binary system, eccentric orbit, and LBV-like primary star." A graphic to the right of the text has two panels, one with a quiescent LBV and one with an outbursting LBV.

A summary slide from Mojgan Aghakhanloo’s talk showing the binary orbit interacting with the outer layer of the massive star.

The big evolved star is not by itself and has a secondary companion in the system, orbiting around it. As the other star gets close, it passes through the outer layers, causing eruptions. And since the layers are so extended, it is likely that the material the path goes through changes, explaining why some eruptions are bigger than others.

These eruptions look just like those that Eta Carinae went through, and makes this a target of “great interest.” The next eruption is likely in March of this year!

Spectacular Nucleosynthesis from Early Massive Stars (Press release)

Alexander Ji (University of Chicago) brought us a really interesting story, a star with such a bizarre composition, that it likely formed from the supernova of a really big star! That’s right: learning about an older star by looking at a current one.

SDSS is a huge survey mission that is “lawn-mowering the sky” taking spectra of stars. It discovered a star with spectacular composition. J0931, an old star, has unusually low magnesium abundance for its metallicity, and was flagged for follow up by the Magellan telescope. The additional observation showed that it also had strangely low amounts of sodium, and tons of strontium.

What does that all mean? Well, if they trace back to when the star is likely to have formed (~10 billion years ago), it must have come from a peculiar cloud of material to have these kinds of elemental ratios. These kinds of elements only form when a star goes supernova, and when compared to theoretical models of the kind of star that would need to go supernova to make that peculiar cloud, (to form the smaller star that exists today) it would have to be massive.

A slide titled Stellar Archaeology. It depicts the explosion of the Barbenheimer star 13 billion years ago and the evidence of that explosion being discovered in old stars present today.

A slide from Alexander Ji’s talk showing the progenitor supernova star before the next star.

So massive, that it would have to be > 50 times the mass of our Sun, even up to 80 solar masses. The challenge is that no model fits all the element ratios they find, and most models predict that stars that big shouldn’t even go supernova! A star that big should collapse directly into a black hole. The presence of this star shows that the existing supernova models are too simple, and that this particular star is a blockbuster.

They’ve given it a special name since they were working on it this summer: The Barbenheimer Star : )

The Nuclear Outflow from the Milky Way (Press release)

Last but not least was Jay Lockman (Green Bank Telescope), who had finally made it to AAS after flight troubles and was given a chance to speak at this press conference rather than the one he missed.

He pointed out that when we look at most large galaxies, they have bursts of energy in their cores that drive winds which carry mass out from the galaxy center. There is data to suggest a similar effect is happening in the Milky Way, but it is hard to see since we are in the plane of the disk. However, there are new observations that show that cold hydrogen clouds are being pushed by the hot wind from black holes or starbursts in the center of our galaxy.

A photograph of the Milky Way running across the sky with blue and green blobby clouds emerging from the center of the Milky Way

A summary slide from Jay Lockman showing gas clouds shot out of the Milky Way.

A good analogy would be that the forces pushing from the center of the galaxy are an astrophysical mixture of  a snow blower and a leaf blower! The movement of the gas is in straight lines out from the source and then spreads out, which is what a snow blower does. However the gas is being pushed around like leaves by a leaf blower. An autumnal/winter analogy!

The team has been attempting to locate over 300 clouds with the Green Bank Telescope. The flows are coming out in two cone shapes, at high velocities, with some clouds approaching the escape velocity of the Milky Way. They likely won’t escape, but it shows that the forces can certainly launch material around the galaxy!

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Annie Jump Cannon Prize Lecture: Marta Bryan (University of Toronto) (by Ali Crisp)

In her lecture, 2023 Annie Jump Cannon Prize award winner Marta Bryan led us through her research on the dynamics of giant exoplanets and how dynamics can provide insight into the formation mechanisms of giant planets, their impacts on other planets in their systems, and even how they affect the potential habitability of a system.

To begin, she briefly explained what planetary properties we can learn from more “traditional” exoplanet studies using the radial velocity and transit techniques: the mass of the planet from radial velocity measurements, the radius of the planet from transit detections, and the orbital period, inclination, and eccentricity from either. She then adds that with new atmospheric detections, you can get information about the composition, spin, planetary obliquity, and weather on a giant planet.

But what does combining all these properties tell us? For one thing, characterizing planetary spin and comparing it to the host star’s spin can give us information about how the planet and star formed. In a perfect system, the spin of the star and planet would be aligned, and their equators would be parallel. However, we see even in our own system that this isn’t the case. Uranus, for instance, is tilted on its axis 98 degrees relative to the equator of the Sun, and Venus spins in the opposite direction from all the other planets. Constraining the orbital dynamics of exoplanets and finding any misalignments or spin oddities can indicate some sort of gravitational interaction occurred. In systems with close-in super-Earths and far-out giant planets, these suggested interactions could indicate that the giant planet caused misalignments or spin changes through, e.g., migration during its formation.  

Bryan ends by contextualizing her observations and constraints in the search for biosignatures. As the number of confirmed exoplanets increases, it becomes impossible for us to characterize all their atmospheres. Since we know our own solar system hosts life and contains both close-in terrestrial planets and far-out gas giants, we could prioritize observations of similar systems for biosignatures and hopefully help constrain what constitutes habitability.

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Press Conference: Stars, Disks & Exoplanets (by Isabella Trierweiler)

This session provided new insights into a variety of planetary systems and included two projects led by undergraduate students!

Stellar Paternity Tests: Matching High-Latitude B Stars to the Open Clusters of Their Birth (Press release)

Brandon Schweers and Ginny McSwain (Lehigh University)

Star formation in the Milky Way is generally believed to be restricted to the thin disk of the galaxy. However, there is an interesting population of B-type stars that have been observed far outside of the thin disk. Brandon Schweers, an undergrad at Lehigh University, sought to trace back the trajectories of these so-called “orphan” B stars to figure out whether they did indeed form in the thin disk and migrated away from home, or whether they represent a different pathway for star formation.

Schweers used kinematic data from Gaia to reconstruct the trajectories for stars in and around clusters over the past 30 million years. They then used those trajectories to see whether orphaned stars ever crossed paths with a potential “parent” cluster. Overall, Schweers found 22 intersections between orphan stars and parent clusters, with some stars intersecting multiple clusters. To validate whether the paired orphans and parents were indeed related, Schweers constructed color–magnitude diagrams for the parent clusters and checked whether the orphaned stars fell within the cluster’s parameter space. From this analysis, Schweers found 15 matches between orphan stars and parent clusters and was able to estimate the times at which the stars were originally ejected from their host clusters, as well as the initial velocities at the time of ejection. Based on the ejection velocities, Schweers found that one star was ejected due to a very energetic event, like a supernova, while the rest were likely ejected due to dynamical interactions with their parent cluster. Interestingly, a few orphan stars never intersected with any clusters, bringing up the question of whether there may be some star formation going on above and below the thin disk after all.

Weakened Magnetic Braking in the Exoplanet Host Star 51 Pegasi (Press release)

Travis Metcalfe (White Dwarf Research Corporation)

51 Pegasi (51 Peg) is one of the most famous stars in exoplanet science, as it hosts the first exoplanet astronomers ever discovered around a main-sequence star. Despite its planet being so well known, Travis Metcalfe showed that there is still more to learn about 51 Peg from its magnetic field structure. 51 Peg is a Sun-like star, which means it was likely born with a rapid spin and eventually slowed down as it shed angular momentum. The main mechanism for slowing rotation in a young star is called magnetic braking, where angular momentum is carried away by stellar winds, and the rate of the loss of angular momentum is depending on both the strength and complexity of the magnetic field around the star.

To map the magnetic field structure around 51 Peg, Metcalfe used data from the Large Binocular Telescope to first map the magnetic surface of the star and then reconstruct the magnetic field lines. Interestingly, he found that 51 Peg follows an unusual trend in magnetic braking where young, rapidly rotating stars have relatively strong braking, and then somewhat suddenly fall to a weakened braking state as they age. While the source of the drop is not entirely clear, it may have to do with changes in the complexity of the magnetic field structure around the aging stars. The Sun seems to have gone through this drop in braking as well, and curiously the timing of the drop in magnetic braking corresponds to emergence of land-based life on Earth, raising the question of how magnetic evolution of host stars and planet habitability may be intertwined.

JWST’s New View of Beta Pictoris Suggests Recent Episodic Dust Production from an Eccentric, Inclined Secondary Debris Disk (Press release 1, press release 2)

Christopher Stark (NASA Goddard)

Beta Pictoris is another well-known exoplanet system, remarkable both because its two known exoplanets reside in a debris disk and because it has shown evidence of exo-comets. Beta Pictoris’s debris disk has been a point of interest for decades, and more recently it was shown to have two components: an edge-on main disk and a somewhat warped secondary disk with interesting CO emissions. The complexity doesn’t stop there though; using NIRCam and MIRI data, Christopher Stark showed that even more features are hidden in Beta Pictoris’s disk!

The new MIRI images show a fork, an elongated feature (named the “cat’s tail”), and several shorter nebulous features. The data show that these features are connected to the secondary disk of Beta Pictoris, and that the material of the secondary disk appears to be different both in temperature and in composition from the main disk. Stark says the secondary disk material seems to be consistent with fluffy, organic, refractory material, not unlike the samples obtained by OSIRIS-REx. As far as the origins of the cat tail and other features, the most likely explanation is that they are the tails left by collisions within the debris belt. Stark showed that such a collision would need to occur in about the last 150 years to create the observed features, and furthermore that the shape of the cat tail is consistent with the same organic, refractory material extrapolated from the MIRI data. To complete the picture, the 150-year estimated timescale fits nicely with the observed CO emission. CO dissociates in about 150 years, so the observed CO would have been created relatively recently, and the collision that created the cat tail is a perfect candidate for emitting CO into the disk! Stark noted that in addition to providing more insight into the Beta Pictoris disk, these observations prove that debris disks could be a lot more active than we previously thought and should definitely be further investigated using JWST.

How Do Ultra-Massive Planets Form? Gaining New Insight by Measuring the Orbital Tilt of a Rare Transiting Brown Dwarf (Press release)

Steven Giacalone (Caltech)

Thus far, planets have been observed at a huge range of size scales, from our terrestrial planets up to Jupiter masses. However, there’s currently a gap between objects of Jupiter mass and low-mass stars. The few ultra-massive planets / brown dwarfs in this gap are intriguing objects, and their origins are an ongoing question. There are generally two options for their formation: either they form like planets, accreting in disks around stars, or they form like binary stars and collapse directly from gas. So far, most of the brown dwarfs appear to have orbits and compositions that are consistent with star-like formation. However, Steven Giacalone has a new observation that brings planet-like formation back into the picture.

For this study, Giacalone measured the orbital tilt of a brown dwarf, GPX-1b. GPX-1b is 20 times more massive than Jupiter and resides quite close to its host star. The orbital tilt is related to the formation pathway because brown dwarfs that form as planets should be aligned with the spin of the host star (like the planets in our own solar system), while brown dwarfs that form similar to stars could have any orbital orientations. Giacalone used the Keck Planet Finder to observe the brown dwarf’s transit. To measure the orbital tilt, he analyzed the wiggles in the transit spectrum that arise from the transiting brown dwarf crossing first the blue-shifted and then red-shifted portions of the star’s surface. From this method, he found that the tilt is aligned with the star, indicating that GPX-1b likely formed as a planet. Brown dwarfs are relatively rare objects, so this was the first measurement of its kind, and it introduces interesting new evidence for brown dwarf formation!

An Earth-Sized Addition to a 400-Myr Planetary System in the Ursa Major Moving Group (Press release)

Alyssa Jankowski and Melinda Soares-Furtado (University of Wisconsin – Madison)

Young planets are really important to our understanding of planet formation, but they are generally very difficult to find and reliably date. Alyssa Jankowski, an undergraduate at the University of Wisconsin-Madison, leveraged the power of moving groups, or stars that all formed from a common molecular cloud, to better date planet ages and search for young systems. In particular, Jankowski studied the system HD 63433, which is part of a moving group that includes many stars in the Big Dipper. HD 63433 is a Sun-like star, but it’s only about 400 million years old (compared to our solar system’s 4.6-billion-year age).

Previous work on the system unveiled two sub-Neptune sized plants, both on very short orbits. However, using new TESS data, Jankowski identified a third, Earth-sized planet in the system! The new planet has an incredibly short period of only 4 days, and while it is interior to the two sub-Neptunes, the whole system still fits within the orbit of Mercury. As the new planet is so close to the host star, it is likely tidally locked, leading to day-side temperatures of 1500K and a likely lava hemisphere. The new planet is really intriguing and presents an interesting opportunity to study atmospheric loss, a common trademark of young planets. Jankowski says there are plans to re-observe the system with Hubble and JWST soon and check for any heavy-element outgassing. 

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Plenary Lecture: Investigating the Early Universe, Jamie Bock (California Institute of Technology) (by Isabella Trierweiler)

In his plenary lecture, Jamie Bock shared some exciting new insights into the early universe, along with the technological improvements that will help us probe this era in greater detail in the coming years. In particular, Dr. Bock is interested in inflation, the period of time when the universe grew exponentially. Inflation is especially difficult to study; it was an incredibly high-energy event, making it impossible to study through experimentation (the energy scale is 1016 GeV, whereas the Large Hadron Collider currently reaches about 104 GeV), and it was a period of time when the universe very quickly moved from quantum scales to large-scale structures, complicating any attempts at simulation or computation. Thus direct observations remain our most powerful tool in studying the early universe.

global projection of the cosmic microwave background temperature fluctuations

A map of temperature fluctuations in the cosmic microwave background from WMAP. This map shows temperature deviations of up to 200 microkelvin. [NASA]

Since its discovery in 1964, the cosmic microwave background (CMB) has been our main means of studying inflation. The CMB is the earliest light we can detect, made up of the photons that come from the moment the universe cooled enough for light to pass freely through space. To first order, all parts of the CMB are the same temperature, 2.7K. This is strong evidence of inflation because it means all parts of the sky needed to have been in contact at one point before growing to its current size. However, very small fluctuations exist in the CMB, and it is these fluctuations that allow us to more precisely study inflation. The fluctuations are a result of inflation amplifying quantum fluctuations in the early universe, and we can work backwards from the fluctuations to characterize inflation. 

To characterize the fluctuations, we collect all the information about the size and strength of the fluctuations into a plot called the power spectrum. The goal of the power spectrum is to understand whether temperatures in the CMB are more correlated at particular spatial scales than others. Constructing the power spectrum is somewhat complex, but you can roughly imagine picking two points on the sky at some set distance apart and checking whether their temperatures are the same, and then repeating this for every set of points on the sky at that same set distance, and then doing the whole thing again at all possible distances. The structure of the resulting plot determines parameters like the geometry of the universe and the density of matter and dark matter. Over the past few decades, we’ve been able to fill in more and more of the power spectrum, and we have now reached a point where further measurements are only limited by photon noise. 

So far, the results are well in favor of inflation. However, the difficulty now is to come up with a specific model for how it occurred. Currently over 100 proposed models exist, conveniently packaged into this 777-page document. Dr. Bock says there are two main questions to address to narrow down the options: 1) Is there a primordial gravitational wave background, and 2) so far CMB statistics seem to be Gaussian, but is there a non-Gaussian component? The gravitational wave background would tell us the energy scale of inflation, while the non-Gaussian component would show whether a single decaying field or multiple fields were responsible for causing inflation. So far, the BICEP and Keck arrays have been used to measure CMB polarization, concluding that inflation does not proceed simply along a power law. Meanwhile, the upcoming SPHEREx mission is poised to start measuring patterns in large scale structure, looking for correlations in the geometries of the structure to answer the question of non-Gaussian components and further narrow down the set of potential inflation models. 

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Newton Lacey Pierce Prize Lecture: Characterizing the Properties of Accreting Neutron Stars Through X-ray Observations, Renee Ludlam (Wayne State University) (by Ivey Davis)

We’ve heard quite a bit about the power of pulsars in astrophysics through the lectures on Monday and Tuesday, but today, Renee Ludlam focuses more generally on neutron stars, the various ways they can exist, and what that can tell us about physics.

As mentioned in previous talks, neutron stars push the extremes of our understanding of physics since we can’t measure such conditions on Earth. They have extreme pressures, densities, and magnetic fields that we could (presumably) never hope to replicate on Earth. Such extremes push our understanding of physics, especially how we describe the radial profiles of density, pressure, and temperature, called equations of state (EOSs). Although we have many ideas for what the EOS of neutron stars might be, it’s difficult to constrain what the correct solution is without being able to identify both the mass and the radius of the neutron star.

Because neutron stars push our understanding of physics to such extremes, we don’t know which model of neutron star interiors is most accurate. In order to constrain this, it’s important to understand the neutron star’s mass (somewhat well constrained in binary systems) and radius (much harder to constrain). Ludlam uses NuSTAR and NICER observations of X-ray binaries in order to put constraints on neutron star radii. These are systems that include a neutron star in a binary system (usually) with a main-sequence star. The neutron star occasionally accretes material from its companion star and produces X-rays. Constraining a neutron star’s radius requires measuring properties of the accretion disk around the neutron star in such a binary. But, this in turn relies on making assumptions about the process responsible for making the accretion disk. By studying the observational properties of accretion onto neutron stars, and how it compares with our models of the accretion, we can start to make conclusions about the system as a whole, as well as about the properties of the individual neutron star.

By observing extreme systems like ultra-compact X-ray binaries, Ludlam has additional spectral lines to study the effects of accretion onto neutron stars, which has helped to further put constraints on neutron star radii. As we continue to observe the unique effects of accretion onto neutron stars, and the various ways that this accretion can occur, there should be more and more stringent constraints on the EOS for neutron stars, and therefore a more robust understanding of physics and how it operates in such extreme circumstances.

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illustration of a brown dwarf with auroral emission

Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on BlueSky for more coverage. The usual posting schedule for AAS Nova will resume on January 16th.

Table of Contents:

Plenary Lecture: Radio Astrophysics and Cosmology from the Moon, Jack Burns (University of Colorado, Boulder) (by Briley Lewis)

Day 2 started off with a science fiction dream becoming reality: putting telescopes on the far side of the Moon. Jack Burns, Professor Emeritus at University of Colorado, Boulder, detailed the actual plans to do so in this morning’s plenary. This isn’t a new idea — radio telescopes on the lunar far side were envisioned even before the Apollo 11 landing. Science fiction author Arthur C. Clarke (most famous for 2001: A Space Odyssey) at the time said, “In a few generations, all serious astronomy will be with telescopes on the Moon or in space.” Burns noted that “it has now been a few generations” and we have incredible space telescopes like JWST, leaving only the Moon part left to do.

What makes the lunar far side so appealing is that it’s uniquely radio quiet, with a dry and stable environment and no ionosphere to generate interference. There’s one particular signal radio astronomers and cosmologists want to chase: the well-known 21-centimeter line, which can act as a cosmological probe to explore the dark ages and reionization in the early days of the universe.

NASA is already going back to the Moon with its Artemis program, and its Commercial Lunar Payload Services initiative partners with private companies to deliver more scientific payloads to the Moon. One such project is Radio Wave Observations at the Lunar Surface of the Electron Sheath (ROLSES), which will fly aboard Intuitive Machines 1 in February. The experiment consists of telescoping antennas which will pop out in a spring-loaded system with a classic spectrometer, and will cover a wide frequency range to detect radio signals from a variety of astrophysical signals. It plans to land at the lunar south pole near Shackleton crater, setting the record for closest landing to the lunar south pole; the Indian Chandrayaan-3 probe recently landed 30 degrees away, and this project will only be 10 degrees away.

ROLSES has many science goals, including measuring the electron sheath created by interactions between solar wind and lunar regolith, which is expected to exist but hasn’t yet been measured. It’ll be observing the galactic radio spectrum, measuring the dielectric constant of the lunar subsurface, and — perhaps most importantly — proving that detecting radio signals from the lunar far side is possible, paving the way for future missions. Although ROLSES’ galactic observations won’t reach the pot of gold at the end of the rainbow (the 21-cm line background measurement), it will help characterize the radio emission of the galaxy, which needs to be known, so the Milky Way can be effectively removed from the foreground of future cosmological observations.

Looking further ahead, the LuSEE-Night mission will work on actually measuring that 21-cm line for cosmology purposes in 2025. In the even more distant future, the proposed FARSIDE project would set up an interferometric radio array on the Moon, and the ambitious Far View project would expand such an array to 100,000 dipole antennas, constructed from resources gathered in situ on the Moon.

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Press Conference: Exoplanets and Brown Dwarfs (by Pratik Gandhi)

This press conference had four exciting presentations on brown dwarfs and exoplanets, collectively dubbed “other worlds,” by researchers from the American Museum of Natural History and University of California, Los Angeles!

Extrasolar Worlds Exhibit Exotic Sandy Clouds at the Equator

Background image of Spitzer Space Telescope, with an example BD infrared spectrum shown in the bottom right. A characteristic bump in the middle of the spectrum indicates the presence of sandy clouds.

An example BD infrared spectrum from their sample is shown in the bottom right of this photo. The characteristic feature highlighted in red indicates the presence of sandy clouds in the BD atmosphere.

Kicking off the session was Genaro Suarez, a postdoc at the American Museum of Natural History (AMNH), and member of the Brown Dwarfs in New York City group (or BDNYC), who told us about how the equators of exoplanets are often cloudier than the poles! Brown dwarfs (BDs) are considered the link between the lowest-mass stars and gas giant planets — they have insufficient mass to carry out fusion and radiate like stars, but they often have a little too much mass to be considered “planets.” Suarez’s focus is on L-type BDs, which are the hottest category. Using archival data from the Spitzer Space Telescope (the precursor to JWST), they identified a feature in the spectra of BD atmospheres that is indicative of clouds that are composed mostly of sandy grains (see Figure 1)! Additionally, their team found a correlation between the inclination or viewing angle, cloud cover, and color of the BD atmosphere — all of which suggest that BDs have more sandy clouds along their equators than at their poles.

Using Citizen Science to Identify New Ultracool Benchmark Systems

The second talk of this press conference was by Austin Rothermich, a graduate student at the CUNY Graduate Center, and also a member of the BDNYC collaboration. Rothermich’s presentation demonstrated the power of citizen science projects, and how they can lead to important scientific progress with the invaluable contributions of the citizen scientist volunteers! The problem that Rothermich’s research was trying to address is that BDs often have huge degeneracies in their mass, temperature, and age, making it hard to tell these properties apart. Since it’s easier to determine these properties for regular stars (so-called “main sequence stars”), if one finds a regular star near a BD, one can assume they have similar fundamental properties since they must have formed together — then, by measuring the properties of the star, we can infer those of the hard-to-measure BD. This method is therefore called using “ultracool benchmarks”!

Screenshot collage of volunteers from many countries who participated in the citizen science project, with text saying "thank you!"

A collage showing some of the volunteers who participated in the Backyard Worlds project!

Via the citizen science project “Backyard Worlds,” Rothermich’s team was able to incorporate the work of over 175,000 volunteers who analyzed more than 1 million images from the WISE telescope — by flagging the images, the citizen scientists could indicate whether they found a candidate ultracool benchmark system. Their team then followed up 32 of these systems with spectroscopy, and those observations were often aided by citizen scientists.

Rothermich ended the presentation on a poignant and uplifting note, thanking the volunteers who participated for their time and effort, and talking about how his scientific career as an undergrad was also kick-started via the Backyard Worlds project, from the citizen volunteer side!

JWST Indicates Auroral Signature in an Extremely Cold Brown Dwarf

Comparison of two BD spectra showing a number of squiggles due to different molecules like water and CO2. A bump in one of the spectra to the left indicates the presence of methane emission.

Comparison of two BD spectra showing a number of absorption features due to different molecules like water and CO2. A bump in one of the spectra (in blue) to the left indicates the presence of methane emission.

Next up was Jackie Faherty from AMNH, founder of the BDNYC collaboration, and co-founder of the Backyard Worlds project. Faherty’s results focused on Y-type BDs (the coldest kind), whose surface temperatures range from the setting on a home oven to that of a cold day at the North Pole! Her team used JWST spectra to study the atmospheric compositions of the BDs and found that they were chemically analogous to Jupiter with water ice, methane, carbon dioxide, etc. Faherty showed a comparison of two of their BD spectra, whose “spectra are sculpted by intriguing chemistry,” and discussed how one of them shows a characteristic bump from methane emission (see Figure 3, with the bump towards the left). Normally such a cold object shouldn’t be showing any emission spectra, but using the example of Jupiter they hypothesized that the emission could be due to aurorae at the poles of the BD (similar to those on Jupiter), and that these aurorae could be excited by the presence of a nearby active moon (like Io for Jupiter) or some other internal process. Faherty’s team plans on applying for more JWST time to follow up this system and learn more about whether it has a companion or not. Finally, she ended by discussing how the terms “planet” and “brown dwarf” are often ambiguous, which is why she prefers the term “other worlds” to encompass them all.

WASP-69b’s Escaping Atmosphere Is Confined to a Tail at Least 7 Planet Radii

The final presentation was by Dakotah Tyler, a graduate student at UCLA studying the exoplanet WASP-69b and its curious “tail”-like feature. WASP-69b is one of the 5,000+ known exoplanets, and it belongs to a sub-type known as “hot Jupiters,” or Jupiter-mass planets that orbit really close to their host star and are therefore quite hot. Hot exoplanets can often lose atmospheric mass due to the heating and escape of gaseous material, and Tyler’s team used WASP-69b as a test bed to study exoplanet mass loss in real time. They obtained transit data of the planet crossing the stellar disk, and by looking at helium absorption features in the atmosphere, they found that some of the helium was “blueshifted,” or appeared to be moving fast in our direction — indicating that it had been ejected from the planet’s atmosphere.

Animation showing what a comet-like exoplanet atmosphere "tail" would look like as it crosses in front of it's host star. The planet appears to be slightly to the left of the star, with a gaseous tail extending out towards the left from it.

Animation showing what a comet-like exoplanet atmosphere “tail” would look like as it crosses in front of its host star.

The estimated mass loss rate they found is around one Earth mass per billion years, which is higher than previous studies had measured. They also found that although the planetary outflow might have initially been radial or spherical, by coming into contact with the host star’s stellar winds, it got reshaped into a comet-like tail. Finally, Tyler highlighted that their estimate of the size of the tail is roughly 7.5 Earth radii, which is again larger than previously measured for WASP-69b, thanks to the power of JWST!

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High Energy Astrophysics Division Bruno Rossi Prize Lecture: Anatoly Spitkovsky (Princeton University) (by Ivey Davis)

In the Bruno Rossi Prize Lecture, Anatoly Spitkovsky of Princeton University succinctly summarized the underlying principle of the field of astrophysical plasmas: “How microscopic processes affect macroscopic astronomical objects.” Few systems (if any) better allow for us to examine the most extreme conditions where plasma physics operates than pulsars. As Spitkovsky recounts, since the discovery of pulsars by Dame Jocelyn Bell Burnell in 1967, the incredible consistency in the arrival time of pulsar pulses have been used for studying the structure of the interstellar medium, served as a test for general relativity, and were used as galactic-scale interferometers for studying gravitational waves as was covered in Monday’s first plenary. While pulsars also serve as a “playground” for theorists due to their extreme magnetic field strengths (billions to trillions of times that of the Sun’s field), densities (100 billion times that of Earth), and rotation rates (as short as a millisecond), there remain questions about the emission processes of pulsars that have persisted since their discovery.

Spitkovsky compares the problem-solving process of pulsar magnetic fields and emission to The Incredible Machine — you keep putting pieces together until something finally clicks and the solution is found, even if a bit convoluted (see associated figure). In the world of pulsar theory, more and more puzzle pieces have been incorporated as the computational power available has increased. For instance, until nearly the year 2000, models of pulsars assumed there was no surrounding plasma; this was relatively computationally inexpensive, but inherently non-representative of pulsar environments. To address this problem, the next piece introduced was a global plasma; this could reproduce how pulsars slow down over time, but could not explain the gamma-ray emission we observe. The most recent — and most computationally expensive — piece has been to transition from a global plasma to individual plasma particles that interact with both the magnetic field and each other. This has served to be the most reliable method to date to reproduce the gamma-ray double-peak light curve and the synchrotron spectrum as observed by the Fermi spacecraft, as well as some other unique pulsar emission.

A screenshot from the game The Incredible Machine where players create Rube Goldberg devices. Dr. Spitkovsky used this to explain the convoluted nature of the process of arriving at solutions for astrophysical plasma physics

Spitkovsky’s graphic to explain the process of solving problems for pulsar magnetospheres.

The conclusion of this work not only seemed to robustly address the age-old problem of pulsar magnetic field morphology and its interaction with plasma, but also fundamentally shifted how we understand where the emission is coming from. We now understand that gamma rays are likely generated by the merger of pockets of plasma, and that this occurs much farther from the surface than we originally assumed the emission to be originating from. This solution was decades in the making, and now that we have it, Spitkovsky is enthusiastic about the new opportunities it affords in addressing other phenomena that are unique to pulsars but inform our overall understanding of plasma astrophysics.

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Press Conference: High-Energy Phenomena and Their Origins (by Yoni Brande)

Revealing Dual Quasars and Their Host Galaxy With JWST and ALMA: Yuzo Ishikawa (Johns Hopkins University)

Quasars, ultra-bright actively accreting supermassive black holes (SMBHs), are some of the brightest objects in the sky, often totally outshining the rest of the light from their host galaxies. Most galaxies have a single SMBH in their centers, but some galaxies have two! Yuzu Ishikawa and his collaborators presented their studies of “dual quasars.”

As the name implies, dual quasars have two accreting SMBHs, either as part of two merging galaxies or both in a single galaxy. Most of these have been observed at low redshift, but the dual quasar population at redshifts greater than 1 is not well understood. Perhaps there’s a connection between galaxy mergers and quasar triggering, or the properties of their host galaxies.

To answer these questions, Ishikawa and collaborators studied one particular dual quasar, DQ J0749, at a redshift of 2.17 (or over 10 billion years ago!). The quasars are separated by 3.5 kpc, and the system was discovered with the Hubble Space Telescope. Ishikawa was awarded JWST time to observe the system and found that extended H-alpha emission implies there’s a single host galaxy (a rotating disk!) and that the host is forming lots and lots of stars! The quasars in the system are pretty similar, possibly both accreting gas from the same region in the host. These observations are some of the best-quality data available on these enigmatic high-redshift systems, and Ishikawa and his collaborators hope to learn more about these with future observations.

Breaking Cosmic Scales: JWST’s Discovery of Unexpectedly Massive Black Holes: Fabio Pacucci (Center for Astrophysics | Harvard & Smithsonian)

There’s a well-known relationship between the mass of a SMBH and the mass of the stars in its host galaxy, with the stars outweighing the SMBH by a ratio of about 1000 to 1. However, there’s a population of “overmassive” SMBHS, which JWST has been finding at high redshift (z > 4). Fabio Pacucci and his collaborators studied these to find out if this is an observational bias, or if these mass ratios are being accurately estimated.

At these high redshifts, JWST is able (to paraphrase Dante) “to see the stars again,” allowing Pacucci and collaborators to estimate the stellar mass ratios in these galaxies. They found that, compared to local galaxies, there is a statistically significant difference in these mass ratios, going from 1000 to 1 nearby down to 100 or even 10 to 1 at high redshift.

These results are suggestive of the history of these black holes: by comparing black holes that started their lives light and those that are seeded heavy, the JWST results imply that these overmassive black holes must have started with heavy seeds.

Revealing the Environment of the Most Distant Fast Radio Burst with the Hubble Space Telescope: Alexa Gordon (Northwestern University)

Astronomical transients are non-periodic events that occur and disappear on short timescales. Fast radio bursts (FRBs) are a relatively new class of transients with enigmatic causes that manifest as highly energetic radio pulses on the scale of milliseconds. Alexa Gordon and her collaborators presented a study of FRB 20220610A, the farthest (z = 1) and brightest (4x brighter than any other) FRB yet observed.

Only about 50 or so FRBs have been localized to specific source galaxies, which is critical to understanding the processes that may produce them. Ground-based followup of FRB 20220610A showed inconclusive results as to its source, only showing either a large amorphous galaxy or a merging cluster of three smaller galaxies. Gordon’s team used the Hubble Space Telescope to re-observe the FRB source, and found that it actually originated from a compact group of seven galaxies that together are about the size of the Milky Way! Less than 1% of galaxies at this redshift occur in groups like this!

These galaxies appear to be tidally interacting, which can trigger star formation. Gordon speculates that this tells us about the source of the FRB, as one potential mechanism for FRBs are magnetars, highly magnetized young neutron stars which have very strong emission and are produced as a result of core-collapse supernovae. Gordon and her collaborators are hoping to continue to observe more of these types of FRBs, especially as upgrades to new observatories come online and continue to discover these sources at even higher redshifts.

Burst Chaser: Unveiling the Mysterious Origin of Gamma-ray Bursts with Citizen Science: Amy Lien (University of Tampa)

Gamma ray bursts (GRBs) are the most powerful explosions in the universe. A typical GRB outshines every other source in the gamma-ray sky, combined! The Swift Observatory, NASA’s premier gamma-ray observatory, has detected more than 1,600 of these events across the sky.

GRBs come in many shapes and sizes, with differing energies and pulse traces, with short GRBs (< 2 seconds) typically thought to be produced by mergers of compact objects (like neutron stars or black holes) while long GRBs (> 2 seconds) are thought to be produced by supernovae. However, these are not hard classifications, and Lien and her colleagues turned to citizen science to more accurately classify these energetic signals to more accurately characterize them by their physical origins.

A test program showed that volunteer human classifiers (made up of a beta test group of astronomers and the interested public) perform better than existing GRB classification codes for sorting these traces by their observed shapes. Now, Lien and her collaborators are taking their program to the public, using the Zooniverse website to host their GRB classification data. You can join this project at https://www.zooniverse.org/projects/amylien/burst-chaser.

Seeing Our Sun Through a New Lens: The First Large Catalog of Hot Thermal Solar Flares: Aravind Valluvan (University of California, San Diego)

Solar flares, random broadband energetic bursts from the Sun, are a critical component of space weather. These events typically last about 20 minutes or so, but they could be as short as a few minutes or as long as half a day. These are the most energetic explosions in the solar system, and they have long been known to pose a threat to electronic communications infrastructure and sensitive operations like high-altitude aviation. These effects are important to study, in order to be able to predict them in advance and mitigate their effects.

Aravind Valluvan, from UCSD, studies these flares, looking specifically at “hot thermal flares”: flares with relatively symmetric light curves. The typical “impulsive” flare has a very quick, energetic rising phase and a much more gradual decay, while hot thermal flares increase and decrease in intensity on roughly the same timescales.

Valluvan says that while typical impulsive flares are caused by rapid magnetic field reconnection quickly dumping energy into the solar corona, hot thermal flares instead may be a result of slower magnetic reconnection processes, or slower energy transfer to the corona. Valluvan’s group observed 2,200 of these hot thermal flares and their catalog will be critical to properly interpreting these flares’ formation mechanisms. Are there connections between hot thermal flares and other solar phenomena like coronal mass ejections or solar particle events? Maybe! ISRO’s recently launched Aditya-L1 mission recently reached its final orbit, where it will use its X-ray spectrometer and ultraviolet imager to study the Sun and its energetic outbursts, just in time for solar maximum. Valluvan is hopeful that this mission will help us finally answer some of these critical questions.

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Annie Jump Cannon Prize Lecture: Theories of Planet Formation, Eve Lee (McGill University) (by Briley Lewis)

For the 2022 Annie Jump Cannon Prize lecture, Eve Lee discussed the detailed (and quite complicated!) theoretical physics of planet formation. The planet populations we observe, she reminded the audience, are the consequences of coagulation and chemistry in the protoplanetary disk, disk–planet interactions, orbital dynamics, and atmospheric processes. She considered all these factors to try to explain: (1) a set of three puzzling (and seemingly contradictory) observations, (2) the origin of the Neptune desert, and (3) the favored location of Jupiter-like planets.

Let’s start with the trio of puzzling observations. First, outer giant planets appear to be more common around higher-mass stars. Second, inner super-Earths are more common around lower-mass stars. Third, systems with outer giants tend to have inner super-Earths. At first glance, it seems like the third observation is in tension with the first two — but Lee described in her talk (and also in a paper published last year) why these observations are actually reconcilable, and explainable by physics. Outer giants have inner super-Earths, because if a disk is large enough to form a giant planet, it also likely has enough mass to form a smaller super-Earth. Large stars have larger disks, so they form big planets, and small stars are able to convert pebbles to planetesimals more efficiently because they are cooler.

The Neptune desert — a notable lack of planets similar in size to Neptune in a region close to the host star — isn’t the result of just one factor, according to Lee. Part of the gap is from planets that just formed like that, lacking in metals to effectively cool themselves and accrete a gaseous envelope. Then, the gap is further carved by atmospheric evaporation caused by the star.

Finally, to determine why Jupiters so often form between 1 and 10 au, she considered what’s going on physically at each bound of that range. At the inner boundary, migration cuts off the ability for large planets to exist there. At the outer boundary, dust grains drift faster than they can grow, limiting the size of planets that can form.

Lee’s talk was a great reminder that planetary systems are extremely complex, and we have so much left to learn about how they become the worlds we observe — and even about how our own planet came to be.

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Plenary Lecture: Sukanya Chakrabarti (University of Alabama, Huntsville) (by William Lamb)

Our galaxy rotates faster than it should if it only contains observable matter. This is why astrophysicists predict the existence of a dark matter halo surrounding the Milky Way to account for the extra, unobserved mass that must be there. The problem is, we don’t know much about dark matter because we have never observed it directly, and we don’t know how it is distributed in our galaxy. Sukanya Chakrabarti’s talk focused on probing dark matter by directly measuring the acceleration of stars within the Milky Way’s gravitational potential, which should bring further enlightenment on the effects of dark matter within a galaxy.

Traditionally, astrophysicists would estimate the acceleration induced on galactic stars by gravity by taking observations of the velocities and positions of those stars. This requires the assumption that galaxies are in equilibrium, where the gravitational potential and hydrostatic pressures that affect the motion of stars within the galaxy are balanced. However, galaxies are dynamic — interactions with satellite dwarf galaxies perturb galaxies over time. By directly measuring the acceleration of stars, Chakrabarti’s research enables the study of “real-time galaxy dynamics.”

Her group achieves this in four ways. First, they run dynamic simulations of the Milky Way, as opposed to simulations featuring static potentials. Second, they take high precision radial velocity observations, requiring a precision of 10 cm/s on velocity measurements, to measure the acceleration of some galactic objects. Third, they use pulsar timing measurements, such as those from NANOGrav, to effectively create a “galactic accelerometer” to measure the accelerations of pulsars. And fourth, they take measurements of the mid-points of exoplanetary eclipses, requiring a precision of 0.1 second across a 10-year baseline, to measure the accelerations of stars with exoplanets.

These measurements are extreme and on the edge of the technical capabilities of modern instruments and data analysis techniques. However, Chakrabarti is showing that this is possible, and hopefully insights from her work will further our understanding of dark matter in our galaxy.

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Cassiopeia A, a circular-shaped cloud of gas and dust with complex structure. The inner shell is made of bright pink and orange filaments studded with clumps and knots that look like tiny pieces of shattered glass. Around the exterior of the inner shell, particularly at the upper right, there are curtains of wispy gas that look like campfire smoke. The white smoke-like material also appears to fill the cavity of the inner shell, featuring structures shaped like large bubbles. Around and within the nebula, there are various stars seen as points of blue and white light. Outside the nebula, there are also clumps of yellow dust, with a particularly large clump at the bottom right corner that appears to have very detailed striations.

Editor’s Note: This week we’re at the 243rd AAS meeting in New Orleans, LA. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com for daily summaries, or follow @astrobites.bsky.social on BlueSky for more coverage. The usual posting schedule for AAS Nova will resume on January 16th.

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Fred Kavli Plenary Lecture: NANOGrav: The Dawn of Gravitational-Wave Astronomy at Light-Year Wavelengths, Stephen Taylor (Vanderbilt University) (by William Lamb)

Steve Taylor presenting on a stage

Steve Taylor speaking at the Kavli Plenary Lecture, 8 January 2024. [William Lamb]

Disclaimer: Steve Taylor is my PhD advisor, and I am also a NANOGraver. Seeing him on stage as the Kavli Plenary Lecturer was inspirational and entertaining for me and his other PhDs who were sat close to the front of the room, watching him present on our work as a research group at Vanderbilt University and representing the NANOGrav collaboration. We were kicking ourselves; we should’ve brought some fun signs…

The plenary began by acknowledging the early start to the day and jumping straight into the results from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). In June, in coordination with the European Pulsar Timing Array, the Indian Pulsar Timing Array, the Parkes Pulsar Timing Array, and the Chinese Pulsar Timing Array, we independently published strong evidence for a nanohertz-frequency gravitational wave background using pulsar timing arrays. He built up the talk by describing the gravitational wave spectrum, how pulsar timing arrays detect the background, and the likely astrophysical sources that create the background. To finish, Taylor explored the new science that should result from pulsar timing arrays, from probing supermassive black hole binaries and detecting their electromagnetic counterparts, to constraining “new physics” models that are generating a lot of excitement in the high-energy physics field. I can tell you: it is certainly a very exciting time for NANOGrav.

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Special Session: International Students and Researchers in Astronomy: Issues and a Path Forward (by William Lamb)

For the first time at an AAS meeting, a session was dedicated to discuss the issues faced by international researchers and students that work and study in the US. The intent was to understand what these issues are and how AAS can help to tackle these issues. The session opened with Arpita Roy, a Program Scientist at Schmidt Futures. She shared her story about moving to the US to study astrophysics at Franklin & Marshall College before getting her PhD at Pennsylvania State University, where she worked on exoplanets with instruments from around the world. She reminds us that “astronomy is a global endeavour, but resources can be highly localised.” She remarked how international researcher issues are often framed in the context of logistics — what do they need to get to the US — but we often forget the value they bring to US research, and we should be focusing on that more. “It’s hard to work on your science when as a human being, you are being disrespected.”

The second speaker was Óscar Chávez Ortiz, a 4th-year graduate student at the University of Texas at Austin. He spoke about navigating academia as someone with DACA (Deferred Action for Childhood Arrivals) status. Chávez Ortiz’s family migrated to the US when he was very young, leaving him without lawful status in the US. He didn’t consider higher education until the DACA program existed, which finally “allowed me access to my dream.” However, being a “dreamer” still comes with barriers, such as being unable to leave the US for international conferences and being unable to apply to most, if not all, Research Experience for Undergraduates (REU) programs because applicants require citizenship. The DACA act has been life-changing for Chavez, but he still faces barriers, such as the legal limbo faced by people with DACA status, in particular when a new government administration or state chooses to become hostile to them.

I (William Lamb) spoke about my experience of moving to the US in August 2020 — during the height of the COVID-19 pandemic. I shared stories about my challenge to find safe, affordable accommodation to quarantine while taking online classes when I first moved, and some of the complications that I encountered in my first few months in the US which were exacerbated by the pandemic. I argued that these problems weren’t because of COVID-19, but because of the systematic problems in the US immigration system that urgently need to be addressed.

Following these talks, we were joined by the Chair of the AAS Education Committee, Tania Anderson; AAS agent Rica Sirbaugh French of MiraCosta College; and the organisers of the session, Yaswant Devarakonda from the AAS and Fabio Pacucci from the Center for Astrophysics. During the panel discussion with the audience, I believe we identified some important work and changes that need to be implemented by the AAS. For example, there are a lot of resources to support international researchers out there, but access to those resources is difficult and a lot of those resources conflict with each other. Another issue is the divide between access to REU programs, PhD fellowships, and even grants for professors, between domestic and international researchers. We agreed that the AAS needs to support international researchers significantly more, especially those with DACA status. We were buoyed by the news that the AAS is taking these concerns seriously, and they are planning on establishing a committee to discuss the barriers faced by international researchers.

If you would like to kept in the loop about the AAS’s plans, email Yaswant Devarakonda, who is the John N. Bahcall Public Policy Fellow for the AAS. We also encourage you to show your support for an AAS committee for international students by emailing the AAS with your story.

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Press Conference: Dust, Clouds & Darkness (by Briley Lewis)

The first press conference of AAS 243 was a fun mashup of different topics, all in some way related to one particular fundamental component of the cosmos: dust.

Figure showing the M0.8-0.2 ring and circular magnetic field lines

A diagram from Butterfield’s talk on the M0.8-0.2 polarized dust ring. This illustrates the location of the dust ring in the Milky Way, and visualizes the magnetic field lines within.

The session kicked off with Natalie Butterfield from the NRAO unveiling the discovery of a polarized ring of dust in the Milky Way’s center. This fascinating observation came from one of SOFIA’s legacy programs — FIREPLACE II, the 2nd Far-InfraRed Polarimetric Large Area CMZ Emission survey — that are keeping the flying telescope’s legacy alive even after its retirement. The extreme environment of the galactic center contains dense clouds, with magnetic fields of around 100 microgauss (very tiny compared to refrigerator magnets that may come to mind, but quite strong for interstellar space!).

Diagram showing magnetic field lines crumpled together by a shock

A diagram from Butterfield’s talk showing how an expanding shell of a supernova remnant might sweep up magnetic field lines into the observed circular pattern.

In one specific ring, known as M0.8-0.2, they observed a curved magnetic field, tracing the ring of dust, with strengths around 1 milligauss — at least 10 times stronger than the background of the galactic center. They think this feature is actually a supernova remnant, with an expanding shell sweeping up material and compressing magnetic fields.

Cassiopeia A supernova remnant in false color

The new image of the Cassiopeia A supernova remnant including data from JWST. More details on the image are available in the Chandra press release. [X-ray: NASA/CXC/SAO; Optical: NASA/ESA/STScI; IR: NASA/ESA/CSA/STScI/Milisavljevic et al., NASA/JPL/CalTech; Image Processing: NASA/CXC/SAO/J. Schmidt and K. Arcand]

Up next, Dan Milisavljevic from Purdue University showcased another supernova remnant: the famous Cassiopeia A (Cas A). This object has been observed across wavelengths with all major NASA facilities, and it’s one of the best targets for investigating the dynamics of supernova explosions. It’s a particularly young example of a supernova remnant (only about 340 years old, from our vantage point), and it’s also quite nearby (around three kiloparsecs). Using JWST’s MIRI and NIRCam instruments, they were finally able to disentangle the “green monster” — a strange filamentary structure in the center of Cas A — from the rest of the remnant, revealing unshocked ejecta from the supernova behind it. This is the first map of the inner area of a supernova explosion, where unshocked oxygen exists. Plus, it’s an absolutely gorgeous new image!

Jin Koda (Stony Brook University) and Amanda Lee (U. Mass Amherst) then presented a brand new data set from ALMA, looking at a region on the outskirts of the galaxy Messier 83 for molecular clouds, the sites of star formation. Using multiple telescopes and an international collaboration, they detected molecular clouds at the edges of a galaxy for the first time. Now, this leaves them with the question: how does the diffuse gas in the fringes of Messier 83 end up as molecular clouds?

Karen O’Neil from Green Bank Observatory announced another particularly exciting discovery: a new radio source that just might be the first primordial galaxy we’ve detected. This extremely faint source is about 83 megaparsecs away, with characteristics (like mass and rotation rates) of a pretty normal spiral galaxy. But, it’s extremely low brightness. It has a wealth of gas for star formation, yet not enough stars for it to shine in the sky — a dark galaxy seen before star formation really begins. It’s unclear why this galaxy is so unevolved, but they speculate that the gas may be too diffuse to start forming stars or there haven’t been any major interactions to spur star formation or tear the galaxy apart. Either way, this is likely one of a new class of objects, with hopefully many more to be found in upcoming radio surveys. “This is real,” said O’Neil. “We have spent many hundreds of hours of GBT [Green Bank Telescope] time to pin this down.”

To round out the session, Alison Coil (UCSD) presented another mysterious class of objects: odd radio circles, or ORCs (and yes, this acronym is bringing back how much I wish I saw Gimli in the exhibit hall yesterday!). ORCs were initially discovered in 2021, and they appear as large (~1 arcmin) rings in radio continuum centered on a galaxy, with physical sizes of hundreds of kiloparsecs across. Only about 11 are known, with a new one discovered about every two to three months. One particular ORC (ORC4, originally discovered by ASKAP) is huge, with a massive central galaxy and a radius of 200 kiloparsecs. Recently, astronomers imaged its host galaxy using the Keck Cosmic Web Imager, finding very strong OII emission lines, even far away from the galaxy — but not quite as far as the ORC. They determined that a burst of star formation in the galaxy’s past caused both the ORC and the OII ring. When the wind driven by the star formation burst shuts off, the forward shock (and its corresponding radio emission) continue propagating outwards, while the backwards shock with the OII falls back towards the galaxy. Perhaps ORCs aren’t so odd after all — or at least now we might know where they come from!

Figure in three parts showing how shocks travel outward from the galaxy

A diagram from Coil’s talk illustrating how the forward and reverse shocks from a star formation burst travel over time, creating the outer ORC and inner OII emission ring.

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Helen B. Warner Prize Lecture: The PAH Revolution: Cold, Dark Carbon at the Earliest Stages of Star Formation, Brett McGuire (Massachusetts Institute of Technology) (by Ben Cassese)

Just before the first lunch break in New Orleans, the inhabitants of Grand Hall A were treated to a plenary session delivered by Brett McGuire of the Massachusetts Institute of Technology. McGuire’s day on the plenary stage was a long time coming: he had received the AAS’s Helen B. Warner Prize in 2022, but because of pandemic-related meeting disruptions he could not deliver his talk, “The PAH Revolution: Cold, Dark Carbon at the Earliest Stages of Star Formation,” until now.

A graphic with multiple small images linked with a curved arrow. Each image depicts one phase in the lifecycle of matter collapsing from molecular clouds into stars and planets. A kitten in an astronaut suit floating above Earth stands out among the more serious scientific renderings.

The lifecycle of matter in the universe, from a molecular cloud, to cats, and back. [B. McGuire]

McGuire began with an invocation of Douglas Adams (“In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move.”) and a broad outline of his mission. After explaining that the Big Bang left the universe with only the simplest elemental building blocks, he shared that “My job… is to figure out how you go from hydrogen and helium from the Big Bang to cats.” To do this, McGuire and his many collaborators search the coldest, densest, and darkest corners of the Milky Way for complex molecules, then try to explain where they all come from.

McGuire’s primary tool in this endeavor is the Green Bank Telescope (GBT), and his favorite place to point it is the Taurus Molecular Cloud 1, a frigid but well-studied assemblage of gas and organics that he and collaborators suspected would provide fertile hunting grounds for new molecules. They were correct: in 2018, they found the second 5- or 6-membered ring species ever spotted in space, then went on to discover a laboratory stockroom’s worth of bizarre, complex molecules. Among these are the first four polycyclic aromatic hydrocarbons (PAHs) conclusively identified beyond the solar system, and many long, linear, and sometimes kinked chains of carbon.

A 4-panel meme. The text in the first reads "carefuly constuct a ML model of interstellar chemistry". The next: "Use it to choose what molecules to hunt for". The last two: "Chemistry doesn't care and will do its own thing".

A slide to illustrate why laboratory experiments are necessary counterparts to theory and modeling. [B. McGuire]

Halfway through the talk, McGuire revealed that he is attacking the problems of molecule identification on more than one front. Not only does his collaboration (lovingly but torturously named GBT Observations of TMC-1: Hunting for Aromatic Molecules, or GOTHAM) collect and analyze telescope data, they also perform laboratory experiments to help them interpret their data. Armed with lasers, mirrors, and novel machine learning/automations techniques, their team has measured several molecules in the lab that they then found in their GBT observations.

Overall, McGuire’s talk was a lighthearted and joyful overview of recent advances in laboratory and data processing techniques that have uncovered dozens of new molecules in space. One left certain both that the recent past few years of cosmochemistry have been exciting, and that the next few will be even more so.

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Press Conference: Stars, Protostars & More Clouds (by Mark Popinchalk)

At this conference there were four speakers, shining bright and talking about stars!

Asymmetric Gamma-ray Emission from the Quiet Sun

Slide demonstrating how the Sun's activity changes over an 11-year period, and the corresponding magnetic field flip

A slide from Elena Orlando’s press conference showing the solar activity cycle.

The first presenter was Elena Orlando (University of Trieste and Stanford University), telling us about asymmetry in our Sun seen in gamma rays. The Sun has a steady state of gamma radiation due to cosmic rays from beyond our solar system hitting it. This was first discovered in 2000. However, the Fermi mission has better sensitivity and angular resolution. The Sun crosses in front of Fermi daily, although to get good images one needs to integrate a few hundred days of data. Still, the researchers had Fermi data from 2008 to today to look through that covered the entirety of the solar 11-year activity cycle.

In the hundred-day window that included the peak of the solar activity, Orlando’s team noticed that there were more high-energy gamma rays from one pole and more low-energy gamma rays from the other! This peak in activity happens when the solar magnetic field flips. Orlando doesn’t yet have a full explanation, but this does suggest a crucial role of the magnetic field and opens up a link between astronomy, particle physics, and plasma physics.

A Colossal Star Erupts: Examining One of the Largest Stars in the Milky Way as It Fades From View

Narsireddy Anugu (CHARA Array; Georgia State University) introduced us all to RW Cephei, a huge hypergiant that has undergone a recent eruption! One of the largest stars in the galaxy, it reached an historical faintness in 2023. Anugu and collaborators wanted to learn more, but even with the star’s great size, it appears a million times smaller than our full Moon. Therefore they needed to use the CHARA array, the world’s largest optical interferometer. It combines six telescopes to make an effective diameter of 360 meters!

Slide with two images of RW Cephei, one during the star's faint period in December 2022 and one during a brightening period in July 2023.

A slide from Narsireddy Anugu’s press conference showing the change in brightness of different regions of RW Cephei.

From these observations they were able to get an idea of the brightness of the object, and they saw that while there was one side that was fainter during the dimmest observation, it changed when the star started to brighten.

Anugu and collaborators proposed a similar mechanism to Betelgeuse’s great dimming event: a convective cell ejected a gas cloud, and as the cloud cools and forms dust it falls back onto the surface of the star, causing it to dim. These ejections might impact the mass of the star, which in turn might determine its ultimate fate!

Early Evolution of Planetary Disk Structures Seen for the First Time

Cheng-Han Hsieh (Yale University) changed the topic by releasing baby pictures of planetary systems — that is, some of the youngest planetary disk structures ever seen. Planets form in big dusty protoplanetary disks. Previous studies using ALMA targeted large luminous disks of more evolved disks with ages greater than 2 million years, but substructures in younger disks are hard to find.

Multiple images of protoplanetary disks, including "donut-like" disks that are empty at the center, and "bun-like" disks that are filled through the center.

A slide from Cheng-Han Hsieh’s press conference showing tasty-looking protoplanetary disks.

The team used ALMA to survey nearly all the embedded protostars in seven young stellar populations. They grouped the substructures into two classes: those that seem to look like a donut (rings with a large central cavity), and those that look like filled buns (multiple ring systems with center filled). To be clear, this session was held directly after lunch, but this astrobiter certainly left hungry.

These disk substructures started to appear for sources that were at least 300,000 years old, which could perhaps be the start of giant planet evolution! But another question that arises is that if these two groups represent different kinds of disk populations, which population(s) can create solar systems like our own?

The Wondrous 3D World of Protostellar Shocks in NGC 2071

Finally Nicole Karnath (Space Science Institute) wanted to show us that young stars like to rock and roll. To do this, she and her collaborators looked at NGC 2071 IR, a star-forming region that hosts seven young stellar objects, including two protostars named HOPS-361 A and C. These are both intermediate-mass protostars, which will become stars bigger than our Sun. However, intermediate-mass stars aren’t as well studied. There is a need to assess the driving of turbulence in these regions, since if the stars are lashing out in their youth they could be lowering the overall star-formation efficiency in their surroundings. To do this, there needs to be an accurate map of the 3D motion of the gas the young stars are kicking off. This is difficult to obtain.

Fortunately, the team had the right tools: the Hubble Space Telescope (HST) and the SOFIA airplane-based telescope. They used an archival HST image that had the outflow from HOPS 361-A, and then another image from 2021. Just by comparing the two images you can see the gas moving!

photos of a young star's outflow over time

A slide from Nicole Karnath’s press conference showing the outflow of gas from a young star.

HOPS 361-A has a compact, complex outflow of gas. The amount of gas kicked out seems to be the same between the 2009 and 2021 images, and the outflows are shooting off at hundreds of kilometers per second. Normally, it’s thought that most of the outflow material should be moving in a similar direction, but the outflows are going in different directions. It looks like this young star is very messy! Meanwhile HOPS 361-C has a knot of gas that is slowing down. Furthermore, it’s wobbling as it is throwing out gas, spinning over a loop every 2,000 years.

Finally, the data from SOFIA were included to show the full 3D movement, which wouldn’t have been possible without the infrared coverage (and it remains an open question of where the field can get similar data now that the mission has been ended.) Ultimately these two stars are causing very different outflows in NGC 2071 IR.

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Helen B. Warner Prize Lecture: The Milky Way as a Cosmological Laboratory, Ana Bonaca (Carnegie Institution for Science) (by Kerry Hensley)

In the second Warner Prize lecture of the day, Ana Bonaca (Carnegie Institution for Science) introduced the study of stellar streams and how it can help us understand the nature of dark matter. Dark matter is a mysterious substance thought to make up 85% of the matter in the universe by mass. The nature of dark matter is encoded in its spatial distribution: hot dark matter produces a smooth distribution, while warm dark matter has a little structure, and cold dark matter clumps into structures and substructures down to low masses.

images of the stellar streams surrounding two galaxies

These images highlight the ghostly stellar streams looping around Messier 94 (left) and Messier 63 (right). Stellar streams are the remnants of globular clusters or dwarf galaxies. [Giuseppe Donatiello / Michele Trungati; Public Domain]

To learn more about dark matter’s properties, we need to figure out the size of the structures it forms. Studying dark matter’s influence on the dynamics of stars is a promising way to do just that. Bonaca searches for dark matter subhalos — clumps of dark matter embedded within a galaxy’s dark matter halo — by studying stellar streams surrounding the Milky Way. Stellar streams are thin trails of stars that form when globular clusters or dwarf galaxies are torn apart by gravitational interactions. If dark matter is distributed smoothly throughout our galaxy’s dark matter halo, stellar streams will form smooth lines. If instead dark matter is uneven and clumpy, stellar streams might appear discontinuous, contain over- and under-dense regions, or have stars that appear to have fallen out of the stream.

Using data from multiple sources, especially the Dark Energy Survey and the Gaia spacecraft, Bonaca and collaborators have discovered and characterized numerous stellar streams. The Milky Way contains about a hundred known stellar streams, mostly within 65,000 light-years, but Bonaca estimates that more than a hundred streams remain to be found — especially farther out. These far-out streams are enticing targets because they are farther from the gravitational disturbances created by the Milky Way’s spiral arms and central bar of stars, making the streams more sensitive to the influence of dark matter.

Of the known stellar streams, many have signs of past perturbations that could point to a close encounter with a dark matter subhalo. Modeling of one particular disrupted stellar stream suggested a fairly recent encounter with a massive (5 million solar masses or so) object, and Bonaca’s team will use the Hubble Space Telescope to study the stream further and narrow in on the location of the purported perturbing dark matter subhalo.

Bonaca identified three focus areas for future study: 1) Stellar streams with known progenitors (i.e., it is known which globular cluster or dwarf galaxy the stream came from), 2) stellar streams in the outer regions of the Milky Way, and 3) the population of stellar streams as a whole. Advancing each of these goals will require precise radial-velocity measurements, wide sky coverage, and the ability to study very faint targets. To that end, Bonaca and collaborators started the VIA project to build a spectrograph that meets their requirements, and the proposed project will involve a five-year survey that produces three million spectra. The Rubin Observatory’s Legacy Survey of Space and Time will also expand our understanding of stellar streams, helping us to study streams that are farther away and in much greater detail than is possible today.

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Plenary Lecture: The Rarity of Life in the Universe, Alan Lightman (Massachusetts Institute of Technology) (by Yoni Brande)

It’s hard for most people to grasp the scales on which the universe exists. With a width of a hundred billion light-years, from 13.6 billion years in the past to a possibly infinite existence in the future, we are, as Carl Sagan put it, “on a mote of dust suspended in a sunbeam” in the universe. Alan Lightman’s plenary lecture today focused on putting ourselves into perspective, reflecting on our cosmic insignificance, as well as the immense significance of our unique position as observers of, and in, the universe.

Humans have been wondering about our place in the universe for our entire history as a species. Twenty thousand years ago, cave paintings in the Lascaux complex depicted the Pleiades star cluster, debates over differing cosmologies raged between geocentrism and heliocentrism, spiral nebulae and island universes, and the static and expanding universe. The development of modern astronomy, Lightman posits, is characterized by the continuing realization that we are not special in our place in the universe. We are, in fact, starstuff, made up of elements originally synthesized in the Big Bang and then in the explosive deaths of massive stars as supernovae.

In Lightman’s view, the vastness of the universe — with hundreds of billions of galaxies all made up of hundreds of billions of stars each — implies that life (and even intelligent life) must exist elsewhere in space and time. However, even if every habitable planet in the universe was teeming with life, the greatest fraction of living matter in the universe would be akin to a few grains of sand in the great Gobi desert.

Life must be rare in time as well as space, and perhaps even more concerning, Lightman says, is the fact that life has an end date. Life probably was able to arise after a billion years or so after the Big Bang, and in a hundred thousand billion years, the expansion of the universe will have stripped every galaxy away from every other galaxy, never to meet again. Lightman predicts this isolation will be the final nail in life’s coffin, lasting a mere 105 years out of a total potential universal lifetime of 1,084 years, from a Planck time after the Big Bang until the final proton decay, after which the universe will be in an eternal steady state. Life must be fleeting, Lightman says, but this gives it, and us, meaning. We must share a curiosity about and a consideration for our own isolation and mortality with everyone and everything that has ever or will ever live.

Lightman closed with a philosophical example: the “reverence for life” of Albert Schweitzer, German-French Nobel Laureate, physician, and philosopher. If Schweitzer’s biocentrism holds that there is a common kinship between all living beings on Earth, Lightman’s “cosmic biocentrism” extends this to all living things in the universe. “We few grains of sand in the desert are the only means by which the universe can consider itself. The cosmos will grind on for eternity long after we’re gone — cold and unobserved — but for these few powers of ten, we have been, we have seen, we have felt, we have lived.”

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Plenary Lecture: LeRoy E. Doggett Prize Lecture: It All Began with Tebbutt! The Peripatetic Path from New Zealand to New Orleans, Wayne Orchiston (by Ali Crisp)

To wrap up Day 1 of AAS 243, we had the “first ever” evening plenary at the conference, given by Wayne Orchiston. His talk was primarily biographical, focusing on his own journey from a young boy inspired by the night sky to his talk tonight as the LeRoy E. Doggett Prize recipient for his contributions to the history of astronomy. A common theme throughout was the inspiration he took from the Australian astronomer John Tebbutt.

Orchiston explained that he first became interested in Tebbutt and historical astronomy in general as a teen, when his father’s job caused the family to move from Lincoln, New Zealand, to Sydney, Australia. There he discovered the Windsor Observatory — founded by Tebbutt — and the thousands of letters, observing logs, journals, and other documents of Tebbutt. He held onto this interest through several jobs: working as a radio telescope operator with CSIRO as he worked on his undergraduate degree, a postdoc in geology and human evolution in Melbourne, and director of the museum studies and astronomy programs at Victoria College.

During his time at Victoria College, the centennial of many of Tebbutt’s contributions, such as the discovery of the Great Comet of 1881 and the Australian bicentennial, fanned the flames of Orchiston’s interest in history of science research. He went on to explain how the papers he published about Tebbutt led him to new information about other astronomers or areas of astronomy, and to new job opportunities. Ultimately, through (by his count) 12 moves, Dr. Orchiston ended up living in Thailand with a remote position at the University of Science and Technology of China, where he hosts workshops with his wife/research collaborator, co-edits the open source Journal of Astronomical History and Heritage, and hosts a monthly virtual lecture series on the history of astronomy.

Orchiston closed his lecture by sharing amazement with where his career has taken him, describing himself as “a geography teacher who lost his way.” He stated that the Prize is one of his proudest achievements, and emphasized the main things he believes have led him to this point: opportunity, networking and role models, dedication, getting his work out there, flexibility, maintaining passion in his work, and the support of his wife.

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photo of Astrobiters staffing the booth at the grad school fair at AAS 243

This week, AAS Nova and Astrobites are attending the American Astronomical Society (AAS) winter meeting in New Orleans, LA.

AAS Nova Editors Kerry Hensley and Susanna Kohler and AAS Media Fellow Ben Cassese will join Astrobites Media Intern Briley Lewis and Astrobiters Ali Crisp, Pratik Gandhi, Ivey Davis, Isabella Trierweiler, Mark Popinchalk, William Lamb, Yoni Brande, and Junellie Gonzalez Quiles to live-blog the meeting for all those who aren’t attending or can’t make all the sessions they’d like. We plan to cover all of the plenaries and press conferences, so follow along here on aasnova.org or astrobites.org! You can also follow Astrobites on BlueSky at astrobites.bsky.social for more meeting content.

Where can you find us during the meeting? We’ll be at the Astrobites booth in the Exhibit Hall all week — stop by and say hello! We’ll also be engaged in several education and outreach activities throughout the meeting (please note that many of these links will take you to the AAS 243 block schedule; you must be logged in for the links to take you to the correct session):

Briley Lewis will give a talk during the Enhancing Learning Experience in Astronomy Courses session titled “Exploring the Effects of Astrobites Lesson Plans on Undergraduate Astronomy Students” on Wednesday, January 10, from 3:00 to 3:10 pm CST in Room 222 (program number 345.07). Briley will also be giving a presentation on Astrobites at the exhibitor theater in the Exhibit Hall on Wednesday, January 10, at 3:30 pm CST.

poster detailing the community discussions hosted by the Rainbow Village

This flyer lists the community discussions hosted by the Rainbow Village. Click to enlarge. [Arianna Long]

Junellie Gonzalez Quiles invites all meeting attendees to stop by the Rainbow Village in the Exhibit Hall throughout the week. The Rainbow Village is a collaboration between the AAS Committee on the Status of Minorities in Astronomy (CSMA), #BlackinAstro, VanguardSTEM, and the League of Underrepresented Minoritized Astronomers (LUMA) that aims to create a gathering place for people of color and allies at AAS meetings. Stop by for support, celebration, daily discussions, and more! They’re even collecting a list of presentations by BIPOC astronomers, so you can show your support. You can learn more about the Rainbow Village and read interviews with organizers Junellie Gonzalez Quiles, Arianna Long, Ashley Walker, and Nicole Cabrera Salazar.

There are several social events associated with the Rainbow Village, including a dinner hosted by 1400 degrees on Monday from 6:30 to 9:00 pm, an AAS Committee for Sexual-Orientation & Gender Minorities in Astronomy LGBTQIA+ Meet and Greet on Monday from 6:30 to 8:00 pm, a Black in Astro networking dinner on Tuesday from 6:00 to 8:00 pm, and a CSMA meet and greet on Wednesday from 6:00 to 7:30 pm. Lastly, be sure to attend the Astronomy’s Poverty Problem session and the Effective Partnerships with Historically Black Colleges and Universities session.

Mark Popinchalk will be representing Astronomy on Tap NYC. You can join Astronomy on Tap Tuesday, January 9, at Republic NOLA (Doors and food at 6 pm CST, event starts 7 pm CST), which aims to be the largest Astronomy on Tap yet!

Finally, you can read the currently published AAS 243 keynote speaker interviews here. Be sure to check back all week as the remainder are released!

Banner advertising the 243rd meeting of the American Astronomical Society in New Orleans, LA

AAS 243 is nearly here! The AAS Publishing team looks forward to connecting with meeting attendees in New Orleans, LA, and we’re excited to share a preview of upcoming publishing-related events. Attending the meeting will be Julie Steffen (AAS Chief Publishing Officer), Ethan Vishniac (AAS Journals Editor in Chief), Frank Timmes (AAS Journals Associate Editor in Chief), and Chris Lintott (Editor of Research Notes of the AAS). The entire AAS Journals data editing team will be in attendance as well — that’s Gus Muench, Greg Schwarz, and Katie Merrell. Finally, Jennifer Kelzenberg from IOP Publishing will be on site to talk about the AAS Chandrasekhar Style Guide. Be sure to stop by the AAS booth in the Exhibit Hall to say hello and pick up some swag, including some newly designed AAS Nova bookmarks!

AAS Nova Editors Kerry Hensley and Susanna Kohler, AAS Media Fellow Ben Cassese, Astrobites Media Intern Briley Lewis, and the rest of the Astrobites team will also be available at the Astrobites booth in the Exhibit Hall.

Data Editors Help Desk

The AAS Journals data editors will be staffing a help desk in the Exhibit Hall for the first time at AAS 243. Stop by the help desk to learn more about the work of the data editors, how they can help you present and organize your data in published research articles, and get one-on-one assistance with your data challenges. The data editors will be available anytime the Exhibit Hall is open. One-on-one sessions are also available over email; reach out to data-editors@aas.org for more information.

AAS Peer Review Workshop

Building on the successes of the first-ever in-person peer review training at AAS 242, this workshop led by the scientific editors of the AAS journals will teach participants about the peer review process, give them the opportunity to see both poor and exemplary referee reports, and provide them with hands-on experience in writing a peer review report. Participants will receive a graduation certificate.

While signups for this instance of the peer review workshop are closed, another workshop is planned for AAS 244 in Madison, WI, so keep an eye out for more information about upcoming opportunities!

Open Science at AAS 243

Note: The following section contains links to the AAS 243 block schedule. You must be logged in for these links to direct you to the correct session; otherwise, they will take you to the main block schedule page.

There are many exciting sessions, splinters, and exhibit hall booths occurring this week on the hot topic of Open Science. Love ADS? On Monday, the oral session #134 Laboratory Astrophysics and Open Science (Room R05) includes a talk presenting the ADS for All of NASA Science — the all new SciX! Don’t miss any of the Tuesday’s wide-ranging iPoster session #258 Data Tools and Open Science. The main session for talking to the presenters about their open-source codes and analysis techniques is Tuesday at 5:30–6:30 pm, though their iPosters are available all week.

Wednesday brings two important forums for learning about and engaging with Open Science. In the morning, a public splinter session titled Transform to Open Science Ethos Training runs from 9:00 am to 11:30 am in Room 242 and intends to introduce the ethos of open science. Learners will become familiar with the definitions central to open science and explore some concrete examples of the benefits to researchers, the pace and quality of science, and the public. Wednesday afternoon (1:00–2:30 pm, Room 237) brings the Astrophysics and Open Science session that includes a panel of members of the NASA Astrophysics Division, the Science Mission Directorate Science Data Office, the Transform to Open Science (TOPS) mission, and the NSF to speak to NASA and NSF efforts to enable Open Science and answer queries about the same.

Be sure to stop by some of the related exhibitor booths to talk more Open Science! TOPS and Science Mission Directorate representatives will be at the NASA booth (#702), while ADS can be found at the Center for Astrophysics | Harvard & Smithsonian booth (#315). Lastly, the AAS Journal Data editors are hoping you’ll stop by our new Data Help Desk (#822) to talk open science, data archiving, and everything else in between.

Hubble images of Saturn

Editor’s Note: This week we’ll be writing updates on selected events at the 55th Division for Planetary Sciences (DPS) meeting, held jointly with the Europlanet Science Congress (EPSC) in San Antonio, Texas, and online. The usual posting schedule for AAS Nova will resume on October 9th.

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Alexander Prize Lecture: Results from Monitoring the Giant Planets with Hubble (Amy Simon)

The Claudia J. Alexander Prize is awarded to a mid-career planetary scientist “who has made and continues to make outstanding contributions that have significantly advanced our knowledge of planetary systems, including our solar system.” This year’s award went to Amy Simon (NASA Goddard Space Flight Center), who described in today’s plenary lecture an ongoing Hubble Space Telescope program to monitor the four giant planets in our solar system.

Illustration of the inconsistent observing history of the giant planets

Illustration of the inconsistent observing history of the giant planets. Click to enlarge. [Slide by Amy Simon]

Jupiter, Saturn, Uranus, and Neptune are giant planets with dynamic atmospheres. While some of the atmospheric changes on these planets occur on long timescales, unfurling over centuries — think Jupiter’s Great Red Spot — other changes happen rapidly, with visible differences cropping up year after year. Our understanding of these changes and their causes has been limited by our observations of the giant planets. Even the best-studied of the giant planets, Jupiter, which has been observed with the Hubble Space Telescope for more than a decade and visited (including flybys) by Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, New Horizons, and now Juno, had too inconsistent of a data record to derive reliable trends. And though there are many ground-based observations of the giant planets, differences in observing setups can make combining data sets difficult.

The solution? The Outer Planet Atmospheres Legacy (OPAL) program, which began in 2014 and continues to monitor each of the four giant planets on an annual basis using the Hubble Space Telescope. Each year, Hubble monitors the four planets through two planetary rotations, and the data become immediately available to the public, with the global maps having a dedicated page on the Hubble archive. These observations have allowed us to study storms on Saturn, Saturn’s color changes and changes to its north polar hexagon, the evolution of polar hazes on Uranus, the emergence of new dark spots on Neptune, and much more.

infrared image of the giant planets from JWST

Infrared images of the outer planets from JWST. Click to enlarge. [Slide by Amy Simon]

While the current program is scheduled to continue as long as Hubble is able to make the observations, Simon already has an eye on JWST’s infrared observing capabilities. Speaking about the possibility of undertaking a similar observing campaign with JWST, Simon says simply, “Why not?”

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Round Table Discussion: The Search for Liquid Water Beneath the Martian South Polar Layered Deposits (Roberto Orosei, David Stillman, Ali Bramson, and Jack Holt)

The final plenary session of the meeting was a discussion of an ongoing debate in the planetary science community: whether radar observations show the presence of liquid water beneath Mars’s south polar ice cap. Numerous research articles have argued both sides of the issue, and today four scientists presented their arguments before opening the floor to discussion.

First, a quick primer on the technique used to make the contested measurements. The supposed detection of liquid water was made using radar subsurface sounding, which can peer beneath the surface of a planet. The radar signal is reflected when the electric permittivity (related to how a material responds when exposed to an electric field) changes, such as where a layer of rock meets a layer of ice. How long it takes the signal to return and the brightness of the return signal can be used to map the layers below the surface.

Roberto Orosei (Italian National Institute of Astrophysics) and David Stillman (Southwest Research Institute) presented their evidence for the presence of liquid water first. They noted that the larger the contrast in permittivity of two materials, the stronger the radar reflection will be at their interface. Water or brine (a mixture of water and salts) has a permittivity around 80, while dry materials like rock have permittivities in the 3–15 range. Mixing water into other materials, such as Martian surface material or regolith, also causes a sharp increase in permittivity.

Example subsurface radar echo

Example subsurface radar echo. [From slide by Roberto Orosei]

When the team observed strong radar reflections beneath the south polar layered deposits on Mars, liquid water was an obvious candidate. The team observed the strong radar echoes over many different spacecraft orbits, during different seasons, and at different frequencies, showing that the signal is not a fluke. Analysis of the signal suggested that the permittivity of the material is greater than 20 — far too large for a dry material. Orosei and Stillman propose that water mixed with salts and sediment, which would have a lower freezing/melting point, is the cause. Furthermore, research has found that the radar echo properties are similar to those of subglacial lakes on Earth.

Orosei and Stillman addressed four common rebuttals of their argument:

  1. It is too cold beneath the polar deposits for water or brines to be liquid … but brines can be liquid down to 197K, which could be cool enough for them to be liquid in the extreme cold beneath the polar cap, according to the weakening of the radar signal that suggests temperatures below 230K.
  2. Geologic evidence doesn’t support the presence of a body of water, and the bright radar reflections don’t overlap with the expected locations of lakes … but our data don’t have fine enough vertical resolution to truly determine where lakes should be located beneath the glacier, and the surface features are consistent with what we see above subglacial lakes on Earth.
  3. Other materials like clays, saline ices, hematite, and smectites can have equally bright radar reflections … but measurements of the permittivities of some of these materials at cold, Mars-like temperatures are too low to explain the bright reflections, and you’d need an unreasonably large amount of hematite to create a similar radar echo. Radar echoes from dense basalts are a possibility.
  4. The echoes could be an electromagnetic artifact … but looking at raw data or frequency-dependent behavior should rule out this possibility, and the team doesn’t claim that every single bright radar echo is evidence of water.

Next, Ali Bramson (Purdue University) and Jack Holt (University of Arizona Lunar and Planetary Laboratory) took to the stage to present their arguments. First, Bramson outlined how much heat it would take (in the form of geothermal energy radiating out of Mars’s surface) for liquid water to be present beneath the north polar region. The expected heat flux is 10–30 milliwatts per square meter, which could bring temperatures up to 170K, but liquid water with a melting point of 273K would require at least 200 milliwatts per square meter. Even with salts mixed in to the ice, the melting point hovers around 200K, which still requires an increased amount of heating. Bramson and collaborators investigated possible ways to increase the geothermal heat flux, settling on magmatic activity within the past few hundred thousand years as a possibility. However, past magmatic activity is likely to be ancient, and most signs of “recent” volcanism are located near Mars’s equator, not its poles.

Holt introduced multiple different objections to the liquid water hypothesis, starting with the lack of geological evidence. Subglacial lakes on Earth are overlain by layers that have “drawn down” over time as layers above the lake undergo melting, but there’s no evidence of this drawing down on Mars. Similarly, there are no springs present due to flowing water. Holt pointed out that there are many bright radar echoes in the south polar layered deposits, some of which are located close to the edge where the ground is less insulated and temperatures are far too cold for even fully saturated brines to be liquid. Past research has also suggested that if the entirety of Mars were covered with layered deposits as seen at the south pole, much of the planet would have similarly bright radar echoes without the need for liquid.

SHARAD observation of a weak radar echo

SHARAD observation of a weak radar echo using new technique. [Slide by Jack Holt]

Where do we go from here? Both teams mentioned the Shallow Radar, or SHARAD, instrument on the Mars Reconnaissance Orbiter, which operates at a higher frequency than the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument whose data were scrutinized in this session. If SHARAD can detect echoes from beneath the south polar cap, the frequency-dependent behavior of the material should help us unravel the mystery of its composition. So far, no high signal-to-noise echoes have been reported, though experimenting with a new technique in which the spacecraft rolls by 120 degrees has been promising. With more than 20 research articles already published on this topic, we can expect to hear many more arguments in the case of Mars’s south polar water!

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JWST image of Jupiter

Editor’s Note: This week we’ll be writing updates on selected events at the 55th Division for Planetary Sciences (DPS) meeting, held jointly with the Europlanet Science Congress (EPSC) in San Antonio, Texas, and online. The usual posting schedule for AAS Nova will resume on October 9th.

Table of Contents:

New Solar System Discoveries from the JWST (by Ben Cassese)

Though JWST was initially conceived to tackle questions involving galaxies, cosmology, and the grand scale of our universe, it has proved a wonderful tool for the planetary sciences as well. One of the plenary sessions on Wednesday was dedicated to advances in our understanding of the solar system enabled by this new observatory, and it was split between three speakers.

First up was Stefanie Milam, the JWST Deputy Project Scientist for Planetary Science, who gave an overview of the investigations already underway with the latest flagship space telescope. Beyond our solar system, JWST has broken records in nearly every subfield of astronomy: it discovered and confirmed the most distant galaxy known to date, revealed an entirely new type of object in the Trapezium Cluster, and imaged rings of protoplanetary disks that had previously gone unseen in the glare of their host stars. Closer to home, it has collected the most detailed spectra of comets ever recorded, detected water vapor around a main belt comet for the first time, and provided never-before-seen views of the planets and their moons. These solar system observations are particularly impressive from a technical standpoint, since they required the ungainly assembly of mirrors and sunshades to move rapidly in order to stay focused on objects as they (and it) move around the Sun. As recently as a decade ago, the JWST science team was told that the telescope would not be able to observe something as bright, extended, and fast as Mars. Thanks to the advocacy of the scientists, the ingenuity of the engineers, and the skill of the project managers, JWST has already out-performed these assumed limitations.

A collage of photographs of Jupiter, Saturn, Uranus, and Neptune.

Images of the giant planets taken with JWST. [Slide by Lee Fletcher]

Leigh Fletcher of the University of Leicester came next. He delivered a presentation titled “New Views of the Giant Planets,” and his slides could have been sold as a dazzling coffee table book. Embedded within each of the gorgeous images of the four largest planets bound to our Sun were plenty of scientific “firsts.” These included the first H3+ aurorae found at Neptune; maps of the temperature variations on Uranus; observations of the region around Saturn just as detailed as those taken by the Cassini spacecraft when it was actually there, in orbit; and spectra of Jupiter and its Great Red Spot. Fletcher dedicated a portion of his time to a mention that the moons of these planets hadn’t escaped scrutiny either, and throughout his presentation emphasized that this enormous quantity of high-quality data had been collected in just the first year of operations.

A three-panel wavelength vs. reflectance plot, each of which corresponds to one object. The spectra are mostly similar, but deviate in a few places.

Spectra of Sedna, Gonggong, and Quaoar collected by JWST. [Slide by Ana Carolina de Souza Feliciano]

Rounding out the session was Ana Carolina de Souza Feliciano of the University of Central Florida. Her presentation took the audience’s thoughts to the very edge of the solar system and described JWST’s investigation of the small objects in the trans-Neptunian region. Several groups have already used the observatory to collect spectra of these distant, icy worlds: one of the largest projects, called DiSCo-TNOs, aimed at 59 individual objects. This dataset revealed that trans-Neptunian objects can be grouped into three different groups according to the amount of CO2 present in their spectra. JWST also observed the most famous of the trans-Neptunian objects, the fallen planet Pluto. While the New Horizons spacecraft only got a good view of one hemisphere when it zipped past in 2015, JWST patiently waited for the dwarf planet to spin around and managed to image it in four different orientations. Other dwarf planets have gotten the JWST treatment as well, including Sedna, Gonggong, Quaoar, Eris, Makemake, and Haumea. More observations are planned, and all involved are certain that more will be discovered.

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Arm in Arm: Allies in Adversity (Robert Salcido Jr.) (by Kerry Hensley)

In the final plenary presentation of the day, the Executive Director for the Pride Center San Antonio, Robert Salcido Jr., described the challenges facing the LGBTQ+ community of San Antonio, where the DPS–EPSC conference is being held. The Pride Center serves as a hub for the community and offers free counseling, case management, and group therapy, filling a need for mental health services.

comparison of American adults and LGBTQ+ adults in San Antonio on the Kaiser ACE scale

Comparison of Kaiser adverse childhood experience scale results for American adults and LGBTQ+ adults in San Antonio. Click to enlarge. [Slide by Robert Salcido Jr.]

To better understand the needs of the community it serves, the Pride Center started the Strengthening Colors of Pride project in 2017. This project includes a survey of the San Antonio area LGBTQ+ community, conducted every three years. The 2020 survey leveraged the Centers for Disease Control–Kaiser Permanente adverse childhood experiences scale, which tallies the number of adverse experiences that respondents experienced as children, such as having a member of their household go to prison. Having four or more of the experiences included in the scale is correlated with poor health outcomes as adults. When comparing the results for the San Antonio area against the United States as a whole, the team found that there were far more people in the San Antonio area with adverse childhood experiences than Americans on average; a full 26% of San Antonian respondents scored a six or higher on the scale.

Additionally, the survey revealed ongoing challenges faced by the LGBTQ+ community in San Antonio, especially in healthcare settings; 1 in 10 of the adults surveyed didn’t know where to access affordable or appropriate healthcare, and that number rose to 1 in 4 for transgender respondents. These responses underscored the need for better healthcare — both physical and mental — and was used to inform the structure of the clinical practice at the Pride Center.

Zooming out to look at Texas as a whole, Salcido notes that the state is a “hotbed” for attacks against the LGBTQ+ community. In 2023, about 600 bills were filed statewide that aimed to restrict the rights of people who identify as LGBTQ+, especially when it comes to gender-affirming care. Compare this to 2013, when just 20 bills were filed, none of which passed. In 2021, this rose to 76 filed bills, one of which passed, and in the most recent legislative session, 141 bills were filed. These bills targeted the use of puberty blockers for trans kids, banned trans athletes from competing at the collegiate level, and banned drag shows, to name just a few. In other words, bills are being filed in Texas that seek to exclude transgender people from everyday life — despite the fact that a recent survey from the Trevor Project found that 71% of Texans support the LGBTQ+ community.

Salcido ended his talk by prompting the audience to think about what it means to be an ally in your profession, for your friends, and for your family. Ally isn’t just a noun, it’s also a verb, and action is important — but it may not look the same for everyone. What’s important is showing up in support of communities to which you don’t belong: advocating for LGBTQ+ people, standing against oppression, acknowledging one’s own prejudices, and working to understand what matters to people within the community.

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Press Conference (Briefing video) (by Kerry Hensley)

Lynnae Quick (NASA Goddard Space Flight Center) started off the press conference with a presentation on icy ocean exoplanets. Previous research has suggested that Earth-sized terrestrial exoplanets are likely to be ice covered and have subsurface oceans. If these frosty worlds are heated, either through tidal stresses or the decay of radioactive materials, they could be a promising place to look for life beyond Earth. In a new study, Quick and collaborators investigated 17 Earth-sized exoplanets thought to be icy worlds with subsurface ocean. The list of planets includes well-known planets like the outer planets of the TRAPPIST-1 system as well as Proxima Centauri b. Quick’s team constrained the tidal and radiogenic heating rates of these planets, many of which had heating rates greater than Europa and Io. Since Europa and Io are both thought to have subsurface oceans, this suggests that these planets have subsurface oceans as well.

Ice shell thicknesses of some of the exoplanets observed in this study

Ice shell thicknesses of some of the exoplanets observed in this study compared to Earth and Europa. Click to enlarge. [Slide by Lynnae Quick]

In addition, the team’s calculations show that these planets have colder surface temperatures than previously thought, supporting the hypothesis that they have icy shells. When Quick’s team investigated the thickness of the planets’ ice shells and how much ocean material might emerge through the crust in the form of geysers, they found that the ice thicknesses ranged from 0.04 to 24 miles, and many of the planets could have geysers even more productive than those of Europa. For the planets with the thinnest ice shells, this could mean liquid is transported directly from the subsurface ocean to the surface, distributing material that is possibly rich in biosignatures. | Presentation slides

Jon Zink (California Institute of Technology) took a wide view of planet formation, beginning with the formation of the Milky Way 13 billion years ago. Even as our galaxy was forming from a cloud of gas, planets were forming, too, and the different stages of galaxy formation may have left an imprint on planets forming at each stage. In the first stage, our galaxy formed a thick disk of stars as core-collapse supernovae exploded, spewing gas rich in alpha elements (e.g., oxygen, silicon, and neon; these elements are important for terrestrial planet formation — Earth is 75% silicon and oxygen) into space. Next, a merger with another galaxy created the galactic halo. After that, the solar system formed and a thin disk of stars was created. Around this time, Type Ia supernovae, which arise in binary systems containing a white dwarf, created an abundance of iron, which is thought to provide the seeds for giant planet formation.

plots of planet occurrence versus galactic oscillation amplitude

Super-Earth and sub-Neptune exoplanets are less common around stars with large galactic oscillation amplitudes. Click to enlarge. [Slide by Jon Zink]

As a consequence of the chemical and structural evolution of our galaxy, planet occurrence is “address dependent” — different types of planets are more likely in different parts of the galaxy. Using stellar position and velocity data from the Gaia spacecraft, Zink’s team found that small planets were less likely to be found around stars with high galactic oscillation amplitudes (i.e., those that travel high above the galactic plane). Three potential regions for this trend are internal dynamics of stellar systems, galactic dynamics, and changes in the composition of protoplanetary disks. | Presentation slides

Pietro Matteoni (Freie Universität Berlin) brought things back to our solar system with a close look at one of the best places to search for life beyond Earth: Jupiter’s moon Europa. Europa has an ice shell, a subsurface ocean, a rocky interior, and a metallic core. Europa is thought to produce plumes of water that carry material from beneath the crust and distribute it on the moon’s surface. However, given the thickness of Europa’s ice shell — likely on the order of kilometers — it’s unlikely that these plumes are carrying material directly from the subsurface ocean. Instead, shallow pockets of water within the ice are probably the source.

Aerial view of study regions on the surface of Europa

Aerial view of the two regions studied. Click to enlarge. [From slide by Pietro Matteoni]

Using data from the Galileo spacecraft, Matteoni’s team studied two regions that have surface features that could be associated with shallow water pockets. The first, Mènec Fossae, appears to have been shaped by tectonic activity and contains many features in a small area that could be linked to subsurface activity. In particular, the elevation profiles of certain features match perfectly what is expected if there is a shallow water pocket below. The second region, Thrace Macula, is known to be geologically young and contains material from the moon’s interior. This region is characterized by a tectonic fault, and the fault lines may provide a way to transport material to the surface. Thrace Macula will be observed by the upcoming Juice and Europa Clipper missions, so we’ll soon learn much more about this region! | Presentation slides

Gordon Kai Hou Yip (University College London) addressed a pressing question: how can artificial intelligence help us answer questions about exoplanet science? Yip is the Principal Investigator of the Ariel Data Challenge, an event that entices machine learning experts to apply their skills to pressing questions in exoplanet science — in particular, how to relate a planet’s spectrum to its atmospheric properties. This is a critical question given the shift in exoplanet research from finding planets to characterizing them, and many upcoming telescopes — like the European Space Agency’s Ariel mission that is slated to launch in 2029 — will return an immense amount of data that we don’t fully know how to handle yet. Enter machine learning: a set of computing techniques in which computers discover their own algorithms, usually being trained on a “known” set of inputs and outputs before applying the algorithms to new inputs.

Yip suggests that solving these problems will require input from experts in many fields, but it can be challenging to bring people with different areas of expertise together; thanks to field-specific jargon, these researchers aren’t even speaking the same language. The Ariel Data Challenge partners with machine-learning conferences and so far has engaged more than 300 researchers around the world. Researchers form teams and develop machine-learning techniques in an attempt to predict atmospheric properties of exoplanets from spectroscopic data. Based on the results of these challenges, Yip’s team has several takeaways: 1) machine-learning models don’t like surprises, and they don’t perform well when given data that’s outside the bounds of the known parameter space — but that’s exactly where upcoming exoplanet missions will take us; 2) money is important to researchers (the winners of the challenge get a monetary prize), but passion for machine learning and the science of exoplanets is a bigger draw for the challenge participants; and 3) physicists are required to win the game — all the winning teams partnered with researchers who had a background in physics. So don’t worry too much about machines replacing astrophysicists — we’re still critical to making exoplanet investigations a success!

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Editor’s Note: This week we’ll be writing updates on selected events at the 55th Division for Planetary Sciences (DPS) meeting, held jointly with the Europlanet Science Congress (EPSC) in San Antonio, Texas, and online. The usual posting schedule for AAS Nova will resume on October 9th.

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Kuiper Prize Lecture: Some Problems and Challenges in the Origin and Evolution of Icy Satellites and Dwarf Planets (William McKinnon)

Hubble image of Pluto and Charon

Our best view of Pluto and Charon as of 1994, taken with the Hubble Space Telescope. [Dr. R. Albrecht, ESA/ESO Space Telescope European Coordinating Facility; NASA; CC BY 4.0]

William McKinnon (Washington University in St. Louis) is the winner of the 2023 Gerard P. Kuiper Prize, which is awarded annually for outstanding contributions to planetary science. Though McKinnon’s planetary science career began with an exploration of craters on the Moon, the arrival of Voyager 1 and Voyager 2 at the Jupiter system changed the trajectory of his career. The icy satellites of Jupiter and the other outer planets provided an entirely new arena in which to study the formation of craters, which led to an investigation of the icy worlds themselves. As Herman Melville wrote in Moby-Dick, McKinnon found himself “[…] tormented with an everlasting itch for things remote,” and just as his interests had turned from Earth’s satellite to those of Jupiter and Saturn, so did his interests in turn expand even farther afield, to one of the most interesting unexplored worlds of that era: Pluto and its moon, Charon.

The post-Voyager era brought about the beginning of a lengthy quest to get a mission to Pluto off the ground. That mission, New Horizons, eventually launched in 2006 and flew past Pluto in 2015, the observations exceeding McKinnon’s expectations “by an order of magnitude.” The second major milestone of the mission, a flyby of the Kuiper Belt object Arrokoth, was perhaps even more astounding, giving us the first look at a nearly pristine primordial object left over from the formation of the solar system.

In addition to major missions like New Horizons, the 21st century brought new models to explain how our solar system came to be as it is: the Nice model, which describes how the migration of the giant planets generated structures like the Kuiper Belt and triggered events like the Late Heavy Bombardment; the streaming instability/pebble accretion models, which explain how tiny grains might bulk up into planetesimals and eventually planets; and the great isotopic dichotomy, in which the growth of Jupiter’s core opened a gap in the disk of material in which the planets formed, restricting movement of material across this gap.

Infographic demonstrating where we've collected samples from in the solar system

Collecting material from the icy satellites of the outer solar system is a missing piece in our sample return collection. Click to enlarge. [Slide by William McKinnon]

McKinnon ended by looking forward to what the next 30–50 years might bring. Using the example of how plate tectonics can be monitored on Earth using GPS, and we’ve started to be able to do this using spacecraft on the Moon and Mars, as well, McKinnon suggested that we could do this on icy satellites using passive probes embedded in the ice. Farther out in the solar system, observations with JWST and soon the Rubin Observatory give us a way to interrogate the Nice model by determining the architecture and chemistry of the Kuiper Belt. The holy grail of planetary exploration may be sample return, which allows us to study planetary materials on the atomic level; McKinnon suggests that “honorary icy satellite” Io be our next target.

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Urey Prize Lecture: Exploring Asteroids and Comets with Meteor Science (Quanzhi Ye)

The 2023 Harold C. Urey Prize, awarded annually to an early-career planetary scientist in recognition of their outstanding achievements, went to Quanzhi Ye (University of Maryland) for his studies of asteroids and comets. Humans have kept track of comets and meteor showers for millennia, as evidenced by drawings from more than two thousand years ago. The connection between meteor showers and comets was realized in the 1800s, and as we’ve discovered more and more meteor showers, we’ve needed to develop sophisticated mathematical methods to connect these events to the comets that created them.

Graphic demonstrating how the lack of a meteor shower associated with D/Lexell helped researchers track down the comet's current location

Graphic demonstrating how the lack of a meteor shower associated with D/Lexell helped researchers track down the comet’s current location. [Slide by Quanzhi Ye]

Today, researchers perform statistical significance tests using models of the near-Earth object population to determine whether certain comets and meteor showers are linked. Interestingly, this method has confirmed several tentative connections and has also cast doubt on some seemingly firm connections as well. It also may have helped Ye and collaborators find the long-lost comet D/Lexell, which was discovered 250 years ago and seemed to have vanished. A close encounter between the comet and Jupiter suggested that the comet had left the solar system entirely, but Ye’s team used the fact that there don’t seem to be meteors associated with this comet to track down a known comet that may in fact be D/Lexell.

Studying the meteors themselves as they streak through Earth’s atmosphere can also help us learn about the objects they came from. For example, the altitude at which a chunk of material becomes luminous as it travels through the atmosphere is related to its material strength; meteorites that become luminous high up have low material strength and tend to come from comets, while those that become luminous lower down have high material strength and tend to come from asteroids. Ultimately, researchers have a wealth of dynamical, compositional, and physical measurements that can be used to study meteor parent bodies, and an expanding global network of telescopes used for meteor studies will provide new opportunities for study as well.

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The Double Asteroid Redirection Test (DART): One Year After Impact (Cristina Thomas)

Cristina Thomas (Northern Arizona University) described what we’ve learned from the DART mission in the year since impact. The DART mission’s target was a binary asteroid system consisting of Didymos, which is less than a kilometer in diameter, and its small companion Dimorphos, which is just 150 meters across. The goal of the mission was to crash a spacecraft into Dimorphos, change the orbital period of the binary, measure the change in the orbital period, and then characterize the impact and the impact site. These results can tell us how useful crashing a spacecraft into an oncoming asteroid would be as a planetary defense strategy.

Observations showing how Dimorphos's orbital period changed as a result of the impact

Observations showing how Dimorphos’s orbital period changed as a result of the impact. Click to enlarge. [Slide by Cristina Thomas]

A worldwide observing campaign began in July 2022, continued through impact in September 2022, and concluded in March 2023. These observations confirmed that Dimorphos’s orbital period changed as a result of the impact, decreasing from 11 hours and 55 minutes to 11 hours and 22 minutes. The impact also appears to have reshaped Dimorphos, and the object may now be tumbling as it orbits.

Our studies of the impact of the DART mission are far from over; Thomas notes that there will be another observing campaign in 2024 to study the ongoing evolution of Dimorphos’s orbit, and the European Space Agency’s Hera mission will study the aftermath further. This mission, slated for launch in 2024 and arrival in 2026, will perform a detailed study of Dimorphos, helping us to understand the details of the asteroid-impact technique for planetary defense as well as allowing us to investigate a binary asteroid system.

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Planetary Defense: DART & LICIACube (Elisabetta Dotto)

An image of the ejecta plumes from the DART impact

An image of the ejecta plumes from the DART impact. Didymos and Dimorphos are oversaturated in this image, allowing the fainter plumes to be visible. [Slide by Elisabetta Dotto]

Elisabetta Dotto (INAF — OAR) brought the session to a close with a discussion of the findings of the Light Italian Cubesat for Imaging of Asteroids, or LICIACube, which rode along with DART during the interplanetary cruise and was released 10 days before impact. As the main spacecraft met its end in a collision with Dimorphos, LICIACube watched from a safe distance. Using its two cameras, LUKE and LEIA, LICIACube snapped pictures of the ejecta plume and searched Dimorphos’s surface for signs of an impact crater. No crater was visible because the asteroid’s surface was blanketed with ejecta, but the photographs of the plume show a large amount of structure, including filaments, dust grains, and boulders. These observations can also be used to constrain the shape that the asteroid took after the impact.

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illustration of an asteroid

Editor’s Note: This week we’ll be writing updates on selected events at the 55th Division for Planetary Sciences (DPS) meeting, held jointly with the Europlanet Science Congress (EPSC) in San Antonio, Texas, and online. The usual posting schedule for AAS Nova will resume on October 9th.

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Farinella Prize Lecture (Federica Spoto and Diego Turrini) (by Ben Cassese)

The week of science kicked off with a plenary session that was split between award winners and explorers of our innermost planet, Mercury.

First up was Federica Spoto of the Minor Planet Center in Cambridge, Massachusetts. She was one of the two recipients of the 2023 Farinella Prize, an award given to younger planetary scientists active in areas of research that captivated Italian scientist Paolo Farinella before his tragic premature death in 2000. Her presentation detailed recent advances in the last decade in the Minor Planet Center’s ability to disseminate alerts about asteroids about to strike Earth.

An image of a meteor as seen from the ground, and the names of 7 asteroids beside it at left.

The seven asteroids discovered prior to their impact with Earth. [Slide by Federica Spoto]

To date, we have caught seven small asteroids before each of them collided without significant damage, and when looking back on their detections, one might be forgiven for assuming they tried to evade the asteroid police of Cambridge. One of the first, 2014AA, was only observed by one astronomer who spotted it on New Year’s Eve: without an automated system in place to distribute alerts and with the staff of the Minor Planet Center either asleep or busy ringing in 2014, no one else knew of it until after impact. In the decade since, however, systems have been upgraded and now operate nearly completely automatically. They now work so efficiently that Spoto only had to casually supervise them when the first observations of the most recent pre-discovered impactor streamed in during Rihanna’s Super Bowl Halftime Show. She successfully coordinated follow-up observations while watching the pop icon’s performance.

Up next was the other winner of this year’s Farinella Prize, Diego Turrini of the National Institute for Astrophysics – Turin Astrophysical Observatory. Turrini presented on the recent advances in our understanding of small impactors and the cumulative effects of their tiny craters. Excitingly, this included insights not only from within our own solar system, but also from observations of other, distant solar systems as they form. With the help of the ALMA observatory’s unprecedented sensitivity to dust emission around faraway stars, we are beginning to empirically measure the properties of colliding protoplanets in laboratories beyond our own backyard.

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BepiColombo en Route to Mercury: Mission Overview and First Results: (Johannes Benkhoff and Anna Mililo) (by Ben Cassese)

The session concluded with a two-part talk delivered by Johannes Benkhoff and Anna Mililo on the BepiColombo mission to Mercury. Benkhoff was the lead off hitter, and he took his time on the plenary stage to give an overview of the joint European–Japanese mission to the innermost planet. This included a description of the complex, three-part spacecraft, and assembly that consists of a solar-electric powered cruise stage and two separate orbiters that will eventually circle Mercury upon their arrival in December 2025. The whole craft has been operating as expected since its launch in 2018, and it has completed six of the nine required flybys needed to maneuver inwards through the solar system before its final orbital insertion.

A black and white image of a cratered surface, partially blocked by a spacecraft boom in the foreground.

BepiColombo’s view of Mercury during its first flyby prior to eventual orbit insertion. [ESA/BepiColombo/MTM]

Mililo then focused her time on the science that has already been done even before the mission reaches its target. This includes several very close flybys of Venus, an enigmatic world that we’ve only visited with robotic emissaries a handful of times. As BepiColombo skimmed the tops of the Venusian clouds (nearly, at least: its second flyby passed the planet at an altitude of less than 600 km), it turned on many of its instruments and dutifully recorded data on its atmosphere and ionosphere. These rare and precious measurements are keeping the team busy in the years leading up to the main show, and will likely be analyzed for years afterwards while we wait for missions dedicated to Venus itself to arrive.

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Press Conference (Recording available here) (by Kerry Hensley)

Anicia Arredondo (Southwest Research Institute) kicked off the first press conference of DPS–EPSC with a discussion of new findings about asteroid (16) Psyche. Psyche is a 170-mile-diameter asteroid in the asteroid belt between Mars and Jupiter, and our observations indicate that Psyche is 30–60% iron by volume. This suggests that the asteroid was once the core of a small planet like Earth or Mars that experienced a massive collision during its formation, losing its rocky mantle and leaving only the metal core behind. A NASA mission to the asteroid, also named Psyche, is slated to launch on 12 October 2023, reaching the asteroid in 2029 and embarking on 26 months in orbit around this metallic world. The mission will allow us to study how planets form in an entirely new way, and in preparation for its arrival, researchers are using all available means to study Psyche.

spectra of Psyche

Spectra of Psyche showing the difference in features seen with the Spitzer Space Telescope (top) and SOFIA (bottom). Click to enlarge. [Slide by Anicia Arredondo]

Arredondo reported on spectroscopic observations of Psyche’s surface made using the Stratospheric Observatory for Infrared Astronomy (SOFIA). Peering at Psyche’s north pole, SOFIA saw a featureless spectrum indicative of a metal-covered surface. This contrasts with previous observations using the Spitzer Space Telescope that found evidence of rocky particles on Psyche’s surface — but at the south pole rather than the north pole. This suggests that Psyche has a complex and varied surface, and since the upcoming mission will orbit the asteroid from pole to pole, we’ll soon be able to test our hypotheses. | Presentation slides | Press release

Sonia Fornasier (LESIA-Université Paris Cité) discussed photometry of Phobos, the larger of Mars’s two small moons. The origins of Mars’s moons (the other moon is named Deimos) has long been debated, with two leading theories: 1) the moons are captured asteroids, which explains their reddish colors that match that of other asteroids, or 2) the moons formed where they are, in orbit around Mars, in the aftermath of a giant collision, which explains their nearly circular orbits. Neither theory fits all the available data — it’s not clear how captured asteroids would fall into such circular orbits, and Phobos and Deimos are spectrally dissimilar from Mars. Luckily, the Japanese Space Agency’s Martian Moons eXploration (MMX) mission will help solve this riddle, returning samples from two distinct regions on Phobos’s surface.

Phobos’s reflectance properties place it in the realm of asteroids rich in carbonaceous material. Click to enlarge. [Slide by Sonia Fornasier]

In this press conference, Fornasier presented recent analysis of Mars Express data that show how Phobos’s reflectance changes as a function of phase angle. When the phase angle is extremely small (i.e., the Sun, Phobos, and Mars Express were nearly in a line), the reflectance increases sharply, a phenomenon known as the opposition surge. Modeling of these observations suggests that Phobos’s surface is coated with a thick layer of dust made up of particles larger than 10 microns (1 micron = 10-6 meter). This is similar to the properties of comet 67P/Churyumov–Gerasimenko, which was visited by the Rosetta mission, as well as primitive asteroids. | Presentation slides

Adeene Denton (University of Arizona) wrapped up the session with a look at Pluto and its moon, Charon. The Pluto–Charon system is interesting because of how large Charon is relative to Pluto; Charon is larger compared to Pluto than the Moon is to Earth, and the center of mass of the system lies outside Pluto. One possibility for how the system came to be as it is today is through a giant collision, which is also how the Earth–Moon system is thought to have formed. Things are a little different 40 au from the Sun, though, as objects tend to be less massive and move more slowly. This means that the effects of material strength — the ability of a material to resist deformation — are important in determining the outcome of a collision.

comparison of model outputs when material strength is or is not included

Comparison of model snapshots when material strength is neglected (left) and included (right). Click to enlarge. [Slide by Adeene Denton]

Using computer simulations, Denton showed that a collision between Pluto and Charon that neglects material strength exaggerates the amount of deformation and results in a single body rather than two bodies. Including material strength results in a very different collision: the two bodies collide, stick together, spin around, then decouple and remain in a close orbit. This process also heats Charon’s interior long term, which may have implications for the formation and survival of oceans on Charon and other icy Kuiper Belt objects.

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