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)
• Press Conference: Exoplanets and Brown Dwarfs
• High Energy Astrophysics Division Bruno Rossi Prize Lecture: Anatoly Spitkovsky (Princeton University)
• Press Conference: High-Energy Phenomena and Their Origins
• Annie Jump Cannon Prize Lecture: Theories of Planet Formation, Eve Lee (McGill University)
• Plenary Lecture: Sukanya Chakrabarti (University of Alabama, Huntsville)

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

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”!

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 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 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.

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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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:

• Fred Kavli Plenary Lecture: NANOGrav: The Dawn of Gravitational-Wave Astronomy at Light-Year Wavelengths, Stephen Taylor (Vanderbilt University)
• Special Session: International Students and Researchers in Astronomy: Issues and a Path Forward
• Press Conference: Dust, Clouds & Darkness
• Helen B. Warner Prize Lecture: The PAH Revolution: Cold, Dark Carbon at the Earliest Stages of Star Formation, Brett McGuire (Massachusetts Institute of Technology)
• Press Conference: Stars, Protostars & More Clouds
• Helen B. Warner Prize Lecture: The Milky Way as a Cosmological Laboratory, Ana Bonaca (Carnegie Institution for Science)
• Plenary Lecture: The Rarity of Life in the Universe, Alan Lightman (Massachusetts Institute of Technology)
• LeRoy E. Doggett Prize Lecture: It All Began with Tebbutt! The Peripatetic Path from New Zealand to New Orleans, Wayne Orchiston

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

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

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.

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!).

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.

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]

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!

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.

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

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

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

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!

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.

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!

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.

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]

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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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.

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!

Editor’s Note: This week we’re at the 242nd AAS meeting in Albuquerque, NM, and online. 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 on Twitter for live coverage. The usual posting schedule for AAS Nova will resume on June 12th.

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• Plenary Lecture: Meenakshi “Mini” Wadhwa (Arizona State University)

Plenary Lecture: Meenakshi “Mini” Wadhwa (Arizona State University) (by Lucas Brown)

The final plenary lecture of AAS 242 was given Thursday morning by Dr. Meenakshi “Mini” Wadhwa from Arizona State University on the role of sample return missions in exploring the past and present of our solar system. From Apollo to Mars Sample Return, these missions have and will continue to provide unique and invaluable insight into the formation of our solar system, the origins of life, and beyond.

Sample return missions, which are missions to collect material directly from extraterrestrial sources, have existed since the 1960s, beginning with the Apollo missions. While it has been possible to study extraterrestrial materials for much of human history through examining meteorites which land on the surface of Earth, the utility of meteorites is limited by the fact that we don’t have direct context for their origins; where a particular meteorite originated from in the solar system is often unknown. Additionally, when these objects come into contact with Earth’s atmosphere and surface, their properties and composition can change relative to when they were floating through space. On the other hand, space missions are limited in how much analysis they can do due to constraints on the size and mass of satellites that can be launched on existing rockets. Dr. Wadhwa explained that bringing samples back enables higher resolution and more precise analyses, and it also allows for experiments to be reproduced across numerous labs and with multiple techniques — all increasing the reliability of the results. Additionally, sample return missions greatly increase the number of researchers who can be involved in analysis, and these missions can inspire the broader public. To give a specific example of the impact of a past sample return mission, the return of lunar regolith and rock samples during the Apollo missions led to the finding of the first evidence of magma oceans in the Moon’s early formation history, which is now foundational in many theories attempting to explain the formation history of rocky planets.

Still image from a video taken by the Hayabusa2 spacecraft depicting the cloud of debris ejected from the surface of asteroid Ryugu after the spacecraft launched a copper projectile into it. The spacecraft was able to collect subsurface material from this cloud of debris, later returning the material to Earth for analysis. [JAXA]

An ambitious plan is in the works to return samples of material from the surface of Mars known as Mars Sample Return. The Perseverance Mars rover has already collected samples into sealed canisters which have been deposited onto the surface for later retrieval. One such canister is visible in the foreground of this photo, with the location of others also being highlighted. [NASA/JPL-Caltech/ASU/MSSS]

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