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.
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. 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 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?”
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. [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:
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.
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.
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.
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 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!
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.
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.
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.
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.
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 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.
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 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.
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 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!
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.
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.
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.
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. [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.
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. 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.
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.
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.
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.
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.
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.
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.
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 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 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.
Engineer-turned-astronomer Katie Merrell recently joined the AAS Publishing team as the third journals data editor. Read on to learn about her first few months on the job, how the data editors work to serve our authors, and how the astronomical data landscape has changed in just the last few years.
A Perfect Fit
AAS Journals Data Editor Katie Merrell
Katie Merrell didn’t start out as a wrangler of astronomical data or even as an astronomer. After graduating college, she began her career as an engineer for Boeing, working to ensure that flight control system hardware complied with safety standards. But her interest in astronomy had been simmering on the back burner, and she made the leap to a PhD program. At Georgia State University, she studied supermassive black holes in nearby galaxies, determining their masses by monitoring the orbits of stars in their neighborhoods.
After completing her PhD, Katie was on the hunt for a position that would allow her to have a hand in all areas of astronomy while incorporating the aspects she liked best about working in a corporate setting: being part of a team, getting organized, and ensuring adherence to quality control standards. Ultimately, her advisor pointed out the listing for the data editor position. “This is exactly what I wanted to do before I even knew that this was a possibility,” Katie said.
The position proved to be a perfect fit. As a data editor, Katie and fellow editors Greg Schwarz and Gus Muench ensure that the data products in AAS journal articles — tables, figures, archived data sets, and the like — meet the journals’ standards and are presented in a clear, compelling way. This could mean anything from converting a table to a standardized, machine-readable format to encouraging authors to create an interactive figure that better showcases their data.
The Rapid Evolution of Data Editing
In 2021, we checked in with Greg and Gus to get their perspective on the past two decades of data editing at the AAS journals. Now, just two years later, the landscape has changed considerably as the result of a substantial push from funding agencies, governments, and the scientific community for open science. For example, the White House Office of Science and Technology Policy has named 2023 the Year of Open Science. As part of the Year of Open Science, NASA has launched the Transform to Open Science (TOPS) mission, which aims to “rapidly transform agencies, organizations, and communities to an inclusive culture of open science.”
To support these goals, one of the most common tasks the AAS data editors take on is handling authors’ machine-readable tables — tables of data in a standardized format that can be easily accessed and read by researchers looking to reproduce or build on an author’s results. Roughly 35% of the accepted manuscripts the data editors handle contain at least one such table.
The change in the number of various data products handled by the data editors from 2000 to 2022. Click to enlarge. [Greg Schwarz]
But data products in scientific articles go beyond tables now: one of the fastest-growing categories is that of citable, persistent links (Digital Object Identifiers or DOIs) to datasets hosted in repositories. More than a quarter of data-edited manuscripts contain references to NASA-related datasets, and the practice of citing these datasets to enable reproducibility is becoming increasingly common. The growth in the category labeled “other” in the plot to the left is mostly due to authors referencing data from the Mikulski Archive for Space Telescopes, or MAST, which houses data from JWST, Hubble, Kepler, and other prolific space telescopes.
With NASA, the AAS, and other organizations strengthening their support of open science practices, the number of data products included with journal articles is expected to grow, giving the data editors even more to do; in 2022, the AAS journals data editors worked to improve 1,181 manuscripts, and that number is projected to jump up to 1,522 this year.
Lending a Hand to Readers and Researchers Alike
What all this means for researchers is that making your data accessible to others is increasingly important, and the data editors exist to make your life easier! “We want to make sure that it’s easy for people to understand and reproduce work, and giving credit where credit’s due is also really important,” Katie said. The data editors help shape manuscripts as soon as they’re submitted, which means that when you receive a referee report, it might contain a note from one of our editors. The data editors’ roles continue beyond when your manuscript is accepted, helping to ensure that your data is accessible and complies with any requirements from your funders. Ultimately, they help to enhance the clarity and accessibility of your data, which play a huge role in making your work reproducible — a key principle of sound science.
Curious how the AAS journals data editors can help you? Have burning questions about how to organize, store, and present your data? You can contact the data editors’ help desk at data-editors@aas.org. And if you prefer to meet our data editors face to face (they’d love to chat!), be sure to stop by their booth at the next AAS meeting in New Orleans in January 2024.
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.
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]
While many robotic sample return missions have occurred in the decades since Apollo, Dr. Wadhwa focused much of her talk on Hayabusa2, a Japanese mission launched in 2014 to the asteroid Ryugu. This mission not only orbited and mapped the asteroid, but also landed on its surface several times, collecting samples of subsurface material by launching copper projectiles into the surface and collecting the ejected material in internal compartments. Through work done in part by Dr. Wadhwa and her collaborators, careful analysis of the composition of the asteroid was performed, including analysis of the titanium, chromium, and strontium isotopes present in the Ryugu samples. Understanding the presence of these elements can help us understand the distribution of materials in the protoplanetary disk from which our solar system formed, and it also allows us to determine the age of the asteroid, which closely matches the estimated age of the solar system (around 4.5 billion years).
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]
Looking ahead to the future, Dr. Wadhwa spoke about Mars Sample Return (MSR), a proposed multi-step, multi-vehicle, multi-agency mission to return material from the surface of Mars. While such a mission has been proposed for many decades now, always claimed to be just “10 years away,” there now exists real funding and extensive planning to make this a reality within the next 10 years (for real this time). In fact, Perseverance — NASA’s newest rover, which landed on the surface of the red planet in 2021 — has already begun the process of collecting interesting sample material, dropping sample canisters along the way for future missions to retrieve. Such a retrieval will require the launch of additional spacecraft, one of which will land on the surface, intake the sample canisters, and then launch them into orbit with an on-board miniature rocket. The samples, once in orbit, will be retrieved by another craft and flown back to Earth. This plan is complex, introducing many never-before-demonstrated procedures, such as the ability to launch a payload into orbit from the surface of another planet. The intense efforts involved in MSR go to show the immense interest that exists within the scientific community for sample return missions.
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.
The first plenary lecture of the day, titled “Now What? Making Astro2020 a Reality,” was given by John O‘Meara from W.M. Keck Observatory. He started by acknowledging the land that Albuquerque is on and acknowledging the Indigenous people of this land. He then talked about the Decadal Survey and how it has “controlled our destinies” since 1964. He showed the front pages of the decadal surveys throughout the years and mentioned the different missions that the various surveys prioritized. The Astro2020 Decadal Survey hopes to prioritize topics including Worlds and Suns in Context, New Messengers, and New Physics and Cosmic Ecosystems. John tried to put all of the priorities from the Decadal Survey in one question: How did the universe enable biology? With the recommendation of the Habitable Worlds Observatory (see Figure 1), he encouraged the attendees to think about it in two ways: Habitable Worlds (for looking for new worlds in the universe) and Observatory (for studying the mysteries of the universe).
John had a wish before the Astro2020 Decadal Survey was released: “I wish for a bold, visionary, pragmatic, and actionable report that not only sets the stage for scientific discovery that can change humanity, but also for a path for humanity to change how it does astronomy.” He shares that his wish was granted when the report came out! But, then he explained he felt like the fish in plastic bags floating in the ocean in Finding Nemo, asking himself, “Now what?” When thinking of this question, he realized that to enable great science, we need funding. He then evaluated the budget that we get to do astronomy research, which is around 0.025% of the US budget. John remarks that even though that seems like a tiny portion, it is still over one billion dollars! But, the current budget for the Astro2020 Decadal Survey is the Fiscal Year (FY) 2024 budget, which doesn’t have enough for the field to fulfill its goals. Therefore, we still need more funding for FY 2024, and John mentions that the budget is very similar to ping pong, where there is a lot of back and forth with the government to be able to get the necessary funding. He then says the budget is like a moving dumpster fire on a truck. But who is driving the truck? We are! John highlights the power we all have to make a difference in the budget and in general with policy matters. He emphatically says to “get out there and start talking!”
John nears the end of his talk by pointing out that we need a long term solution to how we operate facilities and that while the science leadership of the United States is at risk, there is still an immense opportunity to improve and strengthen it. “There is no such thing as a partisan photon,” he emphasizes, and impressed upon the audience that all political parties do care about science in their budgets, and we shouldn’t assume they don’t. John transitions to talking about JWST and how long it took to get the mission going and encourages us to think about how we can improve the process for the Habitable Worlds Observatory. He also highlights the different programs created for the Habitable Worlds Observatory and how we can all get more involved!
To conclude his plenary, he then highlights the importance of improving the state of the field, how crucial it is to support and lift the voices of the LGBTQ+ community as well as the voices of minority groups if we want to create a better environment for people to thrive in their search to understand the universe.
Press Conference: Get Ready for the North American Solar Eclipses (by Sumeet Kulkarni)
The final press conference of AAS 242 focused on two exciting solar eclipses gracing North America within the next 12 months: the annular eclipse on October 14, 2023, and the Great North American total solar eclipse on April 8, 2024.
Angela Speck from the University of Texas at San Antonio, and part of the AAS solar eclipse task force, introduced these two events and emphasized how rare they are to occur so close to each other, especially taken in conjunction with the 2017 total solar eclipse. Eclipses themselves aren’t rare phenomena on a global scale, Speck said. Our planet is treated to one every year, but when considering one given location, they only arrive around once every 375 years! San Antonio, where Speck is based, is incredibly lucky to be witnessing both upcoming eclipses. She gave an overview of how these two events are different. The October 14 eclipse is an annular eclipse, wherein the Moon will be at its apogee or the farthest point in its elliptical orbit. Hence, it won’t quite cover the full disk of the Sun, leading to a “ring of fire” forming around the Moon’s outline. While a strip of land stretching from the northwest to the southeast portion of the continent will observe “full annularity” with the ring of fire, the entire continent will be able to see a partial solar eclipse, Speck said. Within six months, April 8, 2024, will see a more magnificent total eclipse where the Moon will completely block out the Sun, turning skies dark for about 4 minutes and enabling people to see the brilliant solar corona. The path of totality in this eclipse will also cut across North America diagonally, but this time from the southwest to the northeast.
Rick Fienberg, who leads the AAS solar eclipse task force, followed Speck by providing tips and guidelines on how to experience these eclipses, particularly the 2024 total solar eclipse. “You may want to drive the shortest distance (to totality),” he said, “but an important consideration is to look up the expected cloud cover at that time of the year.” Here is one resource that can help us keep track of this. Only going into the path of totality can offer one the complete eclipse experience. The Sun is so bright that our pupils do not start dilating to compensate for the decrease in light even when it is 75% blocked. Even when it’s 95% blocked (e.g., in an annular eclipse or 5 minutes before totality), it is still as bright as a cloudy day. “There is no such thing as a 99% total eclipse. It’s all or nothing,” Fienberg said.
Fienberg went on to stress the importance of safety in eclipse viewing. It is safe to look at the Sun with the naked eye (and even binoculars and telescopes) ONLY when it is completely blocked during totality — but one should be very careful to know exactly when totality ends. At any other time during the eclipse, or during a partial eclipse or even during the maximum coverage of an annular eclipse, everyone absolutely needs to wear protection. Safe solar filters only transmit 1 part in 100,000 of the sunlight intensity. Fienberg advised buying eclipse glasses and filters that pass standards or from suppliers listed on this AAS page. Detailed information on how to safely observe the eclipse is also available on https://eclipse.aas.org/.
Jayne Aubele from the New Mexico Museum of Natural History and Science next gave a local flavor of observing the October 2023 annular eclipse from Albuquerque, which she labeled as ground zero for this eclipse. It is expected to begin around 9:15 am and last almost three hours. The full annularity will start from 10:34 am and last 4 minutes and 45 seconds. To add further excitement, October 14th is also the last Saturday of the renowned International hot air balloon fiesta in Albuquerque! However, for anyone hoping to enjoy a dual balloon-eclipse ride, Aubele noted that the last balloon comes down well before the time full annularity will hit.
The following two presentations were given by Craig DeForest and Cherilynn Morrow, representing the Southwest Research Institute and NASA’s Polarimeter to UNify the Corona and Heliosphere (PUNCH) mission. DeForest spoke about Citizen CATE (Continental-America Telescopic Eclipse), a novel experiment that aims to capture images of the inner solar corona using a network of more than 60 telescopes operated by citizen scientists, high school groups, and universities. While the total solar eclipse will only last about four minutes from any given location, anyone interested in studying the Sun’s corona would not see it change much during this time. However, with the help of volunteer citizen scientists across the entire path of totality, the Citizen CATE project plans to make a 60+ minute movie of the Sun as it is blanketed by the Moon and showcasing its brilliant corona. These results will help augment PUNCH, NASA’s own mission that studies the solar corona.
The solar eclipse petroglyph in Chaco Canyon, New Mexico. [Slide by Cherilynn Morrow]
Morrow followed up by stressing the importance of connecting our own eclipse viewing experience with that of other cultures and people belonging to generations preceding us. To this effect, NASA PUNCH aims not to have target audiences, but collaborators, including Native American/Hispanic youth and families, as well as blind and low-vision learners. “There are some cultures that don’t want to look at the eclipse” that we need to be cognizant of, Morrow said. Some people will be fasting and praying — it’s important to know this as we prepare our community outreach efforts. She concluded by reminding us about how ancient people witnessed the same phenomenon here that we are about to, by showcasing the fascinating eclipse petroglyph from the year 1097 AD in Chaco Canyon close to Albuquerque. These stone carvings possibly represent a total eclipse during high solar activity (lots of coronal spikes) and a nearby Venus!
Plenary Lecture: Joel H. Kastner (Rochester Institute of Technology) (by Wei Vivyan Yan)
This plenary talk was delivered by Dr. Joel H. Kastner from the Rochester Institute of Technology. Dr. Kastner shared the latest studies on planetary nebulae (PNe; singular PN), which impact fundamental topics such as products of asymptotic giant branch (AGB) nucleosynthesis, late stages of interacting binary systems, origins of white dwarfs, and jet launching.
PNe formation and evolution on the HR diagram. [Slide by Dr. Joel H. Kastner]
Dr. Kastner first introduced where PNe are located in the stellar evolution diagram (Figure 1). When a solar- to intermediate-mass star (~0.8–8 solar masses) grows old and moves away from the main sequence, it enters the AGB region, where its stellar envelope ejects and its stellar core rapidly is rapidly exposed. Intense ultraviolet emission ionizes the envelope when the core hits a temperature of ~30000K, which creates a glowing nebula. Eventually, this PN disperses and evolves into a white dwarf. The star loses ~30%–80% of its initial mass during this process. Therefore, as white dwarf generators, PNe document the “end game” of stellar evolution and provide unique insight into the initial-to-final mass relation from the stellar mass loss.
Dr. Kastner then showed the “classical” structure model of PN formation (left panel in Figure 2), demonstrating different layers and interacting winds inside a PN. When the AGB star ejects its envelope, the inner shock produces fast winds (velocity ~1,000 km/s) and forms the inner layer called the “hot bubble.” Dr. Kastner presented many X-ray observations as the key to unveiling wind interactions. For example, we can see very clear shells and layers in the images from ChanPlaNS (Chandra X-ray survey of PNe), which revealed the “hot bubble” and central stars emitting X-rays (right panel in Figure 2).
Left: The classical structure of a PN (Marigo et al. 2001). Right: X-ray images of PNe with different morphologies from ChanPlaNS. [Kastner et al. 2012, Freeman et al. 2014, Montez et al. 2015; Visualization credit: K. Arcand]
PNe have different morphologies, such as round/elliptical, hourglass/bipolar, and multipolar/point symmetric. Dr. Kastner took a deeper look at the bipolar morphology, which contains two lobes, a pinched waist, and a binary companion inside a torus structure (Figure 3). Dr. Kastner noted that the origin of the torus and the bipolar shape that may be caused by the binary companion is a longstanding problem. Whether the center should be a single star or a binary system is still debatable. According to a previous review paper (Jones & Boffin 2017, Nature Astronomy), the binary hypothesis fits better in most systems compared to a single-star scenario. But details about PNe’s structures, formation, and evolution may be even more complicated.
A bipolar PN with two lobes, a pinched waist, and a binary companion inside a torus structure. [Slide by Dr. Joel H. Kastner]
HST’s imaging survey overlaid on Chandra’s view of NGC 7027 [Moraga Bae et al. 2023 and A. Pagan]
Are some PNe products of multiple stellar systems? Dr. Kastner showed Hubble’s and Chandra’s overlaid views of NGC 7027 (Figure 4). We can see clear details of structures like shells and rings along with different outflows to study the shocking and shaping of this young PN. Similarly, Dr. Kastner was very excited about the publicly released Southern Ring Nebula (NGC 3132) images from the JWST early release observations. After emphasizing ionized and molecular gas distribution, this PN system, which was previously known for its visual binary central star, actually has five central stars! The latest Submillimeter Array carbon monoxide mapping also confirmed the existence of a multiple stellar system.
Dr. Kastner suggested two different (binary/multiple stars) origin stories for PNe with different morphologies based on how much molecular gas they have. Bipolar and ring-like nebulae contain rich molecular chemistry, observed by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array, and tend to dominate detections of molecular gas. On the other hand, round or elliptical PNe with X-ray-emitting bubbles generally lack detectable molecular gas.
Dr. Kastner concluded this talk with many open questions and future directions in PN research. In addition to the challenges in the binary hypothesis for PN shaping, Dr. Kastner wanted to use upcoming data and instruments (e.g., eROSITA, ALMA) to better understand how shocks persist, the spatial distribution of molecular masses, and the evolution of light-element abundances over cosmic time. “We are standing at the astrophysical crossroads,” says Dr. Kastner.
Plenary Lecture: Kathryne “Kate” Daniel (University of Arizona) (by Emma Clarke)
“This one is gonna be special,” said Grant Tremblay as he began to introduce the next plenary speaker, Kathryne “Kate” Daniel. “No pressure on Kate,” he added. If there was pressure, Kate Daniel didn’t show it. She began with a thanks for the introduction, followed by opening remarks of her own — in an Indigenous language of her ancestors. Translating, she repeated “Hi, I’m very happy to be here,” shared her name, and explained that she is of Comanche, Chickasaw, and European heritage. She conveyed honor and respect to her ancestors and the people who came before her, as well as her colleagues, the AAS, NSF, NASA, and the Heising-Simons Foundation, and recognized the Sandia and Ancestral Puebloan peoples, whose homeland AAS 242 is being held on.
She then explained a game her grandfather used to play with her. He would invite her to look at a bird, for example, and think about what the bird was thinking. Next, he’d ask her to imagine sitting on the back of the bird, and to think about what it felt like, what it looked like, and what the surroundings looked like. Finally, he would ask her to think like the bird, to be like the bird, and know like the bird. She explained that this was an important lesson in perspective; that there is no central perspective, much less her own, and that she exists in and with and in relationship to the world. She encouraged the audience to play this game during her talk.
The central bulge of the Milky Way Galaxy has a boxy-peanut shape. [Slide from K. Daniel with figure from Ness et al. 2016.]
The next part of her talk focused on her science: studying how galaxies evolve themselves. She explained that galaxies evolve within an environment, through mergers and gas accretion, for example, but the questions that interest her are about the internal work galaxies do to evolve themselves. She explained that a galaxy can be looked at as a composition of stars, or alternatively, as a set of orbits. Galaxy morphology is built from the orbits: when the orbits are populated, we get shapes, such as the boxy-peanut shaped bulge of the Milky Way Galaxy.
Dr. Daniel then explained the work that she and her students and other collaborators have done to study the internal evolution of galaxies and galaxy structure. In particular she discussed dynamical resonances, such as the “corotation resonance,” a way in which orbits can be rearranged in the disk of a galaxy without any other kinematic signatures. She explained that as orbits evolve, the morphology evolves and emerges. Another important takeaway is that there is rich structure in galaxies such as the Milky Way, which is not in an equilibrium state, but has the influence of spiral arms. She concluded by noting that the works she presented, which all aim to understand the structure and internal evolution of galaxies, try to understand the same problem from multiple perspectives and that this has led to deeper knowledge and understanding.
In the second part of her talk, Dr. Daniel spoke specifically in terms of two-eyed seeing, an approach which applies both Western and Indigenous perspectives. She started by showing an image of Mauna Kea from two perspectives: one showing the observatories on the top and the other a representation of the cultural importance of Mauna Kea. She argued that the two images are not mutually exclusive; that it is not astronomy or cultural significance, but rather “and.” She explained that the only way to find “and” is through relationships. Along this vein she highlighted community-based models of astronomy. In particular, she described Cosmic Explorer, a future experiment which she is a director of. This gravitational wave experiment is named 24 times in the ASTRO2020 decadal survey, which identifies the priorities of the astronomy community. (Dr. Daniel encouraged everyone to have a look at the appendices of ASTRO2020 to see the reports from individual panels, and not just the executive summary, which is a compilation of the reports!) Cosmic Explorer increases gravitational wave sensitivity (over LIGO) tenfold and promises unprecedented and transformation science, but not only that — it takes power sharing with the community to heart. This is notable in its management structure, which has directors for areas including DEI and Land Partnerships. She noted that we have not only the responsibility but also the opportunity to do things differently and think about power sharing models. For example, scientists work with the public even before naming a location for observatories.
Photograph of the top of Mauna Kea; Right: Representation of the cultural importance of Mauna Kea. [Slide from K. Daniel]
Dr. Daniel then highlighted some things that have been important to her with regards to bringing different perspectives to the astronomy community. She discussed the Society of Indigenous Physicists, which she co-founded, and shared a photo from their first meeting (over Zoom!) in 2020. She invited everyone to check out their social media and website and encouraged anyone who identifies as Indigenous to contact her. Next she highlighted mentorship networks, explaining they are much more effective than one-on-one mentoring relationships, namely because a single individual cannot and should not be expected to meet all mentorship needs.
Dr. Daniel concluded by tying both parts of the talk together, explaining that two-eyed seeing is about gaining dimensions: in perspective, in problem solving, an understanding the universe, and in the manner in which we exist. She explained that the collection of dynamics — whether in galaxies or among people — leads to emergent dynamics. “We have the ability to guide ourselves into emergent structures to broaden participation and evolve into something we may not otherwise imagine.” With that, she thanked the audience — in English and the languages of the Comanche and Chickasaw.
The last plenary talk of the day was given by Dr. Klaus Pontoppidan from the Space Telescope Science Institute. He talked to us about the “Origin of Rocky Planets and their Atmospheres: A Rhapsody in Infrared.” He started by talking about the Roskilde Cathedral in Denmark, an example of a church that would take a very long time to make and those who started working on it would maybe not see the end result. He draws the parallel with astronomy and future observatories; these missions take years to build and future generations will be the ones using these telescopes. Klaus has been involved with JWST and is part of the team that produced the first images of the mission!
Through his talk he walks us through how our understanding of planets has evolved over time. Exoplanets were theorized for a long time, but were only confirmed a few decades ago. Millimeter interferometry also has helped demonstrate the existence of protoplanetary disks. Klaus also highlights that Earth is actually depleted in volatiles and mentions that Jupiter is mildly enriched, except for oxygen. Similarly, Klaus reminded us about the results from the Oberg+ 2011 paper that pure freeze-out models predict carbon-to-oxygen ratios higher than the Sun’s for planets outside of the snowline. Pebble drift and water vapor advection concentrates planet-forming mass, which leads to the question: once exoplanet atmospheres are connected to the chemistry of protoplanetary disks, where exactly do planet-forming regions lie?
The speaker then shows detailed images of protoplanetary disks where dark gaps can be seen at large radii, which leads to the question of whether planets could be forming at such large radii in these systems. For several years, the Spitzer spectra of planet-forming disks looked smooth, but another group published the first detections of water and organics. Klaus then thought to himself, could the Spitzer data reflect that? He went back to the Spitzer legacy surveys and removed some methods used to analyze the data and found water! Then to connect it with JWST, Klaus found JWST-MIRI does not trace water all the way out to the snowline. To finish the talk, the speaker talked about characterizing the chemical diversity of planet-forming regions and shared that there is an upcoming paper talking about many water lines detected through the survey!
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.
Hale Prize Lecture: George H. Fisher (University of California, Berkeley) (by Emma Clarke)
The Solar Physics Division awarded this year’s Hale Prize, which recognizes “outstanding contributions over an extended period of time to the field of solar astronomy,” to George Fisher of the University of California, Berkeley. His talk, “Understanding the Dynamics of Magnetic Field and Plasma in the Interior and Atmosphere of the Sun,” reviewed the contributions to the field by himself and collaborators.
He began by discussing solar flares. First he described what happens when a solar flare occurs. This begins with the reconnection of magnetic field lines in the solar plasma. These newly reconnected field lines are filled with energetic electrons (which we can see due to their collisions with ions in the solar atmosphere and subsequent bremsstrahlung radiation). An enormous amount of energy is released in the reconnection event and transported into the solar chromosphere. An outstanding question many years ago was what happened to the solar atmosphere when heated by the energetic electrons. In 1989, Fisher described the downflows of chromospheric plasma driven by these energetic electrons and developed a generalized theory for the flare-driven chromospheric downflow’s amplitude and time variation. These predicted downflows are now routinely observed. Later, researchers wondered whether the solar flare models could be applied to stellar flares — flares on other stars. Working with Suzanne Hawley, originally a grad student and now a professor at the University of Washington, Fisher applied solar flare models to stellar flares more generally.
An illustration of the regions of the Sun’s atmosphere and interior. Click to enlarge. [NASA/Goddard]
Dr. Fisher’s second topic was magnetic fields on the solar surface. These fields most likely come from the tachocline, a transition region at the base of the convection zone with large shear. From the tachocline, magnetic active regions emerge at the solar surface as magnetic flux tubes. In the flux-tube model, the magnetic field is concentrated in a thin tube. The dynamics of the tube can be described by the forces acting on a thin 1D tube embedded in a 3D model of the solar interior. Fisher said that the flux tubes do an excellent job of explaining the observed relationship between how sunspots are “tilted” and their solar latitude (known as Joy’s law). Sunspots have the property where the leading side (in the sense of the rotation of the Sun) is more compact relative to the more broken-apart side that follows. He has argued that the higher field strength of the leading side allows the tube to better resist being broken apart by turbulent convection.
Next Dr. Fisher discussed work on determining which magnetic quantity best correlates with observed X-ray output of active regions on the Sun. With collaborators he found that X-ray output is best correlated with the unsigned (think absolute value) magnetic flux. Despite advances in understanding the relationship between solar magnetic fields and X-ray emission, reproducing an observed X-ray image with simulations has been a challenging problem; observed and computed images still do not show compelling agreement. Fisher and collaborators speculate that the main cause of the disagreements is in how the coronal loops are heated.
The final part of the talk was about efforts to develop a data-driven physics-based model of the 3D magnetic field above the photosphere. Dr. Fisher explained that such a model would require (1) a model for the evolution of the 3D magnetic field — such as a magnetohydrodynamic model or magnetofrictional model — and (2) a method to derive the electric field and/or velocity field from the photospheric magnetic field data in order to implement Faraday’s law, which describes the evolution of the magnetic field in time. Dr. Fisher discussed the challenges of the second requirement. While velocity along the line of sight can be determined with Doppler shift methods, the other two “horizontal” components are more difficult to estimate. In 2008, Fisher and Welsch developed the FLCT code, based on the Local Correlation Tracking (LCT) technique, to find the horizontal components of the velocity from magnetogram data. Their code can construct the velocity field using two images taken at slightly different times. FLCT has been applied to find flows in many different settings, some of which Fisher never imagined it would be used for! Two applications that he found surprising were deriving streamline maps of the flows and deriving proper motion flows from nebula images taken years apart.
The other approach to the second requirement is to determine the electric field. One option is to compute the poloidal–toroidal decomposition electric field from all three components of the magnetic field. Fisher and collaborators do this using a technique called PDFI, which stands for “poloidal–toroidal decomposition (PTD) plus Doppler plus Fourier local correlation tracking (FLCT) plus ideal.” Fisher says that this technique does a “pretty decent job” of reproducing the electric field. The electric field has now been computed using PDFI for most emerged active regions observed by the Solar Dynamics Observatory.
Dr. Fisher concluded by sharing his excitement for solar physics research and the many unsolved problems in the field. He proposed that we are entering a “golden age” of solar physics, especially with regards to solar magnetism.
The first press conference of the day was moderated by Dr. Kerry Hensley, AAS Deputy Press Officer, and she introduced the three speakers for the session. First up, we had Olivia Gaunt, a PhD student from Tufts University speaking about “Rare Signals from Stars in Triangulum Galaxy.” Olivia used the Keck II telescope and specifically the Imaging Multi-Object Spectrograph (DEIMOS) to observe the Triangulum Galaxy. The Triangulum Galaxy (Messier 33), is 2.73 million light-years from Earth and has an estimated 40 billion stars. Out of these stars, Olivia is interested in Wolf-Rayet stars, which are a rare class of emission-line stars that exist in an intermediate stage between big and hot O-type stars and Type Ibc supernovae. These stars are also typically characterized by an expanding bubble of ionized gas. Olivia specifically looked at Broad Emission Line Luminous Sources, also referred to as BELLS, in the Triangulum Galaxy. In one object (BELLS 1), the team saw exciting changes to the star’s emission over a 4-year timescale, which has not been observed before! Lastly, some of these objects are even an even more rare type of Wolf-Rayet stars, which gives a new insight to this area of astrophysics.
Next up, we had Jim Jackson from the Green Bank Observatory who talked to us about star formation triggered by an expanding bubble in the Nessie Nebula. The birthplaces of baby stars (protostars) are dense, cold, filamentary molecular clouds. When high-mass (greater than 8 times the mass of our Sun) stars are formed, they put large amounts of energy into the surrounding gas, which ionizes it and forms expanding bubbles (H II regions). This phenomenon drives the main question of the study: does this energetic feedback trigger or hinder star formation? To answer this question, Jackson’s team looked at the Nessie Nebula, an extremely filamentary infrared dark cloud, which is cold, dense, and opaque. The Nessie Nebula also contains the Nessie bubble in which they see a feature that looks like a question mark. They see the expanding bubble, which interacts with the filament and at their intersection they see a luminous protostar. Its location strongly suggests that the collision between the expanding bubble and the Nessie filament triggered star formation. To determine this, they used the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Australia Telescope Compact Array (ATCA) to observe the Nessie Nebula. Through detection of ammonia, they were able to see that there are signs of shock, which means the expanding bubble is slamming into the filament at supersonic speeds and the collision triggered a star to form. [Press release]
To finish off the press conference, we had Stephen Walker from University of Alabama in Huntsville talking to us about X-ray observations of a group of galaxies falling into the Coma Cluster. X-rays provide us with a view of the hot (100 million K) intracluster medium filling clusters. They allow us to observe how galaxies move and merge into clusters. The team used XMM-Newton to observe the Coma Cluster. They observe the infalling group NGC4839 that has a 1.5 million light-year-long tail behind it, and their new observations are the most detailed of an infalling group! The Coma Cluster is preceded by a shock front traveling at around 3 million mph. Their edge detections show ripples like Kelvin Helmholtz instabilities. Through studying the shape of its tail, they are able to constrain the properties of the gas such as viscosity, which is important for understanding how galaxy clusters grow through mergers. [Press release]
XMM-Newton (left) and Chandra X-ray Observatory (right) images of the Coma Cluster. [From slides by Stephen Walker]
Plenary Lecture: Julia Blue Bird (National Radio Astronomy Observatory) (by Wei Vivyan Yan)
This plenary talk today was delivered by Dr. Julia Blue Bird from the National Radio Astronomy Observatory, sharing the latest discoveries on galactic properties and evolution with CHILES. Thanks to all the amazing instruments to study both neutral hydrogen (HI) and molecular hydrogen, “It is really an amazing time to be a radio astronomer,” says Dr. Blue Bird.
Dr. Blue Bird first introduced CHILES as “a pathfinder for future radio astronomy surveys.” CHILES is short for COSMOS HI Large Extragalactic Survey, a blind survey on the HI emission using the Karl G. Jansky Very Large Array (VLA), covering the part of the COSMOS field with no strong ratio continuum sources (Figure 1). Since the HI emission line is faint and requires long integration times to observe, HI studies with previous large surveys are mostly limited to the nearby Universe (up to z = 0.06). Anything beyond z = 0.25 is considered high redshift. With a 1000-hour single pointing, CHILES could observe the HI line up to z = 0.5, which is a huge step forward.
The redshift (left) and sky coverage (right, black circle, as big as the Moon) of CHILES. [Slide by Dr. Julia Blue Bird]
The primary goal of CHILES is to tell the story of individual galaxies. Here, Dr. Blue Bird used CHILES observation to examine the connection between the comic web and galaxy gas. Since CHILES provided us with the opportunity to study both local and large-scale environments beyond z = 0.1 for the first time, Dr. Blue Bird was able to extend this discussion to higher redshift regimes.
CHILES observed the filamentary network of the cosmic web at z < 0.1 The blue filament lines overlaid the distribution of galaxies (top-down view). [Slide by Dr. Julia Blue Bird]
By identifying the filamentary network of the cosmic web over CHILES’ field of view, we can locate the distance between a galaxy and the filaments (Figure 2). The closer a galaxy lies from the filament, the less HI gas this galaxy owns. Therefore, in the regions close to the filaments, we tend to find redder, passive, and more massive galaxies. In addition to this HI gas fraction, galaxy orientation is also related to the galaxy location to the surrounding filaments. CHILES showed that low-mass galaxies generate spins that align with filaments by accreting onto the filaments, while high-mass galaxies generate spins perpendicular to filaments by merging along filaments, which agreed with theoretical predictions.
Very tight correlation between HI mass and disk diameter values directly from CHILES data (Dr. Blue Bird’s favorite scaling relation!), suggesting a nearly constant HI surface density. Click to enlarge. [Slide by Dr. Julia Blue Bird]
Dr. Blue Bird also examined the connection between star formation histories and galaxy gas, which appears as scaling relations. These relations also serve as excellent “sanity checks” for the data! Among all scaling relations (HI & stellar mass, specific star formation rate & stellar mass…) checked with CHILES data, Dr. Blue Bird’s favorite one is a very tight correlation between HI mass and disk diameter values directly from CHILES data (Figure 3). This relation suggests that the HI surface density remains nearly constant as the disks grow.
At higher redshift, Dr. Blue Bird also found some fascinating individual sources at high redshift. For example, a very exciting starburst galaxy at z = 0.38 observed with CHILES shows a large amount of CO and a surprisingly high star formation ratio. More like galaxies at z > 2! Although most detections of individual distant galaxies are generally limited compared to nearby galaxies, stacked spectra of those distant samples can demonstrate the average properties at high redshift. Stacked gas fraction seems to rise along higher redshifts, indicating a possible evolutionary trend. More tests are needed for these hints of the galaxy evolution!
CHILES filled in gaps of missing data points. [Slide by Dr. Julia Blue Bird]
Dr. Blue Bird concluded this talk with the potential and capability of CHILES. CHILES is ongoing and has already filled in many missing measurements and data points (Figure 4). It will make more significant contributions to the scientific community. Dr. Blue Bird also offered acknowledgments not only to the land but also to the students of the land at the end of this presentation.
Press Conference: Hot Jupiters and Hungry Black Holes (by Lucas Brown)
Today’s second press conference was massive — ranging from investigations of massive Jupiter-like exoplanets and explosive nova events to new observations of a famous black hole binary and studies exploring the behavior of supermassive black holes in cosmic voids.
Plot showing the semi-major axis versus mass for planets within our solar system as well as the observed population of exoplanets. “Hot Jupiters” are exoplanets with small semi-major axes but large masses, and they appear in this plot towards the top left. It is not completely understood how these planets migrated to be so close to their host stars. Click to enlarge. [Songhu Wang]
In the first of four presentations, Songhu Wang from Indiana University spoke on the aforementioned “hot Jupiters.” First showing a plot of semi-major axis versus mass for each of the planets in our solar system, Wang noted the prevalence of gas giants in our outer solar system led researchers to believe for a long time that the temperature gradient of our solar system allowed larger amounts of icy, solid material to exist farther from the Sun, causing the larger planets to form there. However, in exoplanet systems, it is actually incredibly common for Jupiter-sized planets to exist extremely close to their host star — hence, “hot Jupiters.” This discrepancy suggests that some additional mechanism must be bringing these planets inwards over time. Two popular models exist for this mechanism: “disk migration” and “high-eccentricity migration.” The latter method typically doesn’t permit hot Jupiters to end up in orbits close to other planets, so it has been of much interest to researchers to determine how “lonely” hot Jupiters are. While previous research has suggested hot Jupiters are indeed lonely, Wang and his team recently employed a method called transit timing variation to search for planets in orbits close to hot Jupiters, and they found evidence that such companion planets might be much more common than previously thought! Further research is needed to confirm this finding and explore its implications for planetary migration models, but it’s nice to think those hot Jupiters out there aren’t so lonely after all.
Next up was something much hotter than a hot Jupiter — a nova! Montana Williams from New Mexico Tech presented on new observations of a particularly strange nova. A nova is an astrophysical event that occurs when hot plasma accreting onto a white dwarf in a binary star system becomes hot enough to temporarily sustain a fusion reaction. The nova in question, dubbed V1674H, was imaged by a collection of radio telescopes collectively known as the Very Long Baseline Array (VLBA). This event was remarkably fast for a nova, as it dimmed 2 magnitudes over the course of just around one day. This observation marked only the second time a system like this was observed using the VLBA, and as a result the researchers were able to learn about the structure and dynamics of the ejected stellar material.
Artist’s impression of the OJ287 black hole binary system. When the smaller secondary black hole crosses the accretion disk of the primary black hole, the system increases in brightness. [S. Zola & NASA JPL]
Stepping up in mass once again, Mauri Valtonen from the University of Turku announced a possible first-ever direct detection of light coming from a secondary black hole in a black hole binary. The binary system, denoted OJ287, has been studied for a very long time. There are even images on photographic plates of the system that date back to the late 1800s! Part of what makes this system interesting is that the ~12-year orbit of the secondary black hole means that astronomers can predict when the secondary black hole will cross the accretion disk of the primary black hole. Whenever this happens, the system gets significantly brighter. However, up until now it has been impossible to distinguish between light coming off of the accretion disk or jets of the primary black hole and light coming off of the secondary system. Valtonen’s team performed an analysis of recent disk crossings and believes a particular set of variable flares they found corresponded to gas rushing into a stable area around the secondary black hole known as its Roche lobe. If this is indeed what the team spotted, it would mark the first direct detection of light from the secondary black hole in a black hole binary system.
Following the theme of hungry black holes accreting gasses, the final presentation of the day was a report on initial results from a research project lead by Anish Aradhey, a student at Harrisonburg High School, on the properties of supermassive black holes (SMBHs) at the center of galaxies in cosmic voids. Cosmic voids are huge underdense regions that occupy around 50% of the universe’s volume while containing less than 20% of the universe’s galaxies. The motivation for this work was to explore the hotly debated theory that galaxy interactions and mergers cause central SMBHs to accrete more material (or as Aradhey puts it — ”snacking”). Galaxies in cosmic voids are the loneliest of them all, so they provide an interesting point of comparison for this theory. Aradhey and his team used more than 8 years of NASA WISE data to look for the variability of mid-infrared light galaxies, which is a different method than is commonly employed in looking for “snacking” SMBHs. Typically, measurements are made of a galaxy’s mid-infrared light at one moment, and researchers look for bright red signatures associated with accretion onto SMBHs. This method can misclassify systems which are active but highly variable, so this new work attempts to avoid this issue by focusing on variability in this part of the spectrum. Aradhey and his team ultimately discovered that midsize and dwarf galaxies tend to have more “hungry” black holes in cosmic voids than in the general population, possibly because their isolation allows gas to more efficiently transfer to the center. On the other hand, central SMBHs appeared less active in the cosmic voids for larger galaxies.
Harvey Prize Lecture: Bin Chen (New Jersey Institute of Technology) (by Sumeet Kulkarni)
Every year, the AAS Solar Physics Division awards the Karen Harvey Prize to an early-career scientist who shows outstanding productivity within ten years of their dissertation. This year’s winner is Dr. Bin Chen, an associate professor of physics at the New Jersey Institute of Technology. Chen gave a plenary talk on using the Sun as a laboratory to study some of the most energetic plasma physics phenomena.
Chen said our closest star is a stepping stone to studying all stars in astronomy. Indeed, we use units such as solar mass and luminosity to base our understanding of various happenings in the universe. While we can’t go there in a lab coat, the Sun also serves as a great laboratory for all of stellar physics. First and foremost, it is BRIGHT, making it easy to track dynamic phenomena happening on its surface in human timescales. For example, a one-second exposure time is enough to image a rising solar flare that can change its shape and form within seconds. In contrast, other dynamic phenomena such as supernova outflows need hours of observing time to collect data and show changes over a timescale of years.
Additionally, we can study the Sun at multiple wavelengths and resolve it extremely well spatially as well as temporally. Chen and his solar physics colleagues have leveraged these abilities to understand solar flares in exquisite detail.
Solar flares release humongous amounts of energy, totalling up to 1032 erg — 10 million times greater than a volcanic explosion. The size of the corona participating in this release is equivalent to a large fraction of the size of the Sun, with the flare rising as high as 0.1 times its radius. The cause of this energy release is magnetic reconnection, a process wherein magnetic field lines of opposite poles approach each other, increasing the electric field and current density in a very thin layer called the “current layer.” This process also accelerates particles such as electrons up to very high speeds, close to the speed of light. Combining theoretical models and observations using the Very Large Array (VLA) and the Expanded Owens Valley Solar Array (EOVSA), Chen has added new insights to where and how this particle acceleration occurs in solar flares.
According to current theoretical models, a standard solar flare forms a long and thin current sheet that tapers in the middle, leading to high velocities of particles in this region. EOVSA can take frequent, broad-band microwave spectra of solar flares, from which it is also possible to distinguish spectra coming from within each region of a flare. This helps us study how magnetic fields vary within the flare structure.
Based on these data, Chen said the magnetic field profile of the observed current sheet matched very well with theoretical models. The field had a local maximum (around 500 Gauss) and minimum (called the “bottle”). The bottle portion had a lower magnetic field at the center surrounded by high fields at two ends. But unexpectedly, the spot with the maximum high magnetic fields has lower concentrations of energetic electrons, which are more prevalent in the bottle region.
Magnetic reconnections are seen in other places too: the Tokamak nuclear fusion prototype reactor and neutron stars. But they are especially important with planetary magnetic fields such as the Earth’s magnetosphere, which protects our atmosphere from evaporation due to solar winds and is thus crucial to sustaining life on our planet.
That is why it is important to study this physical process in further detail. Chen said the future observatories such as the Frequency Agile Solar Radiotelescope (FASR) would have the ability to resolve the shapes of solar flares like never seen before, as seen in the simulated image below. It is sure to flare up as many new questions as it answers!
A comparison of EOVSA observations and simulated observations of solar flares using the proposed FASR telescope [Slide by Bin Chen]
Plenary Lecture: Linda Shore (Astronomical Society of the Pacific) (by Ben Cassese)
The final plenary of the day offered something new for those who remained in the largest exhibition hall into the early evening: a talk not on astronomy research, but on public outreach and science communication. Dr. Linda Shore, the CEO of the Astronomical Society of the Pacific and winner of the 2023 AAS Education prize, split her time between a discussion of principles on how to effectively communicate with the public and anecdotes/examples from throughout her career as an educator.
After noting that science communication is more important than ever in the age of misinformation and proliferating conspiracy theories, Dr. Shore shared three keys to effective science education: all activities, whether hands-on museum demonstrations or sit-down lectures, should aim to foster participants’ Science Identity, Science Agency, and Science Capital.
An effective way to hit all three areas is to let participants explore somewhat on their own and reach a conclusion through their own questioning. The Exploratorium, a museum in San Francisco where Dr. Shore worked for many years before joining the ASP, takes this concept to the extreme. From the moment they arrive, guests of all ages are presented with interactive exhibits that come with very few instructions. For example, a giant concave mirror that sat along one wall was not accompanied by any text explaining the concepts of basic optics, like a focal point or magnification. Even so, by approaching the mirror from different directions at different distances, visitors learned that the image flipped and warped depending on their viewing geometry. Many also discovered that sound behaves like light and can be focused as well, allowing them to whisper to a friend across the hall if they stood just the right distance from the mirror.
Although the Exploratorium educates the public about science, it also is a hub for teachers to teach teachers. Dr. Shore shared several classroom experiments developed during the long-running Exploratorium Teachers Institute, a forum for teachers to develop their own strategies for effective communication, often under the guidance of veteran teachers who went through the programs themselves.
Short on time, Dr. Shore unfortunately had to skip some of the recent initiatives she has spearheaded for practicing astronomers to better their own science communication abilities. But, they are many, and include the AAS-ASP Ambassadors Program and On-The-Spot Feedback Program.
We thank Dr. Shore for her informative and enjoyable presentation, and congratulate her on the well-deserved 2023 AAS Education Award!
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.
Fred Kavli Plenary Lecture: Dan Scolnic (Duke University) (by Lucas Brown)
AAS started off tense this year — that is, it started with a presentation about two measurements that are in tension with each other. Professor Dan Scolnic of Duke University took the stage to give this meeting’s Fred Kavli Plenary Lecture, which focused on his work measuring the expansion of the universe with Type Ia supernovae. Over the past ten years, these sorts of “direct” measurements of the expansion rate (denoted “H0”) have honed in on a value around 73 km/s/Mpc while precise measurements of the cosmic microwave background (CMB) combined with the standard model of cosmology have suggested a value around 67.5 km/s/Mpc. What gives?
The first portion of Prof. Scolnic’s talk helped bring us up to speed on the history of the Hubble constant and the idea of the expanding universe itself. More than 100 years ago, Einstein completed his general theory of relativity, and he set out to apply his new theory to the universe as a whole to understand its cosmological implications. Quickly, he found that in order to have a static, eternal universe, a constant term had to be added to his field equations — the “cosmological constant.” Einstein insisted for much of his life that any non-static models of the universe derived from his theory had to be wrong in some way, Prof. Scolnic noted, but the idea of a dynamic universe was eventually vindicated through observations. Those observations, carried out initially by Harvard astronomer Henrietta Leavitt and then expanded upon by Edwin Hubble, involved measuring the distances to far away galaxies using Cepheid variable stars, whose intrinsic brightness can be deduced from their period of brightening and dimming. By tracking the relation between the distance to a galaxy and the velocity at which it recedes from us, Hubble and his successors demonstrated the expansion of the universe.
This plot demonstrates the distance ladder technique used by cosmologists to measure the scale of the universe as well as cosmological parameters like the rate at which the universe is expanding. Local measurements using stellar parallax are used to calibrate distance estimates for Cepheid variable stars, which are then used to calibrate distance estimates for Type Ia supernovae. Click to enlarge. [Reiss et. al. 2021]
Type Ia supernovae, like Cepheid variables, have an intrinsic brightness that can be tightly constrained. This, combined with their extreme luminosities, makes them ideal for measuring the expansion of the universe on even larger distance scales. Precise measurements of this expansion using supernovae revealed that the universe is not only expanding but accelerating, which encouraged the re-introduction of Einstein’s cosmological constant into cosmology. Today, measuring the expansion rate of the universe H0, as well as the value of the acceleration, are major aspects of observational cosmology. Prof. Scolnic works in large collaborations like Pantheon+ and SH0ES to measure these values using Type Ia supernovae and other objects with well-constrained intrinsic brightness, known as “standard candles.” The process of combining distance measurements from different types of standard candles to estimate farther and farther distance scales is known as the “distance ladder” method. In contrast, one can also infer H0 from measurements of the CMB. Prof. Scolnic likened this approach to looking at a human growth chart: the CMB acts as a “baby picture” of our universe, and when we combine this picture with a cosmological model we can generate an expected growth-chart to predict the properties of the universe today. However, in recent years it has become clear that CMB measurements are predicting a lower value of H0 today than is actually measured using the distance ladder technique.
This discrepancy, known as the “Hubble tension,” has led to large amount of criticism being levied at the work of Prof. Scolnic and his collaborators, as some believe the tension is most easily explained as being the result of systematic errors in their analysis. However, Prof. Scolnic and his teams have worked diligently over the past several years to address these concerns. In his presentation, Prof. Scolnic demonstrated how even tweaking over a dozen aspects of their analysis couldn’t get H0 below about 72.5 km/s/Mpc, still far from the 67.5 km/s/Mpc derived from CMB measurements. Removing entire “rungs” on the cosmic distance ladder also fails to resolve the tension. Prof. Scolnic believes that their measurements are indeed correct, and that part of why other physicists are so apprehensive about the analysis is that there isn’t anything immediately obvious on the theoretical side that can fix the tension. In many theoretical explanations, a radical change in the dynamics of the universe must occur at either very early or very recent times. Prof. Scolnic largely dismisses the latter conclusion, highlighting a paper that speculates on the possibility that a rapid change in the gravitational force ~100 million years ago may have occurred, coinciding with the extinction of the dinosaurs. The bizarre connection here is meant to demonstrate how sparse the evidence is for these recent-universe changes. On the other hand, Prof. Scolnic thinks some theories which modify early-universe dynamics may be promising, such as “early dark energy.” Regardless of what exactly turns out to resolve the Hubble tension, there is clearly a lot left to learn about the history of our universe.
Press Conference: Discoveries in Distant Galaxies (by Sumeet Kulkarni)
The press office at AAS 242 decided to begin their press conference schedule from a long, long time ago and in galaxies far away, with subsequent press conferences bringing us gradually closer to home by Wednesday. This first one, though, was all about discoveries in distant galaxies using new-age probes that extend humanity’s sense-making capabilities almost beyond comprehension — through gravitational wave detectors such as LIGO and Virgo and telescopes like JWST.
First up, representing the “audible” sector of astronomy — listening to the “sounds” of spacetime via gravitational waves — was Ore Gottlieb from Northwestern University’s Center for Interdisciplinary Exploration and Research in Astrophysics. While detectors such as LIGO and Virgo now regularly catch the chirps from merging binary neutron stars and black holes, there are other, yet undiscovered sources of gravitational waves that researchers hope to uncover in their fourth observing run (O4). One of these is catching the combined cacophony of gravitational wave sources, also known as the “stochastic gravitational wave background,” as opposed to hearing individual events. While compact binaries also contribute to this background, Gottlieb focussed on two additional possibilities that can set spacetime in motion: Supernovae and the progenitors of gamma ray bursts (GRBs). The latter can create extended “cocoon” structures powered by jets in 20-40-solar-mass stars, and these promise to be the most likely stochastic background candidate. However, Gottlieb noted that there is only about 1% chance of detecting cocoon signatures in O4, and realistically, we will need third-generation observatories. [Press release]
The first speaker, Marcia Rieke from Arizona State University introduced the JADES project and its latest data release. This was followed by Kevin Hainline from the Steward Observatory who gave an outline of exactly how early of an universe their team is probing. JADES’ dataset of galaxies from less than 600 million years since the Big Bang now numbers at 717, up from only a dozen or so before JWST! “It’s exciting that we can even talk about these (early) times,” Hainline said. More than 93% of these galaxies, which formed the early hydrogen and helium crucial for the evolution of our universe, were never seen before JWST. But now, not only can we detect these infant galaxies, but we can also see complex structures in them, including one dumbbell-shaped early galaxy which is Hainline’s favorite. [Press release]
Ryan Endsley from UT Austin gave the next JWST update about dwarf galaxies. He said that ultraviolet emission lines from the recombination of hydrogen ions are valuable probes of star formation in early galaxies. In particular, they are great probes to study dwarf galaxies, given JWST’s ability to detect emission lines from galaxies that are 50 times fainter than what was possible before. It is now also possible to compare whether bright and faint galaxies from the early universe developed differently. And indeed, the JADES team found that the brightest galaxies underwent more star-formation bursts — events wherein matter equivalent to several tens of Suns formed at once. [Press release]
JWST image of the Einstein ring of a lensed galaxy 12 billion light-years away (in red) surrounding a foreground galaxy (in blue) 3 billion light-years away. Click to enlarge. [Slide by Jane Rigby]
The next presentation emitted smoke, not quite from fireworks, but from a new discovery that definitely warrants setting some off — that of complex organic molecules in early galaxies. Jane Rigby presented these results from the TEMPLATES project, which uses JWST observations of four distinct galaxies. She made sure to spotlight two researchers to be credited with this discovery: Justin Spilker from Texas A&M University and Kedar Phadke from the University of Illinois. Through observing a galaxy 12 billion light-years away that got bent, warped and magnified by a closer clump of galaxies 3 billion light-years away in what is known as gravitational lensing, the team could make out signatures of organic molecules that lead to smoke or smog-like structures in their images. [Press release]
The final press briefing of this morning was given by Patrick Kamieneski from Arizona State University, who talked about a dusty and warped Milky Way-like galaxy nicknamed “El Anzuelo.” Spanish for a fish-hook, this term aptly describes the shape of this galaxy which is 11 billion light-years away. While similar in size and a dustier version of our own galaxy, El Anzuelo forms stars at more than 80 times faster than the Milky Way. JWST’s incredible infrared detection capabilities have made it possible to dramatically improve the way in which we can study such objects, as emphasized by the image below.
Animated gif comparing Hubble and JWST images of El Anzuelo galaxy. [Patrick Kamieneski]
Oral Session: Daytime & Dark Sky Heritage in American Southwestern Archaeoastronomy (by Emma Clarke)
Example of a gnomon — a vertical construction that casts a shadow. Pebbles mark the shadow’s trajectory over time as the Sun makes its daily path across the sky. [From slide by Tony Hull]
Tony Hull from the University of New Mexico started this session by discussing a simple and accurate method to define cardinal directions. In an experiment in Chaco Canyon, New Mexico, researchers used a portable light stand constituting a gnomon and pebbles to track the trajectory of the gnomon shadow. They showed that on the equinox, the tip of the shadow follows a straight line, oriented accurately east–west. They concluded that the equinox gnomon is sufficient to establish the cardinality of the Great House Pueblo Bonito in Chaco Canyon. However, this is not ethnographic evidence that the method was used, rather that it could have been used.
Next up, Cherilynn Morrow discussed the outreach program associated with NASA’s PUNCH mission: four “suitcase-sized” spacecraft focused on the inner heliosphere between the Sun and Earth that is scheduled to launch in 2025. The PUNCH outreach program focuses on the sun as a natural extension of the human understanding of the sun and its rhythms. The program shares the interconnections between historical sun watching, such as interpreting the “eclipse” petroglyph site at Chaco Canyon, and modern Sun-watching, both by NASA missions and all contemporary people observing sunrise, sunset, light and shadow cast by the Sun, and eclipses.
The “eclipse” petroglyph in Chaco carved by the Ancestral Puebloan people may have been inspired by the total solar eclipse in 1097. [From slide by Cherilynn Morrow]
The third speaker, J. McKim Malville, discussed the astronomy connected with the Great Houses in Chaco Canyon and what it meant for the inhabitants, residents, and visitors during astronomical events. One unanswered question is why the 15 Great Houses were built in such a resource-poor location and not totally abandoned when leaders moved northward. Perhaps the canyon and buildings were sacred places with astronomical significance.
Closing the session, Michael Rymer spoke briefly about archaeoastronomy and international dark sky places. The International Dark-Sky Association’s International Dark Sky Places Program encourages areas around the world to preserve dark sites through policies and public education. Two dark sky places in the US — Chaco Culture and National Historic Park in New Mexico, and Hovenweep, on the border of Utah and Colorado — are also archaeoastronomical sites. Protection of the dark night sky at these places not only makes better stargazing, but is also important for preservation of wildlife and plants. There is a growing list of potential future sites of dark-sky parks in the US.
Plenary Lecture: Edwin “Ted” Bergin (University of Michigan, Ann Arbor) (by Junellie Gonzalez Quiles)
Murthy Gudipati from the Jet Propulsion Laboratory (JPL) introduced the Laboratory Astrophysics Division and invited everyone to become familiar with the division and join as members. He then introduced the plenary speaker, Prof. Edwin “Ted” Burgin from the University of Michigan, Ann Arbor. His talk titled “The Birth of Planets and the Story of Carbon” started with his recognition of laboratory astrophysicists and their role in helping understand the fundamentals needed to study astrophysical phenomena. Ted then transitioned to mentioning how the search for life has driven the connection between chemistry in protoplanetary disks to the atmospheric composition of exoplanets. This link is essential if we want to fully understand how planetary systems are formed and, therefore, how individual exoplanets are formed.
Shown here is the bulk carbon to silicon ratios for the Earth and solar system bodies. Click to enlarge. [Slide by Ted Bergin, from Bergin et al. 2015]
Throughout his talk, he took us on a journey where he explained what protoplanetary disks look like, how there are dark gaps or rings, which can mean that planets may be forming in that region, and explained to us one of the ways you can create exoplanets: pebble accretion. Through planet formation, exoplanets can have different bulk compositions depending on where they form and whether they are mainly made of refractory, semi-volatile, or volatile elements. Öberg et al. 2011 shows the relationship between the carbon to oxygen ratio (℅ ratio) and the snowlines in a planetary system, and Ted mentioned that in systems that have a ℅ ratio higher than 1, we know that oxygen must be present as ice on grains. Knowing the carbon to oxygen ratio is important to understand in the context of planet formation.
Here you can see the TW Hya system and their C2H detection from the Bergin et al. 2016 paper. Click to enlarge.
During his plenary, he also spoke about isotopic fractionation and how it offers a new window into planet formation. He showed the TW Hya system, where they looked at the ratio of 12C to 13C. This can be done for other planetary systems to say whether the system could be carbon rich (see Figure 1). He then ended his talk by talking about our own planet. Earth is relatively carbon poor compared to our Sun, Venus, and other types of chondrites (see Figure 2). Earth was formed of mainly refractory materials with small amounts of soot and water, and he aims to understand soot in the context of exoplanets. He also studied the geological processes that could lead to outgassing on exoplanets and how the carbon inventory can lead to methane in their atmospheres and potentially hazes as well.
He is very interested in how all of these aspects of planetary formation and evolution could impact the habitability of exoplanets, and it is certainly something to look out for in our search for life in other worlds!
Press Conference: Solar Swirls, Satellites, and Saving the Night Sky (by Lucas Brown)
The second press conference of the day switched gears from the distant reaches of the universe to our local corner of space, with presentations on a new solar weather phenomenon, the positives and negatives of artificial satellites for astronomy, and updates on efforts to preserve the night sky.
First up was Oana Vesa from New Mexico State University, who spoke on new research into solar tornadoes. That’s right — there are tornadoes on the Sun. Only discovered in 2008, there is little known about the formation mechanisms behind these tornadoes or their overall role in the solar environment. Vesa explained that these tornadoes, consisting of hot, swirling plasma, are bound to the surface of the Sun magnetically, and can channel mass and energy up through different levels of the solar atmosphere. And like most things on the sun, their scale is massive. These chaotic solar vortexes vary from the size of a city all the way up to the size of Earth. Through new observations performed at the Dunn Solar Telescope, Vesa’s team has tracked dozens of these events, and they have begun the process of cataloging and analyzing their behaviors. So far, the team has found the tornadoes to have an average lifespan of about 8 minutes, and some have been seen to form in pairs or exhibit chaotic spiraling patterns. There’s a lot left to learn about these fiery storms. [Press release]
An image of the main science component of ORCASat, containing a laser module, photodiodes, and an integrating sphere, also known as a Lambertian sphere. ORCASat is designed to help calibrate ground-based telescopes. Click to enlarge. [ORCASat/University of Victoria Centre for Aerospace Research]
Next up was Justin Albert from the University of Victoria, who gave an overview of ORCASat, a recent cubesat mission that intends to demonstrate the utility of specialized satellites for calibrating ground-based telescopes. ORCASat contains a specialized cavity known as a Lambertian sphere, which evenly disperses incoming laser light before some of that light reflects down towards Earth. This system allows for on-board photodiodes to very accurately measure the intensity of light which will be beamed through the atmosphere. In turn, ground-based equipment can observe the satellite in orbit and determine how much light was lost as it passed through the atmosphere, providing a very sensitive method of calibration. The satellite has been in orbit since November of last year, and in the ensuing months, one complete exposure (in good lighting conditions) has been taken of the satellite streaking across the sky, providing a first proof-of-concept of the method. NASA and NIST are expected to develop a more advanced satellite for this purpose in the future, which will hopefully help increase the accuracy of measurements taken by ground-based telescopes. [Press release]
Plots showing how the Median Radon Transform algorithm can identify satellite trails in imagery from the Hubble Space Telescope (HST). The top plot is a HST image containing a satellite trail, while the bottom right image is produced by applying a Median Radon Transform. The satellite trail now appears more similar to a point source. [Figure 3 in Stark et. al. 2022]
While satellites like ORCASat may help increase the accuracy of ground-based astronomy through its intentional emission of light, most satellites in orbit are actually detrimental to ground-based astronomy due to their reflection of light, occasionally creating bright streaks in astronomical imagery. For this reason, astronomers around the world have been working on developing algorithms to automatically detect such streaks and remove them or toss out the affected imagery. David Stark from the Space Telescope Science Institute (STScI) spoke on this in his talk, highlighting the development of a new algorithm which greatly increases the accuracy of satellite-trail detection. The algorithm employs a method known as a “Median Radon Transform,” which essentially looks for the median pixel brightness in every possible straight line one could trace within an image. A large outlier in a given line’s median value is a strong sign that that line contained an abnormal amount of light, often due to a satellite trail. This method significantly improved satellite-trail detection over previous methods developed at STScI. In testing the method on Hubble Space Telescope (HST) data, Stark and his team found that the number of satellite trails in HST imagery had roughly doubled over its lifetime, but noted that the rate was still so small that it did not hinder HST’s ability to do science. [Press release]
Closing out today’s second press conference, James Lowenthal from Smith College spoke about efforts to protect the night sky from light pollution. He noted that terrestrial light pollution from cities is in many ways a more significant threat to astronomy than satellite trails, and has many other negative effects such as harming plants and animals which are all used to a particular day-night cycle that has been disrupted in recent years. He also highlighted the spiritual significance of the night sky to many native communities. Lowenthal noted that dark sky advocacy groups have grown in recent years thanks in part to renewed interest due to the growth of satellite mega-constellations like SpaceX’s Starlink. Through the efforts of dark sky groups and their partnerships with native communities, local governments, and industry, some strides have been made towards preserving the night sky, such as creating new lighting standards centered around preserving the night sky while still illuminating cities. However, much more work has to be done given that recent research has shown that light pollution is increasing at much higher rates than previously thought due in part to the proliferation of LEDs. One of the success stories Lowenthal highlighted in his talk was the protections enacted in Coconino County, Arizona, home to numerous historic observatories. Another recent example given was the enacting of official dark sky protections in central Maine, one of the last remaining dark sky sites east of the Mississippi River. [Press release]
Plenary Lecture: Greg Taylor (University of New Mexico) (by Ben Cassese)
Greg Taylor of the University of New Mexico delivered the third plenary of the day. Over the course of 45 minutes, Prof. Taylor took the denizens of Ballroom C and the Zoomiverse on a whirlwind tour of science conducted with the Long Wavelength Array (LWA) over the past decade. This instrument, a collection of 256 individual antennae spread throughout a 100-meter ellipse, has touched an impressive number of subfields in that time: From pulsars to the solar wind, the LWA has seen (and measured) it all.
A schematic of how the LWA detects an incoming meteor. [Prof. Greg Taylor, University of New Mexico]
After joking that his talk would last 6 hours and cover each of the roughly 80 papers built on LWA data, Taylor settled for summaries of some of the highlights. Many of these centered on the detection and characterization of meteors as they streak through the atmosphere and leave a wake of radio-bright ionized material trailing behind. There was a satisfying arc to this line of research: When Taylor and collaborators first saw these brief signals, they did not know what to make of them. They could think of no astronomical source for these transients scattered evenly throughout the sky, and only with careful analysis and cross-checking with other techniques did they realize that they had built a uniquely capable meteor detector. The team has since made the study of disintegrating meteors and their fireballs a major research focus.
Taylor also shared an overview of observations designed to test models of the solar wind. Here, the LWA stared at a pulsar (during the day! Radio astronomy is great like that) and measured how its signal changed as the Sun edged closer and closer to their line of sight. This let the team probe different regions of interplanetary space and constrain the ionized material that hovers within the solar system and slightly distorts radio signals.
Plans for the “swarm” of detectors to complement/supplement the LWA. Click to enlarge. [Prof. Greg Taylor, University of New Mexico]
After including very brief overviews of a few other projects, Taylor pivoted to the future of the LWA. The team has already constructed a second, similar array far from the original, which they can connect to form a longer baseline and better angular resolution. In the coming years, they hope to repeat this improvement in the extreme and build a “swarm” of small arrays dispersed across the United States. Some of these sites are purely aspirational, but some already have committed funding; in all, it looks like the next decade will be even more productive than the last.
Plenary Lecture: Jeyhan Kartaltepe (Rochester Institute of Technology) (by Sumeet Kulkarni)
“Far and wide eyes of the JWST” was the theme of the final plenary session at AAS 242 on Monday. Prof. Jeyhan Kartaltepe from the Rochester Institute of Technology talked about results from two wide-ranging projects from the first JWST observing cycle and how they are constantly molding our knowledge of cosmic history.
Kartaltepe began with a brief overview of JWST’s capabilities and how its infrared eyes unlock the deepest reaches of the universe by detecting light that has been redshifted to those wavelengths due to cosmic expansion. JWST was always going to be pathbreaking, and all astronomers knew it. When asked how many in the plenary woke up early (in US time zones) to watch it launch on Christmas day in 2021, 90% of the hall raised its hands.
The reach of different deep field images towards the early universe in terms of redshift. [Prof. Guinevere Kauffmann, MPA Garching]
The first project Kartaltepe’s plenary featured was CEERS, which observes a 100 square arcminute patch of the sky to demonstrate, test, and validate efficient extragalactic surveys. An early science result from CEERS was the discovery of a faraway galaxy, now known as Maisie’s galaxy after the daughter of one of the project PIs. Maisie’s galaxy looks like a red blob among a sea of usual-looking galaxies, as is typical for such early galaxies. But the interesting thing was that it wasn’t a standalone galaxy in CEERS data! There were several more candidates found in JWST images, challenging our understanding of how quickly galaxies started to form and mature in our universe.
But among the exciting early galaxy candidates also hide several mimickers: nearby, dusty galaxies also have the same red, blobby appearance which can be mistaken to be one due to high redshift by photometry (studying properties of the images) alone. But JWST does much more than just click pictures of these galaxies. It can also study their character using a spectroscope, or a prism that splits light to unveil the telltale signatures of molecules within it. The spectroscopic data from JWST of Maisie’s galaxy was so clean, that it “looked just like that of a nearby galaxy,” said Kartaltepe. This helped them confirm its age of being only around 390 million years after the Big Bang! Spectroscopy also helps confirm (or reevaluate) the age of early galaxy candidates. Kartaltepe gave an example of a galaxy first believed to have a redshift of 16 (placing it among the earliest ever detected galaxies), which was then reduced to 4.9 thanks to the JWST’s NIRSpec data.
The scale of COSMOS-Web observations [Jeyhan Kartaltepe]
The second project that Kartaltepe is excited about is Cosmos-Web. This project covers a relatively big patch of the sky, just larger than the full Moon, but goes deep into it with JWST’s far-reaching eye to record all galaxies near and far that lie within. This patch of the sky was chosen because part of it has been extensively studied by the Hubble space telescope, allowing for extracting science out of the two sets of observations in tandem. As of today, Cosmos-Web has completed about half of its observations and is already finding large numbers of high-redshift galaxy candidates, dusty star-forming galaxies, and more!
Kartaltepe concluded her plenary by stressing the importance of mentorship in furthering our field and supporting the progress of students and early career researchers. “I wouldn’t be here if not for excellent mentors,” she said, and urged all students today to pick an advisor who prioritizes seeing them as a person first.
This week, AAS Nova and Astrobites are attending the American Astronomical Society (AAS) summer meeting in Albuquerque, NM, and online.
AAS Nova Editors Kerry Hensley and Susanna Kohler and AAS Media Fellow Ben Cassese will join Astrobites Media Intern Sumeet Kulkarni and Astrobiters Lucas Brown, Emma Clarke, Wei Vivyan Yan, 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 on astrobites.org! You can also follow @astrobites on Twitter for the latest updates.
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! In addition, you can catch Kerry, Ben, and Sumeet at the press conferences all week, and Sumeet will be presenting an iPoster on Astrobites as an educational resource at 5:30–6:30 pm MT on Tuesday, 6 June.
