The welcome reception will be held in the atrium on the second floor of Rudolph Hall, beginning at 6pm.

Breakfast will be provided outside of Emerson Auditorium

Opening Remarks

Perspectives on the Early Solar System from Extinct Radionuclides in Extraterrestrial Materials

There is now extensive evidence for the presence of several extinct radionuclides, i.e., those with half-lives of up to a few tens of millions of years (such as 10Be, 26Al, 53Mn, and 60Fe), in a variety of undifferentiated and differentiated meteorites and samples returned by spacecraft missions. The origin and distribution of these radionuclides is of great interest since they have implications for the astrophysical environment in which our star, the Sun, originated as well as the timescales of events in the early Solar System. In this talk, I will discuss the current status of this area, with some examples of work conducted in my laboratory, the roots of which can be traced to work I did as a graduate student in the MCSS.

New Approach to N-Body Dynamics for Spherical Systems

For many years, computationally intensive N-body simulations have been the tool of choice for simulating the evolution of self-gravitating systems, such as galactic dark-matter halos. If, however, the system is assumed to be spherically symmetric, the calculation can be streamlined and accelerated by orders of magnitude. With this approach, the evolution of dark-matter halos with with self-interacting dark matter, decaying dark matter, tidal stripping, with evolving Newton's constant, can be accomplished in a matter of minutes on a laptop.

The Persistence of Nonlinear Gravitational Wave Memory

Nonlinear gravitational wave memory is a surprise of theoretical physics. Whereas it is understood that a gravitational wave induces oscillatory squeezing and stretching motion in a collection of freely-falling test masses, it is unexpected that the wave leaves a residual displacement of the test masses. This displacement is the tribute "in memoriam" to the passing wave. The memory originates in a nonlinear feature of gravitation. Whilst merging black holes are a significant source of gravitational waves, the gravitational wave energy itself is a further source of gravitational waves. The memory is often described as a permanent displacement of the test masses caused by a burst of primary gravitational waves. But as we show, memory vanishes at late times in a sea of echoes.

Break

The First Decade of Presolar Grain Research at the MCSS

Largely due to the vision of MCSS founding director Bob Walker and the laboratory wizardry of Ernst Zinner, the Compton 4th floor group was central to the discovery of presolar grains in meteorites in 1987 and to the rapid growth of their use as tools for astrophysics and cosmochemistry. I was fortunate to join the group as a PhD student in 1991 and thus participate in the burgeoning new field. This talk will discuss the early history of presolar grain research at Washington University and the fundamental contributions of a large number of MCSS faculty, postdocs, and students in the early 1990s.

Revisiting Solar System Bulk Composition: Insights from Bennu’s Returned Samples

Ivuna-type (CI) carbonaceous chondrites have long been considered proxies for bulk solar system elemental composition due to their similarity to the solar photospheric abundances and their higher enrichment in moderately volatile and volatile elements than other chondrite classes. However, CI chondrites have experienced terrestrial alteration. NASA’s OSIRIS-REx mission returned pristine material from asteroid Bennu, providing an opportunity to refine solar system composition estimates. Our bulk analysis of Bennu samples reveals that they are more enriched in moderately volatile and volatile elements than CI chondrites at a statistically significant level. Comparisons to the solar photosphere show that Bennu’s composition aligns closely with it. We propose revising the current solar system composition estimates using our Best Bulk Bennu (BBB) composition. This revised solar system composition has significant implications for the volatile budget of Earth and other terrestrial planets. If the revised solar system composition is more volatile-rich than CI chondrites, it implies that Earth and other terrestrial planets may be more volatile-depleted than previously thought. Moreover, the elevated Zn and K levels in the BBB composition could refine models of Earth’s building blocks, suggesting that even less outer solar system material is needed to account for Earth's volatile inventory and implying that Earth’s composition is dominated by inner solar system sources.

Lunch will be provided outside of Emerson Auditorium

Pebble Accretion as a Mechanism for Terrestrial Planet Formation

Pebble accretion refers to the process whereby a seed mass orbiting around the star accretes infalling pebbles leading to a rapid growth of planetesimals and ultimately planetary embryo. For this process to occur: 1) a seed mass must be generated early in the nebular history; 2) the nebula must persist long enough for the planetesimal to grow and 3) there must be sufficient pebble-size material to grow the planets. All conditions are met, and the process of growth by rapid coalescence of small grains – so-called pebble accretion – should have occurred based on simple physical principles.

There are a number of fundamental differences between the outcomes of the traditional model of impact growth and pebble accretion. First, the timescales are vastly different. Whereas impact collision takes 10⁷-10⁸ years to form terrestrial planets, pebble accretion results in planetary embryos in as little as 2 My. As a result, pebble accretion may lead to incorporation of a high degree of early-formed refractory inclusions that are otherwise not found (or are rare) in our meteorite collections. Second, pebble accretion leads to the formation of planetary embryo-sized bodies while the nebula was still extant, so that large amounts of volatiles were ingassed into a magma ocean. Third, pebbles raining down through a hot H-rich atmosphere should undergo volatilization, leading to partial modification of their elemental and isotopic chemistry. This process also will reduce FeO to Fe metal, producing H₂O which can then be incorporated into the growing planet. Finally, pebble accretion selectively incorporates mm-size pebbles (chondrules, refractory inclusions, metal grains) but mostly excludes dust (matrix in chondrites). In this scenario, we are able to match the Earth’s major element composition (Fe, Ni, Ca, Mg, Si, Al, O) within uncertainties using pebble components, whereas we are unable to do the same with any combination of chondrites (C-chondrite, E-chondrite, O-chondrite and iron meteorite mixing). When we use chondrite components rather than chondrites, we find that the e⁵⁴Cr and e⁵⁰Ti compositions of our ‘best fit’ model are virtually identical to Earth’s presumed composition. The reason for this is that there is a population of C chondrules with negative e⁵⁴Cr and e⁵⁰Ti values.

Discovering Worlds Young and Old: Adventures with the Transiting Exoplanet Survey Satellite (TESS)

The Transiting Exoplanet Survey Satellite (TESS) is NASA’s ongoing MIDEX mission for discovering planets outside the solar system, and for exploring the time-variable sky. TESS is spearheading progress toward the goal of finding life elsewhere in the Galaxy, a major priority expressed in the 2020 Astronomy and Astrophysics Decadal Survey.

This spring, TESS completed its 7th year of operations since its launch in 2018. The observatory is not only healthy, but its scientific output has continued to grow rapidly. This past year, the mission enabled a publication rate of nearly ~2 refereed journal publications based on TESS discoveries per day!

TESS’s 2nd Extended Mission (2023-2025) has brought its sky coverage to >95%. As of this month, TESS has established 623 confirmed exoplanets orbiting and 7643 new planet candidates.

The upcoming 3rd Extended Mission (2026-2029) should increase the total number of TESS planet candidates to >10,000; moreover, the number of planet candidates which should be characterizable via Doppler mass measurements from the ground should more than double, while the number of suitable TESS planets for atmospheric characterization by JWST will more than triple.

A selection of some of the most recently-discovered TESS planets will be discussed, including some that seem to be exhibiting unusual temporal behavior and some that are members of multi-planet systems.

I will also briefly discuss TESS’s role as a “finder scope” for >10⁸ time domain and multi-mission (TDAMM) candidate astrophysics targets for JWST and other major observatories. This capability is enabled by the wide FOV of the four TESS cameras, which provide precise, simultaneous optical photometry over 2400 sq. degrees of sky during their month-long stares, thus creating a fundamental and lasting legacy for the astronomical community at large.

Using Mercury Isotopes to Trace the Origin of Volatile Elements in Terrestrial Planets

Variations in the abundances of moderately volatile elements (MVE) are key geochemical signatures distinguishing the terrestrial planets. The origins of these variations—whether due to nebular processes, planetary volatilization, differentiation, or late accretion—remain uncertain. Mercury (Hg), one of the most volatile MVEs and a strongly chalcophile element, exhibits significant mass-dependent (MDF) and mass-independent (MIF) isotopic fractionations. Traditionally used to trace biogeochemical cycling in surface environments, Hg is also among the few elements for which the solar composition is poorly constrained and its concentration highly variable in primitive meteorites, likely due to terrestrial contamination. For example, the Hg abundance of various Orgueil fractions can vary by orders of magnitudes. It is therefore necessary to estimate the Hg abundance and isotopic composition on uncontaminated samples.

I will present the Hg isotopic and elemental data obtained from Ryugu samples returned by the Hayabusa2 mission and demonstrate that they are the best samples to estimate the composition of the Solar System. Including this newly determine concentration we will show that the Hg abundance of the BSE falls in the volatility trend defined by other moderately volatile elements, suggesting the absence of Hg in the Earth's core. To establish the Hg isotopic composition of the bulk silicate Earth (BSE), we analyzed samples least affected by crustal recycling—high 3He/4He lavas from Samoa and Iceland—yielding Δ199Hg = 0.00 ± 0.10, Δ201Hg = -0.02 ± 0.09, and δ202Hg = -1.7 ± 1.2 (2SD). We further demonstrate that Hg isotopes can be used to trace crustal recycling: terrestrial subaerially-derived materials exhibit negative Δ199Hg, whereas subaqueously-derived marine sediments show positive values. For example, HIMU-type lavas display positive Δ199Hg, reflecting the influence of altered oceanic crust in their mantle source.

Our extensive dataset on meteorites reveals that the BSE falls within the chondritic range for both MIF and MDF. However, considering our Ryugu data, we will show that most of our previous and new data are contaminated and not representative of the meteorite parent body. Considering only the least contaminated samples we found that Hg isotopes also follow the CC/NC dichotomy with the Earth falling in between, as previously observed for Zn. Combining all these results show that a small fraction of the Earth's volatile must be originated from an outer solar system materials (Ryugu-like) with a major fraction being inner solar system (NC-like) materials.

Break

On the Age of the Moon (and the Earth)

A well-regarded estimate for the age of the Earth at ~4.55 billion years was established by Patterson and colleagues in the mid-1950s without necessarily defining precisely what is meant by this “age”. Since then, a “Giant Impact” model for formation of the Earth – Moon system via collision of a planetary embryo with the proto-Earth has become the consensus view, albeit with differing proposed specific scenarios. Regardless of the details, one can consider that the time of the impact provides a well-defined event for TEarth+Moon, reducing the problem of determining the age of the Earth to that of the Moon, which is in principle easier, since its ancient crust is much better preserved than that of the Earth. Therefore, it is surprising that after 50+ years of analyses of lunar rocks, the age of the Moon is controversial with estimates varying by over 160 million years.

I will discuss a multi-technique and multi-institutional approach utilizing the U-Pb and Lu-Hf radioactive decay systems in individual Apollo zircons to determine model ages for the final crystallization of the lunar magma ocean (LMO). Our recent data [1] show that the LMO achieved >99% crystallization at 4,429 ± 76 Ma, indicating a lunar formation age of ~4,450 Ma or possibly older, depending on thermal evolution models for cooling of the magma ocean. Consideration of other chronological constraints suggests a temporal window for the Giant Impact of between ~60 to ~120 million years after solar system formation.

[1] N. Dauphas, Z.J. Zhang, X. Chen, M. Barboni, D. Szymanowski, B. Schoene, I. Leya, & K.D. McKeegan, Completion of lunar magma ocean solidification at 4.43 Ga, Proc. Natl. Acad. Sci. U.S.A. 122 (2) e2413802121, (2025).

Stardust in Samples from Asteroid (101955) Bennu

Carbonaceous asteroids offer insight into the primordial materials that formed planets in the protoplanetary disk. They contain organic matter and tiny dust particles known as presolar grains, which originate from the envelopes of aging stars and the remnants of stellar explosions, such as novae and supernovae, prior to the birth of our Solar System. These stardust grains are essential for understanding the building blocks of our Solar System.

The recent sample return from asteroid (101955) Bennu by NASA’s OSIRIS-REx mission presents a new opportunity to examine the distribution and abundance of presolar grains in carbonaceous asteroids. In my talk, I will present results from the laboratory analysis of the Bennu samples.

Stardust, Asteroid Goo, Moon Water and the Frontiers of Astromaterials Microscopy

Astromaterials available for study in the laboratory range from nanoscale dust grains formed in the outflows of ancient stars older than the Sun, to macromolecular organic polymers products of mud-ball asteroids, to water molecules and He-filled bubbles from solar wind implantation into lunar soil grains. Transmission electron microscopy studies of these diverse astromaterials provide important constraint of the materials formation conditions and subsequent astrophysical processing. TEM observations of the differences in the crystal structure and sub-grain compositions of presolar silicon carbide grains, for example, can be linked to difference in composition of the progenitor circumstellar envelopes and cooling histories. This presentation will provide highlights of recent electron microscopy studies of nanodiamonds, asteroid organic matter and space weathered lunar soils, and discuss emerging microscopy capabilities and needs for future space exploration.

Noble Gases in the Early Earth

We determine the chemical behavior of noble gases in the primordial magma ocean (MO) by performing ab initio molecular dynamics simulations at temperatures and pressures along the MO adiabat.

Our simulations show that at the bottom of the magma ocean, He partitions preferentially into the MO rather than the liquid core. The origin of the ocean island basalts reflects a large contribution and contamination from mantle sources and no necessary contribution from the top of the outer core, which is depleted in primordial He. We suggest searching for the He reservoirs at the base of the solid mantle. ^[1]

At the top of the MO, beneath the hot, dense early atmosphere, He primarily remained in the MO and degassed only later, at low atmospheric pressure. However, we found that the simultaneous presence of incompatible volatiles, such as CO2 and He, results in significant loss from the MO. Our findings indicate that the early Earth’s atmosphere was carbon-rich, with a high concentration of He and other noble gases, and must have been thicker and hotter than previously believed. ^[2]

Finally, during crystallization, He remains in the melt and continues to accumulate in the melt until the last droplets of the MO solidify. However, the heavier noble gases, such as Xe, which diffuse very slowly, may be partially trapped in the newly forming bridgmanite crystals, while Ne hovers on the brink of crystal entrapment. Consequently, Ar, Kr, and Xe, which are trapped in bridgmanite, would be more evenly distributed throughout the solid mantle, whereas He would concentrate in specific deep reservoirs. ^[3]

References:
[1] Ozge Ozgurel, Razvan Caracas (2023) The magma ocean was a huge helium reservoir in the early Earth. Geochemical Perspective Letters, 25, 46-590 (2023)
[2] Adrien Saurety, Ozge Ozgurel, Chris Mohn, Razvan Caracas (2024) Diffusion, chemical bonding, and kinetic fractionation of noble gases in the primordial magma ocean. Geochimica et Cosmochimica Acta, 378, 144-152.
[3] Anne H. Davis, Razvan Caracas (2024) Degassing of CO2 triggers large-scale loss of helium from magma oceans. Communications Earth and Environment, 5, 344.

At the beginning of the poster session, we will be taking a group photo on the stairs in the Frick Forum. Be sure to join us!

Gabrielle Adams, WashU
Mass Loss Rates of M-type, S-type, and C-type Asymptotic Giant Branch Stars

Megan Broussard, WashU
Major and Trace Elemental Composition of the CI Chondrite Oued Chebeika 002

James Buckley, WashU
The Antarctic Demonstrator for the Advanced Particle-Astrophysics Telescope (ADAPT)

Paul Carpenter, WashU
Mineralogy and Oxygen Isotopic Composition of CI1 Chondrite Oued Chebeika 002, Including Discovery of Hydrated Na-Mg Phosphate

John Christian, WashU
Characterization of Compositional Endmembers in PIXL Scans
PDS Geosciences Web Map Service Pilot: CRISM MRDR Tiles

Ekrem Esmer, WashU
Characterizing Circumbinary Planet Populations with Multi-Method Surveys

Andrea Gokus, WashU
Blazar Flares at the Cosmic Dawn: Uncovering High-Energy Processes at z>4

Anne Hofmeister, WashU
Origin and Evolution of Axial Spin of Planets and Sub-Solar Stars and Consequences for Interior Processes

Jonathan Katz, WashU
Flare Stars vs. Solar Flares

Abigail Knight, WashU
2025 Update on the NASA PDS Geosciences Node
Characterization of Sub-µm-Scale Mars Dust with PIXL: Implications for Potential Human Space Flight

William McKinnon, WashU
Exploration of Kuiper Belt in the 21st Century, What Have We Learned about Planet Formation and What is to Come?

Cameron Moye, WashU
Artemis III Candidate Landing Regions: Illumination Constraints on the Likelihood of Ice Deposits in the Upper Meter of Regolith

Daniel Scholes, WashU
The PDS Geosciences Node's Orbital Data Explorer for Data Discovery and Download

Thomas Stein, WashU
PDS Analyst's Notebook

Scott VanBommel, WashU
In Situ X-ray Spectrometers in Space Exploration: Past, Present, and Future
MCSS and the Discovery of Native Sulfur on Mars

Kun Wang, WashU
Revisiting Solar System Bulk Composition: Insights from Bennu’s Returned Samples

Bryce Wedig, WashU
The Roman View of Strong Gravitational Lenses

Nathan Whitsett, WashU
Planet-induced Stellar Flare Candidates from the TESS Mission

Chengzheng Yong, WashU
Laboratory Simulations of Aqueous Reactions in Lunar Polar Regions

Judy Zhang, WashU
Experimental Insights into Early Solar System Silicate Magmatism: Melt Origin and Evolution of EC002
Highly Siderophile Element Systematics of Winonaites: Insights into Early Parent Body Processing and Constraints on the Winonaite-IAB Connection

Breakfast will be provided outside of Emerson Auditorium

Middle-Sized Icy Moons: Big Punches in Small Packages

The Solar System is blessed with a dozen mid-sized icy moons, not quite planet-sized but bigger than lumpy "potatoes." These moons display an astonishing variety, from active to long dead, and each has had a unique history that reveals fundamental processes occurring in these planetary systems, related not only to how they were formed but what they are made of and the dynamic systems they are in.

Probing the Ice of Mars with Radar Sounding

The presence of water ice on and below the surface of Mars makes it a favorable target for radar sounding. Also known as ground penetrating radar, radar sounding can be accomplished from orbital spacecraft. Pulses of radio energy are emitted at rates of hundreds per second, and their echoes are received onboard for digital recording. Once downlinked to Earth, the data can be processed into images that portray the surface and subsurface of the planet as a kind of cross section, known as a radargram. The data can also be analyzed to constrain composition, such as the relative proportions of ice and lithic materials. Two radar sounders, MARSIS and SHARAD, have been collecting data continuously for nearly two decades. This presentation will show the key results of these experiments, including the distribution of water ice on the poles, in the mid-latitudes and in remnant glaciers. These ice deposits are prime targets for future exploration, both for seeking evidence of habitable environments and for potential utilization of resources by human visitors.

Modeling the Mysterious Moons of Mars

The Earth's Moon and the two moons of Mars, Phobos and Deimos, represent the only long-lived natural satellites of the terrestrial planets. By nearly every metric, the moons of Mars appear vastly different than Earth's. Earth's Moon has a mean diameter of ~3475 km, is differentiated, and has had a long history of volcanic activity, making it practically a fifth terrestrial planet. In contrast, Phobos and Deimos are much smaller, with mean diameters of ~22.2 km for Phobos and ~12.5 km for Deimos, are both significantly prolate, and have low densities. Observations by the Viking Orbiter spacecraft in the 1970s showed that the surface of Phobos was most similar to carbonaceous chondrites in its visible to near infrared spectra. On the basis of their small size, density, and surface spectra, it was proposed that they were captured carbonaceous asteroids originating in the main asteroid belt, rather than being formed from a giant impact in the late stage of terrestrial planet accretion like Earth's Moon. This would make Phobos and Deimos analogous to the irregular satellites of the giant planets. However, unlike the irregular satellites both Phobos and Deimos orbit deep in the gravity well of Mars, have orbits that are nearly circular, aligned with the equator, and moving in the same direction as the spin of Mars. Such orbits are characteristic of bodies formed from an accretion disk, like the regular satellites of the outer planets and the Earth’s Moon, and not those of captured bodies. In this talk, I will discuss ongoing efforts to understand the origin of Phobos and Deimos from a giant impact, and the many surprises that have emerged from efforts to model their long-term dynamical evolution. I will describe a novel hypothesis for a history of Phobos that involves an ongoing ring/moon cycle of destruction and rebirth. I will demonstrate how oft-neglected Deimos provides constraints on the history of the martian system as a whole, and the role that the "Sesquinary Catastrophe" may have played in its history.

Break

A Comparison of Inner Solar System Volcanism

The volcanic landforms, eruptive sites and longevity of activity on Mercury and the Moon contrast substantially with those of Earth, Venus and Mars. In this talk, I synthesize global maps of volcanic and tectonic features for these five worlds and, from the collective records of volcanic activity in the inner Solar System, draw conclusions about the long-term behavior of terrestrial planets in general. Mercury and the Moon differ from the larger planetary bodies in terms of not only size and composition (and so shorter periods of melt production) but also by their being affected by a horizontally compressive stress state arising from a reduction in planetary volume as they cooled. The phenomenon of global contraction also readily accounts for the dearth of widespread extensional tectonic structures on Mercury and the Moon. From this comparative analysis, the most promising extrasolar planets on which to focus future searches for evidence of active, radiogenically driven volcanism are probably the larger rocky bodies in a mature planetary system or those worlds in relatively young systems.

How Does Chemical Composition Affect the Initiation of Plate Tectonics on Rocky Exoplanets?

For planets to develop narrow, dynamic plate boundaries that resemble Earth’s, the rocks that make up the lithosphere must be able to localize deformation. Decades of field studies have shown that plate boundary deformation manifests as frictional faults at shallow depths and mylonitic ductile shear zones below the brittle-plastic transition, with individual strands as narrow as 10-100s of meters. The physical mechanisms that produce mylonites from a primary lithosphere are of considerable interest since it is presumably impossible to create or sustain Earth-like plate tectonics without them. Experimental studies demonstrate that the characteristic microstructures in mylonites form through the serial processes of dynamic recrystallization and phase mixing. However, the rapidity with which this occurs depends on temperature, grain-size, and composition, and the volume fraction and viscosity contrast between constituent mineral phases. As such, the mineralogical composition of a rocky planet will determine whether the planet can (a) localize deformation, and (b) initiate and sustain Earth-like plate tectonics. This contribution will review experimental evidence for the onset of mylonitization and show the results of models that predict the time scales (and therefore ease) with which planets of different compositions can localize deformation. Drawing on data from the Hypatia catalog of exoplanets, these models identify specific stars with exoplanets that may be most amenable to forming Earth-like plate tectonics.

Accelerator Mass Spectrometry: Applications to Terrestrial and Extra-Terrestrial Problems in the Geosciences

Accelerator mass spectrometry enables the measurement of rare radionuclides, such as Be-10, C-14, Al-26, Cl-36, Ca-41, and I-129. These radionuclides can be produced by cosmic-ray interactions with both extra-terrestrial and terrestrial materials. The measurements of the radionuclides yield information about the exposure conditions and durations. These measurements have been used to study lunar regolith processes and meteorite exposure ages, most recently on samples returned from Hayabusa and Bennu. Measurements of terrestrial cosmic-ray produced nuclides provide information on glacial chronologies, erosion rates, and burial ages.

Lunch will be provided outside of Emerson Auditorium

Formation of the South Pole–Aitken megabasin

The South Pole–Aitken (SPA) basin-forming impact, was a key event in the Moon’s history producing its largest basin. Details of this impact including the direction of the impact and fate of the ejecta remain uncertain. Here we simulate the formation of SPA reproducing its crustal structure. We find producing a basin in the observed shape of a southward tapered ellipse is only possible for a differentiated impactor with a north-to-south trajectory. Our impact simulations demonstrate that mantle ejecta is distributed in the cross-range and the downrange direction, with much of it collapsing into the basin interior, consistent with the observed distribution revealed by gravity data. These results suggest that the Artemis landing sites should contain abundant ejecta from SPA including mantle material. Therefore, we expect samples from the Artemis missions will reveal the age of SPA and the composition of the Moon’s interior.

Almost 50 Years of X-Ray Supernovae: Shocking Tales, Numerical Simulations, and Multi-Wavelength Synergies

The first X-ray supernova (SN) was discovered in 1980. The pace of discovery was initially slow, but picked up after the launch of the Chandra and XMM, and later Swift satellites.

I will review what we currently know about X-ray SNe. I will display the variety of X-ray light curves of SNe, some of which extend over 4 decades in time. The light curves can provide useful information on the density structure of the surrounding medium, and the evolution of the SN shock waves in this medium. A few SNe have light curves that are distinct from the majority of the SN population, suggesting an unusual evolution. In one case, exceptional high resolution spectroscopic data, combined with numerical simulations, have allowed us to infer an asymmetry in the source, and decipher the three-dimensional structure of a point source extragalactic object.

Finally, I will present concurrent multi-wavelength observations of a young SN, and show how they enable us to get a clearer picture of the complicated structure of the ambient medium into which the SN is evolving. Numerical simulations help to better interpret the observed emission, and provide insight into the nature of the SN progenitor star, which may have evolved in a binary system.

On the Acceleration of Atomic Nuclei to a Hundred Joule

Cosmic rays are observed to have energies measured to be as high as 200 EeV. A major puzzle is to explain how they are accelerated. I will summarize what we have learned about the composition, spectrum and isotropy from non-relativistic to these “Ultra High" energies. I will then briefly outline the most promising of the mechanisms that have been proposed. Finally I will sketch a scheme in which the entire spectrum is produced, hierarchically, by a “bootstrap” process operating at astrophysical shock fronts of successively larger scale associated with supernova explosions, galactic winds and cluster shocks.

Break

I-Pu-U-Xe Age of the Moon-forming Giant Impact

The Moon-forming giant impact triggered the last catastrophic outgassing event on the young Earth. The classical I-Pu-Xe closure age model assumes perfect open-system loss of volatiles prior to closure of the silicate Earth, and a perfectly closed system after the last giant impact. Here we present an augmentation to the classical I-Pu-Xe closure age for Earth's mantle to account for partial retention of gas accreted during the main stages of accretion and outgassing that occurred after the Moon-forming giant impact.

Science Results from CALET on the International Space Station

The Calorimetric Electron Telescope (CALET) continues to collect excellent data after nine and a half years of operation on the International Space Station. CALET, which started operations in October 2015, was designed to measure the spectra of the highest-energy electrons and positrons through the TeV energy decade to search for nearby sources and/or signatures of dark matter processes, and measure the spectra of the hadronic components up to a PeV. Secondary science goals include measuring the relative abundances of the ultra-heavy galactic cosmic rays (UHGCRs) above Z=28 (nickel) that probe the processes involved in cosmic-ray acceleration and propagation in the galaxy. The CALET calorimeter is also sensitive to GeV-energy gamma rays and is being used to study persistent and transient astrophysical sources, the galactic center excess, and to search for signatures of dark matter. The CALET Gamma-Ray Burst Monitor (CGBM) also monitors the sky for X-ray and soft gamma-ray transients, including in connection with gravitational wave events. Additionally, CALET has made many significant space weather measurements, having demonstrated sensitivity to events in observations of variability in the flux of geomagnetically trapped particles, especially using on-board measurements of precipitating electrons.

Saponite Bearing Material Excavated During the Formation of a Recent 25 m Diameter Impact Crater in Southeastern Arabia Terra on Mars

Mars Reconnaissance Orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), Context Imager, and HiRISE imager observations were analyzed for a 25 m wide impact crater located on the southeastern side of the dust-covered Arabia Terra region. Repeat image coverage shows that the impact occurred between 2010 and 2012. The crater shape, proximal and far-ranging rayed ejecta deposits, together with impact simulations, indicate that the cratering event was from a hypervelocity impact from an incoming heliocentric bolide. A CRISM along track oversampled observation (0.45 to 3.75 µm) was processed to retrieve surface single scattering albedos (SSA) and surface temperatures, followed by regularization of the overlapping 18 m wide pixels to a projected spatial resolution of 12 m/pixel. The data show that the ejecta emplacement altered the thermophysical properties of the surface by exposing and/or depositing coarser materials as compared to the undisturbed dusty surfaces. CRISM data also show that the ejecta, excavated from only several meters depth, contain saponite bearing materials. Ejecta deposits show decay of spectral absorption strengths with increasing distance from the crater, consistent dilution due to increased areal dispersal of ballistic ejecta with increasing range, together with incorporation of excavated local material during emplacement. The crater and its ejecta deposits thus provide a rare opportunity to document the presence of a mineral produced in an aqueous environment and located in the shallow subsurface of this otherwise dusty terrain.

The symposium dinner will be held at the James S. McDonnell Planetarium in Forest Park. 

Transportation will be available from the Knight Center, pre-registration is required.

Breakfast will be provided outside of Emerson Auditorium

X-ray Observatories: From XRISM to Future Calorimeter Spectrometer Missions

High-resolution X-ray spectroscopy is a transformative tool for exploring the high-energy universe. The grating spectrometers aboard the Chandra and XMM-Newton satellites ushered in a new era of X-ray astronomy, yet critical gaps remained: 1) the need for imaging spectroscopy to study extended cosmic sources, and 2) high energy resolution at higher X-ray energies, particularly in the Fe-K band around ~6 keV. To address these challenges, next-generation astrophysical X-ray missions are deploying arrays of calorimeters. These detectors combine exquisite spectral resolution with high quantum efficiency across a broad X-ray energy range. In this talk, I will review the operating principles of calorimeters, highlight the Resolve spectrometer aboard XRISM—launched in October 2023 with a pioneering calorimeter array—and discuss exciting future missions enabled by large-scale, high-resolution X-ray imaging spectrometers.

JAXA’s Sample Return Missions and Sample Curation: From Hayabusa 1/2, OSIRIS-REx to MMX

Japan Aerospace Exploration Agency (JAXA) has a strategic small-body sample return program to understand the formation, evolution, and migration of planetary building blocks, water, and organics in the early solar system. The JAXA's sample return program started with Hayabusa for S-type asteroid Itokawa in 2010, followed by Hayabusa-2 for C-type asteroid Ryugu in 2020, and the future mission of Martian Moons eXploration (MMX) for Phobos in 2031. My presentation covers the recent achievement of Hayabusa 2, OSIRIS-REx, and MMX sample curation at ISAS/JAXA and how the curation activity contributes to the science community.

Title: TBD

Abstract

Break

Tigers, Dragons and More: Ultra-heavy Cosmic Rays to Planetary Elemental Compositions

In this talk I will discuss a path that started out with the initial Trans-Iron Galactic Element Recorder (TIGER) experiment, and is currently moving towards new elemental composition measurements at the M-class asteroid (16) Psyche, Mars’ moon Phobos, and Saturn’s moon Titan. An organizing theme for all these experiments is galactic cosmic rays. At the McDonnell Center, the study of galactic cosmic rays has been a foundational area of research. The start of this path was my PhD work on the initial TIGER experiment, which has led to a series of increasingly complex and successful experiments. From that starting point, the path continues with experiments that measure the elemental composition of planetary bodies. Specifically, these experiments use the technique of planetary nuclear spectroscopy, where gamma rays and neutrons that are generated by galactic cosmic rays on planetary surfaces provide quantitative measurements of elemental compositions. Initial nuclear spectroscopy experiments provided key information about the Moon, such as enhanced hydrogen abundances at the lunar poles, and global thorium abundances. Current experiments that are either in space or under development are the following. The Psyche Gamma-Ray and Neutron Spectrometer (GRNS) will measure the elemental composition at the M-class asteroid (16) Psyche and provide key data to understand the nature of this mysterious, metal-rich asteroid. The Mars-moon Exploration with GAmma rays and NEutrons (MEGANE) experiment on the Japanese Martian Moons eXploration (MMX) mission will quantify the elemental composition of Mars’ moon Phobos with the goal to understand how Phobos formed. Finally, the Dragonfly Gamma Ray/Neutron Spectrometer (DraGNS) is part of the NASA Dragonfly mission that will explore Saturn’s moon Titan using a car-sized, nuclear-powered octocopter. Results and current development status of these missions will be described.

The Black Hole Explorer

The Black Hole Explorer, or BHEX, is a proposed SMEX-class submillimeter VLBI mission. I will describe the mission and highlight some its capabilities. We expect that BHEX will produce high resolution sequences of images of the black holes in the galactic center and M87, resolve the photon ring in M87, resolve the horizon for several new black holes, and enables high resolution studies of the launching region in several extragalactic radio jets.

Future Exploration of the Jupiter System

NASA and ESA have launched ambitious, comprehensive missions to explore the satellites of Jupiter, Europa in the case of the US (Europa Clipper) and Ganymede in the case of ESA (Jupiter Icy Moons Explorer). Operating at the same time frame in the early 2030s, opportunities for synergistic science are now being explored. Less well known, China has also announced its plan to send a mission to Jupiter, Tianwen-4, that will ultimately focus on the outermost Galilean satellite, Callisto.

Closing Remarks