Lunchtime Seminar Schedule

Dr. Kaitlyn McCain, Jacobs, NASA Johnson Space Center

Theme: Early Solar System
Ryugu sample return: Exploring the early outer solar system

February 1, 2023 at 12:00 pm (Virtual)

Abstract: On December 6, 2020, the Japanese Aerospace Exploration Agency's Hayabusa2 mission returned to Earth with more than 5 grams of pristine material collected from asteroid 162173 Ryugu. Extensive analysis campaigns in the following two years have shed light on outer Solar System materials, environments, and events. In this talk, I will discuss a few key discoveries enabled by Ryugu material and share how I and my colleagues have used this unique resource to explore the timing and chemistry of water and organic-rich fluid systems active early in the Solar System's history.
About the speaker: Dr. Kaitlyn McCain is a NanoSIMS scientist working at NASA's Johnson Space Center as part of the Jacobs-JETSII contract. Her work focuses on developing novel analytical techniques to support in-situ isotopic measurements of solar system materials including meteorites, interplanetary dust particles, Stardust particles, and more. She earned a Ph.D. in Geochemistry from UCLA in 2022, examining the timing and chemistry of fluid alteration in primitive meteorites and Ryugu particles.

Prof. Steve Desch, Arizona State University

Theme: Mercury
Giant Impacts and Geochemistry

February 8, 2023 at 12:00 pm (Virtual)

Abstract: Giant impacts are widely accepted to have been common in the early Solar System, and have been invoked as the cause of Mercury's high core mass fraction, and of the Earth-Moon system. Most studies of giant impacts have focused on the dynamical aspects of the collisions, but giant impacts could have important chemical consequences for planets, particularly if the impacts happen early in a planet's evolution. I will discuss the possibility that Mercury experienced a giant impact just after its magma ocean crystallized, at about 5 Myr after the Solar System's formation. This could simultaneously explain the lack of ejecta reaccretion and the curious enrichments of elements in Mercury's mantle, and could connect Mercury with meteorites like NWA 7325. I will also discuss evidence from D/H ratios in lunar samples, silicon isotopes, and other geochemical evidence that suggests the Theia impactor had ingassed solar nebula hydrogen into its magma ocean and was Mercury-like in its composition. Geochemistry opens a new window into giant impacts, constraining their timing and other aspects.
About the speaker: Professor Steve Desch is a Professor of Astrophysics in the School of Earth and Space Exploration at ASU. His research focuses on developing models of star and planet formation, using data from meteoritics and planetary science. He especially studies the origins of chondrules and meteorites. He also works in the fields of exoplanets and astrobiology and has also been the Principal Investigator (PI) of the NASA-funded NExSS grant to study geochemical cycles on exoplanets to aid searches for signs of life on other planets. He has modeled small icy bodies to explore the likelihood of subsurface water on Pluto and its moon, Charon, the asteroid Ceres, and others. He has recently advocated the concept of Arctic Ice Management, to study how to increase sea ice in the Arctic in response to climate change. Asteroid 9926 Desch is named after him.

Dr. Qian Yuan, California Institute of Technology

Theme: Earth (Geophysics)
The "missing" Moon-forming impactor, Theia

February 15, 2023 at 12:00 pm (Virtual)

Abstract: The Moon is widely recognized as having formed from the “Giant Impact”, when a small planet named Theia collided with the proto-Earth, but direct constraints on the existence of the putative Theia remain elusive. Here, we demonstrate that the mantle remnants of Theia explain fundamentally important features of the largest seismically-imaged anomalies within Earth – the two large low velocity provinces (LLSVPs). We combine state-of-art evidence from theoretical and computational astrophysics, geodynamics, mineral physics and seismology to demonstrate how Theia mantle remnants naturally provide an explanation for a compositionally distinct origin for LLSVPs, as well as their age, density and size. This study substantially expands the influence of giant-impact planetary processes to the evolution of Earth, and implies similar mantle heterogeneities caused by impacts may also exist in the interiors of other rocky planets within or beyond our solar system.
About the speaker: Dr. Qian Yuan is now an O.K. Earl Postdoctoral fellow at California Institute of Technology. He received his Ph.D. degree in geodynamics with an emphasis on the dynamics of lower mantle structures from Arizona State University in 2022. He holds a B.S. degree and EngD in economic geology from China University of Geosciences, Wuhan. His research focuses on dynamic processes in the interior of Earth, and how these processes influence surface geological activities such as plate tectonics and volcanic eruptions. He primarily uses geodynamic simulations, as well as a range of geophysical observations, petrological and geochemical analyses in pursuing related research. His long-term goal is to integrate the geophysical, geochemical and planetary processes into a self-consistent model that could help better understand the evolution and habitability of Earth and beyond.

Dr. Aleisha Johnson, University of Arizona

Theme: Earth (Geochemistry)
"Ti isotopes as a new tool for probing the formation and evolution of the continental crust"

February 22, 2023 at 12:00 pm (Virtual)

Abstract: Titanium (Ti) stable isotopes are found to undergo mass-dependent fractionation during magmatic differentiation, driven primarily by the crystallization and removal of Fe-Ti oxides. This fractionation behavior, combined with Ti's unique geochemistry, make Ti isotopes an ideal tool for understanding the formation and evolution of the continental crust. Intriguingly however, Ti isotopes appear to fractionate to different extents in different magmatic series, which has complicated attempts to apply Ti isotopes to crustal studies. In this talk I will review the most recent efforts to quantify the controls on Ti isotope fractionation and discuss several new and ongoing applications of Ti isotopes to petrologic systems.
About the speaker: Dr. Aleisha Johnson received her PhD from Arizona State University in 2020, where she performed mineral oxidation experiments and isotope modeling to quantify the first rise of oxygen in Earth's atmosphere. She found that central to ancient Earth studies were questions regarding the extent and composition of Earth's continental crust, which can now be reexamined using newly developed isotope systems. She was awarded an NSF Postdoctoral Fellowship to work at the University of Chicago, where she further developed paired Fe and Ti isotope analyses in magmatic systems, and is now working as a postdoc at the University of Arizona to develop new applications for Ti isotopes.

Dr. Amanda Stadermann, University of Arizona

Theme: Moon
Evidence for Mg-rich Volcanism on the Moon from Apollo 16

March 1, 2023 at 12:00 pm (Virtual)

Abstract: The magnesian suite (Mg-suite) of rocks record some of the earliest intrusive magmatism on the Moon. Studies of these Mg-suite rocks find they are plutonic or hypabyssal, formed typically kilometers under the lunar surface. I provide evidence for Mg-rich volcanism based on clasts embedded in Apollo 16 impact melt rock 68815. These clasts are Mg-rich and have similar petrology and geochemistry to spinel troctolites, but lack plutonic textures. If confirmed as extrusive Mg-suite volcanism, these lavas may have been similar to komatiites on Earth and this finding would broaden the known diversity of lunar volcanism during the initial stages of secondary crust building.
About the speaker: Dr. Amanda Stadermann recently defended her PhD at the University of Arizona's Lunar and Planetary Laboratory. Her work mostly focuses on lunar geochemistry and petrology. Of particular interest to her is the diversity of lunar magmatism and the effects of impact cratering on lunar material. She has investigated these topics using remote sensing and experimental petrology, in addition to electron beam techniques such as electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD).

Dr. Maria Valdes, Field Museum

Theme: Meteorites
Calcium isotopes in meteorites and Antarctic fieldwork to find more of them

March 8, 2023 at 12:00 pm (Virtual)

Abstract: The past five decades, and the last decade in particular, have seen significant advancements in analytical capabilities and with it a marked increase in the use of Ca isotopes to advance our understanding of the Solar System’s and Earth’s evolution. In this talk I will give an overview of mass-dependent and non mass-dependent Ca isotopic data from bulk meteorites and chondrite components. I will discuss how Ca isotopes record nebular processes, including evaporation/condensation and mixing of chemically and isotopically distinct reservoirs in the protoplanetary disk. I will also discuss non mass-dependent Ca isotopic variations as tracers of the nature and timing of stellar mass contributions to the parental molecular cloud, and the constraints Ca isotopic data place on the nature of and the relationships among planetary building blocks. This talk also explores the effects of parent body-based and terrestrial secondary processes, along with the variable sampling of isotopically heterogeneous Ca-rich components, on bulk meteorite compositions.
Building increasingly comprehensive models of Solar System evolution benefits not only from analytical advancements, but on expanding the number meteorites available for scientific study. Antarctica is a premier hunting ground for meteorites; in fact, although Antarctica makes up only 9% of the world’s land surface area, over 60% of meteorite finds have been made there. I will share details about my recent expedition to identify new possible meteorite and micrometeorite accumulation zones in the areas surrounding the Belgian Princess Elisabeth Antarctic station in the Sør Rondane Mountains. After a month of fieldwork, the team brought back five new meteorites from previously unsearched territory, including a 17-pound specimen— one of the largest ever found in Antarctica.
About the speaker: Dr. Maria Valdes is currently a research scientist at the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum. After completing an undergraduate degree in Geophysical Sciences at the University of Chicago, she completed a Masters degree in Earth and Planetary Sciences at Washington University in St. Louis, a Ph.D. in Geochemistry and Cosmochemistry at the University of Brussels, Belgium, and a postdoctoral position at Cambridge University. She studies the history and evolution of the Solar System through the chemistry of meteorites, windows into our ancient past. Her current projects include studying HED meteorites, which are thought to derive from the Asteroid Vesta, and micrometeorites, which are dust-sized meteorites that fall to Earth in great abundance. Using chemical methods to understand them, she hopes these samples will eventually help contextualize our own planet’s origin and evolution within the Solar System.

Dr. Jiaqi Li, UCLA

Theme: Mars
Martian Crustal Structures Revealed by the InSight Mission

March 29, 2023 at 12:00 pm (Virtual)

Abstract: Much of what we have known about the interior of the Earth comes from seismology, starting about 100 years ago. Recently, planetary seismology took a big step with the touchdown of the InSight seismometer on Mars in 2018. Over the last two years, I have been working as a member of the InSight Science Team where I am involved in many diverse projects, from the Martian crust to its core. In this talk, I will present my contributions to understanding the structure and formation of the Martian crust: the evidence of seismic anisotropy in the crust, the possible cause of crustal layerings beneath the lander, and the discovery of an intracrustal discontinuity away from the InSight landing site.
About the speaker: Dr. Jiaqi Li is a postdoc in Prof. Caroline Beghein's group at UCLA, where he works on investigating the Martian crust using the InSight seismic data. Jiaqi holds a B.S. (2014) and Ph.D. (2019) in Geophysics from Peking University (China), where he imaged the subduction zone structures using seismology. Prior to moving to UCLA in 2021, he was a postdoc at Michigan State University. At MSU, Jiaqi has worked on deriving high-resolution tomography images with full-waveform inversion and super-computing. He has also been serving as an Early Career Member and Communication Specialist from the AGU Seismology Section from 2021-2023.

Dr. Kaveh Pahlevan, SETI Institute

Magma oceans and primordial atmospheres of Earth, Mars, and the proto-lunar disk

April 12, 2023 at 12:00 pm (Virtual)

Abstract: The terrestrial planets of the Solar System are thought to have grown via mutual collisions of solid bodies. Rapid release of gravitational energy accompanying these impacts — possibly supplemented by the heat of decay of short-lived radionuclides — melted the growing planets during accretion, producing global magma oceans. Magma oceans in turn facilitated the gravitational separation of planetary metals into cores and planetary gases into outgassed atmospheres. Whereas the process of core-mantle separation has been studied via the geochemical signatures remnant in planetary mantles, the process of mantle-atmosphere separation — sometimes called catastrophic magma ocean outgassing — has been difficult to constrain. In this talk, I will review the evidence that the Earth, Mars, and the proto-lunar disk melted and experienced catastrophic outgassing during accretion, and describe models that link the chemical composition of the resulting primordial atmospheres with the remnant isotopic record.
About the speaker: Dr. Kaveh Pahlevan is a research scientist at the Carl Sagan Center at the SETI Institute. He received his B.S. in astronomy at UMD and his M.S. and Ph.D. in planetary science at Caltech developing the observable consequences of lunar formation via giant impact. His research focuses on linking the physics and chemistry of terrestrial planet formation to observations of the modern planets and samples of their reservoirs. He is currently a Principal Investigator (PI) for NASA’s Emerging Worlds and Solar System Workings programs, and working to identify the processes that lead to the earliest habitable environments in the Solar System.

Dr. Jan H. Render, Lawrence Livermore National Laboratory

Using isotopic signatures to trace protoplanetary disk formation & evolution

April 19, 2023 at 12:00 pm (Virtual)

Abstract: Ancient migrations of the gas giants appear to have substantially disturbed and altered the original structure of the early Solar System, hampering our understanding of where meteorites and planetary bodies accreted. One particularly useful signature to shed light on the primordial architecture of the protoplanetary disk are isotope anomalies of nucleosynthetic origin, which arise from the heterogeneous distribution of presolar matter in the early Solar System. In this talk I will present isotopic data for various meteorite samples in a suite of elements with varying geo- and cosmochemical behavior, fingerprinting the matter from which meteorites and planetary bodies eventually formed. Collectively, these data indicate a trend in the distribution of presolar matter as a function of distance from the Sun, permitting ‘cosmolocation’ of the accretion orbits of various Solar System materials.
About the speaker: Dr. Render obtained his PhD from the University of Münster in Germany and is currently a postdoctoral researcher in the Nuclear and Chemical Sciences Division at the Lawrence Livermore National Laboratory. His research focuses on the isotopic compositions of meteorites and the components therein to help understand the structure and evolution of the Solar System. Such signatures cannot only be used to constrain processes acting on individual samples—including neutron capture, planetary differentiation, and loss of volatile species—but can also provide spatial and chronological information.

Dr. Zhendong Zhang, MIT

Seismic wavefield imaging of the ice sheet: from shallow to deep

April 26, 2023 at 12:00 pm (Virtual)

Abstract: Seismic waves traveling through shallow and deep ice, contain valuable information about the ice velocities and discontinuities, which help us better understand glacier structures, melt rates, and processes. We analyzed the ambient-noise and active-source seismic data acquired by a linear array deployed on the West Antarctica Ice Sheet in 2019 and applied cutting-edge seismic wavefield imaging methods to estimate the compressional and shear wave velocities in the top 200 m and to image seismic discontinuities within the ice sheet and bedrock. The estimated velocity models are then used to estimate the firn-air and firn thicknesses, the ice crystal fabric orientation, and the porosity profile. We observe englacial reflections at frequencies lower than previous studies and bed reflections with multiple branches. Such reflection waves are further used to calculate the seismic images of discontinuities in the ice sheet and the bedrock, revealing a multiple-layering composition of ice near the bed and a highly fractured bedrock with a strong topography.
About the speaker: Dr. Zhendong Zhang is currently working as a Postdoctoral Associate at MIT Earth Resources Lab. He received a B.Sc. degree in geophysical prospecting from the China University of Petroleum (Beijing) in 2013, and a Ph.D. degree from King Abdullah University of Science and Technology in 2019. His research focuses on imaging the Earth’s interior across scales using novel seismic wavefield based methods such as wave-equation dispersion spectrum inversion for velocity estimation in the near-surface, machine-learning aided elastic full-waveform inversion for reservoir characterization and reverse-time migration full-waveform imaging of the mantle discontinuities. Dr. Zhang is now an Associate Editor of Geophysics and was named the 2022 winner of the Geophysics Reviewer of the Year Award by the Society of Exploration Geophysics (SEG).

Prof. Orit Sivan, Department of Earth and Environmental Sciences, Ben Gurion University of the Negev, Israel

Methane related iron reduction in aquatic sediments

May 3, 2023 at 12:00 pm (CHM 0215)

Abstract: Microbial iron reduction (MIR) is likely one of the first evolutionary metabolisms, and plays a key role in the reductive dissolution of Fe(III) minerals in the natural environment. It is part of the microbial anaerobic respiration processes in sediments that are coupled to the reduction of electron acceptors along a cascade of decreasing free energy yield. However, surprisingly, in many aquatic sediments significant MIR has been observed also much below its expected traditional depth, in the methanogenesis zone, sometimes accompanied by methane decrease. We investigate this unexpected microbial reduction of iron linked to methane in sediment diffusive profiles in lakes, estuaries and marine sediments. This is by quantifying the rates and mechanisms of the processes controlling this reduction, mainly using geochemical isotopic approach.
About the speaker: Prof. Sivan's research interest is to explore fundamental biogeochemical processes across different types of interfaces, including the sediment-water interface and the fresh-saline groundwater interface in coastal aquifers, using a quantitative geochemical approach. Most of her research emphasizes on using isotope ratios to quantify anaerobic microbially mediated processes at these interfaces. The ultimate goal is to improve our understanding on the redox cycling of important species involved in these interactions, and the biogeochemical evolution and related quality of porewater and groundwater. Her research deals with environmental issues that are related to global climate change (including the production and consumption rates of the greenhouse gas methane and the effect of seawater intrusion into coastal aquifers). She combines field-work, laboratory experiments, chemical measurements, and reactive-transport models.

The coordinator for the Colloquium Series is Dr. Soumya Ray. You can contact her at soumray [at] umd [dot] edu.