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
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
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
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
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. Zhendong Zhang, MIT
April 26, 2023 at 12:00 pm (Virtual)
The coordinator for the Colloquium Series is Dr. Soumya Ray. You can contact her at soumray [at] umd [dot] edu.