Planetary Science Seminar - spring-2025
Modelling the Lunar Thermal Emission Phase Function
Feb. 11, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Elisha Jhoti - UC Los Angeles
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The lunar thermal emission phase function (EPF) describes how the Moon emits in the thermal regime depending on the position of the Sun, observer, and topographic slope. The thermal emission is not isotropic, meaning it is not the same from all angles, largely attributed to small-scale surface roughness. This effect is more pronounced at high latitudes (near the poles) where illumination conditions are more extreme, due to the Moon’s low obliquity. It is vital to include this behavior when modelling surface temperatures as it can change predicted temperatures by tens of Kelvin. High resolution thermal models use these surface temperatures to predict potential locations for water ice and other volatiles. The lunar poles are of special interest as water ice may be present in large quantities in permanently shadowed regions. To accurately predict the location and distribution of this water ice, an EPF model must be incorporated into any high-resolution thermal model. In this talk I will present our EPF model that is based on generating roughness via meter-centimeter scale bowl-shaped craters and demonstrate that it fits lunar thermal data for multiple illumination conditions.
Uranus’ magnetosphere was observed in an anomalous state by Voyager 2
April 4, 2025
noon - 1 p.m.
Slichter 3853
Presented By:
- Dr. Jamie M. Jasinski - Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
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The Voyager 2 flyby of Uranus in 1986 revealed an unusually oblique and off-centered magnetic field. This single in situ measurement has been the basis of our interpretation of Uranus' magnetosphere as the canonical extreme magnetosphere of the solar system; with inexplicably intense electron radiation belts and a severely plasma-depleted magnetosphere. However, the role of external forcing by the solar wind has rarely been considered in explaining these observations. In this talk, we will revisit the Voyager 2 dataset to see that Voyager 2 observed Uranus’ magnetosphere in an anomalous, compressed state that is estimated to be present less than 5% of the time. If the spacecraft had arrived only a few days earlier, the upstream solar wind dynamic pressure would have been ~20 times lower, resulting in a dramatically different magnetospheric configuration. Such a compression of the magnetosphere could increase energetic electron fluxes within the radiation belts and empty the magnetosphere of its plasma temporarily. Therefore, the interpretation of Uranus’ magnetosphere as being extreme may simply be a product from a flyby which occurred under extreme upstream solar wind conditions. I will also present ongoing modelling efforts that try to understand the role of magnetic reconnection at Uranus’ magnetosphere including the reconnection voltages at the magnetopause during Voyager 2’s approach to the planet. Finally, we will conclude by looking towards what an orbital tour of the magnetosphere could look like by a potential Uranian flagship mission in the future.
An Integrated Investigation of Biogenic Halomethane and Methylated Gases as Exoplanet Biosignature Candidates
April 11, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Michaela Leung - UC Riverside
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Methylated gases such as methyl chloride and dimethylsulfide have been previously established as biosignature candidates for Earth-like, anoxic, and sub-Neptune exoplanets. These gases belong to larger groups of compounds potentially applicable as biosignature candidates, including methylated halides, methylated metals, and halomethane gases. I will present additional methylated gas and halomethane candidates as target biosignatures for a range of planetary and stellar conditions, incorporating laboratory and field measurements of gas fluxes to fully integrate atmospheric modeling with known biological limitations. Analysis of detection prospects has revealed that these additional targets are promising for current and future instrumentation.
A Fluid Dynamical Playground — the Fruits of an Interdisciplinary Approach to Jovian Atmospheric Modeling
April 18, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Dr. Ali Hyder - Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
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Jupiter's oxygen content is inextricably tied to its formation history and the evolution of the early solar system. Observations of trace disequilibrium chemical species that are hosted in the deeper atmosphere, such as CO, are thought to be the result of vertical diffusive mixing and are tied to the planet’s water abundance. Recent one-dimensional thermochemical modeling of CO showed that the planet's bulk water content could be subsolar, in stark contrast to the water enrichment determined near the equator using the Juno spacecraft. In this talk, I will showcase results from our hydrodynamic model that pertain to Jupiter's atmospheric dynamics at and below the water cloud level with disequilibrium thermochemistry. Our coupled approach allows us to explore the effect of hydrodynamics on disequilibrium chemical abundance in the troposphere. We include PH3 and GeH4 as tracers and demonstrate their lack of sensitivity to the water content in low enrichment cases. Our results suggest an oxygen enrichment range of 2.5-5x solar using updated CO thermochemistry. We also reveal a correlation between moist convection and the CO abundance at the water cloud level using the conventionally adopted CO timescale. If such a correlation is found observationally, subsolar water abundance can be ruled out, which will further constrain the planetary formation processes that were dominant during the infancy of our Solar System.
Interannual Variability of Seasonal Frost Coverage and Potential Atmospheric Drivers from the Northern Hemisphere of Mars
April 25, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Jacob Widmer - UCLA
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The exchange of seasonal volatiles (CO2 and H2O) between the atmosphere and surface affects the interannual variability of atmospheric and surface processes on Mars. By quantifying the variability of surface activity, we can work backward and begin to identify specific processes driving variability in the present-day Martian climate system. In the northern hemisphere, previous studies have mapped seasonal frosts during the winter and spring months. However, a critical gap exists in the literature for multi-year records of seasonal frost extent when composition can be distinguished. In this work, we fill this literature gap, quantify the interannual variability of seasonal frost extent for CO2 and H2O, respectively, and compare our results with atmospheric measurements of dust, water vapor, and temperature via the polar vortex to investigate potential connections between surface changes and atmospheric processes. We identify the edge of seasonal CO2 and H2O frost extents with binary ice mask products, derived from CRISM mapping-style observations taken during Mars Year 28-33 (MY 28-33, based on nomenclature proposed by Clancy et al. 1999). We find that the extent of H2O seasonal frost can change by ~3.9° of latitude between years, but the extent of CO2 seasonal frost is much more consistent, changing by ~1.5° of latitude. Correlations between these results and atmospheric measurements of dust, water vapor, and the polar vortex suggest that 1) variability in CO2 seasonal frost extent is controlled by the polar vortex, 2) variability in H2O seasonal frost extent is controlled by the availability of water vapor, and 3) atmospheric dust heavily influences seasonal variability as it affects both, the polar vortex and water availability, and by extension, the deposition and removal of seasonal ice.
Thermal interactions between dune sands and underlying ice in the Northern Polar Region of Mars
April 25, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Imani Lawrence - UCLA
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Within Mars’ Northern Polar Region there are dune fields that interact with underlying ice as they migrate, influencing the planet’s surface evolution. In this work, we investigate whether dune sands in this region conduct enough heat to sublimate the underlying ice. Using the KRC thermal model, we simulate one-dimensional, two layer temperature profiles for different sand-ice combinations under current Martian conditions. The upper layer represents dune sands, basalt sand and gypsum sand, while the lower layer the polar ices, CO2 ice and H2O ice. Our results show that while CO2 ice at the sand-ice interface reaches temperatures above its sublimation threshold, H2O ice remains stable. These findings suggest that seasonal CO2 frost coverage in the Northern Polar Region plays a crucial role in thermal dynamics, limiting heat conduction to the subsurface, therefore preventing H2O ice sublimation under present-day conditions. Additionally, we examine how doubling atmospheric pressure affects heat conduction and ice stability, providing insight into potential past climate conditions. Future work will explore higher obliquity to determine whether variations in Mars’ axial tilt could have further influenced H2O ice sublimation.
A Superconducting MKID High Resolution Multi-Object Spectrograph Testbed for the Detection and Characterization of Exoplanets
May 2, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Dr. Ronald Lopez - University of California, Santa Barbara
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Conventional high-resolution echelle spectrographs are typically designed to take detailed spectra of a very limited field of view, such as a slit or fiber. Alternatively, multi-object spectrographs are designed to acquire spectra of multiple targets simultaneously at the expense of spectral resolution, wavelength coverage, and/or instrument cost. The inherent energy resolution of superconducting microwave kinetic inductance detectors (MKIDs) can be used to eliminate the need for a cross-dispersing element in an echelle spectrograph, dramatically simplifying the optical design and freeing up valuable detector space that can be allocated to the spectra of multiple objects. This testbed lays the foundation for a new class of high-resolution multi-object spectrographs (HRMOS) that do not need to compromise resolution or coverage. A future, fiber-fed MKID HRMOS for HWO or the extremely large class of telescopes will be able to sample a comprehensive region around a star with an R~100,000 to simultaneously detect and characterize exoplanet atmospheres using high-dispersion coronagraphy (HDC). With this technique, star/planet contrast can be increased by a factor of 1000, which is a large step towards reaching the contrast goals of 10-10 for characterizing earth like planets around sunlike stars.
Dating Dune Fields on Earth and Other Planets
May 9, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Alana Archbold - UCLA
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Aeolian dunes are found on all continents and six planetary bodies, making them invaluable tools for understanding sediment-atmosphere relationships. When there is a continuous flux of sediment and wind is at or above threshold velocity for grain movement, dune migration is viable. By measuring the dune spacing formed by migration combined with the migration rate, grain size, grain density, and percentage of time that wind is at or above threshold velocity, we estimate the age of the dune field using a computational model called the Real-Space Cellular Automaton Model (ReSCAL).
Formation, Migration, and Evolution of Mars-Analog Meter-Scale Aeolian Bedforms near Fossil Falls, CA
May 9, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Sarah Preston - UCLA
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Aeolian (wind-blown) bedforms, such as dunes and ripples, are found on Earth, Mars, Venus, Titan, Pluto, and 67P/Churyumov-Gerasimenko. Meter-scale aeolian bedforms are common on Mars, but rare on Earth; the meter-scale large ripples that form from basaltic sands in active Martian dunes have few terrestrial analogues. Here, I will present on a field of basaltic Mars-analog meter-scale bedforms, including analyses of the grain size, shape, and mineralogy; ripple planform and cross-sectional morphology; and agreement between my observations and previously described meter-scale bedforms on Earth and Mars.
CSI: Solar System — Answering the Questions “Whodunnit, Where, When, and How?” Using Orbitraps, Extraterrestrial Materials, Laboratory Clues, and Chemical Physics
May 16, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Dr. Amy Hofmann - Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
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Isotope geochemists are fundamentally forensic scientists. We pull trace evidence from natural materials and process that evidence through Machines That Go Ding. We situate the results within the context of other clues from the same samples, their environments, observations, computational models, and laboratory experiments, and then interpret the whole within the framework of the chemical physics that underlie isotope effects. Over the past 20 years, significant advances have been made in both our understanding of and our ability to interrogate the intramolecular isotopic compositions of simple organic and inorganic molecules. This burgeoning field aims to constrain 1) isotopic compositional differences between different chemically inequivalent sites within a molecule (i.e., “position specific isotope effects”) and 2) the natural distributions of multiply substituted isotopologues in a given compound (i.e., “clumped isotope effects”). When measured at high accuracy and precision, intramolecular isotopic signatures such as these can be used to identify, among other things, progenitor species, mechanisms of irreversible reactions, and temperatures of equilibration—information complementary to, but inaccessible by, compound-specific isotope measurements alone. In this seminar, I will present a case study in cosmochemical isotope forensics aimed at addressing one of the Big Questions in planetary science: “Where and how are organics synthesized in the Solar System?” Our investigation focuses on the intramolecular isotopic compositions of soluble polycyclic aromatic hydrocarbons extracted from the Murchison meteorite. I will demonstrate how analyses of extraterrestrial materials via ultrahigh resolution Orbitrap-based mass spectrometry, and the contextualization of those results within astrochemical observations and theoretical chemistry, enable us to deduce the provenances of and processes experienced by organic compounds across environments from the interstellar medium to the Murchison parent body.
Sulfur Chemistry in Small Bodies: Insights from Laboratory Simulations and Comet 67P
May 23, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Dr. Ahmed Mahjoub - Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
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Studying sulfur chemistry is crucial for understanding molecular clouds and presolar nebulae, as sulfur-bearing molecules trace key physical and chemical processes. Much of sulfur is missing from the gas phase in molecular clouds, likely locked in refractory materials or complex organosulfur compounds. Its chemistry is shaped by grain-surface reactions, influencing planetary system evolution. Complex organosulfur species have been detected in comet 67P, asteroid samples, and meteorites, highlighting their importance in presolar chemistry. To investigate their formation, our team at JPL conducts laboratory experiments by irradiating ice mixtures, simulating solar system conditions. This research aims to investigate the chemistry leading to complex organosulfur species in small bodies. By linking these findings to space observations, we aim to enhance our understanding of sulfur’s role in astrochemical evolution of the solar system. In this talk, I will present our latest laboratory simulations and how they, combined with ROSINA instrument data from the Rosetta mission, deepen our understanding of complex sulfur chemistry in comet 67P, offering new insights into chemistry in the presolar nebula. This work has been conducted at the JPL, Caltech, under a contract with the National Aeronautics and Space Administration (NASA)
From Islamic Afghanistan to the City of Angels and the universe around us
May 30, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Ibrahim Amiri and Meghan Li - UCLA
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The penultimate lecture of this spring’s Planetary Science seminar series is being given by two of our graduate students and address their contributions to education and public outreach. Remarkably, their stories span the globe in providing insights into how their lives and dedication to sharing with the public the wonders of planetary science and astronomy. Their presentation, From Islamic Afghanistan to the City of Angels and the Universe Around Us, chronicles their individual odysseys into education and public outreach, ranging from Afghanistan making astronomy accessible to young students to Los Angeles and the leadership role and growth seen in UCLA’s annual program Explore Your Universe. Taken together, their biographies tell a remarkable story, and their presentation scheduled for Friday, May 30 at noon in 3853 Slichter Hall is open to the public. Their biographies follow.
Drops of Jupiter: How stable helium rain layers differentiate Jupiter and Saturn
June 6, 2025
noon - 1 p.m.
3853 Slichter Hall
Presented By:
- Dr. Stephen Markham - New Mexico State University
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Saturn and Jupiter are nearly the same size and composition, but their magnetic fields behave very differently. Jupiter exhibits a tilted, highly complex, multipolar field; meanwhile Saturn's field is perfectly aligned with its spin axis, and completely axisymmetric. In this work we rationalize these differences by considering the thermodynamics of the helium rain layers of both planets. Using computational characterization of the hydrogen-helium phase diagram and equation of state, we find that moist convection and diffusive convection are inhibited, implying a stable helium rain layer in both Jupiter and Saturn. We estimate the helium rain latent heat flux on both planets, finding that while on Saturn the latent heat flux is sufficient to accommodate nearly its entire heat flow, on Jupiter it is not. Therefore, we predict a thin (~tens of km) stable layer on Jupiter, while Saturn's helium rain layer can be thick (a large fraction of its total radius). Finally, we use Juno spacecraft data to present evidence of a systematic attenuation of the non-azimuthally symmetric components of Jupiter's magnetic field relative to both the Earth and a theoretical fully stochastic model. Such behavior is consistent with a thin (~70km) stable layer in Jupiter's deep interior. By contrast, Saturn's magnetic field is completely axisymmetric, consistent with a thick stable layer. We therefore suggest the differences between the two planets' magnetic fields may be attributed to the way their different masses and luminosities interact with the thermodynamics of the hydrogen-helium system.