planet20.txt

Becky Alexander (PI) Yuk Chun Chan (FI) 
Institution:  University Of Washington, Seattle  
PLANET20-0028, Modeling the multi-phase production of perchlorate in planetary atmospheres 
 
Over ten years after Phoenix lander’s detection of perchlorate (ClO4-) on Mars, still relatively little is known about its natural origins on rocky planets. On Earth, perchlorate is produced by the industry as rocket fuel, but a high level of perchlorate, which sometimes occurs naturally in deserts, can poison humans. For life on Mars, be it indigenous or originated from Earth, the presence of perchlorate poses both threats and opportunities. It has long been suspected that the production of natural perchlorate couples with the chlorine cycle in planetary atmospheres, but the gas-phase reactions alone are unable to explain the observed abundance. The uncertain origin and distribution of the oxychlorine family (ClmOnk-) has become an impasse in the research on present-day liquid water and organic matter at the surface of Mars. In light of the recent breakthroughs in understanding the roles of reactive halogens and multi-phase reactions in atmospheric chemistry on Earth, we propose to re-examine the enigma of atmospheric production of perchlorate via a modeling approach.  
  
 Our project consists of three major tasks. In Task 1, we will build parametrizations of multiphase chemistry of perchlorate based on the latest kinetic studies of perchlorate chemistry. The new perchlorate chemistry module can be integrated into any state-of-the-art photochemical models for simulating perchlorate dynamics. In Task 2, we will implement the perchlorate chemistry module into the GEOS-Chem 3-D global chemical transport model (GC) in order to validate the parametrization using the Earth’s observations. The GC-simulated deposition flux of perchlorate will be compared with the perchlorate concentration measured in the precipitation samples. We will use isotopic measurements of oxygen and chlorine, ice-core records of perchlorate, and the estimated abundance of minerals in arid regions as additional observational constraints for the model. Re-interpretation of these proxies will also have implications for the chlorine cycle in the current and paleo atmosphere of Earth. In Task 3, we will add the validated perchlorate chemistry module into the Atmos 1-D photochemical model to simulate perchlorate’s production and deposition on Mars. By using updated Atmos, we will run a large number of simulations for Mars under different scenarios of climate change and volcanic activities. Analysis of these model outputs under a Bayesian framework and comparison with observations of Martian perchlorate will give us an improved estimate of the evolution of volcanism and climate. To prepare for the sample-return from Mars and the follow-up sample characterization, the validated version of Atmos can also make predictions about the properties of perchlorate along the proposed route for the NASA Mars 2020 rover mission. 
  
 Combined with information extracted from isotopic measurements, mineralogical observations, and ice-core records, the simulations produced by our updated models will greatly enhance our understanding of the historical evolution of atmospheric chemistry on Mars under the vigorous changes in climate and volcanism, as compared to Earth. Our model estimates can support the projects in the NASA Mars exploration program, specifically those regarding the ongoing search of liquid water and organic matter at the surface, as well as the upcoming sample-return missions. The modeling tools built in this project can also assist atmospheric chemists and planetary scientists to tackle the other challenging questions regarding the relationship between perchlorate, volcanism, climate, and biology during different eras on Mars. Our modeling project provides a solid roadmap to advancing the knowledge of the formation of the perchlorate in the solar system, the underlying chemical processes in planetary atmospheres, and the influence of Martian perchlorate on human exploration; these outcomes are all in line with the goals of the NASA Planetary Science Division. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Ariel Anbar (PI) Dan Sullivan (FI) 
Institution:  Arizona State University  
PLANET20-0226, Bridging the O2 Gap: Using Rhenium Isotopes to Detect Low O2 in Ancient Oceans 
 
Geochemical data from ancient marine sedimentary rocks indicate that many major steps in the evolution of life are tied to changes in the oxygenation of the oceans and atmosphere (e.g., Lyons et al., 2014). There are geochemical indicators of ocean-basin-scale oxygenated and anoxic (0 uM O2) conditions, but currently there is not a global geochemical tool to detect when large parts of the oceans are in an intermediate-leaning-toward-anoxic condition termed suboxic(d10 uM O2). Detecting suboxic conditions is particularly important because some aerobic organisms can live in extremely low-O2 waters (down to ~10 nM O2; Stolper et al. 2010), and so it is of import to know when large parts of the ocean first crossed from anoxic to suboxic. Rhenium (Re) isotopes (´187Re) measured in marine sedimentary rocks are a novel global paleoredox tool that has the potential to be the first proxy that can detect suboxic conditions. 
  
 The ability of Re isotopes to track suboxic conditions comes from the unique geochemical behavior of this element. Under oxic conditions, Re exists primarily as perrhenate (ReVIIO4-), an ion that is highly unreactive and therefore accumulates in seawater (e.g., Koide et al., 1986; Colodner et al., 1993). In low-O2 conditions, ReVII is reduced to ReIV, leading to efficient removal coupled to organic carbon burial (Colodner et al., 1993,1995; Kendall et al., 2010; Morford et al., 2012). Rhenium has two stable isotopes, 187Re and 185Re. Preliminary data indicate that the light isotope is preferentially reduced (Miller et al., 2015), causing a shift in the isotopic composition of residual Re remaining in seawater to heavier values. As a result, ´187Re variations in ancient sediments that sample the isotope composition of seawater could provide a sensitive tool to track the global extent of suboxic seafloor through time. 
  
 In this proposal I outline the development of the Re isotope proxy to track changes in the extent of suboxic conditions in the ocean. This proxy can be applied to any time in Earth history during which major changes in oceanic oxygenation occurred. –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Jessica Barnes (PI) Zoë Wilbur (FI) 
Institution:  University Of Arizona  
PLANET20-0036, Investigating Degassing Histories of Apollo 15 and 17 Lunar Basalts with 3D Visualization and Coordinated Microanalysis 
 
The abundance, distribution, and sources of volatiles on the Moon were questioned after NASA missions discovered water ice on the lunar surface. Amidst the developing field of lunar volatiles, there are debates regarding the timing of volatile accretion to the Moon and the sources of these volatiles. Therefore, investigations of the Moons bulk volatile concentration, loss, and mobilization are of critical importance to understanding the origin of lunar magmatic volatiles. Volatile elements and halogens, such as H, H2O, CO2, S, Cl, F, change the mechanical properties of minerals and melts, thereby affecting magma eruption processes. In order to understand the indigenous volatile inventory of the Moon, we must identify magmatic and secondary processes that may have affected the volatile contents now present in lunar samples.  Here I propose to investigate the magmatic, volcanic, alteration, and terrestrial histories of a suite of Apollo 15 and Apollo 17 mare basalts, which includes samples from The Terrace, Central Valley, Camelot Crater, and Steno Crater locations on the Moon.  These samples span a range of basalt types. The Apollo 15 Terrace samples are low-Ti, olivine normative and vesicular, while the Apollo 17 Camelot Crater and Central Valley samples are high-Ti (70215 is Type B, 70035 is Type U, and 75035 and 75055 are Type A). The Steno Crater samples are high-Ti, Type B basalts and may contain 20-40 vol.% void spaces (vesicles or vugs). These void spaces often contain late-stage crystallizing minerals protruding into them. The work proposed here targets these void spaces present in lunar mare basalts, as they directly record the conduit conditions during eruption. I propose to scan and visualize these basalts in 3D using micro X-ray computed tomography (XCT), as it is vital to the understanding of fabrics in these samples and will allow for the determination of void dimensions and abundances. By investigating void space morphology, it is possible to understand the eruption history of a group of chemically diverse basalts collected at different geologic locations on the Moon. Additionally, a 3D petrographic view of the Apollo basalts will give the opportunity to locate minerals (olivine/pyroxene) protruding into the vesicles and vugs. These late-stage crystallizing minerals in vesicles are ideal candidates for the analysis of their surfaces to better understand the volatile species which once occupied the voids during eruption. Once these minerals are located, they will be analyzed with Raman spectroscopy, secondary electron microscopy (SEM), focused-ion beam (FIB), and transmission electron microscopy (TEM) to understand volatile loss and mobilization in a suite of mare basalts.  
 The work proposed here will ultimately allow for a comparison of the evolution of Type A, B, and U lunar volcanism and may provide important clues on the differentiation history of the Moon. Moreover, my results may offer a novel point of comparison for the newly opened Apollo Next Generation Sample Analysis (ANGSA) Apollo 17 core (73002), potentially offering an analog to the mm-sized basalt clasts observed in XCT scans of the regolith core. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– David Baum (PI) Lena Vincent (FI) 
Institution:  University Of Wisconsin, Madison  
PLANET20-0194, Searching for dynamic biosignatures among lifelike systems isolated by chemical ecosystem selection 
 
A core question in origins of life research is how simple organic molecules became selforganized into systems that could both self-propagate and evolve. Answering this question is critically important both for mapping out the conditions needed for life to emerge, and for identifying essential features of life that could serve as biosignatures of living systems on other worlds. One possibility is that the first evolvers were self-sustaining (autocatalytic) chemical systems localized on mineral surfaces and composed of molecules that could catalyze each other’s formation. My strategy to evaluate this model is to use chemical ecosystem selection (CES), an analog of experimental evolution in which chemical systems are repeatedly selected for their ability to colonize new mineral surfaces. The approach involves incubating mixtures of chemical inputs, or ‘food’, with mineral grains and performing serial transfers to select for spontaneously-formed, surface-associated systems that are better at being transmitted from grain to grain. A key advantage of CES is that lifelike systems are detected based not on the appearance of particular chemical species, but on systematic changes over transfers in emergent chemical proxy traits.  
  
 I recently reported the results of CES experiments conducted on a simulated prebiotic soup incubated with pyrite which yielded evidence of complex dynamics that are consistent with the emergence of lifelike chemistry, including a distinctive oscillatory pattern suggestive of sequential fluctuations in cycles of a dynamically maintained chemical system. In addition to further characterizing the chemical basis of this putative lifelike system, I propose deploying CES on others conditions to assess whether the current candidate constitutes a rarity or reflects a broader phenomenon. To this end, I will deploy long-term CES experiments on simpler inputs modeled after recent computational analyses of protometabolic and radiolytic cycles and use chromatography-MS techniques to establish whether systemic changes seen over serial transfers might indicate self-propagation and pre-genetic evolution. Finally, I will use the CES framework to search for evidence of lifelike chemistry in the products of chemical synthesis experiments carried out under Titan haze conditions. Comparing the system-level patterns observed in these experiments will allow me to distinguish between complex dynamics that constitute true biosignatures from those that are ‘false positives’ in that they can be produced by non-living processes. Overall, the proposed experiments are expected to provide multiple examples of chemical systems that display dynamic patterns resembling life and advance our understanding of how readily evolvable chemical systems emerge and where they might arise in the universe. Therefore, the proposed research aligns well with NASA’s Planetary Science Objective 1.5 to ‘improve our understanding of the origin and evolution of life on Earth to guide our search for life elsewhere.’ 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Christopher Bennett (PI) Katerina Slavicinska (FI) 
Institution:  University Of Central Florida  
PLANET20-0097, The Influence of Carbon-Bearing Species during the Space Weathering of Asteroids and Meteorites: Implications for Remote Observations and the Production of Complex Molecules 
 
Characterization of the mineralogical and organic inventories of airless icy and/or rocky bodies like interstellar ices, meteorites, asteroids, moons, and planets without atmospheres is essential to understanding the formation of our solar system and the evolution to its present-day state and provides information that is vital to target selection in both flyby and sample return missions. Due to the dramatic effects of space weathering on the composition, morphology, exospheres, and, subsequently, optical properties of these airless bodies, studying the mechanisms and effects of space weathering is crucial to this characterization. Since the large-scale return of lunar regolith samples via the Apollo missions, spectral effects of both real and laboratory-simulated space weathering on lunar soil has been thoroughly investigated, providing invaluable insights into the Moon’s surface composition and its evolution. By comparing spectra of highlands and mare regolith samples and simulating space weathering of regolith analogs like olivine, submicroscopic metallic iron (SMFe) was established as the primary cause of the spectral effects observed on space-weathered lunar samples: the reddening of the spectral slope, the lowering of albedo, and the diminishing of absorption features’ intensities. Although this explains many of the observations of space weathered surfaces quite well (e.g., the Moon), observational spectra of asteroids and radiation experiments performed on carbonaceous chondrites indicate that their trends observed upon exposure to space weathering are far more complicated. Here, we propose that the organic inventory of these bodies is the culprit, since carbon is often present at approximately the 1% level. Space weathering of organics can lead to the formation of more graphene-like material, which has very low albedo and has visible and near-IR spectra that can counteract those observed from minerals. Therefore, we will investigate the effects of organic contributions in a systematic manner in this proposal by adding various organics to high-fidelity simulants, expose them to space weathering agents under vacuum conditions, and observe the visible, near-IR and mid-IR spectra utilizing bidirectional diffuse reflection spectroscopy (similar to NASA's RELAB facility). The mid-IR region is particularly interesting since it permits observation of molecular vibrations, which should allow us to actually pinpoint the space weathering level that organics are exposed to. The proposed work will not only help provide a baseline for the visible and near-IR observations, but the mid-IR work will also lead to testable results that should be observable when telescopes such as James Webb become operational. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Devon Burr (PI) Anthony Maue (FI) 
Institution:  Northern Arizona University  
PLANET20-0208, Seeking sediment signals in SAR: Enhancing interpretations of Cassini radar for Titan 
 
Synthetic aperture radar (SAR) is a powerful tool for understanding the fine-scale properties of a planetary surface despite relatively coarse spatial resolution. Numerical simulations of radar scattering indicate that coarse rounded sediment can explain the high radar backscatter of some fluvial features on Saturn’s moon Titan. However, theory-based models lack realistic sedimentological variations in size and shape distributions, among other factors. The proposed work would develop correlations of SAR return to various grain parameters measured in the field in and around Death Valley National Park. Analyses of field data previously collected by the FI, in addition to data from a proposed supplemental trip in fall 2020, will investigate empirical relationships across a variety of alluvial deposits (Task 1). Testing how variation in the properties of real alluvial sediment affects backscatter for SAR images of Earth will enable extrapolation to better understand conditions on other planetary bodies-specifically Titan. In year 1, the key objectives will be to expand the field dataset, analyze correlations to radar, and publish a peer-reviewed manuscript on the results and methods of quantifying sediment properties from SAR for arid, sediment-rich targets. 
  
 After completing mapping of Titan’s radar-bright fluvial features while awaiting any revisions in year 1, the key objective in year 2 will consist of applying the empirical SAR model to understand downstream variations in these features in a global context. The findings of Task 1, in addition to constraints on the mechanical properties of icy sediment from the FI and PI’s previous lab work, will allow for enhanced interpretations of sedimentary deposits on Titan (Task 2). Specific focus will be on the variety of radar-bright fluvial features interpreted as dry, gravel-bedded braided rivers. Radar brightness trends along the length of 60 such features will be measured by the FI and linked to possible sedimentological changes due to downstream rounding and fining from abrasion and selective transport, input from nearby sediment sources, and global variation in composition and flow conditions due to the local geology and environment. This work will have significance for understanding the transport history of fluvial sediment on Titan, with implications for its many sedimentary features, including vast equatorial dune fields for which rivers may provide sand. The occurrence of ostensibly familiar processes under conditions different from the Earth’s enable interplanetary comparison. Results and implications for Titan’s sedimentary processes will be published in a second peer-reviewed manuscript. 
  
 The proposed work is relevant to the Planetary Science Division’s goals to ‘explore and observe the objects in the Solar System to understand how they formed and evolve,’ and to ‘advance the understanding of how the chemical and physical processes in the Solar System operate, interact and evolve,’ by placing limits on physical processes of sedimentation, examining possible interaction between fluvial and aeolian activity, and studying the global variation among sedimentary features, with implications for the evolution of Titan’s surface. Furthermore, the proposed work specifically supports the Planetary Research Program’s calls for ‘investigations which enhance the scientific return of NASA Planetary Science Division missions through the analysis of data collected by those missions,’ and for ‘analog studies, laboratory experiments, or fieldwork to increase our understanding of Solar System bodies or processes and/or to prepare for future missions,’ by developing an improved model based on field data to interpret the sedimentological properties of Titans radar-bright alluvial deposits, also supported by the PI and FI’s previous lab studies. The properties of sediment on Titan, and its sources and sinks, will provide valuable context for the upcoming New Frontiers mission Dragonfly. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Nancy Chanover (PI) David DeColibus (FI) 
Institution:  New Mexico State University  
PLANET20-0098, What Processes Control Surface Composition in the Inner Uranian System? 
 
The five major moons of Uranus are relatively under-studied, with only one spacecraft flyby over 30 years ago (Voyager 2, 1986).  With telescopic observations the only alternative, one of the most effective methods of studying the surface compositions of the moons is near-infrared spectroscopy. This has taught us that the primary composition of the moons is water ice, with three of them showing definitive evidence of CO2 ice deposits on their trailing hemispheres. Infrared spectroscopic coverage of a wide range of longitudes of the four largest moons has identified trends in surface composition across the satellites, primarily in the longitudinal (leading hemisphere vs. trailing hemisphere) and planetocentric (distance from Uranus) sense. 
These trends include the strength of water ice absorption features, the abundance of CO2 ice, and the presence of hemisphere-dependent reddening. The near-infrared signatures of water ice absorption are strongest on the leading hemispheres of the moons, strongest closest to the planet, and with greater leading-trailing asymmetry closer to the planet. The smallest and innermost moon, Miranda, has a much more limited near-infrared dataset. However, the longitudinal asymmetry in water ice seems to be much weaker, and possibly even indicating more water ice on the trailing hemisphere. This is contrary to the expected surface modification processes operating in the Uranian system. 
  
 We propose to undertake a near-infrared spectroscopic observing campaign with a 4m-class telescope to obtain much more complete longitudinal coverage of Miranda, with the aim of investigating the factors and processes controlling the distribution of water ice on Miranda's surface. Assessment of water ice absorption band areas will measure the abundance and the temperature of Miranda's water ice, and provide comparisons to existing literature and the other Uranian moons.  Spectral modeling via linear mixture modeling and Hapke modeling can constrain the existence of additional compounds, such as the potential presence of low levels of CO2 ice or ammonia (NH3) hydrates, and investigate the surface properties of the moon's regolith. 
  
  In the 2014 NASA Science Mission Directorate Plan, section 4.3, our proposed research is relevant to the Planetary Science Division, the Planetary Research Program, and two of their stated goals: ``Explore and observe the objects in the solar system to understand how they formed and evolve'' and ``Advance the understanding of how the chemical and physical processes in our solar system operate, interact and evolve''. Miranda was the moon most closely investigated by the Voyager 2 flyby, but because of the 98 degree axial tilt of the Uranian system, the southern hemisphere that was in sunlight in 1986 is now in shadow. A future mission to the Uranian system, even if funded now, likely would not arrive for another twenty years, in northern summer. This data can thus serve as a bridge between Voyager and a future mission, building on the Voyager legacy, investigating potential seasonal change in the Uranian system, and understanding the surface processes controlling surface composition on outer planet satellites. The Uranian moons have properties that lie on a spectrum of icy bodies between the warmer, well-investigated Jovian and Saturnian systems and the cold, distant trans-Neptunian objects- thus it is vital to understand the processes operating on small icy bodies, especially given the current interest in Enceladus and Europa and the growing desire in the planetary science community for another mission to the ice giants. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Christopher Edwards (PI) Ari Koeppel (FI) 
Institution:  Northern Arizona University  
PLANET20-0138, Identifying the Thermophysical Signatures of Weathering in Mars Analog Deposits 
 
The goal of this project is to characterize the variability in thermophysical properties of Mars analog deposits on Earth as a tool for interpreting infill deposits on Mars. In doing so, this study will: 1) generate a new toolset for investigating alteration and reworking in mafic sedimentary deposits on Mars and Earth, 2) improve our understanding of a unique class of geologic features, thereby providing a valuable complement to in situ NASA rover mission data from Gusev, Gale and Jezero craters, and 3) further our knowledge of past surface conditions on Mars including the potential role of liquid water. These objectives closely align with NASA's goals to: 1) "advance the understanding of how the chemical and physical processes in the Solar System operate, interact and evolve’, 2) “explore and find locations where life could have existed..." and 3) assess how ‘layered sedimentary rocks record the present-day and past climate and the volcanic and orbital history.’ The proposed work will accomplish these goals through three distinct tasks to be completed by the FI with guidance from the PI and Collaborator:  
 Task 1 - Data collection of Mars-orbital-instrument-relevant and in situ morphological, mineralogical, textural, and thermophysical data for multiple friable mafic deposit styles on Earth. 
 Task 2 - Data analysis through generation of a numerical model for thermal inertia from thermal emission data, along with a statistical assessment of the relationships between Mars-orbitalinstrument-relevant observations and other weathering signatures. 
 Task 3 - Application of model to produce weathering process-likelihood maps of representative crater infill deposits in Mars’ Southern Highlands. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Larry Esposito (PI) Daniel Sega (FI) 
Institution:  University Of Colorado, Boulder  
PLANET20-0099, Advanced Bending Wave Model for Saturn’s Rings Based on Cassini Occultations 
 
Objectives 
1.	Develop a bending wave model that recreates the observed variations in optical depth in the Mimas 5:3 bending wave region for Cassini UVIS, RSS and VIMS by including new mechanism of angular momentum transport (viscosity) and self-gravity wakes (clumps of particles). 
2.	Develop a new dispersion relation for the bending wave by relaxing the linear approximations made by Shu et al., or the assumption of uniform surface mass density. 
3.	Use Cassini star occultations to test out and motivate a new advance bending wave theory via shear box numerical simulations that may be applied to other bending waves in the rings, like the Tian 0:-1. 
  
 Methodology 
  
        We will model the self-gravity wakes as rotating solid bars in order to calculate the tidal acceleration at the end of the bars. This will yield an expression for the transfer of angular momentum from the wave to the self-gravity wakes. In addition to this, well use numerical methods, specifically a shearing box method, to generate self-gravity wakes, and add to this the kinematic equations of a particle in a bending wave seen. The motion of the particles in the clumps within a bending wave must emerge from these simulations. 
        For the case of the new dispersion relation, Dr. Glen Stewart has been working on relaxing assumptions made to derive the relation in question. Particularly the assumption that the slope is small breaks down for the Mimas 5:3 Bending wave. We will attempt to find an analytical solution that keeps a second order term in the expansion of the self-gravity force that yields the dispersion relation. This second order dispersion relation can be tested numerically with the shear box models mentioned above and then compared to Cassini data. If this fails, then the inconsistency may be arising with the assumption of a constant surface mass density.  In this 
 
case, we will use a dispersion relation that allows for surface mass density variation and get this variation from the numerical shear-box models.  
  
 Relevance to NASA 
  
      This proposed research directly addresses NASAs strategic goals for planetary science: ‘ascertain the content, origin, and evolution of the solar system and the potential for life elsewhere.’ We study Saturn’s system and the formation of gaps within disks may have an important role within the planet formation process. We also align with the strategic objective 1.1 -Discovering the secrets of the universe- by using ‘space-based observing and sampling capabilities; creating the context and capabilities to interpret the resulting data; and maximizing the return on investment in the acquisition of data.’ In our case we’ll enhance the return of the Cassini mission. 
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Glenn Flierl (PI) Santiago J. Benavides (FI) 
Institution:  Massachusetts Institute of Technology  
PLANET20-0021, Effects of rotation and magnetic fields in the weakly conducting regions of gas giant planets. 
 
Historically, numerical studies on the dynamics of gas giant atmospheres have focused either on the molecular (electrically neutral) outer layer or the metallic (electrically conducting) interior. The former are interested in explaining the characteristics of the relatively shallow flows, such as jets and vortices, seen on the surfaces of Jupiter, Saturn, and Hot Jupiters. The latter group is interested in the dynamo process -- the generation of the planet's magnetic field as well as what explains their different morphologies. Despite the separation of these groups in practice, the properties of gas giants' atmospheres vary continuously and these two regions interact with each other. An interest in the understanding of the coupling between the neutral and conducting regions has been explicitly expressed by both communities, but few studies have attempted to address or model its effects, and indeed fewer have studied in detail the turbulent dynamics of what we're calling the transition region. As an attempt to fill this literal and metaphorical gap, I propose to study the turbulent dynamics of a plasma with low conductivity in the presence of both a uniform background magnetic field and rotation using a series of idealized numerical simulations. These are the physical conditions found in, and unique to, the transition region. My work has the following three aims. Aim 1: Characterize the turbulent behavior of the flow as we vary the strengths and relative angle between the rotation and uniform background magnetic field. I will be looking to see how the cascade of energy to larger or smaller scales depends on these parameters, as they could affect the presence of jets and vortices, among other things.  Aim 2: Determine if or when the presence of a uniform background magnetic field interacting with a weakly conducting fluid can be considered to have the effect of a friction-like term on the momentum equation. This is a common technique to model interactions with the conducting interior by those who study the neutral outer layer. However, the rigor of this approach has been called into question. Aim 3: Find, if possible, a simplifying model or closure for this type of turbulent system which could then be applied to a larger-scale problem, such as the global simulations mentioned above. The successful achievement of the three above aims would provide a significant improvement on the understanding of how neutral and conducting regions interact in gas giant planets found in our Solar System and in other star systems. My proposed study touches upon many points of interest in the latest NASA missions to Jupiter and Saturn. Both Juno and Cassini missions were tasked with measuring the geometry of the magnetic field and, in fact, the latest theories for Saturn's surprisingly axisymmetrical magnetic field rely on phenomena occurring in the transition region. Furthermore, one of Juno’s main objectives was to estimate the depth of Jupiter's jets using gravity measurements, and at the heart of these results is the question of the jets' interaction with the transition region and the ionized, conductive interior. Our study is also relevant for hot Jupiter exoplanets, whose upper atmospheres are thought to be partially ionized and might fall in similar parameter regimes in terms of conductivity and rotation. Indeed, low conductivity as a source of drag is a key component in studies of these atmospheres. My project addresses topics of interest which NASA has outlined under the Planetary and Astrophysics Research Programs. I have explicitly outlined in the proposal our aim to ‘advance the understanding of how the chemical and physical processes in the Solar System operate, interact and evolve,’ and how we will also extend this knowledge to ‘study planets around other stars’. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Christopher Hamilton (PI) Joana Voigt (FI) 
Institution:  University Of Arizona  
PLANET20-0041, Deciphering Effusive Eruption Styles throughout Elysium Planitia, Mars: Linking Lava Emplacement Dynamics with Magmatic Storage Conditions 
 
The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has recently identified marsquakes along the Cerberus Fossaea series of volcano-tectonic fissures that sourced the youngest volcanic eruption products on Mars. However, the region also includes widely distributed small lava shields. These Late Amazonian volcanic features represent two important components of the volcanic and thermal history of Mars, suggesting that a transition occurred from an earlier lava shield-building phase to the emplacement of younger and much higher volume flood lava flows. The presence of these two distinct volcanic products in the same region implies a fundamental change in eruption style. I propose to investigate lava flow features in Elysium Planitia to infer emplacement dynamics and related magma storage depths. I will use this information to test the hypothesis that the effusion rate for individual eruptions have increased during the Late Amazonian Epoch due to the eruption of less frequent, but larger volume lava flows from deeper fissure-focused magmatic sources.  
  
 To conduct this hypothesis test, I will complete the following three tasks: 
  
 Task 1-Determining flow areas, emplacement dynamics, and ages. I will analyze the spatial distribution, stratigraphic position, and crater surface retention ages. Using Mars Reconnaissance Orbiter (MRO) Context (CTX; 6 m/pixel) camera, MRO High Resolution Imaging Science 
Experiment (HiRISE; 0.3 m/pixel) images, and Mars Express High Resolution Stereo Camera (HRSC; 12.5 m/pixel) data, I will digitalize lava margins, determine flow areas, characterize their surface texture, and constrain ages using crater size-frequency distributions (CSFD). Flow margins will be mapped using ESRI ArcGIS. CSFDs will be analyzed using CraterTools and Craterstats 2.0 software. 
   
 Task 2-Determining flow thickness, volumes, and effusion rate. I will determine the thickness of the flow units by generating digital terrain models (DTMs) of flow margins using HiRISE stereopairs. Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) data to examine flow thicknesses where HiRISE stereo-pairs are not available. Additionally, I will constrain lava thicknesses by analyzing subsurface reflectors identified using MRO SHAllow RADar (SHARAD) data, and combine thickness information with mapped flow areas (from Task 1) to calculate flow volumes. This is a critical parameter that I will use in combination with established models to estimate flow velocity, instantaneous effusion rates, and time-averaged discharge rates for channelized and inflated flows, respectively. 
   
 Task 3-Demining magmatic source depths. I will use my volume and flux estimates to constrain established conduit flow models and infer the magmatic storage depths. Smaller volume lavas can originate from shallow crustal reservoirs, erupted at relatively low mass flux rates from a neutral buoyancy depth. In contrast, large volume lavas can be erupted from a deeper reservoir, penetrating directly from the asthenosphere to the surface to feed higher effusion rate eruptions. For this Task, I will use established analytical models to constrain if there was a change in time from a crustal magma storage to a deeper reservoir transported from the asthenosphere. 
   
 These tasks will provide new insight into eruption styles and magma source depths in Elysium Planitia during the Late Amazonian. This study is timely and compelling because it quantifies the volcanic and related magmatic activity in the same region as the active InSight mission, and will have significant benefits for interpreting InSight’s new geophysical measurements. Further, constraining input parameters for thermal evolution of Mars addresses the first two science goals in NASA’s Planetary Science Division Research Program. Changing the thermal regime in the shallow crust affects the habitability of Mars and thus addresses the third and fourth science goals. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Walter Harris (PI) Alessondra Springmann (FI) 
Institution:  University Of Arizona  
PLANET20-0063, Inner Coma Grain Environments of Jupiter Family Comets 
 
Large grains in the inner coma region of comets provide information about the near-surface environment of these small Solar System objects, including grain composition and connections to volatile species in the inner and outer coma. Understanding grain ejection from comets’ surfaces and whether this corresponds to the presence of volatile species such as CN or carbon gives a broader view of the interaction of species at the surface and in the near-surface environment of comets. 
 
 Between 2016 and 2018, three ~1 km Jupiter-family comets (JFCs) passed within 60 lunar distances of Earth, affording excellent opportunities to study these small bodies at high spatial and temporal resolutions, the closest look we can get of comet comae until 2038 without a dedicated space mission. The close approach of these objects enables study of the dust particle sizes in multiple wavelengths from ground-based telescopes as part of a coordinated observing campaign. Visible wavelength observations yield size information of micron-scale particles in the coma, while radar observations can constrain the distribution of particles larger than 2 cm in diameter in the inner coma region. 
 
 In this proposal we focus on the close approach of three comets--41P Tuttle-Giacobini-Kresak (TGK), 45P/Honda-Mrkos-Pajdusakova (HMP) and 46P/Wirtanen (Wirtanen)--observed between February 2017 and December 2018 with the planetary radar system at Arecibo Observatory. A polarized, 12.6-cm wavelength continuous radio wave was transmitted at the comets and returned echoes observed. Analysis of the radar echoes showed detectable depolarization of the returned signal, consistent with scattering off of 2 cm and larger particles in the coma of HMP. (The returned signal from TGK showed no such depolarization, implying a lack of large grains in the coma.) 
 
 By modelling large grains ejected from the surfaces of the three JFCs to fit the observed radar data, I will constrain the size-frequency distribution of large grains in the coma, particle ejection directions, particle velocities, residence time, and mass loss rates of material from the nucleus of the comet. Further, I can investigate whether jets of large grains follow the emission of gas species in the inner coma region to gain an additional perspective on how nucleus heterogeneity, local heating, and temporal patterns of solar illumination affect both coma grain production and surface composition. 
 Connecting results from continuous wave radar observations with visible imaging of volatile species and smaller dust particles, as well as radar-derived shape models of nuclei allows for a more holistic understanding of processes contributing to mass ejection from the surface of these comets and the origin of these grains. Understanding the near-surface inner coma environment of comets is important for future sample return missions, understanding the composition of comet nuclei in the context of their location of origin in the protoplanetary disk, and studying these comets as near-Earth objects as future mission targets. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Mark Harrison (PI) Andrew F. Parisi (FI) 
Institution:  University of California, Los Angeles  
PLANET20-0215, A Test of the Late Heavy Bombardment Hypothesis: Concordancy in Multiple Isotopic Systems 
 
Apollo-era explorations radically altered our views of lunar origin and the evolution of the early solar system. Based on disturbances to U-Pb and Rb-Sr isotopes in highland samples, Tera et al. (1974, EPSL 22, 1) concluded that these rocks had experienced a short-lived impact pulse leading to near complete thermal resetting of the lunar surface; a ‘terminal cataclysm’ (later termed the Late Heavy Bombardment; LHB). This interpretation presented something of a conundrum as Pb-U fractionation was ascribed to Pb volatilization, but the undisturbed Rb-Sr whole rocks imply that Rb was not similarly affected. Tera et al. (1974) acknowledged that the lack of a mechanism to explain this differential behavior ‘remains a basic problem’. 
Subsequently, many researchers argued that 40Ar/39Ar age spectra also support a thermal pulse at ca. 3.9 Ga. If this hypothesis is correct, it has tremendous implications for lunar history but also for Earth habitability and surface cratering chronologies on other worlds. Returned lunar rocks typically sample regolith that has been reworked by billions of years of impacts. The traditional 40Ar/39Ar step heating method uses small amounts of crushed sample that nonetheless still contain domains of varying provenance, as it is typically not possible to isolate regions of only a single rock-forming age. Recently, in situ analysis on lunar samples using an ion microprobe or laserprobe to sputter or ablate, tiny amounts of sample directly from the surface of a polished section, have been undertaken. These studies achieved unprecedented precision in documenting age trends within individual samples. For example, Mercer et al. (2015) determined that Apollo 17 sample 73217 contained 3 distinct lithologic domains, and determined texturally correlated age peaks at 3.81±0.01, 3.66±0.02, 3.63±0.027 and 3.273±0.02 Ga. This illustrates the complexity in determining the age of a unique event from a breccia formed from multiple provenances. Which, if any, of those ages can be directly related to the LHB, or any impact event? Indeed, to our knowledge, no claim of concordancy among multiple dating systems on lunar melt rocks has yet been substantiated. 
  
 As a first step towards testing the LHB hypothesis, we propose to determine U-Pb formation ages of accessory minerals in the same temporally defined regions of samples 73217 and 77115 of Mercer et al. (2015). These samples are in our possession and in situ elemental mapping indicates the presence of numerous phosphate minerals and zircons which can be U-Pb dated; this includes both small, neoformed grains which appear to have grown from the impact melt, and fractured relict clasts. U-Pb formation ages of zircons and phosphate minerals will be measured in those previously defined regions using both our CAMECA ims1290 and ims1270 ion microprobes. If the accessory mineral U-Pb ages match those previously determined by 40Ar/39Ar, this would provide confidence that they date the impact event that formed that particular melt domain. However, age discrepancies between the two dating techniques would call into question the extent to which any specific measurement relates to a specific impact. Following this initial study, the research will be expanded to other well characterized samples. Prof. Kip Hodges and colleagues have nine additional lunar highland melt samples on which they are undertaking in situ 40Ar/39Ar analyses that they will provide us. These eleven samples should provide a clear picture of whether concordancy exists between different isotopic systems in a texturally-clear petrogenetic setting. If so, this approach can then be extended to a wider variety of lunar melt rocks, potentially permitting formation ages of breccias to be determined and refinements to be made to the LHB hypothesis. If not, then this would seriously challenge the foundation of the LHB hypothesis. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Roland Hatzenpichler (PI) George Schaible (FI) 
Institution:  Montana State University, Bozeman  
PLANET20-0007, Cellular differentiation within multicellular magnetotactic bacteria: 
implications to the evolution of complex life on Earth and other worlds 
 
On the path to complexity, all organisms must step through a gateway in order to evolve from a single cell to a multicellular organism. What constraints exist around this gateway are not yet known, thus making the evolution of multicellularity a pertinent question for the origin and evolution of life in the universe. The emergence of multicellular organisms radically changed the course of evolution on Earth and understanding the modes through which multicellularity evolves will guide future investigations for complex life in the universe. This proposal seeks to investigate the underpinnings of multicellularity through studying the only known example of an obligate multicellular microbe, i.e. a microorganism without a single cell stage, Multicellular Magnetotactic Bacteria (MMB). These recently discovered microbes defy the traditional concept of bacteria as single celled organisms. MMB are composed of 15-60 cells symmetrically organized around an acellular compartment and can orient themselves for movement using magnetosomes that detect Earth’s geomagnetic field. While examples of bacteria that are capable of multicellular stages exist, these examples persist as a unicellular organism at some point in their life cycle. MMB are the only known exception to this and have never been observed as individual cells, existing solely as multicellular consortia. Moreover, microbial life is prevalent in nearly all environments on Earth. If life is found in our universe, it is likely to be in the form of microbes. It is therefore relevant to study multicellular bacteria found on Earth as model organisms to inform any possible findings of extraterrestrial multicellular life. By employing comparative genomics, correlative stable isotope probing - Raman spectroscopy - electron microscopy - and confocal laser scanning microscopy, in addition to bioorthogonal labeling and super resolution microscopy, this project aims to investigate the existence of specialized cells within MMB do determine if a division of labor and clonality exists in these consortia. If MMB are shown to indeed harbor differentiated cells that engage in a division of labor, they would arguably be the most complex multicellular bacteria currently known. This might fundamentally transform how we interpret the nature of complex life in the universe. The culture-independent techniques proposed in this project will provide a foundation upon which future studies of complex extraterrestrial multicellular microbes - if they are found - could be studied. Any extraterrestrial microbes are expected to be recalcitrant to cultivation efforts and techniques described in this proposal can provide a set of methods through which uncultured microbes can be studied. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Brian Hynek (PI) Bernerd Richard Archer (FI) 
Institution:  University Of Colorado, Boulder  
PLANET20-0212, Investigating the influence of salinity on aqueous chemistry, alteration mineralogy, and microbiology at Mars analog hydrothermal systems 
 
The Planetary Decadal Survey (2011) recognized the importance of Mars’ hydrothermal environments: ‘In all epochs, the combination of volcanism and water-rich conditions might have sustained hydrothermal systems in which life could have thrived.’  While pervasive evidence exists for extended hydrothermal systems at Mars, chlorine enhancement, and interaction of magmas with chlorine-rich brines, no research to date has detailed Mars analog hydrothermal systems and the effects of Cl-enrichment of the fluids and its impact on biota, which is the primary objective of this proposed work. 
  
 Our study will investigate two nearby high temperature (~573K) hydrothermal field sites in Iceland: (1) Gunnuhver, being coastal, with seawater source water and (2) Krysuvik, an inland hydrothermal vent of similar temperature range and same basement tholeiitic basalt (11.15% Fe2O3T) but with meteoric source water. We will survey aqueous chemistries, microbial communities and associated mineralogies from both Gunnuhver (1 main geyser and approximately 12 fumaroles) and Krysuvik (approximately 12 springs and 10s of fumaroles). We will sample over a range of temperatures and pH, as well as characterize co-located mineralogies and microbial communities. Collectively, the results from this study will establish microbial relationships to both aqueous chemistry and mineralogies of two Icelandic Mars analogue hydrothermal systems, Gunnuhver and Krysuvik, informing future Mars sample return biosignature analysis. 
  
 This proposed research is directly relevant to multiple NASA SMD Goals and Programs.  SMD objective referenced in Chapter 4.3 of the SMD 2014 Science Plan ‘explore and find locations where life could have evolved or could exist today’ is satisfied by this study. A second SMD objective which is satisfied is likewise clarified in Chapter 4.3 of the SMD 2014 Science Plan, specifically, ‘Improve our understanding of the origin of life on Earth to guide our search for life elsewhere.’  This proposed effort is relevant to the following SMD programs:  NASA Habitable Worlds (mineralogy/aqueous chemistry studies of Mars analog environments) and Exobiology (microbiological surveys of martian analog environments). 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Brandon Johnson (PI) Camille Denton (FI) 
Institution:  Purdue University  
PLANET20-0029, Sputnik Planitia as a probe for Pluto’s interior structure and global tectonic evolution 
 
Though we cannot directly characterize the interior structure of Pluto, its interior can be probed remotely by observing its response to impact-induced deformation. Sputnik Planitia is a 1200 x 2000 km putative impact basin whose large size, location, and relationship to extensional tectonic features has led researchers to suggest that it preserves a positive mass anomaly (mascon), produced from uplift of a subsurface ocean during basin formation and loading. However, the thickness of the ocean as well as the thermal state of the overlying ice shell remain unknown. The long-term goal of our work is to directly inform the development of improved thermomechanical models for Pluto’s interior. Our overall objective is to determine the sensitivity of surface and subsurface deformation surrounding Sputnik Planitia to the presence and thickness of an ocean as well as ice shell thermal structure. 
  
 We propose to investigate mascon formation associated with Sputnik Planitia using a sequential, self-consistent modeling approach: we utilize the iSALE shock physics code to model the initial basin-forming impact for Sputnik Planitia (Task 1); the resulting geometry and thermal/density structure of the post-collapse basin are then applied as the initial conditions for the commercial finite element code Abaqus to simulate cooling and modification of the basin over time (Task 2); the basin is then subjected to N2 loading to assess the final stress state of the basin and quantify the regional tectonic response in comparison to global extension and true polar wander stresses (Task 3). The initial conditions introduced to our models span the predicted range of initial thermal and mechanical conditions for Plutos subsurface. 
  
 This work reflects the goals of the NASA Planetary Science Division: it contributes to understanding the origin, evolution, and geologic properties of massive impact basins, which dominate the geologic signature of planetary bodies across the Solar System, while continuing the legacy of data returned from the New Horizons mission. Further, our assessment of Plutos putative subsurface ocean provides implications for the longevity of environments conducive to the formation and evolution of life on ocean worlds. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Julia Kennefick (PI) Paul Bonney (FI) 
Institution:  University of Arkansas, Fayetteville  
PLANET20-0216, Constraining the Habitability of High Priority TESS Candidates With 1D and 3D Global Climate Models 
 
The search for habitable Earth-like planets has been greatly advanced by the Transiting 
Exoplanet Survey Satellite (TESS). The most recent TESS Object of Interest (TOI) to make headlines, TOI 700 d (Gilbert et al., 2020; Rodriguez et al. 2020), is a prime example of a terrestrial planet orbiting well within its star’s habitable zone (HZ). With the impending launch of the James Webb Space Telescope (JWST) and other upcoming and proposed observatories (e.g.  E-ELT, LUVOIR, HabEx), it is increasingly important to strategically search for signs of habitability within available data. Doing so enables differentiation and prioritization of the myriad confirmed and candidate exoplanets for future observation. 
  
 In most of the recent cases of observations targeting exoplanets, 3D General Circulation Models (GCMs) are used to infer planet composition and structure or to predict observations of scientific interest. This could be used as a powerful tool for prioritizing the observation of potentially habitable exoplanets. However, previous modeling has focused on parameter spaces that are not statistically linked to the observational data (e.g. Del Genio et al. 2019a, Turbet et al. 2016) because of the computationally-intensive nature of 3D models. Accurate statistical modeling is vital to the confirmation of other habitable worlds. 
  
 To address the problem, we will create a method to statistically investigate the habitability of exoplanets with a suite of 1D and 3D models using the GCM ROCKE-3D (Way et al. 2017) informed by analysis of TESS observations. Furthermore, we will apply this method to three TESS-observed planets and candidates which were highly prioritized by our previous work, TOIs 256, 203, and 700. This will constitute an end-to-end investigation of real TESS exoplanets to constrain the possibility of liquid water being present and assess the ability of next generation telescopes to confirm its presence. 
  
 This method will be a more efficient, data-based method for assessing the habitability of exoplanets. In addition, the work will provide estimates for the habitability of three TESSobserved planets and candidates. This will generate robust limits for future planned observations of the atmospheres of these exoplanets for upcoming and future NASA missions like JWST, helping to answer the question: is there life beyond Earth? 
  
 The work is primarily relevant to the Planetary Science Research and Analysis Program in the 
Planetary Science Division. Though the observational analysis of this work is relevant to the Astrophysics Division, the bulk of this research focuses on the modeling and data analysis necessary to characterize exoplanet systems’ habitability. This is especially responsive to the Planetary Science Division’s stated science goal to find locations where life could have existed or could exist today. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Edwin Kite (PI) Alexandra Warren (FI) 
Institution:  University Of Chicago  
PLANET20-0109, Small exit breach craters as probes of Martian climate since 3.5 Ga 
 
The availability of liquid water at the Martian surface is strongly affected by Martian climate. On present day Mars, where atmospheric pressure is 6 mbar, water boils at 273 K and freezes below this temperature (Murphy and Koop, 2005). It is well accepted that the climate of Early Mars (>3.5 Ga) was very different, enabling the formation of abundant fluvial features and lakes (e.g. Mangold et al., 2008; Fassett and Head, 2005) and hydrous minerals that require temperatures above freezing (e.g. Bishop et al., 2018). A thicker CO2 atmosphere ‘ since lost ‘ with additional greenhouse gasses (e.g. Ramirez, 2017; Wordsworth et al., 2017) is proposed to explain this warming. However, there is increasing evidence that conditions enabling the stability of surface liquid water extended later into Mars history (e.g. Kite et al., 2019; Wilson et al., 2016; Dickson et al., 2009), potentially extending Mars’ habitability into the Amazonian (e.g. Kite et al., 2017). The geomorphic role of later surface water can be used to constrain how much water was present, where it came from, and how long it remained at the surface.  
  
 Wet events on Mars since the main Late Noachian and Early Hesperian valley network (VN) forming fluvial activity are recorded by young alluvial fans (Kite et al., 2019; Grant and Wilson, 2011), Fresh Shallow Valleys (FSVs) (Wilson et al., 2016; Mangold, 2012) and small exit breach craters or ‘pollywogs’ (Wilson et al., 2016). Pollywogs cannot be dated using crater statistics due to their small size, but their preserved crater rims indicates that they post-date periods of intense fluvial activity during the Late Noachian and Early Hesperian (Wilson et al., 2016). Pollywogs are craters with one or more valleys leading outwards from the crater rim, but no inlet valleys (Wilson et al., 2016). These outlet channels are thought to form during overflow of water from within the crater. The process(es) that form pollywogs were not localized to one part of the Marssurface, but were able to occur in multiple locations. We will obtain a lower limit on the volume of water and number of outflow events required to produce observed pollyog outflow depths using a new breach erosion model that couples lake draining and sediment transport. 
  
 We will compare the results of our breach erosion model in with measurements from 7 new pollywog DEMS to constrain the minimum number of crater overspill events. Modelling channel breach erosion processes and the freezing/evaporation of water on the past Martian surface addresses the Solar System Workings group interest in the evolution and modification of surfaces, particularly how the Martian hydrosphere and cryosphere interacted with Mars’ surface during the drier parts of its history (Section 1 of C.3 Solar System Workings 2019). This is also relevant to MEPAG Goal II, Investigation C2.2. 
 
 We will carry out time-dependent, energy balance modelling of evaporation and freezing processes at the Martian surface under different atmospheric pressure and annual average temperature conditions. This will constrain minimum water delivery rates from two possible sources: groundwater and precipitation/snowmelt. We will use Darcy’s law to find constraints on aquifer properties that permit the rapid filling of a crater with water. We will adapt our evaporation/freezing model to address the stability of a body of crater-filling ice to constrain the annual average delivery rate of water by precipitation consistent with crater overspill. 
Characterizing potential water sources for filling pollywog craters will constrain Mars’ climate, hydrology, and the geomorphic role of water after the VN forming period in the Late 
Noachian/Early Hesperian, which addresses Goal II, Investigation C2.1 of the Mars Exploration 
Program Analysis Group (MEPAG) Mars Science Goals, Objectives, Investigations, and 
Priorities: 2020 Draft: ‘Find and interpret surface records of past climates and factors that affect climate.’ 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Nikole Lewis (PI) Ishram Mishra (FI) 
Institution:  Cornell University  
PLANET20-0103, Providing New Constraints on Europa's Surface Composition 
 
We wish to advance our understanding of Europas surface composition by 1) developing an open-source analysis package called FROSTIE, based in Bayesian inference methods, that will enable us to statistically quantify and constrain a candidate species on the surface of Europa 2) Use currently available optical constants of astrobiologically important oxidants CO2 and SO2 to constrain their abundances by applying FROSTIE to the new, hitherto un-analyzed, Juno/JIRAM data of Europa  3) Perform lab work to measure and publish optical constants of other major non-ice components, out to 5 microns, starting with sulfuric acid octahydrate or SAO and incorporate them into ongoing analysis with FROSTIE.  
 
 The advantage of using a Bayesian inference framework is that 1) it allows for an optimized exploration of a huge parameter space, look for non-unique solutions and obtain un-certainties on the derived best-fit/maximum-a-posteriori parameters 2) it is robust to low-SNR data when it comes to constraining the parameters 3) Bayesian model comparison provides a mechanism to quantify the detection significance of the different components in our system (the planetary surface with amorphous water ice,  crystalline water ice,  etc.)  and overcomes the pitfalls of traditional tools like reduced chi-squared when working with non-linear models.  
 
 Our Bayesian inference framework will be wrapped around a comprehensive and physically motivated version of Hapke’s bi-directional refelctance model. The code will be modular , so that different parameters of the Hapke radiative transfer equation can easily be enabled/disabled or added later. We are adding and testing more sophisticated elements of Hapke’s model than what previous studies have used, like regolith porosity, coated grains and/or ones with internal scatterers, multilayered model and thermal emission. All the code we will write and the optical constants we measure will be published on public databases.  
 
 This proposal is responsive to the following FINESST program goals, as stated in the ROSES Section E.6, Subsection 2.3: 1) ‘Explore and find locations where life could have existed or could exist today’ (we plan to study Europa, a prime astrobiological target) 2) ‘Investigations which enhance the scientific return of NASA Planetary Science Division missions through the analysis of data collected by those missions’ (we plan to analyze Juno, Galileo and other archival NASA mission data) 3) ‘Analog studies, laboratory experiments, or fieldwork to increase our understanding of Solar System bodies or processes and/or to prepare for future missions.’ (we plan to evaluate new optical constants).  
 
 The ‘capability of detecting organics’ on the surface of Europa has been recognized as a key step in determining the extent of its habitability and guiding the future search for life on its surface (NASA Visions and Voyages (2011)). To achieve this goal, NASA’s 2018 Strategic Plan emphasizes the needed to ‘develop tools for determining the relative habitability of present or ancient environments. FROSTIE is such a tool. Our proposed research is a foundational step to remotely constraining organics on Europa as it will provide the context in which their trace signals might be present. Once the optical constants of relevant organics are available, an advanced tool like FROSTIE will be needed to quantify their presence in low SNR archival data. In combination with an instrument simulator, FROSTIE can also help inform the requirements or help quantify the organics detection capability of spectrometers on upcoming NASA missions like Europa Clipper and JWST, proving crucial to their success. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Ralph Milliken (PI) Melissa Meyer (FI) Institution:  Brown University  
PLANET20-0073, Remote Geologic Interpretation at Rover, Airborne, and Orbital Scales: Improving our Ability to Recognize Potential Biosignatures on Mars 
 
Searching for evidence of past life and habitable conditions is a central goal of current and upcoming rover missions to Mars. Sulfates and clays have been detected in sedimentary on Mars in a wide range of settings by both orbiters and rovers, some of which may indicate ancient habitable environments. But how confident are we that we would be able to recognize environmentally diagnostic geologic features or preserved biosignatures in these Martian rocks, should we encounter them using only robotic exploration?  
  
 To answer this question, we will examine ancient sulfate- and clay-rich strata on Earth as mineralogically and texturally relevant Martian analogs. The proposed field site, near Carlsbad, New Mexico, exposes the Seven Rivers Formation evaporites of the Guadalupe Mountains. These evaporite sequences present an interesting terrestrial analog for many Martian sedimentary processes and compositions. As such, the site hosted the Curiosity rover slow motion field test in 2007. This field site preserves a variety of biosignatures (i.e, fossils, stromatolites, molecular organic compounds) as evidence of past life. Our work will examine how diagnostic rock textures, compositions, and these biosignatures may or may not be properly identified by remote sensing instruments at the rover (micrometer to meter), airborne (decimeter to meter), and orbital (meter to kilometer) scales.  
  
 Examination will be completed in four tasks:  
       Task 1. We will prioritize a comprehensive geologic evaluation that would typically be conducted by a traditional terrestrial field geologist. This includes methodically describing the rock types observed in the field, selecting representative samples, and noting how they vary across layered sequences. Task 1 seeks to answer the question: What are the characteristics key geological characteristics and biosignatures are important for a rover to identify in this field site?        Task 2. A laboratory characterization will be completed on selected samples in order to identify preserved (molecular and morphologic) biosignatures and rock features associated with their occurrence. We will include measurements using optical and infrared microscopy, x-ray diffraction mineral analysis, visible and near-infrared reflectance spectroscopy, and Mars 2020 rover Planetary Instrument for X-Ray Lithochemistry elemental abundance mapping. Task 2 seeks to answer the question: What is the nature of preserved biosignatures and to what extent can they be identified by rover-analog instrumentation? 
      Task 3. We will evaluate the spatial scales and types of remote measurements that are needed to properly recognize biosignatures and key geologic features in outcrops along a rover traverse. Employed instrumentation will include digital cameras, a handheld XRF instrument, a VIS-NIR ASD FieldSpec3 point spectrometer, and a Headwall Photonics hyperspectral VIS-NIR imaging spectrometer. Task 3 seeks to answer the question: To what degree are biosignatures and the rock textures associated with their occurrence observed by rover-analog remote sensing instrumentation?\ 
      Task 4.  Rover-traverse observations will be integrated with larger-scale observations made from readily available AVIRIS (airborne) and ASTER (satellite) hyperspectral imaging data. Task 4 seeks to answer the question: To what degree do airborne and satellite remote sensing datasets capture the geologic variability observed across the field site? 
  
 The proposed work is directly relevant to the Science Mission Directorate’s strategic planetary science goal to explore for and find locations where life. The proposed work will provide a strategic framework for current and future rover exploration in the ancient Martian sedimentary environments of both Gale and Jezero crater and lead to a better understanding of how to properly integrate rover and orbital datasets to interpret Martian geologic processes. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– David Mitchell (PI) Kathleen Hanley (FI) 
Institution:  University of California, Berkeley  
PLANET20-0191, The Beginning of Ion Escape at Mars: Supply and Initial Acceleration of Ions Above the Exobase 
 
How did Mars lose its once Earth-like atmosphere? Ion escape from high altitudes contributes significantly to atmospheric loss at Mars, but the initial acceleration of ions from the top of the atmosphere to high altitudes has not yet been investigated. The efficiency of upwards ion acceleration, along with the supply of ions available to the exobase region (~200 km altitude), limits the ion escape rate at Mars, but the relative importance of these factors is unknown. Does the exobase act to throttle ion escape, controlling the amount of upgoing ions which can be easily accelerated away from the planet? Or, conversely, are acceleration processes inefficient at removing ions from low altitudes?  
  
 The proposed study is a statistical analysis of data collected at altitudes between 120 km and 
1000 km by the SupraThermal And Thermal Ion Composition (STATIC) instrument on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft at Mars. STATIC measures particle fluxes as a function of energy, angle and mass, from which we can derive densities, temperatures, and bulk velocities for the major planetary ions. Using STATIC data publicly available on the Planetary Data System, it is possible to infer which processes heat and accelerate ions above the exobase. Changes in the measured ion velocity distribution functions with respect to altitude can be searched for and interpreted to find evidence of specific acceleration and heating mechanisms, such as interactions with waves or an ambipolar potential. Once those mechanisms are understood, the number of escaping ions can be compared to the supply of ions at the exobase to determine whether the escape rate is source- or process-limited. This analysis would be the first comprehensive investigation into the plasma heating and acceleration processes occurring in and above Mars’ ionosphere. 
  
 Understanding the processes occurring at Mars and the history of its climate were identified as high-priority science goals in the 2013-2022 Planetary Science Decadal Survey. An understanding of the factors controlling ion escape, which this study aims to provide, is critical in order to achieve those goals. The proposed study of ion escape processes occurring today at Mars would improve extrapolations back in time, allowing for more accurate characterization of the planet’s early atmosphere. In Section 4.3 of the 2014 Science Plan, the Planetary Science Division expressed the goals to ‘understand how [the objects in the solar system] formed and evolve’ as well as to ‘advance the understanding of how the chemical and physical processes in our solar system operate, interact and evolve.’ The accomplishment of those objectives is impossible without comprehensive study of ion escape processes at Mars. –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– John Mustard (PI) Christopher Kremer (FI) 
Institution:  Brown University  
PLANET20-0023, Cross-Over Infrared Spectroscopy: A New Tool for Remote Assessment of Olivine Composition 
 
The central objective of my proposed work is to develop a promising new remote sensing technique that will provide unique insights into the composition of olivine on other planets. The mineral olivine exists on numerous Solar System bodies, but its chemical composition on those bodies remains elusive. Olivine comprises a solid solution series between forsterite (Mg2SiO4) and fayalite (Fe2SiO4), and the relative amount of Mg and Fe in olivine (referred to as Mg#) reflects the degree of magmatic differentiation of igneous rocks. Remotely determining Mg# of olivine would therefore directly inform our understanding of the thermal and chemical evolution of other planetary bodies.  
  
 The technique that I plan to develop is ‘cross-over’ infrared spectroscopy, which utilizes spectra in a generally unexplored region of the infrared (4-8 micrometers) that lies between the more thoroughly explored visible-near infrared (VNIR, 0.5-3 micrometers) and mid-infrared (MIR, 815 micrometers). My preliminary study of a suite of >50 olivine samples indicates that the positions of two spectral ‘bands’ at approximately 5.6 and 6.0 micrometers shift systematically with the relative amount of magnesium vs. iron in a sample (Mg#), meaning that the Mg# of olivine may be determined using these bands’ wavelength-positions alone. 
  
 In order to apply this technique to the Moon, I must study how environmental and geological conditions on the Moon might affect ‘cross-over’ spectra. The specific objectives for the proposed work are: 1) assess the accuracy of olivine Mg# derived from the position of the 5.6 and 6.0 micrometer spectral bands in the ‘cross-over’ region; 2) determine detection limits (i.e. minimum detectable modal abundance) of olivine in ‘cross-over’ region spectra of olivineanorthite mixtures; and 3) evaluate the degree to which space weathering affects the shape and position of the 5.6 and 6.0 micrometer bands of olivine in the ‘cross-over’ region. 
  
 I will accomplish these objectives by measuring infrared spectra of olivine and olivine-bearing samples in the laboratory. This sample suite will include olivine-bearing Apollo lunar samples, a well-known terrestrial olivine standard, particulate mixtures of anorthite and olivine, and olivine and olivine-anorthite mixtures subjected to laboratory-simulated space weathering. I will then perform band analysis on the effect of the variations in these parameters on the position, shape, and intensity of the 5.6 and 6.0 micrometer bands.  
  
 Assessing the potential for ‘cross-over’ region spectroscopy in a lunar context would directly inform the design of spacecraft spectrometers for the remote sensing of the Moon. A successful study would also open up measurement opportunities elsewhere in the Solar System. Developing and validating a new technique for the remote determination of olivine Mg-Fe composition would facilitate fundamental insights into planetary evolution and so is directly relevant to NASA’s goal to understand the chemical evolution of the solar system’s planets. Specifically, this proposed work uses laboratory measurements to ‘increase our understanding of Solar System bodies or processes and to prepare for future missions’ and so is directly relevant to the Planetary Science Research Program. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Derek Richardson (PI) Julian C. Marohnic (FI) 
Institution:  University of Maryland, College Park  
PLANET20-0211, Simulating tidal and spin-up disruption of rubble piles with irregular particles 
 
We are proposing to use our group's N-body code, pkdgrav, to investigate the effects of particle shape on disruption and shape change induced in rubble-pile asteroids by spin-up and tidal encounters. In other words, when subjected to tidal forces or spin-up, do rubble piles made up of irregularly shaped particles behave differently than those composed of spherical particles? More specifically, we aim to answer the following five questions. How does particle shape affect the shear strength of rubble piles? When a tidal or spin-up disruption does occur, does the manner in which the disruption proceeds depend on particle shape in any quantifiable way? Does particle shape affect how readily disruptions produce binaries? Do the equilibrium states of disrupted rubble piles have a different size or shape distribution depending on the shape of the particles that compose them? To what degree, if any, do the answers to the above questions depend on interparticle cohesion? We will use a variety of quantitative metrics, which we describe in our proposal, to study these questions. 
  
     pkdgrav is an numerical gravity solver that allows for soft-sphere contacts between particles, meaning that grains in contact can interpenetrate slightly as a proxy for deformation of the particle surfaces. Twisting, rolling, and static friction models are also included. Recently, pkdgrav was updated to include the ability to quickly simulate large numbers of irregular particles by treating arbitrary assemblies of spherical particles as rigid aggregates. This capability will allow us to study the effects of irregular particle shape on spin-up and tidal disruption of rubble piles at high resolutions for relatively low computational cost. In addition, the Department of Astronomy at the University of Maryland has ample computational resources available to complete this task. Specifics are included in the complete proposal. 
  
     We believe that this work has great significance to NASA interests in particular and to the field of small solar system bodies in general. Shape change and disruption of rubble-pile bodies caused by spin-up and tidal encounters are common in our solar system and their effects play a major role in shaping the surfaces of terrestrial worlds. The creation of binary asteroids and crater chains are both tied to the disruption of rubble-pile bodies, and the relative efficiencies of spin-up and tidal disruption are important to understanding these events. Recently, spacecraft have returned images of the asteroids Bennu and Ryugu, both of which have distinctive "spinning-top" shapes, which are thought to be caused by YORP-induced spin-up. These processes are also important for understanding the evolution of the surfaces of small bodies via granular convection and surface mobility. While these phenomena have been studied in the past, prior work has either been limited to using only spherical particles or to low-resolution simulations. We now have the capability to investigate tidal and spin-up disruption without these restrictions and to bring increased realism to simulations of these processes. Specifically, this research proposal is relevant to the Solar System Workings program and to the broader SMD goals because it involves investigations of the interior structure and surface of small solar system bodies using numerical modeling. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Tomce Runcevski (PI) Christina McConville (FI) 
Institution:  Southern Methodist University, Inc  
PLANET20-0227, Experimental Models of Minerals on Titan, Saturn's Moon 
 
Many potential Titanean minerals are well-known organic compounds; therefore, it could be expected their properties to be thoroughly studied. Surprisingly, the knowledge on the solid-state chemistry of the smallest organic molecules is very scarce. For example, the crystal structure of propionitrile (which is proven to form aerosols and surface minerals on Titan) remains unknown. An obvious culprit is the pervasive challenge of growing high-quality single crystals at cryogenic conditions, as many compounds tend to crystallize as polycrystalline powder. The most appropriate methods for analysis of polycrystalline powders are powder X-ray diffraction and powder neutron diffraction. In this proposal, we will use various powder diffraction methods coupled with thermal analyses and neutron spectroscopy to recreate the structure and composition of model minerals on Titan. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Hilke Schlichting (PI) Akash Gupta (FI) 
Institution:  University of California, Los Angeles  
PLANET20-0037, Investigating Planet Evolution under the Core-Powered Mass-Loss Mechanism at Longer Orbital Periods and Determining its Observable Signatures 
 
NASA's Kepler mission has revolutionized the field of planetary science by discovering more than 4000 planetary candidates. One of Kepler's key findings is that planets which are 1 to 4 Earth radii in size are quite common and intriguingly, that there is a lack of close-in (orbital period < 100 days) planets of sizes 1.5-2.0 Earth radii, i.e. a radius ‘valley’. Follow-up observations have revealed a transition in planet densities around 1.6 Earth radii. Smaller planets with higher densities are consistent with rocky Earth-like compositions while larger planets with lower densities suggest that they are engulfed in large H/He atmospheres. Studies have thus suggested that this valley is a transition regime between smaller, rocky planets, i.e. ‘super-Earths' and larger planets with significant H/He atmospheres, i.e. ‘sub-Neptunes’. 
  
 Typically, this valley in the size distribution of close-in planets has been attributed to photoevaporation (PE) of atmospheres due to the high-energy radiation of the host stars. More recently, however, studies have shown that atmospheric mass-loss driven by the cooling luminosity of the planet itself, i.e. core-powered mass-loss (CPML), can also reproduce this radius valley, even without PE. 
  
 In reality, the observed planet distribution was likely sculpted by a combination of CPML and PE as well as other formation and evolution pathways. However, there is uncertainty regarding which, if any, mechanism dictates planet evolution and how this depends on the planet and host star properties. Furthermore, since we can explain much of the close-in planet size distribution by CPML (or PE) alone, begs the question if CPML is crucial for evolution at longer periods too, particularly for those in the habitable zones of FGK stars. In addition, if most of the planets form before the protoplanetary disk disperses, this question becomes even more crucial because planet evolution under CPML would then have an influence on the late-stage physical and chemical evolution of the planets and thus, ultimately on their habitability. 
  
 These arguments thus motivate us (1) to understand how small exoplanets evolve under the CPML mechanism at longer periods, including those in the habitable zone and (2) to determine new observable signatures of the CPML mechanism. 
  
 I will tackle these problems by building upon the theoretical and numerical framework from my previous papers. This will involve revisiting and questioning the physics underlying the phases of gas accretion, thermal evolution, and atmospheric mass-loss under CPML. For instance, I will investigate if the continuum approximation to atmospheric outflow is always valid as is typically assumed in the evolution of close-in planets, and what happens if that is not the case. Moreover, I will determine observable signatures of CPML including the occurrence rates of He/metallicity enhanced planets, mass-loss rates and limiting masses of super-Earths. This work will involve numerically evolving populations of millions of planets at long and short periods to understand how planet evolution depends on a wide range of planet and host star parameters like core composition and stellar mass. I will use cutting-edge observational data to model stellar and planetary populations and for comparison with our results. 
  
 The proposed study is directly relevant to NASA’s strategic plan and Planetary Science Division goals because this work entails understanding the formation and evolution of small exoplanets at long orbital periods including those in the habitable zone, determining observable signatures of CPML to investigate the dominant planet evolution mechanism(s), probing the dependence of planet evolution on stellar environment and constraining properties of observed planets and stellar environment, and providing initial conditions relevant to studies investigating late-stage physical and chemical evolution of planets and their habitability. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– John Spear (PI) Emily A. Kraus (FI) 
Institution:  Colorado School Of Mines  
PLANET20-0139, Genomic investigations of microbial life within subsurface rock from a terrestrial site of serpentinization 
 
This proposal will examine the distribution and metabolic abilities of microbial life residing in rock core from a Martian subsurface analog environment. Rock core samples for biological study were collected to minimize contamination from the drilling process, humans, and other environmental contaminants.  Protocols have been developed by the future investigator to extract microorganisms and their DNA from rock cores.  Preliminary testing shows successful recovery of DNA and identification of microbes known to reside in the subsurface aquifer of the sampling site.  
  
 This proposal seeks first to estimate the biomass native to the subsurface and benchmark these estimates against direct cell counts of the same samples to ensure the developed extraction protocols are functioning. Second, the geochemical, mineralogical, and physical factors controlling the distribution of life in subsurface rock will be investigated. Third, the metabolic capabilities and possible differences between the native microorganisms will be studied. Results of this proposed work will characterize the subsurface biosphere of a Martain analog environment and aid in protocol development for biological handling and genomic analysis of low biomass rock samples. 
  
 Genomic methods will be used to accomplish these objectives. A unique DNA extraction protocol and sequencing of a gene universal to all life (the 16S small subunit ribosomal RNA gene, 16S SSU rRNA) are employed in preliminary work, initial testing, and in completion of the second objective.  Real-time (quantitative) polymerase-chain reaction (qPCR) will be used to complete the first objective. Lastly, whole community (‘shotgun’) metagenomic sequencing methods will be employed to accomplish the third objective. Bioinformatic analysis using open source programs will be used throughout the proposed work. 
  
 The proposed work seeks to directly address the Planetary Science Division objectives to ‘improve our understanding of the origin and evolution of life here on Earth to guide our search for life elsewhere’ and to ‘explore and find locations where life could have existed or could exist today’ (Chp. 4.3) by characterizing microbial life from a Martian subsurface analog. The research herein will generate insight into the Earth’s deep subsurface biosphere with implications in narrowing the search for life in our solar system. Contamination minimization protocols will be published which are directly applicable to exploration missions, such as the Mars Exploration Program, with a sample return or subsurface drilling component. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Amanda Stockton (PI) Chinmayee Govinda Raj (FI) 
Institution:  Georgia Tech Research Corporation  
PLANET20-0255, Quantitative Compositional Analysis of Organic and Inorganic Chemical Species on an Icy Moon Penetrator Organic Analyzer 
 
Our understanding of the astrobiological importance of the Jovian moon Europa is increasing by the day. Telescopic and flyby mission data strongly suggest the presence of an ionic global subsurface liquid ocean containing potentially biogenic chemistries. Recent efforts to prioritize lander missions including the Europa lander has opened up a plethora of scientific opportunities that could not have been explored except from the surface. Through this work, I propose to design and implement low power, compact, low mass, low cost, and highly sensitive analytical instrumentation techniques for organic and inorganic analysis of Europa’s subsurface ice. These instruments will be compatible with a Discovery-class mission via the Icy Moon Penetrator Organic Analyzer (IMPOA, a NASA PICASSO funded project) instrument platform that is capable of withstanding extremely high impact forces. Ice crust penetration occurs upon impact, thereby avoiding complex soft landing and ice drilling capabilities. A typical Discovery-class payload can approximately contain sixteen IMPOA payloads. Upon impact of the Discovery mission payload, IMPOA payloads can be ejected to occupy a larger area thereby collecting geographically varied samples. I will be building a capillary electrophoresis-laser-induced fluorescence (CE-LIF) system for quantitative compositional analysis of amino acids and capillary electrophoresis-capacitively coupled contactless conductivity detector (CE-C4D) system for analysis of salts. Characterizing amino acids adds to our ability to identify potentially biogenic compounds, their origin, history, and subsurface habitability. Characterizing salts will help with determining bio-viability, surface material provenance and feed information into resurfacing models that have not been built due to lack of in situ data. The instrumentation techniques discussed can be incorporated into any lander mission that focuses on organic and inorganic analysis including Europa, Enceladus or even the  Martian polar ice caps. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Stephen Tegler (PI) Anna Engle (FI) 
Institution:  Northern Arizona University  
PLANET20-0193, Experimental Studies to Determine the Impact of Propane, Acetylene, and Ethylene In and Around Titan's Lakes 
 
Titan, the largest moon of Saturn, is the only body in the Solar System aside from Earth with stable liquid on its surface. Although the Cassini-Huygens mission has provided invaluable insight into the lakes and seas at Titans poles much is left to be explored. One particular aspect is getting a better constraint on the compositions. Current studies provide ranges for methane, ethane, and nitrogen, but with methane photochemical processes occurring in the atmosphere it is thought that other hydrocarbons reside in the lakes and seas as well. Aside from ethane, the most common by-products of the ongoing photochemistry are propane, ethylene, and acetylene. With this in mind the proposed research aims to use Raman spectroscopy to better understand the quantity in which propane, ethylene, and acetylene might be found in the lakes as well as the possible implications to the immediately surrounding environments.  
  
 At Titan surface conditions propane is a liquid whereas ethylene and acetylene are solid. That said, we intend to carry out the research by probing the phase transitions of three systems: 1) nitrogen-methane-ethane-propane, 2) nitrogen-methane-ethane-propane-ethylene, 3) nitrogenmethane-ethane-propane-acetylene all at 1.5 bar. Three sets of mixing ratios will be used for the nitrogen-methane-ethane system and will be based on quantities found by Mastrogiuseppe et al. (2019) for the north polar lakes. While keeping the mixing ratios of the ternary system proportional, we will add a range of 0% to 20% of propane and record how the liquidus and solidus are affected with the addition. Noting mixing ratios of interest, we will then add 0% to 20% of ethylene and then acetylene respectively to the nitrogen-methane-ethane-propane system.  
  
 By the end of the proposed project, we aim to constrain the temperatures at which the mixtures are fully liquid, fully solid, and a combination of the two. This will also be paired with identifying the ratios of the components, especially in the case when both liquid and solid material are present. In doing this, we will expect to gain a better understanding of the composition of the liquid portion of the lakes in addition to what may be found on the lake floors. Further analysis is also anticipated to clarify the composition and the impact to the geology immediately surrounding the lakes. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Michelle Thompson (PI) Laura Camila Chaves (FI) 
Institution:  Purdue University  
PLANET20-0172, Investigating the Role of Sulfides and Fe-Oxides in the Space Weathering of Asteroidal  Regoliths 
 
Space weathering modifies the chemical, microstructural and spectral properties of grains on the surfaces of airless bodies and is driven by micrometeorite impacts and solar wind irradiation (Hapke 2001). Optically, this process causes the attenuation of characteristic absorption bands and reddening and darkening of reflectance spectra. In addition to spectral changes, space weathering causes the formation of Fe nanoparticles (npFe), vesiculated textures, and amorphous rims on grain surfaces. Previous studies of returned samples and laboratory simulations of space weathering processes have focused on the effects of this phenomenon on the silicate minerals which dominate lunar soils (e.g., Loeffler et al., 2016; Keller et al., 1997; Noguchi et al., 2011). However, the situation is less constrained for minerals found on more compositionally-complex regoliths, e.g., chondritic bodies. Examples of these understudied minerals include Fe- and Fe-Ni sulfides (troilite, pentlandite, pyrrhotite) and Fe-oxides (magnetite). These minerals have all been identified in returned samples from S-type asteroid Itokawa, in carbonaceous chondrite meteorites thought to be analogs of the target bodies of the Hayabusa2 and OSIRIS-REx missions, or in remotely sensed data from these asteroids (Bland et al., 2004; Noguchi et al., 2011, 2014, Lauretta et al., 2019). Despite their prevalence in our sample collection, the physicochemical behavior of sulfides and Fe oxides under space weathering conditions are still poorly understood. To better understand the response of these phases to space weathering processes, in Task 1, I will perform laboratory simulations of micrometeorite impacts and solar wind irradiation, using pulsed-laser and ion-irradiation, respectively, on sulfide and Fe-oxides minerals. I will then use transmission electron microscopy (TEM) to characterize their microstructural and chemical response to these simulated weathering events. In Task 2, I will investigate the microstructural and chemical features in naturally space weathered sulfidebearing grains from asteroid Itokawa returned by the Hayabusa mission. I will use ultramicrotomy and focused ion beam scanning electron microscopy (FIB-SEM) to prepare the samples for analysis in the TEM, and I will use energy dispersive X-ray spectroscopy (EDS) to analyze their chemical composition. Combining returned sample analyses with laboratory experiments will allow me to attribute specific chemical and microstructural features in naturally space-weathered samples to individual constituent processes. This comparison will enable me to investigate the relative contributions of micrometeorite impacts and solar wind irradiation in the space weathering of asteroidal regoliths. The proposed analyses will maximize the scientific return of the Hayabusa mission and will help us prepare for sample return from the ongoing OSIRIS-REx and Hayabusa2 missions. These results will also contribute to a better understanding of remote sensing data of airless bodies surfaces and help build a model for space weathering across the inner solar system. 
 
 This research is directly relevant to the NASA Laboratory Analysis of Returned Samples (LARS) program, and will directly address section 2 (origin and evolution of solar system bodies) of appendix C.18 (NNH19ZDA001N-LARS) of the ROSES-2019 NRA. My goal is to ‘maximize the science derived from planetary sample-return missions’ by performing ‘direct analysis of samples already returned to Earth’ specifically with particles collected by the Hayabusa mission 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Francois Tissot (PI) Haoyu Li (FI) 
Institution:  California Institute of Technology  
PLANET20-0236, Revisiting Early Solar System chronology: a combined investigation of U, Pb and Al-Mg systematics of mineral separates from CAIs. 
 
As the oldest dated solids in the solar nebula, CAIs play a pivotal role in defining the start-ing point of the Early Solar System (ESS) and anchoring absolute and relative chronometers. A particular interest of ESS chronology is the fact that the two most precise ages of the oldest CAIs do not agree within uncertainty. This discrepancy could be caused by a few biases that are currently unaccounted for. 
  
 The first question is the reliability of Pb-Pb ages of CAIs. Pb-Pb dating has long assumed that U isotopes were invariant, which was challenged because significant U isotope variability was found in CAIs. Given that the variation in the absolute 238U/235U can have a significant impact on the accuracy of Pb-Pb ages, outside of stated uncertainties, both U and Pb isotopes are supposed to be measured to obtain precise and accurate absolute ages. Although U isotopes corrected ages of CAIs have been published, an assumption is always made that the bulk CAI and its mineral constituents have the same U isotope composition, and the bulk ´238U is used to correct the ages derived from the pyroxene fraction. A growing body of evidence, however, suggests that minerals in igneous samples, are characterized by different U isotope compositions. Compared to ´238U var-iations between bulk CAIs, intermineral variations are expected to be smaller. These smaller varia-tions would still result in significant ages corrections, relative to the errors on the Pb-Pb ages. The second question is the concordance between absolute ages (Pb-Pb) and relative ages (Al-Mg). Given the still relatively recent development that high-precision U isotope analyses represent, pub-lished studies on CAI chronology have typically not combined U-corrected Pb-Pb age determina-tion and Al-Mg analyses on the same bulk CAIs and/or their mineral fractions. To have a comprehensive view of ESS chronology, Al-Mg systematics also should be revisited for the same set of samples. 
  
 Here, we propose to assess the reliability of CAI ages by conducting high-precision analy-sis of the U and Al-Mg systematics in mineral separates from CAIs that will also be dated using the Pb-Pb method. The major contribution of the proposed work will be to revisit the Pb-Pb ages of CAIs, which are the oldest known solids in the solar system. Given that substantial U isotopic variability exists in CAIs, assessing the homogeneity of U isotope compositions in different miner-al fractions within CAIs can provide a more subtle view of the impact of U isotopic compositions on the correction of Pb-Pb ages. This, in turn, will allow us to assess the level of agree-ment/discrepancy between absolute and relative chronologies. The proposed work is highly rele-vant to NASA’s high-level Strategic Objective 1.1: Understand the Sun, Earth, Solar System, And Universe. 
  
 There are four main objectives in this proposal: 
 Objective 1: To measure the ´238U on mineral separates from coarse-grained CAIs.  Objective 2: To characterize, both in-situ and by solution, the Al-Mg systematics of the same CAIs.  
 Objective 3: To investigate whether systematic differences in 238U/235U exist between different mineral phases in CAIs, assess their potential impact on Pb-Pb age corrections.  Objective 4: To combine the Pb-Pb corrected ages and the Al-Mg data to revisit ESS chronology. 
  
 For the proposed work, six coarse-grained CAIs have already been extracted and characterized. Epoxy mounts of these CAIs have been made for in-situ Al-Mg analysis by SIMS. A representative fragment of the bulk CAIs will be kept for solution work of Al-Mg systematics, while remain-ing samples will be crushed and separated into mineral fractions with the combination of hand-picking and magnetic separation. Mineral separates and bulk CAIs will be dissolved and purified with well-established protocols. Mg and U isotopes will be measured by MC-ICPMS. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Benjamin Weiss (PI) Elias Mansbach (FI) 
Institution:  Massachusetts Institute of Technology  
PLANET20-0009, Determining the Structure of a Primitive Achondrite Parent Body Using Paleomagnetism 
 
The early solar system was filed with ~1-500 km bodies called planetesimals that served as the building blocks of planets. Today we have samples of planetesimals in the form of meteorites that provide unique records of early planetary evolution. Meteorites have been traditionally divided into two principal groupings: chondrites, which are unmelted accretional aggregates, and achondrites, which are products of planetary melting processes. The existence of chondrites and achondrites has commonly been interpreted as evidence for a dichotomy in the planetesimal population: these bodies would have either never been melted or otherwise have melted throughout their entire interiors. A third class of meteorites, however, has been recently recognized. Termed primitive achondrites, these meteorites have textures and compositions intermediate between chondrites and achondrites. The existence of primitive achondrites demonstrates that some planetesimals only experienced partial melting prior to disruption.   Acapulcoites and lodranites (ALs), one class of primitive achondrites, give us a rare glimpse into the differentiation process of planetesimals since the parent body did not go to completion. While it is generally thought that differentiated bodies originally accreted as unmelted, chondritic objects, we have little understanding of the processes by which planetesimals undergo igneous differentiation. Despite the extensive study of ALs in the past few decades, the size, cooling history, and structure of the AL parent body are unknown and highly debated. I propose to conduct a paleomagnetic investigation of ALs to (1) determine whether the AL parent body generated a planetesimal dynamo in an advecting metal core; (2) constrain the cooling rate and structure of the AL parent body; (3) constrain the efficiency of core formation on planetesimals. Of particular interest to this proposal is whether chondrites, primitive achondrites, and achondrites could form on the same parent body. A positive test for a dynamo on the AL parent body would suggest a radially layered structure with a metallic core surrounded by fully melted and then partially melted achondritic layers, in turn covered by decreasingly metamorphosed chondritic material moving towards the surface. In addition, given previous studies suggest that the AL parent body had a radius of < 250 km, there is a debate whether buoyancy forces on the planetesimal were sufficient to transport metal to the center of the body and create the conditions for a dynamo. 
 
 I propose to conduct a paleomagnetic investigation of ALs by analyzing two potential magnetic recorders in ALs: cloudy zones (CZs) in metal grains in ALs and iron blebs in AL silicate cores 
  
I.	CZs form through the spinodal decomposition of taenite at 320C and are capable of recording a natural remanent magnetization. Due to their high coercivity, they are not likely to have been remagnetized after acquiring a magnetic remanence.  
II.	‘Dusty’ silicates in ALs have 1 micrometer and smaller iron blebs that are in many ways analogous to ‘dusty olivines’ found in chondrules in chondrites and have been shown to be reliable magnetic recorders.  
  
 This work will be conducted by Ph.D. student Elias Mansbach under the supervision of Prof. Benjamin Weiss in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology (MIT). 
 
 This research proposal is relevant to the Planetary Science Division science goals described in the FINESST solicitation, namely to ‘explore and observe the objects in the Solar System to understand how they formed and evolve.’ and ‘advance the understanding of how the chemical and physical processes in the Solar System operate, interact and evolve.’ A paleomagnetic investigation of ALs will address these goals by furthering our understanding of how planetary bodies evolved from unmelted planetesimals to radially layered bodies such as Earth. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– James Wray (PI) Angela Dapremont (FI) 
Institution:  Georgia Tech Research Corporation  
PLANET20-0159, Mars Mud Volcanism in Color: An Alternative Approach to the Study of Subsurface Sediment Mobilization Products 
 
Debate regarding the interpretation of positive-relief landforms on the surface of Mars as the result of igneous or mud volcanism (MV) is ongoing within the planetary science community. Despite the value of orbital remote sensing datasets in clarifying the volcanic origin of these features on Mars, compositional information has been an underutilized tool. My previous PhD dissertation work, using visible and near-infrared spectroscopy data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), revealed only hydration signatures and a lack of specific mineral identifications associated with suggested Mars MV products. Thus, a study using high resolution (0.25-1.0 m/pixel) quantitative color band ratio data from the High Resolution Imaging Science Experiment (HiRISE) camera should be conducted as a novel approach to acquire additional knowledge about proposed Mars MV feature mineralogy.    
  
 To conduct this study, I will acquire reflectance (I/F) values from Mars MV features using 
HiRISE JPEG2000 Reduced Data Record color products. HiRISE IR/RED and BG/RED band ratios will be calculated and compared with CRISM library and U.S. Geological Survey laboratory spectra for mineral identification. 
  
 MV sites on Mars are worth investigation due to: 1) their potential as astrobiology sites of interest and 2) the ability to gain insight into the subsurface and/or deep biosphere of a celestial body. This proposed project is therefore relevant to the NASA Planetary Science Division science goal to explore and determine locations of extinct or extant life. This proposed work also aligns with NASA Strategic Objective 1.1, due to the potential for project results to be used a guide for future robotic or human landing sites on Mars. This project maximizes the data acquisition investment return pertaining to the Mars Reconnaissance Orbiter, which includes both the CRISM and HiRISE instruments. This proposed work is also relevant to NASA Strategic Objective 3.3 due to the existence of multiple publicly accessible channels which are available for access and interaction with Mars MV HiRISE data to inspire, engage, and inform the public. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Qing-zhu Yin (PI) Supratrim Dey (FI) 
Institution:  University Of California, Davis  
PLANET20-0178, Establishing Planetary Genealogy of Iron Meteorites and Pallasites using Nucleosynthetic Isotope Anomalies of Chromium and Titanium 
 
The primary objective of the proposed research is to establish the genealogy of important groups of planetary materials and to determine the provenance of their parent bodies in the early Solar System using nucleosynthetic isotopic anomalies in meteorites. The proposed work will focus on establishing the genealogy of IAB-IIICD (now known as IAB-complex), IIIAB, and IIE iron meteorites, the main group pallasites, and select anomalous pallasites. The origin of these meteorites is still enigmatic, limited largely by their metallic composition. The compositions of their parent bodies are mostly unknown to inform any melting experiments or petrogenetic models. I propose to measure nucleosynthetic isotopic anomalies of 54Cr and 50Ti in select meteorites from these groups for which there is currently only sparse data available. This research will reveal the ‘genetic relationships’ of iron meteorites and pallasites with other known planetary materials, and potentially discover previously unknown groups of planetary materials and geochemical reservoirs within the early Solar System. The lack of such information has hindered establishing reliable petrogenetic models for these important meteorite groups. The proposed project directly addresses the objective of the Planetary Science Research Program, to ‘advance the understanding of how the chemical and physical processes in the Solar System operate, interact and evolve’ (NASA SMD 2014 Science Plan). The proposed work is focused on understanding the origin and evolution of planetesimals and their interrelationships in the early Solar System. 
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Zhaohuan Zhu (PI) Shangjia Zhang (FI) 
Institution:  University Of Nevada, Las Vegas  
PLANET20-0082, Self-consistent Dust and Thermal Structure in 3-D Protoplanetary Disk Models: Constraints on Disk and Young Planet Properties 
 
The discovery of thousands of planets orbiting around stars has brought new perspectives of our place in the universe. Like our Solar System, these planetary systems were evolved from protoplanetary disks. The dust in the disk grows from micrometer-sized grains all the way to kilometer-sized planetesimals and finally becomes planets. The interactions between the embedded forming planets and the disk leave imprints on the disk morphology. To explain the formation and evolution of planetary systems, it is natural to observe protoplanetary disks and young planets directly, understand their physics and make connections to the current Solar System and planetary systems. 
  
 Recent observations by ALMA and ground-based telescopes provide diverse structures of protoplanetary disks, including cavities, gaps, rings, arcs, and spirals. While 2D models with simplified physics can provide some implications to these features, only 3D models with more realistic physics can possibly interpret the increasing amount of high-resolution observations. These include the polarization vector maps observed by ALMA, the shadow present in near-IR scattered light images, and the dippers observed by Kepler. 
  
 To understand these observations, 1) we will use a Monte Carlo radiative transfer code 
RADMC-3D to calculate the 3D dust distribution with different dust species. The density and temperature structure will be in thermal equilibrium after iterations. we will explore a large parameter space and compare it with polarization observations. This will give constraints on disk vertical and radial dust size distributions and surface density. The 3D distributions of um-to-cmsized particles help us understand how planetesimals form. 2) We will also carry out 3D radiation hydrodynamic simulations to study the dynamics of protoplanetary disks using Athena++ code. Both stellar irradiation and disk thermal radiation will be included. We will focus on the effects of asymmetric illumination from the central star or the shadowing from the inner disk to the outer disk. These simulations will be able to explain the shadows commonly observed in near-IR scattered light images and dippers observed by Kepler and TESS, hopefully constraining misaligned planets if they are present at the early disk stage. Since the thermal structure affects dynamics, a realistic implementation of radiation will improve our understanding of the disk dynamics too. 
  
 Relevance: This proposal is relevant to SMD Planetary Science and Astrophysics Divisions and in the scope of the ROSES E.3 Exoplanets research. It helps ``improve understanding of the origins of exoplanetary systems'', and helps ``detect the exoplanets''. It is also highly related to the D.4 Astrophysics Theory since it includes ``development of theoretical astrophysics models''. The radiation module will be valuable to other astrophysical objects, too. It is also related to the C.2 Emerging Worlds, in that this proposal is in line with ``studies of all aspects of materials present and processes occurring in and affecting the protoplanetary disk''. This project helps explain results from Kepler K2 and incoming TESS data on dippers. The 3D planet-disk interactions radiation simulations will help interpret the protoplanetary disk targets in JWSTs Guaranteed Time Observations (GTO). The proposed work will also constrain the mass and the position of the inferred young planets in deep gaps of protoplanetary disks, and help explain observations already in GTO, and find more targets for future JWST observations.