¹Rhianna D.Moore,¹Anna Szynkiewicz
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115342]
¹Dept. of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN, United States of America
Copyright Elsevier

The Meridiani Planum region on Mars has extensive sulfate-rich sedimentary deposits (~20 wt% SO42−) that are hypothesized to have formed from regional groundwater upwelling that led to the precipitation of secondary Fe-, Mg-, Ca-sulfate minerals and cementation of basaltic sediments. However, the primary source of sulfur (S) for these abundant secondary sulfate minerals is unclear. Therefore, in this study the contributions of volcanic S via surface water and groundwater were investigated in the terrestrial basaltic analogs of Hawaii and Iceland to determine the importance of active volcanism and climate on S cycling as well as the resulting timescale of aqueous activity in the Meridiani Planum region. SO42− fluxes (contributions) were calculated in metric tons/yr using historical data from online repositories and normalized to the catchment area to determine the SO42− load in metric tons/yr/km2. Our results show that the SO42− load is greatly affected by climate, typically ranging from ~7.3 to 170 metric tons/yr/km2 under wetter conditions and ~ 2.6 to 43 metric tons/yr/km2 under dry conditions. Active S degassing and accompanying S-rich mineralization from current hydrothermal activity greatly increased the SO42− loads (~2.8 to 170 metric tons/yr/km2) compared to non-active catchments (2.6 to 13 metric tons/yr/km2). Younger basaltic bedrock with greater permeability and groundwater-rock interactions was also found to be important, resulting in higher SO42− loads (~26 to 170 metric tons/yr/km2) compared to older, less permeable catchments (~2.6 to 12 metric tons/yr/km2). Based on these terrestrial SO42− loads in Hawaii and Iceland, we calculated a range of possible loads and timescales of SO42− transport in Meridiani Planum under variable environmental conditions. Results show that the smallest SO42− loads and longest timescales would occur in Meridiani under dry, non-volcanically active conditions, typically requiring ~16 to 65 Ma of an active aqueous system, as in the older catchments of Hawaii and Iceland. Conversely, the largest SO42− fluxes and shortest timescales would occur under wet, volcanically active conditions, requiring ~1.0 to 6.9 Ma, as in the younger catchments of Hawaii and Iceland. Our results suggest that moderately wet conditions with some active hydrothermal S input would be needed to transport and deposit the equivalent mass of SO42− currently present in the sulfate-rich deposits of Meridiani Planum.

^1,2,3Jack Diab,³Mohit Melwani Daswani,³Julie Castillo-Rogez
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115339]
¹Southern Oregon University, 1250 Siskiyou Blvd., Ashland, OR 97520, USA
²University of California Los Angeles, 607 Charles E. Young Drive East. Box 951569, Los Angeles, CA 90095-1569, United States of America
³Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA
Copyright Elsevier

Ceres is the largest object in the asteroid belt and the only dwarf planet in the inner solar system. In 2015, carbon, and organic compounds, were found by the Dawn mission in high abundance in the surface of Ceres. Here, we use thermodynamic modeling with the goal of constraining the speciation, stability, and abundance of organic compounds formed via abiotic reactions in the early subsurface ocean of Ceres and its mud-bearing mantle. We vary environmental conditions such as temperature, pH, reduction potential, solution composition, and pressure to analyze the variables that lead to optimal formation of organics. Primary results predict that in-situ organic production is negligible for most cases in the subsurface ocean if Ceres primarily accreted CI carbonaceous chondrites yet may be more significant if Ceres formed from cometary material. Carbonate concentration is 3–6 orders of magnitude higher than organics in the chondritic models, while a cometary composition favors significant alcohol and carboxylic acid derivative production, among other organic species. Results also indicate that temperature and pH are drivers of organic formation by water-rock equilibrium, with temperature having the greatest effect. Further analysis reveals that a mixture of ≲ 80 wt% CI chondrite and ≳ 20 wt% cometary material is favorable to in situ organic production of reduced organics. Observational constraints from the Dawn mission indicate that our model results could be representative of the organic observations on the surface. While our models favor organic production in Ceres’ ocean with moderate amounts of cometary material, further studies into alternative mechanisms of production and concentration on the surface of Ceres are needed.