^1,2A. Mojarro,³A. Buch,¹J. P. Dworkin,¹J. L. Eigenbrode,⁴C. Fressinet,¹D. P. Glavin,⁴C. Szopa,⁴M. Millan,⁵A. J. Williams,⁶R. E. Summons
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007968]
¹NASA Goddard Space Flight Center, Greenbelt, MD, USA
²Oak Ridge Associated Universities, Oak Ridge, TN, USA
³CentraleSupélec, Université Paris-Saclay, Paris, France
⁴Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université Paris-Saclay, Paris, France
⁵Department of Geological Sciences, University of Florida, Gainesville, FL, USA
⁶Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
Published by arrangement with John Wiley & Sons

The Sample Analysis at Mars (SAM) instrument aboard the Curiosity Rover at Gale crater can characterize organic molecules from scooped and drilled samples via pyrolysis of solid materials. In addition, SAM can conduct wet chemistry experiments which enhance the detection of organic molecules bound in macromolecules and convert polar organic compounds into volatile derivatives amenable to gas chromatography-mass spectrometry analyses. Specifically, N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) is a silylation reagent whereas tetramethylammonium hydroxide (TMAH) is a thermochemolysis methylation reagent. Shortly after arriving at Mars, the SAM team discovered that at least one of the MTBSFTA cups was leaking, contributing to a continuous background inside SAM with the potential to interfere with future TMAH reactions. Therefore, here we characterized possible interactions between the two reagents to determine byproducts and implications for the detection of indigenous organics. SAM-like pyrolysis experiments supplemented with flash pyrolysis were accordingly conducted with fragments of the Murchison meteorite as a reference for exogenous organic matter delivered to Mars. Flash TMAH experiments yielded various aromatic acids, dicarboxylic acids, and amino acids while SAM-like pyrolysis presented mixtures of methylated and non-methylated compounds due to decreased reaction efficiency at slower ramp rates. All experiments in the presence of simulated MTBSTFA vapor produced pervasive silylated byproducts which co-elute and obscure the identification of Murchison-derived compounds. Despite challenges, a significant diversity of pyrolyzates and TMAH derivatives could still be identified in flash pyrolysis in presence of MTBSTFA. However SAM-like experiments with TMAH and MTBSTFA are hindered by both decreased methylation yields and additional co-eluting compounds.

^1,2Emma R. Rogers,¹Briar R. Qualizza,¹Joseph R. Heidenreich,^1,3Henry G. Dawson,¹Briony H. N. Horgan
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE007881]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
²Department of Earth Sciences, Dartmouth College, Hanover, NH, USA
³Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
Published by arrangement with John Wiley & Sons

A small basin on the Southwest (SW) margin of Melas Chasma in Valles Marineris, Mars, hosts a variety of previously identified sedimentary fans and layered strata hypothesized to have been formed by one or more paleolakes. This basin also contains light-toned layered mounds that have distinct spectral absorption bands consistent with amorphous hydrated silica (e.g., opal). While the general morphology and mineralogy of these features and the basin itself have been previously characterized, the formation mechanism of the hydrated silica features and their temporal relationships with the proposed paleolake remain to be determined. We use Compact Reconnaissance Imaging Spectrometer for Mars visible through short-wave infrared reflectance spectra (0.35–2.65 μm) and High Resolution Imaging Science Experiment digital terrain models and images to analyze the stratigraphic location and morphology of the opaline silica-bearing features in the SW Melas basin. We find that the basin hosts fourteen high-relief “mounds,” eight low-relief “patches,” and two extended layers within the sedimentary strata that are light-toned, fractured, and often exhibit hydrated silica-like spectral signatures. We hypothesize that the mounds are spring deposits formed by sub-aerial hydrothermal activity, while the patches and layers correspond to sub-lacustrine hydrothermal activity. The varied elevations of the mounds and patches indicate at least one fluctuation of lake level in the basin during its history. The combination of contemporaneous hydrothermal and lacustrine activity to form silica-cemented sedimentary deposits in a nutrient-rich subaqueous environment would have been conducive to forming and preserving biosignatures in the SW Melas basin.