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Evolved Gas Analysis and Raman Spectroscopy of Nitrate-Mineral Mixtures: Implications for the Detection and Identification of Nitrates on Mars

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe (Posters)

Presenting Author:

Joanna Clark

Authors:

Clark, Joanna V¹, Sutter, Brad², Casbeer, Patrick³, Jakubek, Ryan⁴, Stern, Jennifer C⁵, Haney, Nikole C⁶

(1) Texas State University – Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA, (2) Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA, (3) Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA, (4) Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA, (5) NASA, Goddard Space Flight Center, Greenbelt, MD, USA, (6) Texas State University – Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA,

Abstract:

Nitrate salts were detected in sedimentary rocks in Gale crater, Mars by the Sample Analysis at Mars-Evolved Gas Analyzer (SAM-EGA) but have not been detected by the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument in Jezero crater, Mars. The presence of fixed nitrogen (i.e., nitrates) on Mars has implications for past habitability because of its critical role in biomolecules (e.g., DNA, RNA, and proteins) on Earth. It is currently unknown which cation-species of nitrates are present on Mars and if there are factors that affect their detection by SAM-EGA and SHERLOC. This work investigated the effect of three martian-analog phases (palagonite, magnetite, and labradorite) on the thermal decomposition of various nitrates as well as the detection of nitrates using SHERLOC-like Raman. Fe, Mg, Ca, Na, and K nitrate solutions (0.04 M) were added by micropipette to empty Al₂O₃ crucibles, and to crucibles with 5 or 20 mg of powdered magnetite, palagonite, and labradorite. Sample crucibles were vacuum desiccated and then analyzed on a SHERLOC-analog Raman instrument as well as a SAM-analog evolved gas instrument.

The thermal decomposition temperatures of nitrates depended on the cation-species as well as the mineral phases with which they were mixed. Nitrates analyzed individually evolved NO (m/z 30) peaks in the order: Fe nitrate (318 °C), Mg nitrate (418 °C), Ca nitrate (544 °C), K nitrate (536 °C), and Na nitrate (570 °C). Palagonite caused the greatest decrease in nitrate decomposition temperatures (as much as 281 °C when mixed with Na nitrate), except for Fe nitrate where little to no effect on the thermal decomposition temperature was detected. The shift in decomposition temperature may be caused by catalysis or the formation of Fe nitrates (and subsequent decomposition) during heating, which may be facilitated by the melting of the nitrates at low temperatures (below 350 °C except for Ca nitrate). SHERLOC-like Raman demonstrated that individual nitrates, except for Fe nitrate, were detectable. The nitrates were undetectable in the magnetite and palagonite mixtures due to strong Raman absorption by Fe. The presence of Fe-bearing minerals in samples complicates identification of cation-species of nitrates by SAM-EGA and could potentially inhibit the detection of nitrates on the surface of Mars by SHERLOC Raman.