Oxidized and Reduced Sulfur Observed by the Sample Analysis at Mars (SAM) Instrument Suite on the Curiosity Rover Within the Glen Torridon Region at Gale Crater, Mars

Abstract

The Mars Science Laboratory (MSL) Curiosity rover has been assessing the habitability and geologic history of Gale crater, Mars since landing in 2012. One of the primary objectives of the mission was to investigate a clay-bearing unit identified using orbital spectral data, designated the Glen Torridon (GT) region. This region was of particular interest because of its elevated abundance of clay minerals that may have preserved geochemical evidence of ancient habitable environments. The Curiosity rover explored the GT region for ∼750 sols and analyzed eight drilled samples with the Sample Analysis at Mars (SAM) instrument suite using evolved gas analysis-mass spectrometry. Evolved sulfur-bearing gases provided insight about the composition of sulfur-containing compounds in Martian samples. Evolved gases were analyzed by three methods to understand the oxidation state of sulfur in the samples: (a) SO 2 evolution temperature, (b) quadratic discriminant analysis comparing SAM data to SAM-like laboratory investigations, and (c) sulfur isotope values from evolved 34 SO 2 / 32 SO 2 . The results of these three methods were consistent with the majority of sulfur in the GT region being in an oxidized state, but two of the eight samples analyzed by SAM were consistent with the presence of small amounts of reduced sulfur. The oxidized and reduced sulfur could have a variety of sources and represents a nonequilibrium assemblage that could have supported putative ancient chemolithotrophic metabolisms.

Sedimentary Organics in Glen Torridon, Gale Crater, Mars: Results From the SAM Instrument Suite and Supporting Laboratory Analyses

“…Most of the mid-temperature (~500 ºC) SO2 evolved by Glen Torridon samples was consistent with an Fe sulfate source based on an analysis of peak SO2 release temperatures, statistical comparisons to laboratory analog data, and δ 34 S calculations . KM was the only sample found to show strong evidence for the presence of a sulfide mineral, which was consistent with Jura member Vera Rubin ridge samples (Wong et al, 2020). Additionally, the Oxalates (CO)…”

“…Ethanethiol and thiophene were present as is in the sample or formed during pyrolysis by chemical reactions between martian organic matter and the inorganic sulfur species (e.g., SO2, COS, CS2, H2S) released from the sulfur minerals (e.g., sulfates, sulfides) (Francois et al, 2016;Wong et al, 2020). Ethanethiol and thiophene were previously detected at Pahrump Hills in Gale crater,…”

Evolved Gas Analyses of Sedimentary Rocks From the Glen Torridon Clay‐Bearing Unit, Gale Crater, Mars: Results From the Mars Science Laboratory Sample Analysis at Mars Instrument Suite

“…If the 9.2 Å phase is an authigenic clay mineral such as mixed layer G‐M hypothesized by Thorpe et al. (2022) the siderite may have been deposited from the same fluids as formed the G‐M, since these minerals are known to occur together in terrestrial settings. Then, reduced sulfur, probably in trace sulfides, in the GT Jura (Wong et al., 2022), and the Jura exposed on VRR (Wong et al., 2020), may have been formed during a fluid event associated with the alteration of the VRR Jura that also affected the adjacent GT Jura. The sulfides could be formed, for example, by disproportionation of sulfite in sulfite‐bearing fluids, as hypothesized by Wong et al.…”

“…% (GG2) (Table 1). Detections of OCS, CS 2 and other key evolved volatiles as well as the isotopic composition of evolved SO 2 suggest that one of the samples, KM, may contain some reduced sulfur (Wong et al, 2022). The KM subsamples and the GE1 and GE2 subsamples evolved significant SO 2 at temperatures >∼700°C, while GE3, GR and GG had smaller SO 2 releases and MA evolved very little above ∼700°C (Figure 6).…”

“…Trace G‐M may have formed during the same fluid event that precipitated the siderite if it was authigenic. Then, reduced S, probably in trace sulfides, in GT Jura (Wong et al., 2022) and VRR Jura (Wong et al., 2020) formed during fluid interactions that affected both VRR Jura and the proximal GT Jura. Next, an alteration event or events affected the VRR Jura member but not the GT Jura.…”