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

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) SO2 evolution temperature, (b) quadratic discriminant analysis comparing SAM data to SAM‐like laboratory investigations, and (c) sulfur isotope values from evolved 34SO2/32SO2. 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. Plain Language Summary The Mars Science Laboratory (MSL) Curiosity rover has been searching for ancient habitable environments in Gale crater, Mars, since 2012. Orbital data indicated the presence of a clay mineral‐rich region along the rover's traverse, which could have preserved geochemical evidence of ancient habitable environments. MSL drilled several samples from this region, now called the Glen Torridon region, and analyzed the samples' chemistry. The work here describes analyses of the sulfur chemistry from these samples as determined from the Sample Analysis at Mars (SAM) instrument suite. The chemical state of sulfur in the samples was determined by a combination of SAM data and comparative laboratory investigations. While most of the sulfur in this clay‐bearing region was consistent with the presence of sulfate (SO42−), two samples were consistent with the presence of small amounts of sulfide (S2−). The presence of both sulfide and sulfate could have supported the energ