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 similar to 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 (SO2)-S-34/(SO2)-S-32. 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.

Automated summary

The Mars Science Laboratory Curiosity rover has been studying the habitability and geological history of Gale crater on Mars since 2012. One of its main objectives was to investigate the Glen Torridon region, which has a high abundance of clay minerals that could preserve evidence of ancient habitable environments. The analysis of sulfur-bearing gases in samples from this region revealed that the majority of sulfur is in an oxidized state, with small amounts of reduced sulfur also present.