Possible Global Distribution of Reduced Carbon in Surface Sediments on Mars: Evidence from Volatiles Released from the Rocknest Eolian Drift, Gale Crater

Abstract:

The Rocknest eolian drift sediments were pyrolyzed in the Science Analysis at Mars (SAM) instrument on the Curiosity rover, yielding a small, discrete peak of C1-C3 volatiles, which were detected by direct mass spectrometry. This peak was observed to have a maximum intensity at ~820°C in all four evolved gas analysis (EGA) experiments of the scooped and sieved (to ≤ 150 mm) Rocknest sediment, though it is strongest in the second and third analyses. It was not observed in any blanks or subsequent samples of drilled rocks. Estimates of the total reduced carbon concentration are 16 ± 4 ppm carbon by weight in the sample. Evolved gas analysis does not support definitive identification of trace molecules in gas mixtures, however the masses that define the observed peak are consistent with primarily CO₂ (oxidized carbon phase; 9 ± 2 ppmw carbon ) and CO, with 1-2 orders of magnitude less C1-3 hydrocarbons. The observed mass composition and temperature of evolution for the Rocknest-820°C peak are suggestive of reduced carbon in a refractory state within the sample and inconsistent with reaction products that one might expect from terrestrial organic materials that are part of SAM’s background. These carbon volatiles are most likely released from inclusions or decrepitating minerals and this entrapment may be responsible for their preservation after significant exposure to ionizing radiation and mechanical weathering. Detection of these volatiles indicates reduced carbon phases are present in some Martian surface sediment. Carbon concentrations for Rocknest are within the range reported for magmatic carbon in Martian meteorites and the composition is comparable to volatiles released from terrestrial basaltic glasses. The Rocknest drift deposit is considered representative of the global dust on Mars. The very-high-temperature volatile release from Rocknest implies a possible global distribution of reduced carbon on the Martian surface.

The National Aeronautics and Space Administration (NASA) supported the research described here.