Depleted carbon isotope compositions observed at Gale crater, Mars

Obtaining carbon isotopic information for organic carbon from Martian sediments has long been a goal of planetary science, as it has the potential to elucidate the origin of such carbon and aspects of Martian carbon cycling. Carbon isotopic values (813CVPDB) of the methane released during pyrolysis of 24 powder samples at Gale crater, Mars, show a high degree of variation (-137 +/- 8%o to +22 +/- 10%o) when measured by the tunable laser spectrometer portion of the Sample Analysis at Mars instrument suite during evolved gas analysis. Included in these data are 10 measured 813C values less than -70%o found for six different sampling locations, all potentially associated with a possible paleosurface. There are multiple plausible explanations for the anomalously depleted 13C observed in evolved methane, but no single explanation can be accepted without further research. Three possible explanations are the photolysis of biological methane released from the subsurface, photoreduction of atmospheric CO2, and deposition of cosmic dust during passage through a galactic molecular cloud. All three of these scenarios are unconventional, unlike processes common on Earth.

Automated summary

Obtaining carbon isotopic information from Martian sediments can help us understand the origin and cycling of carbon on Mars. The measurements of carbon isotopes in methane released during pyrolysis experiments at Gale crater show significant variations, with some values potentially linked to ancient surface. There are multiple possible explanations for the observed depleted 13C, but further research is needed to confirm them.