Depleted carbon isotope compositions observed at Gale crater, Mars
TL&#x2F;DR: A paper reports (appropriately conservatively) on tantalizing evidence from Gale crater. Curiosity&#x27;s SAM lab heated 24 powdered rock samples to 850 °C, releasing their solid carbon as methane gas. The onboard Tunable Laser Spectrometer then measured the carbon isotopes in that gas and found more 12C than would be expected based on the 12C to 13C ratio in the modern Martian atmosphere. On Earth, life preferentially uses 12C over the heavier 13C, bioaccumulating it, so we observe significantly more 12C than 13C in ancient rocks where life grew. Did ancient Martian microbial methanogenesis concentrate this isotope at Gale crater as it built up complex organic molecules? Maybe. Two other hypotheses offer abiotic explanations: one suggests that UV light could have caused CO2 in the Martian atmosphere to form isotopically enriched carbon monoxide molecules that settled to the surface, the other wonders if the isotopes arrived from space when our solar system drifted through a 13C-depleted giant molecular cloud hundreds of millions of years ago. “On Earth, processes that would produce the carbon signal we’re detecting on Mars are biological,”[1] but we don’t understand the Martian carbon cycle well enough yet to have any real confidence. As with all tantalizing results about microbial extraterrestrial life so far, this will probably turn out to be due to a physicochemical process we don’t yet understand. Or maybe not.<p>I&#x27;ll be covering this more in the next issue of Orbital Index (<a href="https:&#x2F;&#x2F;orbitalindex.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;orbitalindex.com&#x2F;</a>).<p>[1] <a href="https:&#x2F;&#x2F;www.nasa.gov&#x2F;feature&#x2F;goddard&#x2F;2022&#x2F;nasa-s-curiosity-rover-measures-intriguing-carbon-signature-on-mars&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.nasa.gov&#x2F;feature&#x2F;goddard&#x2F;2022&#x2F;nasa-s-curiosity-r...</a>