Carbonates Identified By The Curiosity Rover Indicate A Carbon Cycle Operated On Ancient Mars

Ancient Mars had surface liquid water and a dense carbon dioxide (CO₂)–rich atmosphere. Such an atmosphere would interact with crustal rocks, potentially leaving a mineralogical record of its presence.

We analyzed the composition of an 89-meter stratigraphic section of Gale crater, Mars, using data collected by the Curiosity rover. An iron carbonate mineral, siderite, occurs in abundances of 4.8 to 10.5 weight %, colocated with highly water-soluble salts.

We infer that the siderite formed in water-limited conditions, driven by water-rock reactions and evaporation. Comparison with orbital data indicates that similar strata (deposited globally) sequestered the equivalent of 2.6 to 36 millibar of atmospheric CO₂.

The presence of iron oxyhydroxides in these deposits indicates that a partially closed carbon cycle on ancient Mars returned some previously sequestered CO₂ to the atmosphere.

Geological context of the drill samples. (A) Stratigraphic column indicating elevations and sedimentological interpretations of the 89-m vertical section traversed by the rover. Group, formation, and member designate the sedimentary units. Hatching styles indicate the lithology, as indicated in the legend. Black circles indicate drill sample locations: CA, Canaima; TC, Tapo Caparo; UB, Ubajara; and SQ, Sequoia. Vertical thick lines extend between sample elevations where Mg-sulfate minerals (solid line) and siderite (dashed line) have been detected. (B) Orbital optical image mosaic of Gale crater, overlain with Curiosity’s traverse (white line) up Mt. Sharp. Member (mbr) boundaries correspond to the section in (A). The difference between ChemCam observation points and the median Chenapau bedrock composition (19) is plotted as colored circles (as indicated in the color bar) at locations where ChemCam analyses were performed. Chenapau member chemistry is homogeneous and closely resembles the chemistry of the upper section of the Amapari member, near the Canaima drill site. — Science

Carbonates identified by the Curiosity rover indicate a carbon cycle operated on ancient Mars, Science (open access)
Astrobiology,