Carbonates identified by the Curiosity rover indicate a carbon cycle operated on ancient Mars

• DOI: 10.1126/science.ado9966
• Publication Date: 2025-04-17T18:00:31Z
• Authors: Benjamin M. Tutolo; Elisabeth M. Haus...; Edwin S. Kite; Elizabeth B. Rampe; Thomas F. Bristow; Robert T. Downs; Allan Treiman; Tanya S. Peretyazhko; Michael T. Thorpe; John P. Grotzinger; Amelie L. Roberts; P. Douglas Archer; David J. Des Marais; David F. Blake; David T. Vaniman; Shaunna M. Morrison; Steve Chipera; Robert M. Hazen; Richard V. Morris; Valerie M. Tu; Sarah L. Simpson; Aditi Pandey; Albert Yen; Stephen R. Larter; Patricia Craig; Nicholas Castle; Douglas W. Ming; Johannes M. Meusb...; Abigail A. Fraeman; David G. Burtt; Heather B. Franz; Brad Sutter; Joanna V. Clark; William Rapin; John C. Bridges; Matteo Loche; Patrick Gasda; Jens Frydenvang; Ashwin R. Vasavada

Ancient Mars had surface liquid water and a dense carbon dioxide (CO 2 )–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 CO 2 . The presence of iron oxyhydroxides in these deposits indicates that a partially closed carbon cycle on ancient Mars returned some previously sequestered CO 2 to the atmosphere.