Planetary Lunch Seminar (PLS) – Eva Scheller (MIT)

Title: Characterizing Mars’ carbonate sink with Raman spectroscopy on the Perseverance rover

Abstract:

Mars’ present atmosphere is thin (6.35 mbar) and its surface is frozen, but geological evidence suggests past liquid water. This would have required a thicker atmosphere of one to several bars of CO2 that was lost over time. Two dominant mechanisms are thought to be responsible for this loss of CO2: (1) atmospheric escape and (2) crustal carbonate formation. Carbonate minerals typically form when CO2 dissolved in water reacts with rocks and form weathering products. However, satellite infrared spectroscopy has observed very little carbonate on Mars, giving rise to the “missing carbonate problem on Mars”.

The strongest orbital signals of carbonate minerals on Mars, attributed to hydrated magnesium carbonate, occur in Jezero crater. We use the SHERLOC and PIXL instruments on the Perseverance rover to study the abundance, chemistry, and formation environment of carbonate minerals in Jezero crater. We observed carbonate in many geological regions where carbonate was not detected from orbit. We found that anhydrous Fe/Mg-dominated carbonate formed: (1) in reactions of liquid water with olivine-rich igneous rocks, and (2) through carbonate cementation of sandstone in a fluvial-lacustrine sedimentary environment. These observations show that orbital observations underestimate the abundance of carbonate minerals on Mars and that the reactions of minerals in ancient olivine-rich Mars crust with water form Fe/Mg-carbonate minerals rather than hydrated magnesium carbonates. These insights lead to new constraints on the formation, distribution and abundance of carbonate on Mars, and reconstructions of its past climate.