Carbonate Detection with SuperCam in Igneous Rocks on the floor of Jezero Crater, Mars

Perseverance explored two geological units on the floor of Jezero Crater over the first 420 Martian days of the Mars2020 mission. These units, the Maaz and Seitah formations, are interpreted to be igneous in origin, with traces of alteration. We report the detection of carbonate phases along the rover traverse based on laser-induced breakdown spectroscopy (LIBS), infrared reflectance spectroscopy (IRS), and time-resolved Raman (TRR) spectroscopy by the SuperCam instrument. Carbonates are identified through direct detection of vibrational modes of CO3 functional groups (IRS and TRR), major oxides content, and ratios of C and O signal intensities (LIBS). In Seitah, the carbonates are consistent with magnesite-siderite solid solutions (Mg# of 0.42-0.70) with low calcium contents (<5 wt.% CaO). They are detected together with olivine in IRS and TRR spectra. LIBS and IRS also indicate a spatial association of the carbonates with clays. Carbonates in Maaz are detected in fewer points, as: (a) siderite (Mg# as low as 0.03); (b) carbonate-containing coatings, enriched in Mg (Mg# similar to 0.82) and spatially associated with different salts. Overall, using conservative criteria, carbonate detections are rare in LIBS (similar to 30/2,000 points), IRS (similar to 15/2,000 points), and TRR (1/150 points) data. This is best explained by (a) a low carbonate content overall, (b) small carbonate grains mixed with other phases, (c) intrinsic complexity of in situ measurements. This is consistent with orbital observations of Jezero crater, and similar to compositions of carbonates previously reported in Martian meteorites. This suggests a limited carbonation of Jezero rocks by locally equilibrated fluids. Plain Language Summary Carbonates are mineral phases that generally form by alteration of primary, magmatic minerals. This alteration process may occur under a variety of environmental conditions, which affect the resulting carbonate phase: its abundance, composition, spatial distribution and the mineral phases it is associated with. Consequently, carbonates keep track of the environmental conditions under which they formed, and in particular, the amount of CO2 and liquid water involved in their formation. Understanding the history of both water and CO2 on Mars is critical to better understand the evolution of the red planet and its atmosphere, but also the origin of the water on Earth, and possibly the origin of life. Since the beginning of the Mars2020 mission in Jezero Crater, the SuperCam instrument has analyzed more than 200 rocks of the crater floor, and detected carbonates along Perseverance's traverse. Carbonates are found in low amounts, and are therefore complex to identify; we use SuperCam's combination of investigation techniques and a specifically developed methodology to strengthen the identification of carbonate phases and their characterization. Even though Jezero crater hosted a lake billions of years ago, the detected carbonates appear to have formed in smaller amounts of water, after the lake had disappeared.