Investigation on the Clay-Carbonate Mixture with SuperCam/IRS, Perseverance Rover
Résumé
The Perseverance rover (Mars 2020 mission, NASA) is exploring the mineral diversity of the paleolake within Jezero crater and is searching for potential biosignatures and past habitability. Amongst its science payload, the SuperCam instrument plays a central role in the Mars habitability investigation by providing rapid, synergistic, fine-scale mineralogy, chemistry, and color imaging [1, 2]. In particular, it carries the first near-infrared spectrometer, IRS, to be operated on the Martian surface. IRS is a miniaturized point spectrometer (1.15 mrad field of view) located in the SuperCam’s mast unit. Its spectral range (1.3 – 2.6 µm range) covers major silicate, salts and hydrated mineral absorption features [3].
Mineral identifications are performed by analyzing the position and shape of diagnostic absorption bands. The recent results on the instrument’s radiometric calibration [4] enabled the identification of a 2.50 - 2.53 µm absorption feature attributable to carbonates. Carbonates also exhibit a 2.3 µm band similar to the 2.30 - 2.33 µm Fe/Mg-OH band of several phyllosilicates. Thus, this 2.5 µm feature is key to decorrelate the presence of phyllosilicates and carbonates. In the Crater Floor unit, it has been identified only in the Séitah formation, with the support of LIBS investigation [5], and many occurrences have been detected in the Delta.
The study of the band depth ratio between the 2.3 and 2.5 µm bands, in terms of detection quality (signal to noise ratio, Fig. 1), shows that positive carbonates detections are consistent with phyllosilicate-carbonate mixtures with a low Mg/Fe-carbonate content. In the Crater Floor, this low carbonate content in presence of phyllosilicates and silicates points towards an alteration of the mafic phase with a CO2-rich fluid. Work is in progress to better understand deconvolution of carbonates from phyllosilicates.