Comparison of orbital and Supercam in situ investigation of the floor Units of Jezero crater

On February 18, 2021, NASA’s Mars 2020 Perseverance rover landed successfully on the floor of Jezero crater. Two geological and compositional units had previously been identified from orbital data analysis within the floor of Jezero crater [1,2]: a dark pyroxene-bearing floor unit and an olivine-bearing unit exposed in erosional windows [3]. During the 420 first sols of the mission, the rover has completed an in situ exploration campaign of these two units.

The SuperCam instrument contains a suite of techniques including passive spectroscopy in the 0.40-0.85 (VIS) and 1.3-2.6 microns (IR) wavelength ranges, Raman spectroscopy, Laser Induced Breakdown Spectroscopy (LIBS) and a camera providing high resolution context images [4,5]. Since the landing, SuperCam has acquired more than 3 thousands of observations.

From orbit the two geological units in the floor of Jezero have distinctive morphology and spectral signature. The crater floor unit called Cf-fr (Crater floor fractured rough) has a pyroxene signature [2] with no clear evidence of alteration.  The unit is laying on the top of the olivine rich unit. The interpretations varied from lacustrine deposits to volcanic deposits. The underlying unit seems to be part of the regional olivine-rich deposits with parts altered into carbonates and clays [1,6]. Interestingly, this regional olivine rich unit has a unique spectral signature on Mars, an effect of either grain size or composition [7]. Many hypotheses have been suggested: Isidis impact related ejectas layer [8], pyroclastic deposits [i.e. 6] or clastics deposits [9].   

In situ, we discovered that the Cf-fr, composed of different sub-units is not layered, composed of grainy rocks, dominated by plagioclase and Fe-rich pyroxenes [10] with a restricted but pervasive multistage [10]. From in situ data, Maaz is interpreted lava flows [11, 12] emplaced before the last lacustrine activity associated with the main western delta fan. Below the cf-fr, Seitah occurs as layered Mg-olivine rich rocks generally flat but slightly plunging below Maaz on the edges. The rocks are dominated by mm grains of pristine Olivine and some pyroxenes [10, 13, 14] .  The various spectroscopic methods detected alteration phases such as Mg- phyllosilicate and Mg Carbonates. [15, 16]. The rock texture and petrology of Seitah were interpreted as an olivine cumulate with limited alteration.

Lessons learned from this in situ campaign will be presented such as how accurate are the orbital spectral analyses, the morphological analysis and how to transfer the results of Jezero to the other places on Mars investigate by orbital data only.  

References :  [1] Horgan et al., 2020 [2] Goudge et al., 2015  [3] Tarnas, et al., 2021. [4] Wiens, et al., 2021. ; [5]  Maurice et al., , 2021 ; [6] Mandon et al., 2020.  [7] Ody et al.,2013   [8] Mustard et al., 2006 [9] Rogers et al., 2018, [10] Wiens et al., 2021 ; [11] Udry et al., 2022, [12] Horgan et al., 2022, [13] Liu et al., 2022, [14] ; Beyssac et al., 2023 [15] Mandon et al., 2022 [16] Clave et  al., 2022.