Comparison of Orbital and in situ NIR-spectra in Jezreo Crater: insight from the first Supercam Infrared Spectrometer data

 

Introduction: On February 18, 2021, NASA’s Mars 2020 Perseverance rover landed successfully in Jezero crater, a 50 km crater located on the margin of the Isidis basin on Mars. The Mars 2020 mission is the first step of a Mars sample return campaign, as Perseverance has the capability of collecting and caching samples.

The detailed mineralogy of the landing site has been extensively studied using the OMEGA and CRISM Visible and Near infrared spectroscopic-imagers [1, 2]. Jezero crater displays a variety of spectral signatures that revealed a large variety of minerals. Several compositional units have been identified within Jezero crater [3,4]: a pyroxene-bearing cratered dark floor unit, an olivine-bearing unit exposed in erosional windows below the dark floor unit that is variably altered, including phyllosilicates and carbonates [5], and a deltaic complex and marginal carbonate-bearing unit [3]. Orbital observation of the distinctive compositional units are one of the assets of Jezero landing site probably related to the low dust coverage of the site (e.g. 4).

Perseverance landed in Octavia E. Butler Site, located within the dark crater floor unit and has started to investigate the rocks (float rocks as well as possible bedrock exposures) along its traverse.

The SuperCam instrument onboard Mars2020 contains a suite of techniques including passive spectroscopy in the 0.40-0.85 (VIS) and 1.3 to 2.6 microns (IR) wavelength ranges [6], therefore covering a similar range of wavelengths as the OMEGA and CRISM spectrometers that were used for the mineralogical assessment of Jezero before landing. During the first two months at the surface of Mars, >100 VISIR spectra were acquired both on the rocks around the rover [7] and at long distance (several kilometers) on targets of interest: the front of the Delta, Santa Cruz butte, and possible delta remnants like Kodiak mesa and Seitah deposits. A direct comparison between the orbital spectral signatures of the landing site and long distance targets is the purpose of this contribution.

Methods: We processed the CRISM data cube HRL000040FF covering both the landing site and the long distance observations performed by Perseverance. The processing included: calibration, correction from the atmospheric contribution and ratioing methods [8]. We processed SuperCam IR data by ratioing to the white calibration target first acquired on sol 20 . See also [9] for additional details of SuperCam’s IR processing. The preliminary residual atmospheric contribution for long distances is removed using a distance dependent model of atmospheric contribution scaled on the CO₂ 2 µm absorption band.

Results : From orbit, this dark crater floor unit Perseverance landed on is overall pyroxene-bearing, potentially calcium-rich [3, 4]. The delta front exhibits a spectral mixture of olivine, low calcium pyroxene (LCP) and phyllosilicates [3].  Santa Cruz also displays spectra with possible low calcium pyroxene spectral signatures mixed with hydrated mineral signatures, possibly phyllosilicates. The Seitah deposits are olivine-bearing deposits mixed with hydrated minerals [5].

SuperCam IR spectra of the rocks within the workspace show spectral signatures mainly dominated by a 1.9 µm absorption feature indicative of the presence of one or several hydration phases. Occasionally, this 1.9 µm feature appears correlated to the 1.4 and 2.28-2.3 µm bands, suggesting the presence of phyllosilicates. The rocks show some spectral diversity possibly indicative of iron-rich phyllosilicates and/or (oxy-)hydroxydes. The soils in the workspace are less hydrated than the rocks. . See also [10] for initial elemental composition results in the workspace. For the long distance observations, the front of the delta shows spectral signatures indicative of Fe-Mg phyllosilicates possibly mixed with low calcium pyroxene. The observation of Santa Cruz also reveals Fe-Mg phyllosilicates, potentially with a stronger spectral signature of  low calcium pyroxeneCP. The delta remnant Kodiak also shows phyllosilicates likely Fe-Mg. Finally, Seitah deposits observed at long distance display spectra in agreement with olivine and Fe-Mg phyllosilicates.

Discussion/Conclusion: Most of the IRS spectra confirm what has been observed from orbit  but there are also differences. The 1.9 µm band linked to hydration is deeper in all ground based observations. It seems that the hydrated phases are the most dominant spectral signal on the ground for the areas sampled so far. 

 

 

Figure 1 : Left : CTX image mosaic showing the different compositional unit and the locations of the SuperCam spectral observations as well as CRISM observation (the red square corresponds to Seitah observation, the blue square corresponds to Octavia E. Butler landing site). Right : IR spectra of CRISM data (3*3 averaged ratioed spectra);the spectra have been ratioed to the median of the column of the non-projected data cube HRL40FF [8]; offset of -0.6 has been applied for clarity; SuperCam results are an average of 20 spectra acquired on Seitah and average of >100 spectra acquired on the rocks of the rover workspace until Sol 70 .

 

References

[1] Mangold et al., JGR, 2007 [2] Murchie et al., JGR, 2009 [3] Horgan et al., Icarus, 2020 [4] Goudge et al., JGR, 2015  [5] Tarnas, et al., GRL, 2019. [6] Wiens, et al., Spectroscopy, 2017.  [7] Mandon et al., this conference ; [8] Quantin-Nataf et al., PSS, 2018. [9] Royer et al., this conference ; [10] Cousin et al., this conference