^1,2P. Beck et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115840]
¹Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France
²Univ. Grenoble Alpes, ISTerre, F-38000 Grenoble, France
Copyright Elsevier

Onboard NASA’s Curiosity rover, the ChemCam LIBS instrument has provided a wealth of information on the chemistry of rocks within Gale crater. Here, we use ChemCam in order to search for carbonates among the >3500 individual targets analyzed by this instrument. Because the carbon-lines are a combination of signal from the CO2-rich atmosphere and possible carbon from the targets, we developed a laboratory-based univariate calibration obtained under Mars-like atmosphere. We measured different type of carbon-bearing samples (sediments, coals, carbonates) and their mixture with a basaltic powder. Based on this work, the preferred approach to qualitatively assess carbon under a CO2-rich atmosphere is to use a ratio to an oxygen line (777 nm) and the estimated limit of detection for carbon in a single LIBS point are found to be of 4.5 wt% and 6.9 wt% for reduced and organic carbon, respectively. Considering carbonate, this LOD correspond to about 50 wt% carbonate in the analyzed volume.

Analysis of data obtained on Mars by ChemCam up to sol 3350 reveals the presence of a correlation between the intensity of carbon and oxygen lines, as observed in the laboratory, confirming that most carbon signal is related to ionization of the atmosphere. Some variability in the carbon signal appears related to the physical state of the atmosphere (density, temperature).

Based on a combined analysis of carbon lines and major element compositions (Ca, Fe, Mg), there was no detection of carbonate in the ChemCam dataset up to sol 3355. Therefore, we conclude that carbonate was not present as a major constituent (>50%) in the ChemCam LIBS targets, and that soils are not enriched in carbon beyond the limit of detection. The dominant salts present are sulfate, chlorides, and the lack of carbonates in Gale, while observed in Jezero, may at least partly be related to a difference in protolith.

¹M. S. Huber,^1,2E. Kovaleva,³A. S. P. Rae,^4.5N. Tisato,^4,5,6S. P. S. Gulick
Journal Geophysical Research (Planets) (in Press) Open Access Link to Article [10.1029/2022JE007721]
¹Department of Earth Science, University of the Western Cape, Bellville, South Africa
²Helmholtz Centre Potsdam, GFZ, Potsdam, Germany
³Department of Earth Sciences, University of Cambridge, Cambridge, UK
⁴Department of Geological Sciences, Jackson School of Geoscience, University of Texas at Austin, Austin, TX, USA
⁵Center for Planetary Systems Habitability, University of Texas at Austin, Austin, TX, USA
⁶Institute for Geophysics, Jackson School of Geoscience, University of Texas at Austin, Austin, TX, US
Published by arrangement with John Wiley & Sons

The record of terrestrial impact events is incomplete with no Archean impact structures discovered, despite the expected abundance of collisions that must have occurred. Because no Archean impact structures have been identified, the necessary conditions to preserve an impact structure longer than 2 Byr are unknown. One significant effect of shock metamorphism is that the physical properties of the target rocks change, resulting in distinctive geophysical signatures of impact structures. To evaluate the preservation potential of impact structures, we evaluate the deeply eroded Proterozoic Vredefort impact structure to examine the changes in physical properties and the remnant of the geophysical signature and compare the results with the well-preserved Chicxulub impact structure. The major structural features of Vredefort are similar to the expected profile of the Chicxulub structure at a depth of 8–10 km. The Vredefort target rocks, while shocked, do not preserve measurable changes in their physical properties. The gravity signature of the impact structure is minor and is controlled by the remnant of the collapsed transient crater rim and the uplifted Moho surface. We anticipate that erosion of the Vredefort structure by an additional 1 km would remove evidence of impact, and regardless of initial size, erosion by >10 km would result in the removal of most of the evidence for any impact structure from the geological record. This study demonstrates that the identification of geologically old (i.e., Archean) impact structures is limited by a lack of geophysical signatures associated with deeply eroded craters.