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Article Dans Une Revue Planetary and Space Science Année : 2020

Geological appraisals of core samples using the ExoMars 2020 rover instrumentation

Frédéric Foucher
Steven Pelletier
  • Fonction : Auteur
Fabio Messori
  • Fonction : Auteur
Frances Westall

Résumé

The ExoMars 2020 mission will characterise a Martian locality with potential former habitability-Oxia Planumand attempt to identify preserved physical and chemical biosignatures. The payload will include a drill retrieving cores from the subsurface (up to 2 m depth), which will be imaged at high resolution by two instruments: the Panoramic Camera High Resolution Camera (PanCam HRC) and CLose UP Imager (CLUPI). These instruments will provide guiding interpretation and govern the approach used by the analytical instruments, which will conduct their analyses after crushing of the core sample. Blind tests using Mars-analogue lithological samples provide valuable mission training in terms of maximising scientific return. Previous blind tests evaluating the abilities of ExoMars 2020 payload to conduct geological approaches used solid rock hand samples as test specimens. Here, we prepared samples of ExoMars mission-equivalent shapes and dimensions (3 x 1 cm cores). Imaging these samples using mission-equivalent original resolutions to avoid image processing artefacts, we found that the difficulty inherent in making definitive geological conclusions using traditional 'field petrography' approaches is increased when only limited amounts of core sample are available for observation. Issues inherent in interpreting core samples include scale-representativeness, distinction between layer-specific characteristics at the sub-centimetre to centimetre scale, mechanical effects, such as drill marks and dust covering, and correlation between analyses of the outcrop and the core. These issues vary depending upon the rock type and change as a function of the mechanical properties (and thus composition) of the sample. Despite these challenges, we find that CLUPI and PanCam HRC images alone allow many accurate and detailed geological observations; however, confidence and detail of interpretation are notably increased when additional geochemical data are provided, in this case, Raman spectra reflecting the contribution of the Raman Laser Spectrometer (RLS) instrument. Our results argue for the importance of core imaging during the experimental phase of the rover mission despite the challenges involved in interpretation, since HRC and CLUPI images offer a great degree of synergy. Inter-instrumental collaboration will be essential during the ExoMars 2020 rover mission (and indeed in any rover mission), since no single payload instrument is able to perform a comprehensive assessment of a putative biosignature within its geological context, and since the instrument suite provides highly complementary data at multiple scales that are key to maximising scientific return.
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Dates et versions

hal-03025724 , version 1 (26-11-2020)

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Keyron Hickman-Lewis, Frédéric Foucher, Steven Pelletier, Fabio Messori, Frances Westall. Geological appraisals of core samples using the ExoMars 2020 rover instrumentation. Planetary and Space Science, 2020, 180, pp.104743. ⟨10.1016/j.pss.2019.104743⟩. ⟨hal-03025724⟩
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