Igneous rock powder identification using colour cameras: A powerful method for space exploration

1F.Foucher,1N.Bost,2G.Guimbretière,1,3A.Courtois,4 K.Hickman-Lewis,1,3E.Marceau,5P.Martin,1F.Westall
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114848]
1CNRS, Centre de Biophysique Moléculaire, UPR4301, 3E avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
2CNRS, Laboratoire de l’Atmosphère et des Cyclones, UMR8105, 15 avenue René Cassin, 97744 Saint-Denis Cedex 9, La Réunion, France
3Université d’Orléans, Château de la Source, avenue du Parc Floral, BP 6749, 45067 Orléans Cedex 2, France
4Department of Earth Sciences, The Natural History Museum, Cromwell Rd, South Kensington, London SW7 5BD, United Kingdom
5CNRS, Laboratoire de Physique et de Chimie de l’Environnement et de l’Espace, UMR73028, 3E avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
Copyright Elsevier

Powdered rocks are commonly present at the surface of extraterrestrial bodies and are widely analysed by in situ space probes. Moreover, a number of rovers exploring the surface of Mars are equipped with drills enabling them to access unaltered material and collect samples. During drilling operations, a cone of powder made of the drilled materials forms at the surface. These powders will be particularly large during the ESA/Roscosmos ExoMars 2022 mission since the rover Rosalind Franklin will drill to 2 m depth below the Martian surface. These fines are generally observed by the rovers’ cameras after the drilling process and analysed by a limited range of instruments. In order to maximise the scientific return of planetary missions to Mars and other bodies in the solar system, we propose to use the images taken by rover cameras to identify the composition of the powdered materials. This could be particularly useful during the ExoMars 2022 mission where the CLUPI camera will take pictures during drilling and could thus document changes in the regolith composition (Josset et al., 2017). In the absence of a controlled light source, we used an image processing method called CaliPhoto that we previously developed for generic purposes. To test the ability of the method to identify volcanic rocks, more than twenty Mars-analogue samples were crushed at various grain sizes and photographed. The images were then processed via the CaliPhoto method and used to construct a database of reference images. New images were then taken under different lighting conditions, processed using the same method, and compared to the database. We show that it is possible to estimate igneous rock powder lithology with greater than 90% accuracy considering the uncertainties. Furthermore, when using images of polished and powdered samples, identification reaches 100%. We also show that the method permits precise lithological identification of samples that are not in the initial database. Finally, we demonstrate that the proposed method is extremely efficient, while at the same time very easy to implement on any in situ space probe. It could thus be used to help in identifying powdered igneous rocks during future missions to Mars or other rocky body in the solar system.

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