Curiosity identifies the nature of the hydration of the Martian soil

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During the first 100 days spent at the surface of Mars, the ChemCam instrument onboard the Curiosity rover was able to remotely analyze a large number of samples of the Martian soil with an unprecedented accuracy. These first analyzes carried out by researchers from IRAP (OMP – University of Toulouse III – Paul Sabatier / CNRS) in collaboration with the Franco-American teams of ChemCam showed a large chemical diversity of the finest grains of the Martian soil, but also that the grains the richest in iron and magnesium are hydrated. According to the authors, this moisture could be an important part of the water tank on the surface of Mars observed during previous missions. The origin of this reservoir is one of the keys to the understanding of the evolution of the Martian climate. This work is published in the journal Science on September 27, 2013, in a series of five articles devoted to the first results of Curiosity .

The chemical composition, mineralogy and physical properties of the Martian soil are indicators of the erosion, weathering and transport processes that have altered the surface of the planet over geological time. The analysis of the Martian soil therefore makes it possible to study the evolution of the planet’s environment and climate, itself closely linked to the evolution of the water cycle on which the conditions of habitability of the planet depend. Moreover, meteorite bombardment and wind erosion have also contributed to homogenize the surface composition, so soil analysis may provide access to the average composition of the planet’s crust.

Images of the Martian ground before and after the ChemCam laser shots. 1: Mastcam image 2: RMI ChemCam images Credits: NASA/JPL-Caltech/LANL/CNES/IRAP/IAS/CNRS

The Curiosity rover, which has been scouring the bottom of Gale Crater since August 6, 2012, has a number of new instruments on board to characterize the Martian soil, including the ChemCam instrument. This Laser Induced Breakdown Spectrometer (LIBS) coupled with a camera (Remote Microscopic Imager) allows sub-millimetre scale analyses of the chemical composition of the Martian soil, revealing possible mixtures between different chemical poles and determining its

During the first 100 days of the mission, ChemCam remotely analyzed approximately 140 soil samples along a nearly 400-metre traverse. These analyses revealed a great chemical diversity associated with different grain sizes. The coarsest gravels (a few millimetres) are rich in silicon, aluminium and alkalis (felsic composition). This first category, close to the landing site, seems to result from the mechanical erosion of conglomerates of fluvial origin, probably carried from the rim of Gale Crater by the Peace River. This type of composition had not yet been encountered by previous missions.

The second chemical pole analyzed, richer in iron and magnesium (mafic composition), is associated with the finest grains of sand, which are found incorporated in all the soils analyzed, particularly in wind formations. The ChemCam and APXS (Alpha Particle X-ray Spectrometer) instruments showed that its chemical composition was close to that of soils analysed in other regions by the Sojourner, Spirit and Opportunity rovers, and close to the composition of atmospheric dust. Nevertheless, this composition differs from that of the surrounding rocks. These results suggest either global mixing processes that homogenized the smaller grains of the Martian soil, or the preponderance of regions of similar basaltic composition.
In addition, ChemCam analyses revealed that this fine fraction of soil and atmospheric dust were hydrated. Curiosity stopped for several weeks to analyze more finely a small sand dune called Rocknest sand shadow. This step was an opportunity to use the analytical capabilities of the two instruments CheMin (X-ray diffraction) and SAM (Sample Analysis on Mars, measuring volatile organic and inorganic compounds). Their combined analyses indicate that fine soil hydration is associated with an amorphous phase, rather than hydrated crystalline phases. The chemical similarity between these samples and those analysed elsewhere on the planet probably allows the results obtained by Curiosity to be extrapolated to a more global scale. For example, variations in the hydrogen content of the Martian surface, measured from orbit by the Mars Odyssey probe, could be explained by different proportions of this soil type and hydrated phase. Finally, ChemCam analyses suggest that diurnal water vapour exchanges with the atmosphere are limited.

The measurements made by ChemCam, coupled with the analyses of the other Curiosity instruments, thus allow a better understanding of the chemical diversity of the Martian soil, its hydration, and its relationship with the geological context of the Gale crater and Mars as a whole.

Mars Curiosity’s ChemCam instrument at work analyzing the composition of the Martian soil. Credits: NASA/JPL-Caltech

French laboratories involved in MSL :

  • Institut de Recherche en Astrophysique et Planétologie (CNRS/Université Toulouse III -Paul Sabatier)
  • Laboratoire atmosphères, milieux, observations spatiales (CNRS/Université Versailles Saint-Quentin-en-Yvelines/Université Pierre et Marie Curie, IPSL)
  • Laboratoire Interuniversitaire des Systèmes Atmosphériques (CNRS/Université Paris-Est Créteil/Université Paris Diderot, IPSL)
  • Géologie et Gestion des Ressources Minérales et Energétiques (CNRS/Université de Lorraine, Nancy)
  • Géosciences Environnement Toulouse (CNRS/Université Toulouse III – Paul Sabatier, CNES, Institut de Recherche pour le Développement)
  • Institut d’Astrophysique Spatiale (CNRS/Université Paris Sud, Orsay)
  • Institut de Physique du Globe de Paris (CNRS/Universités de Paris-Diderot, Paris)
  • Institut des Sciences de la Terre (CNRS/Universités de Savoie/Université Joseph Fourier, Institut de Recherche pour le Développement, Institut Français des Sciences et Technologies des Transports, de l’Aménagement et des Réseaux, Grenoble)
  • Laboratoire de Géologie de Lyon, Terre, Planètes, Environnement (CNRS/Université Claude Bernard, ENS Lyon)
  • Laboratoire de Planétologie et de Géodynamique de Nantes (CNRS/Université de Nantes, Nantes)
  • Laboratoire de Minéralogie et Cosmochimie du Muséum (CNRS, Muséum National d’Histoire Naturelle)


  • Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars P.-Y. Meslin, O. Gasnault, O. Forni, S. Schröder, A. Cousin, G. Berger, S. M. Clegg, J. Lasue, S. Maurice, V. Sautter, S. Le Mouélic, R. C. Wiens, C. Fabre, W. Goetz, D. Bish, N. Mangold, B. Ehlmann, N. Lanza, A.-M. Harri, R. Anderson, E. Rampe, T. H. McConnochie, P. Pinet, D. Blaney, R. Léveillé, D. Archer, B. Barraclough, S. Bender, D. Blake, J. G. Blank, N. Bridges, B. C. Clark, L. DeFlores, D. Delapp, G. Dromart, M. D. Dyar, M. Fisk, B. Gondet, J. Grotzinger, K. Herkenhoff, J. Johnson, J.-L. Lacour, Y. Langevin, L. Leshin, E. Lewin, M. B. Madsen, N. Melikechi, A. Mezzacappa, M. A. Mischna, J. E. Moores, H. Newsom, A. Ollila, R. Perez, N. Renno, J.-B. Sirven, R. Tokar, M. de la Torre, L. d’Uston, D. Vaniman, A. Yingst, MSL Science Team. Science, Vol. 341,

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