Hydrogen detection with ChemCam at Gale crater

S. Schröder (1) , P.-Y. Meslin (1) , O. Gasnault (1) , S. Maurice (1) , A. Cousin (2) , R.C. Wiens (2) , W. Rapin (1) , M.D. Dyar (3) , N. Mangold (4) , O. Forni (1) , M. Nachon (4) , S. Clegg (2) , J.R. Johnson (5) , J. Lasue (1) , S. Le Mouélic (4) , A. Ollila (6) , P. Pinet (1) , V. Sautter (7) , D. Vaniman (8)

1 IRAP - Institut de recherche en astrophysique et planétologie
2 LANL - Los Alamos National Laboratory
3 Department of Astronomy
4 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
5 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
6 IOM - Institute of Meteoritics [Albuquerque]
7 MNHN - Muséum national d'Histoire naturelle
8 PSI - Planetary Science Institute [Tucson]

One of the main advantages of ChemCam’s LIBS (Laser-Induced Breakdown Spectroscopy) instrument onboard the Curiosity rover is its potential to detect light elements such as hydrogen at fine scales, which has never been achieved on Mars. Hydrogen lines are detected in most of the data obtained within the first 320 sols of the mission at Gale crater, Mars. This work is a description of the hydrogen signal and its variability in the ChemCam LIBS spectra; it discusses the challenges of qualitative and quantitative analysis. Data acquisition and processing steps are investigated and optimized for the detection of hydrogen on Mars. Subtraction of an appropriate dark spectrum and the deconvolution of the superimposed emission of carbon from the low-pressure CO2-dominated atmosphere are particularly important. Because the intensities of hydrogen are also affected by matrix effects, the hydrogen signal was investigated within groups of targets sharing common chemical features and similar matrices. The different groups cover a variety of rock and soil compositions encountered along the traverse (calcium sulfate veins, mafic soils, felsic, Mg-rich and Fe-rich rocks) including data from both drill holes and their tailings. Almost all these targets were found to be hydrated to variable extents. Soils have systematically higher hydrogen signals than rocks and pebbles, probably as a result of their alteration. The results from rocks suggest that various alteration processes leading to their hydration have taken place, which is consistent with the fluvial lacustrine context, the diagenetic features, and the mineralogy observed by Curiosity in Yellowknife Bay.

Domaines: Planète et Univers [physics]

S. Schröder, P.-Y. Meslin, O. Gasnault, S. Maurice, A. Cousin, et al.. Hydrogen detection with ChemCam at Gale crater. Icarus, 2015, 249 (1), pp.43-61. ⟨10.1016/j.icarus.2014.08.029⟩. ⟨hal-01131364⟩