Hydrogen detection with ChemCam at Gale crater

International audienceOne of the main advantages of ChemCam’s LIBS (Laser-Induced Breakdown Spectroscopy) instrumentonboard the Curiosity rover is its potential to detect light elements such as hydrogen at fine scales, whichhas never been achieved on Mars. Hydrogen lines are detected in most of the data obtained within thefirst 320 sols of the mission at Gale crater, Mars. This work is a description of the hydrogen signal andits variability in the ChemCam LIBS spectra; it discusses the challenges of qualitative and quantitativeanalysis. Data acquisition and processing steps are investigated and optimized for the detection of hydrogenon Mars. Subtraction of an appropriate dark spectrum and the deconvolution of the superimposedemission 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 investigatedwithin groups of targets sharing common chemical features and similar matrices. The differentgroups cover a variety of rock and soil compositions encountered along the traverse (calcium sulfateveins, 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 higherhydrogen signals than rocks and pebbles, probably as a result of their alteration. The results from rockssuggest that various alteration processes leading to their hydration have taken place, which is consistentwith the fluvial lacustrine context, the diagenetic features, and the mineralogy observed by Curiosity inYellowknife Bay