An international team involving five French laboratories, including IRAP (University Paul Sabatier of Toulouse & CNRS) identifies traces of ancient continental crust on Mars. This work was published in the journal Nature Geoscience.
Until now, Mars was seen as a planet almost entirely covered with basaltic rocks, dark rocks that on Earth form the ocean floor. But the walls of the Gale Crater, where Curiosity landed, contain fragments of very old (about 4 billion years old) and lighter rocks, which the ChemCam laser microprobe provided the composition. Scientists from France (1) and the United States have analysed the images and chemical data of 22 of these rock fragments. Verdict: they are light rocks, rich in feldspar and sometimes quartz, similar to the granitic continental crust found on Earth. More specifically, these relics of primitive Martian crust closely resemble the TTG (Tonalite-Trondhjemite-Granodiorite) complexes, the dominant rocks in the Earth’s crust during the Archean era (more than 2.5 billion years ago). This is the first evidence of the existence of continental crust on Mars (2). This work is published in the journal Nature Geoscience.
This discovery was made possible because the Gale Crater, formed 3.61 billion years ago in older terrain, is a veritable window into the primitive rocks of the Red Planet. Its walls offer a natural geological cross-section 2 to 3 kilometres thick, whereas the spectrometers of the orbiting probes only analyse the surface over a few tens of micrometres (millionths of a metre).
This work has received financial support from NASA (Mars Exploration Program) and CNES.
(1) The French laboratories involved are :
- the Institute of Mineralogy, Physics of Materials and Cosmochemistry (CNRS/UPMC/IRD/MNHN), in Paris
- the Institute for Research in Astrophysics and Planetology (CNRS/University Toulouse III – Paul Sabatier), in Toulouse
- the Georessources laboratory (CNRS/University of Lorraine/CREGU), in Nancy
- the Nantes Laboratory of Planetology and Geodynamics (CNRS/University of Nantes/University of Angers)
- the Grenoble Institute of Planetology and Astrophysics (CNRS/UJF)
(2) Until now, there were only clues: clear rocks spotted by orbiting probes, but no information on their composition or age. Or the Martian meteorite Black Beauty, containing feldspars more than 4 billion years old.
- Article : In-situ evidence for continental crust on Early Mars, V. Sautter, M. J. Toplis, R. C. Wien, A. Cousin, C. Fabre, O. Gasnault, S. Maurice, O. Forni, J. Lasue, A. Ollila, J. C. Bridges, N. Mangold, S. Le Mouélic, M. Fisk, P.-Y. Meslin, P. Beck, P. Pinet, L. Le Deit, W. Rapin, E. M. Stolper, H. Newsom, D. Dyar, N. Lanza, D. Vaniman, S. Clegg and J. J. Wray. Nature Geoscience , 13 juillet 2015. DOI: 10.1038/ngeo2474
- Web INSU : “Curiosity trouve des traces d’une croûte continentale primitive sur Mars”
- Olivier Gasnault, IRAP, email@example.com, 05 61 55 75 53