Curiosity, the NASA Martian vehicle, after landing in August 2012 in the Gale crater impact, moved towards a small depression, about 500m away, called “Yellowknife Bay.” This area is of high interest for the researchers, since it appears to host lake deposits. International teams, involving French researchers, in collaboration with the CNES1, have studied in detail the first samples of these sedimentary rocks. Analyses of these rocks show an ancient Martian environment distinct from the current environment and maybe more similar to that of the Earth more than 3 billion years ago. These works form the basis of four publications to appear this week in the journal Science2.
I – A river-lake area environment observed in Yellowknife Bay, Gale Crater, MarsA
The Curiosity rover has observed sedimentary rocks whose fineness of the grains indicates that they were once deposited at the bottom of a lake in the Gale crater. This deposit environment could have provided for a possible primitive life on the surface due to favorable chemical conditions such as neutral pH, low salinity and variable redox of both iron and sulfur. Key elements forming living organisms are carbon, hydrogen, oxygen, sulfur, nitrogen and phosphorus – they were detected by the rover in these sediments. Those favorable conditions may have lasted a few hundred to tens of thousands of years, highlighting the interest of the river-sediment context observed by Curiosity.
II – Elementary geochemistry of sedimentary rocks from Yellowknife Bay, Gale crater, MarsB
The fluvio-lacustrine sediments analyzed come from the erosion of igneous rocks, whose composition resembles that of the average Martian crust, which were present on the walls of the Gale crater. The fine lacustrine sediments at the basis of the series do not contain pronounced evidence of tampering, which suggests an arid deposit context, perhaps in cold conditions. The absence of chemical changes suggests that the magnetite and the clay minerals identified by the CheMin instrument [cf Article Vaniman et al. , below], and which show up a notable alteration, formed after the deposition of the sediments by fluid circulation of relatively neutral pH. A second alteration phasis has subsequently given rise to many structures as clear veins, raised wrinkles and nodules analyzed by ChemCam, respectively revealing compositions of calcium sulfates type (such as gypsum) and enrichments in magnesium and chlorine. Thus, the geochemistry of Yellowknife Bay reveals a complex history from the sediment deposition until altered by fluids during burial (diagenesis) .
III – Mineralogical composition of rocks drilled in Yellowknife BayC
Sediment drilled by Curiosity were analyzed by the CheMin instrument that performed an analysis of X-ray diffraction revealing the mineralogy of the deposits. These show a high diversity with minerals typical of usual basaltic rocks (feldspar, pyroxene, olivine) but also iron sulphides, calcium sulphates, clay minerals (smectite) and amorphous phases. The small amount of olivine compared to the surrounding sediments suggests a transformation in situ of the olivine in smectite and magnetite during the early diagenesis of the sediments.
IV – Organic and volatile composition of sedimentary rocks from Yellowknife BayD
At Yellowknife Bay, drilling (6.4 cm depth) of the sedimentary
stratigraphic unit allowed to collect unaltered rocks with deposits of
calcium sulfate (CaSO4) coming from the precipitation of a liquid phase
rich in salts.
The drilling of these reddish rocks showed a greenish gray powder, which testifies a lack of oxidation at depth. The heating of the sample by the SAM (Sample Analysis at Mars) instrument produced water into two phases. The first one is due to the release of adsorbed water during the dehydration of minerals (such as CaSO4(H2O)0.5 bassanite). The second one, at higher temperature, is largely due to the dehydroxylation of clays (smectite, saponite). Some of these minerals was observed by CheMin which analyzed by X-ray diffraction, the same powder. The second peak was not observed in the sand of Rocknest, it brings out the aqueous character of the sedimentary rocks analyzed in Yellowknife Bay.
As in Rocknest, the scientists have observed the production of O2 and HCl and the presence of perchlorates (eg. CaClO4), previously observed by the rover Phoenix in 2009, but close to the North Pole. Chlorinated hydrocarbons (CH3Cl, CH2Cl2, etc..) are also present. They come from reactions between the perchlorates and traces of heavy organic compounds onboard SAM to enable the analysis of complex molecules. However, differences appear between the amounts of chlorinated hydrocarbons observed in the analysis of Rocknest (sand, a priori low organic matter) and those observed at Yellowknife (sedimentary rock). Work in progress deal with other types of organic molecules, in order to conclude on the presence or absence of organic molecules belonging to Mars.
- List of French laboratories actively participating in the project Mars Curiosity, through the ChemCam (Chemical Camera) and SAM (Sample Analysis at Mars) instruments. The CNES, the French space agency, is the prime contractor of the French contribution to Curiosity. Scientists and engineers pilot together ChemCam and SAM, especially from a mission center based at the CNES in Toulouse, the FIMOC. • 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)
• Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA)
• GéoRessources (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 d’Astrophysique de Bordeaux (CNRS/Université de Bordeaux1)
• 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)
• Laboratoire Biominéralisations et Paléoenvironnements (CNRS/Université Pierre et Marie Curie)
• Laboratoire de Génie des Procédés et Matériaux (Ecole Centrale de Paris)
• Laboratoire Synthèse et Réactivité des Substances Naturelles (CNRS/Université de Poitiers)2. The set of four articles on Science website : http://www.sciencemag.org/site/extra/curiosity/index.xhtml3. List of the Curiosity instruments : http://mars.nasa.gov/msl/mission/instruments/4. Cf. L.A.Leshin et al. DOI 101126/science.1238937 (2013) : http://www.sciencemag.org/content/341/6153/1238937.abstract
- A : Grotzinger et al., A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars. Contribution française : N. Mangold, S. Maurice, G. Dromart.
- B : Source : Mc Lennan et al., Elemental Geochemistry of Sedimentary Rocks in Yellowknife Bay, Gale Crater, Mars. Contribution française : A. Cousin, G.Dromart, C. Fabre, O. Forni, O. Gasnault, S. Le Mouelic, N. Mangold, S. Maurice, M. Nachon.
- C : Vaniman et al., Mineralogy of a mudstone on Mars. Contribution française : S. Maurice, G. Berger.
- D : Ming et al., Volatile and Organic Compositions of Sedimentary Rocks in Yellowknife Bay, Gale crater, Mars. Contribution française : M. Cabane, P. Coll, P. François, C. Szopa, S.Teinturier.
- Sylvestre Maurice, firstname.lastname@example.org
- Olivier Gasnault, email@example.com
- Olivier Forni, firstname.lastname@example.org
- Gilles Berger, email@example.com