ExoMars: Mars analogue rocks in the European lithotheque at Orleans
Résumé
ExoMars has joined up with the American Max-C rover in a joint, two rover mission to Mars in 2018. The science objectives of ExoMars are to search for traces of past or present life and to document the water/geochemical environment as a function of depth in the shallow subsurface. Max-C seeks to determine the habitability of the surface of Mars with the aim of selecting and caching rocks potentially containing traces of life for the future Mars Sample Return mission. The ExoMars rover will embark a number of scientific instruments to investi-gate rock outcrops and subsurface materials: for observation a variety of cameras and a close up imager, for mineralogy Raman and IR spectrometry as well as an XRD, and GCMS and LDMS for chemical characterisation of the organics. A drill will provide subsurface access to hopefully preserved organics. Max-C will be distinguished by a suite of arm-based tools for observation and mineralogical/elemental mapping. These instruments provide good compara-tive information. In order to optimize the science return of the various instrument suites, it will be useful to test flight instrumentation with the same suite of Mars-analogue rocks. With this objective in mind, a rock library or lithoth'que of rocks that have been fully characterised by standard laboratory instrumentation is being prepared by the Observatoire de l'Univers de la region Centre (OSUC) at Orléans. The ultimate goal is to offer the scientific community a lithoth'que coupled to a database comprising the maximum information on rocks that are analogues of Mars and other planetary bodies. The data base will contain both reference (lab) data and results from experiments using the planetary instruments or models. Here we present a preliminary selection of ten samples for testing the ExoMars instruments. Other samples will become ready as our lithotheque expands. The samples chosen cover a range of lithologies found on Mars -a variety of basalts (plus cumulates), a Late Archaean stromatolitic carbonate (Pongola, South Africa), Early-Mid Archaean shallow-water volcanic sands (Barberton, South Africa; the Pilbara, Australia), an Early Archaean banded iron formation (Pilbara), and a clay (nontronite). The four types of basalts include an ultramafic basalt from Svalbard (Norway) containing dunite xenoliths; an altered basalt from Tenerife (Spain), a primitive basalt from Stromboli (Italy), and silicified altered basalts from Barberton. Apart from their compositional relevance, many of the rocks were formed at a time period equivalent to the Noachian of Mars, and some of them contain fossil (and sometimes recent) biosignatures. These samples have been analysed by optical microscopy, Raman, IR and Müssbauer o