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Interview in Mars mineralogy and surface water evolution

Jean-Pierre Bibring
Mars Express OMEGA Principal Investigator and ExoMars Microscope co-Team Coordinator, Institut d'Astrophysique Spatiale, France

Subjects: Mars mineralogy and surface water evolution
As the person responsible for the mineralogical mapping spectrometer on board Mars Express, you have been actively involved in Martian science for many years. Which one of your team’s discoveries do you consider most important?

OMEGA has profoundly revised the history of Mars, on the basis of minerals identified at its surface, which record the evolution of its environment.

My answer to your question about what I consider most important would be the discovery, identification and mapping of hydrated phyllosilicates (clays) a specific family of minerals formed by aqueous alteration. By finding and studying them, OMEGA has opened a window in ancient Mars History during which Mars might have harboured a key ingredient for habitability: stable liquid water.

Does this relate to the search for traces of life on Mars, and how?

Yes it does. It indicates where one should search for potential bio-relics.

If life ever emerged on Mars, it likely required liquid water to be stable for long durations. The discovery of hydrated phyllosilicates in the most ancient terrain indicates that such conditions might have occurred. In the search for sites and samples that have preserved this past record: phyllosilicate-rich areas are favoured targets for future in-situ missions. Potential bio-relics would be associated with such minerals.

As team coordinator of the MicrOmega instrument on board ExoMars, what are your expectations for the future?

Supposing ExoMars lands in a phyllosilicate-rich area, that will be extremely exciting. MicrOmega would be able to analyse, at microscopic scales, the structure and composition of samples of key relevance to astrobiology. It would study the association of phyllosilicates and other phases such as carbonates, on which carbon-rich molecules might have grown.

If life ever started on Mars, MicrOmega would be in position to identify bio-relics and their mineralogical environment, either or both through their structure and molecular composition.

Note for Clay
Clay is a naturally occurring material, composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when fired or dried, and variable amounts of water trapped in the mineral structure by polar attraction. Organic matter and materials which do not impart plasticity may also be a part of clay deposits.

Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. These solvents (usually acidic) migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lake and marine deposits.

Release link: http://www.esa.int/esaCP/index.html