Meteors and Micrometeorites
The data provide a very strong argument that at least some particular SNC meteorites comes from Mars. There are now eightteen SNC meteorites known in total. The two SNC meteorites EETA79001 and ALH84001 supply new and highly interesting information. A subsample of EETA79001, excavated from deep within the meteorite, has been subjected to stepped-combustion. The CO2 release from 200°C to 400°C suggests the presence of organic molecules.
Because Mars had a warm and wet climate in the past, its surface must be covered by both impact generated regolith and sedimentary rocks deposited by running and/or still water. Such consolidated sedimentary hard rocks should be among the Martian meteorites but are not known. It is possible that they did survive escape acceleration from the Martian surface but did not survive terrestrial atmospheric entry because of decrepitation of the cementing mineral. The STONE experiment is aimed at studying the physical and chemical modifications in sedimentary rocks during atmospheric infall.
A basalt, a dolomite (sedimentary rock) and an artificial Martian regolith (80% crushed basalt and 20% gypsum) were embedded into the ablative heat shield of Foton 12 which was launched on September 9 and landed on September 24, 1999. The recovered entry samples were analyzed for their chemistry, mineralogy and isotopic compositions by a European consortium. Atmospheric infall modifications are made visible by reference to the untreated samples. The results suggest that some Martian sediments could in part survive terrestrial atmospheric entry.
Even if the evidence for ancient life in ALH84001 is not firmly established, two SNC meteorites show the presence of organic molecules, suggesting that the ingredients required for the emergence of a primitive life may have been present on the surface of Mars. Therefore, it is tempting to consider that microorganisms may have developed on Mars until liquid water disappeared. Since Mars probably had no plate tectonics and since liquid water seems to have disappeared from the Mars surface very early, the Martian sub-surface perhaps keeps a frozen record of the very early forms of a terrestrial-like life.
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