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Saturday, October 27, 2012

Organic carbon on Mars is abiotic

The Tissint meteorite, a 58 gram sample of which is shown here, landed 
near Tata, Morocco in July of last year and was confirmed as martian in 
January. A new study shows that it and several other martian meteorites 
contain organic carbon of non- biological origin.
Photo credit: Department of Earth and Atmospheric Sciences, University of Alberta

Curiosity, NASA’s latest Mars rover, will begin its search for chemical evidence of past life on the red planet in early August. But according to a new paper in Science, the surface of Mars contains organic carbon generated by non-biological sources, which could make that search even harder.
Very rarely, material ejected from the surface of Mars by cosmic impacts can make its way to Earth in the form of meteorites. Only about 60 martian meteorites are known, eleven of which were part of the study conducted by an international team of experts, including Chris Herd of the Department of Earth and Atmospheric Sciences at the University of Alberta. Inside the martian minerals, the team found particles of carbon. “What's interesting about this stuff is that it’s not just graphite, it's organic macromolecular carbon,” says Herd. Organic carbon is present in the dust from which the solar system formed, as evidenced by primitive meteorites which can contain anything from polycyclic aromatic hydrocarbons to amino acids. Similar material would have been incorporated into Mars as it formed, stored in its interior, and could later have reached the surface by means of lava flows.
To test this theory, lead author Andrew Steele of the Carnegie Institution of Washington used confocal Raman spectroscopy, which allows for accurate determination of both the form and location of the carbon within a given meteorite’s crystal structure. In every case, the organic carbon particles were found in inclusions within igneous minerals. “The only way it could get there is if it was present in the original magma,” says Herd. “If it had been formed by some kind of biological process, you'd expect to find it associated with rust or material that formed through alteration by water, not with the igneous minerals.” Although the finding doesn’t completely rule out the possibility that Mars once harboured life, it serves as a reminder of just how hard Curiosity will have to work to prove otherwise.

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