Martian Meteorites Contain Abiotic Carbon

Although scientists have debated the possible biogenic origins of large organic molecules found in numerous martian meteorites, two new studies suggest that the molecules formed during volcanic processes. In the first study, Andrew Steele at Carnegie Institution for Science and colleagues examined 11 martian meteorites that had fallen to Earth, using confocal Raman imaging spectroscopy (Science, DOI: 10.1126/science.1220715). They found the large organic molecules encapsulated within tiny volcanic olivine and pyroxene crystals that formed as magma from martian volcanoes cooled. The second report, in press in American Mineralogist, focused on ALH84001, the famous martian meteorite that contained putative biogenic compounds within carbonate globules (DOI: 10.2138/am.2012.4148). Steele’s group detected graphite—a key indication of abiotic processes—in the globules. The results suggest, the authors say, that reduced organic carbon is nearly ubiquitous in martian basaltic rocks and that it formed via igneous, not biological, processes. The authors caution eager martian life seekers looking forward to results from the Mars Science Laboratory (MSL): “A positive detection of organics (especially polycyclic aromatic hydrocarbons) on Mars by MSL may be detecting this abiotic carbon reservoir.”