Take a piece of a meteorite and irradiate it with UV light – and methane is produced! This happens in the lab of the Atmospheric Physics and Chemistry Group at the IMAU, but likely also on Mars. So life is not necessary to explain methane on Mars.
It was a sensation when scientists discovered methane in Mars’ atmosphere nine years ago. Many saw the presence of the gas as a clear indication of life on the inhospitable planet, because on Earth methane is produced predominantly by biological processes. Measurements largely performed at Utrecht University, in collaboration with the Max Planck Institute for Chemistry in Mainz and the University of Edinburgh have now been able to show that methane escapes from a meteorite if it is irradiated with ultraviolet light under Martian conditions.
Unlike Earth, Mars has no protective ozone layer that could absorb most of the UV radiation from space. Moreover, the Martian atmosphere is very thin, so that a smaller portion of the meteoritic material burns up in the atmosphere compared to Earth. The meteorite matter used in the experiments in the APCG laboratory stems from the Murchison meteorite, a 4.6 billion-year-old meteorite fell to Earth in 1969 in the Australian town of Murchison. It contains several percent carbon and has a similar chemical composition to most of the meteoritic matter that lands on Mars. Under irradiation conditions similar to those on Mars, the meteorite emitted considerable quantities of methane almost immediately. This shows that carbonaceous compounds in the meteoritic matter are decomposed by the high-energy UV radiation, and methane molecules are formed in the process. Methane was the primary product, and the results indicate that a large fraction of the carbon content of meteorites could be transformed to methane.
The findings could dampen the hopes of all those who firmly believe in the biological origin of the methane on Mars. However, the new results cannot exclude the existence of Martian microbes. Still, they present a rather straightforward explanation for methane on Mars, for which life is not necessary. The researchers hope that Curiosity, the Mars Rover that NASA expects to land on our neighboring planet at the beginning of August, will provide more details on the formation of methane, and maybe even final clarification as to whether there is life on Mars.
Ultraviolet radiation induced methane emissions from meteorites and the Martian atmosphere, Frank Keppler, Ivan Vigano, Andy McLeod, Ulrich Ott, Marion Früchtl and Thomas Röckmann, Nature, 31 May 2012; DOI 10.1038/nature11203 (2012)