A new study by European scientists has suggested that intense ultraviolet radiation on Mars releases methane from organic materials which meteorites transport onto its surface.
This chart depicts the calculated methane concentrations in parts per billion on Mars during summer in the Northern hemisphere, violet and blue are indications for little quantities of methane, red areas for larger ones (NASA)
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, as on Earth methane is produced predominantly by biological processes. Another hypothesis assumed the source to be geological methane sources in Mars’ interior. To date, none of the theories has been able to conclusively explain the large quantity of 200 to 300 tones of methane annually which are produced on Mars, according to projections.
Without an expedition to Mars and with nothing more than a meteorite to help them, the researchers at the Max Planck Institute for Chemistry in Mainz, University of Utrecht and Edinburgh University have now found a major source.
They have suggested that methane escapes from a meteorite if it is irradiated with ultraviolet light under Martian conditions. Since meteorites and interplanetary dust from space, which carry along carbonaceous compounds, continuously impact on the Martian surface, the researchers have concluded that high-energy ultraviolet radiation may trigger the release of methane from the meteorites.
Unlike our planet, Mars has no protective ozone layer which could absorb most of the ultraviolet radiation from space. Moreover, the Martian atmosphere is very thin, so that a significantly smaller portion of the meteoritic material burns up in the atmosphere compared to Earth.
To confirm their theory, the researchers irradiated samples of the Murchison meteorite with ultraviolet light. This 4.6 billion-year-old meteorite fell to Earth in 1969 in the Australian town of Murchison. The researchers selected conditions identical to those on Mars for the ultraviolet irradiation, which caused considerable quantities of methane to escape from the meteorite almost immediately.
“The meteorite contains several percent of carbon and has a similar chemical composition to most of the meteoritic matter that lands on Mars,” explained Dr Ulrich Ott, a co-author of the study published in Nature.
Since the temperature on the Red planet varies from -143 degrees Celsius at the poles to 17 degrees Celsius at equator, the scientists also investigated the meteoritic samples at appropriate conditions. The warmer the meteoritic fragments became, the more methane was released. This temperature dependence also agrees with the different methane concentrations at different locations in the Martian atmosphere.
“Methane is produced from innumerable, small micro-meteorites and interplanetary dust particles that land on the Martian surface from space,” concluded Dr Frank Keppler of the Max Planck Institute for Chemistry, a lead author of the study. “The energy is provided by the extremely intense ultraviolet radiation.”
However, the researchers said they cannot fully exclude the hypothesis of Martian microbes.
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Bibliographic information: Keppler F., Vigano I., McLeod A., Ott U., Früchtl M. and Röckmann T. 2012. Ultraviolet radiation induced methane emissions from meteorites and the Martian atmosphere. Nature, 31 May 2012. doi 10.1038/nature11203
