Did ‘Martian’ methane signal come from Earth? – space – 23 December 2010 – New Scientist

Claims that Mars’s atmosphere contains methane, which have fuelled speculations that the planet hosts life, may be premature.

A key piece of evidence for methane on Mars may actually be due to Earth-based methane, say researchers led by Kevin Zahnle of the NASA Ames Research Center in Moffett Field, California. “This is not a done deal,” says Zahnle, despite a widespread perception that methane has been found on the Red Planet.

The clearest evidence for methane on Mars came in 2009 from a team led by Michael Mumma at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. They used ground-based telescopes to look at light emitted by Mars and attributed dips in the spectrum to martian methane absorbing those frequencies.

The readings, taken several years apart, suggested that methane’s lifetime in the Martian atmosphere is unexpectedly – and inexplicably – short. While most researchers have assumed that this was due to an as-yet-unknown Martian process, Zahnle’s team offers an alternative explanation: the dips in the spectrum are not due to alien methane.

Spectral dips

Mumma’s team focused on readings taken when Mars was either moving toward or away from Earth, when any dips in its light would be shifted to higher or lower frequencies and so could be separated from dips caused by methane in Earth’s atmosphere. But Zahnle’s team notes that the frequency of a spectral dip attributed to Martian methane could also be caused by earth-based methane containing carbon-13 instead of the more common carbon-12 isotope.

Mumma, however, is confident his team measured Martian methane. “My group does not publish until we’re certain we’ve exhausted all other possible explanations,” he says.

Clearer answers to the methane question may be on the way soon, with the launch of NASA’s Mars Science Laboratory (MSL) rover in 2011 and a joint NASA-ESA orbiter called the Trace Gas Orbiter scheduled for launch in 2016.

In June, Mumma and colleagues also finished a 10-month-long campaign to hunt for Martian methane using three large telescopes in Chile and Hawaii. They hope to have new methane results in a few months to help NASA whittle down a set of four potential landing sites for MSL. The rover is set to launch in November 2011.

via Did ‘Martian’ methane signal come from Earth? – space – 23 December 2010 – New Scientist.

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