We will know by 2018

clouds on mars by FlyingSinger

Spaceman
[Via BBC News | Science/Nature | World Edition]

Methane on Mars: Esa and Nasa get down to business

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Funny to think we sent men to the moon in about the same time it will take us to send this mission to Mars. Perhaps it has something to do with an accommodating launch data for getting to Mars the most efficiently.

But they seem to have things planned out well, with a set of rovers to follow up and look at any site that has high levels of methane. One of the possibly interesting things will be if the ratios of C12/C13 in the methane (which is CH4) are different than expected.

Life on Earth likes C12 better than C13, whereas there is no selection from volcanoes. So, an altered ratio could be indicative of life.