In less than 100 days, the most ambitious Mars mission ever devised is due to land on the Red Planet. Mars Science Laboratory
's main task is to search for signs of life, a $2.5 billion testament to our desire to know for sure whether we are alone in the universe.
Don't expect a straight answer. The search for life on Mars isn't black and white. Consider recent findings that Earthly bacteria can survive on Mars (see "Martian austerity no barrier to life").
This is a mixed blessing for alien hunters. It suggests Mars is habitable, and that any life that evolved there may be clinging on. But it also means any such discovery will be tinged with doubt. Unless Martian life is distinct from life as we know it, how do we rule out the possibility that it is actually from Earth?
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