Existence of life in Mars was once a hypohethesis (Mars Rover sIntroduction)

One of NASA's two Mars Rovers (Image: NASA)

In space, a year can be a long time. Back at the beginning 2004, the idea that the Red planet had once been covered with rivers, lakes and seas was just a hypothesis. By 2005, two quad-bike-sized, roving laboratories had collected abundant evidence on the ground that turned the idea into an established fact, including stratified sediments, and minerals that probably formed in the presence of water.

At the beginning of 2004 it was scientific heresy even to talk of the possibilityof life existing today on Mars and previous missions had been ill-equipped to detect it. But with the proof that water might have lasted for aeons - plus evidence from the European Space Agency's Mars Express orbiter that there was recently methane in the atmosphere - it became a subject for serious discussion. Water is a pre-requisite for life as we know it, and, on Earth at least, most methane is produced by living organisms.