A huge crater on the surface of Mars may hold the strongest evidence yet that there was life on the Red Planet.
Research published in the journal 'Nature Geoscience' suggests that the components required to sustain simple microorganisms could have been present on Mars for much of its history.
Scientists studying the McLaughlin crater, which was made when a meteorite smashed into the surface of the planet, believe that the ingredients of life may have been present in the "Martian subsurface" - a zone up to three miles beneath the surface.
A number of rocks thrown up by the impact of the meteorite contain minerals and clay whose chemical structure appears to have been altered by water.
Professor John Parnell, of Aberdeen University, and Dr Joseph Michalski, lead author and planetary geologist at the Natural History Museum, now believe the findings could show life existed below the surface of Mars.
The discovery came after the scientists scrutinised data from the powerful Mars Reconnaissance Orbiter and ESA's Mars Express spacecrafts.
With over half of life on earth being made up of simple microorganisms that live in below the surface, scientists have suggested that the same may have been true for Mars.
Dr Joseph Michalski, lead author of the study said: 'All the ingredients were there for life, but only small single-cell organisms could have survived in those conditions.
'But I would now be more surprised if there was never any life on Mars, than I would be if we did one day discover that simple life lived in that environment. 'And if life existed then, there is a chance it could still exist now.'