London - Martians may well have existed, but not in any recognisable form.
Scientists believe the discovery of minerals below the Red Planet's surface is the strongest evidence yet it may have supported life.
But far from hosting little green men, our celestial neighbour was likely inhabited by simple microorganisms.
A new study led by the Natural History Museum, with the University of Aberdeen, found that all the ingredients for life were present just below the planet's surface for much of its history.
When meteorites strike the surface of Mars, they act like natural probes, bringing up rocks from far beneath the crust.
Looking at data from NASA's Mars Reconnaissance Orbiter and ESA's Mars Express spacecrafts, they analysed rocks and found they contain clays and minerals whose chemical make-up has been altered by water.
With up to half of life on Earth consisting 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 and planetary geologist at the Natural History Museum 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.'
Some deep craters on Mars also acted as basins where groundwater likely emerged to produce lakes, which contain clay and carbonate minerals.
The fluids that formed these minerals could one day tell us more as to whether there was life beneath the surface, and also carry clues to how life developed on Earth.
Dr Michalski, whose study is published in the journal Nature Geoscience, said: 'We don't know how life on Earth formed but it is conceivable that it originated underground, protected from harsh surface conditions that existed on early Earth.
'Due to plate tectonics, however, the early geological record of Earth is poorly preserved so we may never know what processes led to life's origin and early evolution.
'Exploring these rocks on Mars, where the ancient geologic record is better preserved than on Earth, would be like finding a stack of pages that have been ripped out of Earth's geological history book.
'Whether the Martian geologic record contains life or not, analysis of these types of rocks would certainly teach us a tremendous amount about early chemical processes in the solar system.'
Nasa's Mars probe, the Curiosity rover, will begin drilling on the planet's surface in the next few days for rock samples.
It is the most highly anticipated milestone since the six-wheel, nuclear-powered rover landed near the Martian equator five months ago. - Daily Mail