Craters from asteroid impacts may be one of the best places to look for life on Mars, a study suggests.
Scientists have found microbes thriving more than a mile under a US crater where a space rock smashed into the Earth 35 million years ago.
They believe craters may provide a refuge protecting bugs from events such as ice ages or global warming.
Drilling beneath crater sites on Mars could potentially uncover similar life forms, say the scientists.
Researchers from the University of Edinburgh drilled almost two kilometres (1.24 miles) below one of the biggest asteroid impact craters on Earth at Chesapeake Bay in Virginia.
Samples revealed microbes spread unevenly through the rock.
Heat from an asteroid collision would kill everything living at the surface. But deep fractures in the rock would allow water and nutrients to flow in and support life, the researchers believe.
Professor Charles Cockell, from the University of Edinburgh's School of Physics and Astronomy, said: "The deeply fractured areas around impact craters can provide a safe haven in which microbes can flourish for long periods of time. Our findings suggest that the subsurface of craters on Mars might be a promising place to search for evidence of life."
The findings are published in the journal Astrobiology.