As a new Nasa rover explores the surface of Mars looking for ancient life, could living things be lurking right beneath its wheels?
A new study has suggested that not only could life survive beneath the surface of Mars, it could still be there now.
Future missions to the red planet could use drills to reach such life-forms, the researchers say.
Researchers analysed meteorites from Mars that landed on Earth, looking for rocks that could sustain buried communities of microbes.
They found that the rocks (if in contact with water) could produce enough chemical energy to support microbial communities, similar to ones seen deep under the Earth.
The findings suggest that much of the Mars subsurface could be habitable.
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Jesse Tarnas, a postdoctoral researcher at Nasa's Jet Propulsion Laboratory, said: "The big implication here for subsurface exploration science is that wherever you have groundwater on Mars, there's a good chance that you have enough chemical energy to support subsurface microbial life.
"We don't know whether life ever got started beneath the surface of Mars, but if it did, we think there would be ample energy there to sustain it right up to today."
Scientists have discovered that Earth's depths are home to a vast biome that exists largely separated from the world above.
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Lacking sunlight, these creatures survive using the byproducts of chemical reactions produced when rocks come into contact with water.
One of those reactions is radiolysis, which occurs when radioactive elements within rocks react with water, breaking water molecules into their constituent elements, hydrogen and oxygen.
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Microbes can ingest the dissolved hydrogen as fuel and use the oxygen to "burn" that fuel.
In places like Canada's Kidd Creek Mine, microbes have been found living more than a mile underground, in water that hasn't seen the light of day in more than a billion years.
For this new study, the researchers wanted to see if the ingredients for radiolysis-driven habitats could exist on Mars.
The study found that in several different types of Martian meteorites, all the ingredients are present in adequate abundances to support Earth-like habitats.
Recent advances in small drill probes could soon put the Martian depths within reach.
Professor Jack Mustard of Brown University said: "The subsurface is one of the frontiers in Mars exploration. We've investigated the atmosphere, mapped the surface with different wavelengths of light and landed on the surface in half-a-dozen places, and that work continues to tell us so much about the planet's past.
“But if we want to think about the possibility of present-day life, the subsurface is absolutely going to be where the action is."
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