Meteorites found on the surface of Mars may contain fossilised evidence of life 鈥� which could be investigated by current and future rovers on the Red Planet.
When meteorites fall on Earth they are known to experience rapid contamination by microbes. These can leave telltale markers of their presence behind. For instance, some may burrow into the meteorite and create microscopic tunnels. Others might subtly change the chemical composition of the rock. But it was unclear how successfully meteorites might preserve this evidence.
at Monash University in Australia and his colleagues analysed seven meteorites they found on the Nullarbor plain in southern Australia, some of which landed up to 40,000 years ago. They found that all contained evidence of fossilised microorganisms, which had become entombed within the meteorite, as well as chemical changes wrought by the microbes. 鈥淣o one鈥檚 really looked at meteorites preserving microbes before,鈥� says Tait.
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About 3 billion years ago, Mars may have had the necessary conditions for life, including a thicker atmosphere and liquid water on its surface. Tait says that any meteorites that fell on Mars before or during this period, in a habitable location, could have been contaminated by Martian life in the same way meteorites falling to Earth become contaminated by terrestrial life. 鈥淭hey would have essentially been a time capsule,鈥� he says.
A Martian meteorite recovered on Earth in 1996, Allan Hills 84001, was once thought to contain evidence of life, but .
at the University of Glasgow, UK, says that meteorites聽on Mars were already known to offer a 鈥渞eally good鈥� record of the geologic history of the planet. 鈥淭hey are pristine when they arrive and distinct from the Martian surface,鈥� she says, so they could feasibly contain a record of past habitability. 鈥淚f there was life, you would expect to see evidence of that.鈥�
However, meteorites that have been sitting on the surface of Mars for billions of years will have been bombarded by radiation, perhaps erasing any such evidence. 鈥淭he radiation environment would be a big factor,鈥� she says.
Dozens of meteorites have been found on Mars by current and former rovers. Tait says such rocks could be prime targets for signs of ancient life, both by NASA鈥檚 Perseverance rover that is currently on Mars and collecting samples to return to Earth, and ESA鈥檚 upcoming ExoMars rover, which has been delayed by Russia鈥檚 invasion of Ukraine.
Tanja Bosak from the Massachusetts Institute of Technology, part of a team selecting samples for Perseverance to collect for possible return to Earth, says there are no plans for the rover to gather meteorites yet. 鈥淚t鈥檚 hard to recognise a rock as a meteorite,鈥� she says. 鈥淲e don鈥檛 have the time to stop and examine all random rocks.鈥�
Sara Motaghian at Imperial College London, however, is developing analytical tools for ExoMars鈥� cameras to quickly identify meteorites on Mars. She says the same tools could be used by Perseverance. 鈥淲e can study them with the drill or by crushing them with the wheels,鈥� she says, noting that the interiors of some Mars meteorites could even provide shielding from radiation and be 鈥渢iny habitats鈥� for life that may be there now.
Even if the rovers don鈥檛 directly sample meteorites, Tait says that some of the samples returned by Perseverance will contain meteoritic material that has been mixed into the Martian soil. 鈥淚f some of those fragments are big, we might be able to look for life,鈥� he says.
Astrobiology
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