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Microorganisms may be able to survive just under the surface of Mars for far longer than researchers thought. In a new set of experiments, researchers found that dried-up bacteria could stay alive in Mars-like conditions for up to 280 million years, which would improve our chances of finding evidence for them if Mars ever hosted life.

Most previous experiments to test whether microorganisms could survive the intense radiation on Mars have used hydrated bacteria at room temperature – the longest-lived of those were thought to be able to survive for up to about a million years. at Northwestern University in Illinois and his colleagues took a different tack, desiccating a variety of bacteria and yeast and freezing them before subjecting them to radiation similar to what a buried life form on Mars would experience and measuring the damage.

“There’s this phenomenal multiplication of the resistance when you get rid of the water and you cool everything down,” says Hoffman. It is similar to freeze-drying food to make it last longer. Mars is dry and cold, so it is likely that any bacteria there would be as well. The researchers’ samples were damaged so little by the radiation that they estimated the bacteria could survive for up to about 280 million years.

If the freeze-dried bacteria were warmed up and exposed to water during that time, they would emerge from their dormant state. “It opens some possibilities that you could get revitalisation if a meteor with some water comes down and splashes on the surface, it could regenerate,” says Hoffman. “The probability that it’s still alive now has increased from zero to the tiniest thing you could imagine – it’s non-zero, but it sure as hell ain’t big.” It is estimated that Mars dried up about 3 billion years ago, so even the heartiest of bacteria are most likely dead by now.

This longevity could make it easier for us to find preserved evidence of any bacteria that once lived on Mars, but it also means that if we contaminate it with Earthly organisms, that contamination would be practically permanent.

“If we contaminate the area that we land in, how do we know whether what we find was there before we got there or whether it was something we deposited?” says Hoffman. “If we can’t tell what’s ours and what’s theirs, so to speak, then it’s impossible to tell whether there was life there.”