It was already nicknamed "Conan the Bacterium" for its ability to withstand radiation. Now it seems Deinococcus radiodurans could, in theory, survive dormant on Mars for over a million years.
Lewis Dartnell at University College London and colleagues froze the bugs to -79 °C, the average temperature at Mars's mid-latitudes. Then they zapped them with gamma rays to simulate the dose they would receive under 30 centimetres of Martian soil over long periods of time.
The team worked out that it could take 1.2 million years under these conditions to shrink a population of the bacteria to a millionth of its original size.
Earlier studies suggested that the bacterium can endure four times as much radiation in the Martian cold as at room temperature. If a cell is frozen, radiation does less damage to it because the free radicals it creates are much less mobile. "Cold is good in that respect," Dartnell says. "It improves the chances of cells surviving radiation."
Dartnell's team also isolated three new strains of bacteria from the Dry Valleys of Antarctica, where winter temperatures drop to -40 ºC.
The hardiest of the bugs, a new strain of Brevundimonas, could persist for 117,000 years on Mars before its population would be reduced by a factor of a million, the team's work suggests.
"The more we learn about Earth life, the more likely it appears that it could survive in other parts of the solar system," says Cassie Conley of NASA in Washington DC.
But even if terrestrial microbes could survive on Mars itself, they might not fare so well on the journey there, she cautions. To simulate spaceflight, she suggests that the experiments be repeated in a high vacuum, which can desiccate microbes. "In space, you suck off nearly all the water molecules," Conley says. This removal of water could make it more difficult for cells to repair radiation damage.
Conley, who makes sure NASA missions minimise the risk of contaminating other worlds with microbes, says the agency's policy on planetary protection already takes into account that some microbes are amazingly radiation resistant.
"The policy is that we won't contaminate other planets or moons, because just one colonising event could screw up our ability to study indigenous life forever," she told New Scientist.
Journal reference: Astrobiology (DOI: 10.1089/ast.2009.0439)
This post originally appeared on New Scientist.