It was already nicknamed 鈥淐onan the Bacterium鈥� for its ability to withstand radiation. Now it seems Deinococcus radiodurans could, in theory, survive dormant on Mars for over a million years.
at University College London and colleagues froze the bugs to -79 掳C, the average temperature at Mars鈥檚 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.
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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. 鈥淐old is good in that respect,鈥� Dartnell says. 鈥淚t improves the chances of cells surviving radiation.鈥�
Antarctic bugs
Dartnell鈥檚 team also isolated three new strains of bacteria from the Dry Valleys of Antarctica, where winter temperatures drop to -40 潞C.
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鈥檚 work suggests.
鈥淭he more we learn about Earth life, the more likely it appears that it could survive in other parts of the solar system,鈥� says Cassie Conley of NASA in Washington DC.
High vacuum
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. 鈥淚n space, you suck off nearly all the water molecules,鈥� 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鈥檚 policy on planetary protection already takes into account that some microbes are amazingly radiation resistant.
鈥淭he policy is that we won鈥檛 contaminate other planets or moons, because just one colonising event could screw up our ability to study indigenous life forever,鈥� she told 麻豆传媒.
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