Terrestrial microbes that hitch a ride to Mars on spacecraft may be able to survive under special circumstances, according to a new laboratory study.

The research suggests scientists should take extra care when analysing potential signs of life during future missions to the Red Planet.

Most spacecraft that touch down on Mars have not been thoroughly sterilised by heat or radioactivity – so they carry with them living microbes from Earth. But Mars’s thin atmosphere allows such intense ultraviolet radiation to reach the planet’s surface – triple that found on Earth – that any life inadvertently carried on the spacecraft is thought to be wiped out quickly. Indeed, Martian-level doses of UV radiation have destroyed some microbe species in just seconds in laboratory tests.

But now, an international team has tested the endurance of a particularly hardy type of blue-green alga – or cyanobacterium – that thrives in dry deserts from Antarctica to Israel. The resilient bacterium, called Chroococcidiopsis sp. 029, was chosen as a “worst-case scenario” for contamination of the planet.

The team found that dormant spores of the bacterium had mostly died after five minutes of Martian UV exposure. However, the bacteria were able to stay alive if they were shielded by just 1 millimetre of soil during the tests, which ran for up to 24 hours.

By Maggie McKee

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