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Make yourself at home (Image: David Howells/Corbis)

LANDING humans on Mars won鈥檛 wreck the search for life on the Red Planet. That鈥檚 according to researchers who simulated the impact of a crewed mission to a pristine world by driving across the Canadian Arctic.

Space agencies currently take great care to sterilise spacecraft bound for Mars, to avoid contaminating the planet with Earth microbes that could make it harder to find native Martian life.

But humans are impossible to sterilise. We are crawling with microbes, inside and out, so when we eventually go to Mars, the risk of contamination will be high.

聯Humans are impossible to sterilise, so when we go to Mars the contamination risk should be high聰

Or at least, that鈥檚 what we had assumed. To find out, Andrew Schuerger of the University of Florida in Gainesville and Pascal Lee of the SETI Institute in Mountain View, California, took advantage of an Arctic road trip.

During a series of trips between April 2009 and July 2011, Lee was part of a team driving a specialised vehicle from mainland Canada to the inhospitable Devon Island, the site of a simulated Mars mission.

Although the main purpose of the trip was to deliver the vehicle to Devon Island, the team also took the opportunity to simulate the activities of a crewed rover on another planet, with the pristine snow and sea ice they drove over standing in for Mars.

During a week-long drive in April 2009 between Kugluktuk and Cambridge Bay, the team made three stops. At each, they took samples from inside the vehicle as well as the surface snow 10 metres away, to see the extent of their microbial footprint.

鈥淲e had a wonderful opportunity to sample the snow and try to get some measure of how far microorganisms were being dispersed,鈥� says Schuerger.

The samples were frozen, then later melted and cultured in the lab to look for bacteria and fungi. It turned out that 85 different microorganisms were found inside the rover, but only one bacterium and one fungus grew in samples from the snow outside (Astrobiology, ).

The pair also found that levels of microbes in the rover declined over time, suggesting the threat of contamination will fall as crewed missions progress. The intense UV radiation on Mars should help to keep things contained, says Schuerger: the vast majority of microbes will be killed after around 15 minutes of exposure. Even fossilised microbes won鈥檛 last long enough to be a concern, new research suggests (see 鈥�Ancient aliens? Not so fast鈥�).

鈥淭hese results are a huge surprise,鈥� says Alberto Fair茅n of Cornell University in Ithaca, New York. 鈥淭he theory says that the moment a human sets a foot on Mars, every effort to prevent contamination of the planet would go out the window.鈥�

Fair茅n has previously argued that space agencies are being too cautious when it comes to Mars 鈥� sterilisation and other planetary protection for the Viking Mars landers in the 1970s cost $100 million. 鈥淎 serious rethinking of where time and money are allocated in planetary exploration is clearly in order,鈥� he says.

NASA鈥檚 planetary protection officer Catharine Conley points out that the methods the pair used wouldn鈥檛 necessarily catch all microbes, so contamination could be worse than they measured. The search for life on the Red Planet is so important that extreme caution is a must if we want to find a true Martian microbe, she says. 鈥淭he more contamination you have, the less easy it is to figure out whether [a Martian microbe] is real.鈥�

This article appeared in print under the headline 鈥淢essy humans won鈥檛 spoil Mars鈥�