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 鈥� so they carry with them living microbes from Earth. But Mars鈥檚 thin atmosphere allows such intense ultraviolet radiation to reach the planet鈥檚 surface 鈥� triple that found on Earth 鈥� 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 鈥� or cyanobacterium 鈥� that thrives in dry deserts from Antarctica to Israel. The resilient bacterium, called Chroococcidiopsis sp. 029, was chosen as a 鈥渨orst-case scenario鈥� for contamination of the planet.
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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.
Making a living
Under such a protective coating, the bacteria 鈥渃ould survive 鈥� and potentially grow 鈥� under the high Martian UV flux if water and nutrient requirements for growth were met鈥�, write the researchers in the journal Astrobiology.
鈥淲e think there are places on Mars where Earth life could make a living,鈥� says John Rummel, NASA鈥檚 planetary protection officer in Washington, DC, who is charged with preventing microbes from contaminating worlds beyond Earth. He says this study shows 鈥渆ven the toughest stuff doesn鈥檛 survive for long鈥� on the surface of spacecraft, but he says live microbes probably do take shelter within the spacecraft bodies.
So if a Mars rover fell off a cliff or a spacecraft broke open in a crash 鈥� like NASA鈥檚 lost Mars Polar Lander may have 鈥� these microbes might find a toehold for survival provided they landed in the right place, he says.
Such places include Martian gullies that may periodically be flooded with liquid water, or areas around the poles, where 鈥渕icrobes and ice could make a happy partnership鈥�, Rummel told New 杏吧原创.
Fake signature
Another finding in the study may also help shape future missions to Mars, says Andrew Schuerger, one of the research team. He is a plant pathologist at the University of Florida in Gainesville and conducts research at NASA鈥檚 Kennedy Space Center.
The study revealed that the 鈥渂iogenic鈥� signs of life, including the molecular signatures of DNA and chlorophyll, are detectable for hours 鈥� and perhaps much longer 鈥� after the bacteria themselves have died. So Schuerger says future lander missions to Mars should contain experiments to detect both life itself 鈥� in the form of live cells 鈥� as well as these signature molecules.
鈥淚 think it was common to believe that finding one or the other was enough to say there was life,鈥� Schuerger told New 杏吧原创. 鈥淏ut you have to look for both simultaneously to be sure you鈥檙e detecting life on Mars 鈥� or life from Earth that made the trip to Mars.鈥�
