Radiation-tolerant microbes might be able to live beneath Mars’ surface for hundreds of millions of years and may yet persist today, thanks in part — counterintuitively — to the Red Planet’s frigid, arid conditions.
Martian surfaces are constantly exposed to cosmic rays, charged particles, and other radiation coming from space. Previous studies have shown that desiccation vastly extends a microbe’s potential for surviving by limiting the production of highly reactive oxygen-bearing chemicals that can damage proteins and DNA, among other vital molecules within its tissues. To see how long microbes might survive such an onslaught on Mars, researchers desiccated five species of bacteria and one type of yeast, stored them at −80° Celsius and then irradiated them.
Experiments showed that some microbes may not be viable for more than a few thousands of years. But one species — Deinococcus radiodurans, a particularly radiation-hardy greebly that some scientists have nicknamed “Conan the bacterium” — They could live up to 280,000,000 years if they are protected from radiation at ground depths of 10 metres or moreBrian Hoffman, a physical chemist, and his colleagues report online on October 25, Astrobiology.
D. radiodurans Radiation damage is prevented by multiple copies of the chromosomes in each cell. High levels of manganese antioxidantsThat help to eliminate DNA-damaging chemicalsSN: 9/3/10). If similar microbes evolved on Mars, they too could persist for lengthy intervals, even possibly until now — which is “improbable but not impossible,” says Hoffman, of Northwestern University in Evanston, Ill.
Even if microbes that evolved on Mars ultimately succumbed to the harsh conditions, remnants of their proteins or other macromolecules may remain — offering hope that future missions, if equipped with the proper equipment, might be able to detect those signs of former life.
