Radio-tolerant microbes could live under the Martian surface for hundreds of millions of years and still persist today, in part — counterintuitively — in the cold and dry conditions of the Red Planet.
The Martian surface, in addition to being cold and dry, was constantly emitting cosmic rays, charged particles and other radiation from space. Previous studies have shown that dehydration greatly extends the ability of microbes to survive by limiting the production of highly reactive, painful chemicals that can damage proteins and DNA, among other vital molecules in their tissues. To see how long the microbes could survive such an attack on Mars, the researchers dried five species of bacteria and one type of yeast, placed them at 80° Celsius and then irradiated them.
Experiments have shown that some microbes could remain viable for only a few tens of thousands of years. but one species – Deinococcus radioduransA particularly radiation-hardy strain, which some scientists have dubbed the “Conan bacterium,” could have survived for as long as 280 million years if shielded from radiation at depths of 10 meters or more, physicist Brian Hoffman and colleagues report online Oct. 25. in Astrobiology.
D. radiation resists radiation damage by having multiple copies of chromosomes and other genetic material in each cell, as well as carrying high levels of manganese and enzymes that help remove DNA-damaging chemicals (SN: 9/3/10). If similar microbes evolved on Mars, they could persist even over long distances, possibly even now — which is “unlikely but not impossible,” says Hoffman, of Northwestern University in Evanston, Ill.
Although the microbes that evolved on Mars eventually died out in the harsh conditions, the remnants of proteins or other macromolecules remain – they offer hope that future missions, if equipped with the proper instruments, will be able to detect those signs of previous life.
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