The chances of anything coming from Mars have taken a downward turn with the finding that the surface of the red planet contains a “toxic cocktail” of chemicals that can wipe out living organisms.
Experiments with compounds found in the Martian soil show that they are turned into potent bactericides by the ultraviolet light that bathes the planet, effectively sterilising the upper layers of the dusty landscape.
The discovery has wide-ranging implications for the hunt for alien life on the fourth rock from the sun and suggests that missions will have to dig deep underground to find past or present life if it lurks there. The most hospitable environment may lie two or three metres beneath the surface where the soil and any organisms are shielded from intense radiation. “At those depths, it’s possible Martian life may survive,” said Jennifer Wadsworth, a postgraduate astrobiologist at Edinburgh University.
Wadsworth’s research was driven by the discovery of powerful oxidants known as perchlorates in the Martian soil some years back. Hints of perchlorates first showed up in tests performed by Nasa’s Viking lander missions 40 years ago, but were confirmed recently by the space agency’s Phoenix lander and Mars rover, Curiosity. In 2015, the Mars Reconnaissance Orbiter spotted signs of perchlorates in what appeared to be wet and briny streaks that seeped down Martian gullies and crater walls.
Many scientists suspected that perchlorates would be toxic for microbial Martians, but in theory at least, alien bacteria might find a way to use the chemicals as an energy source. If life could thrive in perchlorate-rich brines, then aliens might be thriving in the damp patches on Mars.
Working with Charles Cockell, an astrobiologist at Edinburgh, Wadsworth looked at what happened to Bacillus subtilis, a common soil bacterium and regular Earthly contaminant found on space probes, when it was mixed with magnesium perchlorate and blasted with ultraviolet rays similar to those witnessed on Mars. She found that the bugs were wiped out twice as fast when perchlorate was present. Other perchlorates found on Mars had a similar bactericidal effect.