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?????????????????????????????????????????????????Friday, July 7, 2017
Mars covered in toxic chemicals that can wipe out living organisms, tests reveal
Discovery
has major implications for hunt for alien life on the red planet as it
means any evidence is likely to be buried deep underground
Mars is bathed in ultra violet light which turns the Martian soil sterile. Photograph: Reuters
Ian Sample Science editor-Thursday 6 July 2017
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.
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.
Further tests found that the UV rays broke down the perchlorate into
other chemicals, namely hypochlorite and chlorite, and it is these that
appear to be so destructive to the bacteria.
The scientists followed-up with another round of experiments that looked
at the toxic effects of iron oxides and hydrogen peroxide, which are
also found in Martian soil. These tests yielded even more bad news for
microscopic Martians: when the bacteria were hit with UV rays in the
presence of perchlorates, iron oxide and peroxide, the bugs were killed
11 times faster than with perchlorates alone. Writing in Scientific Reports,
the researchers say that the inhospitable conditions on Mars are caused
by a “toxic cocktail of oxidants, iron oxides, perchlorates and UV
irradiation.”
The findings mean that damp streaks on the Martian surface that have
been spotted from orbit may not be prime spots to find alien microbes.
The briny patches would be likely to concentrate perchlorates, making
the streaks even more toxic than the surrounding soil.
“I can’t speak for life in the past,” said Wadsworth. “As far as present
life, it doesn’t rule it out but probably means we should look for life
underground where it’s shielded from the harsh radiation environment on
the surface.”
Chris McKay, a planetary scientist at Nasa Ames
Research Center in California, said the study was “a big step forward”
in understanding the ramifications of finding high levels of perchlorate
on Mars. From a Mars exploration point of view, he said the results
were both good and bad news. On the plus side, it means that any
microbes that hitch a ride on landers sent to Mars will be swiftly
destroyed on the surface, alleviating concerns about contaminating a
potentially inhabited planet. “This should greatly reduce planetary
protection concerns as well as any concerns about infection of
astronauts,” he said. “But the bad news is that this means we have to
dig to quite some depth to reach a biological record of early life that
is not completely destroyed by the reactive UV-activated perchlorates.”
In 2020, the European Space Agency plans
to send its ExoMars rover to the red planet on a mission to search for
alien life. The rover is equipped with a drill that can bore two metres
into the ground to retrieve soil samples in which microscopic Martians
may be found.
There's water on Mars, but is there life? – video by Guardian
Andrew Coates, a planetary scientist at UCL who leads the ExoMars panoramic camera team, said the work shows that the surface of Mars today is more hostile to life than thought. “This, combined with the solar and galactic particle radiation environment at the Martian surface, makes it all the more important to sample underneath the surface in the search for biomarkers,” he said.
“With the ExoMars rover, we will drill to retrieve and analyse samples
from up to 2m under the surface,” he added. “This is important as a
millimetre or two will get us below the harmful ultraviolet, one metre
will get us below the oxidants such as perchlorates, and 1.5m gets us
below the ionising radiation from the sun and galaxy.”