Drilling deep enough beneath the surface of Mars to find intact dormant life will require new technologies, British researchers say.
Credit: NASA
SYDNEY: Probes designed to find life on Mars do not drill deep enough to find dormant living cells, according to a new British study.
"Finding hints that life once existed - proteins, DNA fragments or fossils - would be a major discovery in itself, but the Holy Grail for astrobiologists is finding a living cell that we can warm up, feed nutrients and reawaken for studying," said lead author Lewis Dartnell, of University College London.
According to the researchers, current drills may find tell-tale fragments that life once existed on Mars in the distant past. Finding 'reawakenable' cellular life, however, would require new technology to enable drilling many metres below the surface - beyond the reach of the solar radiation that pummels the Red Planet's surface.
The team's research, published in the journal Geophysical Research Letters, focussed on mapping cosmic radiation levels at various depths on Mars. Unlike Earth, Mars is not protected by a global magnetic field or thick atmosphere and for billions of years it has been laid bare to radiation - high energy light and particles from our own Sun and other stars and objects in space.
"It just isn't plausible that dormant life is still surviving … within the first couple of metres below the surface in the face of the ionising radiation field," said Dartnell. "Finding life on Mars depends on liquid water surfacing on Mars, but the last time liquid water was widespread on Mars was billions of years ago. Even the hardiest cells we know of could not possibly survive the cosmic radiation levels near the surface of Mars for that long."
Many microorganisms can go into dormant states in which they can ride out harsh periods such as liquid water turning to ice - reawakening when conditions improve. But on Mars' high-radiation surface, explained the researchers, survival times for such organisms could reach only a few million years.
To find dormant organisms, they claimed future missions will need to dig deeper and target very specific areas such as recently formed craters or areas where water has recently surfaced. In these environments, such as within the ice at the Elysium region's newly found subsurface 'frozen sea' - believed to have formed in the last few million years from water swept toward the equator by volcano-induced floods - life would be better protected from radiation and may have withstood the ravages of time.
According to the team, the key reason for looking for life in low-radiation environments is that when cells are dormant - such as those that may be frozen underground on Mars - they are unable to repair DNA breaks caused by ionising radiation, and the damage accumulates to the point where the cell becomes permanently inactivated.
According to Dartnell, "With this model of the subsurface radiation environment on Mars and its effects on the survival of dormant cells we have been able to accurately determine the drilling depth required for any hope of recovering living cells. The frozen sea in Elysium represents one of the most exciting targets for landing a probe, as the long-term survival of cells here is better than underground in icy rock.
"This could be crucial for the scientists and engineers planning future Mars missions to find life," he said.
