Scientists believe liquid water may have flowed on Mars just a few hundred thousand years ago, and could do so again – with implications for the possibility of life on the Red Planet.
Mars was once a warm and wet planet – not dissimilar to Earth – but around three billion years ago it lost all of its liquid water, becoming the dusty hyper-arid planet seen today.
All of the planet’s remaining water is trapped in permafrost at the poles.
However, a team of scientists studying the planet’s deep gullies suggest they were carved not by carbon dioxide frost as previously thought, but by running water.
‘We know from a lot of our research and other people’s research that early on in Mars’s history, there was running water on the surface with valley networks and lakes,’ said lead author Professor Jim Head, of Brown University, Rhode Island.
‘We show here that even after that and in the recent past, when Mars’s axis tilted to 35 degrees, it heats up sufficiently to melt snow and ice, bringing liquid water back until temperatures drop and it freezes again.’
One day, Mars will tilt to 35 degrees again, bringing with it the potential for water to flow, it has been claimed.
Professor Head said: ‘Could there be a bridge, if you will, between the early warm and wet Mars and the Mars that we see today in terms of liquid water?’
‘Everybody’s always looking for environments that could be conducive to not just the formation of life, but the preservation and continuation of it.
‘Any microorganism that might have evolved in early Mars is going to be in places where they can be comfortable in ice and then also comfortable or prosperous in liquid water.
‘In the frigid Antarctic environment, for example, the few organisms that exist often occur in stasis, waiting for water.’
Nasa’s mantra in the search for extraterrestrial life is to ‘follow the water’.
On Earth, all life forms require water to survive. Among the planets in our solar system, only Earth has a more hospitable climate than Mars, and it is thought to have once sheltered primitive, bacteria-like organisms.
Last year, Nasa’s Perseverance rover found traces of organic carbon that are thought to have a ‘biological basis’, resembling fossilised remains of microbial life in Australia that date back 2.7 billion years.
For the latest study, the team used a computer model to simulate a ‘sweet spot’ when conditions on Mars allow the planet to get above freezing – leading to periods of flowing liquid water.
As Mars tilts on its axis to 35 degrees, the atmosphere becomes dense enough for brief episodes of melting to occur at gully locations.
Data was matched to spells when gullies in a region known as Terra Sirenum are believed to have expanded rapidly downhill from high elevation points.
The phenomenon could not be explained without the occasional presence of water.
Professor Head and his colleagues believe gully formation was driven by melting ice, combined with CO2 frost evaporation in other parts of the year.
The researchers found this has likely occurred repeatedly over the past several million years – with the most recent occurrence about 630,000 years ago.
If ice was present, conditions would have been right for melting as temperatures rose above 273 degrees Kelvin, equivalent to around 0C.
Co-author Jay Dickson, now at California Institute of Technology, said: ‘Our study shows the global distribution of gullies is better explained by liquid water over the last million years.
‘Water explains the elevation distribution of gullies in ways that carbon dioxide cannot.
‘This means that Mars has been able to create liquid water in enough volume to erode channels within the last million years, which is very recent on the scale of Mars geologic history.’
The study is published in the journal Science.
MORE : Nasa rover Perseverance makes ‘strange’ discovery on Mars
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