Martian life most likely to have existed miles below the surface, study finds

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Alien life on Mars would have the highest chance to prosper several miles below the surface of the planet due to subsurface melting of thick ice sheets fuelled by geothermal heat, a Rutgers-led study has found.

Approximately four billion years ago, the Sun was much fainter and cooler than it is today so the climate of early Mars should have been freezing.

However, the surface of Mars has many geological indicators, such as ancient riverbeds, and chemical indicators, such as water-related minerals, that suggest the Red Planet had abundant liquid water about 4.1 billion to 3.7 billion years ago, which is known as the Noachian era.

This apparent contradiction between the geological record and climate models is known as the faint young sun paradox.

On rocky planets like Mars, Earth, Venus and Mercury, heat-producing elements like uranium, thorium and potassium generate heat via radioactive decay.

In such a scenario, liquid water can be generated through melting at the bottom of thick ice sheets, even if the Sun was fainter than now. On Earth, for example, geothermal heat forms subglacial lakes in areas of the West Antarctic ice sheet, Greenland and the Canadian Arctic. It’s likely that similar melting may help explain the presence of liquid water on cold, freezing Mars four billion years ago.

The scientists examined various Mars datasets to see if heating via geothermal heat would have been possible in the Noachian era.

They showed that the conditions needed for subsurface melting would have been ubiquitous on ancient Mars.

Even if Mars had a warm and wet climate four billion years ago, with the loss of the magnetic field, atmospheric thinning and subsequent drop in global temperatures over time, liquid water may have been stable only at great depths. Therefore, life, if it ever originated on Mars, may have followed liquid water to progressively greater depths.

“Even if greenhouse gases like carbon dioxide and water vapour are pumped into the early Martian atmosphere in computer simulations, climate models still struggle to support a long-term warm and wet Mars,” said the study’s lead author Lujendra Ojha.

“I and my co-authors propose that the faint young sun paradox may be reconciled, at least partly, if Mars had high geothermal heat in its past.

“At such depths, life could have been sustained by hydrothermal [heating] activity and rock-water reactions,” Ojha said. “So, the subsurface may represent the longest-lived habitable environment on Mars.”

Nasa’s Mars InSight spacecraft landed in 2018 and may allow scientists to better assess the role of geothermal heat in the habitability of Mars during the Noachian era, according to Ojha.

In July, Nasa’s Perseverance rover blasted off to the Red Planet with the aim of finding former signs of life and collecting samples from the surface.

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