Heat inside Mars may have melted ice and made watery habitats for life

Martian surface

A vertically exaggerated view of a large, water-carved channel on Mars

ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO. 3D rendered and colored by Lujendra Ojha

Geothermal energy on Mars billions of years ago may have been sufficient to melt some of its subsurface ice into water, creating an environment that might have been suitable for life.

Studies of Mars suggest it had liquid water on its surface about 4 billion years ago, evidenced by the discovery of minerals on the planet that formed in a water-rich environment and even ancient riverbeds.

However, given that the sun was 30 per cent less luminous at the time – coupled with Mars losing its magnetic field early in its life, leaving the solar wind free to strip away the planet’s protective atmosphere – explaining the presence of this water without a sufficient heat source has been difficult.

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Now Lujendra Ojha at Rutgers University in New Jersey and his colleagues say they have a solution. They suggest that water could have been produced and kept as a liquid beneath Mars’s surface thanks to geothermal heat, perhaps for hundreds of millions or even billions of years. Some of the water may have made its way to the surface.

Modelling early Mars, they say that the decay of radioactive elements like uranium, thorium and potassium in the crust and mantle would have generated enough residual heat to melt the base of some Martian ice sheets.

“There’s absolutely no doubt that Mars had water,” says Ojha. “We said, ‘Well, if 4 billion years ago Mars’s surface was really cold, what if the [river] channels and these minerals we see were formed by geothermal heat?’”

Larger concentrations of these radioactive elements in the distant past means some regions of the Martian subsurface would have experienced up to four times as much heating as today, according to the team’s calculations – enough to melt the base of the ice, which was up to 2 kilometres thick.

Crucially, this melting could have provided potential habitats for life over long periods of time. “Life would have found a refuge only in the subsurface, where you still have this geothermal heat,” says Ojha. “With this work, we can pinpoint places on Mars that would have been more habitable.”

Journal reference: Science Advances, DOI: 10.1126/sciadv.abb1669

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source: newscientist.com

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