Ancient valleys on Mars may have been carved by glaciers

Devon island

Early Mars may have looked like Devon Island in Canada

Anna Grau Galofre

Mars’s southern highlands are covered in vast networks of valleys that are thought to have been created by running water long ago. But a new analysis suggests they may actually have been carved out by glaciers, indicating that early Mars may have been cold and icy, not warm and wet.

To determine how Mars got its trenches, Anna Galofre at Arizona State University and her colleagues examined data on 10,276 of these features in 66 valley networks across the planet. They compared the topology of the valleys with a set of 40,000 simulations of valleys formed by four different sources of erosion: rivers created by rain or snow, glacial movement, water melting beneath glaciers, and groundwater seeping up through the surface.

The researchers used a computer analysis to group the valleys by topological characteristics, including how any tributaries branch off them, the relationship between length and width of the valleys and the curving of their paths.

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Despite prior, less detailed work suggesting that most or all of the valleys should come from groundwater flowing to the surface, they found that just 3 of the 66 networks were most likely to be the result of this. In contrast, 22 seemed to have been formed by water melting and flowing beneath glaciers.

Nine of the networks were most similar to simulated networks formed directly by glaciers, 14 were closest to rivers formed by precipitation and 18 weren’t distinct enough to be confidently attributed to any one formation mechanism, probably because of erosion over billions of years.

“Glaciation can explain a lot of those valleys very easily without having to invoke any strange mechanisms to explain things like channels flowing uphill or huge spaces between valleys,” says Galofre. “We can finally reconcile what the climate models have been saying for a long time – that extensive glaciation was likely to occur in the past – with the geological record.”

The idea that many of the valleys resulted from glaciers suggests that huge areas on early Mars were probably covered in enormous ice sheets. This is a controversial idea, says Galofre, because many studies have suggested that Mars was warmer in its past.

Luckily, even colossal sheets of ice wouldn’t kill the idea of life on Mars. “The ice sheets could provide an environment that’s not so bad for life – it would be thermally stable, protected by ice from dangerous radiation on the surface, and it could supply a steady reservoir of water,” says Galofre. “It would be a slightly different environment to the warm and wet Mars that many people think of on ancient Mars, but still an environment where life could thrive.”

NASA’s Perseverance rover, which launched on 30 July, will help answer the question of whether Mars used to be habitable and look for signs of ancient life there. When it arrives in February 2021, it will start looking for evidence on the surface and may help us figure out if the planet was actually warm and damp or if it was cold and covered in sheets of ice.

Journal reference: Nature Geoscience, DOI: 10.1038/s41561-020-0618-x

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source: newscientist.com