Many of Mars' stream valleys might have formed under an ice sheet - Ars Technica

Among the relics of the watery past are networks of valleys incised into Mars’ surface.

So a team led by Anna Grau Galofre at Arizona State set out to analyze the valleys on Mars to see if any would better match a sub-glacial origin.

They worked with topographic data for over 10,000 valleys in almost 70 connected valley networks, characterizing each by a number of metrics.

That includes some simple things, like valley width, the number of tributaries upstream, and the angle between connected channels.

Valley width, for example, is good at picking out valleys that are carved by glacial ice here on Earth.

And sub-glacial drainage valleys tend to meet at angles closer to 90 degrees and undulate up and down—driven by high water pressure under a glacier.

Of the 66 networks of valleys, 18 couldn’t be identified and three looked like the result of groundwater springs.

But nine valley networks had the characteristics of glacial erosion, and 22 fell under the sub-glacial drainage category.

To see if that made sense, the researchers compared the locations of the sub-glacial drainage valleys against a previously published ice sheet model.

Laid out on a map, those 22 valley networks do generally sit in the region where the ice sheet model predicts they should—between the edge of the ice sheet and the “equilibrium line” that divides the melt zone from the accumulation zone.