Many of Mars’ stream valleys might have formed under an ice sheet

Enlarge / Examples of different types of valleys on Mars. (credit: Galofre et al./Nature Geoscience)

The further back into Earth’s history your mind wanders, the more work your imagination has to put in. That’s even more true for Mars. None of us have physically stepped foot on the present-day version of the planet, and its past was clearly very different from its present, with evidence pointing to flowing and standing water.

Among the relics of the watery past are networks of valleys incised into Mars’ surface. The Red Planet’s southern hemisphere highlands host many valleys, which have largely been interpreted as formed by rivers and groundwater springs. The source of water in rivers—whether rainfall in a warm climate or just melt from glacial ice—has been a question mark.

It’s thought that Mars’ past was generally quite cold, so a connection between the valleys and glacial ice is quite plausible. But how direct is that connection? We can identify the drainages in which water flows beneath ice sheets based on physical characteristics of the valleys left behind. 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.