We have a story of water on Mars appearing in Nature Geoscience under first author Anna Grau Galofre. For those of you who have been following the plight of the study of waters on Mars, you know that over the past couple of decades we’ve gone from thinking that all the amazing features we see on Mars were probably formed by aeolian processes – sand blowing in the wind – to thinking that they happened via fluvial processes, or liquid flowing across the surface. For there to be liquid flowing on the surface of Mars, we had to imagine a history in which Mars was, once upon a time, warm and wet. 

You can get liquid water in lots of different ways. We have liquid water on Earth in lots of different places. The science of comparative geology allows us to look at what’s going on here and match it to what’s going on there. Researchers here on Earth looking around our planet, trying to find riverbeds and valleys that looked like those that we see on Mars, found them. They found them on Devon Island in the Arctic Sea around Canada, and these riverbeds weren’t formed by water flowing across the surface of the Earth under open blue skies. They were formed by rivers rushing underneath the pressure of massive glaciers. 

This changes our thinking on Mars, reminding us that Mars can have massive amounts of ice on its surface. We see this in its polar caps. This tells us that maybe a lot of those rivers and valleys we see carved on Mars weren’t carved by rivers we’d recognize but were instead carved by rivers under glaciers such as we rarely get to see. This kind of comparative geology is sadly made possible thanks to the recession of glaciers on our own planet that allow us to see what the geology underneath them looks like. 

So maybe Mars wasn’t as warm in the past as we thought for as long as we were starting to hope. We don’t know. This is one of those things about Mars where we just have to say we don’t know. We’re still trying to figure it out, and every time we look at the observations, we learn something new. It turns out Mars is far more complicated and interesting than we had previously given it credit for. 

More Information

Western University press release 

Arizona State University press release 

“Valley Formation on Early Mars by Subglacial and Fluvial Erosion,” Anna Grau Galofre, A. Mark Jellinek & Gordon R. Osinski, 2020 Aug. 3, Nature Geoscience