When scientists discovered liquid water flowing on Mars last year, one thing was particularly puzzling. How was water able to remain liquid long enough to produce large streaks on the surface?
Now, a team of scientists led by the University of Nantes think they might have an answer. Published in Nature Geoscience, the team has found that water on Mars should boil in a decidedly non-Earth-like manner, dislodging debris and creating the dark streaks known as recurring slope lineae (RSL).
“Our research shows that you need a lot less water than thought to form such features,” co-author Dr. Susan Conway from the University of Nantes told IFLScience.
The Martian atmosphere is so thin that water coming to the surface from underground should almost instantly boil and evaporate. We had theorized previously this would happen, although this hadn’t directly been observed. But this study helps to constrain exactly how that process may shape features on the surface.
The research was performed at the Open University in Milton Keynes, where the researchers used a “Mars chamber” to simulate the conditions on the Martian surface. They placed a block of ice at the top of a slope of sand, with the melting water seeping under the sediment. As the water came into contact with the air, it evaporated, causing the sediment to jump.
<iframe width="560" height="420" src="https://www.youtube.com/embed/ge1IaLViB_A" frameborder="0" allowfullscreen></iframe>
Above, a video of the experiment. NPG Press
On Mars, a similar process likely takes place. The water seeps up from under the Martian surface (through a process that is still not understood) and, as it reaches the surface, it boils. Small debris on the surface is moved by the resulting water vapor, and eventually you get a cascade of material down a slope, creating the dark streaks known as RSL.
“Paradoxically, instead of requiring the stability of substantial water or brines, it is the instability of water on Mars that may explain the morphological activity needed to form the observed features,” said Wouter Marra from the University of Utrecht in a Nature News and Views article.
The study ultimately suggests that not as much water is needed on Mars to produce its famous dark streaks, helping us describe the alien processes taking place on the surface in conditions that shouldn’t really allow water to remain a liquid for very long.
In fact, one reason the researchers think this hasn’t been picked up on before is that it is unlike anything seen on Earth. “I think people overlooked a lot because we don’t have any terrestrial features on Earth caused by these mechanisms,” said Dr. Conway. “It’s important to do these experiments in the lab, to actually look and see what happens.”