Planning to waterski on Mars? Not so fast. Following up on earlier speculation concerning what appears to be water on Mars, NewScientist (25 March 2017) is reporting that what has been thought to be streaks of water may be something else:
“There’s part of your brain that immediately tells you that it should be ice melting,” says Sylvain Piqueux at NASA’s Jet Propulsion Lab in Pasadena, California. “The problem is, it’s really hard to melt ice on Mars.”
Now, Frédéric Schmidt at the University of Paris-South and his colleagues have an idea that needs no liquids: sand avalanches caused by sunlight and shadow.
When sunlight hits the sand, it heats up the top layer while leaving deeper layers cool. This temperature gradient changes the pressure of tiny gas pockets around the sand particles, shifting the gas upward. This in turn jostles grains of sand and soil, causing them to slip down the Martian slopes.
The effect should be most pronounced in afternoon shadows cast by boulders or outcrops. In this situation, the contrast between the cooling surface and the still-warm layers just below creates a pressure gradient as well, shifting the gas and sand even more (Nature Geoscience, doi.org/b4jr).
