Probes orbiting Mars have long observed mysterious, seasonal streaks on the slopes of the planet’s surface. These odd features have excited scientists with the possibility that they are formed by flowing water. But it’s also possible that the streaks are just avalanches of dry soil.
Now an international team led by Marion Massé of the University of Nantes shows that both these dry and wet processes may be at work. In lab experiments that re-create the thin atmosphere of Mars, the researchers found that the low-temperature boiling of liquid water sends soil particles jumping down hillsides, creating a combination water-sand slide (Nat. Geosci. 2016, DOI: 10.1038/ngeo2706).
Inside a chamber that mimicked Mars’s low atmospheric pressures, the group placed a block of ice at the top of a slope covered with sand. At such low pressures, ice almost instantaneously melts into water, then boils. This boiling caused the sand to bounce, gradually moving both water and sand downhill.
The result was a flow pattern that closely resembles the geomorphology observed on Mars: a swath of lumpy, ridged soil.
In stark contrast, the same experiment under Earth-like conditions produced a thin, smooth flow of liquid water down the slope.
To confirm this mechanism, spacecraft would need higher resolution imaging equipment than is now possible, notes Wouter A. Marra of Utrecht University in an accompanying perspective.
Still, Mikhail Kreslavsky, an earth and planetary sciences professor at the University of California, Santa Cruz, calls the experiments “spectacular,” noting that they show “a small amount of meltwater on Mars can potentially do a very significant amount of work on surface shaping.”
Nilton Renno, a professor of climate and space sciences and engineering at the University of Michigan, Ann Arbor, says the fact that most of the liquid under Mars-like conditions percolated downslope, rather than forming a surface liquid film, has important implications for understanding martian terrains.