Scientists believed they found evidence of water on Mars after spotting dark streaks on the red planet in 2011. These streaks, called recurring slope linae (RSL), appeared to indicate the presence of water beneath the surface. However, researchers now think the RSL may actually be granular flows of sand and dust.
The study was published in the journal Nature Geoscience and was a joint venture by the US Geological Survey, the Planetary Science Institute, the University of Arizona and Durham University in England.
The RSL appear during Mars’ warmest season and gradually disappear in winter. Thousands of them appear on the planet’s hilly, rocky slopes in areas such as the equator, northern plains, and southern mid-latitudes reports CNN. The lines look like water, but scientists were baffled because they only appeared on the tops of steep slopes.
After examining 151 RSL at 10 sites, researchers determined that the streaks acted like sand on an active sand dune. Colin Dundas, lead study author, and US Geological Survey scientist told CNN in an email: “We’ve shown that RSL are likely granular flows, which changes our assessment of what they mean for flowing liquid water on Mars and points to formation processes with little or no liquid.”
Mars does have water, just not near the surface.
“There’s still plenty of other evidence for H2O on Mars,” Dundas said. “There is a lot of ice in the subsurface and at the poles, and deliquescent salts can draw water out of the atmosphere and form liquid under some conditions. The rovers have made several discoveries pointing to a range of environments with liquid water in the past, and there are hydrated minerals bound in the rocks. But there may be little liquid at the surface today.”
Researchers are still learning about the RSL.
“While the new report suggests that RSL are not wet enough to favor microbial life, it is likely that on-site investigation of these sites will still require special procedures to guard against introducing microbes from Earth, at least until they are definitively characterized,” Mars Reconnaissance Orbiter Project Scientist Rich Zurek of NASA’s Jet Propulsion Laboratory said in a statement. “In particular, a full explanation of how these enigmatic features darken and fade still eludes us. Remote sensing at different times of day could provide important clues.”