Two years ago, NASA made a big splash when it announced the discovery of flowing water on the surface of Mars. But it turns out, the space agency might have been wrong. The surface features that NASA thought were made up of liquid water may actually be flowing grains of sand instead, according to new research from the US Geological Survey. And that could decrease the chances of microbial life living on the Red Planet.
The features in question are dark streaks that show up periodically on Martian hills, known as recurring slope lineae, or RSLs. When one of NASA’s spacecraft, the Mars Reconnaissance Orbiter, studied these lines more closely, it found that the RSLs were made up of hydrated salts — meaning they were mixed with water molecules. At the time, NASA thought that was significant evidence that flowing liquid water caused these bizarre streaks.
But researchers at the USGS say these features look identical to certain types of slopes found on sand dunes here on Earth. Those slopes are caused by dry grains of sand flowing downhill, without the help of any water. It’s possible the same thing is happening on Mars, too. Since liquid water is key for life here on Earth, many thought these strange lines of flowing water may help support life on the Martian surface. But now these RSLs may not be the best place to look for life anymore.
Of course, it’s still possible that life could exist on Mars, but researchers may want to focus on other places, like under the surface. It’s thought that liquid water exists underground, where it’s a bit warmer and easier for water to stay a liquid. “Mars still has water now, it just might be in fewer accessible places,” Michael Meyer, the lead scientist for NASA’s Mars Exploration Program, tells The Verge.
The RSLs seemed to contain water because of the weird way they behave: the streaks seem to seep down the hills, a bit like water trickling downward. That, and they grow thicker in the warmer months. While Mars is pretty frigid, its temperatures can exceed -9 degrees Fahrenheit during the summer, making the surface a bit more accommodating for water. In fact, water on Mars is thought to contain a type of salt called perchlorates that can make it easier for water to exist as a liquid at colder temperatures. Scientists thought that maybe the warm summers allowed this salty water to flow.
But the USGS thinks there’s another explanation for how the streaks form: researchers studied the shapes of 151 RSLs and found that all of them are located on slopes steeper than 27 degrees. But the flows appear to stop when the slopes become less steep — which water wouldn’t do. Instead, the RSLs all seem to form at slopes similar to what you’d find with piles of sand on Earth, according to lead study author Colin Dundas. Plus, the dark streaks seem to flow out of the tops of the hills, but water probably wouldn’t sprout out of the the tops of slopes at these angles, he says. Instead, the water would probably start flowing out somewhere farther down the slope.
Researchers still think that what the Mars Reconnaissance Orbiter found is solid, and that hydrated salts are involved. But they’re probably not as wet as NASA originally thought. “This suggests there isn’t a large amount of liquid water associated with RSLs,” Dundas, a research geologist with the USGS, tells The Verge. “There may be a small amount of liquid water involved… but this is pointing to a relatively dry mechanism.”
So this may mean Mars’ surface isn’t as habitable as we thought, but that doesn’t mean the search is over yet. “There are lots of things that speak to Mars at least having the potential for life early on,” says Meyer. “And if it did happen, it has the potential for life hidden deep down below the surface.”