By: Erin Ruberry
Images taken by NASA's Mars Reconnaissance Orbiter indicate that dry ice and not liquid water formed gullies on the surface of Mars.
"As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water," said researcher Colin Dundas, of the U.S. Geological Survey, in a statement. "We were able to get many more observations, and as we started to see more activity and pin down the timing of gully formation and change, we saw that the activity is in winter."
Dry ice (frozen carbon dioxide) is abundant on the red planet, NASA says.
According to the new report, "all of the fresh-appearing gullies seen on Mars can be attributed to processes currently underway, whereas earlier hypotheses suggested they formed thousands to millions of years ago when climate conditions were possibly conducive to liquid water on Mars."
This 2013 video from NASA's Jet Propulsion Laboratory demonstrates what happens when dry ice meets sand dunes.
Here's a closer look at the search for signs of water on Mars: