Gullies on Mars Carved from Dry Ice, Not Water

The gullies that crisscross the surface of Mars were not carved out by running water, but dry ice, in fact, according to new research.

These channels remain active and tend to form during cold weather, implicating frozen carbon dioxide - known as dry ice - rather than liquid water, which would freeze at such low temperatures.

"As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water," study lead author Colin Dundas of the US Geological Survey's Astrogeology Science Center in Flagstaff, Ariz., said in a NASA 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 occurs in winter."

Dundas and his team used the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) to examine gullies at 356 sites on Mars, since they were first discovered in 2006. The researchers found that 38 of these sites had active gully formation.