Craters gouged into the ruddy martian terrain revealed subsurface water ice closer to the red planet’s equator than would be expected, new images from NASA’s Mars Reconnaissance Orbiter (MRO) show.

The ice also appears to be 99 percent pure, instead of the dirty dust and ice mixture some scientists expected to see, scientists said during a Sept. 24 press briefing organized by NASA.

In August 2008, members of the MRO Context camera team examined images of the northern martian mid-latitudes for any dark spots or other changes not seen in earlier images.

After the team found several of the dark spots — an indication of recent meteorite impacts — MRO’s HiRISE camera team followed up by snapping high-resolution images of these suspected impact craters.

“We saw something very unusual when we followed up on the first of these impact craters,” said HiRISE team member Shane Byrne of the University of Arizona. “And that was this bright blue material poking up from the bottom of the crater. It looked a lot like water ice.”

A few days later, MRO’s Compact Reconnaissance Imaging Spectrometer took a read of the material and found the spectral signature of water. The behavior of the material over the ensuring days also helped clinch its identity: “When we started monitoring the material, it faded away like you’d expect water ice to fade, because water ice is unstable on Mars’ surface and turns directly into water vapor in the atmosphere,” Byrne said.

The scientists’ findings are detailed in the Sept. 25 issue of the journal Science.