A cross-section of underground ice is exposed at the steep slope that appears bright blue in this enhanced-color view from the HiRISE camera on NASA's Mars Reconnaissance Orbiter. The scene is about 550 yards wide. The scarp drops about 140 yards from the level ground in the upper third of the image. Photo: NASA/JPL-Caltech/UA/USGS

A decade ago, Martian orbiters identified pockets of water ice tucked beneath the surface of the red planet, relatively close to the surface. But they couldn’t tell exactly how far down, or how accessible they were.

The precious frozen water is just a yard or two deep beneath some steep slopes in the mid-latitudes of the fourth planet, according to a new study of the latest Mars Reconnaissance Orbiter observations. The findings, published today in the journal Science, indicate that it’s a rich source of water for future exploration by both rovers and astronauts.

“Ice with low rock and dust content occurs at shallow depths as small as ~1 to 2 meters and extends to at least many tens of meters in depth,” concludes the NASA and USGS team.

The ice was first spotted with spectrometry aboard NASA’s Mars Odyssey orbiter, and with assistance from ground-penetrating radar aboard that orbiter and the European Space Agency’s counterpart, the Mars Express. NASA’s Phoenix lander confirmed buried water ice at 68 degrees north latitude, at a single site.

But this latest study confirmed eight locations, ranging from 55 to 58 degrees in both the north and south latitudes, as described in the paper.

The tools used were the Reconnaissance Orbiter’s High-Resolution Imaging Science Experiment (HiRISE), as well as the Mars Odyssey Thermal Emission Imaging System, and the orbiter’s Company Reconnaissance Imaging Spectrometer for Mars.

Together, they found the steep slopes are distinct in color, and the late-afternoon temperatures at the sites are warm enough, meaning that the formations are unchanging and are not seasonal frost. Also, the relatively blue color of topographically-determined frost is not present, they add.

The scientists said the visible pockets of water could provide a kind of frozen time capsule into the history of the Martian global climate – like an “ant farm,” once accessed.

“There is shallow ground ice under roughly a third of the Martian surface, which records the recent history of Mars,” said Colin Dundas, the lead author, of the USGS Astrogeology Science Center. “What we’ve seen here are cross-sections through the ice that give us a 3-D view with more detail than ever before.”

For future human exploration missions, the eight sites identified at mid-latitudes would be much more hospitable than the polar ice sites previously identified, said Shane Byrne, of the University of Arizona, another of the authors.

“Astronauts could essentially just go there with a bucket and a shovel and get all the water they need,” said Byrne.

NASA continues to make new discoveries about the abundance of the frozen water on Mars. However, liquid water has been elusive. Despite a major announcement of streaks of liquid water on some slopes on the red planet in late 2015, findings have since shown it is instead granular flows of sand or other particulate material making the dark lines.