Washington, D.C. - NASA's Mars Reconnaissance Orbiter has (MRO) made its second significant discovery: There are vast Martian glaciers of water ice under protective blankets of rocky debris – outside the polar caps.

The findings, published in the Nov. 21 edition of Science, include data provided by the MRO’s “ground-penetrating” radar, suggesting there are immense water resources on Mars, which are packed in glaciers that   extend for dozens of miles from the edges of mountains or cliffs. NASA said that a layer of “rocky debris” is covering the glaciers, which are believed to be “remnants from an ice sheet that covered middle latitudes during a past ice age.“ Layers of rock may have also prevented the ice from vaporizing.

NASA scientists said that radar waves sent from the MRO were used to identify the ice. The echoes received by the MRO are analyzed by measuring how the waves pass through the surface and reflect off a deeper surface below. The apparent velocity of radio waves passing through the ground is consistent with a composition of water ice, NASA said.

"Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that is not in the polar caps," said John Holt of the University of Texas at Austin, who is lead author of the report. "Just one of the features we examined is three times larger than the city of Los Angeles and up to half a mile thick. And there are many more. In addition to their scientific value, they could be a source of water to support future exploration of Mars."
 
What makes this discovery even more stunning is that scientists now are certain to have an answer as to what is beneath the Mars aprons, gently sloping areas at massive geographical structures, which were first observed by the Viking orbiters in the 1970s.  "These results are the smoking gun pointing to the presence of large amounts of water ice at these latitudes," said Ali Safaeinili, a shallow radar instruments team member with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Holt and 11 co-authors report the buried glaciers lie in the Hellas Basin region of Mars' southern hemisphere. The radar also has detected similar-appearing aprons extending from cliffs in the northern hemisphere. "There's an even larger volume of water ice in the northern deposits," said JPL geologist Jeffrey J. Plaut, who will be publishing results about these deposits in the American Geophysical Union's Geophysical Research Letters. "The fact these features are in the same latitude bands, about 35 to 60 degrees in both hemispheres, points to a climate-driven mechanism for explaining how they got there."