"These results are the smoking gun," said Ali Safaeinili, a shallow-radar instrument team member with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The glaciers are the largest reservoir of water ice found on Mars that isn't at the polar caps, John Holt of the University of Texas at Austin's Jackson School of Geosciences wrote the journal Science.

"Just one of the (glacial) features we examined is three times larger than the city of Los Angeles, and up to one-half-mile thick, and there are many more," he said.

"In addition to their scientific value, they could be a source of water to support future exploration of Mars," Holt said.

The buried glaciers lie in the 1,400-mile-wide, 6-mile-deep Hellas Basin region of Mars' southern hemisphere, thought to have been formed some 4 billion years ago, when a large asteroid hit the surface.

Radar has also detected similar-appearing aprons extending from cliffs in the northern hemisphere, Holt and 11 co-authors said.

"The fact that 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," Jet Propulsion Laboratory Mars Odyssey Project Scientist Jeffrey Plaut said.