In a discovery that partly answers the question of where all the water went on Mars, scientists have found vast, debris-covered glaciers much nearer the equatorial region than anyone had expected, according to a report Friday in the journal Science.
The glaciers, estimated to contain at least as much water as Lake Huron and possibly as much as the entire Great Lakes, were found by ground-penetrating radar on NASA's Mars Reconnaissance Orbiter spacecraft.
"We have found a big chunk of the missing water that people have known must be there," said Ali Safaeinili, a member of the radar team at the Jet Propulsion Laboratory in La Canada Flintridge.
Scientists analyzing Martian topography have seen lots of evidence of water-caused erosion on the planet, but until now the only deposits of ice have been seen at the poles.
One of the glaciers has been estimated as being the size of Los Angeles and as much as half a mile thick.
How did the ice get there? The best guess, said John W. Holt, a researcher for the Institute of Geophysics at the University of Texas, is that climate change was brought on by changes in Mars' rotational axis over time. Because Mars doesn't have a large moon to keep its axis relatively stable, as the Earth does, the planet can tilt dramatically, redistributing the sun's heat and energy and shifting the poles.
These icy deposits may have lain hidden in their current state as long as 200 million years, Holt said.
The discovery wasn't a complete surprise. Scientists had previously noticed rocky debris "aprons" that seemed to flow away from steep hills as if something underground was lubricating their movements. But there was no proof until the Mars Reconnaissance Orbiter's Italian-built radar confirmed the presence of ice.
The discovery could be one of the most significant for those who want to see a manned mission to the Red Planet, a goal that was announced by President Bush in 2004 but has since been quietly de-emphasized by NASA.
Knowing that astronauts could obtain water in the temperate regions would probably make the mission more feasible.
It is still unclear, however, whether the water is accessible from the surface. Holt said the radar measurements indicated that it could be covered by as much as 30 feet of debris.
"If you could get a backhoe in there, you could get at it," said Jeffrey Plaut, a geologist at JPL. "You'd have to figure out how to get a backhoe to Mars."