The Mars Reconnaissance Orbiter has detected what NASA scientists believe are huge glaciers of water ice lying beneath a layer of rocky debris.
The finding is significant because it helps scientists better understand a feature of the Martian surface that has puzzled them for decades. In the 1970s, the Viking orbiters sent back images that showed what have been dubbed "aprons," or large, gently sloping deposits of debris situated at the base of tall geographic formations like cliffs. Several theories for what created these aprons have been posed over the years. This research indicates that what's just beneath that debris is of much greater interest.
To investigate the planet's surface, the MRO spacecraft uses a radar instrument, donated for the project by the Italian Space Agency, that can penetrate the Martian ground. The instrument detected radio waves bouncing off a layer of material beneath the surface that were consistent with what is found in areas covered with water ice glaciers.
One of the things that makes the glaciers so interesting is their location. They're in the middle latitudes, far from the planet's polar caps where other signs of water ice have been discovered. The glaciers observed in this study are in the southern hemisphere, but similar features have been spotted in the same latitude bands in the northern hemisphere. That led researchers to believe that, however the glaciers got there, they're the result of a climate-based phenomenon.
And they're big, too. The glaciers reach for dozens of miles. One is three times larger than the city of Los Angeles and is up to a half-mile thick.
"Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that is not in the polar caps," lead author John W. Holt, of the University of Texas at Austin, said in a report.
The findings will be reported in Friday's edition of the journal Science.