As the Mars rover Curiosity celebrates its first full Martian year of exploration -- 687 Earth days -- it finds itself moving through terrain that was covered with glaciers 3,500 years ago, scientists say.
The Gale Crater the rover is currently traversing once had extremely cold, liquid water running through its lower-lying regions, freezing into glaciers and creating landscapes similar to some found today on Earth in Alaska or Iceland, they say.
Ancient Mars is believed to have possessed abundant quantities of water in a giant sea, partially covered in ice and surrounded by glaciers formed on the plains in the Red Planet's northern hemisphere.
That's been borne out by Curiosity's investigation in Gale Crater, says researcher Alberto Fairén, from Spain's Centro de Astrobiología and Cornell University in the United States.
"This crater was covered by glaciers approximately 3,500 million years ago, which were particularly extensive on its central mound, Aeolis Mons," he says.
Not all the water in the crater all those millions of years ago was in the form of frozen ice, he adds.
"However, at that time there were also rivers and lakes with very cold liquid water in the lower-lying areas within the crater," Fairén says, suggesting the planet had the capability of "maintaining large quantities of liquid water (an essential element for life) at the same time that giant ice sheets covered extensive regions of its surface."
The evidence comes from analysis of Curiosity data and of images captured from Mars orbit by NASA's Mars Reconnaissance Orbiter and the European Space Agency's Mars Express probe, the researchers report.
The images provide evidence of ancient glaciers within the Gale Crater by revealing concave basins, so-called "lobated" structures, the signs of moraines, and distinctive fan-shaped geological deposits, all features of glacial systems seen on Earth today.
"For example," Farién says, "there is a glacier on Iceland -- known as Breioamerkurjokull -- which shows evident resemblances to what we see on Gale crater, and we suppose that is very similar to those which covered Gale's central mound in the past."
Other Earthly glaciers in the Antarctic, Alaska and the northernmost areas of Canada have features matching what is seen on Mars, the researchers say.
Scientists believe Gale Crater was created during the impact on the Red Planet of a giant meteorite around 3,600 years ago and filled with water and glaciers soon afterward.
There may have even been glaciers already covering the area where the meteorite hit, suggesting an interesting possibility regarding life on Mars, Fairén says.
"The energy delivered after the impact, combined with the ice on the surface, could have generated very interesting environments from an astrobiological point of view, like hydrothermal areas, for example."