PROVIDENCE, R.I. -- New images of the surface of Mars provide the first direct evidence that the climate of Mars changed during the last 100,000 years, much more recently than the hundreds of millions of years scientists had previously thought, according to Brown University geologist John Mustard. The high-resolution images show evidence of water ice closer to the equator than had previously been observed.
Mustard, with graduate student Christopher Cooper and undergraduate Moses Rifkin, wrote about the findings in the July 26 issue of Nature.
The images were recorded by the Mars Orbiter Camera aboard NASA's unmanned Mars Global Surveyor. They show a unique surface terrain of pits and hummocks that appears to have been soil once impregnated by water ice. The ice has since evaporated, leaving a five-meter thick mantle of porous terrain that is being broken up by wind and other factors.
"Where the mantle is still intact, you could conceive of water ice not far below the surface," Mustard said. "Where it's broken into pits and hummocks, the water is gone."
[A high-resolution image of Mars' surface, left, shows an ice-rich layer that appears to be flowing downhill. The newly observed terrain is a mixture of water ice and dust and was formed in the past 100,000 years, much more recently than previously thought.]
The geologically young terrain was observed in two bands north and south of the equator at 30 to 60 degrees latitude. The location is significant because it shows that ice in the soil was once present as close to the equator as 30 degrees and as recently as 100,000 years, while previous observations had shown that ice had been present in the polar regions.
Due to climate change, it now appears the icy region moved from the planet's poles to nearer its equator, and has now retreated to the poles, the most recent of probably many such cycles, Mustard said.
"While we have always thought the climate of Mars has changed over time, this is direct evidence for change. And that change fits with the theory of periodic climate change, similar to the change that causes the ice ages on Earth," Mustard said.
"Maybe we don't have to go to the poles to find water ice. It's easier for a spacecraft to survive at the equator," Mustard said.
The work was supported by grants from NASA.