NASA plans to announce "significant findings" about the history of water on Mars discovered by its Opportunityrover.
Opportunityhas been studying rocks and soil for evidence that the Red Planet was once a wetter place that could have been hospitable to life.
"The primary mission of the rovers really dealt with the history of water on Mars and we'll be reporting new findings that bear on that," NASA spokesman Mr Don Savage said.
The findings were to be released today during a press conference at NASA headquarters in Washington.
Other than a statement characterising the findings as "significant" the space agency revealed no details in advance. But participants in the twin rover mission managed by Jet Propulsion Laboratory in Pasadena, California, said last week that scientists were excited by data that the Opportunityrover was sending back to Earth.
Opportunity has been studying an outcropping of layered rock close to its landing site in a small crater on an area of Mars called Meridiani Planum.
The six-wheel robot has been using microscopic photography, a rock-abrasion tool that grinds off surface layers and spectrometers to determine the composition of the outcropping, particularly a piece dubbed "El Capitan".
While Opportunityhas stayed close to its landing site to explore the outcropping, its twin rover, Spirit, has been travelling on the other side of the planet, studying rocks and soil en route to a big crater named "Bonneville" that scientists hope will give the rover a view of geology below the surface.
AP