Mars once had a briny pool of standing water on its surface that could have supported life in the now-frozen planet's distant past, NASA scientists said Tuesday.

Scientists announced earlier this month that the Opportunity (search) rover found evidence of water long ago on Mars (search), but it was unclear whether the water was underground or on the surface. The new findings suggest there was a pool of saltwater at least two inches deep.

A rocky outcropping examined by the rover had ripple patterns and concentrations of salt -- considered telltale signs that the rock formed in standing water.

The findings add to the growing body of evidence that the Red Planet was once was a warmer and wetter place that may have been conducive to life.

"We think Opportunity is now parked on what was once the shoreline of a salty sea on Mars," said Cornell University astronomer Steve Squyres, the mission's main scientist.

Although Squyres referred to the water as a sea, scientists said it was not clear how big the body of water might have been or whether it was a permanent fixture. Instead, the site could have been a desert basin or salt flat that periodically flooded with water.

The evidence also does not indicate when water covered the broad and flat region where Opportunity landed, called Meridiani Planum (search), or for how long. Nor does it indicate if any organisms actually lived on Mars.