Stream revealed on Mars

PASADENA, Calif. - The landing site of the Mars rover Curiosity was once covered with fast-moving and possibly waist-high water that could have possibly supported life, NASA scientists announced Thursday.

While planetary scientists have often speculated that the now-desiccated surface of Mars was once wet, Curiosity cameras provided the first proof that flowing water was present on a least one part of Mars for "thousands or millions of years."

The early finding led Mars Science Laboratory mission top scientist John Grotzinger to conclude that Curiosity had already found a potentially "habitable" site - a central goal of the mission - well before heading to its primary destination.

While the area may not have other attributes needed for life, he said, the team now has a "hall pass" on the question of flowing water, and the Gale Crater landing site seemed even more appealing.

"A long-flowing stream can be a habitable environment," he said. "We're still going to Mount Sharp [a three-mile-high mound at the center of the crater], but this is insurance that we have already found our first potentially habitable environment."

Curiosity team scientists determined that flowing water was once present near the Gale Crater landing site based on the telltale size, shape and scattering of pebbles and gravel nearby, especially those found in conglomerate rocks at three different sites.

The roundedness of the pebbles is especially significant, they said, and strongly suggests that the rocks were carried down a roughly 20- to 25-mile stream or river and were smoothed along the way.

William Dietrich, professor of geomorphology and member of the Curiosity imaging science team, presented some rounded earthly pebbles, which he said are similar to those found in the images.

"Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them," Dietrich said. "This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it."

Curiosity made its dramatic landing in early August, and it has spent much of its time since testing out systems and instruments and preparing for its two-year drive.

But the rover's suite of cameras began sending back images of the conglomerate rock with small pebbles soon after landing, and they provided sufficiently detailed pictures to convince scientists that the pebbles and gravel had a watery past.

Gale Crater was selected as a landing site in part because satellite imaging had earlier found what appeared to be a sizable cut in the crater wall that looked like a dried river or stream bed.

The bed continued into the crater and then spread out in the shape of a delta.