Washington: NASA's Mars rover Curiosity has discovered geologic evidence that a fast-flowing stream historically coursed across the Martian surface.
A Planetary Science Institute researcher announced the discovery during a Thursday mission briefing.
Images by Curiosity's mast cameras of rocks on two Martian outcrops containing ancient stream bed gravels indicate long-distance transport by the vigorous flow of surface water on Mars due to the rounded shape of some of the stones. The materials range in size from a grain of sand to a golf ball.
"The shapes tell you they were transported and the sizes tell you they couldn't be transported by wind. They were transported by water flow," said PSI Senior Scientist Rebecca Williams, a Curiosity mission science co-investigator.
"This is wonderful 'concrete' evidence of water-transported gravels on Mars. It is very exciting to have ground truth confirmation of the hypotheses developed from analyzing orbital data," Williams said.
"With this finding, we can now better constrain the amount and duration of water flow activity at this site, a critical step in identifying habitable environments on Mars," she added.
Researchers believe that based on the size of the gravels it carried, the water moved at about three feet per second and was between ankle and hip deep.
The site is between the north rim of Gale Crater and the base of Mount Sharp on the downslope of an alluvial fan.
The rocks in the outcrops were formed when water transported gravels downslope to bottom of alluvial fan, where they remained for some time. Other materials were deposited on top of them, and the material was eventually cemented together by salts or carbonates.
Researchers are yet unable to say how long ago, or for what duration, water flowed in the region.
While earlier evidence exists of the presence of water on Mars, and researchers have long looked at surface channels on Mars, this marks the first time scientist have actually seen water-transported gravel on Mars, said William Dietrich, Curiosity science co-investigator from the University of California, Berkeley.