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Scientists announced today they now have confirmation that water once flowed vigorously across the surface of Mars. The evidence comes from pictures taken by NASA's 1-ton, six-wheeled rover Curiosity that's been crawling around the floor of a Mars crater named Gale since mid-August.
NPR's Joe Palca has more on what it's found.
JOE PALCA, BYLINE: In a way, today's announcement is no surprise. When scientist chose Gale crater as the rover's landing site, they did so because pictures from orbit showed what appeared to be an alluvial fan on the floor of the crater. As the name suggests, an alluvial fan is a fan-shaped formation that forms when rapidly moving water suddenly pours down a slope or the side of a mountain.
This formation occurs in several places on Earth. The pictures taken from Mars' orbit show a channel leading to the edge of Gale crater and then the distinctive fan shape formation spreading out onto the crater floor.
The rover is still in its checkout phase, so scientists weren't expecting any major discoveries, at least until they reached a spot about 500 yards from the landing site called Glenelg.
JOHN GROTZINGER: As we were driving along on the way to Glenelg, we encountered some really interesting outcrops that were surprising to the team.
PALCA: John Grotzinger of the California Institute of Technology is the lead scientist on the Curiosity mission. He spoke at a news conference held at NASA's Jet Propulsion Laboratory in Pasadena. Curiosity's landing site is on the bottom edge of the alluvial fan. Scientists were hoping to find rocks that might have been carried along the crater floor by the alluvial fan's streams of water.
The rock outcrop presented a perfect opportunity for study. Rebecca Williams is at the Planetary Science Institute in Tucson and a member of the Curiosity science team.
REBECCA WILLIAMS: When a geologist goes into the field, what they want to do is see a fresh exposure of rock to look at things like the grain size, the shape, the color and the arrangement of those grains, and that tells you a lot about the formation history of that rock.
PALCA: Williams says the pebbles in the rock have rounded edges, something that's consistent with being tumbled around by rapidly moving water.
Michael Malin of Malin Space Science Systems is the chief scientist for two of the rover's cameras. He says pebbles and larger rocks got smushed together as they rolled down the side of the crater and across the crater floor.
MICHAEL MALIN: Other materials were deposited on top of them. Eventually, they were cemented together by salts or some other material to act as a means of holding the rock together.
PALCA: This formed basically a new rock made out of other rocks.
Caltech's Grotzinger says it would be nice to have chemical or mineralogical evidence that confirmed water played a role in the formation of this rock. That's something the rover will be able to do later. But there are times in geology when the picture say it all, and this is one of them.
GROTZINGER: This is a rock that was formed in the presence of water. And we can characterize that water as being a vigorous flow on the surface of Mars.
PALCA: This isn't the first time scientists have seen signs of water on the now cold and dry planet. But evidence like this that there was once huge floods of water increases the chance that life might have once existed on Mars.
Seeing this rock may not be a surprise, but Rebecca Williams says it's gratifying all the same.
WILLIAMS: This is just wonderful ground truth confirmation of water-transported material that was predicted based on analysis of orbital images.
PALCA: Now, scientists will go back to testing instruments on the rover, pleased to have their first scientific discovery under their belts.
Joe Palca, NPR News. Transcript provided by NPR, Copyright NPR.
NASA's Curiosity rover has found definitive proof that water once ran across the surface of Mars, the agency announced today. NASA scientists say that new photos from the rover show rocks that were smoothed and rounded by water. The rocks are in a large canyon and nearby channels that were cut by flowing water, making up an alluvial fan.
Pathfinder, 1997: The first mission to land a rover on Mars, Pathfinder touched down in Ares Vallis, an ancient flood plain in the planet's northern hemisphere. Among the 2.3 billion bits of data sent back by the lander and its rover, Sojourner, were 15 chemical analyses of rocks and soil, which suggested Mars had once had liquid water and a thicker atmosphere.
Spirit, 2010: When NASA's Spirit rover got stuck in Martian sand, it proved to be a lucky break: The spinning wheel churned up soil that provided evidence of rocks formed in the presence of water.
Opportunity, 2004: Opportunity discovered tiny mineral spheres — nicknamed blueberries — poking out of rocks that were likely formed by water. Researchers using Opportunity's science instruments identified them as concretions rich in the mineral hematite, deposited by water saturating the bedrock.
Curiosity 2012: A wider view of the outcrop of a former streambed shows bedrock that scientists believe was likely exposed by meteorites striking the surface of Mars.
NASA says it has found proof that water shaped the rocks on the left, in a photograph taken by the Mars rover Curiosity (left). For comparison, the agency released an image of rocks from the Earth (right).
NASA's Curiosity rover has found definitive proof that water once ran across the surface of Mars, the agency announced today. NASA scientists say new photos from the rover show rocks that were smoothed and rounded by water. The rocks are in a large canyon and nearby channels that were cut by flowing water, making up an alluvial fan.
"You had water transporting these gravels to the downslope of the fan," NASA researchers say. The gravel then formed into a conglomerate rock, which was in turn likely covered before being exposed again.
The agency's scientists presented their findings of the former streambed on Mars at a news conference today.
"A River Ran Through It," Curiosity's operators tweeted Thursday. "I found evidence of an ancient streambed on Mars, similar to some on Earth."
"From the size of gravels it carried, we can interpret the water was moving about 3 feet per second," said Curiosity science co-investigator William Dietrich, "with a depth somewhere between ankle and hip deep."
The rocks have not undergone scientific analysis. But the NASA team says that taken with geographic data from Mars orbiters, the photographs tell a story all their own.
The images show rocks with round, smooth surfaces; many of them have been broken down into sizes smaller than one inch in diameter.
"The shapes tell you they were transported and the sizes tell you they couldn't be transported by wind," co-investigator Rebecca Williams said. "They were transported by water flow."
"There is earlier evidence for the presence of water on Mars," the agency said in a press release, "but this evidence — images of rocks containing ancient streambed gravels — is the first of its kind."
NASA's team has named the rock outcrop that reveals the former streambed "Hottah," after Canada's Hottah Lake.
Scientists have not yet estimated the age of the rocks, which may have been buried beneath the surface. Their age could be several billion years.
The next step will be to find a good spot to drill into the rock, NASA says. And they'll be looking for possible carbon deposits to determine whether the water on Mars once supported life.
The photographs released Thursday are among more than 13,000 raw images Curiosity has captured. The rover took the photos during its mission to Mars' Gale Crater. The rocks in question lie between the crater's north rim and Mount Sharp, a mountain inside the crater.
NASA investigators presented the results of their analysis at NASA's Jet Propulsion Laboratory in Pasadena, Calif. You can read other posts about Curiosity in our archive.