Curiosity Finds Ancient Streambed

By: J. Kelly Beatty September 28, 2012 12

NASA's newest rover has shown that its landing site inside Gale crater bears rich evidence that liquid water once flowed across the Martian surface.

Yesterday scientists for NASA's Mars Science Laboratory, a.k.a. Curiosity, announced that the rover has encountered a striking rock outcrop jutting from the dusty terrain along its route. "It looks like someone came along on the surface with a jackhammer and lifted up a sidewalk at a construction site," comments project scientist John Grotzinger.

NASA's Curiosity rover found evidence for an ancient, flowing stream on Mars at the rock outcrop pictured here, which the science team has named for Hottah Lake in Canada's Northwest Territories. The Hottah outcrop has rounded pieces of gravel embedded in it, indicating that they were transported by a vigorous flow of water. Click on the image for a larger version.

NASA / JPL / MSSS

The rover reached this rocky outcrop, nicknamed Hottah, about two weeks ago. When the team took close-up images of the exposed rock, using the rover's mast-mounted camera equipped with a 100-mm-focal-length lens, it became clear that it's a layer of loosely cemented gravel and sand, strikingly similar to geologic features common in dry stream beds on Earth. Moreover, Hottah looks much like a second outcrop, called Link, spotted earlier in its trek and also like the crusty material exposed by rocket exhaust during the landing.

The Curiosity team believes that the the mix of material at all three locations was deposited by a flowing stream in the distant past. "The rounded gravel tells us the particles have been transported by water or wind, wears away the edges to yield a smooth surface," explains investigator Rebecca Williams (Planetary Science Institute. However, she continues, "These are too large to be transported by wind, so we think they were transported by water in a vigorous stream."

Compare Curiosity's image of the outcrop called Link (left) with a typical sedimentary conglomerate formed by gravel fragments in a stream on Earth (right). The larges pebbles are about 1 inch (2½ cm) across.

NASA / JPL / MSSS / PSI

"From the size of gravels it carried," says William Dietrich (University of California, Berkeley), "the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep."

It's an important scientific find, though not an unexpected one. MSL scientists chose to drop Curiosity onto the floor of Gale crater, in part, because nearby is an extensive fan-shaped deposit at the end of a long channel, named Peace Vallis, that runs downslope from the crater's inner wall. This fan of sediment, built up by a long-duration succession of flows down a half-mile-long channel, apparently extends to the rover's landing site.

To get the details of this important find — the first of what will likely be many during Curiosity's two-year mission — head to the NASA press release.

Comments

Anthony Barreiro

September 28, 2012 at 5:30 pm

It's very satisfying to read that MSL Curiosity is finding clear evidence to support planetary scientists' understanding of Martian geological history. And the pictures are really nice! Curiosity's pictures are making me look at humble terrestrial features, like dry stream beds, with new interest and appreciation.