NASA Rover Finds Old Streambed on Martian Surface
Scientists are studying the images of stones cemented into a layer of conglomerate rock.
PASADENA, Calif. -- NASA's Curiosity rover mission has found evidence a stream once ran vigorously across the area on Mars where the rover is driving. There is earlier evidence for the presence of water on Mars, but this evidence -- images of rocks containing ancient streambed gravels -- is the first of its kind.Scientists are studying the images of stones cemented into a layer of conglomerate rock.  The sizes and shapes of stones offer clues to the speed and distance of a  long-ago stream's flow."From  the size of gravels it carried, we can interpret the water was moving about 3  feet per second, with a depth somewhere between ankle and hip deep," said  Curiosity science co-investigator William Dietrich of the University of  California, Berkeley. "Plenty of papers have been written about channels  on Mars with many different hypotheses about the flows in them. 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."The  finding site lies between the north rim of Gale Crater and the base of Mount  Sharp, a mountain inside the crater. Earlier imaging of the region from Mars  orbit allows for additional interpretation of the gravel-bearing conglomerate.  The imagery shows an alluvial fan of material washed down from the rim,  streaked by many apparent channels, sitting uphill of the new finds.The  rounded shape of some stones in the conglomerate indicates long-distance  transport from above the rim, where a channel named Peace Vallis feeds into the  alluvial fan. The abundance of channels in the fan between the rim and  conglomerate suggests flows continued or repeated over a long time, not just  once or for a few years.The  discovery comes from examining two outcrops, called "Hottah" and  "Link," with the telephoto capability of Curiosity's mast camera  during the first 40 days after landing. Those observations followed up on  earlier hints from another outcrop, which was exposed by thruster exhaust as  Curiosity, the Mars Science Laboratory Project's rover, touched down."Hottah  looks like someone jack-hammered up a slab of city sidewalk, but it's really a  tilted block of an ancient streambed," said Mars Science Laboratory  Project Scientist John Grotzinger of the California Institute of Technology in  Pasadena.The  gravels in conglomerates at both outcrops range in size from a grain of sand to  a golf ball. Some are angular, but many are rounded."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 Curiosity  science co-investigator Rebecca Williams of the Planetary Science Institute in  Tucson, Ariz.The  science team may use Curiosity to learn the elemental composition of the  material, which holds the conglomerate together, revealing more characteristics  of the wet environment that formed these deposits. The stones in the  conglomerate provide a sampling from above the crater rim, so the team may also  examine several of them to learn about broader regional geology.The  slope of Mount Sharp in Gale Crater remains the rover's main destination. Clay  and sulfate minerals detected there from orbit can be good preservers of  carbon-based organic chemicals that are potential ingredients for life."A  long-flowing stream can be a habitable environment," said Grotzinger.  "It is not our top choice as an environment for preservation of organics,  though. We're still going to Mount Sharp, but this is insurance that we have  already found our first potentially habitable environment."During  the two-year prime mission of the Mars Science Laboratory, researchers will use Curiosity's 10 instruments to investigate whether areas in Gale Crater have ever offered environmental  conditions favorable for microbial life.NASA's  Jet Propulsion Laboratory, a division of Caltech, built Curiosity and manages  the Mars Science Laboratory Project for NASA's Science Mission Directorate,  Washington.For  more about Curiosity, visit:http://www.jpl.nasa.gov/msl,http://www.nasa.gov/mslandhttp://mars.jpl.nasa.gov/msl.You  can follow the mission on Facebook and Twitter at:http://www.facebook.com/marscuriosityandhttp://www.twitter.com/marscuriosity.