After the Rock Show Curiosity Sees Old Streambed on Mars

After touching the Martian rock with its robotic arm for the first time on Sept 22, NASA's Curiosity has detected a stream that once ran vigorously across the area of Mars where the rover is driving.  Prior to this there was evidence for the presence of water on Mars but the images provided by Curiosity of rocks containing ancient streambed gravels is the first of its kind.

These stones are being cemented into layer of conglomerate rock is being analyzed by the scientists. Based on the sizes and shapes of stones the scientists are able to grab some clues regarding the speed and distance of the 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 stream flow was traced between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater.  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.  Based on the abundance of channels in the fan between the rim and conglomerate they suggest that the flow continued or repeated over a long time.

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.

"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 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.

Curiosity will be further used to learn the elemental composition of the material, which holds the conglomerate together, in order to learn more about the characteristics of the wet environment that formed these deposits. 

"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."

Curiosity has been designed with 10 instruments for a two year mission to investigate whether areas in Gale Crater have ever offered environmental conditions favorable for microbial life.