NASA/JPL: Comparing Mars photos (left) with rock outcrops from ancient stream beds on Earth (right)

NASA/JPL: Comparing Mars photos (left) with rock outcrops from ancient stream beds on Earth (right)

NASA’s Curiosity rover mission has found evidence a stream once ran vigorously across the area on Mars where the rover is driving. Scientists have long anticipated the possibility of water on Mars, and it was hoped that Curiosity would help to prove this. This evidence — images of rocks containing ancient stream bed gravels — is an historical scientific watershed.


Mars Curiosity has entered a new word into our everyday vocabulary, “Sol”. Sol is a Martian Day. Just as the Earth day is the time it takes for one complete rotation of the Earth on its axis – 24 hours, a “Sol” is the time that Mars takes to rotate once, which is approximately 40 minutes longer than Earth’s day.

Curiosity landed on Mars on August 5, 2012. On Sol 26 and Sol 27, Curiosity sent from Mars a photo of a conglomerate rock sitting on the surface. The finding site lies between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater. The evidence of water comes from examining two outcrops, called “Hottah” and “Link.”


Scientists are studying the images of stones, which could only be formed by the presence of water. This is a conglomerate rock made up of stream bed stones that are cemented together. 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 stream bed material to direct observation of it.”

In the photo, on the right, is an image of a rock 100 million years old found in central Utah. It was formed by river sediments, and the pebbly texture indicates that sand and gravel cemented into a larger conglomerate rock. Compare that to the similarities in the rock from Mars on the left of the photo. Other imagery sitting uphill from the finds shows an alluvial fan of material washed down from the rim, streaked by many apparent channels, which indicates once rushing water.

“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 rounded shape of some stones in the conglomerate indicates long-distance transport from above the crater rim. The abundance of channels in the alluvial fan between the rim and conglomerate suggests flows continued or repeated over a long time, not just once or for a few years.

“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.

As of this writing, chemical tests are yet to be performed. 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 of stones washed from the crater rim, so the team may also examine several of them to learn about broader regional geology.


The slope within the crater called “Glenelg” – an intentional palindrome to signify the coming and going of Curiosity – remains the rover’s main destination. The mission will continue to analyze conditions that are conducive to making life possible. Clay and sulfate minerals detected there from orbit can be good preservers of carbon-based organic chemicals that are potential ingredients for life.

Mars Science Laboratory researchers will use Curiosity’s 10 instruments over the two-year mission to investigate whether conditions in Gale Crater were ever favorable for microbial life.

A QUICK LOOK:  Curiosity science team member Sanjeev Gupta explains how rounded pebbles spotted by the rover are convincing evidence of an ancient streambed on Mars [VIDEO].

TAKE A CLOSER LOOK: NASA’s Curiosity Rover Finds Old Streambed on Mars – A Panel of Scientist discuss Q&As with the media [VIDEO]