Scientists have theororized for years that Mars once had liquid water flowing on its surface, but a big discovery by the Curiosity rover gives these theories some more weight.
On Thursday, NASA announced that Curiosity discovered evidence of a stream that once coursed somewhere between the north rim of Gale Crater and the base of Mount Sharp—not far from where the rover landed over the summer. This latest evidence of water on Mars comes in the form of images of rocks containing gravel that appears to be from an ancient streambed. The shape and size of the gravel in conglomerates suggests that they were transported by water flow as opposed to wind.
Curiosity science co-investigator William Dietrich explained:
"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. 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."
Mars currently has frozen water locked away in its polar ice caps, and scientists believe that a layer of permafrost may lie below the planet's surface. Various other Mars probes and rovers have also discovered various bits of evidence that suggest that Mars once had water flowing on its surface, and in 2000, NASA said that Mars might still have some water flows (though this evidence is far from conclusive).
This story, "Curiosity finds ancient streambed on Mars" was originally published by TechHive.