What's significant about the latest find is that the rocks are the "first ever" discovered on the Red Planet to contain streambed gravels. The rocks were found by Curiosity last fall. Examining them over time, researchers actually were able to determine how deep and fast the water flowed at that location.
"At a minimum, the stream was flowing at a speed equivalent to a walking pace -- a meter, or three feet, per second -- and it was ankle-deep to hip-deep," Rebecca Williams of the P
According to MSL scientists based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., the ball isn't as big as it looks — it's approximately one centimeter wide. Their explanation is that it is most likely something known as a "concretion." Other examples of concretions have been found on the Martian surface before — take, for example, the tiny haematite concretions, or "blueberries", observed by Mars rover Opportunity in 2004 — and they were created during sedimentary rock formation when Mars was abundant in liquid water many millions of years ago.