NASA's Curiosity Rover finds 'round rock' on Mars

Curiosity Rover has found a spherical rock on the Martian land atop a rocky outcrop.

The rock, which was dusty, appeared a little darker than the surrounding rock and seemed like an old cannonball or possibly a dirty golf ball.

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.