Mystery White Rock Inexplicably Appears Near NASA Mars Rover

The images are from Opportunity's panoramic camera (Pancam). The one on the left is from 3,528th Martian day, or sol, of the rover's work on Mars (Dec. 26, 2013). The one on the right, with the newly arrived rock, is from Sol 3540 (Jan. 8, 2014). ( NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.)

Scientists are stumped as to how a rock mysteriously appeared in images taken two weeks apart by NASA's Mars rover Opportunity.

The rover, which landed in an area known as Meridiani Planum a decade ago, is exploring the rim of a crater for signs of past water.

Another rover, Curiosity, touched down on the opposite side of the planet in 2012 for a more ambitious mission to look for past habitable environments. For the moment, however, scientists are pondering a more immediate question.

On Jan. 8, while preparing to use its robotic arm for science investigation, Opportunity sent back a picture of its work area.

Oddly, it showed a bright white rock, about the size of a doughnut, where only barren bedrock had appeared in a picture taken two weeks earlier. Scientists suspect the rock was flipped over by one of the rover's wheels.

It also may have been deposited after a meteorite landed nearby.

Either way, the rock, dubbed "Pinnacle Island" is providing an unexpected science bonus.

"Much of the rock is bright-toned, nearly white," NASA said in a statement on Tuesday. "A portion is deep red in color.

Pinnacle Island may have been flipped upside-down when a wheel dislodged it, providing an unusual circumstance for examining the underside of a Martian rock."