Mars mystery rock
PASADENA, CALIFORNIA- NASA says the Mars rover Opportunity found a rock on the red planet that wasn't there 12 days ago.
Opportunity took a photo then that showed no rock and took a picture of the same spot and the rock was there.
Scientists have theories but aren't sure how the rock got there.
The discovery comes as NASA celebrates ten years since the Spirit and Opportunity rovers landed on Mars.
Spirit's mission ended almost four years ago when it lost the use of two wheels and stopped communicating.
Opportunity is still active and sending back pictures.