Scientists figure out mystery of 'jelly doughnut' in Mars images

This composite image provided by NASA shows before and-after images taken by the Opportunity rover. At left is an image of a patch of ground taken on Dec. 26, 2013. At right is in image taken on Jan. 8, 2014 showing a rock shaped like a jelly doughnut that had not been there before. (AP Photo/NASA)

PASADENA, Calif. -- Scientists have solved the mystery of the "jelly doughnut" rock on Mars that appeared to come out of nowhere.

NASA said Friday that a wheel of the rover Opportunity broke it off a larger rock and then kicked it into the field of view.

The Internet was abuzz last month when the space agency released side-by-side images of the same patch of ground. Only one image showed the rock, which was white around the outside and dark red in the middle, and less than 2 inches wide.

Scientists had suspected that one of Opportunity's wheels kicked the rock as it drove. They received confirmation after analyzing recent images of the original piece of rock.

Opportunity recently celebrated 10 years on Mars. Its twin Spirit stopped communicating in 2010.