The `` jelly doughnut '' rock that seemed to appear out of nowhere on Mars last month did not fall out of an extraterrestrial pastry box . The rock had been mysterious to scientists because Mars rover Opportunity photographed it in a spot where the rock had not been present just four days earlier . Steve Squyres , lead scientist of the Mars Exploration Rover mission , described it as a white rock with a dark red low spot in the middle . The rock , more than 1.5 inches wide , was named Pinnacle Island . So where did it come from , then ? Drumroll please : . Researchers now say Pinnacle Island is a piece of a larger rock , which Opportunity broke and moved with its wheel in early January . Further images from the rover reveal the original rock that the rover 's wheel must have struck . `` Once we moved Opportunity a short distance , after inspecting Pinnacle Island , we could see directly uphill an overturned rock that has the same unusual appearance , '' said Ray Arvidson of Washington University in St. Louis , deputy principal directory of Opportunity , in a statement . `` We drove over it . We can see the track . That 's where Pinnacle Island came from . '' No , that 's not as exciting as if the rock had crawled into view on its own or been dropped there by aliens . But now that this puzzle has been solved , the rover team plans to drive Opportunity south and uphill to look at exposed rock layers on a slope . The rock has high levels of manganese and sulfur , which may have been concentrated in the rock because of water , researchers say . `` This may have happened just beneath the surface relatively recently , '' Arvidson said , `` or it may have happened deeper below ground longer ago and then , by serendipity , erosion stripped away material above it and made it accessible to our wheels . '' Opportunity weighs 384 pounds and measures about 5 feet in both length and height . It recently celebrated 10 years since its January 25 , 2004 , landing . Opportunity 's twin , Spirit , landed on January 4 , 2004 . Spirit stopped communicating in 2010 , but Opportunity continues to reveal details about the Red Planet 's former habitable conditions . NASA : 2 places on Mars could have been habitable . Opportunity is the older , less technologically advanced of the two NASA rovers currently exploring Mars . The car-sized Curiosity rover , representing a $ 2.5 billion mission , is now on its way to Mount Sharp , a sedimentary formation that will allow the rover to explore Mars ' history by driving up the peak 's slope and exploring rock chemical composition layer by layer . NASA is planning to launch another Curiosity-sized rover in 2020 , which could collect samples that later missions might return to Earth .
Researchers : Mars Opportunity rover 's wheel broke off a piece of rock . That piece is the 'mystery rock ' that looks like a doughnut . Comment: