( CNN ) -- Did Mars rover Opportunity order a jelly doughnut ? Not quite , but scientists are baffled by a white rock with a dark red low spot in the middle that `` just plain appeared at that spot '' on the planet where the rover is situated , says Steve Squyres , lead scientist of the Mars Exploration Rover mission . In recent weeks , Opportunity took photos of the same spot on Mars , 12 days apart . The rover 's panoramic camera showed only barren bedrock on mission day 3528 ( in Mars time ) , but on day 3540 , a photo of the same scene revealed the mysterious , doughnut-shaped rock . Squyres showed photos of this ghostly geological dessert at a recent NASA event celebrating 10 years since the Spirit and Opportunity rovers landed on Mars . Spirit 's mission ended in 2010 after losing the use of two wheels , and ceasing to communicate . But Opportunity is still chugging along and finding new surprises , such as this rock . `` One of the things I like to say is that Mars keeps throwing new things at us , '' Squyres said at the event , gesturing toward the rock photo and laughing . NASA : Watch the presentation . The photos of the outcrop showing the absence , and then presence , of the pastry-sized rock were taken 12 days apart . The rover had not driven over that spot , Squyres said . There are two leading theories about where the rock , called `` Pinnacle Island , '' came from . Neither of them include the possibility of an intergalactic Dunkin ' Donuts . The most likely scenario is that Opportunity flicked the rock with one of its wheels . `` We had driven a meter or two away from here , and somehow maybe one of the wheels , kind of , managed to spit it out of the ground , and have it slide to this position , '' Squyres said . Alternatively , there could be a smoking hole in the ground nearby and the rock could be a piece of crater ejecta , or piece of matter spewn from the impact of a meteorite . Squyres does n't think this is as likely as the idea that the rover displaced the rock , however . Opportunity is now studying the mystery rock more extensively , making measurements and taking pictures . Its instruments have shown scientists that the `` jelly '' part is `` like nothing we 've ever seen before , '' Squyres said . It 's very high in sulfur and magnesium , and it has twice as much manganese as has ever been seen in anything on Mars . No one knows what that means . `` We 're completely confused , we 're having a wonderful time , everyone on the team is arguing and fighting , '' Squyres said . Spirit landed on January 4 , 2004 , followed by Opportunity on January 25 , 2004 . Their primary missions were designated for a mere 90 days , but both far outlasted that target . Squyres said he used to think that no matter how long the rovers lasted , at some point there would be a point in the mission where the team could say `` We 're finished '' -- that they had learned everything could about Mars with those particular vehicles . But the Red Planet is n't like that . `` There will be something tantalizing , something wonderful just beyond our reach that we did n't quite get to , and that 's the nature of exploration , '' he said . Opportunity has otherwise encountered scientifically important phenomena during its decade of investigation . At Endeavor Crater , where it is today , the rover found clay minerals that form in watery conditions , and indicate that water with a neutral pH could have once been there , which would be conducive to microbial life if there had been any . Endeavor has also unveiled veins of a mineral that appears to be gypsum , which is deposited by water . Opportunity is not the only robot roaming Mars . NASA 's 2-ton Curiosity rover , which landed in 2012 , has an even more powerful suite of scientific instruments . Because of Curiosity 's findings , NASA announced for the first time last year that life could have existed on Mars . NASA is planning another rover mission in 2020 -- and that future robot could , possibly , collect samples that would later return to Earth for further study . Such sophisticated technologies will help us see what other mysterious `` sweets '' the planet can deliver . Follow Elizabeth Landau on Twitter at @ lizlandau .
A mysterious rock , shaped and sized like a doughnut , has appeared on Mars . The rover team is studying the rock . Rock appeared in 2004 , 12 years after previous images showed no rock . Opportunity has been exploring Mars since January 2004 .