NASA’s long-lived rover Opportunity has returned an image of the Martian surface that is puzzling researchers. “This is one of the most extraordinary pictures from the whole mission,” said Opportunity’s principal investigator, Steve Squyres of Cornell University in Ithaca, N.Y.

These spherical objects, concentrated at an outcrop called Kirkwood on the western rim of Endeavour Crater, differ in several ways from the iron-rich spherules nicknamed “blueberries” the rover found at its landing site in early 2004.

NASA Science News has the full story.