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The strange spheres Opportunity found on Mars Image: NASA

Curiosity was the rover on everyone’s mind this summer, but it is a young whippersnapper compared to the veteran Opportunity, which has been hard at work on Mars since 2004 and shows no signs of stopping.

Last Friday, NASA announced that Opportunity had found an unusual rock formation. The beaded surface at first appeared very similar to spheres that Opportunity located back in 2004, soon after it landed. Those original spheres were nicknamed blueberries (we can only assume the scientists were hungry at the time):

The original ‘blueberries’ Image: NASA

Further research showed that the blueberries were iron-rich concretions, a formation commonly seen on Earth. These concretions form as a coating is deposited on a piece of debris, building outward into a sphere-like shape. (Think of the coating of a jawbreaker.)

But the new nodules found by Opportunity are vastly different from the originals, and scientists are thrilled to have a new piece to the Red Planet puzzle.

In a NASA press release, principal investigator Steve Squyres of Cornell University sums it all up, comparing the new formations to the ‘blueberries’ found 8 years ago:

“They seem to be crunchy on the outside, and softer in the middle…They are different in concentration. They are different in structure. They are different in composition. They are different in distribution. So, we have a wonderful geological puzzle in front of us. We have multiple working hypotheses, and we have no favorite hypothesis at this time. It’s going to take a while to work this out, so the thing to do now is keep an open mind and let the rocks do the talking.”

Your move, Curiosity.

More from Smithsonian.com:

Remember the Face on Mars?
Dirty Curiosity Rover Could Seed Mars With Earthly Bacteria
 Life on Mars?