More than eight years into its mission, Mars Exploration Rover Opportunity is still sending back data and images that consistently fill us with wonder and periodically leave scientists scratching their heads. Consider the image above. Taken by Opportunity at an outcropping on the rim of Endeavour Crater known as Kirkwood, it reveals a small stretch of ground littered with tiny spheres, and geologists have no idea what they are or how they got there.
via Popular Science

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