What are these strange little spheres doing on on Mars? The Opportunity rover happened upon these unusual beads while exploring a place named Kirkwood near the rim of Endeavour Crater. This picture, taken by the rover’s Microscopic Imager, shows that some ground near the rover was filled with these unusual spheres, each only about 3 mm across. This sometimes-fractured balls appear similar to small rocks called blueberries which Opportunity found eight years ago. However, unlike the blueberries, these spheres are densely compacted and have little iron content. Although it is thought that these orbs formed naturally, no one has come up with a reasonable explanation of how.

Image Credit: NASA

Where would you want to spend the winter on Mars? As winter approached in the southern hemisphere of Mars last November, the Opportunity rover had just this problem. It needed a safe place to go. The reduced amount of sunlight falling on its solar panels could not keep up with the power needed to keep equipment warm. That would drain the rover’s batteries. So Opportunity was instructed to climb onto the 15 degree incline of Greeley’s Haven, the rocky slope ahead in this picture. The tilt of the incline increased power input to the solar panels through greater exposure to sunlight. Beyond Greeley Haven lies expansive Endeavour Crater, the ancient impact basin that Opportunity will continue exploring as the Martian winter concludes in a few months—if it survives.

Image Credit: NASA/JPL