Strange Grooves on Phobos Were Caused by Boulders Rolling Around on its Surface

Much of Phobos' surface is covered with strange linear grooves. New research bolsters the idea that boulders blasted free from Stickney crater (the large depression on the right) carved those iconic grooves. Image Credit: NASA/JPL-Caltech/University of Arizona

Back in the 1970s, NASA’s Mariner and Viking Missions were sent out to explore other planets in our Solar System. All three of them (there were two Viking missions) captured images of Mars’ moon Phobos during their travels. They were our first images of the tiny, potato-shaped moon, and the images held a mystery: strange linear grooves on the moon’s surface.
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