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Mars boasts two of the ugliest moons in the Solar System, including Phobos—an oddly shaped, pockmarked moon featuring a distinctive set of stripes. Astronomers have debated the origin of these grooves for decades, but a new computer simulation suggests Phobos’ stripes were made by rolling and bouncing boulders…
https://gizmodo.com/bouncing-boulders-may-finally-explain-how-mars-ugliest-1830588532