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Explanation: Stickney Crater, the largest crater on the martian moon Phobos, is named for Chloe Angeline Stickney Hall, mathematician and wife of astronomer Asaph Hall. Asaph Hall discovered both the Red Planet's moons in 1877. Over 9 kilometers across, Stickney is nearly half the diameter of Phobos itself, so large that the impact that blasted out the crater likely came close to shattering the tiny moon. This stunning, enhanced-color image of Stickney and surroundings was recorded by the HiRISE camera onboard the Mars Reconnaissance Orbiter as it passed within some six thousand kilometers of Phobos in March of 2008. Even...

HiRISE image of Stickney Crater on Phobos. Credit: NASA/JPL/University of Arizona. Stickney crater is almost half the diameter of Phobos itself. Why did the impact not shatter this small moon? The color picture above is a composite from two pictures taken about 10 minutes apart in order to give the 3-dimensional aspect. A recent Picture of the Day described some of the large-scale formations on Phobos, especially Stickney Crater, but this more dramatic picture, which has recently become available, deserves another showing because it portrays the distinctive features of an Electric Discharge Machining (EDM) event with greater clarity. The...