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Twin Pits
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Twin Pits

October 26, 2009
Some impact craters occurring on Earth and on other planetary bodies come in close pairs. These double craters are sometimes the result of the chance superimposition of two distinct impact events. However, a few double craters are also thought to have formed by the impact of two similarly sized bodies that are traveling in close orbit or touching each other. The near-Earth asteroid 4769 Castalia, which has been imaged by radar, is one of the most promising candidates for being such a "contact binary."

This image, taken on June 10, 2000, from an orbital altitude of 51 kilometers (32 miles), caught an obliquely illuminated view of a double crater on Eros. The two craters are so close to each other that they merge into the single dumbell-shaped depression in the center of the image. Each of the two craters is about 550 meters (1800 feet) across. The whole scene is 1.9 kilometers (1.2 miles) across.