South-Pole Aiken Basin
One of largest impact craters in the solar system is the lunar South Pole Aiken Basin. Located on the far side of the moon (which never faces the Earth) it was only possible to discover this feature with robotic probes. Since the mid-1960s, scientists have recognized its enormous dimensions: roughly 2,500 km across, while the moon itself is only 3,500 km in diameter to begin with.
The image above comes from the Lunar Reconnaissance Orbiter, one of NASA’s most recent missions. It contrasts well with the first image of the moon taken by a U.S. spacecraft — the Ranger 7 mission of 1964 – which shows several craters. The large crater in the center right is called Alphonsus, flanked above by Ptolemaeus and below by Arzachel.
Image may be NSFW.
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Images: 1) NASA/Goddard 2) NASA/JPL
