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The Biggest Crater

Week of August 24, 1998
I know that there has been a lot of hype about asteroid and comet impacts in the press lately (and of course on these pages as well), but how can I resist one more take on it? So I'll ask a question of you, O Bitesized Reader: where and how big is the largest impact crater in the solar system?

I personally would have guessed either a planet like maybe Mars, near the asteroid belt, or an outer moon of Jupiter, where the big planet's gravity would give an impactor an extra nudge of velocity. But I would be wrong. The answer is: our very own Moon.

While looking up some info for a potential Bad Astronomy page, I stumbled across an image of the Moon on the wonderful Astronomy Picture of the Day Site. The picture is of the Moon, taken by the Clementine probe, and shows the South Pole-Aitken Basin, an impact scar over 2000 kilometers across! That's a bit more than the north-south extent of the United States, to give you an idea of what would have happened had it hit here instead.

Amazingly, this crater is not the largest relative to the parent body. That distinction goes to the crater Herschel, on Saturn's moon Mimas.

©2008 Phil Plait. All Rights Reserved.

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