Mimas and Tethys, two small moons of Saturn, are scarred by giant impact craters that make them resemble a "Star Wars" Death Star. On Mimas (left), the crater Herschel is about 80 miles in diameter, while Odysseus Crater on the larger moon Tethys is about 280 miles across. The impacts that created these craters were so powerful that they almost pulverized the moons. [NASA/JPL/SSI]
Moon and Saturn
The Moon probably formed after Earth got a big whack. A body as big as Mars slammed into Earth, blasting molten rock into space. Much of this material then quickly coalesced to form the Moon.
Many other bodies in the solar system have suffered big whacks of their own. Three examples are found among the more than 60 known moons of Saturn. Saturn is to the right of our Moon this evening, and looks like a bright golden star.
The moon Tethys is about 660 miles across. Its major feature is Odysseus Crater, which is more than a third of the diameter of the moon itself. The impact that gouged the crater was so powerful that it would have shattered a solid body. That suggests that Tethys was still partially molten at the time of the collision. That provided enough “give” to keep Tethys from flying apart.
Mimas is smaller than Tethys, but it has a crater of similar proportions to Odysseus. Known as Herschel, the crater is much fresher and deeper than Odysseus. It’s so pronounced that it makes Mimas look like a Star Wars death star.
Finally, Dione appears to have been spun halfway around its axis. It has more craters on its trailing hemisphere than on its leading hemisphere — exactly the opposite of what you’d expect. A possible explanation is that a good-sized impact turned it around. But it seems odd that it would have been turned precisely 180 degrees, so scientists are still looking into the history of this odd little moon.
Script by Damond Benningfield, Copyright 2014
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