Saturn’s Other Death Star Moon

Bad Astronomy
The entire universe in blog form
Dec. 7 2012 11:28 AM

That’s No Moon … Oh Wait. Yes It Is.

I wonder what Han, Luke, Chewie, and Obi Wan would’ve thought if they were taking the Millennium Falcon into the Saturn system and saw this:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Tethys, a fully armed and operational moon of Saturn.
Tethys, a fully armed and operational moon of Saturn. Click to wompratenate.

Image credit: NASA/JPL-Caltech/Space Science Institute

That’s not Vader’s Death Star, that’s Tethys, a moon of Saturn, seen by the Cassini spacecraft in late June, 2012. Tethys is about 1,100 kilometers (660 miles) across, a third the size of our Moon. Unlike the Earth’s moon, Tethys is mostly water ice: It’s actually less dense than water, so it would float!

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Its surface is heavily cratered, as you can tell in this picture. And of course there’s that one whopper of a crater, named Odysseus, which is 400 km (240 miles) across. That was a heckuva impact.

Funny, too: Tethys is not the only Death Star moon Saturn has; it’s not even the best. That role belongs to Mimas, the clear winner here:

Saturn's moon Mimas, with the rings in the background.
Saturn's moon Mimas, with the rings in the background. Click to embiggen.

Image credit: NASA/JPL-Caltech/Space Science Institute

That photogenic scene was also taken by Cassini, back in 2005. Mimas is less than half the size of Tethys, but like its big sister is also mostly ice. That giant crater, named Herschel, dominates the moon. In fact, if whatever hit Mimas to make Herschel had been much bigger, it probably would’ve shattered the moon to pieces upon impact, so really this is the biggest crater you can get on that tiny world.

If only it were equipped with some sort of superlaser weapon it could’ve used to prevent the bombardment …

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