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SYFY WIRE Bad Astronomy

That’s No Moon … Oh Wait. Yes It Is.

By Phil Plait

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?

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!

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:


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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