The Death Star Moons of Saturn

Quick guess: Is this Mimas or Tethys?

By Tommy Hough

Yes, I realize the title of this blog sounds like an science fiction action movie, but when I first saw the  photo above I was certain the moon in question was Mimas. Okay, so what's Mimas? Discovered in 1789 by German astronomer William Herschel -- the same astronomer who discovered Uranus -- Mimas is one of the 62 moons of Saturn, but also one of the best known, in part for a unique feature on its surface.

I was fascinated by planetary science as a kid, and I continue to be fascinated by it. I used to have several Time-Life and National Geographic books I would go to for space geekery, and when Carl Sagan's Cosmos hit the public airwaves, I couldn't get close enough to the TV set. Frankly, if I could do math effectively, I probably would've been some kind of scientist today.

As it is, I'm not a planetary scientist. I'm still terrible at mathematical formulas, but I love the idea of the planets, moons and stars, and it's given me a great sense of humility about my place and our species' place on earth and in the universe. We're all made of starstuff: the same building blocks of comets and galaxies. That's pretty amazing.

Layperson zest aside, it turns out the moon I thought I was ogling at is not Mimas. In fact, it's another moon of Saturn called Tethys. Tethys was discovered by Italian astronomer G.D. Cassini in 1684, on the eve of The Enlightenment (about 80 years after Galileo was jailed for his observation and scientific survey of the heavens). The reason for the confusion is simple: both Tethys and Mimas share one very distinctive thing in common – a massive impact crater on each moon that looks very similar to the Death Star's giant laser dish.

Furthrer proof the most fascinating and awe-inspiring things aren't always fiction, or aren't found in superstition. Real life, and the amazing bits and pieces of the universe resulting from physics, speed and gravity, are all around us.

Kudos to Ralph McQuarrie and the production design team of the first Star Wars movie too, because in the mid-1970s planetary flybys were in their infancy (Voyager hadn't even been launched yet), and there were no close-up or high-resolution photos of the moons of our solar system's outer planets.

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The Death Star eyeball moons of Saturn: Mimas (left) and Tethys.