All Hail Mimas: Our 'Death Star' Moon

It's not in a galaxy far, far away or even another star system -- this alien world is right in our planetary backyard, a mere 900 million miles away in orbit around Saturn.

It's not in a galaxy far, far away or even another star system - this alien world is right in our planetary backyard, a mere 900 million miles away in orbit around Saturn. It's called Mimas, and although it undeniably is a moon it does bear an uncanny resemblance to a certain well-known sci-fi space station.

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The image above was captured by NASA's Cassini spacecraft on Feb. 13, 2010, and shows the hallmark of Mimas' expert Star Wars cosplay: the (relatively) enormous Herschel crater on its northern hemisphere. Spanning 88 miles (140 km), Herschel is a full one-third the diameter of the 246-mile (396-km) wide moon, and with a prominent central peak it's nearly a spot-on match for the Death Star's infamous planet-killing superlaser cannon.

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(Unlike the aforementioned, no Bothans were harmed in the obtaining of this data.)

In comparison if Earth were to have a crater of a relative size to Mimas' monster Herschel, it would be 2,500 miles across - about the distance from New York City to Los Angeles!

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Mimas is composed mostly of water ice and a small bit of rock. At its low surface temperature of -350 degrees Fahrenheit (-208 degrees Celsius) water is as hard as rock is here on Earth. Like its bigger sister moons Rhea and Dione, Mimas is covered with impact scars - it is literally one of the most heavily-cratered worlds in the solar system.

Unlike the similarly-sized Enceladus, though, Mimas lacks any current evidence of a subsurface ocean. Somehow its water has remained solidly frozen for a very long time despite being closer to to Saturn and having an even more eccentric orbit than Enceladus. Scientists are still trying to determine why this is the case.

Discovered in 1789 by German astronomer William Herschel, Mimas orbits Saturn at an average distance of 115,277 miles (185,520 km) - about half the distance that our moon is from us.

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And if you simply must have the comparison, the very real Mimas is - according to the resource site Wookieepedia - about 100 miles (160 km) wider than the fictional Death Star(s) of the Star Wars universe. It may lack laser turrets or a planet-destroying cannon but it's also well without any poorly-placed thermal exhaust shafts and, long after the destruction of the Galactic Empire, Mimas is still around.

Source: NASA/JPL

"That's no moon, it's a space station..."

On August 4, the much-anticipated "Wonders of the Solar System" will premier on the Science Channel.

Presenter and physicist Prof. Brian Cox will show you the hidden mysteries of our interplanetary neighborhood, as well as breathtaking sights of the planets, moons and the sun. Cox will also examine some of Earth's extreme environments to see how life has adapted, perhaps helping us understand whether life can exist elsewhere in our solar system. To provide a taster of what you can expect from "Wonders," Discovery News has gathered some facts, figures and the best images of our solar system to assemble a special Wide Angle supporting this groundbreaking documentary. So, let's dive into orbit of the ringed gas giant, Saturn...

Moons of Saturn: Enceladus

Welcome to Enceladus, one of Saturn's icy inner moons. The streams of light you see are actually jets of water shooting out of the surface. The Cassini spacecraft discovered the geysers in December 2005, shown here in false-color. Researchers think gravitational kneading of its core heats subsurface water into vapor, causing it to spew out of the moon's chilly -328 degrees F surface.

Moons of Saturn: Tethys

This 665-mile-wide moon of Saturn, pronounced "teeth-this," has an ice-covered surface criss-crossed with cracks and faults. In this Cassini snapshot, a small mountain range inside the Odysseus crater can be seen. Covering about two-fifths of Tethys' surface, the crater is enormous, and the mountains are thought to have formed from shifting surface ice.

Moons of Saturn: Epimetheus

Set against a large smoky Titan and Saturn rings, Epimetheus stands out as the "lil' white moon," as scientists have nicknamed it. This image is in false color, but not without purpose. It allows us to see Titan, Saturn and Epimetheus clearly and compare their sizes -- Epimetheus is 72 miles across while giant Titan is 3,200 miles across.

Moons of Saturn: Pan

Like its storybook counterpart, Saturn's moon Pan likes to play around. Cassini found it on Aug. 1, 2005 circling in and out the Encke Gap of Saturn's A ring, shown here. Pan is small compared to some of its brothers and sisters -- only 16 miles across -- and looks something like a walnut. Despite its small size, Cassini was able to capture it from about 500,000 miles away.

Moons of Saturn: Iapetus

What is Saturn's walnut-shaped moon Iapetus covered in? Scientists think perhaps a bit of both dust and ice, though the particulars are sketchy. The moon's mysterious dark splotches are probably made of carbon-based gunk that seeped from below. By using Cassini's images, NASA researchers determined that the carbon residues came from sub-surface volcanoes or geysers similar to those found on Enceladus.

Moons of Saturn: Phoebe

This hunk of rock circling Saturn under the guise of a moon could have once been a comet. Cassini snapped this photo on June 30, 2004 and researchers have since been studying its unusual pox surface, backwards orbit, low density and extremely dark features. They think Phoebe might have been a Kuiper Belt object close to Neptune before Saturn's gravitational pull snagged it.

Moons of Saturn: Mimas

Nope, this isn't the Death Star hanging around Saturn for its chance to blast Earth. This is Mimas, and it's a lucky survivor from an ancient, colossal collision. At 80 miles wide, the "eye" -- called Herschel crater -- covers a good portion of the 247-mile-wide moon.

Moons of Saturn: Hyperion

This strange Saturn moon might look like a rocky sponge, but scientists think Hyperion is made mostly of ice. Cassini shot this high-contrast image in 2005 to peek down inside the thousands of craters bored into its surface. What did it find? Mysterious dark gunk that might be a few feet thick in places.

Moons of Saturn: Dione

Giovanni Cassini, who spent a good part of his life looking at Saturn through a telescope, discovered Dione in 1684. Like most Saturn satellites, it's made mostly of ice. The Cassini spacecraft -- named after you-know-who -- found cliffs of ice hundreds of feet high in late 2004. Scientists think movement of the crust split it open to create the towering structures.

Moons of Saturn: Titan

Scientists think of Titan, mightiest of all the Saturn moons, as a sort of early Earth chock full of organic compounds and a thick atmosphere. In January 2005, the Huygens probe landed on Titan's surface, revealing many of the orange-brown world's secrets. That makes Titan the only moon aside from Earth's to receive a robotic surface visit from humans. This false-color photo shows Titan's surface in green and its sunlight-absorbing stratosphere in red.

Moons of Saturn: Janus

Janus is a tiny, potato-shaped satellite that is typical of Saturn's 17-plus moons: cratered and icy. It's the big brother to the moon Epimetheus, which hangs out in nearly the same orbit. By studying Cassini spacecraft images closely, scientists have noticed both moons hang out in a thin but wide ring of dust and ice -- likely the leftovers of meteorite impacts over the eons.

Moons of Saturn: Rhea

Sadly, Saturn's 949-mile-wide moon Rhea doesn't look like this in normal light. The image is cast in false color (for scientific reasons, of course) using images taken in several different wavelengths. Scientists aren't certain what to make of the stripes that appear in the composite image, but they do think Rhea is about one part rock and three parts ice. Like Dione, it also seems to have huge cliffs of ice.

Slide show originally published in June 2008.