Alex McColgan

When you look at MIMA's invisible light, this difference completely disappears.

The surface looks totally uniform.

Nothing at all correlates to the anomaly we observe.

This led astronomer Dr. John Spencer to playfully joke that Mimas might actually be the Death Star, and that Darth Vader simply applied a clever coat of paint to fool our visible light cameras, hiding the truth from everything except the prying infrared eyes of Cassini.

Now, this thermal anomaly wasn't exactly a sign of internal heat, but rather a sign of how MIMAS interacts with its environment.

You see, MIMAS orbits right inside Saturn's radiation belts.

The moon is constantly bombarded by high-energy electrons trapped in Saturn's magnetic field.

These electrons slam into the leading face of Mimas, welding the powdery snow regolith into hard-packed ice crystals, a process called sintering.

Now, this hard ice has high thermal inertia.

That means that, just like a dense rock on Earth, it absorbs heat during the day and conducts it deep underground, leaving the surface cool.

At night, that stored heat radiates back out.

The mouth of Pac-Man, on the trailing side, is sheltered from this bombardment, so the surface there remains relatively fluffy and powdery, acting like an insulator that heats up quickly in the sun, but holds no heat at night.

This solved the mystery of the thermal map, but in doing so, it also reinforced the idea that MIMOS was a passive object.

The anomaly was due to surface effects rather than anything internal.

But whilst MIMOS is known for its surface features, it's governed by something else.

Its gravitational dance with Saturn, an interaction that creates one of the most famous features in the solar system.

If you look at Saturn through a telescope, you'll see its glorious ring system.

And if your telescope is good enough, you'll see a dark gap splitting the rings in two.

This is the Cassini Division, a 4,800 km wide chasm separating the A ring from the B ring.

This gap exists largely because of Mimas.