Alex McColgan

MIMOS orbits Saturn once every 22 hours and 36 minutes, and particles orbiting within the inner edge of the Cassini division circle Saturn exactly twice every one orbit of MIMOS.

This is a 2-1 orbital resonance.

Every time MIMOS completes an orbit, it tugs on these ring particles at the exact same point in their path.

It's like pushing a child on a swing.

If you push at the right moment every time, the swing goes higher and higher.

Mimosa's gravity adds energy to these particles, stretching their orbits into ellipses until they collide with other particles or are ejected from the gap entirely.

For years, before Voyager flew past in 1980, revealing the Herschel crater, this resonance was the primary claim to fame for MIMIS.

It was the shepherd of the rings, the gravitational influence that kept the Cassini division clear.

But recent simulations have suggested that MIMIS didn't just clear a pre-existing gap.

Instead, it may have acted more like a snowplough.

standard planetary system models suggest moons migrate outward over time.

But in 2019, when researchers Kevin Bailey and Benoit Noyel were attempting to explain why the Cassini division was so wide, they found this couldn't be the case here.

Their theory instead suggests that Mimas migrated inward towards Saturn somewhere between 4 and 11 million years ago.

As it did so, its resonance moved with it, pushing ring particles aside and carving out the division over millions of years.

This interaction is crucial because it tells us that Mimas is not dynamically static, its orbit changes.

and it was this orbital movement, specifically the way Mimas wobbles, that led to the most recent revelation about this tiny world.

Before we get into exactly what scientists found about Mimas, we have to address an elephant in the room, Enceladus.

Enceladus is Mimas's neighbour.

It's roughly the same size, composed of similar materials, and orbits just outside Mimas.

But Enceladus is spectacular.