Alex McColgan

It has tiger stripe fractures at its south pole that blast geysers of water vapour into space, creating Saturn's E-ring.

And we now know Enceladus has a global subsurface ocean that is warm and potentially habitable.

I have another video on the latest discoveries here if you want to take a look.

The problem is that according to standard tidal heating models, Mimas should be the active one.

Mimas is closer to Saturn than Enceladus, and its orbit is much more eccentric.

Both of these factors mean that tidal heating, the friction generated inside a moon as it gets stretched and squeezed by gravity, should be much stronger.

The math says that Mimas should be experiencing significantly more tidal heating than Enceladus.

So why was Enceladus melting while Mimas looked like a frozen block of ice?

This is what researchers have long called the Mimas Paradox.

The prevailing theory was that Mimas was simply too cold.

If a moon freezes solid, its ice becomes rigid and it can't flex.

This means that it doesn't generate friction, instead entering a state of high Q or quality factor, which implies low dissipation.

Imagine hitting a bell.

The energy isn't absorbed, instead the bell rings.

Enceladus, for whatever reason, stayed warm and slushy, allowing the tides to keep adding energy to its interior.

Mimas, on the other hand, we assumed, missed its window.

It froze early and stayed frozen.

But that isn't the end of the story.

In 2014, researchers noticed something wasn't quite right.

They measured the Libration of Mimas, the slight wobble it experiences as it rotates.