1.3.14 Orbital resonances at Saturn?
In fact there are two examples of 2:1 orbital resonances among Saturn’s principal moons. Mimas (0.942 days) and Tethys (1.888 days) are in 2:1 resonance with each other (2.0, rounded from 1.9832) and Enceladus (1.370 days) and Dione (2.737 days) are also in 2:1 resonance with each other (2.0, rounded from 1.9978).
The orbital resonance between Enceladus and Dione probably accounts for the present-day activity on Enceladus.
Resonant orbits do not remain constant. Their eccentricity (and hence the amount of heating) can increase or decrease over millions of years, and moreover moons can drift in and out of resonant relationships. Curiously, Mimas shows no signs on its surface that it was ever subject to significant tidal heating, but both Tethys and Dione show features that can be attributed to tidal heating in the distant past.
Next week you’ll find out more about moons, including what they are made of, but before that there’s the first end-of-week quiz.