I seem to recall that 2 of Saturn's smaller moons turned out to be in almost exactly the same orbit, so close that they should have collided as one overtook the other. The gravitational attraction as they approached each other slowed one and sped up the other, which moved them into orbits just sufficiently different that they could pass each other safely. As they receded, gravity changed their speeds in reverse and they slipped back into the original orbits.
Beautifully elegant. Who needs magic? Orbital mechanics is just as amazing...
Post by Aramis of Erak on Jun 26, 2021 20:47:12 GMT -5
The moon of a moon situation has a couple interesting potentials... but for their effects on the parent world, it's little difference from one larger moon of the sum of their masses - their barycenter (center of rotation based upon mass) and the sum of the masses will closely approximate the net effects.
Whereas, two moons of non-coorbital orbit and significant mass (remember, our moon is extremely large compared to its parent) will massively amplify the tidal stresses, as two different speeds result in more flexation (and thus heating and liquid dragging.
Most worlds moons are likely to be smaller; ours is due to a lucky/disastrous collision; it's too big to have been captured. (Sagan, 1987 or so.) To get two significant moons, we'd need to have been hit again without also battering the first moon out of stability by gravitational or kinetic means
Now, even more fun are the "horseshoe orbits" like Asteroid 3753 Cruithne... they're stellar orbitals in a bizarre resonance that makes their relative orbit appear as a horseshoe; it's got a 1:1 resonance with Earth. It's expected to get nudged out in a few centuries.
If it were a more significant mass, the biannual increased tide would be a fun but minor tweak... but think how it would be considered... probably the moon of magic.
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