Can moons have their own moons?
This isn’t an XZibit joke; it’s a real scientific question. And the answer may be that it’s possible after all.
“People who work every day are kind of scared of things they don’t understand.” -Young Jeezy
In the Solar System, we have the central Sun, a great many planets, asteroids, Kuiper belt objects, and moons. While most of the planets have moons, and some of the Kuiper belt objects and even asteroids have natural satellites that orbit them, there are no known “moons of moons” out there. It may not be because we’re just unlucky; there may be some fundamentally important rules of astrophysics that make it extraordinarily difficult for such an object to stably exist.
When all you’ve got is a single, massive object in space to consider, everything seems pretty straightforward. You’d intuit that gravitation would be the only force at work, and so you’d be able to place any object into a stable, elliptical-or-circular orbit around it. Under that setup, you’d expect that it would continue on that way forever. But there are other factors at play, including the fact that:
- this object can have some sort of atmosphere, or a diffuse “halo” of particles around it,
- this object isn’t necessarily stationary, but can spin —…
