Why do celestial objects have an innermost stable circular orbit? What causes the instability of an orbit below this radius?

Question

Edit: People are confusing [this concept](https://en.m.wikipedia.org/wiki/Innermost_stable_circular_orbit) with the [Roche limit](https://en.m.wikipedia.org/wiki/Roche_limit). Wikipedia isn’t very helpful in explaining why the innermost stable circular orbit exists, but it does lay out the basic concept. It’s the innermost point at which an object can orbit another object at all, not the point at which it begins breaking up from tidal forces.

In: 5

Answer 1

Yeah, /u/FlyingNapalm is talking Roche Limit, which is important close to a star or planet, but it’s not what you’re asking about.

I suspect the unstable inner orbit has something to do with General Relativity.

Try asking in /r/astrophysics