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
high school explanation: Okay, so gravity is a force that is inversely proportional to the square of distance. The closer you are the stronger the force. If the body close by is massive enough, the difference in the gravitational force at the point closest and the point furthest is so high it overcomes the force of attraction keeping the large object together.
5 yo explanation: imagine the orbits as a race track SUCH that the closer in you are the faster you have to run. You and your friend and running in nearby tracks keeping pace with each other, and you keep hopping to an inner track. At a certain point you and your friend 10 tracks down are running at such a different speed that you cannot stay together coz you are just not fast enough and you do not stay a together anymore.
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