Some questions, based on things I've heard, but don't know to be true: The rotation of the moon has slowed down to the point that one revolution and one rotation have the same period. A number of the moons of Jupiter and Saturn also have this property. Mercury does something similar to this - something like 3 rotations for every 2 revolutions. Will this phenomenon ever occur to the other planets? Is the Earth day becoming longer? How does this occur? Also, I have heard of something called a "Roche" limit. When a moon's orbit comes within this limit, the planet's gravitational forces will cause the moon to break apart and the moon will become rings. Whether or not a moon will ever become a part of a ring system depends on whether the moon orbits the planet clockwise or counterclockwise as viewed from "above" the solar system. In other words, a moon either spirals in towards the planet or out from a planet (at an exceedingly slow rate) depending on the way it orbits the planet. Is this true for all orbits? Are the planets spiraling in towards the Sun? Could Mercury become a ring system of the Sun? When a moon becomes a ring system, is the new oribt stable or do the particles eventually become incorporated into the planet? Why does this spiraling occur?