The Roche limit is the distance around a planet or moon that asteroids or other objects in space cannot get close to, because the gravitational pull of the planet or moon would cause them to break apart. Imagine if you threw a ball at a wall - it would stay in one piece. Now imagine if you threw it too hard and it got close to the wall - it would break apart. The same thing happens with asteroids near a planet or moon. The gravitational pull is so strong that it breaks the asteroids apart!