The solar system is as regular as a clock. Planets orbit the Sun year after year, and moons orbit their planets.
Scientists can predict where and when many objects will be positioned in space. But not always, because sometimes accidents happen.
For example, many asteroids cross the orbits of planets, and if they do that when a planet is in the way, you can guess what happens. Asteroids are small, and planets are big. In a head-on collision, the planet probably “wins.” And the asteroid probably becomes part of the planet.
Crashes and near-misses don’t happen often, so scientists get excited when they do.
