Ask Ethan: Why Don’t Comets Orbit The Same Way Planets Do?

Ask Ethan: Why don’t comets orbit the same way planets do?

“Why [do] comets orbit the Sun in a parabolic path, unlike planets which orbit in an elliptical one? Where do comets get the energy to travel such a long distance, from the Oort cloud to the Sun & back? Also, how could interstellar comets/asteroids come out of their parent star [system] and visit other ones?”

When we see comets in our Solar System, they can be either periodic, passing near the Sun and then extending very far away, to return many years later, or they could be a one-shot deal. But comets are driven by the same gravitational laws that drive the planets, which simply make fast-moving, nearly-circular ellipses around the Sun. So what makes these orbits so different, particularly if they’re obeying the same laws? Believe it or not, most of the would-be comets out there are moving in exactly the same nearly-circular paths, only they’re far more tenuously held by the Sun. Gravitational interactions might make small changes in their orbits, but if you’re already moving very slowly, a small change can have a very big effect!

Why don’t comets orbit the same way as the planets? Find out on this edition of Ask Ethan!