Science Common Sense

105 - What makes a planet a planet?

To be a planet, a thing in space must meet three rules:

  1. It must be round (or nearly round) because of its own gravity.
  2. It must be in orbit around a star (like the Sun).
  3. It must be big enough to clear its area around its orbit, meaning it's the biggest thing in its path.

If something in space meets these rules, it's a planet.

PrevHomeNext