• Question: Why does every planet have a moon?

    Asked by SpaceFan★★★★★ to Betty, Isaac, Kieran, Silvia, Will on 18 Nov 2016.
    • Photo: Silvia Pardo

      Silvia Pardo answered on 18 Nov 2016:

      We think that moons are just chunks that planets lost when the solar system was very young and asteroids crashed into them all the time.
      But not all planets have moons! In particular Venus and Mercury don’t: Mercury is so close to the Sun and so small in comparison than it wouldn’t be able to hold a moon in orbit, the gravity pull from the Sun is so strong that any moons would fall to it and get “eaten”. Venus is a bit of a mystery, but we think it had a moon in a unstable orbit that ended up falling back to the planet.