• Question: Jupiter has many moons. Each one looks like it is made of very different stuff. This one is rock, that one is ice... Why, if they condensed out of the same cloud of dust when the solar system was made?

    Asked by wesaal786 to Ben, Ezzy, Sam on 22 Mar 2012. This question was also asked by clummy.
    • Photo: Elizabeth Pearson

      Elizabeth Pearson answered on 22 Mar 2012:

      A very good question. That’s something a lot of people have been asking for a long time and we’re still not 100% sure.

      The moon was created when a meteor smashed into the earth and kicked up this lump of rock. Jupiter is a gas giant though, so that doesn’t really work. Most likely the moons are captured from asteroids etc as they streak past. So asteroids from different areas of the solar system where there are different types rock and ice come towards Jupiter and get caught, then form moons.

    • Photo: Ben Smart

      Ben Smart answered on 22 Mar 2012:

      We don’t know for sure, but the fact they are made of different things suggests that they didn’t all come from the same dust-cloud, or at least not all at the same time. Some moons may have originally been asteroids that got caught up in Jupiter’s gravity. Another thing to think about it that the different moons will have different densities and different masses, and different velocities as they orbit Jupiter. It’s possible that different materials (rock, ice, etc.) each with different densities, could only form stable orbits (and so clump together to form a moon) at certain distances away from Jupiter, depending on the properties of the materials. If a material with a given density and velocity was too far away from Jupiter, or too close, then it wouldn’t orbit around jupiter and would fly off into space. Only the stuff left in stable orbits would form moons. I could be wrong about that one, but that’s where my problem solving lead me. 🙂