What common factors do outer planets share in terms of composition, size and mass?
Well, all the outer planets (Jupiter, Saturn, Uranus and Neptune) are all considered ‘gas giants’, in opposition to the inner terestrial planets. They’re all much larger than the earth, their mass on the order of 10^25 to 10^27 kg. They all have quite a few moons (because they’re so much larger, thus having a much stronger gravitational field). They all have a small rocky core, with a thick atmosphere made mostly of light elements (like hydrogen and helium). For more information, check out the websites I mention below.
