The solar nebula theory describes the formation of a solar system, from cloud collapse to a star with planets and moons. Which of the following observations would necessitate adjustment to this theory?
a) A gas giant with a cratered surface.
b) A solar system similar to ours but where Venus has a moon.
c) The observation of a gas giant within the frost line.
d) A solar system similar to ours where Earth would have a ring around it.