Question

Why are the inner planets rocky while others are mostly in gaseous form?

Answer 1

A planet is a rock ball or cold giant or hot giant etc depending on the balance between its initial gravity (size) and the intensity of the heat from the sun. A large initial size allows accretion of hydrogen and helium thus forming a cold giant if far from the sun. If a very large initial rock core forms near to the sun then there is a possibility that a hot giant may form.Since however the central region of a solar system is the most crowded area hot giants are more likely to be disrupted. I think we will find there is a distribution of solar system arrangements all the way from actual double stars to systems with no gas giants at all, with all possible combinations of hot and cold giants in between.