How did gas giant planets form?

The term "gas giant" is misleading because it only refers to planets that are primarily composed of hydrogen and helium; only Jupiter and Saturn are considered true gas giants because the pressures at their centers are so high that even hydrogen will solidify.

Since Neptune and Uranus are composed of heavier substances known as ices, they are essentially ice giants.

Since the formation of gas giants has never been witnessed, we are forced to rely on theories and computer simulations.

The conventional wisdom holds that a rocky core would eventually gather gaseous material to form a gas giant, but simulations show that this process would be too slow and that the gas would have dispersed before the planet could form.

There are currently theories explaining how gas in the solar system's formation disc clumped together to form gas giants very quickly.

Core accretion and gravitational instability are the two processes that lead to the formation of gas giant planets: in the former case, a solid core forms first and draws gas from the protoplanetary disk; in the latter case, unstable regions of the disk collapse directly into gas giant planets.