History of Solar System formation and evolution hypotheses full of hydrogen and helium gas and exchange of angular momentum between giant planets and the particles in the protoplanetary disc. The detailed features of the planets are another problem. The solar nebula hypothesis predicts that all planets will form exactly in the ecliptic plane. Instead, the orbits of the classical planets have various (but small) inclinations with respect to the ecliptic. Furthermore, for the gas giants it is predicted that their rotations and moon systems will also not be inclined with respect to the ecliptic plane. However, most gas giants have substantial axial tilts with respect to the ecliptic,
Giant planet contain enough heavy elements. Also, these stars have high UV radiation and winds that could photoevaporate the gas in the disk, leaving just the heavy elements.<ref name="mass/radius sold"></ref> For comparison, Neptune's mass equals 17 Earth masses, Jupiter has 318 Earth masses, and the 13 Jupiter-mass limit used in the IAU's working definition of an exoplanet equals approximately 4000 Earth masses. Because of the limited techniques currently available to detect exoplanets, many of those found to date have been of a size associated, in the Solar System, with giant planets. Because these large planets are inferred to share more in common