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,
Sudarsky's gas giant classification Sudarsky's gas giant classification Sudarsky's classification of gas giants for the purpose of predicting their appearance based on their temperature was outlined by David Sudarsky and colleagues in the paper "Albedo and Reflection Spectra of Extrasolar Giant Planets" and expanded on in "Theoretical Spectra and Atmospheres of Extrasolar Giant Planets", published before any successful direct or indirect observation of an extrasolar planet atmosphere was made. It is a broad classification system with the goal of bringing some order to the likely rich variety of extrasolar gas-giant atmospheres. Gas giants are split into five classes (numbered using Roman numerals) according to