Geochemistry source for chemical abundance, despite their rareness (only five have been recovered on Earth). The planets of the Solar System are divided into two groups: the four inner planets are the terrestrial planets (Mercury, Venus, Earth and Mars), with relatively small sizes and rocky surfaces. The four outer planets are the giant planets, which are dominated by hydrogen and helium and have lower mean densities. These can be further subdivided into the gas giants (Jupiter and Saturn) and the ice giants (Uranus and Neptune) that have large icy cores. Most of our direct information on the composition of the giant
History of Solar System formation and evolution hypotheses itself. Most of the mass collected in the centre, forming the Sun; the rest of the mass flattened into a protoplanetary disc, out of which the planets and other bodies in the Solar System formed. There are, however, arguments against this hypothesis. French philosopher and mathematician René Descartes was the first to propose a model for the origin of the Solar System in his "Le Monde" (ou Traité de lumière) which he wrote in 1632 and 1633 and for which he delayed publication because of the Inquisition and it was published only after his death in 1664. In his view,