Fictional planets of the Solar System while yet others are purely fictional and were never intended as serious hypotheses about the structure of the Solar System. Vulcan was a hypothetical planet supposed to revolve around the Sun inside the orbit of Mercury, invoked to explain certain irregularities in Mercury's orbit. The planet was proposed as a hypothesis in 1859, and abandoned not later than 1915. The name "Vulcan" has been used for various other fictional planets, in and out of the Solar System, that do not correspond to the hypothetical planet Vulcan. The planet Vulcan in the "Star Trek" franchise, for instance, is specified as orbiting
History of Solar System formation and evolution hypotheses of dynamics makes capture most unlikely as it requires special conditions. Swiss astronomer Louis Jacot (in 1951, 1962, 1981), like Weisacker and Ter Haar, continued the Cartesian idea of vortices but proposed a hierarchy of vortices or vortices within vortices, i.e., a lunar system vortex, a Solar System vortex, and a galactic vortex. He put forward the notion that planetary orbits are spirals, not circles or ellipses. Jacot also proposed the expansion of galaxies (stars move away from the hub), and that moons move away from their planets. He also maintained that planets were expelled, one at a time, from