 Often such objects continued to be used in literature long after the hypotheses upon which they were based had been abandoned.Other non-existent Solar System objects used in fiction have been proposed or hypothesized by persons with no scientific standing, 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.