Fifth planet (hypothetical) Fifth planet (hypothetical) In the history of astronomy, a handful of Solar System bodies have been counted as the fifth planet from the Sun. Under the present definition of a planet, Jupiter is counted as the fifth. There are three main ideas regarding hypothetical planets between Mars and Jupiter. During the early 19th century, as asteroids were discovered, they were considered planets. Jupiter became the sixth planet with the discovery of Ceres in 1801. Soon, three more asteroids, Pallas (1802), Juno (1804), and Vesta (1807) were discovered. They were counted as separate planets, despite the fact that they shared an
HD 147018 b HD 147018 b HD 147018 b is a gas giant extrasolar planet which orbits the G-type main sequence star HD 147018, located approximately 140 light years away in the constellation Triangulum Australe. This planet has minimum mass more than twice that of Jupiter but this planet orbits a lot closer to the star than Jupiter to the Sun by a factor of 22. Meanwhile, it has an eccentric orbit. The planet can get as close to the star as 0.13 AU or can get as far as 0.35 AU. Further out, there is another superjovian planet HD 147018 c, which