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 65216 b of Mars from the Sun, but at periastron the planet is a fifth closer to the star than Earth from the Sun and at apoastron it is over twice as far. HD 65216 b HD 65216 b is an extrasolar planet located approximately 116 light-years away in the constellation of Carina, orbiting the star HD 65216. This planet was discovered by the Geneva Extrasolar Planet Search Team in 2003. Like most planet candidates so far, it was detected with the radial velocity method. The planet has a minimum mass about 20% more than Jupiter. Since the discovery method gives only