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
Jupiter mass outer planets and extrasolar planets. It may also be used to describe the masses of brown dwarfs, as this unit provides a convenient scale for comparison. The current best known value for the mass of Jupiter can be expressed as : which is about as massive than the sun (about ): in scientific notation, Compared to the mass of Earth, Jupiter is 318 times more massive. Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycenter with the Sun lies beyond the Sun's surface at 1.068 solar radii