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
Distant minor planet Distant minor planet A distant minor planet, or "distant object", is any minor planet found beyond Jupiter in the outer Solar System that is not commonly thought of as an "asteroid". The umbrella term is used by IAU's Minor Planet Center (MPC), which is responsible for the identification, designation and orbit computation of these objects. , the MPC maintains 3497 distant objects in its data base. Most distant minor planets are trans-Neptunian objects and centaurs, while relatively few are damocloids, Neptune trojans or Uranus trojans. All distant objects have a semi-major axis (average distance from the Sun) greater than 6