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 170469 b HD 170469 b HD 170469 b is a gas giant exoplanet located approximately 212 light-years away in the constellation Ophiuchus, orbiting the star HD 170469. This planet was discovered in April 2007. The star is 1.1 solar mass and the planet is at least 67% the mass of Jupiter, orbiting about half the distance of Jupiter from the Sun. The mass value is only minimum since the inclination is unknown. The orbital distance is more than twice the distance from Earth to the Sun, although taking over three Earth years to orbit the star. The combined distance and period would