Planet



A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity. Planets in the Solar System are divided into two main types: large gas giants, and smaller rocky terrestrial planets. There are eight planets in the Solar System according to the IAU definition. In order of increasing distance from the Sun, there are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites.

Several thousands of planets around other stars ("extrasolar planets" or "exoplanets") have been discovered in the Milky Way. As of 2015, 4,496 known extrasolar planets in 3,198 planetary systems (including 772 multiple planetary systems), ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter, have been discovered, out of which more than 100 planets are the same size as Earth, nine of which are at the same relative distance from their star as Earth from the Sun, i.e. in the habitable zone.