Planet

Planet, any major celestial body that orbits a star and does not emit visible light of its own but instead shines by reflected light. Smaller bodies that also orbit a star and are not satellites of a planet are called asteroids or planetoids. In the solar system, there are nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Planets that orbit stars other than the Sun are collectively called extrasolar planets. Some extrasolar planets are nearly large enough to become stars themselves. Such borderline planets are called brown dwarfs. See also Planetary Science.