Planet

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its orbit of other debris. The term planet comes from the Ancient Greek word πλανήτης (planētēs), meaning "wanderer," as ancient astronomers noted that their motion was unlike that of the fixed stars. In Hebrew, the word for planet is כוכב לכת (kókháv lékhát). In other languages, the term translates as planète in French, planeta in Spanish and Portuguese, Planeten in German, and 惑星 (wakusei) in Japanese. Key contextual information includes the eight planets in our Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto, once considered the ninth planet, was reclassified as a dwarf planet in 2006. Planets are generally divided into two main types: terrestrial (or rocky) planets and gas giants. Terrestrial planets are composed primarily of rock and metal, while gas giants are largely composed of hydrogen and helium.