![]() In antiquity, this word referred to the Sun, Moon, and five points of light visible by the naked eye that moved across the background of the stars-namely, Mercury, Venus, Mars, Jupiter and Saturn. The word planet probably comes from the Greek planḗtai, meaning "wanderers". The giant planets bear planetary rings, the most prominent being those of Saturn. Apart from Venus and Mars, the Solar System planets generate magnetic fields, and all except Venus and Mercury have natural satellites. All planets of the Solar System other than Mercury possess a considerable atmosphere, and some share such features as ice caps, seasons, volcanism, hurricanes, tectonics, and even hydrology. These planets each rotate around an axis tilted with respect to its orbital pole. The Solar System has at least eight planets: the terrestrial planets Mercury, Venus, Earth and Mars, and the giant planets Jupiter, Saturn, Uranus and Neptune. ![]() Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. The eight planets of the Solar System with size to scale (up to down, left to right): Saturn, Jupiter, Uranus, Neptune (outer planets), Earth, Venus, Mars, and Mercury (inner planets)Ī planet is a large, rounded astronomical body that is neither a star nor its remnant. ![]()
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