User:XOR'easter/sandbox/Planet lede


 * Inserted into planet with this edit. XOR&#39;easter (talk) 23:15, 7 May 2022 (UTC)

A planet is a large astronomical body that is neither a star nor a stellar remnant. At least eight planets exist in the Solar System: the terrestrial planets Mercury, Venus, Earth and Mars, and the giant planets Jupiter, Saturn, Uranus and Neptune. The word probably comes from the Greek planḗtēs, meaning "wanderer", which in antiquity referred to the Sun, Moon, and five bodies visible as points of light that moved across the background of the stars. These five planets were Mercury, Venus, Mars, Jupiter and Saturn. Earth was recognized to be a planet when heliocentrism supplanted geocentrism during the sixteenth and seventeenth centuries. With the development of the telescope, the meaning of "planet" broadened to include objects not visible to the naked eye: the ice giants Uranus and Neptune; Ceres and other bodies later recognized to be part of the asteroid belt; and Pluto, later found to be the largest member of the collection of icy bodies known as the Kuiper belt. The discovery of other large objects in the Kuiper belt, particularly Eris, spurred debate about how exactly to define "planet". The International Astronomical Union adopted a standard by which the four terrestrials and four giants qualify, placing Ceres, Pluto and Eris in the category of dwarf planet, though this standard has not been universally embraced. Further advances in astronomy led to the discovery of over five thousand planets outside the Solar System. These include hot Jupiters — giant planets that orbit close to their parent stars — like 51 Pegasi b, super-Earths like Gliese 581c that have masses in between that of Earth and Neptune, and planets smaller than Earth like Kepler-20e.

According to the best available theory, planets form when a nebula collapses to create a protostar and a surrounding protoplanetary disk, in which planets grow by the process of accretion.

The planets of the Solar System, including Earth, each rotate around an axis tilted with respect to its orbital pole, and some share such features as ice caps and seasons. Since the dawn of the Space Age, close observations by space probes have found that Earth and other planets share additional characteristics such as volcanism, hurricanes, tectonics and even hydrology. Apart from Venus and Mars, the Solar System planets generate magnetic fields, and all of them save Venus and Mercury possess natural satellites. In addition, the giant planets bear planetary rings, the most prominent being those of Saturn.

Historically, planets have had religious associations. Multiple cultures identified celestial bodies visible to the naked eye with gods, and these connections with mythology and folklore persist in the schemes for naming newly-discovered Solar System bodies.