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[[File:Planet_collage_to_scale.jpg|thumb|upright=1.5|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 (planet)|Mercury]] (inner planets)]] | [[File:Planet_collage_to_scale.jpg|thumb|upright=1.5|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 (planet)|Mercury]] (inner planets)]] | ||
A '''planet''' is a large, [[Hydrostatic equilibrium|rounded]] [[Astronomical object|astronomical body]] that is generally required to be in [[orbit]] around a [[star]], [[stellar remnant]], or [[brown dwarf]], and is not one itself.<ref | A '''planet''' is a large, [[Hydrostatic equilibrium|rounded]] [[Astronomical object|astronomical body]] that is generally required to be in [[orbit]] around a [[star]], [[stellar remnant]], or [[brown dwarf]], and is not one itself.<ref>{{Cite journal |last=Lecavelier des Etangs |first=A. |last2=Lissauer |first2=Jack J. |date=2022-06-01 |title=The IAU working definition of an exoplanet |url=https://www.sciencedirect.com/science/article/pii/S138764732200001X |journal=New Astronomy Reviews |volume=94 |pages=101641 |doi=10.1016/j.newar.2022.101641 |issn=1387-6473}}</ref> The [[Solar System]] has eight planets by the most restrictive definition of the term: the [[terrestrial planet]]s [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], and [[Mars]], and the [[giant planet]]s [[Jupiter]], [[Saturn]], [[Uranus]], and [[Neptune]]. 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]]. Planets grow in this disk by the gradual accumulation of material driven by [[gravity]], a process called [[accretion (astrophysics)|accretion]]. | ||
The word ''planet'' comes from the Greek {{lang|grc|[[wikt:πλανήτης#Ancient Greek|πλανήται]]}} ({{Transliteration|grc|planḗtai}}) {{gloss|wanderers}}. In [[Classical antiquity|antiquity]], this word referred to the [[Sun]], [[Moon]], and five points of light visible to the naked eye that moved across the background of the stars—namely, Mercury, Venus, Mars, Jupiter, and Saturn. Planets have historically had religious associations: [[History of astronomy#Early History|multiple cultures]] identified celestial bodies with gods, and these connections with mythology and [[folklore]] persist in the schemes for naming newly discovered Solar System bodies. Earth itself was recognized as a planet when [[heliocentrism]] supplanted [[Geocentric model|geocentrism]] during the 16th and 17th centuries. | The word ''planet'' comes from the Greek {{lang|grc|[[wikt:πλανήτης#Ancient Greek|πλανήται]]}} ({{Transliteration|grc|planḗtai}}) {{gloss|wanderers}}. In [[Classical antiquity|antiquity]], this word referred to the [[Sun]], [[Moon]], and five points of light visible to the naked eye that moved across the background of the stars—namely, Mercury, Venus, Mars, Jupiter, and Saturn. Planets have historically had religious associations: [[History of astronomy#Early History|multiple cultures]] identified celestial bodies with gods, and these connections with mythology and [[folklore]] persist in the schemes for naming newly discovered Solar System bodies. Earth itself was recognized as a planet when [[heliocentrism]] supplanted [[Geocentric model|geocentrism]] during the 16th and 17th centuries. | ||