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Planets (from Ancient Greek ἀστὴρ πλανήτης (astēr planētēs), meaning "wandering stars”) are astronomical objects orbiting a or stellar remnant that is massive enough to be rounded by its own gravity, but is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.
The inner planets of the Solar system, or terrestrial planets because they all have comparable sizes and have solid surfaces like Earth. image:
The term planet is ancient, with ties to history, science, mythology, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of deities.
As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the .
This definition is controversial because it excludes many objects of planetary mass (PlanMos) based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the current definition, some celestial bodies, such as Ceres, Pallas, Juno, Vesta (each an object in the Solar asteroid belt), and Pluto (the first-discovered trans-Neptunian object), that were once considered planets by the scientific community are no longer viewed as such. These smaller planet-like objects of which there may be hundreds are called .