IAU definition of planet

2006 International Astronomical Union definition

In August 2006, the International Astronomical Union (IAU) adopted a new definition of the term planet, which stated that, in the Solar System, a planet is a celestial body that: is in orbit around the Sun, has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and has "cleared the neighbourhood" around its orbit. A non-satellite body fulfilling only the first two of these criteria (such as Pluto, which had hitherto been considered a planet) is classified as a dwarf planet and not a planet. A non-satellite body fulfilling only the first criterion is termed a small Solar System body (SSSB).

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