What is a planet?
1 The body must orbit the Sun. A tug from the Sun's gravity causes the current eight planets to revolve around the fiery body along distinct paths.
2 The body must have enough mass to become shaped into a sphere. As a planet spins around its axis, gravity's center-pulling force molds the planet into a sphere. The greater an object's mass, the greater its gravity, and the more likely it is that it will form into a sphere.
3 The body's path around the Sun must be clear of other celestial bodies. Scientists think that as a planet forms, its gravity pulls in surrounding material, such as dust and gas, causing the planet to grow. Pluto does not meet this standard. As a resident of the Kuiper belt, it occupies the same area of space as many other large rocky bodies.
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|Title Annotation:||International Astronomical Union standards|
|Article Type:||Brief article|
|Date:||Oct 9, 2006|
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