Pluto is a dwarf planet in the Kuiper Belt region of the Solar System. It is the second-largest known dwarf planet next to Eris, and was considered a full-fledged planet until 2006.
Demotion
In 2006, the International Astronomical Union altered the standards for what makes an object a planet. It established three criteria that the object must meet:
- Must orbit the Sun
- Must generate significant enough gravity to force a roughly spherical shape
- Must have cleared other objects out of its immediate area in space
Pluto did not satisfy the third criterion, and was thus downgraded to a dwarf planet.NASA-JPL: Pluto - Overview
References
Fast Facts
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Fact:
Discovered by Clyde Tombaugh
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Discovered on
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Was considered a planet for 76 years
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Downgraded to a dwarf planet on August 24, 2006
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Named after the Roman god of the underworld
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Radius
1,151 kilometers (18% of Earth's)
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Circumference
7,232 kilometers
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Surface area
16.65 million square kilometers (3% of Earth's)
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Mass
1.3x1022 kilograms
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Average distance from the Sun
5.91 billion kilometers
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Atmospheric Composition (percentages unknown)
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Tenth-largest known entity that orbits the Sun
