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Pluto: Overview
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Color image of Pluto and Charon.
One of the final approach images of Pluto and Charon taken by New Horizons in the days before its 14 July 2015 Pluto flyby.

Discovered in 1930, Pluto was long considered our solar system's ninth planet. But after the discovery of similar intriguing worlds deeper in the distant Kuiper Belt, icy Pluto was reclassified as a dwarf planet. This new class of worlds may offer some of the best evidence about the origins of our solar system.

10 Need-to-Know Things About Pluto:

  1. If the sun were as tall as a typical front door, Earth would be the size of a nickel and dwarf planet Pluto would be about the size of the head of a pin.
  2. Pluto orbits our sun, a star, at an average distance of 3.7 billion miles (5.9 billion kilometers) or 39.5 AU.
  3. One day on Pluto takes about 153 hours. That's the time it takes for Pluto to rotate or spin once. Pluto makes a complete orbit around the sun (a year in Plutonian time) in about 248 Earth years.
  4. It is thought that Pluto has a rocky core surrounded by a mantle of water ice with other ices coating its surface.
  5. Pluto has five known moons. Pluto is sometimes called a double-planet system due to the fact that its moon Charon is quite large and orbits close to its parent planet.
  6. There are no known rings around Pluto.
  7. Pluto has a thin, tenuous atmosphere that expands when it comes closer to the sun and collapses as it moves farther away -- similar to a comet.
  8. NASA's New Horizons spacecraft is the first mission sent to encounter the Pluto-system and other members of the Kuiper Belt.
  9. Scientists do not think Pluto can support life as we know it. Although, some scientists believe it is possible Pluto could possess a hidden ocean under its surface.
  10. Pluto was considered a planet from 1930, when it was first discovered, until 2006. The discovery of similar-sized worlds deeper in the distant Kuiper Belt sparked a debate which resulted in a new official definition of a planet. The new definition did not include Pluto.

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Just the Facts
Orbit Size (semi-major axis):  5,906,440,628 km
Mean Radius:  1,151 km
Volume:  6,387,259,783 km3
Mass:  13,032,000,000,000,000,000,000 kg
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Fran Bagenal Fran Bagenal
"I really enjoy my involvement in space missions -- it is the best part of my job -- Voyager, Galileo, Deep Space 1, New Horizons and Juno." Read More...
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Last Updated: 17 Jul 2015