Pluto is a dwarf planet in the outer solar system, second largest in the Kuiper belt. Discovered in 1930, it has a brownish color, three moons, and an average surface temperature of 49 K. The New Horizons spacecraft will approach Pluto in 2015.
Pluto is an outer solar system body formerly known as a planet, but by a 2006 resolution of the International Union of Astronomers it is now known as a dwarf planet, along with Ceres and Eris. It is the second largest member of the Kuiper belt, an icy asteroid belt outside the orbit of Neptune. Pluto’s orbit varies between 2 and 29 AU (Earth-Sun distance) from the Sun. It is one-fifth the diameter of the Earth, smaller than the Moon at one-quarter the size of the Earth. Pluto has an average surface temperature of 49 K (-44 C).
Pluto was discovered in 1930 by Clyde Tombaugh by comparing the variations in two photographic plates. In the early 20th century, scientists began searching for a Planet X, which was said to have caused perturbations in Neptune’s orbit, just as Neptune’s existence was predicted by perturbations in Uranus’s orbit. Although Pluto was found near the position where planet X was predicted to be, it could not have been the predicted planet, because it was too small to affect Neptune’s orbit. It was later discovered that the perturbations in Neptune’s orbit could be explained by Einstein’s new theory of general relativity.
Pluto has a brownish color with a large black spot in the center. It wasn’t until the launch of the Hubble Space Telescope that astronomers saw Pluto as much more than a faint spot. Pluto has three moons; Charon, Hydra and Nix. Charon is substantially larger than the others. When Pluto was discovered, many people sent recommendations for its name. The winner was an 11-year-old Oxford student, Venetia Burney, who presented Pluto.
In 2015, the New Horizons spacecraft will approach Pluto, observing it and its moons up close. This will be the most distant object ever approached by an artificial satellite. After New Horizons passes Jupiter, it will become the fifth probe to exit the solar system.
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