Pluto is an icy dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. Pluto was discovered by Clyde Tombaugh in 1930 and declared to be the ninth planet from the Sun.
The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects.”
Pluto's visual apparent magnitude averages 15.1, brightening to 13.65 at perihelion. In other words, the planet has a range of colors, including pale sections of off-white and light blue, to streaks of yellow and subtle orange, to large patches of deep red.
On average, Pluto is a distance of 39.5 astronomical units, or AU, from the sun. That is almost 40 times farther from the sun than Earth is. Because of its elliptical orbit, Pluto is not the same distance from the sun all the time. Pluto's closest point to the sun is 29.7 AU.
Pluto takes 248 Earth years to make one revolution around the sun. That means one year on Pluto is about 248 Earth years. Pluto takes 6 1/2 Earth days/nights to rotate, so one day on Pluto is about 6 1/2 days/nights on Earth.
Pluto probably consists of a mixture of 70 percent rock and 30 percent water ice. Internal structure: The dwarf planet probably has a rocky core surrounded by a mantle of water ice, with more exotic ices such as methane, carbon monoxide and nitrogen ice coating the surface.
Pluto is not very big. It is only half as wide as the United States. Pluto is smaller than Earth's moon. This dwarf planet takes 248 Earth years to go around the sun.
At its warmest, when it is closest to the sun, Pluto can reach temperatures of minus 369 degrees Fahrenheit (minus 223 degrees Celsius). At its coolest, temperatures can fall to minus 387 degrees F (minus 233 C)
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