Pluto, named after the Roman and Greek god of the underworld, is the coldest, smallest, and outermost planet in our solar system. Pluto and its moon, Charon, are called “double planets” because Charon is so large it seems less of a moon than another planet. Pluto was predicted to exist in 1905 and discovered in 1930. It is the only planet that has not yet been studied closely by a space probe. During each revolution around the sun, Pluto passes inside Neptune’s orbit for 20 years, making Neptune the outermost planet for that time. Pluto passed inside Neptune’s orbit in 1979 and remained there until 1999.
Size: Less than one-fifth the size of Earth in diameterDiameter: 1,423 miles? (2,290 km?)Surface: A giant snowball of methane and water mixed with rockAtmosphere: MethaneTemperature: between –369° and –387°F (–223° and –233°C)Rotation of its axis: 6 days, 9 hours, 18 minutesRotation around the Sun: 248 Earth yearsYour weight: Not knownDistance from Earth: At the closest point, 2.67 billion milesMean Distance from Sun: 3,666 million miles (5,900 million km)Satellites: 1Rings: ?
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