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 diameter
- Diameter: 1,423 miles? (2,290 km?)
- Surface: A giant snowball of methane and water mixed with rock
- Atmosphere: Methane
- Temperature: between –369° and –387°F (–223° and –233°C)
- Rotation of its axis: 6 days, 9 hours, 18 minutes
- Rotation around the Sun: 248 Earth years
- Your weight: Not known
- Distance from Earth: At the closest point, 2.67 billion miles
- Mean Distance from Sun: 3,666 million miles (5,900 million km)
- Satellites: 1
- Rings: ?
Size: Pluto’s diameter is 2372 km and its mass is 1.31×1022 kg, which is less than 17.82% of the Moon (less than 0.24% of Earth). Its surface area is 1.665×107 km2, or roughly the same surface area as Russia. Its surface gravity is 0.063g (compared to 1g for Earth). The diameter of the planet is 1,430 miles (2,302 km), only about two-thirds the diameter of the moon and Less than one-fifth the size of Earth in diameter.