Pluto is the ninth and smallest planet of our solar system. It was discovered by the astronomer Clyde Tombaugh at the Lowell Observatory in Arizona in 1930. Its highly eccentric orbit makes it the eighth-most distant planet from the Sun for part of each orbit. Pluto orbits in a 3/2 resonance with Neptune. Because of its small size and eccentric orbit, there has been some debate over whether it truly should be classified as a planet. There is mounting evidence that Pluto may in fact be a member of the Kuiper Belt, only one of a large number of distant icy bodies. A subclass of such objects have been dubbed plutinos, after Pluto.
- Approximate Mass: 1.29×1022 kilograms
- Approximate Diameter: 2300 kilometres
- Approximate Surface Area: 17 million km2
- Average Distance from the Sun: 39.53 Astronomical units
- Rotational Period: 6.39 days
- Revolution Period: 247.7 years
- Axial Tilt: 122.5 degrees
- Mean Temperature: 37 Kelvin
Pluto has an atmosphere when it is close to perihelion; the atmosphere freezes out as Pluto moves further from the Sun.
The planet is named both for the Roman god Pluto, and for the astronomer Percival Lowell, who predicted that a planet would be found beyond Neptune.