Dwarf Planet Pluto Data:
- Mean Radius: 1150 km
- Mass: 0.0025 (Earth=1)
- Density: 2.03 (g/cm^3)
- Gravity: ? (Earth=1)
- Orbit Period: 247.7 (Earth years)
- Rotation Period: 6.39 (Earth days)
- Semimajor Axis Of Orbit: 39.44 au
- Eccentricity Of Orbit: 0.248
Formerly the ninth planet from the sun (usually), Pluto's composition is unknown. Its density indicates that it is probably a mixture of 70% rock and 30% water ice much like Triton. We also know very little about the atmosphere of Pluto, but it probably consists primarily of nitrogen with some carbon monoxide and methane. Pluto revolves about the Sun once in 247.7 Earth years at an average distance of 5.91 billion km (3.67 billion mi). Its orbit is so eccentric that it brings the planet Pluto inside the orbital path of the planet Neptune. Its rotation is reverse that of other planets. Pluto is about 2,360 km (1,475 mi) in diameter. The planet Pluto is the smallest planet in the solar system.
Pluto has one satellite, Charon, which is about 1200km (750ml) in diameter, making the pair the closest in size of any planet/moon combination.
On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet.