Dwarf planet
Pluto
The famous dwarf planet
Pluto is the best-known dwarf planet, orbiting in the Kuiper Belt beyond Neptune. Discovered in 1930, it was called the ninth planet until 2006, when the International Astronomical Union defined "planet" and reclassified Pluto because it has not cleared its orbital neighborhood of other objects. Pluto is a complex world with mountains of water ice, glaciers of nitrogen ice, a thin atmosphere, and a giant heart-shaped plain called Tombaugh Regio.
Quick facts
- Distance from Sun
- 5.9 billion km (39.5 AU average)
- Diameter
- 2,377 km (0.19x Earth)
- Day length
- 6.4 Earth days
- Year length
- 248 Earth years
- Moons
- 5 (largest: Charon)
- Avg. temperature
- -232 C
What's it like there?
Pluto is a deeply cold world at about -232 C, where nitrogen and methane freeze solid. Its famous heart-shaped glacier, Sputnik Planitia, is a slowly churning sea of nitrogen ice. Water ice is so hard at these temperatures that it forms mountains up to 3.5 km tall. Pluto's largest moon, Charon, is more than half Pluto's size, so the two orbit each other like a double world, always showing the same face to one another.
Notable moons
Charon
Half the size of Pluto; the pair orbit a point between them.
Styx, Nix, Kerberos, Hydra
Four small moons discovered by Hubble.
Fun facts
Pluto is smaller than Earth's Moon.
A year on Pluto lasts 248 Earth years; it has not completed one orbit since its discovery.
Pluto sometimes travels closer to the Sun than Neptune.
Its heart-shaped glacier is a churning sea of nitrogen ice.
Pluto was reclassified as a dwarf planet in 2006 because it has not cleared its orbit.
Exploration history
New Horizons 2015
First (and only) flyby of Pluto, revealing an unexpectedly active world.
Pluto vs Earth
| Property | Earth | Pluto |
|---|---|---|
| Diameter | 12,742 km | 2,377 km |
| Year length | 365 days | 248 years |
| Moons | 1 | 5 |
| Average temperature | 15 C | -232 C |
Scientific Sources & Provenance
All data is verified against official space agency records (NASA, ESA, and IAU).
- NASA Science / Mission Datahttps://science.nasa.gov/dwarf-planets/pluto/
- Official Sourcehttps://www.iau.org/public/themes/pluto/