Pluto
Pluto is a dwarf planet orbiting in the Kuiper Belt, the icy ring of debris beyond Neptune. It was considered the ninth planet from its discovery in 1930 until 2006, when it was reclassified as a dwarf planet. Small, cold, and far from the Sun, Pluto is best known for the giant heart-shaped region of nitrogen ice on its surface.
| Distance from Sun | 3.7 billion miles (5.9 billion km) — 39 AU on average |
| Diameter | 1,477 miles (2,377 km) |
| Length of day | about 153 hours (roughly 6.4 Earth days) |
| Length of year | 248 Earth years |
| Moons | 5 (Charon, Styx, Nix, Kerberos, Hydra) |
| Temperature | average -387°F (-232°C) |
| Atmosphere | Thin, made mostly of nitrogen with traces of methane and carbon monoxide |
Interesting facts
- Pluto was classified as the ninth planet for 76 years before being reclassified as a dwarf planet in 2006.
- Its largest moon, Charon, is about half Pluto’s size — the biggest moon relative to its planet anywhere in the solar system, so the two effectively orbit each other like a double planet.
- Pluto’s orbit is so elongated that it sometimes travels closer to the Sun than Neptune, though the two never actually cross paths.
- NASA’s New Horizons spacecraft was the first, and so far only, mission to explore Pluto up close, flying past in July 2015 after a nine-and-a-half-year journey.
- Pluto’s famous heart-shaped region, informally called Tombaugh Regio, is a plain of nitrogen and methane ice roughly the size of Texas and Oklahoma combined.
- Pluto rotates almost on its side, tilted 57 degrees, similar to Uranus.