♇Pluto
An icy world once counted as the ninth planet. Now a "dwarf planet," but still the king of the Kuiper Belt, marked with a heart.
- Distance from Sun
- 39.5 AU (about 5.9 billion km)
- Diameter
- 2,377 km (0.68× the Moon)
- Orbital period
- 248 years
- Rotation period
- 6.4 days
- Moons
- 5 (Charon, ...)
Science
The scienceDiscovered in 1930, Pluto was long cherished as the Solar System's ninth planet, but in 2006 the International Astronomical Union redefined "planet" and reclassified it as a "dwarf planet." The reason was that it had not cleared the other objects from around its orbit; Pluto is the flagship resident of the "Kuiper Belt," the ring of icy bodies beyond Neptune. In 2015, the New Horizons spacecraft made the first close flyby, vividly capturing a giant heart-shaped plain of nitrogen ice and mountain ranges of ice. Its largest moon, Charon, is half the size of Pluto itself, so the two are closer to a "double body" orbiting face to face.
Name & Myth
The story behind the nameBecause it is the most distant from the Sun and forever wrapped in darkness and cold, it was given the name of Pluto, god of the underworld (the Greek Hades). The name was suggested by an 11-year-old girl named Venetia Burney, and its first two letters "PL" also matched, remarkably, the initials of Percival Lowell, the astronomer who had predicted Pluto's discovery. In East Asia it was rendered "Myeong-wang-seong," meaning ruler of the underworld.