Pluto stamp

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Pluto was originally the ninth planet from the Sun, a status taken away by the International Astronomical Union in August 2006. Discovered only in 1930 by Clyde Tombaugh, Pluto is named after the Roman god of the underworld. It is currently known as a dwarf planet and the largest object in the Kuiper Belt at the frontier of the Solar System. A perpetually cold world composed primarily of rock and ice, Pluto exhibits an eccentric orbit around the Sun, occasionally coming closer to the Sun than Neptune. Pluto and its largest moon Charon constitute one of the Solar System’s few binary systems as both of them also revolve around a point just outside of Pluto. This unique situation has caused some astronomers to name the Pluto-Charon system a ‘double dwarf planet’. Pluto was visited by manmade spacecraft in July 2015 when the New Horizons probe performed the first ever fly-by.

Aphelion: 7,311,000,000 km
Perihelion: 4,437,000,000 km
Diameter at equator: 2,322 km
Rotation period (1 day): 6 Earth days
Orbital period (1 year): 248 Earth years
Av. orbital speed: 5.43 km/s
Av. surface temperature: -229°C
Mass (Earth = 1): 0.002
Satellites: 5 confirmed (cf. Charon)

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I will always consider Pluto the ninth planet.