PLUTO

Pluto is a dwarf planet located in the Kuiper Belt beyond the orbit of Neptune. It was discovered in 1930 by astronomer Clyde Tombaugh and was originally classified as the ninth planet of the Solar System. In 2006, Pluto was reclassified as a dwarf planet after the International Astronomical Union established a formal definition of a planet. Pluto has a surprisingly complex surface. It contains mountains of water ice, vast plains of nitrogen ice and regions with different colours and compositions. Its most famous feature is Sputnik Planitia, a huge bright basin covered mainly by nitrogen ice. Pluto also has a thin atmosphere that expands when the dwarf planet is closer to the Sun and partially freezes onto the surface when Pluto moves farther away. NASA's New Horizons spacecraft flew past Pluto in July 2015, providing the first close-up observations of the dwarf planet and its moons.