Discovered in 1930 and once considered a major planet, Pluto was reclassified as a dwarf planet in 2006. Pluto is sometimes
considered a double planet system because its largest moon, Charon, is about half Pluto’s size. It takes Pluto 248 years to orbit the Sun.
A temporary nitrogen-methane atmosphere forms when Pluto's surface ice thaws, when Pluto is closest to the sun.
Pluto’s rocky core is probably surrounded by a mantle of ice, with methane and nitrogen frost coating its surface.