Pluto

Pluto is a very small, solid dwarf planet made mostly of ices, more like a comet of ice mixed with some rock than either the gas giant planets or the rocky planets, though 10 million comets could fit inside it. Beyond Neptune are more than 1,200 icy Trans-Neptunian Objects, and Pluto, first discovered in 1930, is one of the largest; after another such body was found in 1992, this new class of objects was recognized, and Pluto came to be classified not as a planet but as a dwarf planet. Pluto and its moon Charon are represented here at one 10-billionth actual size, and Pluto’s weak gravity means that a person who weighs 100 pounds on Earth would weigh only 7 pounds on Pluto. The first spacecraft to visit Pluto, New Horizons, was to arrive in 2015.

Washington, District of Columbia · United States