Pluto is the largest object in the Kuiper belt and the second-largest known dwarf planet in the Solar System.

Axial tilt

Like Uranus, Pluto is lying on its "side", with an axial tilt of 120º, leading to extreme seasonal variations. At its solstices, one-fourth of the planet is in continuous daylight, and one-fourth in continuous darkness.

Moons

Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx. Pluto and Charon are sometimes described as a binary system because the barycenter of their orbits does not lie within either body.

Discovery

Discovered in 1930 by astronomer Clyde Tombaugh, Pluto was originally classified as the 9th planet from the Sun. However, the discovery of similar-sized objects within the Kuiper Belt, prompted the International Astronomical Union to re-classify Pluto in 2006 a dwarf planet.

Structure

Crust

Pluto's surface is remarkably varied, with large changes in both brightness and colour: The colour varies between charcoal black, dark orange and white.

The surface of Pluto is thought to be composed of more than 98% nitrogen ice. As Pluto approaches the Sun, it is believed that these ices sublimate to form a thin atmosphere.

Mantle

It is possible that the heat caused by radioactive decay of minerals may have created a subsurface ocean of liquid water.

Core

The decay of radioactive minerals may have heated the ices enough for the rock to separate from them and settle into a dense core