Pluto up close
Credit: NASA New Horizons

Pluto is one of the dwarf planets in the outer reaches of the Solar System.

It was discovered in 1930 by Clyde Tombaugh, and until 2006 was considered to be the ninth planet. It now lends its name to a class of objects, known as plutoids, which are dwarf planets that circle the Sun beyond the orbit of Neptune.

Pluto's has a very eccentric orbit. This means that it follows a stretched out elliptical path during its 248 year travels around the Sun, rather than a circular one. Its orbit is also inclined to the planetary orbits in the Solar System by around 17°.

Pluto in it's dwarf planet system
Credit: NASA/ESA/Frattare

Pluto was visited for the first time by a space-probe, NASA's New Horizons, in July 2015. It retrieved the closest ever images of the dwarf, and found that the surface is covered in craters from being hit by objects. The dwarf planet also has a thin atmosphere, and it frequently snows on the surface. Pluto is also slightly larger than first thought, meaning it is more icy and less rocky.

Astronomers have found 5 moons around Pluto. The largest, Charon, is around half Pluto's size, Hydra and Nix, are much smaller, then recently Kerberos (P4 on the image) and Styx (P5 on the image), which are only tens of kilometers in diameter.