Pluto is the tenth largest body orbiting the Sun, and the former planet is now reclassified as a Plutoid: in French plutoïde, and in Spanish plutoide.The largest member of the Kuiper belt, Pluto, was stripped of its status as a planet in 2006, and it was classified as a dwarf-planet. From its discovery in 1930, Pluto was counted as the ninth planet in the Solar System. Many scientist opposed the idea a changing the status of Pluto, however, it was thought that a more consistent approach to the way objects are classified in the Solar System was needed.
Pluto is small and several moons in the solar system are bigger than Pluto - our own Moon, Io, Europa, Ganymede, Callisto, Titan, and Triton. Pluto is 2/3 the size of Earth's Moon, and its volume is about 0.66% that of Earth. It is cold on Pluto and very icy, temperatures on the surface range from -233°to -223°Celsius. Pluto has a peculiar orbit, which causes Pluto occasionally to come closer to the Sun than Neptune. Pluto's atmosphere consists of a thin cover of nitrogen, methane, and carbon monoxide. As Pluto moves away from the Sun, its atmosphere freezes and falls to the ground. Most of the time the gases are frozen out as methane ice as well as water ice. As it comes closer to the Sun, the temperature of Pluto's solid surface increases, causing the ices to sublimate into gas, which may look like icy fog.
The International Astronomical Union (IAU) defines plutoids as “celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit. Satellites of plutoids are not plutoids themselves, even if they are massive enough that their shape is dictated by self-gravity." In other words, plutoids are small round things beyond Neptune that orbit the sun and have many rocky neighbours.
There are two plutoids in the solar system - Pluto and Eris. Eris is a 1500-mile wide sphere of rock, which has been spotted orbiting beyond Pluto in a region of space beyond the Kuiper belt known as the scattered disc. Eris is bigger and heavier than Pluto is.
The dwarf planet Ceres, located between Mars and Jupiter in the asteroid belt between Mars and Jupiter, is not considered a plutoid. It is, according to current scientific knowledge possible that Ceres is the only object of its kind. New plutoids are expected to be found, and more that 42 known bodies are yet to be determined if they meet the definition of a plutoid.
Plutoids must be a minimum brightness, this makes objects of exactly the same size "plutoids" or "not plutoids" depending on what's covering their surface. Objects covered with dust might consequently not be considered a plutoid.
