smallest planet

The smallest object with the status of a major planet in the solar system is Pluto. With a diameter of only 2324 km, it is about the same size as the north-south extent of the continental United States. It is nevertheless more than four times the size of the largest asteroid (Ceres). With the discovery since 1992 of more than 50 bodies smaller than Pluto also orbiting the Sun in the region beyond Neptune known as the Kuiper Belt, Pluto appears to be the largest of a population of icy planetesimals left over from an early stage in the formation of the planetary system. Pluto was not ejected into the remote Oort cloud because it is locked in a resonance with Neptune: for every three orbits Neptune makes of the Sun, Pluto makes exactly two. This means Pluto has never got near enough to Neptune to succumb to a gravitational 'sling-shot' by its much more massive neighbour.