Most persons of adult age were thus raised with the idea of a solar system consisting of nine planets, their attendant satellites, and an ever-increasing number of smaller irregular rocks. The “clearing” part is a little vague, but serves to distinguish Ceres, the largest object in the asteroid belt, from the accepted planets. Before Pluto was found, astronomy reached no consensus on how many “planets” there were, and Ceres was often counted. Space-age children were not taught that Ceres is a planet, but planetary scientists have accepted it as one, and said so openly. Ceres’ origins are probably like those of the accepted planets, and it has complex interior structure.

Source: National Post September 12, 2018 18:56 UTC