As the technology of telescopes and the capabilities of spacecraft improve, new observations change our perceptions of the bodies that orbit our Sun. In recent years many distant icy worlds have been discovered in the vast cold region beyond Neptune. Some of these discoveries have prompted a passionate and very public discussion about how these objects should be classified. New revelations that challenge our assumptions are an exciting part of the process of exploration.
As we learn more about these primordial building blocks of our solar system, the distinction between asteroids, comets and dwarf planets has become increasingly difficult to make. But even with the shuffling of names and categories in the past several years, we can divide the small worlds into three main categories and share some of their general characteristics.
Ceres is a great example of how scientists’ thinking evolves regarding classification of objects in the solar
system. Ceres was discovered in 1801 by Giuseppe Piazzi. He initially reported it as a comet, but with more observations noticed its movement was slow and uniform. It was ultimately classified as the eighth planet. However, half a century later, as other objects were discovered in the area, scientists realized Ceres represented the first of a class of many similar objects that were called “asteroids,” meaning “star-like.” Ceres retained its comfortable position as asteroid #1, largest and first discovered, for about 150 years.