If a newly discovered object appears fuzzy, then it is a comet. It is likely that, for many comets, the surface ices evaporate completely after dozens of orbits around the Sun. If and when such extinct comets are found, their star-like appearance leads us to classify them as asteroids, even though they have a cometary origin. Scientists categorize asteroids in near-Earth space as Atens, Apollos or Amors. At present, about 200 near-Earth asteroids have been discovered.
Scientists categorize objects displaying cometary properties according to their orbital period.
Although most have orbits that carry them well above and below the plane of Earth's path, approximately 30 short-period comets have low enough inclinations to make them accessible from Earth with modest propulsion systems. Comets are categorized by their orbital periods. One of the more famous short-period comets is Halley's, shown above. Maintaining the Supply of Asteroids and Comets Regardless of their asteroidal or cometary genesis, NEOs are efficiently removed from the inner solar system by collisions or gravitational interactions with the terrestrial planets and the Sun. Because this removal time is short compared with the age of the solar system, the NEO population we see today must be continually resupplied.