2060 Chiron
2060 Chiron is an object discovered in 1977 by Charles Kowal and named after Chiron of Greek legend. Although it was initially classified as an asteroid, later dispute arose as to whether it was an asteroid or actually a comet. It has a radius of about 85 km and an orbit in the outer solar system between those of Saturn and Uranus.In 1988 it was found that Chiron was undergoing an outburst in brightness (by about one magnitude), which is behavior typical of comets but not asteroids. Further observations in 1989 showed that Chiron had developed a cometary coma.
At the time of its discovery, Chiron was close to aphelion, whereas the observation showing a coma were done closer to perihelion, perhaps explaining why no cometary behavior had been seen earlier.
Chiron is officially both a comet and an asteroid, more proof of the very fuzzy dividing line. As a comet, its name is 95P/Chiron. There are two other asteroids that are also listed as comets: 4015 Wilson-Harrington and 7968 Elst-Pizarro.
Chiron is now classified as a centaur, the first of a class of objects orbiting between the outer planets. Centaurs are not in stable orbits and will eventually be removed by the giant planets. Chiron is probably a refugee from the Kuiper belt.
Other centaurs such as 5145 Pholus are being observed for possible cometary behavior, but none has been seen so far.