The Detection of Carbon Monoxide Gas Emission in (2060) Chiron

2060 Chiron is among the small population of large, outer Solar System objects called Centaurs. Chiron's unusual, 51-year orbit ranges in distance from 8.5 to just over 19 AU, and exhibits an inclination to the ecliptic plane of 8.5 deg. Recent dynamical studies (Levison and Duncan, 1994; Dones et al., 1996) show this orbit is unstable to giant-planet perturbations on timescales of < 106 years, indicating that it is a recent addition to the planetary region. This, along with its low-inclination orbit, and its size similarity to the newly-discovered population of 100-400-km-diameter Kuiper Disk objects (Campins et al., 1994; Jewitt and Luu, 1995), provides strong circumstantial evidence that Chiron is an escaped object from the Kuiper Disk. Chiron's present orbit subjects it to much more intense insolation than objects in the Kuiper Disk experience. That insolation generates surface activity, as revealed by a highly variable coma (Hartmann et al., 1989; Meech and Belton, 1990; Bus etal., 1993). The source of Chiron's activity has been speculated on for many years (Stern, 1989) but never observationally identified. We report here the detection of CO molecules in Chiron's coma, which are probably the sublimation agent generating Chiron's activity.