Ethane (C2H6) was detected in Comet C/1995 O1 Hale-Bopp on 13 dates between UT 1996 September 20.3 (Rh = 3.01 AU preperihelion) and 1997 September 25.7 (Rh = 2.83 AU post-perihelion) using high-resolution infrared spectroscopy. Production rates and rotational temperatures were measured, and the derived heliocentric dependence for ethane production was Q = (5.52 ± 0.20) × 1028 [Rh(-2.43±0.13)] molecules s-1. The spatial distribution of C2H6 molecules in the coma was consistent with all ethane being released directly from the nucleus, although the possibility that a small fraction was released as a distributed source cannot be excluded. When our derived production rates for ethane, water, and acetylene (C2H6) are compared, we obtain an average relative abundance of C2H6/H2O = (6.23 ± 0.42) × 10-3, and C2H6/C2H2 = 2.4 ± 0.7. The high ethane abundance relative to acetylene in Hale-Bopp suggests its ices were altered by radiation processing and/or hydrogen-atom addition reactions on the surfaces of ice-mantled grains in the natal cloud. These results are not consistent with ices in Hale-Bopp originating in a thermally or chemically equilibrated region of the solar nebula.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science