Ethane Production and Release in Comet C/1995 O1 Hale-Bopp
Abstract
Ethane (C 2H 6) was detected in Comet C/1995 O1 Hale-Bopp on 13 dates between UT 1996 September 20.3 ( Rh=3.01 AU pre-perihelion) 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)×10 28 [ Rh(-2.43±0.13)] molecules s -1. The spatial distribution of C 2H 6 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 (C 2H 2) are compared, we obtain an average relative abundance of C 2H 6/H 2O=(6.23±0.42)×10 -3, and C 2H 6/C 2H 2=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.
- Publication:
-
Icarus
- Pub Date:
- September 2001
- DOI:
- 10.1006/icar.2001.6678
- Bibcode:
- 2001Icar..153..162D