Ethane Production and Release in Comet C/1995 O1 Hale–Bopp

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2001-09, Vol.153 (1), p.162-179
• Main Authors: Russo, Neil Dello, Mumma, Michael J., DiSanti, Michael A., Magee-Sauer, Karen, Novak, Robert
• Format: Article
• Language: English
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1006/icar.2001.6678

Ethane (C 2H 6) was detected in Comet C/1995 O1 Hale–Bopp on 13 dates between UT 1996 September 20.3 ( R h=3.01 AU pre-perihelion) and 1997 September 25.7 ( R h=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 [ R h (−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.