Water (H2O) was detected in Comet C/1995 O1 Hale-Bopp on 10 dates between UT January 21.8 and May 1.2, 1997, using high-resolution infrared spectroscopy. This is the first study of the heliocentric dependence of water released from a comet using direct detection of H2O itself. Production rates and rotational temperatures were measured, and the derived heliocentric dependence for the water production rate is Q=(8.35±0.13)×1030 [Rh(-1.88±0.18)] molecules s-1. The spatial distribution of H2O molecules in the coma is consistent with water being released directly from the nucleus within 1.5 AU of the Sun, although release of a small fraction from icy grains cannot be excluded. When our derived water production rates are compared to the production of native carbon monoxide and dust, we obtain a dust to ice mass ratio of 5.1±1.2 within a heliocentric distance of 1.5 AU. The abundance of H2O provides a benchmark for the volatile inventory in Hale-Bopp and, when compared to interstellar and nebular material, helps constrain the origin of cometary ices and their processing histories. These production rates derived from the direct detection of H2O provide a sound basis with which water production rates inferred by indirect methods can be compared.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science