Dust-gas interrelations in comets: Observations and theory

The development of the expanding atmosphere from the evaporating cometary n ucleus has traditionally focused on observing and modeling the separate dev elopment of two distinct components, gas and dust, which are coupled dynami cally with one another at distances out to a few tens of cometary radii. In the last decade or so, however, direct evidence from observations and sugg estions from theory suggest that the dusty-gas coma is a tightly coupled sy stem where material is transferred between the solid and gaseous phase as a n important integral part of the basic development of the coma. Comet Hale-Bopp (C/1995 O1) was discovered far from the sun and is the larg est and most productive comet, in the sense of release of gas and dust in m odern times. This has permitted observations to be made over an unprecedent ed range of heliocentric distance. This paper presents a review of a range of important issues regarding interrelations between dust and gas in comets , a description of the gas and dust environment for Hale-Bopp, and a summar y of the preliminary results from Hale-Bopp which are relevant to these iss ues. Particular topics include dusty-gas models, dust fading and fragmentat ion, the role of dust and gas jets, the day/night distribution of gas and d ust, and extended sources of gas.