J.-I. Watanabe’s scientific contributions

The Deep Space 1 Mission is scheduled to encounter comet 19P/Borrelly in September 2001. For the successful outcome of this mission, knowledge of basic properties of the cometary environment is needed. A comet coma model is presented for 19P/Borrelly that consistently represents the dusty cometary environment from the irregularly shaped nucleus surface to the solar wind interaction region with detailed photo and gas-phase chemisty, dust entrainment by the gas with fragmentation and distributed gaseous sources, separate energy balance for electrons, ions, and neutrals, and separate flow of the neutral gas, plasma, and fast atomic and molecular hydrogen. Neutral gas and plasma dynamics and spatial distributions of various cometary species are presented for scientific planning and risk assessment for the Deep Space 1 encounter. The visibility of the nucleus embedded in the dust coma is addressed. Predictions of x-ray emissions are made for coordinating in situ plasma measurements with Earth-based observations as well as other predictions for planning experiments during the encounter. We wish to acknowledge funding from NASA for the Deep Space 1 Science Team.

A versatile model that represents the three-dimensional shape and surface properties of cometary nuclei and asteroids is presented. The model consistently simulates the aspects of illumination, thermal emission, rotational state, and gas production (when volatiles are present). The geometrical model approximates a triaxial ellipsoid by a large number of triangular patches that can be modified to add surface features, such as craters, mounds, and plains. The physical model allows arbitrary illumination and viewing angles with shadowing and scattering properties that may vary over the surface. By considering the energy balance at each surface patch, temperatures and sublimation rates are found which are integrated to yield total thermal emission and gas production. Applications of the model to comets (19P/Borrelly, 10P/Tempel 2, 1P/Halley, and C/Hale-Bopp) and asteroids (951 Gaspra and 216 Kleopatra) are presented. The model is useful for analyzing observations of comet nuclei and asteroids from spacecraft and Earth-based observations when available. This work was partially supported by the NSF Planetary Astronomy Program and the NASA NMP Deep Space 1 Mission.

A general model for representing the three-dimensional shape and surface topography of small, solar system bodies is presented that consistently combines the illumination, thermal emission, rotation, and gas production (if volatiles are present) of these objects. The geometrical model approximates a triaxial ellipsoid by a large number of triangular patches that can be modified to add surface features, such as craters, mounds, and plains. The physical model allows arbitrary illumination and viewing angles with shadowing and scattering properties that may vary over the surface. By considering the energy balance at each surface patch, temperatures and sublimation rates are found which are integrated to yield total thermal emission and gas production. The model is useful for analyzing observations of comet nuclei and asteroids from spacecraft and Earth-based observations. Applications of the model to comets (19P/Borrelly, 10P/Tempel 2, 1P/Halley, and C/Hale-Bopp) and asteroids (951 Gaspra and 216 Kleopatra) are presented.

A comet model is presented for 19P/Borrelly during the Deep Space 1 encounter. The model consistently represents the dusty coma from the irregularly shaped nucleus to the solar wind interaction region with detailed photo and gas-phase chemistry; dust entrainment by the gas with fragmentation and distributed gaseous sources; separate energy balance for electrons, ions, and neutrals; and separate flow of the neutral gas, plasma, and fast atomic and molecular hydrogen. Neutral gas and plasma dynamics and spatial distributions of various species and dust are presented for scientific planning and risk assessment for the Deep Space 1 encounter. The visibility of the nucleus embedded in the dust coma is addressed. Predictions of the x-ray emissions are made for coordinating in situ plasma measurements with Earth-based observations as well as other predictions for experiments planned during the encounter.

Recent progress is presented on a fluid dynamics model for the dusty gas flow in the inner coma of comet Hale-Bopp. Numerical simulations are based on a spherically symmetric coma model with dust entrainment to study the complex interaction between the expanding gas and dust particles. The model can account for a distribution of particle sizes and dust fragmentation. This permits a consistent study of the importance of various physical mechanisms on the exchange of mass, momentum, and energy between the gas and dust particles near the nucleus of a comet. Simulations are performed to investigate the heliocentric distance dependence of dust and gas properties within a cometary coma, in particular, spatial distributions of dust of various sizes, the velocity and temperature structure of the gas and dust including terminal dust velocities, and the dependence of mass-loading and heating of the gas as a function of dust-to-gas mass release ratio, particle size distribution, dust fragmentation, and gas-dust accomodation coefficient. Comparisons with observations of comet Hale-Bopp are made to aid in interpreting the wealth of data concerning this spectacular object.