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[30.02] The Coma of Comet 19P/Borrelly during the Deep Space 1 Encounter

D.C. Boice (SwRI), R. Wegmann (MPIA)

The Deep Space 1 Mission (DS1) successfully encountered comet 19P/Borrelly on 22 September 2001, and returned a wealth of unique information about its nucleus and surrounding environment. A coma model for 19P/Borrelly is presented that consistently represents the comet from the nucleus surface to the solar wind interaction region. Neutral gas and plasma dynamics and spatial distributions of various cometary species are presented in order to interpret the in situ plasma measurements obtained during the encounter.

A summary of the major findings follows: (1) With estimates of the solar wind conditions and the gas production rate at the time of encounter, a bow shock is expected at a distance of about 60,000 to 80,000 km along DS1's trajectory, however, DS1 did not penetrate the contact surface, (2) At closest approach, the plasma speed steadily decreases to about 2 km s^-1, with an ion temperature of about 200,000 K and electron temperature of about 20,000 K (dominated by photoelectrons cooled by collisions), and an ion number density of about 100 cm^-3, and (3) model abundances of water-related ions, O⁺, OH⁺, H_2O⁺, and H_3O⁺, are 1%, 5%, 60%, and 34% of the total water-related fraction, respectively, at the time of closest approach. An initial analysis of the DS1 measurements will be presented within the context of the model results.

Support from NSF Grant #9973186 made this work possible.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.