Analysis of the Pioneer-Venus Lyman-
Image of the Hydrogen Coma of Comet P/Halley
WILLIAM H. SMYTH 1,
MICHAEL R. COMBI 2, and
A. I. F. STEWART 3
1 Atmospheric and Environmental Research, Inc., Cambridge, MA 02139
2 Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109
3 Laboratory for Atmospheric and Space Physics and Department of Astrophysical, Planetary, and Atmospheric Science, University of Colorado, Boulder, CO 80309
Comet Halley passed within 0.27 astronomical unit of Venus on 4 February 1986, 5 days before perihelion. This provided a unique opportunity to observe the comet's coma with the ultraviolet spectrometer orbiting the planet aboard the Pioneer Venus Orbiter spacecraft when the coma was otherwise obscured from Earth's view by the sun's glare. More than 9000 data points acquired systematically over the 5-day period from 2 to 6 February were combined to construct an excellent Lyman-
image of the hydrogen coma. The Lyman- image was successfully reproduced with a comprehensive physical model, thereby verifying and documenting the underlying chemical kinetics and dynamics of the hydrogen coma.
Submitted on March 14, 1991
Accepted on June 25, 1991
