The NH sub 3 and NH sub 2 abundances in comet Halley
A comparison between observations and a model of the NH2 distribution in the coma of comet Halley is presented. The three-dimensional model utilizes Monte Carlo techniques relevant to high production rate comets and molecular species distributed close to the nucleus. The model is calculated specifically for the NH2 molecule in the coma of comet Halley at the time of the Giotto spacecraft encounter. The model represents coma physics more accurately than exospheric models previously used in the study of NH2 in that time dependent gas production rates, anisotropic ejection of molecules from the nuclear surface, and neutral-neutral molecular collisions are included. For comet Halley collisions have significant effects on the model out to a distance of several thousand kilometers from the nucleus, well within the range of ground-based long-slit spectra. In the model H2O molecules are the collision targets for both the NH2 molecule and its parent molecule. The NH2 distribution on the plane of the sky is calculated for the date of the Giotto encounter and is compared with the NH2 surface brightness distributions of comet Halley obtained from the Cerro Tololo InterAmerican Observatory. The relative contribution of CHON particles, N2H4, and NH2CH3 to the observed NH2 is discussed. The model described above, constrained by observational data, provides an improved determination of the abundance ratio NH3/H2O, a sensitive indicator of the physical and chemical conditions in the comet forming regions of the protosolar nebula.
- Research Organization:
- Arizona State Univ., Tempe, AZ (USA)
- OSTI ID:
- 6399294
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
AMMONIA
BRIGHTNESS
CHEMICAL COMPOSITION
COMETS
COSMOLOGICAL MODELS
DATA
HALLEY COMET
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
MATHEMATICAL MODELS
MONTE CARLO METHOD
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
OPTICAL PROPERTIES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
THEORETICAL DATA
WATER