Abstract:
The morphology of the dust fans and shells in the images of comet C/2001 Q4 (NEAT) showed significant changes between 2004 April and June due to rapid changes in the Earth viewing and solar illumination geometry. We model the trajectories of dust grains ejected from distributed sources on the comet to explain the observed dust morphology in the images obtained on 2004 April 16, May 12, 16, and 21, and June 3. From the fit to the observations we derive the direction of the rotation pole of the nucleus as αp = 270° ± 10° and δp = 15° ± 10°. The derived latitudes of the sources vary between -85° and +80°. Six of the sources are found to lie on a single meridian within ±25°. Using theoretical production rates of water from these sources, reported water production rates, and the archived visual light curve of the comet, we estimate the total active area on the comet to be 38.7 ± 5.8 km2 near perihelion. The fractional active area on the comet is 12% ± 2% or 25% ± 4% at perihelion, corresponding to a nuclear radius of 5 or 3.5 km, respectively. The large outgassing areas estimated in the present work can be attributed to the fact that comet 2001Q4 is a comet from the Oort Cloud visiting the inner solar system for the first time.
