Abstract
Possible mechanisms for the production of the extended dust coma observed in comet Bowell (1980b) at the large heliocentric distance of 7.17 AU are considered. It is concluded that a plausible mechanism is electrostatic blow-off of fine, loose dust from an electrically charged H2O dominated nucleus, as recently proposed by Mendiset al. (1981). Of all the other processes considered, dust entrainment by a chemical species more volatile than H2O is considered the most plausible. However, the non-observation of prominent CO+ lines of theA 2Π-X 2Σ band, seems to mitigate against a CO dominated nucleus, particularly if its radius is ≥1 km. A CO2 dominated nucleus, however, cannot be ruled out by this non-observation unless its radius is considerably larger (≈ 5 km). The electrostatic blow-off process predicts that the dust grains in the coma of comet Bowell at 7.17 AU must be very small (r g≤0.4 μ), with a total mass ≤4×108 g, and a spatial extension ≤105 km, which is consistent with the observations (observed coma diameter ≈6×104 km). Both the size and spatial distribution of the dust given by electrostatic blow-off and the gas entrainment processes are shown to be different, and this would be a way of discriminating between the two processes. However, the present observations do not have the resolution to do so.
Published Version
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