3-D Modelling of the Surface Activity of a Comet Nucleus

Abstract

Images taken by the Halley Multicolour Camera (HMC) during the flyby of ESA’s spacecraft Giotto in March 1986 revealed the surface activity of the nucleus of comet P/Halley. These images show a highly asymmetric coma (Keller et al., 1987). Up to now, it is often referenced in literature that dominant gas and dust production is due to an uncovered ice surface corresponding to 10% of the total surface. The other 90% of the surface, which produces less than 10% of the total, is covered by a dust layer. Starting with this hypothesis, we have firstly demonstrated that the measured, permanent gas production, of 6.9 × 10²⁹ molecules/s, can be achieved, at the heliocentric distance of 0.89 AU, with 10% of the surface area, only if the active area is situated permanently at the sub-solar point (synchronous rotation). In all other cases a larger potentially active area is needed. Secondly, in order to show that jet-like features can be obtained even under the extreme assumption of a continuously active surface, we have built up a three-dimensional numerical simulation of a comet nucleus surface, in a general case. Then we have made numerical images of the coma near such an active nucleus, reproducing observation conditions of the HMC. In our model, the activity is only a function of the solar energy received per surface unit. With a “bean”-like surface we have tried to link the surface topography and jet-like features in the near coma.