A TIME-DEPENDENT DUSTY GAS-DYNAMIC MODEL OF AXISYMMETRIC COMETARY JETS

The first results of a new time-dependent, axisymmetric dusty gas dynamical model of inner cometary atmospheres are presented. The model solves the coupled, time-dependent continuity, momentum, and energy equations for a gas-dust mixture between the nucleus surface and 100 km using a 40 × 40 axisymmetric grid structure. The time-dependent multidimensional partial differential equation system was solved with a new numerical technique employing a second-order accurate Godunov-type scheme with dimensional splitting. It is found that narrow axisymmetric jets generate a subsolar dust spike and a jet cone, where a significant amount of the jet ejecta is accumulated. This subsolar dust spike has not been predicted on earlier calculations. The opening angle of the jet cone depends on the jet strength and it also varies during the time-dependent phase of the jet. For weak jets the steady-state half-opening angle is about 50°. In the case of the strong jets the jet cone extends to the nightside in good agreement with the Giotto imaging results. © 1990.