PLASMA STRUCTURES AT WEAKLY OUTGASSING COMETS - RESULTS FROM BI-ION FLUID ANALYSIS

The plasma environment of a weakly out-gassing is considered within th e frame of 2-D bi-ion fluid simulations. The results show that for com etary ion production rates lower than a threshold value of approximate to 5 x 10(26)s(-1) no bow shock is formed only a Mach The heavy comet ary ion fluid moves along a cycloid-type path, undergoing simultaneous ly structuring of its density profile. The latter takes the form of he avy ion bunching along the cycloid trajectory and can be described als o in terms of consecutive clumps ion fluid detaching themselves period ically from the source region and beginning to move in a soliton like density enhancement keeping to the cycloid. Results from 1-D fluid and hybrid code simulations are also reported which help give a better in sight into the dynamics of the bunching. The simulation results can be applied in assessing the expected plasma environment in the early sta ges of the ROSETTA mission. Copyright (C) 1996 Published by Elsevier S cience Ltd