Plasma structures at weakly outgassing comets—results from bi-ion fluid analysis

The plasma environment of a weakly outgassing comet is considered within the frame of 2-D bi-ion fluid simulations. The results show that for cometary ion production rates lower than a threshold value of ≈ 5 × 1026 s−1 no bow shock is formed only a Mach cone. The heavy cometary ion fluid moves along a cycloid-type path, undergoing simultaneously structuring of its density profile. The latter takes the form of heavy ion bunching along the cycloid trajectory and can be described also in terms of consecutive clumps of heavy ion fluid detaching themselves periodically 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 insight into the dynamics of the bunching. The simulation results can be applied in assessing the expected plasma environment in the early stages of the ROSETTA mission.