Cometary Plasma Observations Between the Shock and the Contact Surface
- Alan Johnstone
Published Online: 26 MAR 2013
Copyright 1991 by the American Geophysical Union.
Cometary Plasma Processes
How to Cite
Rème, H. (1991) Cometary Plasma Observations Between the Shock and the Contact Surface, in Cometary Plasma Processes (ed A. Johnstone), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM061p0087
- Published Online: 26 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900278
Online ISBN: 9781118663660
- Space plasmas;
The ICE passage through the tail of Comet Giacobini-Zinner on September 11, 1985 and the flyby of Comet Halley in March 1986 by a fleet of spacecraft have provided for the first time an in situ study of the interaction of the solar wind with a cometary plasma under various solar and cometary conditions.
Several sharp boundaries separating fairly well defined regions and transitions from one flow state to another were observed by the particle and field instruments during the cometary flybys. Near 1 A.U., the cometary particle and field environment is highly complex. Although the main features like the bow shock, the pile-up magnetic region and the contact surface (or ionopause) are relatively close to the theoretical predictions, the in situ measurements have revealed many more structures between the shock and the ionopause. These structures were not anticipated and still remain ill understood, but they are the signs of the plasma processes taking place in the coma of a comet. One important region is the “mystery region” where significant and highly variable fluxes of keV electrons were detected by Giotto. This region is limited by the “mysterious transition” which is seen by all the spacecraft about halfway between the shock and the comet nucleus and seems to be an unpredicted permanent structure of the solar wind- comet interaction at least around 1 A.U.. This transition can be called the cometary transition. The magnetic pile-up region seen by Vega-1 and Vega-2 was gradual but showed a strong gradient on the inbound leg of Giotto: the Magnetic Pile-up Boundary (MPB), may possibly be a convected solar wind effect. On the contrary the Vega-2 “cometopause” is not a plasma boundary and so is not a “pause”.