Ion Pickup, Scattering, and Stochastic Acceleration in the Cometary Environment of P/Giacobini-Zinner

  1. Alan Johnstone
  1. D. D. Barbosa

Published Online: 26 MAR 2013

DOI: 10.1029/GM061p0291

Cometary Plasma Processes

Cometary Plasma Processes

How to Cite

Barbosa, D. D. (1991) Ion Pickup, Scattering, and Stochastic Acceleration in the Cometary Environment of P/Giacobini-Zinner, in Cometary Plasma Processes (ed A. Johnstone), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM061p0291

Author Information

  1. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024

Publication History

  1. Published Online: 26 MAR 2013
  2. Published Print: 1 JAN 1991

ISBN Information

Print ISBN: 9780875900278

Online ISBN: 9781118663660



  • Comets;
  • Space plasmas;
  • Astrophysics


This paper gives a brief review of observations and theory related to the scattering and acceleration of cometary pickup ions with emphasis on comet P/Giacobini-Zinner. A comparison of the regions upstream and downstream of the bow shock is made to assess the relative merits of each as a site for stochastic acceleration of ions above the pickup energy through interaction with low-frequency magnetohydrodynamic waves. In the far upstream region the data are most consistent with a model where pickup ions generate a low level of MHD waves but remain relatively scatterfree following trajectories transverse to the interplanetary magnetic field at an oblique angle to the solar wind velocity. In the downstream region the intense level of magnetic fluctuations gives rise to a rapid isotropization of the ions and a second-order stochastic (Fermi) acceleration. The properties of the MHD power spectrum are related to the energetic ion spectrum in the framework of a leaky box model where the bulk of the acceleration occurs downstream of the shock throughout the cometosheath. Very good agreement of the observations with theory is evident for both P/Giacobini-Zinner and P/Halley.