Observations of the Velocity Distribution of Pickup Ions

  1. Alan Johnstone
  1. A. J. Coates

Published Online: 26 MAR 2013

DOI: 10.1029/GM061p0301

Cometary Plasma Processes

Cometary Plasma Processes

How to Cite

Coates, A. J. (1991) Observations of the Velocity Distribution of Pickup Ions, in Cometary Plasma Processes (ed A. Johnstone), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM061p0301

Author Information

  1. Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking RH5 6NT, UK

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


Ion pick-up is well-established as the process whereby comets interact with the solar wind. Although this mechanism was postulated as such over 30 years ago it was not until the 1985–6 cometary armada reached their goals that direct measurements of the process in the cometary environment could be performed. Here we review the measurements of pickup ion distributions from the various spacecraft, concentrating on the observed pitch angle and energy scattering in the turbulent solar wind upstream of comets. Comparison with simulation and with theory is attempted by way of the inferred timescales for pitch angle and energy diffusion. Measurements of the bulk velocity of the picked-up ions are compared with the guiding centre approximation far upstream of the comet and with the wave phase velocity nearer in.