Observations of Pickup Ions Accelerated in the Vicinity of Comet Halley

  1. Alan Johnstone
  1. M. B. Bavassano Cattaneo,
  2. V. Formisano,
  3. E. Amata,
  4. R. Giovi and
  5. P. Torrente

Published Online: 26 MAR 2013

DOI: 10.1029/GM061p0311

Cometary Plasma Processes

Cometary Plasma Processes

How to Cite

Cattaneo, M. B. B., Formisano, V., Amata, E., Giovi, R. and Torrente, P. (1991) Observations of Pickup Ions Accelerated in the Vicinity of Comet Halley, in Cometary Plasma Processes (ed A. Johnstone), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM061p0311

Author Information

  1. Istituto di Fisica dello Spazio Interplanetario Consiglio Nazionale delle Ricerche, Frascati, Italy

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


The distribution functions of protons and water group ions measured by the Giotto Implanted Ion Spectrometer have been examined systematically over several million kilometers upstream of comet Halley, in order to obtain informations on the acceleration of cometary ions above the pick up energy. The ability of two spectral shapes (namely a power law and an exponential in energy) to represent the data has been investigated. Between cometocentric distances 2.5×106 and 2.5×105 km there are indications that, for both species, the low energy part of the distribution functions is better represented by a power law, suggesting that first order Fermi acceleration is the dominant process, although the possibility of another mechanism operating simultaneously cannot be excluded.