Three Component Plasma Electron Distribution in the Intermediate Ionized Coma of Comet Giacobini-Zinner

  1. Thomas J. Birmingham and
  2. Alexander J. Dessler
  1. R.D. Zwickl,
  2. D.N. Baker,
  3. S.J. Barne,
  4. W.C. Feldman,
  5. S.A. Fuselier,
  6. W.F. Huebner,
  7. D.J. Mccomas and
  8. D.T. Young

Published Online: 19 MAR 2013

DOI: 10.1029/SP027p0181

Comet Encounters

Comet Encounters

How to Cite

Zwickl, R.D., Baker, D.N., Barne, S.J., Feldman, W.C., Fuselier, S.A., Huebner, W.F., Mccomas, D.J. and Young, D.T. (1988) Three Component Plasma Electron Distribution in the Intermediate Ionized Coma of Comet Giacobini-Zinner, in Comet Encounters (eds T. J. Birmingham and A. J. Dessler), American Geophysical Union, Washington, D.C.. doi: 10.1029/SP027p0181

Author Information

  1. University of California, Los Alamos National Laboratory, Los Los Alamos, NM 87545

Publication History

  1. Published Online: 19 MAR 2013
  2. Published Print: 1 JAN 1988

ISBN Information

Print ISBN: 9780875902395

Online ISBN: 9781118668757

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Keywords:

  • Comet Giacobini-Zinner;
  • Electron velocity distribution;
  • Intermediate ionized coma (IIC);
  • Photoelectron distribution;
  • Plasma electron distribution;
  • Solar wind plasma

Summary

On 11 September, 1985, in the interval from 1056 to 1110 UT surrounding closest approach (i.e. within ∼1.2×104 km), ICE encountered a region characterized by an unusually low electron temperature, a high density, a bulk flow speed V < 30 km/s, and a relatively low level of plasma turbulence. We call this region the intermediate ionized coma, IIC. Electron velocity distribution functions in the IIC are composed of three distinct components: cold, mid, and hot. We believe that the cold population represents electrons produced close to the comet nucleus by ionization of cometary matter and subsequent cooling by Coulomb collisions. The mid distribution also appears to be composed of electrons produced by photoionization of cometary neutrals, but sufficiently far from the comet nucleus that the distributions are largely unaffected by Coulomb interactions. Thus, the mid population is not in thermal equilibrium with the cold distribution. The temperature of the mid distribution compares well with the average energy of electrons resulting from the ionization of H2O, which leads us to conclude that the composition of the ion population at this distance is consistent with the interpretation that H2O is the dominant species. The hot component is most likely a population of electrons of solar wind origin. Throughout the IIC the electrostatic potential of the spacecraft was very low (<0.8 eV), implying ICE generated very little impact-produced plasma during its passage.