Astrophysics and Space Science

, Volume 236, Issue 1, pp 77–84 | Cite as

Thermal instability and transport effects in comets

  • A. S. Sharma
  • G. M. Milikh


The localized ion density depletion region observed at comet Halley can be understood in terms of a thermal instability of the cometary plasma due to the excitation of rotational and vibrational levels of water molecules. The electron energy losses due to these processes peak near 4000 K and at higher temperatures a localized cooling leads to the thermal instability due to the increased radiation loss. The resulting increase in recombination leads to the ion density depletion and the estimates for this depletion at comet Halley agree with the observations. The transport effects at the density depletion region due to the diffusion and thermal conductivity are found have time scales larger than the instability time scale and does not affect the formation of the depletion region.


Radiation Thermal Conductivity Recombination Water Molecule Energy Loss 
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  1. Altwegg, K., et al.: 1993,Astron. Astrophys. 279, 260.Google Scholar
  2. Banks, P.M. and Kockarts, G.: 1973,Aeronomy, Academic Press, New York.Google Scholar
  3. Chaizy, P., et al.: 1991,Nature,349, 393.Google Scholar
  4. Cravens, T.E. and Korosmezey, A.: 1986,Planet. Space. Sci. 34, 961.Google Scholar
  5. Damas, M.C., et al.: 1994,Astrophys. J. 432, L143.Google Scholar
  6. Eberhardt, P. and Krankowsky, D.: 1995,Astron. Astrophys. 295, 795.Google Scholar
  7. Eletskii, A.V. and Smirnov, B.M.: 1982,sov. Phys. Usp. 25, 13.Google Scholar
  8. Field, G.B.: 1965,Astrophys. J. 142, 531.Google Scholar
  9. Galeev, A.A. and Khabibrakhmanov, I.Kh.: 1988,Sov. Astron. Letters 14, 112.Google Scholar
  10. Gan, Lu and Cravens, T.E.: 1990,J. Geophys. Res. 95, 6285.Google Scholar
  11. Huebner, W.F. and Keady, J.J.: 1983, in: T.I. Gombosi (ed.),Cometary Exploration, 1 Hungarian Acad. of Sci., Budapest, p. 165.Google Scholar
  12. Ip, W.H., et al.: 1988,Astron. Astrophys. 206, 129.Google Scholar
  13. Korosmezey, A., et al.: 1987,J. Geophys. Res. 92, 7331.Google Scholar
  14. Mendis, D.A., et al.: 1985,Fund. Cosmic Phys. 10, 1.Google Scholar
  15. Milikh, G.M. and Sharma, A.S.: 1995,Geophys. Res. Letters 22, 639.Google Scholar
  16. Neugebauer, M.: 1990,Rev. Geophys. 28, 231.Google Scholar
  17. Vaisberg, O.L., et al.: 1988,Cosmic. Phys. (Engl. Transl.) 26, 9.Google Scholar

Copyright information

© Kluwer Academic Publishers 1996

Authors and Affiliations

  • A. S. Sharma
    • 1
  • G. M. Milikh
    • 1
  1. 1.Department of AstronomyUniversity of MarylandCollege Park

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