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Abstract

The three-dimensional positive ion analyser aboard the Giotto spacecraft has been used to study the interaction between protons and α-particles in the solar wind and positive ions from comet Halley. Although the first impression of the overall structure is that the plasma flow evolves smoothly as the nucleus is approached, three sharp transitions of relatively small amplitude can be identified on both the inbound and outbound legs of the trajectory. The outermost one, at 106 km from the nucleus, appears to be a multiple crossing of a weak bow shock. The innermost one, at 80,000 km, is the boundary where the flowing plasma becomes depleted. On a microscopic scale, the turbulence created by the interaction between the two ion populations extends to a distance of several million kilometres from the nucleus. At Giotto's closest approach to the nucleus, the plasma produced around the spacecraft by dust and gas impacts was much more energetic than had been expected.

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Author information

Affiliations

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

    • A. Johnstone
    • , A. Coates
    •  & S. Kellock
  2. Max-Planck-Institut für Aeronomie, D-3411 Katlenburg-Lindau, FRG

    • B. Wilken
    • , K. Jockers
    • , H. Rosenbauer
    • , W. Studemann
    •  & W. Weiss
  3. Istituto di fisica dello Spazio Interplanetario, 00044 Fracati, Italy

    • V. Formisano
    • , E. Amata
    • , R. Cerulli-Irelli
    • , M. Dobrowolny
    • , R. Terenzi
    •  & A. Egidi
  4. Kiruna Geophysical Institute, 98127 Kiruna, Sweden

    • H. Borg
    •  & B. Hultquist
  5. Southwest Research Instiute, San Antonio, Texas 78284, USA

    • J. Winningham
    •  & C. Gurgiolo
  6. Rutherford Appleton Laboratory, Didcot OX11 0QX, UK

    • D. Bryant
    •  & T. Edwards
  7. Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

    • W. Feldman
    •  & M. Thomsen
  8. University College Cardiff, Cardiff CF1 1XL, UK

    • M. K. Wallis
  9. Max-Planck-Institut für Astrophysik, D-8046 Garching, FRG

    • H. Schmidt
    •  & R. Lust
  10. Max-Planck-Institut für Extraterrestrische Physik, D-8046 Garching, FRG

    • G. Haerendel
    •  & G. Paschmann
  11. Deceased

    • L. Biermann

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DOI

https://doi.org/10.1038/321344a0

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