Comet Halley | Published:

In situ gas and ion measurements at comet Halley

Nature volume 321, pages 326329 (15 May 1986) | Download Citation

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Abstract

The neutral mass spectrometer experiment (NMS) carried by the Giotto spacecraft was designed to determine the abundances and the chemical, elemental and isotopic composition of the gases and low-energy ions in the coma of comet Halley. Its first results show the predominance of water vapour (80% by volume). Preliminary evaluation of the data yields an H2O density of 4.7 × 107 molecules cm−3 at 1,000 km, a neutral gas expansion velocity of 0.9 km s−1 and a total gas production rate of 6.9 × 1029 molecules s−1. The photodestruction scale length for H2O was 3.9 × 104 km. Limits on the abundances of CO2, NH3 and CH4 relative to H2O are given. The contact surface was located at 4,700±200 km, as observed from a change in ion temperature. The water-group ions H3O+, H2O+ and OH+ have been unambiguously identified, along with the ions 12C+, 12CH+, 16O+, Na+, 12C2+, 32S+, 34S+ and 56Fe+. The 34S+/32S+ ratio is 0.045±0.010. General features of the low-energy ion flow at large distances from the nucleus are presented.

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Affiliations

  1. Max-Planck-Institut für Kernphysik, Postfach 103980, Saupfercheckweg, D-6900 Heidelberg 1, FRG

    • D. Krankowsky
    • , P. Lämmerzahl
    • , I. Herrwerth
    •  & J. Woweries
  2. Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland

    • P. Eberhardt
    • , U. Dolder
    • , U. Herrmann
    •  & W. Schulte
  3. Centre de Recherches en Physique de l'Environement Terrestre et Planétaire, CNET-CNRS, 4 avenue de Neptune, 94107 Saint-Maur des Fossés, Paris, France

    • J. J. Berthelier
    •  & J. M. Illiano
  4. University of Texas at Dallas, Richardson, Texas 75083-0688, USA

    • R. R. Hodges
    •  & J. H. Hoffman
  5. Present address: Generaldirektion PIT, CH-3000 Bern 29, Switzerland.

    • U. Herrmann

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https://doi.org/10.1038/321326a0

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