Comet Halley | Published:

In situ gas and ion measurements at comet Halley

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



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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  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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