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  • ASTROPHYSICS  (2)
  • 1
    Publication Date: 2019-07-12
    Description: In this paper, the large-scale enhancements of about 50 s duration in the flux of submicron dust particles from Comet P/Halley recorded by the Dust Counter and Mass Analyzer carried aboard the two Vega spaceprobes are traced back to their source departure points on the nucleus. Evidence is presented that such enhancements which correspond to regions of enhanced particle density in the coma with spatial widths of about 4000 km, are superimposed upon a background flux distribution which is well described by a simple fountain model. Thus, dust production on the sunlit hemisphere of the nucleus is characterized by discrete jet sources superimposed upon relatively low-level isotropic emission. The jet sources at the nucleus responsible for the major enhancements in recorded particle impact rates are narrow and discrete, with each jet accelerating about 10 to the -13th g particles to a narrow range of terminal velocities which decrease with increasing particle mass.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 200; 1-2; 225-247
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  • 2
    Publication Date: 2019-07-12
    Description: Measurements obtained with the Dust Counter and Mass Analyzer instruments on the Vega 1 and 2 spacecraft are used to study properties of the coma of comet P/Halley. Well-defined envelope boundaries for the inverse square dependence of flux with distance from the nucleus are found, and regions of enhanced fluxes above these R exp -2 baselines inside these boundaries are identified as dust jets. The mass spectrum of the giant flux enhancement noted near the closest approach of Vega 1 is shown to be similar to the preencounter spectra. The data suggest the emission from the nucleus of large conglomerates of small particles which disintegrate as they travel outward, explaining the 10 to the -13th g particles observed beyond the envelope boundaries.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2; 742-752
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