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  • ASTROPHYSICS  (5)
  • SPACE SCIENCES
  • 1985-1989  (5)
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  • 1
    Publication Date: 2019-06-28
    Description: Low-energy 1-AU cosmic-ray spectra obtained using the IMP-8 satellite cosmic-ray telescope (Garcia-Munoz et al., 1975) at quiet times during the solar minimum of 1972-1977 are reported and combined with published data on that minimum and the previous one (1965), with a focus on the anomalous He-4 and heavy-nucleus spectra and proton and helium superfluxes observed in 1972-1977. The 56-MeV/nucleon H-2/H-1 and H-2/He-4 abundance ratios and the differential energy spectra are plotted versus time and solar modulation level over an entire cycle, and the proton and He superfluxes, which do not contribute to the anomalies, are attributed to the reduced levels of residual modulation present during 1972-1977.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 294; 455-462
    Format: text
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  • 2
    Publication Date: 2019-06-28
    Description: The development of the polyvinylidene fluoride (PVDF) dust detector for space missions--such as the Halley Comet Missions where the impact velocity was very high as well as for missions where the impact velocity is low was extended to include: (1) the capability for impact position determination - i.e., x,y coordinate of impact; and (2) the capability for particle velocity determination using two thin PVDF sensors spaced a given distance apart - i.e., by time-of-flight. These developments have led to space flight instrumentation for recovery-type missions, which will measure the masses (sizes), fluxes and trajectories of incoming dust particles and will capture the dust material in a form suitable for later Earth-based laboratory measurements. These laboratory measurements would determine the elemental, isotopic and mineralogical properties of the captured dust and relate these to possible sources of the dust material (i.e., comets, asteroids), using the trajectory information. The instrumentation described here has the unique advantages of providing both orbital characteristics and physical and chemical properties--as well as possible origin--of incoming dust.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Workshop on Analysis of Returned Comet Nucleus Samples; p 64-65
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-12
    Description: Measurements from the Ducma dust counter and mass analyzer on the Vega spacecraft are compared with those from the SP-1 sensor on the same spacecraft. It is shown that the sequence of pulses recorded by the SP-1 instruments show deviations from a random distribution. Some of the nonrandom sequences observed by SP-1 are in the same time intervals as the clusters observed by the Ducma instrument. The results support the analysis of Ducma data which showed highly structured variations of dust intensity through the coma and large fluxes of low mass particles extending to great distances beyond the coma (Simpson et al., 1986).
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 9; 3 19
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  • 4
    Publication Date: 2019-07-12
    Description: Measurements of dust particles in comet Halley's coma from Vega spacecraft made with instruments using a new principle of dust detection and having a high time resolution over a large range of dust fluxes and masses are reported. The dust coma, whether quiescent (as seen by Vega 2) or containing a major jet structure, (as seen by Vega 1) displays large, short-term variations throughout which are at times quasi-periodic. The integral mass spectra increase in intensity to the lowest masses measured, and the flux levels lie approximately in the ranges estimated previously from ground-based observations. The coma is highly dynamical on all spatial and temporal scales, suggesting a complex structure of localized regions of dust emission from the nucleus.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 321; 278-280
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  • 5
    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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