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  • 1
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    Solar cycle study of interplanetary Lyman-alpha variations - Pioneer Venus Orbiter sky background results (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: PVO observations of the interplanetary Ly-alpha (IPL) background, obtained over an entire solar cycle (SC) from 1979 to 1985, are compiled and analyzed statistically, along with data from other instruments and earlier solar cycles. The results are presented in extensive tables and graphs and characterized in detail. Findings reported include SC variation of 1.8 for the longitudinally averaged IPL intensity (in agreement with the variation of the 27-d disk-averaged integrated solar Ly-alpha flux), yearly averaged ecliptic H-atom lifetime at 1 AU equal to 1.0 Ms at solar minimum and 1.5 Ms at solar maximum, interplanetary H density equal to 0.07 + or - 0.01/cu cm, and interplanetary H/He within the heliopause but far from the sun of 7 + or - 3.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 964-986
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    NASA TECHNICAL REPORTS
  • 2
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    Out-of-ecliptic Lyman-alpha observations with Pioneer-Venus - Solar wind anisotropy degree in 1986 (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Measurements of interplanetary Lyman-alpha were made over a wide range of ecliptic latitudes by the Pioneer Venus Orbiter Ultraviolet Spectrometer during the tracking of Halley's comet from December 1985 to March 1986. By comparisons with models of the interstellar/interplanetary hydrogen wind, the total solar ionization lifetime at 1 AU is found to be 1.25-1.5 x 10 to the 6th sec, and its variation with solar latitude is found to be 30 + or - 5 percent. The solar wind mass flux variation with solar latitude is found to be very weak (0 + or - 10 percent). These values are appropriate to solar minimum. Comparison of the latitudinal variation with earlier measurements from 1973 to 1977 suggest that the asphericity of the solar wind may increase as solar activity passes through its minimum.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 227; 2 Ja
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    NASA TECHNICAL REPORTS
  • 3
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    Pioneer Venus Lyman-alpha observations of Comet P/Giacobini-Zinner and the life expectancy of cometary hydrogen (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are given of the Pioneer Venus observation of the hydrogen coma of Comet P/Giacobini-Zinner on September 11, 1985 during the fly-by conducted by the International Cometary Explorer (ICE). Analysis of the data with a time-dependent 3-D particle-trajectory model implies a water production rate of 2.2 x 10 to the 28 per second on that day. The model includes the irregular variations in the H lifetime and the H Lyman-alpha fluorescence rate determined from simultaneous measurements of the solar wind by ICE and of the solar UV by the Solar Mesosphere Explorer (SME), respectively. The H lifetime varied from 2 x 10 to the 5 to 3 x 10 to the 6 seconds during the 42 days preceding the observation.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 385-388
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    NASA TECHNICAL REPORTS
  • 4
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    Pioneer Venus measurements of H, O, and C production in comet P/Halley near perihelion (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The Pioneer Venus Orbiter Ultraviolet Spectrometer measured the production of H, O, and C in comet Halley from late December 1985 to early March 1986. Water production rates obtained from the H data rose from 3.3 x 10 to the 29th/s at 1 AU inbound to 1.2 x 10 to the 30th/s at perihelion; there was a further increase to 1.6 x 10 to the 30th/s followed by a slow decline to 1.4 x 10 to the 30th/s at the time of the Vega-1 encounter. The H measurements show a periodic behavior that imply variations in the water production rate having structure within a 7.4-day sidereal period, in phase with similar variations seen in radical and dust production in March and April. Average H:O:C ratios of 1.0:0.7:0.07 were measured from 10 to 26 days after perihelion.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2
    Format: text
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