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  • 1
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    Lyman-alpha observations in the vicinity of Saturn with Copernicus (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: For the first time, high-resolution Ly-alpha observations of the Saturn vicinity were completed with the Princeton spectrometer on board the Copernicus satellite. They showed that near a minimum solar activity the emissions related to several sources are 250 + or - 50 rayleighs for the interplanetary medium in a near-downwind direction, less than 100 rayleighs for the rings, 200 + or - 100 rayleighs for a torus linked to the Titan orbit, and 1400 + or - 450 rayleighs for the disk of Saturn. These results induce some constraints through the corresponding theoretical evaluations: the B ring as the primary source of the atoms for the ring emissions; an efficient production mechanism for hydrogen atoms in the Titan torus; and a slightly larger eddy diffusion coefficient in the Saturn atmosphere than in the Jupiter atmosphere near solar minimum.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 242
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  • 2
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    The Lyman alpha bulge of Jupiter - Effects of non-thermal velocity field (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We outline for the first time the effect of such nonthermal line broadening processes as turbulence, random waves, convection, etc., on the shape and intensity of the H Ly-alpha line resonance scattered from the atmosphere of Jupiter. We show how a nonthermal velocity field confined to the bulge region, in the upper atmosphere of Jupiter, may account for most of the H Ly-alpha bulge features. Both the shape and the brightness of the Ly-alpha line from the bulge region as reported by the IUE instrument and the Voyager UV Spectrometer can be recovered assuming resonant scattering with a total atomic hydrogen of about 4 x 10 exp 17/sq cm, and a nonthermal component H of about 2 x 10 exp 15/sq cm above the thermopause.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 8; p. 747-750.
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  • 3
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    A model for the disc Lyman alpha emission of Uranus (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A new efficient radiative transfer algorithm for nonhomogeneous model atmospheres has been applied to the Uranian atmosphere. The contribution of the scatter solar Lyman-alpha to the Uranain emission is of the order of 300 R, and the Rayleigh contribution may reach 450 R for small values of the eddy diffusion coefficient (EDC). The total solar contribution may then reach about 750 R for a solar flux of 2.5 x 10 to the 11th photons/sq cm/s/A. A level of up to 400 R is confirmed in some directions for the interstellar wind contribution. The values of the atmospheric EDC necessary to mimic the observations are 50-100 sq cm/s. A small additional source located on the dayside Uranian atmosphere seems necessary correctly to fit the shape of the limb to limb intensity variation, especially near the limbs. Its contribution to the emergent intensity would range from 100 to 500 R.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9781-979
    Format: text
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