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  • 1
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    Electron impact excitation and dissociation of N2 via the b 1Pi(u) state (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Electron impact excitation of the b 1Pi(u) state in N2 plays a prominent role in the dissociation of the molecule and thus in the production of atomic nitrogen in planetary atmospheres. Electron impact excitation cross sections combined with electron-impact-induced fluorescence measurements can yield the corresponding dissociation cross sections. Serious discrepancies exist among excitation cross sections reported in the literature. To clarify the situation, these cross sections were measured at two impact energies using electron energy loss spectroscopy. The new results are in agreement with recent values deduced from optical measurements and fall midway between previous results which are too high or low by factors of 2.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 17
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  • 2
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    Hydrogen emission from Jupiter: Hydrogen emission from sunlit atmosphere of Saturn (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Successful IUE observations of the equatorial sunlit atmosphere of Jupiter and Saturn have been obtained. Spectra containing atomic and molecular hydrogen and solar reflection continuum emissions have been analyzed, with the purpose of determining the long term temporal behavior of the electroglow process. Quantitative estimates have been established for the first time using a model analysis of the short wavelength region of the spectrum. Both systems show varying degrees of long term variability in hydrogen emission rate, but the time scale is too short to determine whether there is a dependence on solar cycle activity. As part of the emission modeling program, a preliminary point source spreading function for the IUE SWP instrument has been established, suggesting a wavelength dependence in spectral line width different from previous analyses. Further IUE observations are planned for both Jupiter and Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-180245 , NAS 1.26:180245
    Format: application/pdf
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  • 3
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    A reanalysis of Voyager UVS observations of Titan (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Data from the Voyager 1 Ultraviolet Spectrometer (UVS) encounter at Titan were reanalyzed to reveal new spatial and spectral information. The observations, data reduction and spectrum analysis are discussed. The following conclusions were drawn: Titan's airglow is driven by a combination of mechanisms including both EUV deposition and magnetospheric particle precipitation; the emissions are distributed throughout a range of altitudes in the atmosphere; enhanced nightside emissions of the Helium 58.4 nm line may be the result of a thermospheric diurnal temperature variation; the CD2 spectrum, with enhanced Ly(alpha) and N-2 64.5 and 67.0 nm emission, implies that some of the high altitude excitation is due to impact dissociative excitation of N2 by electrons with E greater than 150 eV; the CD2 spectrum is consistent with the existence of a high altitude bright spot in the dayside disk with dimensions from 400 to 900 km.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: ESA, Symposium on Titan; p 67-74
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  • 4
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    The Mercury atmosphere (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Data available on the composition of Mercury's atmosphere are reviewed, and the sources of these atmospheric components are considered. The known gaseous components in Mercury's atmosphere are H, He, O, Na, and K; among other gases likely to be present are H2 and H2O. Probable sources of these components are the solar wind for hydrogen and helium. The alkalis and water are considered to come from the evaporation of meteoroidal material, with a possible contribution to the former by sputtering and photosputtering.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 5
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    A deficiency of O III in the Io plasma torus (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Evidence for a deficiency of O III ions in the Io plasma torus is reported and implications of this deficiency for the physical processes controlling the plasma are considered. Observations of the O III 5007-A as well as Cl III and S III emissions from the Io plasma torus were made by a ground-based echelle spectrograph and intensified Reticon detector in February and May, 1981. The O III observations allow an upper limit of 4/cu cm to be placed on torus O III abundance, which is inconsistent with expectations for a low density plasma controlled by electron collisions. The inclusion of ion-ion and ion-atom charge exchange reactions and a depleted high energy electron component in the model is found to suppress O III levels, however observed limiting values are only achieved if it is assumed that the O III is kinetically hot. In addition, the charge-exchange model developed is inconsistent with previous observations of the kinetics of the S II-S III system. The present observations also establish upper limits of 2 R on 5518-A and 5538-A Cl III emission, and an emission rate of 58 + or - 40 R for the S III 6312-A line in the hot torus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 264
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  • 6
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    The Saturn spectrum in the EUV - Electron excited hydrogen (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Recent laboratory observations of electron excited H2 in the EUV have brought about the realization that higher Rydberg series band systems make a significant contribution to the emission spectrum. Theoretical cross section estimates for the excitation of the D, D-prime, B-prime, and B-double-prime states agree with these results. Model calculations for particle excitation of the Saturn atmosphere, including the higher states, now show excellent agreement with Voyager auroral and dayside equatorial spectra. The model data also confirm the relative spectral response calibration of the Voyager instruments, providing a basis for accurate analysis of the excitation processes on both Jupiter and Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 88; Jan. 1
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  • 7
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    A new look at the ionosphere of Jupiter in light of the UVS occultation results (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Neutral model atmospheres derived from the Voyager UV Spectrometer's solar and stellar occultation data are used to calculate Jupiter ionospheric electron density profiles, demonstrating the inadequacy of such methods. It is also shown that electron densities calculated by means of standard parameters are larger than those measured by both Pioneer and Voyager. McElroy's (1973) suggestion as to the importance of H2 vibrational excitation is investigated, and it is found that no single vibrational temperature is appropriate for the entire thermosphere. The long recombination time constants involved in the plasma's movement, due to either meridional winds or electric fields, through large vertical distances, is shown to account for the observed electron density profiles. It is suggested that the outflow, and possibly the inflow, of plasma may play a role in the definition of electron density profiles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Planetary and Space Science; 30; Feb. 198
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  • 8
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    Visible aurora in Jupiter's atmosphere (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The darkside limb pictures obtained by the imaging experiment on Voyager 1 have been reexamined. It is concluded that the observed luminosity is very likely due at least in part to Io torus aurora. If the effective wavelength of the emission lies in the 4000- to 5000-A region, the slant intensity is estimated to be about 20 kR. The observed double structure may be due to a number of causes such as horizontal structure in auroral emission, aurora plus twilight or photochemical airglow plus aurora.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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  • 9
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    Overview of the Voyager ultraviolet spectrometry results through Jupiter encounter (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The observations of a number of objects by the Voyager EUV instruments are summarized. The summary is considered to demonstrate the wide ranging application of the EUV spectroscopy. It also marks an important step forward in spectrography and emphasizes the continuing importance of the search and discovery nature of spectroscopic techniques.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Sept. 30
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  • 10
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    The Voyager 1 EUV spectrum of the Io plasma torus (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The Voyager 1 EUV spectrum of the hot Io plasma torus obtained before encounter in 1979 at a range of 4,800,000 km is analyzed in terms of a collisional model with improved collision strengths. Model calculations are based entirely on steady-state equilibrium between electron excitation-deactivation and radiative decay in the subspecies structure, and plasma temperature and species number densities are derived by fitting model spectra to the observations. Lines of S II, S III, S IV, O II, and O III are found to be dominant in the plasma torus, at torus half width densities of 44, 160, 220, 50, and 340/cu cm, respectively, and lines of S V and K III may also be present. An effective electron temperature of 80,000 K is estimated for the central dense region near 6 Jupiter radii. Model calculations are in substantial agreement with other spectroscopic observations of the hot torus; however, the observations exhibit strong morphological differences with recent ground-based observations of S II emission, and calculated ion densities differ from in situ Voyager 1 plasma science measurements.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Oct. 1
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