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  • Other Sources  (11)
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  • 1
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    The ultraviolet albedo of Mars (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Ultraviolet observations have proven successful at studying the composition and structure of the upper atmospheres of the giant planets and Venus. In the case of Mars, the analysis of UV data has concentrated on the spatial distribution and temporal behavior of ozone. The potential of far ultraviolet (FUV) data (shortward of 200 nm) for measuring the atmospheric structure, in particular the vertical distribution of aerosols, is demonstrated. For illustrative purposes, a simple two layer model (atmosphere and surface) is computed using the atmospheric composition measured at the Viking landing sites. This model is then compared to the albedo observed with the International Ultraviolet Explorer (IUE). This comparison clearly shows that a clear atmosphere with the nominal Viking mixing ratios of CO2, O2, and H2O is incompatible with the IUE data shortward of 200 nm. To obtain a better match between data and model, an aerosol has to be introduced that effectively scatters at these wavelengths. The required reduction in effective CO2 pathlength is a factor of 5. The comparison also points out the inadequacy of the IUE to provide data in the critical wavelength region between 195 nm and 210 nm. Such data will be forthcoming from the Hubble Space Telescope and will provide the opportunity to infer the vertical distribution of aerosols on Mars on a global scale.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on the Martian Surface and Atmosphere Through Time; p 164
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  • 2
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    High resolution, low temperature photoabsorption cross-section of C2H2 with application to Saturn's atmosphere (1990)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: New laboratory observations of the VUV absorption cross-section of C2H2, obtained under physical conditions approximating stratospheres of the giant planets, were combined with IUE observations of the albedo of Saturn, for which improved data reduction techniques have been used, to produce new models for that atmosphere. When the effects of C2H2 absorption are accounted for, additional absorption by other molecules is required. The best-fitting model also includes absorption by PH3, H2O, C2H6 and CH4. A small residual disagreement near 1600 A suggests that an additional trace species may be required to complete the model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Goddard Space Flight Center, First International Conference on Laboratory Research for Planetary Atmospheres; p 142-146
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  • 3
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    The Jovian Stratosphere in the ultraviolet (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The center-of-disk reflectivity of Jupiter in the wavelength range from 1500 A to 3000 A was computed from 31 low dispersion IUE spectra taken during solar maximum in 1979/80. The spectra were normalized to a reflectivity scale with the improved solar spectrum of July, 1980. Consideration of wavelength shifts between different IUE spectra and within the solar spectrum improved the apparent noise, especially longward of 2000 A. Six out of seven ammonia bands between 1900 A and 2200 A were detected. A vertically inhomogeneous radiative transfer program is used to compute model reflectivities for various stratospheric compositions. In addition to ammonia, the abundance of acetylene is also well determined because these molecules show narrow absorption bands in the ultraviolet. The abundances of the other molecules in the models (C3H4, C2H4, C4H2, C2H6, C3H6) are very uncertain and therefore are quoted only as upper limits. The best model fit is consistent with infrared observations by Voyager IRIS.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Goddard Space Flight Center Future of Ultraviolet Astronomy Based on Six Years of IUE Res.; p 129-132
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  • 4
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    Tentative confirmation of an aurora on Uranus (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: There have been three recent reports of the detection of Lyman-alpha radiation (due to atomic hydrogen, H, at wavelength 1,216 A) from Uranus by means of the International Ultraviolet Explorer (IUE) satellite. The interpretations of these results differ. Two reports conclude that there is a strong aurora on Uranus, but the third concludes that the source is resonance scattering of solar Lyman-alpha. This paper reports the detection of emission features due to molecular hydrogen, H2, near 1,600 A. This detection is near the limit of the IUE sensitivity. If it is real, the detection of H2 emission strongly supports the conclusion that Uranus has an aurora comparable in strength with those of the inner two giant planets, Jupiter and Saturn. The first published IUE spectra of the Saturn aurora are also presented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 303; May 26
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  • 5
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    Ultraviolet Observations of Uranus and Neptune Below 3000 Angstrom (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: From 2000 to 3000 A, both Uranus and Neptune have albedos that are about two times higher than Jupiter or Saturn's, implying that the outer giants have stratospheres that are relatively free of aerosol absorption. Uncertainties in the absolute calibration procedure allow discrepancies of order 15% between conservative models and the observations. A small amount of aerosol absorption is therefore possible. Below 2000 A the derived albedo is highly dependent on the solar spectrum source used in the data reduction. The most recent result for Uranus, first reported here, is consistent with a secular change in C2H2 mixing ratio from approximately three times ten to the minus eight in 1980 to less than or equal to ten to the minus ninth in 1983. These values are approximately 2 orders of magnitude less than the mixing ratios of this gas on Saturn, and comparable to the amount on Jupiter.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: JPL Uranus and Neptune; p 157-177
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  • 6
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    Solar analogs in the 2600 to 3200 A region (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: No criteria for the selection of solar analogs are found. At low dispersion, the spectra of 16 Cyg A, 16 Cyg B, 18 Sco and alpha Cen A look identical to each other and to sunlight reflected from Galilean satellites with the possible exception of Mg II lambda 2800 being stronger in the stars. The use of alpha Cen A or 16 Cyg B as solar substitutes for planetary photometry is expected to be far superior to using published solar irradiances.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center Advan. in Ultraviolet Astron.; p 277-280
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  • 7
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    Ultraviolet observations of Uranus and Neptune below 3000 A (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: From 2000 A to 3000 A, both Uranus and Neptune have albedos that are about two times higher than Jupiter or Saturn's, implying that the outer giants have stratospheres that are relatively free of aerosol absorption. Uncertainties in the absolute calibration procedure allow discrepancies of order 15% between conservative models and the observations. A small amount of aerosol absorption is therefore possible. Below 2000 A, the derived albedo is highly dependent on the solar spectrum source used in the data reduction. The most recent result for Uranus is consistent with a secular change in C2H2 mixing ratio from approximately 3 x (10 to the -8 power) in 1980 to or = 10 to the -9 power in 1983. These values are approximately 2 orders of magnitude less than the mixing ratios of this gas on Saturn, and comparable to the amount on Jupiter.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center Future of Ultraviolet Astronomy Based on Six Years of IUE Res.; p 501
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  • 8
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    Constraints on the NH3 and PH3 distributions in the Great Red Spot (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Medium resolution (10 A) UV spectra were obtained for the Great Red Spot (GRS) and South Tropical Zone (STZ) of Jupiter using the low dispersion mode of the IUE spectrometers at wavelengths from 1900-2200 A. The scans were carried out to determine the coloring agent for the GRS to improve the database for developing photochemical models of the feature. The wavelengths were selected to cover the absorption features of NH3 and PH3. The resulting data were interpreted using a vertically inhomogeneous Rayleigh scattering radiative transfer model. Various NH3 concentrations were explored in an effort to fit the data, taking into account changes which would occur at different atmospheric pressure levels and due to the projected temperature fields. A forbidden NH3/forbidden H2 mixing ratio that was calculated at the 80-125 mbar pressure level in the GRS was enhanced by 3-10 percent relative to the STZ. An upper limit was obtained for the mixing ratio of PH3 in the GRS that is significantly lower than previously predicted concentrations, implying that vertical transport in the GRS is not much greater than in adjacent regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 66; 188-191
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  • 9
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    The geometric albedos of Uranus and Neptune between 2100 and 3350 A (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are reported from large aperture IUE observations of the stratospheres of Uranus and Neptune. The data were collected using 16 Cyg A and B as solar analog stars. The spectra observed were similar to geometric albedos of the predicted in terms of Rayleigh-Raman scattering in the 2200-2800 A region. A falloff was observed near visible wavelengths, a factor which might be attributable to low-altitude haze absorbing in the 3000-4000 A interval. The data also indicated that the Uranus stratosphere does not strongly absorb UV radiation, and is not a good heating source. The stratospheric haze constituents over Uranus could therefore be condensates of CH4 and H2 photochemistry.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 67; 281-288
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  • 10
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    The Jovian stratosphere in the ultraviolet (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Models of the spectral reflectivity at the center of the disk of Jupiter from 1450 to 3150 angstroms are presented. The reflectivity was computed from 30 low-dispersion IUE spectra taken during the 1978-1980 solar maximum. A vertically inhomogeneous radiative transfer program was used to compute model reflectivities of various stratospheric compositions for comparison. Ammonia and acetylene are well determined because they show narrow absorption bands in the ultraviolet. Possible compositions to improve the fit to the data below 1800 angstroms are suggested. The data are too noisy to detect possible CO Cameron band absorption near 2000 angstroms.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 63; 222-236
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