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  • 1
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    The drift of Saturn's north polar spot observed by the Hubble Space Telescope (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Polar projections of 50 images of Saturn at 889 nanometers and 25 images at 718 nanometers taken by the HST in November 1990, as well as three images at each wavelength taken in June 1991, have been examined. Among them, 31 show the north polar spot, which is associated with Saturn's polar hexagon, in locations suitable for measurement. The movement of the spot with respect to Saturn's system III rotation rate was studied. During the period of observation, the polar spot had first a short-term westward movement and then a long-term eastward drift. The rate of the long-term drift was -0.060 +/- 0.008 deg/day with respect to system III, approximately 50 percent greater than previously determined from Voyager. The original 1980 and 1981 Voyager data were combined with the new Hubble images to form an 11-yr baseline. The eastward drift over the longer period was -0.0569 degrees per day. The long-term drift could be due to uncertainty in the standard value of the internal rotation period. The short-term movement in November 1990 has a rate that is greater in magnitude but opposite in sign and probably represents a real, transient motion of the spot relative to the internal rotation system.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 260; 5106; p. 326-329.
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  • 2
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    The 2-micron polar haze of Jupiter (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Model spectra have been constructed for the CH4 lines of the polar regions of Jupiter in such as way as to encompass the hydrogen pressure-induced opacity and haze layers revealed by high-resolution spectroscopy. Comparisons between observation and model spectra indicate that, for optically thin haze models, the polar haze is primarily located between the 70 and 5 mbar pressure levels; for opaque haze models, the top of the haze layers lies in the vicinity of the 15-mbar level. It is concluded that the polar haze is widely distributed over both polar regions and exhibits no strong correlation with auroral activities.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 91; 145-153
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  • 3
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    International Jupiter Watch - A program to study the time variability of the Jovian system (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The International Jupiter Watch is a program for the encouragement and coordination of the study of temporal variations in the Jovian system. It consists of six discipline working groups concerned with: the Io torus under N. Schneider; the Jovian atmosphere under R. West; the magnetosphere and radio emissions under I. de Peter and M. Klein; aurora under J. Caldwell; the Galilean satellites under W. Sinton and J. Goguen; and laboratory measurement and theory under B. Lutz. To date the IJW has held two workshops and selected several Jupiter Watch periods for coordinated observations. The next Jupiter Watch workshop is tentatively scheduled for 1990 in association with the next COSPAR meeting.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 10; 1, 19
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  • 4
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    Measurements of the methane relaxation times for application to the infrared emission models of the upper atmospheres of outer planets and Titan (1990)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The 7.8 micrometer emission from the nu(sub 4) band of methane (CH4) is a regularly observed feature in the stratosphere of all the giant planets and Titan. On Jupiter, enhancements in this emission are associated with the infrared hot spots in the auroral zone. Attempts to model this phenomenon in particular, and to understand the role of methane in general, have been hampered in part by a lack of adequate laboratory measurements of the collisional relaxation times for the nu(sub 3) and nu(sub 4) levels over the appropriate temperature range. To provide this needed data, a series of laboratory experiments were initiated. In the experimental arrangement the nu(sub3) band of methane is pumped at 3.3 micrometers using a pulsed infrared source (Nd:YAG/dye laser system equipped with a wave-length extender). The radiative lifetime of the nu(sub 3) level (approximately 37 ms) is much shorter than the nu(sub 4) lifetime (approximately 390 ms); however, a rapid V-V energy transfer rate ensures that the nu(sub 4) level is substantially populated. The photoacoustic technique is used to acquire relaxation rate information. The experiments are performed using a low-temperature, low-pressure cell. Experimental apparatus and technique are described. In addition some of the experimental difficulties associated with making these measurements are discussed and some preliminary results are presented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: First International Conference on Laboratory Research for Planetary Atmospheres; p 157-163
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  • 5
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    Middle infrared thermal maps of Venus at the time of the Galileo encounter (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Images of the disk of Venus, taken at wavelengths between 8 and 22 micrometers, were obtained a few days after the Galileo spacecraft's closest approach on February 8, 1990; these images show variations in the thickness of the main H2SO4 cloud deck and the overlying temperature structure. Several features are qualitatively similar to those of earlier observations, such as a hot region at the south pole, surrounded by a cold 'collar', and brightening toward the lower latitudes, where low-contrast banding appears. The collar does have a northern counterpart that is warmer, however. Equatorial limb darkening is quantitatively similar to that of previous observations; fairly constant at wavelengths up to 20 micrometers, where limb darkening increases substantially. In contrast to what was found in previous observations, polar and equatorial limb darkening are nearly the same at most wavelengths. A longitudinal variation is observable that is consistent with a wavenumber-2 behavior and a brightness maximum near local midnight.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 253; 1536-153
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  • 6
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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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  • 7
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    Titan: Evidence for seasonal change - A comparison of Hubble Space Telescope and Voyager images (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A comparison of images of Titan obtained by the HST in August, 1990 with Voyager 1 and 2 images respectively obtained 10 and 9 years earlier has indicated a reversal of the seasonal hemispheric brightness asymmetry near 440 and 550 nm wavelengths; the northern hemisphere is in the more recent observations the brighter of the two, by about 10 percent. Titan's albedo pattern is therefore adequately explained by a seasonal model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 97; 1 Ma
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  • 8
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    The ultraviolet absorption spectrum of CO - Applications to planetary atmospheres (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Laboratory gas-phase photoabsorption cross sections of the CO Cameron 0-0 band and the underlying pseudocontinuum have been measured at a temperature of 147 K and pressures of about 200 mbar, conditions similar to ambient in various planetary and satellite stratospheres in the solar system. A theoretical modeling program has also been used to calculate the band's spectrum. Agreement between the theoretical and the experimental spectra is very good. Models suggest that the observations of the CO Cameron band using the Hubble Space Telescope will be straightforward for Mars, but marginal for Titan.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; E3; p. 5491-5497.
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  • 9
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    Calibration of the 7- to 14-micron brightness spectra of Uranus and Neptune (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An independent measure of the absolute brightness of the disk-averaged spectrum measured by Orton et al. (1987) is attempted via observations of Uranus and Neptune at discrete wavelengths between 8.17 and 13.0 microns. These observations are found to be consistent with the suggested upward recalibrations of the Uranus and Neptune spectra by factors of 1.6 and 1.12, respectively. Both graphic and tabular results are presented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 257-265
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  • 10
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    The ultraviolet continuum albedo of Uranus (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A radiative transfer code explicitly treating the Raman scattering of solar protons by H2 is presently used to analyze the Uranus geometric albedo in the 2000-5000 A range. The Baines and Bergstralh (1986) baseline model used reproduces the geometric albedo peak produced by Raman scattering filling of solar absorption line cores, but is found to be excessively bright for wavelengths below 2400 A. This discrepancy is resolvable through inclusion of an absorbing stratospheric haze layer, and results are thereby obtained which are consistent with the Pollack et al. (1987) model, in which aerosols are generated stratospherically through photochemical effects on hydrocarbons.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 83; 93-101
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