1993 SEB Revival: Expansion Phase
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Mid-Infrared Array Camera↗
Engineering topics
Orton, G. S.
Publications and source records attributed to Orton, G. S..
Thermal structure and energy balance of Uranus
The present study determines the basic properties of the atmospheric temperature field of Uranus through a combination of earth-based and Voyager measurements. Stellar occultation observations indicate both spatial and temporal variability at microbar pressure levels. The tropospheric and stratospheric vertical structure are established via Voyager radio occultation and infrared measurements as well as earth-based full-disk infrared observations. It is found that the measured lapse rate at pressures greater than about 600 microbar exceeds that for fully equilibrated ortho and para hydrogen. The latitude dependence of the upper tropospheric temperatures is determined from Voyager infrared measurements; remarkably little contrast is found. The weak horizontal structure is consistent with tropospheric zonal winds which decay with height and are directed prograde at midlatitudes but retrograde at low latitudes.
Conrath, B. J.↗
Infrared observations of planetary atmospheres
Infrared data was obtained on planetary atmospheres which provides critical information on atmospheric structure, composition, and cloud properties in support of planetary missions such as Voyager and Galileo. Mapping of Jupiter and Saturn in thermal and reflected solar radiation is a high-priority monitoring and exploratory activity. Some of these images of Jupiter are shown. Radiation at 17.8 micrometer probes the upper tropospheric temperature structure where spatial structure bears a strong resemblance to visible and near-infrared reflected sunlight such as at 2.0 micrometer. At 7.8 micrometer, stratospheric temperatures appear to have a three-banded structure, enhancements near the magnetic poles and occasional transient features such as the equatorial filament near the right limb. Clouds or hazes are observed high in the stratosphere looking at wavelengths such as 2.2 micrometer, where gaseous opacity is very strong. Other maps examine cloud properties from thermal radiation not strongly influenced by gaseous opacity and the distribution of condensable gases, such as ammonia. Millimeter and submillimeter filtered radiometric observations were made of Jupiter, Uranus and Neptune via collaborative work. Radiometric observations of Uranus and Neptune at 21 and 32 micrometer were acquired and analyzed as well as grating array spectra in the ranges of 8 to 14 micrometer, 16 to 23 micrometer, and 18 to 32 micrometer. These showed evidence for C2H2 in the stratosphere of Uranus and C2H4 in the stratosphere of Neptune.
Orton, G. S.↗
Submillimeter and millimeter observations of Uranus and Neptune
Neptune and Uranus were studied at submillimeter and millimeter wavelengths for 2 yr using the UK IR telescope and the NASA IR telescope at Mauna Kea and the 12 dish at Kitt Peak, AZ. The brightness temperatures of both planets are provided at various wavelengths over the 0.35-3.3 mm interval scanned in the study. The present data, in combination with data from the 17 microns-3 mm interval scanned in the study. The present data, in combination with data from the 17 microns-3 mm interval taken during previous campaigns, are employed to model the temperature structures in the atmospheres of the two planets over the vertical range 100 mbar-8 bar. The data support the presence of active convection processes at the 1 bar level and deeper in both atmospheres. A static equilibrium however, exists between para-H2 and ortho-H2, along with a constant CH4 fraction of 2 percent. Deficiencies in the current database are detailed.
Orton, G. S.↗
Submillimeter and millimeter observations of Jupiter
Using absolute calibrations referenced to Mars, narrowband photometry has been obtained for the Jovian disk in ten passbands covering the 0.35-3.3 mm wavelength range. Existing atmospheric temperature structure and composition constraints are taken as the context for an analysis of the derived brightness temperature spectrum. Results obtained for the 0.35-0.45 mm range are noted to suggest that radiances can be matched by models which include NH3 ice particles of 30-100 micron size. A 5-percent increase of the absolute calibration scale would yield results well fitted by a clear atmosphere model, obviating the supposition of additional Jovian atmosphere absorption.
Griffin, M. J.↗
Thermal spectrum of Uranus - Implications for large helium abundance
An analysis of the infrared spectrum of Uranus' disk between 7 micrometers and 3 millimeters suggests a volume mixing ratio for helium in the atmosphere of 40 + or - 20 percent, more than for the sun, Jupiter, or Saturn. Alternative explanations require even more extreme assumptions regarding gas abundances or aerosol vertical distribution and spectral properties. The most serious difficulty with a model containing large amounts of helium is devising a credible evolutionary or chemical model explaining the absence or segregation of so much hydrogen.
Orton, G. S.↗
Far infrared and submillimeter brightness temperatures of the giant planets
The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely.
Hildebrand, R. H.↗
Infrared polar brightening on Jupiter. III - Spectrometry from the Voyager 1 IRIS experiment
Spectra from the Voyager 1 IRIS experiment confirm the existence of enhanced infrared emission near Jupiter's north magnetic pole in March 1979. The spectral characteristics of the enhanced emission are consistent with a Planck source function. A temperature-pressure profile is derived for the region near the north magnetic pole, from which quantitative abundance estimates of minor species are made. Some species previously detected on Jupiter, including CH3D, C2H2, and C2H6, have been observed again near the pole. Newly discovered species, not previously observed on Jupiter, include C2H4, C3H4, and C6H6. All of these species except CH3D appear to have enhanced abundances at the north polar region with respect to midlatitudes. Upper limits are determined for C4H2 and C3H8. The quantitative results are compared with model calculations based on ultraviolet results from the IUE satellite. The plausibility of the C6H6 identification is discussed in terms of the literature on C2H2 polymerization. The relation of C6H6 to cuprene is also discussed.
Kim, S. J.↗
Far-infrared and submillimeter brightness temperatures of the giant planets
The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune were measured in the 35-1000 micron range with the 3-m NASA Infrared Telescope Facility (at wavelengths greater than 350 microns) and with the Kuiper Airborne Observatory (at wavelengths less than 350 microns). The data indicate the presence in Jupiter's spectrum of excess radiation (compared to theoretical models) at 300-400 microns. In addition, slightly less flux was observed from Saturn at 200 microns than predicted by atmospheric models, which suggests the possible presence of an unmodeled absorber. The submillimeter fluxes from Uranus and Neptune appear to be most consistent with low mixing ratios (less than 1 percent) of CH4 in their deep atmospheres.
Hildebrand, R. H.↗
Far Infrared and Submillimeter Observations of the Giant Planets
Far infrared measurements of the effective temperatures of Jupiter, Saturn, Uranus and Neptune were made. The measurements presented here cover the range from 35-1000 micrometers in relatively narrow bands. The observations at lambda 350 micrometers were made at the 3m NASA Infrared Telescope Facility (IRTF) of the Mauna Kea Observatory; those at lambda 350 micrometer were made on the Kuiper Airborne Observatory (KAO). All observations of Saturn were made when the ring inclination to Earth was 1.7 deg assuring an unambiguous measurement of the flux from the disk itself. Mars was used as the calibration reference. The results represent a consistent set of calibration standards. In these measurements, it is assumed that sub b(lambda = 350 micrometers) = T sub (lambda 350 micrometers). Measurements have been made of roughly 50% of the total flux emitted by Jupiter, 65% by Saturn, and 92% by Uranus and Neptune. These measurements therefore permit a considerable reduction in the uncertainties associated with the bolometric thermal outputs of the planets. The effective temperatures (T sub e) and the ratios of emitted to absorbed solar radiation were calculated.
Loewenstein, R. F.↗
Optical properties of NH3 ice from the far infrared to the near ultraviolet
The optical constants (n(r), n(i)) for solid ammonia in the cubic phase from 0.14 to 200 microns are displayed in both graphical and tabular form. The refractive indices n(r) were obtained from previously published spectra of the absorption index n(i) by means of the Kramers-Kronig dispersion relation. Mie scattering parameters in the same spectral range are graphically illustrated for particle sizes from 1 to 100 microns. An application of these results to the atmosphere of the planet Jupiter is also presented.
Martonchik, J. V.↗
Clouds and aerosols in Saturn's atmosphere
The physical properties and spatial distribution of aerosol and cloud particles in Saturn's atmosphere are discussed based on data from remote measurement of scattered solar radiation and thermal radiation emitted from Saturn's atmosphere. A brief overview of the relations between particle properties and the scattered and emitted radiation field is given, and observations of Saturn at wavelengths from the ultraviolet to the thermal infrared which bear on the atmosphere's aerosol and cloud properties are reviewed. The single-scattering properties of the particles deduced from observations are discussed, commenting on the possible composition of the particles. The implications of the observations for the vertical and horizontal distribution of the clouds and aerosols are reviewed, and current information and areas for further research on the clouds and aerosols are summarized.
Tomasko, M. G.↗
Observational constraints on the atmospheres of Uranus and Neptune from new measurements near 10 micrometers
Uranus was detected at 10.3, 11.6 and 12.5 micrometers approximately 1 micrometer spectral bandpasses, with respective brightness temperatures of 74.0 + 0.9 or -1.1, 67.6 + 0.5 or -0.7, and 65.5 + 0.6 or -0.7 K and the first detection of Neptune at 10.3 micrometers with a brightness temperature of 77.5 + 0.7 or -0.9 K. We also detected Neptune at 11.36 micrometers with 2 percent spectral resolution at 81.0 + 0.8 or -0.9 K. The 10 micrometers continuous of both Uranus and Neptune may in part be due to reflected solar radiation as well as thermal emission. If all of the observed flux is reflected light, then the maximum geometric albedo of Uranus is 0.115 + or - 0.020, and that of Neptune is 0.229 + or - 0.043. In the context of previous observations in this region, the maximum stratospheric C2H6 mixing ratio is found to be 3 x 10 to the -8 power for Uranus and 3 x 10 to the -6 power for Neptune. A value for the maximum mixing ratio in the stratosphere of Neptune on the order of 1 - 0.004 appears to be consistent with the available data. Previously announced in STAR as N83-29155
Tokunaga, A. T.↗
Thermal infrared constraints on ammonia ice particles as candidates for clouds in the atmosphere of Saturn
Saturn atmosphere thermal IR emission observations have uncovered two phenomena that may be accounted for by large ammonia ice particles: the depression of thermal brightness near the equator, and inconsistent IR and radio occultation results. Ammonia ice particles yield the opacity that can account for the contrast between the equatorial region and a brighter area near 15 deg S, and may also reconcile the 45-micron brightness of these two regions with the mean temperature structure of Voyager 2 radio occultation results. A cloud model whose ice particles are distributed in an equal ratio with gas particles up to the 100 mbar pressure level is found to fit the equatorial data, while a thinner cloud, or one that does not extend higher than the 400 mbar limit of the convective region matches the 15 deg S data.
Orton, G. S.↗
Further observations of 8-micron polar brightenings of Jupiter
North-to-south scans of Jupiter at 7.8-micron wavelength in early 1981 confirm polar brightening events that correlate with LCM (III), such that a polar limb is bright when the corresponding magnetic pole is tilted earthward. The correlation with magnetic features of the planet suggests that the energy source for the brightenings is magnetospheric particles incident upon the polar regions of the atmosphere. The northern polar events are more prominent and more regular than the southern ones. The polar emission may be indirectly related to the ultraviolet absorber observed near the poles by Voyager 2.
Caldwell, J.↗
New observational constraints on the temperature inversions of Uranus and Neptune
The presence of a temperature inversion in the lower stratospheres of both Uranus and Neptune is confirmed by the 20-micron photometric data presented. It is found that the brightness temperature difference between 17.8 and 19.6 microns is 0.8 + or - 0.5 K for Uranus and 1.8 + or - 0.6 K for Neptune, implying that the temperature inversions of both planets are weaker than previously thought. Comparisons with model atmospheres suggested by Appleby (1980) imply that these temperature inversions may be understood as a consequence of heating through CH4 and aerosol absorption of sunlight. The stratospheric CH4 mixing ratio of Neptune must, however, be higher than that at the temperature minimum.
Tokunaga, A. T.↗
Airborne spectroscopy of Jupiter in the 100- to 300/cm region - Global properties of ammonia gas and ice haze
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Orton, G. S.↗
The effect of ammonia ice on the outgoing thermal radiance from the atmosphere of Jupiter
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Orton, G. S.↗