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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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NASA NTRS1977

A model for the temperature inversion within the atmosphere of Saturn

A model for the temperature inversion within the atmosphere of Saturn is proposed and is shown to be consistent with photometric data in the 17- to 25-micron region. The proposed model incorporates solar heating by some 'aerosol', with the aerosol heating per unit mass of the atmosphere being uniformly distributed throughout that portion of the atmosphere overlying the upper cloud deck. For a methane-to-hydrogen mixing ratio of 0.0007, the model results suggest that 20% of the incident solar radiation is absorbed by the aerosol, while this is reduced to 16% for an enhanced methane mixing ratio of 0.0021.

Tokunaga, A.↗
NASA NTRS1978

Saturn's atmosphere: Results of recent investigations

Saturn apparently has a high clear layer of H2 under which lies a comparable layer rich in dusty material. Beneath this is a thicker layer consisting mostly of H2 mixed with haze particles. An NH3 cloud deck probably lies below this layer. Evidence for seasonal variations is presented in the form of changes in the NH3, CH4 and H2 absorptions. Finally, the latest mixing ratios for the gaseous constituents are summarized.

Trafton, L.↗
NASA NTRS1984

Structure and dynamics of Saturn's atmosphere

The large-scale structure and dynamics of Saturn's atmosphere, as revealed in the visible markings, wind patterns, and horizontal variation of temperature, are discussed. The large-scale thermal structure is addressed, including the mean vertical structure and the seasons and jets of the horizontal temperature structure. Earth-based and Voyager wind observations are used to discuss the internal rate of rotation, the zonal wind profile, the eddies, and the eddy transport. Dynamic models of the atmospheric circulation are reviewed, discussing the depth of the zonal flow, upwelling and downwelling, deep convection, eddy-mean flow interactions, long-lived ovals, and the zonal velocity profile.

Ingersoll, A. P.↗
NASA NTRS1984

Composition and chemistry of Saturn's atmosphere

A comprehensive discussion and review is presented of the chemistry and composition of Saturn as determined by earth-based, earth-orbital, and Voyager 1 and 2 spectroscopic observations. The observations imply that there are important differences between the actual composition of Saturn's atmosphere and that predicted for a homogeneous solar-composition planet. The H2, He, Ch4, NH3, and PH3 volume mixing ratios differ from the expected solar composition ratios, implying that during its formation Saturn accreted a significant amount of ice and rock. The depletion of He in the visible atmosphere suggests that this element has preferentially differentiated toward the center of the planet. The D to H ratio is similar to that on Jupiter and has important cosmological implications. Volume mixing ratios for C2H6 and C2H2 are consistent with the theoretically expected photochemical sources for these gases.

Prinn, R. G.↗
NASA NTRS1987

Hydrogen emission from Jupiter: Hydrogen emission from sunlit atmosphere of Saturn

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.

Shemansky, D. E.↗
NASA NTRS1977

The atmosphere of Saturn - An infrared perspective

A model of the radiative portion of the equatorial atmosphere of Saturn, constrained by the infrared data of various observers, has been constructed using a technique which includes the variation of thermal flux with depth. The model has a high-altitude temperature inversion due to the absorption of ultraviolet sunlight. The inversion causes the observed infrared emission peaks at 8 microns (methane) and 12 microns (ethane). Mixing ratios of these gases to hydrogen are computed from these emission features. The bottom of the modeled region occurs at the radiative convective boundary. At this level, an opaque cloud consisting of solid ammonia condensation particles is postulated. Above the cloud is a thin haze, also composed of ammonia particles. The haze is required to match infrared observations near 9.5 microns and hydrogen quadrupole equivalent widths near 0.64 micron. Predictions of the model are given for further observational tests.

Caldwell, J.↗
NASA NTRS2000

Photochemistry of Saturn's Atmosphere: Hydrocarbon Chemistry and Comparisons with ISO Observations - 1

To investigate the details of hydrocarbon photochemistry on Saturn, we have developed a one-dimensional diurnally averaged model that couples hydrocarbon and oxygen photochemistry, molecular and eddy diffusion, radiative transfer, and condensation. The model results are compared with observations from the Infrared Space Observatory (ISO) to place tighter constraints on molecular abundances, to better define Saturn's eddy diffusion coefficient profile, and to identify important chemical schemes that control the abundances of the observable hydrocarbons in Saturn's upper atmosphere. From the ISO observations, we determine that the column 12 densities of CH3, CH3C2H, and C4H2 above 10 mbar are 4 (sup +2) (sub -1.5) x 10 (exp 13) cm (sup -2), (1.1 plus or minus 0.3) x 10 (exp 15) cm (exp -2), and (1.2 plus or minus 0.3) x 10 (exp 14) cm (sup -2), respectively. The observed ISO emission features also indicate C2H2 mixing ratios of 1.2 (sup +0.9) (sub -0.6) x 10 (exp -6) at 0.3 mbar and (2.7 plus or minus 0.8) x 10 (exp -7) at 1.4 mbar, and a C2H6 mixing ratio of (9 plus or minus 2.5) x 10 (exp -6) at 0.5 mbar. Upper limits are provided for C2H4, CH2CCH2, C3H8, and C6H2 sensitivity of the model results to variations in the eddy diffusion coefficient profile, the solar flux, the CH4 photolysis branching ratios, the atomic hydrogen influx, and key reaction rates are discussed in detail. We find that C4H2 and CH3C2H are particularly good tracers of important chemical processes and physical conditions in Saturn's upper atmosphere, and C2H6 is a good tracer of the eddy diffusion coefficient in Saturn's lower stratosphere. The eddy diffusion coefficient must be smaller than approximately 3 x 10 (exp 4) sq cm s (sup -1) at pressures greater than 1 mbar in order to reproduce the C2H6 abundance inferred from ISO observations. The eddy diffusion coefficients in the upper stratosphere could be constrained by observations of CH3 radicals if the low-temperature chemistry of CH3 were better understood. We also discuss the implications of our modeling for aerosol formation in Saturn's lower stratosphere-diacetylene, butane, and water condense between approximately 1 and 300 mbar in our model and will dominate stratospheric haze formation at nonauroral latitudes. Our photochemical models will be useful for planning observational sequences and for analyzing data from the upcoming Cassini mission.

Moses, Julianne I.↗
NASA NTRS2003

Rate Constant for the Reaction CH3 + CH3 Yields C2H6 at T = 155 K and Model Calculation of the CH3 Abundance in the Atmospheres of Saturn and Neptune

The column abundances of CH3 observed by the Infrared Space Observatory (ISO) satellite on Saturn and Neptune were lower than predicted by atmospheric photochemical models, especially for Saturn. It has been suggested that the models underestimated the loss of CH3 due to poor knowledge of the rate constant k of the CH3 + CH3 self-reaction at the low temperatures and pressures of these atmospheres. Motivated by this suggestion, we undertook a combined experimental and photochemical modeling study of the CH3 + CH3 reaction and its role in determining planetary CH3 abundances. In a discharge flow-mass spectrometer system, k was measured at T = 155 K and three pressures of He. The results in units of cu cm/molecule/s are k(0.6 Torr) = 6.82 x 10(exp -11), k(1.0 Torr) = 6.98 x 10(exp -11), and k(1.5 Torr) = 6.91 x 10(exp -11). Analytical expressions for k were derived that (1) are consistent with the present laboratory data at T = 155 K, our previous data at T = 202 K and 298 K, and those of other studies in He at T = 296-298 K and (2) have some theoretical basis to provide justification for extrapolation. The derived analytical expressions were then used in atmospheric photochemical models for both Saturn and Neptune. These model results reduced the disparity with observations of Saturn, but not with observations of Neptune. However, the disparity for Neptune is much smaller. The solution to the remaining excess CH3 prediction in the models relative to the ISO observations lies, to a large extent, elsewhere in the CH3 photochemistry or transport, not in the CH3 + CH3 rate.

Cody, Regina J.↗
NASA NTRS1980

Vertical structure of the ionosphere and upper neutral atmosphere of Saturn from the Pioneer radio occultation

Radio occultation measurements at S band (2.293 GHz) of the ionosphere and upper neutral atmosphere of Saturn were obtained during the flyby of the Pioneer 11 Saturn spacecraft in September 1979. Preliminary analysis of the occultation exit data taken at a latitude of 9.5 deg S and a solar zenith angle of 90.6 deg, revealed the presence of a rather thin ionosphere. It contained a main peak electron density of about 9.4 times 10 to the third/ccm at an altitude of about 2800 above the level of a neutral number density of 10 to the 19th/ccm and a lower peak of about 7000/ccm at 2200 km. Data in the neutral atmosphere were obtained to a pressure level of 120 millibars.

Kliore, A. J.↗
NASA NTRS2005

The Atmospheres of Saturn and Titan in the Near-Infrared: First Results of Cassini/VIMS

The wide spectral coverage and extensive spatial, temporal, and phase-angle mapping capabilities of the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini-Huygens Orbiter are producing fundamental new insights into the nature of the atmospheres of Saturn and Titan. For both bodies, VIMS maps over time and solar phase angles provide information for a multitude of atmospheric constituents and aerosol layers, providing new insights into atmospheric structure and dynamical and chemical processes. For Saturn, salient early results include evidence for phosphine depletion in relatively dark and less cloudy belts at temperate and mid-latitudes compared to the relatively bright and cloudier Equatorial Region, consistent with traditional theories of belts being regions of relative downwelling. Additional Saturn results include (1) the mapping of enhanced trace gas absorptions at the south pole, and (2) the first high phase-angle, high-spatial-resolution imagery of CH4 fluorescence. An additional fundamental new result is the first nighttime near-infrared mapping of Saturn, clearly showing discrete meteorological features relatively deep in the atmosphere beneath the planet's sunlit haze and cloud layers, thus revealing a new dynamical regime at depth where vertical dynamics is relatively more important than zonal dynamics in determining cloud morphology. Zonal wind measurements at deeper levels than previously available are achieved by tracking these features over multiple days, thereby providing measurements of zonal wind shears within Saturn's troposphere when compared to cloudtop movements measured in reflected sunlight. For Titan, initial results include (1) the first detection and mapping of thermal emission spectra of CO, CO2, and CH3D on Titan's nightside limb, (2) the mapping of CH4 fluorescence over the dayside bright limb, extending to approximately 750 km altitude, (3) wind measurements of approximately 0.5 ms(exp -1), favoring prograde, from the movement of a persistent (multiple months) south polar cloud near 88 deg S latitude, and (4) the imaging of two transient mid-southern-latitude cloud features.

Cassini Mission↗
NASA NTRS1990

Vibrationally excited H2 in the upper atmosphere of Saturn

The impact of resonance fluorescense of solar EUV radiation by H2 on the distribution of the vibrational levels of H2 in the upper atmosphere of Saturn is considered. It appears that, for vibration levels, v not smaller than 3, this is the most important source, more important than those due to photoelectron induced fluorescence, recombination of molecular ions such as H3(+), and vibrational excitation of H2 by photoelectron impact. Based on the Voyager limb observations of H2 band emission, it is estimated that some of the higher vibrational levels may have effective temperatures about 3500 K. Such high vibrational densities may have an impact on ionospheric densities.

Majeed, Tariq↗
NASA NTRS1973

Saturn Uranus atmospheric entry probe mission spacecraft system definition study

The modifications required of the Pioneer F/G spacecraft design for it to deliver an atmospheric entry probe to the planets Saturn and Uranus are investigated. It is concluded that it is feasible to conduct such a mission within the constraints and interfaces defined. The spacecraft required to perform the mission is derived from the Pioneer F/G design, and the modifications required are generally routinely conceived and executed. The entry probe is necessarily a new design, although it draws on the technology of past, present, and imminent programs of planetary atmospheric investigations.

Source record↗
NASA NTRS1980

Structure of the ionosphere and atmosphere of Saturn from Pioneer 11 Saturn radio occultation

The paper deals with radio occultation measurements of Saturn's ionosphere and upper neutral atmosphere, made by Pioneer 11 near the terminator at latitudes of 9.7 deg south and 11.6 deg south. The principal electron density peak (of about 11,400 cu cm), in the ionosphere occurred at an altitude of about 1800 km, with a sharp lower peak of about 9000 cu cm at 1200 km. The scale height above the main peak corresponds to an exosphere temperature of about 1150 K for an H(+) ionosphere. Ionization appears to extend to 30,000 km. The low density of the lower portion of the ionosphere may be explained by ring shadowing and equatorial anomaly. In the neutral atmosphere, measurements were made to a pressure level of about 180 mbar, showing a temperature inversion region with a triple minimum.

Kliore, A. J.↗
NASA NTRS1980

Saturn's atmospheric temperature structure and heat budget

The effective temperature of Saturn from 30 deg S to 10 deg N is 96.5 + or - 2.5 K. This value is 1.9 K higher than a preliminary estimate (Ingersoll et al., 1980). The atmospheric mole fraction of H2 + He is 90 + or - 3%. This value is derived by comparing infrared and radio occultation data (Kliore et al., 1980) for the same latitude. The high value of the effective temperature suggests that Saturn has an additional energy source besides cooling and contraction. The high mole fraction of H2 suggests that separation of heavier He toward the core may be supplying the additional energy. Atmospheric temperatures in the 60- to 600-mbar range are 2.5 K lower within 7 deg of the equator than at higher latitudes. An almost isothermal layer exists between 60 and 160 mbar at all latitudes.

Orton, G. S.↗
NASA NTRS2000

Photochemistry Saturn's Atmosphere: Effects of an Influx of External Oxygen - 2

We use a one-dimensional diurnally averaged model of photochemistry and diffusion in Saturn's stratosphere to investigate the influence of extraplanetary debris on atmospheric chemistry. In particular, we consider the effects of an influx of oxygen from micrometeoroid ablation or from ring-particle diffusion; the contribution from cometary impacts, satellite debris, or ring vapor is deemed to be less important. The photochemical model results are compared directly with Infrared Space Observatory (ISO) observations to constrain the influx of extraplanetary oxygen to Saturn. From the ISO observations, we determine that the column densities of CO2 and H2O above 10 mbar in Saturn's atmosphere are (6.3 +/- 1) x 10(exp 14) and (1.4 +/- 0.4) x 10(exp 15)/ square cm, respectively; our models indicate that a globally averaged oxygen influx of (4+/-2) x 10(exp 6) O atoms /sq cm/s is required to explain these observations. Models with a locally enhanced influx of H20 operating over a small fraction of the projected area do not provide as good a fit to the ISO H2O observations. If volatile oxygen compounds comprise one-third to one-half of the exogenic source by mass, then Saturn is currently being bombarded with (3 +/- 2) x 10(exp -16) g/square cm/s of extraplanetary material. To reproduce the observed CO2/H2O ratio in Saturn's stratosphere, some of the exogenic oxygen must arrive in the form of a carbon-oxygen bonded species such as CO or CO2. An influx consistent with the composition of cometary ices fails to reproduce the high observed CO2/H2O ratio, suggesting that (i) the material has ices that are slightly more carbon-rich than is typical for comets, (ii) a contribution from an organic-rich component is required, or (iii) some of the hydrogen-oxygen bonded material is converted to carbon-oxygen bonded material without photochemistry (e.g., during the ablation process). We have also reanalyzed the 5-micron CO observations of Noll and Larson and determine that the CO lines are most sensitive to the 100- to 400-mbar column density for which we derive a range of (0.7-1.5) x 10(exp 17)/square cm; the CO observations do not allow us to distinguish between an external or internal source of CO on Saturn. If we assume that all the extraplanetary oxygen derives from a micrometeoroid source, then the unfocused dust flux at 9.5 AU must be (i) (1 +/- 0.7) x 10(exp -16) g/square cm/s if interstellar grains are the source of the external oxygen on Saturn, (ii) (4 +/- 3) x 10 (exp -17) g/ sq. cm./s if IDPs on randomly inclined, highly eccentric orbits (e.g., Halley-type comet grains) are the source of the external oxygen, or (iii) (2+/- 1.4) x 10(exp -18)/g/sq cm/s if IDPs on low inclination, low eccentricity orbits (e.g., Kuiper-belt grains) are the source of the external oxygen. These estimates can be used in combination with future Cassini dust detection data to determine the ultimate source of the dust at Saturn's distance from the Sun.

Moses, Julianne I.↗
NASA NTRS1981

Measurement of stratospheric aerosol on Saturn using an eclipse of Titan

Measurements of the aerosol content in the Saturn atmosphere made during an eclipse of Titan by Saturn are presented. Observations of the ingress of Titan into the shadow of Saturn on December 20.08, 1979 were made by the 74-in telescope at Kottamia Station in Egypt at an effective wavelength of 6728 A with FWHM of 1000 A. The deviation of the observed light curve after a satellite darkening of 3 mag from that predicted for a clear Saturn atmosphere is interpreted in terms of an aerosol layer decreasing in extinction coefficient from a base altitude 5 km below the planetary tropopause to an altitude of up to 75 km above the tropopause. For an aerosal layer extending to 75 km above the tropopause calculations reveal possible optical depths ranging from 0.020 to 0.050. The range of the optical depth is comparable to that of the Jupiter atmosphere, and suggests that similar processes may be responsible for the stratospheric haze on both planets.

Smith, D. W.↗
NASA NTRS1983

Saturn's upper atmosphere from the Voyager 2 EUV solar and stellar occultations

The temperature and composition of the upper atmosphere of Saturn have been inferred from Voyager 2 ultraviolet-spectrometer-occultation measurements made by observing the sun and the star Delta Scorpii while they were being occulted by Saturn. The observations analyzed here provide atmospheric parameters from 2900 km down to 960 km above the 1-bar level referred to the equator. The temperature in the model simulation of the data is 420 + or - 30 K down to about 1600 km. Below 1600 km the temperature decreases with a variable lapse rate down to 120 + or - 30 K near the methane homopause located at 1010 + or - 40 km. A constant temperature at 120 K is applied in the model for the region of the methane homopause down to 960 km where the present analysis terminates. Column amounts of H2 and H were measured from 2900 km down to about 1100 km, giving respective densities of about 1.0 x 10 to the 8th/cu cm and about 5.5 x 10 to the 6th/cu cm near the exobase at 2500 km. Near the methane homopause the H2 density is = 1.2 x 10 to the 12th/cu cm with a CH4 number-density mixing ratio of 0.00006. The eddy-diffusion coefficient in the vicinity of the methane homopause is estimated to be 5.0 x 10 to the 6th sq cm/sec. The atomic hydrogen density profile suggests a downward H flux of 1.8 x 10 to the 9th sq cm/sec from near the exobase down to a terminal boundary of about 1200 km.

Smith, G. R.↗