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1.
Using a method defined in a previous paper [M. Combes and T. Encrenaz, Icarus39 1–27 (1979)], we reestimated the C/H ratio in the atmospheres of Jupiter and Saturn by the measurements of the weak visible CH4 bands, the CH4 3ν3 band, and the (3-0) and (4-0) quadrupole bands of H2. In the case of Jupiter we conclude that the C/H ratio is enriched by a factor ranging from 1.7 to 3.6 relative to the solar value. In the case of Saturn, our derived C/H value ranges from 1.2 to 3.2 times the solar value. The Jovian D/H ratio derived from this study is 1.2 × 10?5 < D/H < 3.1 × 10?5. The value derived for the D/H ratio on Saturn is not precise enough to be conclusive. 相似文献
2.
《Planetary and Space Science》1999,47(10-11):1201-1210
New models of Jupiter are based on observational data provided by the Galileo spaceprobe, which considerably improved previously existing estimates of the helium abundance in the atmosphere of Jupiter. These data yield for Jupiter’s atmosphere 20% of the solar oxygen abundance and do not agree with the results of the analysis of the collision of comet Shoemaker-Levy 9 with Jupiter (10 times the solar value). Therefore, both the models of Jupiter with water-depleted and water-enriched atmosphere are considered. By analogy with Jupiter, trial models of Saturn with a water-depleted external envelope are also developed. The molecular-metallic phase transition pressure of hydrogen Pm was taken to be 1.5, 2 and 3 Mbar. Since Saturn’s internal molecular envelope is noticeably enriched in the IR-component (its weight concentration, 0.25–0.30, being by a factor of 3–4 higher than in Jupiter), the phase transition pressure in Saturn can be lower than in Jupiter. In the constructed models, the IR-core masses are 3–3.5 M⊕ for Jupiter and 3–5.5 M⊕ for Saturn. Jupiter’s and Saturn’s IR-cores can be considered embryos onto which the accretion of the gas occurred during the formation of the planets. The mass of the hydrogen–helium component dispersed in the zone of planetary formation constitutes ≈2–5 planetary masses for Jupiter and ≈11–14 planetary masses for Saturn. 相似文献
3.
Spectral observations of Saturn from the far infrared spectrometer aboard the Cassini spacecraft [Flasar, F.M., et al., 2005. Temperatures, winds, and composition in the Saturnian system. Science 307, 1247-1251] have revealed that the C/H ratio in the planet is in fact about twice higher than previously derived from ground based observations and in agreement with the C/H value derived from Voyager IRIS by Courtin et al. [1984. The composition of Saturn's atmosphere at northern temperate latitudes from Voyager IRIS spectra - NH3, PH3, C2H2, C2H6, CH3D, CH4, and the Saturnian D/H isotopic ratio. Astrophys. J. 287, 899-916]. The implications of this measurement are reanalyzed in the present report on the basis that volatiles observed in cometary atmospheres, namely CO2, CH4, NH3 and H2S may have been trapped as solids in the feeding zone of the planet. CH4 and H2S may have been in the form of clathrate hydrates while CO2 presumably condensed in the cooling solar nebula. Carbon may also have been incorporated in organics. Conditions of temperature and pressure ease the hydratation of NH3. Such icy grains were included in planetesimals which subsequently collapsed into the hydrogen envelope of the planet, then resulting in C, N and S enrichments with respect to the solar abundance. Our calculations are consistent, within error bars, with observed elemental abundances on Saturn provided that the carbon trapped in planetesimals was mainly in the form of CH4 clathrate and CO2 ice (and maybe as organics) while nitrogen was in the form of NH3 hydrate. Our approach has implications on the possible pattern of noble gases in Saturn, since we predict that contrary to what is observed in Jupiter, Ar and Kr should be in solar abundance while Xe might be strongly oversolar. The only way to verify this scenario is to send a probe making in situ mass spectrometer measurements. Our scenario also predicts that the 14N/15N ratio should be somewhat smaller in Saturn than measured in Jupiter by Galileo. 相似文献
4.
From an analysis of the Galileo Near Infrared Imaging Spectrometer (NIMS) data, Baines et al. (Icarus 159 (2002) 74) have reported that spectrally identifiable ammonia clouds (SIACs) cover less than 1% of Jupiter. Localized ammonia clouds have been identified also in the Cassini Composite Infrared Spectrometer (CIRS) observations (Planet. Space Sci. 52 (2004a) 385). Yet, ground-based, satellite and spacecraft observations show that clouds exist everywhere on Jupiter. Thermochemical models also predict that Jupiter must be covered with clouds, with the top layer made up of ammonia ice. For a solar composition atmosphere, models predict the base of the ammonia clouds to be at 720 mb, at 1000 mb if N/H were 4×solar, and at 0.5 bar for depleted ammonia of 10−2×solar (Planet. Space Sci. 47 (1999) 1243). Thus, the above NIMS and CIRS findings are seemingly at odds with other observations and cloud physics models. We suggest that the clouds of ammonia ice are ubiquitous on Jupiter, but that spectral identification of all but the freshest of the ammonia clouds and high altitude ammonia haze is inhibited by a combination of (i) dusting, starting with hydrocarbon haze particles falling from Jupiter's stratosphere and combining with an even much larger source—the hydrazine haze; (ii) cloud properties, including ammonia aerosol particle size effects. In this paper, we investigate the role of photochemical haze and find that a substantial amount of haze material can deposit on the upper cloud layer of Jupiter, possibly enough to mask its spectral signature. The stratospheric haze particles result from condensation of polycyclic aromatic hydrocarbons (PAHs), whereas hydrazine ice is formed from ammonia photochemistry. We anticipate similar conditions to prevail on Saturn. 相似文献
5.
Infrared spectral observations of Mars, Jupiter, and Saturn were made from 100 to 470 cm?1 using NASA's G. P. Kuiper Airborne Observatory. Taking Mars as a calibration source, we determined brightness temperatures of Jupiter and Saturn with approximately 5 cm?1 resolution. The data are used to determine the internal luminosities of the giant planets, for which more than 75% of the thermally emitted power is estimated to be in the measured bandpass: for Jupiter LJ = (8.0 ± 2.0) × 10?10L⊙ and for Saturn LS = (3.6 ± 0.9) × 10?10. The ratio R of thermally emitted power to solar power absorbed was estimated to be RJ = 1.6 ± 0.2, and RS = 2.7 ± 0.8 from the observations when both planets were near perihelion. The Jupiter spectrum clearly shows the presence of the rotational ammonia transitions which strongly influence the opacity at frequencies ?250 cm?1. Comparison of the data with spectra predicted from current models of Jupiter and Saturn permits inferences regarding the structure of the planetary atmospheres below the temperature inversion. In particular, an opacity source in addition to gaseous hydrogen and ammonia, such as ammonia ice crystals as suggested by Orton, may be necessary to explain the observed Jupiter spectrum in the vicinity of 250 cm?1. 相似文献
6.
《Planetary and Space Science》1999,47(10-11):1183-1200
Interior models of Jupiter and Saturn are calculated and compared in the framework of the three-layer assumption, which rely on the perception that both planets consist of three globally homogeneous regions: a dense core, a metallic hydrogen envelope, and a molecular hydrogen envelope. Within this framework, constraints on the core mass and abundance of heavy elements (i.e. elements other than hydrogen and helium) are given by accounting for uncertainties on the measured gravitational moments, surface temperature, surface helium abundance, and on the inferred protosolar helium abundance, equations of state, temperature profile and solid/differential interior rotation. Results obtained solely from static models matching the measured gravitational fields indicate that the mass of Jupiter’s dense core is less than 14 M⊕ (Earth masses), but that models with no core are possible given the current uncertainties on the hydrogen–helium equation of state. Similarly, Saturn’s core mass is less than 22 M⊕ but no lower limit can be inferred. The total mass of heavy elements (including that in the core) is constrained to lie between 11 and 42 M⊕ in Jupiter, and between 19 and 31 M⊕ in Saturn. The enrichment in heavy elements of their molecular envelopes is 1–6.5, and 0.5–12 times the solar value, respectively. Additional constraints from evolution models accounting for the progressive differentiation of helium (Hubbard WB, Guillot T, Marley MS, Burrows A, Lunine JI, Saumon D, 1999. Comparative evolution of Jupiter and Saturn. Planet. Space Sci. 47, 1175–1182) are used to obtain tighter, albeit less robust, constraints. The resulting core masses are then expected to be in the range 0–10 M⊕, and 6–17 M⊕ for Jupiter and Saturn, respectively. Furthermore, it is shown that Saturn’s atmospheric helium mass mixing ratio, as derived from Voyager, Y=0.06±0.05, is probably too low. Static and evolution models favor a value of Y=0.11−0.25. Using, Y=0.16±0.05, Saturn’s molecular region is found to be enriched in heavy elements by 3.5 to 10 times the solar value, in relatively good agreement with the measured methane abundance. Finally, in all cases, the gravitational moment J6 of models matching all the constraints are found to lie between 0.35 and 0.38×10−4 for Jupiter, and between 0.90 and 0.98×10−4 for Saturn, assuming solid rotation. For comparison, the uncertainties on the measured J6 are about 10 times larger. More accurate measurements of J6 (as expected from the Cassini orbiter for Saturn) will therefore permit to test the validity of interior models calculations and the magnitude of differential rotation in the planetary interior. 相似文献
7.
Upper limits are placed on the D/H ratio in the observed portions of the atmospheres of Jupiter and Saturn from observations at high S/N over the region of the 5-0 R(1) line of HD. The upper limits of 4 × 10?5 and 6 × 10?5 D/H on Jupiter and Saturn, respectively, are not inconsistent with present models for abundance ratios in the primitive solar nebula or with other estimates of this quantity from observations. 相似文献
8.
New measurements of the low-temperature near-infrared absorption of methane (Sihra, 1998, Laboratory measurements of near-infrared methane bands for remote sensing of the jovian atmosphere, Ph.D. thesis, University of Oxford) have been combined with existing, longer path-length, higher-temperature data of Strong et al. (1993, Spectral parameters of self- and hydrogen-broadened methane from 2000 to 9500 cm−1 for remote sounding of the atmosphere of Jupiter, J. Quant. Spectrosc. Radiat. Trans. 50, 309-325) and fitted with band models. The combined data set is found to be more consistent with previous low-temperature methane absorption measurements than that of Strong et al. (1993, J. Quant. Spectrosc. Radiat. Trans. 50, 309-325) but covers the same wider wavelength range and accounts for both self- and hydrogen-broadening conditions. These data have been fitted with k-coefficients in the manner described by Irwin et al. (1996, Calculated k-distribution coefficients for hydrogen- and self-broadened methane in the range 2000-9500 cm−1 from exponential sum fitting to band modelled spectra, J. Geophys. Res. 101, 26,137-26,154) and have been used in multiple-scattering radiative transfer models to assess their impact on our previous estimates of the jovian cloud structure obtained from Galileo Near-Infrared Mapping Spectrometer (NIMS) observations (Irwin et al., 1998, Cloud structure and atmospheric composition of Jupiter retrieved from Galileo NIMS real-time spectra, J. Geophys. Res. 103, 23,001-23,021; Irwin et al., 2001, The origin of belt/zone contrasts in the atmosphere of Jupiter and their correlation with 5-μm opacity, Icarus 149, 397-415; Irwin and Dyudina, 2002, The retrieval of cloud structure maps in the equatorial region of Jupiter using a principal component analysis of Galileo/NIMS data, Icarus 156, 52-63). Although significant differences in methane opacity are found at cooler temperatures, the difference in the optical depth of the atmosphere due to methane is found to diminish rapidly with increasing pressure and temperature and thus has negligible effect on the cloud structure inferred at deeper levels. Hence the main cloud opacity variation is still found to peak at around 1-2 bar using our previous analytical approach, and is thus still in disagreement with Galileo Solid State Imager (SSI) determinations (Banfield et al., 1998, Jupiter's cloud structure from Galileo imaging data, Icarus 135, 230-250; Simon-Miller et al., 2001, Color and the vertical structure in Jupiter's belts, zones and weather systems, Icarus 154, 459-474) which place the main cloud deck near 0.9 bar. Further analysis of our retrievals reveals that this discrepancy is probably due to the different assumptions of the two analyses. Our retrievals use a smooth vertically extended cloud profile while the SSI determinations assume a thin NH3 cloud below an extended haze. When the main opacity in our model is similarly assumed to be due to a thin cloud below an extended haze, we find the main level of cloud opacity variation to be near the 1 bar level—close to that determined by SSI and moderately close to the expected condensation level of ammonia ice of 0.85 bar, assuming that the abundance of ammonia on Jupiter is (7±1)×10−4 (Folkner et al., 1998, Ammonia abundance in Jupiter's atmosphere derived from the attenuation of the Galileo probe's radio signal, J. Geophys. Res. 103, 22,847-22,855; Atreya et al., 1999, A comparison of the atmospheres of Jupiter and Saturn: deep atmospheric composition, cloud structure, vertical mixing, and origin, Planet. Space Sci. 47, 1243-1262). However our data in the 1-2.5 μm range have good height discrimination and our lowest estimate of the cloud base pressure of 1 bar is still too great to be consistent with the most recent estimates of the ammonia abundance of 3.5 × solar. Furthermore the observed limited spatial distribution of ammonia ice absorption features on Jupiter suggests that pure ammonia ice is only present in regions of localised vigorous uplift (Baines et al., 2002, Fresh ammonia ice clouds in Jupiter: spectroscopic identification, spatial distribution, and dynamical implications, Icarus 159, 74-94) and is subsequently rapidly modified in some way which masks its pure absorption features. Hence we conclude that the main cloud deck on Jupiter is unlikely to be composed of pure ammonia ice and instead find that it must be composed of either NH4SH or some other unknown combination of ammonia, water, and hydrogen sulphide and exists at pressures of between 1 and 2 bar. 相似文献
9.
We have obtained 5-μm brightness temperatures and brightness temperature upper limits for Uranus and Neptune which are substantially lower than those of Jupiter and Saturn and which correspond to a geometric albedo of approximately 0.01, in agreement with results reported by F. C. Gillet and G. H. Rieke (1977, Astrophys. J.218, L141–L144). Phospine and CH3D, which are observed at 5 μm on Jupiter and Saturn, are discussed as possible sources of opacity at 5 μm in the atmospheres of Uranus and Neptune. 相似文献
10.
Moderate-resolution spectrophotometry (Δλ/λ～0.015) has shown the effects of known atmospheric constituents (NH3, CH4, C2H6) on the 5–8 μm spectrum of Jupiter. Broadband observations of Saturn at 6.5 μm are also reported. 相似文献
11.
T. Encrenaz 《Earth, Moon, and Planets》1994,67(1-3):77-87
For a long time it was believed that the atmospheres of the giant planets, dominated by molecular hydrogen and helium, were similar in composition to the primordial nebula from which they formed. However, this image has strongly evolved over the past twenty years, due to new developments of ground-based infrared spectroscopy, coupled with the success of the Voyager space mission.Significant differences were measured in the abundances of helium, deuterium and carbon of the four giant planets. The variations in the C/H and D/H ratios have given support to the "nucleation" formation scenario, in which the four giant planets first accreted a nucleus of about ten terrestrial masses, big enough to bind gravitationally the surrounding gaseous nebula; the helium depletion in Saturn has been interpreted as a differentiation effect in Saturn's interior; the apparent helium excess in Neptune, coupled with the recent unexpected detection of CO and HCN in this planet, might imply the presence of molecular nitrogen. In the case of Jupiter and Saturn, disequilibrium species have been detected (CO, PH3, GeH4, AsH3), which are tracers of vertical dynamical motions.In the future, significant progress in our knowledge of the Jovian composition, including the noble gases, should be obtained with the mass spectrometer of the Galileo probe. The ISO mission is expected to provide new far-infrared spectroscopic data which should lead to the detection of new minor species and a better determination of the D/H ratio. 相似文献
12.
T.B. McCord A. Coradini F. Capaccioni G. Filacchione P. Cerroni K.H. Baines J.-P. Bibring E. Bussoletti D.P. Cruikshank V. Formisano Y. Langevin R.M. Nelson B. Sicardy 《Icarus》2004,172(1):104-126
The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of <90°, resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible 13C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data. 相似文献
13.
Allen S. Grossman James B. Pollack Ray T. Reynolds Audrey L. Summers Harold C. Graboske 《Icarus》1980,42(3):358-379
We have calculated evolutionary and static models of Jupiter and Saturn with homogeneous solar composition mantles and dense cores of material consisting of solar abundances of SiO2, MgO, Fe, and Ni. Evolutionary sequences for Jupiter were calculated with cores of mass 2, 4, 6, and 8% of the Jovian mass. Evolutionary sequences for Saturn were calculated with cores of mass 16, 18, 20, and 22% of total mass. Two envelope mixtures, representative of the solar abundances were used: X (mass fraction of hydrogen) = 0.74, Y (mass fraction of helium) = 0.24 and X = 0.77 and Y = 0.21. For Jupiter, the observations of the temperature at 1 bar pressure (T1bar), radius and internal luminosity were best fit by evolutionary models with a core mass of ～6.5% and chemical composition of X = 0.77, Y = 0.21. The calculated cooling time for Jupiter is approximately 4.9 × 109 years, which is consistent, within our error bars, with the known age of the solar system. For Saturn, the observations of the radius, internal luminosity and T1BAR can be best fit by evolutionary models with a core mass of ～21% and chemical composition of X = 0.77, Y = 0.21. The cooling time calculated for Saturn is approximately 2.6 × 109 years, almost a factor 2 less than the present age of the solar system. Static models of Jupiter and Saturn were calculated for the above chemical compositions in order to investigate the sensitivity of the calculated gravitational moments, J2 and J4, to the mass of the dense core, T1BAR and hydrogen/helium ratio. We find for Jupiter that a model having a core mass of approximately 7% gives values of J2, J4, and T1BAR that are within observational limits, for the mixture X = 0.77, Y = 0.21. The static Jupiter models are completely consistent with the evolutionary results. For Saturn, the quantities J2, J4, and J6 determined from the static models with the most probable T1BAR of 140°K, using modeling procedures which result in consistent models for Jupiter, are considerably below the observed values. 相似文献
14.
We present an analysis of observations of the auroral/polar regions of Saturn, carried out in 1999, 2004 and 2005, making use of the facility spectrometer, CGS4, on the United Kingdom Infrared Telescope (UKIRT), Mauna Kea, Hawaii. We obtain temperatures of 380(±70) K in 1999 and 420(±70) K in 2004. (The 2005 data has insufficient spectral resolution for a temperature determination to be made.) Our most probable interpretation is that the temperature of Saturn's auroral/polar H+3 layer should be taken as 400(±50) K. This is lower than the value obtained by Miller et al. [Miller, S., and 10 colleagues, 2000. Philos. Trans. R. Soc. 358, 2485-2502], which is shown to be in error. Our analysis reveals clearly that the line emission due to H+3 varies considerably, showing nearly an order of magnitude increase when one compares the data obtained in 1999 with those of 2004. Our conclusion is that this variability is (mainly) due to the changing H+3 column density. By analogy with modelling results obtained for Jupiter, we estimate that the particle (keV electron) precipitation experienced by Saturn must be ∼20 times greater in 2004 than in 1999, to produce this additional ionisation. The H+3 emission increases, but this is insufficient to offset most of the heating due to the extra particle precipitation, indicating that this ion does not act as a “thermostat” on Saturn, in the same way that it does on Jupiter. 相似文献
15.
16.
We report observation and analysis of a high-resolution 2.87-3.54 μm spectrum of the southern temperate region of Saturn obtained with NIRSPEC at Keck II. The spectrum reveals absorption and emission lines of five molecular species as well as spectral features of haze particles. The ν2+ν3 band of CH3D is detected in absorption between 2.87 and 2.92 μm; and we derived from it a mixing ratio approximately consistent with the Infrared Space Observatory result. The ν3 band of C2H2 also is detected in absorption between 2.95 and 3.05 μm; analysis indicates a sudden drop in the C2H2 mixing ratio at 15 mbar (130 km above the 1 bar level), probably due to condensation in the low stratosphere. The presence of the ν3+ν9+ν11 band of C2H6 near 3.07 μm, first reported by Bjoraker et al. [Bjoraker, G.L., Larson, H.P., Fink, U., 1981. Astrophys. J. 248, 856-862], is confirmed, and a C2H6 condensation altitude of 10 mbar (140 km) in the low stratosphere is determined. We assign weak emission lines within the 3.3 μm band of CH4 to the ν7 band of C2H6, and derive a mixing ratio of 9±4×10−6 for this species. Most of the C2H6 3.3 μm line emission arises in the altitude range 460-620 km (at ∼μbar pressure levels), much higher than the 160-370 km range where the 12 μm thermal molecular line emission of this species arises. At 2.87-2.90 μm the major absorber is tropospheric PH3. The cloud level determined here and at 3.22-3.54 is 390-460 mbar (∼30 km), somewhat higher than found by Kim and Geballe [Kim, S.J., Geballe, T.R., 2005. Icarus 179, 449-458] from analysis of a low resolution spectrum. A broad absorption feature at 2.96 μm, which might be due to NH3 ice particles in saturnian clouds, is also present. The effect of a haze layer at about 125 km (∼12 mbar level) on the 3.20-3.54 μm spectrum, which was not apparent in the low resolution spectrum, is clearly evident in the high resolution data, and the spectral properties of the haze particles suggest that they are composed of hydrocarbons. 相似文献
17.
E. LellouchB. Bézard J.I. MosesG.R. Davis P. DrossartH. Feuchtgruber E.A. BerginR. Moreno T. Encrenaz 《Icarus》2002,159(1):112-131
Observations of H2O rotational lines from the Infrared Space Observatory (ISO) and the Submillimeter Wave Astronomy Satellite (SWAS) and of the CO2 ν2 band by ISO are analyzed jointly to determine the origin of water vapor and carbon dioxide in Jupiter's stratosphere. Simultaneous modelling of ISO/LWS and ISO/SWS observations acquired in 1997 indicates that most of the stratospheric jovian water is restricted to pressures less than 0.5±0.2 mbar, with a disk-averaged column density of (2.0±0.5)×1015 cm−2. Disk-resolved observations of CO2 by ISO/SWS reveal latitudinal variations of the CO2 abundance, with a decrease of at least a factor of 7 from mid-southern to mid-northern latitudes, and a disk-center column density of (3.4±0.7)×1014 cm−2. These results strongly suggest that the observed H2O and CO2 primarily result from the production, at midsouthern latitudes, of oxygenated material in the form of CO and H2O by the Shoemaker-Levy 9 (SL9) impacts in July 1994 and subsequent chemical and transport evolution, rather than from a permanent interplanetary dust particle or satellite source. This conclusion is supported by quantitative evolution model calculations. Given the characteristic vertical mixing times in Jupiter's stratosphere, material deposited at ∼0.1 mbar by the SL9 impacts is indeed expected to diffuse down to the ∼0.5 mbar level after 3 years. A coupled chemical-horizontal transport model indicates that the stability of water vapor against photolysis and conversion to CO2 is maintained over typically ∼50 years by the decrease of the local CO mixing ratio associated with horizontal spreading. A model with an initial (i.e., SL9-produced) H2O/CO mass mixing ratio of 0.07, not inconsistent with immediate post-impact observations, matches the observed H2O abunda nce and CO2 horizontal distribution 3 years after the impacts. In contrast, the production of CO2 from SL9-produced CO and a water component deriving from an interplanetary dust component is insufficient to account for the observed CO2 amounts. The observations can further be used to place a stringent upper limit (8×104 cm−2 s−1) on the permanent water influx into Jupiter. This may indicate that the much larger flux observed at Saturn derives dominantly from a ring source, or that the ablation of micrometeoroids leads dominantly to different species at Saturn (H2O) and Jupiter (CO). Finally, the SWAS H2O spectra do not appear fully consistent with the ISO data and should be confirmed by future ODIN and Herschel observations. 相似文献
18.
The spectral window of Jupiter at 3 μm is analyzed and compared with previously published spectra. The two components of the spectrum, the thermal and the solar reflected contributions, are calculated at low resolution (30 cm?1) between 3300 and 3800 cm?1 for preparing the interpretation of the Galileo Near Infrared Mapping Spectrometer experiment. The calculations yield to the following conclusions: (1) NH3 is the main absorber between 3300 and 3600 cm?1 for both the thermal spectrum and the solar reflected spectrum; H2O appears only in the thermal component above 3600 cm?1. (2) The thermal component can be seen only on the dark side of Jupiter; the atmosphere is sounded down to temperature levels of about 210°K. (3) The solar reflected component can be modelized by a reflecting layer between 135 and 140°K with an albedo of 0.3; high spatial resolution maps of Jupiter at 3 μm should give access to the NH3 spatial distribution on Jupiter. 相似文献
19.
Cassini's Imaging Science Subsystem (ISS) instrument took nearly 1200 images of the Jupiter ring system during the spacecraft's 6-month encounter with Jupiter (Porco et al., 2003, Science 299, 1541-1547). These observations constitute the most complete data set of the ring taken by a single instrument, both in phase angle (0.5°-120° at seven angles) and wavelength (0.45-0.93 μm through eight filters). The main ring was detected in all targeted exposures; the halo and gossamer rings were too faint to be detected above the planet's stray light. The optical depth and radial profile of the main ring are consistent with previous observations. No broad asymmetries within the ring were seen; we did identify possible hints of 1000 km-scale azimuthal clumps within the ring. Cassini observations taken within 0.02° of the ring plane place an upper limit on the ring's full thickness of 80 km at a phase angle of 64°. We have combined the Cassini ISS and VIMS (Visible and Infrared Mapping Spectrometer) observations with those from Voyager, HST (Hubble Space Telescope), Keck, Galileo, Palomar, and IRTF (Infrared Telescope Facility). We have fit the entire suite of data using a photometric model that includes microscopic silicate dust grains as well as larger, long-lived ‘parent bodies’ that engender this dust. Our best-fit model to all the data indicates an optical depth of small particles of τs=4.7×10−6 and large bodies τl=1.3×10−6. The dust's cross-sectional area peaks near 15 μm. The data are fit significantly better using non-spherical rather than spherical dust grains. The parent bodies themselves must be very red from 0.4-2.5 μm, and may have absorption features near 0.8 and 2.2 μm. 相似文献
20.
The near-infrared (0.65–2.5μm) spectral albedo of Jupiter and Saturn with 1.5% spectral resolution is presented for the center of disk and for the limb. There is a distinct difference in the continuum slope between Jupiter and Saturn which may be attributed to a difference in the dust content or composition of the two atmospheres. There is an indication of limb brightening in the deepest CH4 bands on Saturn. No limb brightening is found for Jupiter. 相似文献