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1.
We present far-infrared observations of Saturn in the wavelength band 76–116 μm, using a balloon-borne 75-cm telescope launched on 10 December 1980 from Hyderabad, India, when B′, the Saturnicentric latitude of the Sun, was 4°.3. Normalizing with respect to Jupiter, we find the average brightness temperature of the disk-ring system to be 90 ± 3° K. Correcting for the contribution from rings using experimental information on the brightness temperature of rings at 20 μm, we find TD, the brightness temperature of the disk, to be 96.9 ± 3.5° K. The systematic errors and the correction for the ring contribution are small for our observations. We, therefore, make use of our estimate of TD and earlier observations of Saturn when contribution from the rings was large and find that for wavelengths greater than 50 μm, there is a small reduction in the ring brightness temperature as compared to that at 20 μm.  相似文献   

2.
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   

3.
Recent 3-mm observations of Saturn at low ring inclinations are combined with previous observations of E. E. Epstein, M. A. Janssen, J. N. Cuzzi, W. G. Fogarty, and J. Mottmann (Icarus41, 103–118) to determine a much more precise brightness temperature for Saturn's rings. Allowing for uncertainties in the optical depth and uniformity of the A and B rings and for ambiguities due to the C ring, but assuming the ring brightness to remain approximately constant with inclination, a mean brightness temperature for the A and B rings of 17 ± 4°K was determined. The portion of this brightness attributed to ring particle thermal emission is 11 ± 5°K. The disk temperature of Saturn without the rings would be 156 ± 6°K, relative to B. L. Ulich, J. H. Davis, P. J. Rhodes, and J. M. Hollis' (1980, IEEE Trans. Antennas Propag.AP-28, 367–376) absolutely calibrated disk temperature for Jupiter. Assuming that the ring particles are pure water ice, a simple slab emission model leads to an estimate of typical particle sizes of ≈0.3 m. A multiple-scattering model gives a ring particle effective isotropic single-scattering albedo of 0.85 ± 0.05. This albedo has been compared with theoretical Mie calculations of average albedo for various combinations of particle size distribution and refractive indices. If the maximum particle radius (≈5 m) deduced from Voyager bistatic radar observations (E. A. Marouf, G. L. Tyler, H. A. Zebker, V. R. Eshleman, 1983, Icarus54, 189–211) is correct, our results indicate either (a) a particle distribution between 1 cm and several meters radius of the form r?s with 3.3 ? s ? 3.6, or (b) a material absorption coefficient between 3 and 10 times lower than that of pure water ice Ih at 85°K, or both. Merely decreasing the density of the ice Ih particles by increasing their porosity will not produce the observed particle albedo. The low ring brightness temperature allows an upper limit on the ring particle silicate content of ≈10% by mass if the rocky material is uniformly distributed; however, there could be considerably more silicate material if it is segregated from the icy material.  相似文献   

4.
The spectrum of Saturn was measured from 80 to 350 cm?1 (29 to 125 μm) with ≈6-cm?1 resolution using a Michelson interferometer aboard NASA's Kuiper Airborne Observatory. These observations are of the full disk, with little contribution from the rings. For frequencies below 300 cm?1, Saturn's brightness temperature rises slowly, reaching ≈111°K at 100 cm?1. The effective temperature is 96.8 ± 2.5°K, implying that Saturn emits 3.0 ± 0.5 times as much energy as it receives from the Sun. The rotation-inversion manifolds of NH3 that are prominent in the far-infrared spectrum of Jupiter are not observed on Saturn. Our models predict the strengths to be only ≈2 to 5°K in brightness temperature because most of the NH3 is frozen out; this is comparable to the noise in our data. By combining our data with those of an earlier investigation when the Saturnicentric latitude of the Sun was B′ = 21.2°, we obtain the spectrum of the rings. The high-frequency end of the ring spectrum (ν > 230 cm?1) has nearly constant brightness temperature of 85°K. At lower frequencies, the brightness temperature decreases roughly as predicted by a simple absorption model with an optical depth proportional to ν1.5. This behavior could be due to mu-structure on the surface of the ring particles with a scale size of 10 to 100 μm and/or to impurities in their composition.  相似文献   

5.
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6.
G.H. Rieke 《Icarus》1975,26(1):37-44
Infrared observations of Saturn from 5 to 40 μm are described. There is intense limb brightening at 12.35 μm over the southern polar cap. The C ring is anomalously bright at 10 and 20 μm and has bluer (hotter) colours than the A and B rings. The ring spectra have been extrapolated beyond 40 μm and subtracted from low-resolution far-infrared measurements to show that the far-infrared spectrum of the disk of Saturn is qualitatively similar to that of Jupiter and that Saturn radiates 2.5 ± 0.6 times the energy it absorbs from the Sun.  相似文献   

7.
The 17–28 μm brightness temperature of the center of the disk of Jupiter is 136 ± 4 K. Model calculations yield an effective temperature of 142 ± 4 K at the center of the disk for a helium to hydrogen ratio He/H2 of 0. This corresponds to an effective temperature of the entire disk of 136 ± 5 K. The NEB, SEB, and STeB are shown to emit an excess flux at 20 μm when compared to the neighboring zones. The hot belts were grey in color at the time of the observations and were the source of excess 5-μm flux as well (Keay et al. 1973). The relationships between 5-μm and 20-μm flux excesses and the cloud structures are discussed.  相似文献   

8.
We have used 3-mm Saturn observations, obtained from 1965 through 1977 and with Jupiter as a reference, to derive a ring brightness temperature of 18 ± 8°K. Thebrightness temperature of the disk of Saturn is 156 ± 9° K. Part of the ring brightness (≈62K) may be accounted for as disk emission which is scattered from the rings; the remainder (12 ± 8° K we attributed to ring particle thermal emission. Because this thermal component brightness temperatures is so much less than the particle physical temperature, limits are placed on the mean size and composition of the ring particles. In particular, as found by others, the particles cannot be rocky, but must be either metallic or composed of extremely low-loss dielectric material such as water ice. If the particles are pure water ice, for example, then a simple slab model and a multiple-scattering model both give upper limits to the particle sizes of ≈ 1 m, a value three times smaller than previously available. The multiple-scattering model gives a particle single-scattering albedo at 3 mm of 0.83±0.13.  相似文献   

9.
New broadband observations in several passbands between 30 and 500 μm of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus are presented. The best agreement between the data and various thermal models of Mars, Jupiter, and Uranus is obtained with a slightly cooler absolute temperature scale than that previously adopted by Armstrong et al. (1972). The effective temperature of Uranus is 58 ± 2°K, which is in agreement with its solar equilibrium temperature. The existence of an internal energy source of Saturn has been reconfirmed and must lie within the range of 0.9 to 3.2 times the absorbed solar flux. A depression exists in the spectra of Jupiter, Saturn, and Uranus between 80 and 300 μm, which may be a result of NH3 opacity.  相似文献   

10.
From our telescopic observations of Saturn's rings in 1966, 1979, and 1980, the luminance of the unlit face at λ = 0.58 μm is derived as a function of the height B′ of the Sun above the lit face. A maximum is reached at B′ = 1.9° and a decrease is observed for larger values of B′. Ring B is 1.8 time less bright than ring A and Cassini division. The unlit/lit luminances ratios for the two rings merged together is 8% at B′ = 1.0° and 3% at B′ = 2.8°. The larger value at more grazing incidence is related to the photometric “opposition effect” which reflects more of the incident light backward into the ring plane when the height of the sun is small; the light so reflected is again reflected and scattered and a certain flux reaches the unlit face to escape toward the observer. The unlit face luminances for blue and for yellow light indicate a contribution by micron size particles. The Saturn globe produces a ring illumination which, observed from the Earth, amounts to 1.8 × 10?3 of the disk center reflectance. The rings observed exactly edge-on do not disappear but a faint lineament remains, which produces a flux of (0.30 ± 0.15) 10?3 times the brightness of a segment of 1 arcsec width at Saturn disk center; illuminations of rings' borders or particles outside the exact ring plane are indicated.  相似文献   

11.
Dennis B. Ward 《Icarus》1977,32(4):437-442
The spectrum of Saturn and its rings between 45 and 115 μm has been measured at an average resolving power of 14 from the NASA Lear Jet. The combined brightness temperature of the rings and planetary disk decreases beyond 65 μm, in disagreement with previous results. A brightness temperature of 65 ± 10°K is obtained for the planetary disk in the 80–110-μm wavelength range if a large-particle, constant-emissivity model is assumed for the rings. The possible effects of small particles in the rings are briefly considered.  相似文献   

12.
We observed Saturn at far-infrared and submillimeter wavelengths during the Earth's March 1980 passage through the plane of Saturn's rings. Comparison with earlier spectroscopic observations by D. B. Ward [Icarus32, 437–442 (1977)], obtained at a time when the tilt angle of the rings was 21.8°, permits separation of the disk and ring contributions to the flux observed in this wavelength range. We present two main results: (1) The observed emission of the disk between 60 and 180 μm corresponds to a brightness temperature of 104 ± 2°K; (2) the brightness temperature of the rings drops approximately 20°K between 60 and 80 μm. Our data, in conjunction with the data obtained by other observers between 1 μm and 1 mm, permit us to derive an improved estimate for the total Saturnian surface brightness of (4.84 ± 0.32) × 10?4W cm?2 corresponding to an effective temperature of 96.1 ± 1.6°K. The ratio of radiated to incident power, PR/PI, is (1.46 ± 0.08)/(1 - A), where A is the Bond albedo. For A = 0.337 ± 0.029, PR/PI = 2.20 ± 0.15 and Saturn's intrinsic luminosity is LS = (2.9 ± 0.5) × 10?10L⊙.  相似文献   

13.
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   

14.
Precise relative measurements of the disk brightness temperatures of Venus, Mars, Jupiter, and Saturn have been made at a mean wavelength of 1.4 mm. The rings of Saturn contribute significantly to the observed total emission. Other results include a better understanding of the properties of the NRAO 11-m antenna near its high frequency limit and of atmospheric degradation of observations in this wavelength range.  相似文献   

15.
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   

16.
The spectral reflectivity of Saturn's rings between 0.36 and 1.06 μm is derived from observations of the combined light of the Saturn system and the previously determined spectrum of the disk of Saturn. The rings are red relative to the Sun for wavelengths λ? 0.7 μm; at longer wavelengths, the spectral reflectivity declines. The amplitude of the opposition effect (anomalous brightening at very small phase angles) shows a maximum at both ends of our spectral range.  相似文献   

17.
Interferometric observations of Saturn and its rings made at the Owens Valley Radio Observatory at a wavelength of 3.71 cm ar fit to models of the Saturn brightness structure. The models have allowed us to estimate the brightness temperatures and optical thicknesses of the A, B, and C rings as well as the brightness temperature of the planetary disk. The most accurate results are the ratios of the ring temperatures to the planet temperature of 0.030 ± 0.012, 0.050 ± 0.010, and 0.040 ± 0.014 for the A, B, and C rings, respectively. The best estimates of the ring optical thicknesses are τA = 0.2 ± 0.1, τB = 0.9 ± 0.2, and τC = 0.1 ± 0.1. The actual brightness temperatures, which are affected by the absolute calibration errors, are Tplanet = 178 ± 8, TA = 5.2 ± 2.0, TB = 9.1 ± 1.8, and TC = 7.1 ± 2.6°K. The particle single-scattering albedo that would be most consistent with the observations is slightly less than one, but probably greater than 0.95. The observations are consistent with particles which conservatively scatter the thermal emission from Saturn to the Earth and emit no thermal emission of their own. The 3.71-cm optical depths which we have estimated are very close to the visible wavelength optical depths. This similarity indicates that the ring particles must be at least a few centimeters in size, although we feel that the particles may well be much larger than this in view of the closeness of the visible and microwave optical depths. Particles which are nearly conservative scatterers at our wavelength and at least a few centimeters in size must be composed of a material which is either a very good reflector of microwaves or a very poor absorber of them. At this time, water ice seems to be the most likely candidate since it is a very poor absorber of microwaves and has been detected in the rings spectroscopically.  相似文献   

18.
《Planetary and Space Science》1999,47(10-11):1225-1242
Infrared spectra of Jupiter and Saturn have been recorded with the two spectrometers of the Infrared Space Observatory (ISO) in 1995–1998, in the 2.3–180 μm range. Both the grating modes (R=150–2000) and the Fabry-Pérot modes (R=8000–30,000) of the two instruments were used. The main results of these observations are (1) the detection of water vapour in the deep troposphere of Saturn; (2) the detection of new hydrocarbons (CH3C2H, C4H2, C6H6, CH3) in Saturn’s stratosphere; (3) the detection of water vapour and carbon dioxide in the stratospheres of Jupiter and Saturn; (4) a new determination of the D/H ratio from the detection of HD rotational lines. The origin of the external oxygen source on Jupiter and Saturn (also found in the other giant planets and Titan in comparable amounts) may be either interplanetary (micrometeoritic flux) or local (rings and/or satellites). The D/H determination in Jupiter, comparable to Saturn’s result, is in agreement with the recent measurement by the Galileo probe (Mahaffy, P.R., Donahue, T.M., Atreya, S.K., Owen, T.C., Niemann, H.B., 1998. Galileo probe measurements of D/H and 3He/4He in Jupiters atmosphere. Space Science Rev. 84 251–263); the D/H values on Uranus and Neptune are significantly higher, as expected from current models of planetary formation.  相似文献   

19.
Polarization measurements of Jupiter, Saturn, and Saturn's rings from 1 to 3.5 μm are presented. At 1.6 μm on the discs of the two planets, the radially directed limb polarizations observed in the visible undergo, in some cases, a surprising 90° rotation to a tangential direction, particularly on the poles. The only immediate explanation for this effect is double Mie scattering, due to aerosols which must be of the order of a micrometer in size. On Jupiter the patterns are not uniform and are not stable, reflecting variable aerosol concentrations on the two poles. The ring polarization is uniformly negative (E vector parallel to the ecliptic plane) from the visible through 3.5 μm, and is inversely proportional to the albedo. This is as expected from Wolff's model for scattering from rough solid surfaces; but the degree of polarization seems uncommonly high, exceeding 2% at 3.5 μm.  相似文献   

20.
The variation in infrared equilibrium brightness temperature of Saturn's A, B, and C rings is modeled as a function of solar elevation B′ with respect to the ring plane. The basic model includes estimates of minimum and maximum interparticle shadowing in a monolayer approximation. Simple laboratory observations of random particle distributions at various illumination angles provide more realistic shadowing functions. Radiation balance calculations yield the physical (kinetic) temperature of particles in equilibrium with radiation from the Sun, Saturn, and neighboring particles. Infrared brightness temperatures as a function of B′ are then computed and compared to the available 20-μm data (Pioneer results are also briefly discussed). The A and B rings are well modeled by an optically thick monolayer, or equivalently, a flat sheet, radiating from one side only. This points to a temperature contrast between the two sides, possibly due to particles with low thermal inertia. Other existing models for the B ring are discussed. The good fit for the monolayer model does not rule out the possibility that the A and B rings are many particles thick. It could well be that a multilayer ring produces an infrared behavior (as a function of tilt angle) similar to that of a monolayer. The C ring brightness increases as B′ decreases. This contrast in behavior can be understood simply in terms of the low C ring optical depth and small amount of interparticle shadowing. High-albedo particles (A?0.5) can fit the C ring infrared data if they radiate mostly from one hemisphere due to slow rotation or low thermal inertia (or both). Alternatively, particles isothermal over their surface (owing to a rapid spin, high inertia, or small size), and significantly darker (A?0.3) than the A and B ring particles, can produce a similar brightness variation with ring inclination. In any case, the C ring particles have significantly hotter physical temperatures than the particles in the A and B rings, whether or not the rings form a monolayer.  相似文献   

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