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1.
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   

2.
《Icarus》1987,70(3):506-516
We present 2.7-mm interferometric observations of Saturn made near opposition in June 1984 and June 1985, when the ring opening angle was 19° and 23°, respectively. By combining the data sets we produce brightness maps of Saturn and its rings with a resolution of 6″. The maps show flux from the ring ansae, and are the first direct evidence of ring flux in the 3-mm wavelength region. Modelfits to the visibility data yield a disk brightness temperature of 156 ± 5°K, a combined A, B, and C ring brightness temperature of 19 ± 3°K, and a combined a ring cusp (region of the rings which block the planet's disk) brightness temperature of 85 ± 5°K. These results imply a normal-to-the-ring optical depth for the combined ABC ringof 0.31 ± 0.04, which is nearly the same value found for wavelenghts from the UV to 6 cm. About 6°K of the ring flux is attributed to scattered planetary emission, leaving an intrinsic thermal component of ∼13°K. These results, together with the ring particle size distributions found by the Voyager radio occultation experiments, are consistent with the idea that the ring particles are composed chiefly of water ice.  相似文献   

3.
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   

4.
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   

5.
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   

6.
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7.
B.L. Ulich  E.K. Conklin 《Icarus》1976,27(2):183-189
We have measured the 3.33 mm wavelength disk brightness temperatures of Ganymede (136 ± 21°K), Callisto (95 ± 17°K), Ceres (137 ± 25°K), Uranus (125 ± 9°K), and Neptune (126 ± 9°K). Our observations of Ganymede are consistent with the radiation from a blackbody in solar equilibrium, whereas Callisto's microwave spectrum indicates a surface similar to that of the Moon. The disk temperature for Ceres agrees with that expected from a rapidly rotating blackbody. The millimeter temperatures of Uranus and Neptune greatly exceed solar equilibrium values, implying atmospheres with large temperature gradients.  相似文献   

8.
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   

9.
David Morrison 《Icarus》1974,22(1):57-65
Broad-band radiometry with a spatial resolution of 5 arc sec is presented of Saturn and its rings. The brightness temperature of the B ring is 96 ± 3°K at 20 μm and 91 ± 3°K at 11 μm. These values constrain the bolometric Bond albedo of the ring particles to be less than 0.6, thus requiring a phase integral of less than unity. From differences in the thermal emission of the ansae, I suggest that the leading side of the particles has higher albedo than the trailing side. A measured drop in temperature of the B ring following eclipse of 2.0 ± 0.5°K is consistent with radii for the ring particles of 2 cm or larger.  相似文献   

10.
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   

11.
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   

12.
We have resolved the relative rings-to-disk brightness (specific intensity) of Saturn at 39 μm (δλ ? 8 μm) using the 224-cm telecscope at Mauna Kea Oservatory, and have also measured the total flux of Saturn relative to Jupiter in the same bandpass from the NASA Learjet Observatory. These two measurements, which were made in early 1975 with Saturn's rings near maximum inclination (b′ ? 25°), determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiter's absolute calibration make it possible to compare existing measurementsunambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 μm are all compatible (within 2σ) of a disk brightness temperature of 94°K, and do not agree with the radiative equilibrium models of Trafton; (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for λ ? 40 μm and (3) there is a decrease of ～22% in the relative ring: disk brightness between effective wavelengths of 33.5 and 39 μm.  相似文献   

13.
We have measured the brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 μm. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 ± 4.5, 93.4 ± 3.3, 58.3 ± 2.0, and 60.3 ± 2.0°K, respectively. We discuss the implications of the measurements for bolometric output and for atmospheric structure and composition. The temperature spectrum of Jupiter shows a strong peak at ～350 μm followed by a deep valley at ～450 to 500 μm. Spectra derived from model atmospheres qualitatively reproduce these features but do not fit the data closely.  相似文献   

14.
Titan has been observed with the 5-m Hale telescope at an effective wavelength of 1 mm. Adopting a value of 2700 km for the radius of Titan, we find a brightness temperature of 86±12°K at 1 mm. Comparing our results with previous measurements at longer wavelengths, we conclude that the satellite surface is the source of the 1-mm radiation. Since our measured brightness temperature is close to the equilibrium temperature of a blackbody at the distance of Saturn, we believe there is no significant greenhouse effect on Titan.  相似文献   

15.
We present far-infrared observations of Saturn and Venus made within four spectral bands (31 to 38, 47 to 67, 71 to 94, and 114 to 196 μm) using a 32-cm airborne telescope during May 1977. The set of brightness temperatures obtained from Saturn is analyzed on the basis of thermal models of the atmosphere of this planet. The best agreement is obtained with an effective temperature of about 95°K for the planet itself and a ring contribution corresponding to brightness temperatures ranging from 55 to 70°K. These values of the temperature of the ring system are smaller than the ones measured at shorter wavelengths and could be indicative of a decreasing emissivity of the rings in the far infrared.  相似文献   

16.
We present interferometric observations of Saturn and its ring system made at the Hat Creek Radio Astronomy Observatory at a wavelength of 1.30 cm. The data have been analyzed by both model-fitting and aperture synthesis techniques to determine the brightness temperature and optical thickness of the ring system and estimate the amount of planetary limb darkening. We find that the ring optical depth is close to that observed at visible wavelenghts, while the ring brightness temperature is only 7 ± 1°K. These observational constraints require the ring particles to be nearly conservative scatterers at this wavelength. A conservative lower limit to the single-scattering albedo of the particles at 1.30-cm wavelength is 0.95, and if their composition is assumed to be water ice, then this lower limit implies an upper limit of 2.4 m for the radius of a typical ring particle. The aperture synthesis maps show evidence for a small offset in the position of Saturn from that given in the American Ephemeris and Nautical Almanac. The direction and magnitude of this offset are consistent with that found from a similar analysis of 3.71-cm interferometric data which we have previously presented (F.P. Schloerb, D.O. Muhleman, and G.L. Berge, 1979b, Icarus39, 232–250). Limb darkening of the planetary disk has been estimated by solving for the best-fitting disk radius in the models. The best-fitting radius is 0.998 ± 0.004 times the nominal Saturn radius and indicates that the planet is not appreciably limb dark at 1.30 cm. Since our previous 3.71-cm data also indicated that the planet was not strongly limb dark (F.P. Schloerb, D. O. Muhleman, and G.L. Berge, 1979a, Icarus39, 214–230), we feel that the limb darkening is not strongly wavelength dependent between 1.30 and 3.71 cm. The difference between the best-fitting disk radii at 3.71 and 1.30 cm is +0.007 ± 0.007 times the nominal Saturn radius and suggests that the planet is more limb dark at 1.30 cm than at 3.71 cm. Models of the atmosphere which have NH3 as the principal source of microwave opacity predict that the planet will be less limb dark at 1.30 cm. However, the magnitude of the effect predicted by the NH3 models is ?0.009 and only marginally different from the observed value.  相似文献   

17.
Uwe Fink  Harold P. Larson 《Icarus》1975,24(4):411-420
Reflection spectra of water ice from 1 to 4 μm are presented as a function of temperature. It is found that a feature at 6056 cm?1 changes its intensity sufficiently that it can be used as a spectroscopic measure of the ice temperature. A temperature calibration curve of this feature down to 55 K is developed and is used to determine ice temperatures for the Galilean satellites Europa (95±10 K), Ganymede (103±10 K), and the rings of Saturn (80±5 K). The ice temperatures for the Galilean satellites are lower than their measured brightness temperatures, which can be explained by a higher albedo of the ice covered regions relative to the rest of the satellite and possibly a concentration of the ice near the polar caps.  相似文献   

18.
Radio emission from the planet Saturn was detected and measured by an unusually efficient observing technique at a wavelength of 49.5cm. The corresponding equivalent disk brightness temperature was hence determined to be 390 ± 65°K, providing further evidence for a mild enhancement in the emission at long wavelengths. It is pointed out that the currently available measurements of the disk brightness temperature in the wavelength range 1mm-1m are, as a whole, inadequate for estimating with confidence the detailed shape of the spectrum and that the exiguous, long wavelength observations should be supplemented with more and accurate measurements.  相似文献   

19.
Jupiter's Galilean satellites I–IV, Io, Europa, Ganymede, and Callisto have been observed with the VLA at 2 and 6 cm. The Jovian system was about 4.46 AU from the Earth at the time the observations were taken. The flux densities for satellites I–IV at 2 cm are 15 ± 2, 5.6 ± 1.2, 22.3 ± 2.0, and 26.0 ± 2.5 mJy, respectively, which corresponds to disk brightness temperatures of 92 ± 13, 47 ± 10, 67 ± 6, and 92 ± 9°K, respectively. At 6 cm flux densities of 1.10 ± 0.2, 0.55 ± 0.12, 2.0 ± 0.2, and 3.15 ± 0.2 mJy were found, corresponding to temperatures of 65 ± 11, 44 ± 10, 55 ± 6, and 105 ± 7°K, respectively. The radio brightness temperatures are lower than the infrared, the latter generally being consistent with the temperature derived from equilibrium with absorbed insolation. The radio temperature are qualitatively consistent with the equilibrium temperature for fast rotating bodies considering the high radio reflectivity (low emissivity) as determined from radar measurements by S. J. Ostro (1982). In Satellites of Jupiter (D. Morrison, Ed.). Univ. of Arizona Press, Tucson).  相似文献   

20.
M.A. Janssen  W.J. Welch 《Icarus》1973,18(3):502-504
We report observations of the radio disk temperatures of Mars and Jupiter made during October 1971, at a wavelength of 1.35 cm. The mean disk temperature of Jupiter is 136 ± 5°K, in good agreement with the value 139 ± 6°K obtained by Wrixon et al. (1971) with the same instrument three years earlier. The disk temperature of Mars is 181 ± 11°K, consistent with an essentially wavelength independent disk temperature for Mars at radio wavelengths. The ratio of the two disk temperatures, 1.33 ± .07, is largely free of the systematic uncertainties: antenna gain, pointing, and atmospheric extinction.  相似文献   

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