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1.
We present 20-μm photometry of Uranus and Neptune which confirms the presence of a temperature inversion in the lower stratospheres in both planets. We find the brightness temperature difference between 17.8 and 19.6 μm to be 0.8 ± 0.5°K for Uranus and 1.8 ± 0.6°K for Neptune. These results indicate that the temperature inversions on both planets are weaker than previously thought. Comparison to model atmospheres by J. Appleby [Ph.D. thesis, SUNY at Stony Brook 1980] indicates that the temperature inversions can be understood as arising from heating by the absorption of sunlight by CH4 and aerosols. However, the stratospheric CH4 mixing ratio on Neptune must be higher than that at the temperature minimum. 相似文献
2.
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
3.
B.H. Andrew 《Icarus》1974,22(4):454-458
Brightness temperatures have been measured at 2.85 cm wavelength for Ceres, Pallas, Mars, Uranus, and Neptune. The brightness temperature of Ceres seems to be a little lower than would be expected on the basis of simple theory. 相似文献
4.
Observations of tilts of spectral lines in the spectrum of Uranus and Neptune yield the following rotational periods: “Uranus,” 24 ± 3 hr; “Neptune,” 22 ± 4 hr. Neptune is confirmed to rotate in a direct sense. The position angle of the pole of Uranus, projected onto the plane of the sky, is found to be 283 ± 4°. The value for Neptune is 32 ± 11°. These results agree with the direction of the pole of Uranus inferred from the common plane of its four brightest satellites and with the direction of the pole of Neptune as inferred from the precession of Triton's orbit. The rotational period of Uranus is found to be consistent with modern values of its optical and dynamical oblateness and the theory of solid-body rotation with hydrostatic equilibrium. This is barely the case for the period derived for Neptune and we suspect that future observations made under better seeing conditions may lead to a shorter rotation period between 15 and 18 hr. Because of a substantial difference between our results and those of earlier spectroscopic and photometric investigations we include an assessment of several previously published photometric studies and a new reduction of the original Lowell and Slipher spectroscopic plates of Uranus [Lowell Obs. Bull. 2, 17–18, 19–20 (1912)]. The early visual photometry of Campbell (Uranus) and Hall (Neptune) is found to be more satisfactorily accounted for by periods of 21.6 and 23.1 hr, respectively, than by the periods originally suggested by the observers. Our reduction of the Lowell and Slipher Uranus plates yields a period near 33 hr uncorrected for seeing. This value is consistent with the results based on the 4-m echelle date. 相似文献
5.
R.H. Hildebrand R.F. Loewenstein D.A. Harper G.S. Orton Jocelyn Keene S.E. Whitcomb 《Icarus》1985,64(1):64-87
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
6.
L. Wallace 《Icarus》1984,59(3):367-375
Previous work on the atmosphere of Uranus is extended to Neptune. The variation of effective temperature with latitude and season is evaluated within the approximations that the redistribution of internal heat in the interior results in the temperature at fixed pressure near the top of the convective region being independent of latitude and time, and that the transport of heat in the atmosphere is by means of radiation and convection. Meridional heat transport in the atmosphere is neglected. It is found that as the absorbed solar flux varies with season the flux of internal heat varies in the opposite sense such that the variation in the sum of the two is much smaller than the variation in either. The resulting variation in the flux radiated out the top of the atmosphere, which responds to the sum of the internal and absorbed solar fluxes, is substantially smaller than for Uranus because of the much larger flux of internal heat. For Neptune, the time-averaged effective temperature at the pole is ≈0.2°K greater than at the equator and the seasonal variation in the polar effective temperature is ≈0.8°K. 相似文献
7.
R.F. Loewenstein D.A. Harper S.H. Moseley C.M. Telesco Harley A. Thronson R.H. Hildebrand S.E. Whitcomb R. Winston R.F. Stiening 《Icarus》1977,31(3):315-324
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
8.
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
9.
Using current concepts for the origin of the Jovian planets and current constraints on their interior structure, we argue that the presence of large amounts of “ice” (H2O, CH4, and NH3) in Uranus and Neptune indicates temperatures low enough to condense these species at the time Uranus and Neptune formed. Yet such low temperatures imply orders-of-magnetude fractionation effects for deuterium into the “ice” component if isotopic equilibration can occur. Our models thus imply that Uranus and Neptune should have a D/H ratio at least four times primordial, contrary to observation for Uranus. We find that the Jovian and Saturnian D/H should be close to primordial regardless of formation scenario. The Uranus anomaly could indicate that there was a strong initial radial gradient in D/H in the primordial solar nebula, or that Uranus is so inactive that no significant mixing of its interior has occurred over the age of the solar system. Observation of Neptune's atmospheric D/H may help to resolve the problem. 相似文献
10.
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
11.
Observations of the 24 May 1981 occultation of an uncatalogued star by Neptune made at the Cerro Tololo Inter-American Observatory have been analyzed to yield temperature profiles of Neptune's upper atmosphere for number densities near 5 × 1013 cm?3. The mean temperatures at immersion (latitude ?56°) and emersion (latitude ?16°) obtained by numerical inversion were 140 ± 10°K and 154 ± 10°K, respectively. The immersion and emersion profiles are remarkably similar in overall shape, suggestive of global atmospheric layering. From the astrometry of the event, precise relative positions of Neptune and the occulted were obtained. 相似文献
12.
A stellar occultation by Uranus and its rings was observed on August 15, 1980, from the European Southern Observatory (Chile), at the 3.6-m telescope equipped with an infrared (2.2 μm) photometer. The recording presents the best signal-to-noise ratio obtained since the discovery of the Uranian rings in March 1977. The nine rings were observed, and the profiles of rings α, β, and ? were resolved, the ring α exhibiting a double structure. Strong diffraction peaks are visible in the γ ring profile suggesting an opaque ring with very sharp edges. A broad and faint structure extends outward from the η ring, on a radial scale of about 55 km. Apart from the ring occultations, unexplained sharp and deep events were recorded, and no interpretation is possible until future observations are made. Furthermore, the stellar light curve during the immersion of the star behind the planet provides (via an inversion computation) the temperature profile of the upper atmosphere of Uranus. The temperature is close to 145 ± 10°K at the 3 × 10?2-mbar pressure level and is nearly constant (155 ± 15°K) in the pressure interval from 10?2 to 10?3 mbar. The thermal inversion is as strong as the inversion on Neptune but is located at higher altitudes. This high stratospheric temperature is consistent with the upper limit of the brightness temperature at 8 μm only if CH4 follows its saturation law. 相似文献
13.
Conventional planet formation models via coagulation of planetesimals require timescales in the range of several 10 or even 100 Myr in the outer regions of a protoplanetary disk. But according to observational data, the lifetime of a protoplanetary disk is limited to about 6 Myr. Therefore the existence of Uranus and Neptune poses a problem. Planet formation via gravitational instability may be a solution for this discrepancy. We present a parameter study of the possibility of gravitationally triggered disk instability. Using a restricted N‐body model which allows for a survey of an extended parameter space, we show that a passing dwarf star with a mass between 0.1 and 1 M⊙ can probably induce gravitational instabilities in the pre‐planetary solar disk for prograde passages with minimum separations below 80‐170 AU. Inclined and retrograde encounters lead to similar results but require slightly closer passages. Such encounter distances are quite likely in young moderately massive star clusters. The induced gravitational instabilities may lead to enhanced planetesimal formation in the outer regions of the protoplanetary disk, and could therefore be relevant for the formation of Uranus and Neptune. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
We have examined a wide range of physical, chemical, and thermal models of the atmosphere of Uranus. In that model, which we believe maximizes favorable conditions for the support of life [Weidenschilling and Lewis, Icarus20, 465–476 (1973)], we find the probability of growth of a contaminant terrestrial microorganisms to be nil. If, as is likely, conditions are even more extreme on Neptune, the probability of contamination of both of the outer planets Uranus and Neptune is nil. The Wiedenschilling and Lewis model guarantees the presence of water droplets through the temperature range 0 to 100°C; other published models add water liquid at higher temperatures or fail to provide liquid water at all within this temperature range. In this model the heavy elements (C, N, O, etc.) are enhanced in Uranus by a factor sufficient to form a deep massive cloud layer of aqueous ammonia solution droplets. We can estimate the probability of growth with respect to the following factors: the presence of stable liquid water, convection of parcels of atmosphere to lethally hot depths, solar energy sources reaching the water layer, organic molecular production by solar ultraviolet light, ammonia concentration at the water cloud level, ionic species distribution, and concentrations at the water cloud level. The evaluation of these factors suggests that most terrestrial life as we know it would be excluded on the basis of any one of them. We know of no organism that would be adapted to all the stringent Uranus conditions simultaneously. The discovery of even a single species of Earth organism that can survive or grow under allowable outer planetary conditions would establish new principles in biology.Titan, the methane-rich moon of Saturn, may be more hospitable for terrestrial organisms than any of the other objects of the outer solar system. Even there we see formidable barriers to the growth of an Earth organism in Titan's atmosphere. We recognize that revision of our views concerning Titan must occur as more is learned about this satellite.We advocate the abandonment, in principle, of the probabilistic approach to the estimation of growth of terrestrial organisms on spacecraft, planets, and satellites in the solar system. We do not support an approach which estimates probabilities of qualitatively unknown phenomena. We recommend a strategy which involves identification and intensive study of those organisms most likely to thrive under known conditions for each of the planets respectively. (Unknown environmental conditions may be allowed to vary optimally.) Some explicit areas for Earth-based experimentation are indicated. 相似文献
15.
Eugene E. Epstein Michael A. Janssen Jeffrey N. Cuzzi William G. Fogarty John Mottmann 《Icarus》1980,41(1):103-118
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
16.
We present high-resolution interferometry of Uranus at 6 cm wavelength and single-dish observations of the disk-averaged brightness temperature, TB, at 2.8 and 4.8 cm wavelength. The 1978 measurements of TB of 228 ± 2,243 ± 9, and 259 ± 4 K at 2.8, 4.8, and 6 cm, respectively, support the finding of M. J. Klein and J. A. Turegano (1978, Astrophy. J.224, L31–L34) that the brightness temperature of Uranus has been rising. There is no evidence for radio emission from outside the visible disk at 6 cm. Radiation from a synchrotron radiation belt or from the Uranian rings is certainly less than 10% of the total radio flux. The interferometry shows a possible 55 ± 20 K difference in brightness temperature between the equator and the currently exposed pole. The pole appears to be ～275 K while the equator is ～220 K. However, a permanent gradient of this magnitude is insufficient to account for the rise in disk-averaged brightness by simple reorientation of Uranus' globe relative to our line of sight. The changing insolation probably triggers a redistribution of the trace constituent NH3 which is responsible for the radio opacity. The NH3 may be interacting strongly with H2S on Uranus. 相似文献
17.
Observations of the planet Saturn at wavelengths of 49.5 and 94.3 em are reported. The equivalent disk brightness temperatures were found to be 400 ± 65°K and 540 ± 110°K, respectively. It is suggested that the enhanced portion of the spectrum of the disk brightness temperature favours the idea that the observed long wavelength radiation comes from the planet's atmosphere.However, the possibility of a magnetic field associated with Saturn is not rejected by the observations. Part of the excess temperature could be attributed to weak synchrotron emission coming from a region outside the ring system. 相似文献
18.
An error in the Hayes and Belton (1977), Icarus32, 383–401) estimate of the rotation period of Neptune is corrected. If Neptune exhibits the same degree of limb darkening as Uranus near 4900 Å, the rotation period is 15.4 ± 3 hr. This value is compatible with a recent spectroscopic determination of Munch and Hippelein (1979) who find a period of 11.2?1.2+1.8 hr. However, if, as indirect evidence suggests, the law of darkening on Neptune at these wavelengths is less pronounced than on Uranus, then the above estimates may need to be lengthened by several hours. Recent photometric data are independently analyzed and are found to admit several possible periods, none of which can be confidently assumed to be correct. The period of Neptune most probably falls somewhere in the range 15–20 hr. The Hayes-Belton estimate of the period of Uranus is essentially unaffected by the above-mentioned error and remains at 24 ± 4 hr. All observers agree that the rotation period of Uranus is longer than that of Neptune. 相似文献
19.
We investigated the stable area for fictive Trojan asteroids around Neptune’s Lagrangean equilibrium points with respect to their semimajor axis and inclination. To get a first impression of the stability region we derived a symplectic mapping for the circular and the elliptic planar restricted three body problem. The dynamical model for the numerical integrations was the outer Solar system with the Sun and the planets Jupiter, Saturn, Uranus and Neptune. To understand the dynamics of the region around L 4 and L 5 for the Neptune Trojans we also used eight different dynamical models (from the elliptic problem to the full outer Solar system model with all giant planets) and compared the results with respect to the largeness and shape of the stable region. Their dependence on the initial inclinations (0° < i < 70°) of the Trojans’ orbits could be established for all the eight models and showed the primary influence of Uranus. In addition we could show that an asymmetry of the regions around L 4 and L 5 is just an artifact of the different initial conditions. 相似文献
20.
W.B. Hubbard 《Icarus》1978,35(2):177-181
We extend a Jovian convective-cooling model to Uranus and Neptune. The model assumes that efficient interior convection prevails, so that escape of interior heat is governed by the radiative properties of the atmosphere. A comparison of the thermal evolution of Uranus and Neptune indicates that the larger amount of solar radiation absorbed in Uranus' atmosphere tends to differentially suppress the escape of interior heat. The model is shown to be consistent with recent infrared observations of the thermal balance of Uranus and Neptune, and with the presumed age of these planets. 相似文献