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Joseph A. Burns 《Icarus》1981,45(1):1-3
The Galilean satellites Io, Europa, and Ganymede interact through several stable orbital resonances where and λ1 ? 3λ2 + 2λ3 = 180°, with λi being the mean longitude of the ith satellite and the longitude of the pericenter. The last relation involving all three bodies is known as the Laplace relation. A theory of origin and subsequent evolution of these resonances outlined earlier (C. F. Yoder, 1979b, Nature279, 747–770) is described in detail. From an initially quasi-random distribution of the orbits the resonances are assembled through differential tidal expansion of the orbits. Io is driven out most rapidly and the first two resonance variables above are captured into libration about 0 and 180° respectively with unit probability. The orbits of Io and Europa expand together maintaining the 2:1 orbital commensurability and Europa's mean angular velocity approaches a value which is twice that of Ganymede. The third resonance variable and simultaneously the Laplace angle are captured into libration with probability ～0.9. The tidal dissipation in Io is vital for the rapid damping of the libration amplitudes and for the establishment of a quasi-stationary orbital configuration. Here the eccentricity of Io's orbit is determined by a balance between the effects of tidal dissipation in Io and that in Jupiter, and its measured value leads to the relation with the k's being Love numbers, the Q's dissipation factors, and f a factor to account for a molten core in Io. This relation and an upper bound on Q1 deduced from Io's observed thermal activity establishes the bounds 6 × 104 < QJ < 2 × 106, where the lower bound follows from the limited expansion of the satellite orbits. The damping time for the Laplace libration and therefore a minimum lifetime of the resonance is 1600 QJ years. Passage of the system through nearby three-body resonances excites free eccentricities. The remnant free eccentricity of Europa leads to the relation for rigidity μ2 = 5 × 1011 dynes/cm2. Probable capture into any of several stable 3:1 two-body resonances implies that the ratio of the orbital mean motions of any adjacent pair of satellites was never this large.A generalized Hamiltonian theory of the resonances in which third-order terms in eccentricity are retained is developed to evaluate the hypothesis that the resonances were of primordial origin. The Laplace relation is unstable for values of Io's eccentricity e1 > 0.012 showing that the theory which retains only the linear terms in e1 is not valid for values of e1 larger than about twice the current value. Processes by which the resonances can be established at the time of satellite formation are undefined, but even if primordial formation is conjectured, the bounds established above for QJ cannot be relaxed. Electromagnetic torques on Io are also not sufficient to relax the bounds on QJ. Some ideas on processes for the dissipation of ideal energy in Jupiter yield values of QJ within the dynamical bounds, but no theory has produced a QJ small enough to be compatible with the measurements of heat flow from Io given the above relation between Q1 and QJ. Tentative observational bounds on the secular acceleration of Io's mean motion are also shown not to be consistent with such low values of QJ. Io's heat flow may therefore be episodic. QJ may actually be determined from improved analysis of 300 years of eclipse data. 相似文献
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Previous studies based on radio scintillation measurements of the atmosphere of Venus have identified two regions of small-scale temperature fluctuations located in the vicinity of 45 and 60 km. A global study of the fluctuations near 60 km, which are consistent with wind-shear-generated turbulence, was conducted using the Pioneer Venus measurements. The structure constants of refractive index fluctuations cn2 and temperature fluctuations cT2 increase poleward, peak near 70° latitude, and decrease over the pole; cn2 varies from 2 × 10?15 to 1.5 × 10?14m and cT2 from 4 × 10?3 to 7 × 10?2°K2m. These results indicate greater turbulent activity at the higher latitudes. In the region near 45 km the refractive index fluctuations and the corresponding temperature fluctuations are substantially lower. Based on the analysis of one representative occultation measurement, in the 45-km region. The fluctuations in this region also appear to be consistent with wind-shear-generated turbulence. The turbulence level is considerably weaker than that at 60 km; the energy dissipation rate ε is 4.9 × 10?5m2sec?3 and the small-scale eddy diffusion coefficient K is 2 × 103 cm2 sec?1. 相似文献
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Results are given of the calculations of the group delay time propagating τ(ω, φ0) of hydromagnetic whistlers, using outer ionospheric models closely resembling actual conditions. The τ(ω, φ0) dependencies were compared with the experimental data of τexp(ω, φ0) obtained from sonagrams. The sonagrams were recorded in the frequency range at observation points located at geomagnetic latitudes φ0 = (53?66)° and in the vicinity of the geomagnetic poles. This investigation has led us to new and important conclusions.The wave packets (W.P.) forming hydromagnetic whistlers (H.W.) are mainly generated in the plasma regions at L = 3.5?4.0. This is not consistent with ideas already expressed in the literature that their generation region is . The overwhelming majority of the τexp values differ considerably from the times at which wave packets would, in theory, propagate along the magnetic field lines corresponding to those of the geomagnetic latitudes φ0 of the observation points. The second important fact is that the W.P. frequency ω is less than everywhere along its propagation trajectory, including the apogee of the magnetic force line ( is the proton gyrofrequency). Proton flux spectra keV, responsible for H.W. generation, were determined. Comparison of the Explorer-45 and OGO-3 measurements published in the literature, with our data, showed that the proton flux density energy responsible for the H.W. excitation where Ha is the magnetic field force in the generation region of these W.P. The electron concentration is . The values given in the literature are . The e data considered also leads to the conclusion that the generating mechanism of the W.P. studied probably always co-exists with the mechanism of their amplification. 相似文献
5.
The quenching rate kN2 of by N2 and the specific recombination rate α1D of O2+ leading to are re-examined in light of available laboratory and satellite data. Use of recent experimental values for the transition probabilities in a re-analysis of AE-C satellite 6300 Å airglow data results in a value for kN2 of 2.3 × 10?11 cm3s?1 at thermospheric temperatures, in excellent agreement with the laboratory measurements. This implies a value of JO2 = 1.5 × 10?6s?1 for the O2 photodissociation rate in the Schumann-Runge continuum. The specific recombination coefficient α1D = 2.1 × 10?7cm3s?1 is also in agreement with the laboratory value. Implications for the suggested reaction are discussed. 相似文献
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Absolute spectrophotometry of Neptune from 3390 to 7800 Å, with spectral resolution of 10 Å in the interval 3390–6055 and 20 Å in the interval 6055–7800 Å, is reported. The results are compared with filter photometry (Appleby, 1973; Wamsteker, 1973; Savage et al., 1980) and with synthetic spectra computed on the basis of a parameterization proposed by Podolak and Danielson (1977) for aerosol scattering and absorption. A CH4/H2 ratio of is derived for the convectively mixed part of Neptune's atmosphere, and constrains optical properties of hypothetical aerosol layers. 相似文献
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Measurements of N2+ and supporting data made on the Atmosphere Explorer-C satellite in the ionosphere are used to study the charge exchange process The equality k = (5 ± 1.7) × 10?10cm3s?1. This value lies close to the lower limit of experimental uncertainty of the rate coefficient determined in the laboratory. We have also investigated atomic oxygen quenching of O+(2D) and find that the rate coefficient is 2 × 10?11 cm3s?1 to within approximately a factor of two. 相似文献
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Marcel Nicolet 《Planetary and Space Science》1984,32(7):871-880
The photodissociation of water vapour in the mesosphere depends on the absorption of solar radiation in the region (175–200 nm) of the O2 Schumann-Runge band system and also at H-Lyman alpha. The photodissociation products are OH + H, OH + H, O + 2H and H2 + O at Lyman alpha; the percentages for these four channels are 70, 8, 12 and 10%, respectively, but OH + H is the only channel between 175 and 200 nm. Such proportions lead to a production of H atoms corresponding to practically the total photodissociation of H2O, while the production of H2 molecules is only 10% of the H2O photodissociation by Lyman alpha.The photodissociation frequency (s?1) at Lyman alpha can be expressed by a simple formula where F10.7 cm is the solar radioflux at 10.7 cm and N the total number of O2 molecules (cm?2), and when the following conventional value is accepted for the Lyman alpha solar irradiance at the top of the Earth's atmosphere () qLyα,∞ = 3 × 1011 photons cm?2 s1?.The photodissociation frequency for the Schumann-Runge band region is also given for mesospheric conditions by a simple formula where JSRB,∞(H2O) = 1.2 × 10?6 and 1.4 × 10?6 s?1 for quiet and active sun conditions, respectively.The precision of both formulae is good, with an uncertainty less than 10%, but their accuracy depends on the accuracy of observational and experimental parameters such as the absolute solar irradiances, the variable transmittance of O2 and the H2O effective absorption cross sections. The various uncertainties are discussed. As an example, the absolute values deduced from the above formulae could be decreased by about 25-20% if the possible minimum values of the solar irradiances were used. 相似文献
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The odd zonal harmonics in the geopotential are the terms independent of longitude and antisymmetric about the Equator: they define the ‘pear-shape’ effect. The coeffecients J3, J5, J7,…of these harmonics have been evaluated by analysing the variations in eccentricity of 27 orbits covering wide range of inclinations. We use again most of the orbits from our previous (1969) evaluations, but we now have the advantage of 3 accurate orbits at inclinations between 60° and 66°, where the variations in eccentricity become very large, and 3 near-equatorial orbits, at inclinations between 3° and 15°, whereas previously there were none at inclinations lower than 28°. The new data lead to much more accurate and reliable values for the coeffecients. Our recommended set, which terminates at J17, is . With this new set of values the pear-shape tendency of the Earth amounts to 44.7 m at the poles, instead of the previous 40 m, though the new geoid is within 1 m of the old at latitudes away from the poles. 相似文献
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The paper gives the results of detailed studies of the frequency spectra of the chain of the wave packets Fs(t) of geomagnetic pulsations PC-1 recorded at the Novolazarevskaya station. The bulk of the energy of Fs(t) is concentrated in the vicinity of the central frequencies of spectra—the carrier frequencies of the signals. The velocity of the flux of protons generating these signals correspond to them. The spectra of the signals have oscillations—“satellites” irregularly distributed in frequency. These satellites, as the authors believe, testify to the presence of the individual groups of protons of low concentration whose velocities vary within 103–104 km s?1.Their energy is only of the order of 10?2–10?3 of the energy of the main proton flux. Clearly pronounced maxima on double and triple frequencies are detected. They show that the generation of pulsations PC-1 is accompanied by the generation on the overtones of wave packets called in this paper “two-fold” and “three-fold” pulsations PC-1. Intensive symmetrical satellites of a modulation character have been discovered on frequencies . Frequency differences correspond to them. The authors believe that the values of Δ?±sK are resonance frequencies of the magnetospheric cavity in which geomagnetic pulsations PC-1 are generated. It is established that the values of Δ?±sK coincide closely with the carrier frequencies of geomagnetic pulsations PC-3 and PC-4 generated in the magnetosphere. This leads to the conclusion that the resonance oscillations of the magnetospheric cavity are their source. Thus, the generation of geomagnetic pulsations of different types and resonance oscillations in the magnetosphere are integrated into a unified process. The importance of the results obtained and the necessity to check further their trustworthiness and universality, using experimental data gathered in different conditions, is stressed. 相似文献
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P. Nenovski 《Planetary and Space Science》1985,33(11):1313-1316
In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum , obtained by Nenovski (1978) in the cold plasma limit VA ? VS(VA is Alfvén velocity, and VS, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed. 相似文献
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In this paper we confirm an earlier finding that the reaction constitutes a major source of OI 6300 Å dayglow. The rate coefficient for this reaction is found to be consistent with an auroral result, namely k1 ≈ 6 × 10?12cm3s?1. We correct an error in an earlier publication and demonstrate that reaction (1) is consistent with the laboratory determined quenching rate for the reaction where . Dissociative recombination of O+2 with electrons is found to be a major daytime source in summer above ～220 km. 相似文献
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A new theory of the Alfvén wave generation in inhomogeneous finite β two component plasma is developed (, ρ and B0 are plasma pressure and unperturbed magnetic field, respectively). The analysis was carried out for these waves both for long wave approximation kρi ? 1 as well as for (k and ρi are wave vector and larmor radius of protons). The influence of the loss-cone on the development of the instability is considered. The theory is applied to explain the generation mechanism of Pc 3–5. 相似文献
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Marcel Nicolet 《Planetary and Space Science》1984,32(11):1467-1468
A recent determination by D. R. Bates of the Rayleigh scattering cross section (σRS) for air from 0.2 to 1 μm leads to a simple empirical formula (λ in μm) where for the spectral region 0.2 μm < λ < 0.55 μm ; the accuracy is within ±0.5%. From the visible at 0.55 μm to the infrared (i.r.) at 1 μm, the same accuracy can be obtained using a constant value, x = 0.04. The formula accounts for the degree of depolarization which varies with the wavelength according to the latest determination by Bates. 相似文献
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It is shown that the area Ak(× 106km2) covered by brightest auroras and the area Aq bounded by the auroral oval have a simple relation given by , where A0 denotes the area of the minimum size oval and the quantity (Aq ? A0)2 is proportional to the energy εq which is stored in the magnetotail and is available for substorms. Following the definition of the intensity of solar flares, Ak may be chosen as a measure of the intensity of substorms. It is also found that the joule heat energy produced by the auroral electrojet is also proportional to (Aq ? A0)2. Thus, it may be concluded that the intensity of substorms is proportional to the energy εq stored in the magnetotail. 相似文献
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A mechanism has been proposed for uv-accelerated desorption from Fe2+ sites on mineral surfaces that satisfies kinetic constraints determined in the laboratory by Huguenin. The process is an integral step of the photochemical weathering mechanism for producing dust on Mars, and it now appears that it may play primary roles in stabilizing CO2 against dissociation by sunlight and in controlling the oxidation state of the atmosphere. We propose that adsorption occurs at octahedrally coordinated Fe2+ surface sites to form seven-coordinate transition-state complexes. These complexes acquire 16–18 kcal mole?1 of ligand field stabilization energy. During illumination (λ ≤ 0.35 μm), electrons are photoemitted from the surfaced Fe2+, temporarily oxidizing them to Fe3+. Fe3+ has no ligand field stabilization energy, and the complexes lose 16–18 kcal mole?1 of stabilization energy. This is a large fraction of the 19- to 28-kcal mole?1 activation energy for dissociating the complexes, and desorption should proceed spontaneously. The gases that were observed to undergo adsorption-photodesorption include O2, CO2, CO, H2O, N2, and Ar. Photodesorption can drive several catalytic reactions, one of which is the oxidation of CO to CO2. The rate of this reaction should be limited by the supply of CO and O2 to the surface to ～2 × 1012 cm?2 sec?1 (column photodissociation rate of CO2). By including this surface reaction in models of Martian atmospheric CO2 chemistry, CO2 can be stabilized against photodissociation with eddy diffusion coefficients of only 3 × 105?1 × 107 cm2 sec?1 below 40 km, raising to ～ 109 cm2 sec?1 at 140 km. Odd hydrogen is not needed to catalyze the oxidation of CO below 40 km, and odd hydrogen mixing ratios need only to be to depress ozone concentrations below the observed upper limit in equatorial regions. Another catalytic reaction that should be driven by photodesorption on Mars is . This is an important source of atmospheric O2, amounting to 7 × 1013?2 × 1017 O2 molecules cm?2 yr?1, and it could have a significant effect on atmospheric oxidation state. 相似文献
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Doreen M.C. Walker 《Planetary and Space Science》1984,32(6):717-725
The orbit of the satellite 1967-104B has been analysed as it passed through 29:2 resonance with the Earth's gravitational field between January 1977 and September 1978. From the changes in inclination and eccentricity the following lumped 29th-order geopotential harmonic coefficients were obtained: , , , , , . These values have been compared with existing comprehensive geopotential models: the best agreement is with the model of Rapp (1981). 相似文献
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W.J. Boulton 《Planetary and Space Science》1985,33(6):735-756
The influence of aerodynamic drag and the geopotential on the motion of the satellite 1964-52B is considered. A model of the atmosphere is adopted that allows for oblateness, and in which the density behaviour approximates to the observed diurnal variation. A differential equation governing the variation of the eccentricity, e, combining the effects of air drag with those of the Earth's gravitational field is given. This is solved numerically using as initial conditions 310 computed orbits of 1964-52B.The observed values of eccentricity are modified by the removal of perturbations due to luni-solar attraction, solid Earth and ocean tides, solar radiation pressure and low-order long-periodic tesseral harmonic perturbations. The method of removal of these effects is given in some detail. The behaviour of the orbital eccentricity predicted by the numerical solution is compared with the modified observed eccentricity to obtain values of atmospheric parameters at heights between 310 and 430 km. The daytime maximum of air density is found to be at 14.5 hours local time. Analysis of the eccentricity near 15th order resonance with the geopotential yielded values of four lumped geopotential harmonics of order 15, namely: , , , at inclination 98.68°. 相似文献
20.
K.M. Monahan W.T. Huntress A.L. Lane J.M. Ajello T.E. Burke P. Le Breton A. Williamson 《Planetary and Space Science》1974,22(1):143-149
The cross-section for dissociative photoionization of hydrogen by 584 Å radiation has been measured, yielding a value of 5 × 10?20 cm2. The process can be explained as a transition from the ground state to a continuum level of the ionized state of H2 The branching ratio for proton (H+) vs molecular ion (H2+) production at this energy is 8 × 10?3. This process is quite likely an important source of protons in the Jovian ionosphere near altitudes where peak ionization rates are found. 相似文献