Structure of the satellitary accretion disk of Saturn     

A. Coradini  G. Magni 《Icarus》1984,59(3):376-391

A detailed computation on the equilibrium structure of an accretion disk around Saturn from which the regular satellites presumably originated is reported. Such a disk is the predecessor of the self-dissipating disk that is formed when the mass infall stops (Cassen and Moosman, 1981, Icarus48, 353–376). When determining the disk structure local energy balance was assumed. Convention was taken into account by introducing local energy dissipation and, in an approximate manner, sonic convection. Changes in the disk structure were investigated by varying the free parameters, i.e., the external flux from both the protosun and the protoplanet, the abundance of dust and the strength of turbulence. It has been verified that the external energy flux does not play an important role in the evolution of the disk structure. Models characterized by either longer times (?3 10³ year) or a noticeable depletion of condensable elements (10^?2 times less than the solar value) have a total mass of the order of 0.34?0.1 times the mass of the regular satellites increased by the mass of the light elements. Low turbulence models (Reynolds critical number $\text{Re}{}^1\text{= 150}$) are characterized approximately by a total mass twice as large the mass of the regular satellites. All the studied models present a temperature distribution that allows the condensation of iron, silicate, and, in the outer regions, ice grains. All models but the one with 10^?2 of the solar value of condensable elements are characterized by a wide convective region that contains the formation zone of the regular satellites.  相似文献   

A perturbative treatment of the 21 Jovian resonance     

《Icarus》1987,69(2):266-279

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Chaotic behavior and the origin of the $\text{3}\text{1}$ Kirkwood gap     

Jack Wisdom 《Icarus》1983,56(1):51-74

The sudden eccentricity increases discovered by J. Wisdom (Astron J.87, 577–593, 1982) are reproduced in numerical integrations of the planar-elliptic restricted three-body problem, verifying that this phenomenon is real. Maximum Lyapunov characteristic exponents for trajectories near the $\text{3}\text{1}$ commensurability are computed both with the mappings presented in Wisdom (1982) and by numerical integration of the planar-elliptic problem. In all cases the agreement is excellent, indicating that the mappings accurately reflect whether trajectories are chaotic or quasiperiodic. The mappings are used to trace out the chaotic zone near the $\text{3}\text{1}$ commensurability, both in the planar-elliptic problem and to a more limited extent in the three-dimensional elliptic problem. The outer boundary of the chaotic zone coincides with the boundary of the $\text{3}\text{1}$ Kirkwood gap in the actual distribution of asteroids within the errors of the asteroid orbital elements.  相似文献   

Micropulsations and orthogonal curvilinear coordinates     

P.C. Kendall 《Planetary and Space Science》1979,27(6):895-899

The theory of torsional hydromagnetic oscillations of the magnetosphere is usually cast in terms of orthogonal curvilinear coordinates. For a general magnetic field B with potential Ω it is shown that no coordinates exist in which a suitable solution may be found unless the Alfvén velocity V_A, together with B and Ω satisfy certain functional relationships. In the case V_A = constant, for example we must have . The relationships presented are in fact satisfied by all the magnetic fields considered to date.  相似文献   

Seasonal meridional energy balance and thermal structure of the atmosphere of Uranus: A radiative-convective-dynamical model     

《Icarus》1987,69(1):135-156

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Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies     

B.N. Khare  Carl Sagan  E.T. Arakawa  F. Suits  T.A. Callcott  M.W. Williams 《Icarus》1984,60(1):127-137

As part of a continuing series of experiments on the production of dark reddish organic solids, called tholins, by irradiation of cosmically abundant reducing gases, the synthesis from a simulated Titanian atmosphere of a tholin with a visible reflection spectrum similar to that of the high altitude aerosols responsible for the albedo and reddish color of Titan has been reported Sagan and Khare, 1981, Sagan and Khare, 1982, Orig. Life. 12, 280) and [C. Sagan, B. N. Khare, and J. Lewis, in press. In Saturn (M. S. Matthews and T. Gehrels, Eds.), Univ. of Arizona Press, Tucson]. The determination of the real (n) and imaginary (k) parts of the complex refractive index of thin films of such tholin prepared by continuous D.C. discharge through a 0.9 N₂/0.1 CH₄ gas mixture at 0.2 mb are reported. For $\text{250}\text{A}\text{?}\text{≤ γ ≤ 1000 μ}\text{m}\text{, n}\text{and}\text{k}$ have been determined from a combination of transmittance, specular reflectance, interferometric, Brewster angle, and ellipsometric polarization measurements; experimental uncertainties in n are estimated to be ±0.5, and in k ± 30%. Values of n(?1.65) and k (?0.004 to 0.08) in the visible range are consistent with deductions made by ground-based and spacecraft observations of Titan. Maximum values of k (?0.8) are near 1000 Å, and minimum values (?4 × 10^?4) are near 1.5 μm. Many infrared absorption features are present in k(γ), including the 4.6-μm nitrile band.  相似文献   

An efficient parallel algorithm for O(N2) direct summation method and its variations on distributed-memory parallel machines     

《New Astronomy》2002,7(7):373-384

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Effects of crossed magnetic and (spatially dependent) electric fields on charged particle motion     

K.D. Cole 《Planetary and Space Science》1976,24(5):515-518

The motion of charged particles is examined in the case of a homogeneous magnetic field B together with an orthogonal electric field E, which has a gradient ▽E parallel to E. If , the particles drift at right angles to E and B with a modified gyrofrequency and produce a current in that direction. If , the particles not only drift in the direction of E × B but are also accelerated in the direction of E, in which direction they also produce a current.  相似文献   

Non-adiabatic processes in a two-fluid plasma and energization of the plasma sheet plasma     

A. Hru ka 《Planetary and Space Science》1981,29(12):1325-1332

The change of energy of a collisionless, two-fluid plasma consists of the adiabatic gain or loss of energy, which is due to the work done by the electromagnetic forces, and of the non-adiabatic change associated with the presence of the “rest” field $\text{E}{}^1\text{=}\text{E}\text{+ (}\text{1}\text{c}\text{)}\text{V}\text{×}\text{B}$. The non-adiabatic gain or loss of energy per unit ti may be expressed by the relation where i is the density of conductive current, N the ion number-density, and f (f?) the sum of inertia and pressure divergence of ions (electrons). Symbols of parallelism refer to the direction of B.A special case of non-adiabatic energization of a slowly convecting plasma sheet plasma is discussed in some detail. Regardless of the value of V, the non-adiabatic energization may significantly exceed any conceivable energization associated with the electric field $\text{?(}\text{1}\text{c}\text{)}\text{V}\text{×}\text{B}$.  相似文献   

Geopotential harmonics of order 15 and even degree,from changes in orbital eccentricity at resonance     

D.G. King-Hele  Doreen M.C. Walker  R.H. Gooding 《Planetary and Space Science》1975,23(2):229-246

When a satellite orbit decaying slowly under the action of air drag experiences 15th-order resonance with the Earth's gravitational field, so that the ground track repeats after 15 rev, the orbital eccentricity may suffer appreciable changes due to perturbations from the gravitational harmonics of order 15 and even degree (16, 18, 20…). In this paper the changes in eccentricity at resonance for six satellites in near-circular orbits at inclinations between 56 and 90° have been analysed to derive 11 pairs of equations linking the harmonic coefficients of order 15 and (even) degree l, $\text{C}{}_{\mathrm{l,15}}\text{and}\text{S}{}_{\mathrm{l,15}}$ in the usual notation. These equations (together with eight constraint equations) are solved to give: