共查询到20条相似文献，搜索用时 31 毫秒
1.
This paper describes a new approach based on variational principles to calculate the radial distribution of tidal energy dissipation in any satellite. The advantage of the model with respect to classical solutions, is that it relates in a straightforward way the radial distribution of the time-averaged dissipation rate to its sensitivity to the corresponding distribution of viscoelastic parameters. This method is applied to Io-, Europa-, and Titan-like interiors, and it is tested against the results obtained by two classical methods by determining global dissipation as well as radial and lateral distributions within satellite interiors. By exploring systematically the different parameters defining the interior models, we demonstrate that the presence of a deep ocean below an outer ice layer strongly influences the tidal dissipation distribution in both the outer ice layer and in the innermost part of the satellite. On the one hand, the ocean by imposing a large radial displacement at the base of the outer ice I layer, controls the distribution of tidal strain rate within the outer layer, making the tidal strain rate field very weakly sensitive to the viscosity variations. Conversely, in the high-pressure ice layer below the ocean, both tidal strain rate and dissipation are very sensitive to any variation of the ice viscosity. On the other hand, for identical structures of the mantle and of the core, the presence of a subsurface ocean reduces the strength of dissipation in the silicate mantle. The existence of a liquid layer within Europa makes models of the silicate mantle less dissipative than the predictions for Io. 相似文献
2.
3.
R. Smoluchowski 《Earth, Moon, and Planets》1983,28(2):137-154
The last few years brought progress in our understanding of the interiors of the giant planets especially of the two larger ones which have been visited by Pioneer and Voyager spacecraft. An analysis of the formation of the giant planets also heped to clarify certain important common features. The presently available model of Jupiter is still based on certain somewhat bothersome approximations but it appears to satisfy the main observational constraints. Saturn's interior is much better understood than it was previously although the quantitative aspects of the role of the miscibility gap in the hydrogen-helium system have not yet been entirely resolved. Much attention has been directed at the interiors of Uranus and Neptune and the outstanding question appears to be the location and the amount of ices and methane present in their outer layers. Both the two-and the three-layer models are moderately successful. Serious difficulties arise from the considerable uncertainties concerning the rotational periods of both planets. Also the estimates of the internal heat fluxes and of the magnetic fields of both planets are not sufficiently certain. It is hoped that the forthcoming flyby of these two planets by a Voyager spacecraft will provide important new data for a future study of their interiors. 相似文献
4.
A. Banerjee Abhik Kumar Sanyal Subenoy Chakraborty 《Astrophysics and Space Science》1990,166(2):259-268
In this paper we study the exact solutions for a viscous fluid distribution in Bianchi II, VIII, and IX models. The metric is simplified by assuming a relationship between the coefficients of the metric tensor. Solutions are obtained in two special cases: in one an additional assumption is made where the matter density and the expansion scalar have a definite relation and in the other a barotropic equation of state of the formp= is assumed. While the Bianchi II solutions are already found in the literature the other two classes of solutions are apparently new. 相似文献
5.
In this paper we have presented a method of obtaining varieties of new parametric classes of spherically symmetric analytic
solutions of the general relativistic field equations in canonical coordinates. A number of previously known classes of solutions
has been rediscovered which describe perfect fluid balls with infinite central pressure and infinite central density though
their ratio is positively finite and less then one. From the solutions of one of the class we have constructed a causal model
of polytrope with constant sound speed Corresponding to the polytrope model we have maximized the Neutron star mass 3.26 M⊙ with the linear dimensions 32.27 kms with surface red shift 0.7355 and for other class we have constructed a causal model
in which outmarch of pressure and density is monotonically decreasing and pressure–density ratio is positive and less than
1 throughout with in the ball. Corresponding to this model we have maximized the Neutron star mass 3.09 M⊙ with the linear dimensions 30.55 kms with surface red shifts 0.5811. 相似文献
6.
7.
Multi-dimensional cosmological models with n(n > 1) Ricci-flat spaces and a scalar field are discussed classically and with respect to canonical quantization. These models are integrable. Two classes of solutions are obtained. One class of solutions generalizes the Kasner solutions. For special additional conditions we find another solution describing extended inflation connected with a constant volume of the whole multidimensional space (steady-state). 相似文献
8.
Katherine M. GIETZEN Claud H. S. LACY Daniel R. OSTROWSKI Derek W. G. SEARS 《Meteoritics & planetary science》2012,47(11):1789-1808
Abstract– We have obtained near‐infrared spectra for near‐Earth asteroids (NEA) and Main Belt asteroids by using NASA’s Infrared Telescope Facility. Most of the S complex classes of the Tholen‐Bus‐DeMeo scheme and the S(I)–S(VII) classes are represented. To help interpret the results, we examined visible/near‐IR spectra for ordinary chondrites. The unequilibrated ordinary chondrites (UOC) spectra contain a 2.3 μm feature which is absent in the spectra of the equilibrated ordinary chondrites (EOC). On the basis of literature data and new spectra low‐Ca clinopyroxenes, we suggest that the 2.3 μm in UOC is due to the presence of low‐Ca clinopyroxene in the UOC which is absent in EOC. While this difference can be seen in the raw spectra, we confirmed this observation using a modified Gaussian model (MGM) for spectral analysis. Both the UOC and the EOC plot in the S(IV) field of the band area ratio plot for asteroids. We suggest that many or most S(IV) asteroids have material resembling UOC on their surfaces. An internally heated ordinary chondrite parent object would have EOC material at depth and UOC material on the surface. Cosmic ray exposure ages, and K‐Ar ages for L chondrites, indicate that most EOC came from relatively few objects; however, the age distributions for UOC are unlike those of EOC. We suggest that while EOC come from the interiors of a limited number of S(IV) asteroids, the UOC come from the surfaces of a large number of S(IV) asteroids. 相似文献
9.
Primo? Kajdi? Xochitl Blanco-Cano Christopher T. Russell 《Planetary and Space Science》2011,59(8):705-714
In this work we perform the first multi-spacecraft analysis of two foreshock cavitons observed by the Cluster spacecraft. We also study the characteristics of their surrounding regions. Foreshock cavitons are a relatively new type of phenomena in the Earth's foreshock. They appear in regions deep inside the foreshock and are therefore always immersed in a sea of ULF waves and suprathermal particles. In the observational data the cavitons appear as simultaneous depressions of interplanetary magnetic field and plasma density. The two cavitons presented here have highly structured interiors and exhibit surface irregularities. They propagate sunwards in the reference frame of the solar wind plasma. Since their velocities are smaller than the solar wind velocity, the cavitons are convected towards the Earth by the solar wind flow. Their sizes are comparable to the size of the Earth. We show that the cavitons are different from other foreshock phenomena, such as cavities. The latter are thought to form by thermal expansion due to the excess of thermal pressure caused by intense flux of suprathermal ions in their interiors. Thermal pressure inside the cavitons is the same as in their surroundings, so they cannot form in this way. The proposed mechanism for the caviton formation includes nonlinear interactions between different types of ULF waves deep inside the foreshock. 相似文献
10.
Salah Haggag 《Astrophysics and Space Science》1995,225(1):137-149
Einstein field equations for a static and spherically symmetric perfect fluid are considered. A formulation given by Patiño and Rago is used to obtain a class of nine solutions, two of them are Tolman solutions I, IV and the remaining seven are new. The solutions are the correct ones corresponding to expressions derived by Patiño and Rago which have been shown by Knutsen to be incorrect. Similar to Tolman solution IV each of the new solutions satisfies energy conditions inside a sphere in some range of two independent parameters. Besides, each solution could be matched to the exterior Schwarzschild solution at a boundary where the pressure vanishes and thus the solutions constitute a class of new physically reasonable stellar models. 相似文献
11.
D. Lorenz-Petzold 《Astrophysics and Space Science》1984,98(1):101-113
Using a new method of reduction of the Brans-Dicke vacuum field equations we derive exact vacuum solutions for the class of spatially homogeneous space-times in a unified manner. Exact solutions are given for the isotropic Friedmann-Robertson-Walker models as well as for the anisotropic Bianchi types I-IX and for the related Kantowski-Sachs model. 相似文献
12.
Noam Slonim Rachel Somerville Naftali Tishby Ofer Lahav 《Monthly notices of the Royal Astronomical Society》2001,323(2):270-284
A new method for classification of galaxy spectra is presented, based on a recently introduced information theoretical principle, the information bottleneck . For any desired number of classes, galaxies are classified such that the information content about the spectra is maximally preserved. The result is classes of galaxies with similar spectra, where the similarity is determined via a measure of information. We apply our method to ∼6000 galaxy spectra from the ongoing 2dF redshift survey, and a mock-2dF catalogue produced by a cold dark matter (CDM) based semi-analytic model of galaxy formation. We find a good match between the mean spectra of the classes found in the data and in the models. For the mock catalogue, we find that the classes produced by our algorithm form an intuitively sensible sequence in terms of physical properties such as colour, star formation activity, morphology, and internal velocity dispersion. We also show the correlation of the classes with the projections resulting from a principal component analysis. 相似文献
13.
Using published laboratory data for H2O ice, we have developed a modeling technique by which the bulk density, density and temperature profile, rotational moment of inertia, central pressure, and location of the rock-ice interface can all be obtained as a function of the radius, the heliocentric distance, and the silicate composition. Models of the interiors of Callisto, Ganymede, Europa, Rhea, and Titan are given, consistent with present mass and radius data. The radius and mass of spheres of ice under self-gravitation for two different temperature classes are given (103 and 77°K). Measurements of mass, radius, and I/MR2 by spacecraft can be interpreted by this model to yield substantial information about the internal structure and the ice: rock ratio of the icy satellites of Jupiter and Saturn. 相似文献
14.
We report observations of a set of surface features on Mars that form a distinct class of avalanche scars. These features have a horizontal scale of hundreds of meters, but a depth scale of meters distinguishes them from the shallower features known as slope streaks. The meters-thick avalanche scars have escaped previous attention because of weak contrast between the interiors of the scarred regions and their surroundings. Often the most visible feature is a shadow cast by the trough wall, a band 1-3 pixels wide in Mars Orbiter Camera narrow angle images, indicating maximum depths of 4-10 m. We investigate the morphology of more than 500 such features. Slopes upon which the avalanches occur average about 27°. Impact craters are seen at the heads of some avalanche scars; this subset exhibits statistically wider opening angles. The scars span an estimated several Ma in age. Those found so far occurred mainly in the Olympus Mons lower aureole. We compare shapes of slope streaks to shapes of meters-thick avalanches, and the results support the notion that the two classes are distinct. The newly-discovered avalanches resemble some terrestrial flows of loose, dry material such as dry snow and glass beads. On the basis of these analogs, we suggest a physical model. 相似文献
15.
J. E. Horvath 《Astrophysics and Space Science》1992,187(2):329-332
Pion condensates can help to explain a variety of physical properties owned by pulsars if they are present in their interiors. It has been noted that they offer, for example, an attractive alternative to understand glitches by improving former core-quake models. We discuss this scenario and show in this work some constraints on the properties of this type of matter arise from X-ray observations of the Vela pulsar performed by theEinstein Observatory. Further information on this subject will be soon obtained from improved facilities and we expect them to give further constraints to the viability of those models. 相似文献
16.
Models of the giant planets were constructed based on the assumption that the hydrogen to helium ratio is solar in these planets. This assumption, together with arguments about the condensation sequence in the primitive solar nebula, yields models with a central core of rock and possibly ice surrounded by an envelope of hydrogen, helium, methane, ammonia, and water. These last three volatiles may be individually enhanced due to condensation at the period of core formation. Jupiter was found to have a core of about 40 earth masses and a water enhancement in the atmosphere of about 7.5 times the solar value. Saturn was found to have a core of 20 earth masses and a water enhancement in the atmosphere of about 25 times the solar value. Rock plus ice constitute 75–85% of the mass of Uranus and Neptune. Temperatures in the interiors of these planets are probably above the melting points, if there is an adiabatic relation throughout the interiors. Some aspects of the sensitivities of these results to uncertainties in rotational flattening are discussed. 相似文献
17.
Claudia‐Corina Giese Inge Loes Ten Kate Oliver Plümper Helen E. King Christoph Lenting Yang Liu Alexander G. G. M. Tielens 《Meteoritics & planetary science》2019,54(9):1930-1950
Large polycyclic aromatic hydrocarbons (PAHs) are an important component of the interstellar medium. PAHs have been identified in the soluble and insoluble matter of carbonaceous chondrites (CCs). Here, we study the evolution of PAHs under conditions relevant to the interiors of asteroids and compare our results to PAHs observed in CCs. We have performed long‐term and short‐term hydrothermal experiments, in which we exposed PAH‐mineral mixture analogs of meteorites to temperature conditions representative of those predicted for asteroids interiors. Our results show that small PAHs with melting points within the aqueous alteration temperature of CCs form carbonaceous spherules in the presence of water. In this work, we describe the microstructure and morphology of these spherules. We discuss the similarities and differences compared to globules isolated from CCs. 相似文献
18.
The present study deals with the inhomogeneous plane symmetric models in scalar-tensor theory of gravitation. We used symmetry group analysis method to solve the field equations analytically. A new class of similarity solutions have been obtained by considering the inhomogeneous nature of metric potential. The physical behavior and geometrical aspects of the derived models are also discussed. 相似文献
19.
In the present paper we apply a new method of distinction between ordered and chaotic motion in galactic potentials. The method uses the Fourier Transform of a series of time intervals each one representing the time that elapsed between two successive points on the Poincaré surface of section. Examples of the methods ability to achieve an early and clear detection of an orbit's behavior are provided using two galactic potentials. The new method can also be applied in order to have an early distinction between ordered and sticky orbits. The method is generalized in order to be used in models with more than two dimensions. Finally we have tried to find an one‐number index to give us the nature of the orbit instead of checking by eye the whole spectrum. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
Mark J. Lupo 《Icarus》1982,52(1):40-53
Using improved data for the masses and radii of the satellites of Jupiter and Saturn, models accounting for self-compression effects are presented for the interiors of Europa, Ganymede, Callisto, Rhea, and Titan. For the differentiated models, two different possible scenarios for heat transport are treated, as well as two different compositions for the silicate component. Undifferentiated models are also treated. In each case, the models of Ganymede, Callisto, and Titan show noticeable similarities. It is found that estimates of the ice-rock ratio are dependent upon the assumptions made about the heat transport mechanisms, the rock composition, and on the distribution of rock and ice in the satellite's interior. 相似文献