共查询到20条相似文献，搜索用时 62 毫秒
1.
Carl Bowin 《Icarus》1983,56(2):345-371
The gravity anomalies of Venus, although small by comparison with those on Mars and the Moon, are still much larger than those on Earth for large features. On Venus, even the low-degree spherical harmonic terms for Venus' gravity field indicate a close association of broad positive gravity anomalies with major topographic highs. This is striking contrast to the situation on Earth, where the broad regional gravity anomalies show little correlation with continental masses or plate tectonic features, but instead appear to be caused by deep mass anomalies.A method for estimating radial gravity anomalies from line-of-sight acceleration data, their interpolation, and use of iteration for improved radial anomaly estimates is outlined. A preliminary gravity anomaly map of Venus at spacecraft altitude prepared using first estimate values is presented. A profile across the western part of Aphrodite along longitude 85 E was analyzed using time-series techniques. An elastic plate model would require a plate thickness of about 180 to 200 km to match the general amplitude of the observed gravity anomaly (about 33 mgal): a thickness much greater than that found for earth structures and, because of high surface temperatures, unlikely for Venus. An Airy isostatic model convolved with the topography across Aphrodite, however, provides a better match between the predicted and observed gravity anomalies if the nominal crustal thickness is about 70 to 80 km. This thickness is over twice that for continental crust on the earth, and considerably greater than that of the earth's basaltic ocean crust (only 5 km). A different differentiation history for Venus than that of the earth thus is anticipated. High gravity anomalies (+110 mgal) occur over Beta Regio and over the topographic high in eastern Aphrodite; both highs are associated with regions where detected lightning is clustered, and thus the topographic features may be active volcanic constructs. The large gravity anomalies at these two sites of volcanic activity require an explanation different than that indicated for western Aphrodite. 相似文献
2.
M. Šidlichovskyý 《Celestial Mechanics and Dynamical Astronomy》1983,29(3):295-305
The Hamiltonian of three point masses is averaged over fast variablel and ll (mean anomalies) The problem is non-planar and it is assumed that two of the bodies form a close pair (stellar three-body problem). Only terms up to the order of (a/á)4 are taken into account in the Hamiltonian, wherea andá are the corresponding semi-major axes. Employing the method of elimination of the nodes, the problem may be reduced to one degree of freedom. Assuming in addition that the angular momentum of the close binary is much smaller than the angular momentum of the motion of the binary around a third body, we were able to solve the equation for the eccentricity changes in terms of the Jacobian elliptic functions. 相似文献
3.
In this paper, we conduct a new statistical study on the temporal distribution of the Global Positioning System Total Electron Content (GPS TEC) anomalies prior to the earthquakes with magnitude M≥7.0 in the global area during 2003–2012 by the method of statistical analysis. The temporal distribution of the ionospheric TEC anomalies prior to the earthquakes with magnitude M≥7.0 is for the first time studied. It has been observed that the ionospheric negative anomalies mainly occur in one week prior to the earthquakes, and only when the magnitude is greater than or equal to 7.6, the ionospheric anomalies will have the greatest probability of occurrence in the afternoon to sunset (i.e. between 12:00 and 18:00 local time). They last for approximate 2 hr, but the chance of detecting the significant enhancement in the ionospheric TEC seems not to be a function of time and there is no clear tendency for positive anomalies. In addition, the relationship of the occurrence rate of pre-earthquake ionospheric anomalies and the magnitude of the earthquake is discussed, and it is found that the observed ionospheric TEC anomalies within several days before the earthquakes are highly likely to be related with the earthquakes because the occurrence rate of pre-earthquake ionospheric anomalies seems to increase slightly with the earthquake magnitude increasing. 相似文献
4.
The relation between gravity anomalies, topography and volcanism can yield important insights about the internal dynamics of planets. From the power spectra of gravity and topography on Earth, Venus and Mars we infer that gravity anomalies have likely predominantly sources below the lithosphere up to about spherical harmonic degree l=30 for Earth, 40 for Venus and 5 for Mars. To interpret the low-degree part of the gravity spectrum in terms of possible sublithospheric density anomalies we derive radial mantle viscosity profiles consistent with mineral physics. For these viscosity profiles we then compute gravity and topography kernels, which indicate how much gravity anomaly and how much topography is caused by a density anomaly at a given depth. With these kernels, we firstly compute an expected gravity-topography ratio. Good agreement with the observed ratio indicates that for Venus, in contrast to Earth and Mars, long-wavelength topography is largely dynamically supported from the sublithospheric mantle. Secondly, we combine an empirical power spectrum of density anomalies inferred from seismic tomography in Earth’s mantle with gravity kernels to model the gravity power spectrum. We find a good match between modeled and observed gravity power spectrum for all three planets, except for 2?l?4 on Venus. Density anomalies in the Venusian mantle for these low degrees thus appear to be very small. We combine gravity kernels and the gravity field to derive radially averaged density anomaly models for the Martian and Venusian mantles. Gravity kernels for l?5 are very small on Venus below ≈800 km depth. Thus our inferences on Venusian mantle density are basically restricted to the upper 800 km. On Mars, gravity anomalies for 2?l?5 may originate from density anomalies anywhere within its mantle. For Mars as for Earth, inferred density anomalies are dominated by l=2 structure, but we cannot infer whether there are features in the lowermost mantle of Mars that correspond to Earth’s Large Low Shear Velocity Provinces (LLSVPs). We find that volcanism on Mars tends to occur primarily in regions above inferred low mantle density, but our model cannot distinguish whether or not there is a Martian analog for the finding that Earth’s Large Igneous Provinces mainly originate above the margins of LLSVPs. 相似文献
5.
Earthquakes are one of the most destructive and harmful natural disasters, especially in recent years, the 2008/5/12 Wenchuan M7.9 earthquake, the 2011/3/11 Tohoku M9.0 earthquake and the 2012/4/11 Sumatra M8.6 earthquake have caused a significant impact to the human life. In this paper, we make a study of the temporal and spatial distribution of the Global Positioning System Total Electron Content (GPS TEC) anomalies prior to the three strong earthquakes by the method of statistical analysis. Our results show that the pre-earthquake ionospheric anomalies are mainly positive anomalies and take the shape of a double-crest structure with a trough near the epicenter. The ionospheric anomalies do not coincide with the vertical projection of the epicenter of the subsequent earthquake, but mainly localize in the near-epicenter region and corresponding ionospheric anomalies are also simultaneously observed in the magnetic conjugate region prior to the three earthquakes. In addition, the amplitude and scale-size of the ionospheric ΔTEC are different with the magnitude of the earthquake, and the horizontal scale-size of the greatest anomalies before the Tohoku M9.0 earthquake is ～30° in longitude and ～10° in latitude, with the maximum amplitude of TEC disturbances reaching ～20 TECu relative to the background. The peak of anomaly enhancement usually occurs in the afternoon to sunset (i.e. between 14:00 and 18:00 local time) which lasts for approximate 2 hours. Possible causes of these anomalies are discussed, and after eliminating the effect of solar activities and magnetic storms it can be concluded that the detected obvious and regular anomalous behavior in TEC within just a few days before the earthquakes is related with the forthcoming earthquakes with high probability. 相似文献
6.
Radio Doppler data, generated with NASA's Galileo spacecraft during its second encounter with Jupiter's moon Ganymede, are used to infer the locations and magnitudes of mass anomalies on Ganymede. We construct models for both surface and buried anomalies. With only one flyby and no global coverage, a solution for mass anomalies cannot be uniquely determined. However, we are able to constrain acceptable solutions for mass anomalies to four broad regions—a near polar region and three that are roughly equatorial. If the mass anomalies are constrained to lie at the surface, the centers of the regions are located near the coordinates (77° N, 333° W), (36° N, 0° W), (33° N, 130° W), and (7° N, 194° W). If the mass anomalies are located at the deep ice-rock interface 800 km below the surface, the regions' centers are approximately (65° N, 17° W), (32° N, 30° W), (37° N, 175° W), and (15° N, 211° W). For both models, the regions are up to a few thousand kilometers across. The magnitude of mass anomalies on the surface is on the order of 1017 kg. Mass anomalies at the ice-rock interface are on average no more than an order of magnitude larger (1018 kg). There are two positive and two negative mass anomalies in both the surface and ice-rock interface models. One of the positive mass anomalies at the surface is associated with Galileo Regio. The other positive surface mass anomaly is located at high northern latitudes with no obvious geological association. Negative surface mass anomalies lie near Uruk Sulcus and between Perrine Regio and Barnard Regio near Sicyan Sulcus and Phrygia Sulcus. The locations of the ice-rock interface mass anomalies lie approximately radially below the surface anomalies. Positive mass anomalies at the surface could be associated with the silicate-rich ice or accumulated silicate layers of the dark regions. Negative mass anomalies at the surface could be associated with the relatively clean, low-lying ice of sulci. Alternatively, Ganymede's mass anomalies could be associated with the topography or other mass concentrations at the deep ice-rock interface. 相似文献
7.
Consecutive collision orbits in the limiting case µ = 0 of the elliptic restricted three-body problem are investigated. in particular those in which the infinitesimal mass collides twice with the smaller (massless) primary. A timing condition is presented that allows the extension of previous results to the case of arbitrary relative orientation of the orbits of the infinitesimal mass and the smaller primary. The timing condition is expressed in two general forms - in terms of orbit parameters and eccentric (or hyperbolic) anomalies at the times of collision - for the specific cases of elliptic. parabolic or hyperbolic orbits of the infinitesimal mass. Some families of solutions are presented. 相似文献
8.
Previously, radio Doppler data, generated with NASA's Galileo spacecraft during its second encounter with Jupiter's moon Ganymede, were used to infer the locations and magnitudes of mass anomalies on Ganymede using point-mass models. However, the point-mass solutions do not provide the vertical and horizontal extent of the anomalous mass concentrations. Here, we provide the results of a new study using spherical cap disks to model Ganymede's mass anomalies. The spherical cap disk models not only provide the locations and magnitudes of the mass anomalies, but also their vertical and horizontal dimensions. The new models show that three disks, a positive mass located at (53.0° N, 127.0° W) and two negative masses located at (22.0° N, 87.0° W) and (49.0° N, 219.0° W), can explain the data. The magnitudes of the mass anomalies are on the order of 1018 kg. The diameters of the anomalies are a few thousand kilometers. The positive anomaly is about 100 meters thick and both negative anomalies have a thickness of less than a kilometer. We use the additional information provided by the disk models to investigate the viability of mass anomalies at Ganymede's surface by comparing the diameters of the anomalies to the sizes of regiones and sulci and the anomalies' thicknesses to accumulated layers of rock and clean ice on the surface. We find that the dimensions of the mass anomalies could be explained by concentrations of rock in the regio and rock-free ice in the sulci. These results confirm that mass anomalies may reside on or near Ganymede's surface and that positive mass anomalies are contained within areas of dark terrain and negative mass anomalies within bright terrain. 相似文献
9.
T. Jaakkola N. Holsti E. Laurikainen P. Teerikorpi 《Astrophysics and Space Science》1984,107(1):85-107
In the maps of the galactic structure based on the kinematical method, several systematic heliocentric anomalies are found: in the northern galactic hemisphere the spiral arms are more tightly wound and the extent of neutral hydrogen is smaller than in the southern hemisphere; with separate rotation curves for the north and the south the arms become anomalously circular with a consequent discrepancy to the stellar distribution; there are straight portions in the arms pointing towards the Sun, as well as systematic strong curvatures and knee-like features; the inner arms affect the structure of the outer arms; with the northern rotation model, Hii-regions and Hi avoid the southern tangential circle; in the rear of the Galaxy, at symmetric longitudes, enhanced Hi-densities are found; the Perseus arm is displaced atl=180°. All of these anomalies can be explained with a simple model involving a non-velocity redshift field within the Galaxy, with an enhancement within the spiral arms. This is demonstrated by numerical simulations of the structural anomalies. Reducing the redshift effect from the kinematic data, the Galaxy's structure and kinematics appear symmetric. The significance of the result for the redshift problem is discussed. 相似文献
10.
Transformations are given which change the perturbed planar problem of two bodies into unperturbed and undamped harmonic oscillators with constant coefficients. The orginally singular, nonlinear and Lyapunov unstable equations become in this way regular, linear, and the stable solution may be written down immediately in terms of the new variables. Transformations of the independent and dependent variables are treated separately as well as jointly. Using arbitrary and special functions for the transformations allows a systematic discussion of previously introduced and new anomalies. For the unperturbed two-body problem the theorem is proved according to which if the transformations are power-functions of the radial variable, then only the eccentric and the true anomalies with the corresponding transformations of the radial variable will result in harmonic oscillators. Important practical applications are to increase autonomous operations in space, since by replacing lengthy numerical integrations by transformations, computer requirements are significantly reduced. 相似文献
11.
We calculate the expression forΔ
-s in terms of true anomalies and classical orbital elements, referring to a common fixed plane and working up to power four
of eccentricities and tangents of inclinations. We obtained two final results: the first wheny
′>y, the second wheny>y
′. 相似文献
12.
Donald D. Clayton 《Earth, Moon, and Planets》1978,19(2):109-137
Chemical and isotopic anomalies in meteorites may be understandable in terms of the chemical fractionation routinely expected in the interstellar medium (ISM). Dust of distinct composition is idealized as being of three types: (1) thermal supernova condensates (SUNOCONS), (2) thermal condensation during other stellar mass-loss processes (STARDUST), and (3) nonthermal sticking processes in cold nebulae (NEBCONS). Great depletions in ISM of Ca Al Ti are due to SUNOCONS, although STARDUST is about twice as abundant. An abundance table of interstellar SUNOCONS is presented. Parent bodies in the solar system are accumulated directly from the ISM. No hot solar condensation sequence is assumed. Only relatively volatile elements within NEBOCONS are vaporized in the warm solar accretion disk. Variations in the relative amounts of these components during accumulation processes plus subsequent solid chemistry may have produced such chemical anomalies as the meteoritic fractionation patterns and the Ca Al-rich inclusions. Isotopic anomalies result from four processes that selectively site specific isotopes: (1) extinct radioactivities, (2) distinct supernova shells, (3) gas-dust separation, and (4) gas-dust age difference. Planetary accumulation will have been fingerprinted by the chemical state of the ISM if this picture is correct.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978. 相似文献
13.
David A. Allen 《Earth, Moon, and Planets》1971,2(4):435-462
This paper presents an infrared study of thermal anomalies during the lunar night. From observations of the most intense anomalies at several wavelengths it is deduced that fields of boulders are responsible for the thermal enhancement; the cooling curves of the remainder are consistent with such a model. High resolution Lunar Orbiter photographs of some of the thermal anomalies reveal boulders to be present within them in just the right numbers. The ages and distribution of thermal anomalies are discussed in the light of this model. 相似文献
14.
Lon L. Hood 《Icarus》2011,211(2):1109-218
A re-examination of all available low-altitude LP magnetometer data confirms that magnetic anomalies are present in at least four Nectarian-aged lunar basins: Moscoviense, Mendel-Rydberg, Humboldtianum, and Crisium. In three of the four cases, a single main anomaly is present near the basin center while, in the case of Crisium, anomalies are distributed in a semi-circular arc about the basin center. These distributions, together with a lack of other anomalies near the basins, indicate that the sources of the anomalies are genetically associated with the respective basin-forming events. These central basin anomalies are difficult to attribute to shock remanent magnetization of a shocked central uplift and most probably imply thermoremanent magnetization of impact melt rocks in a steady magnetizing field. Iterative forward modeling of the single strongest and most isolated anomaly, the northern Crisium anomaly, yields a paleomagnetic pole position at 81° ± 19°N, 143° ± 31°E, not far from the present rotational pole. Assuming no significant true polar wander since the Crisium impact, this position is consistent with that expected for a core dynamo magnetizing field. Further iterative forward modeling demonstrates that the remaining Crisium anomalies can be approximately simulated assuming a multiple source model with a single magnetization direction equal to that inferred for the northernmost anomaly. This result is most consistent with a steady, large-scale magnetizing field. The inferred mean magnetization intensity within the strongest basin sources is ∼1 A/m assuming a 1-km thickness for the source layer. Future low-altitude orbital and surface magnetometer measurements will more strongly constrain the depth and/or thicknesses of the sources. 相似文献
15.
P. Vielva Y. Wiaux E. Martínez-González P. Vandergheynst 《Monthly notices of the Royal Astronomical Society》2007,381(3):932-942
Significant alignment and signed-intensity anomalies of local features of the cosmic microwave background (CMB) are detected on the three-year Wilkinson Microwave Anisotropy Probe data, through a decomposition of the signal with steerable wavelets on the sphere. In addition to identifying local features of a signal at specific scales, steerable wavelets allow one to determine their local orientation and signed intensity. First, an alignment analysis identifies two mean preferred planes in the sky, both with normal axes close to the CMB dipole axis. The first plane is defined by the directions towards which local CMB features are anomalously aligned. A mean preferred axis is also identified in this plane, located very close to the ecliptic poles axis. The second plane is defined by the directions anomalously avoided by local CMB features. This alignment anomaly provides further insight on recent results. Secondly, a signed-intensity analysis identifies three mean preferred directions in the southern Galactic hemisphere with anomalously high or low temperature of local CMB features: a cold spot essentially identified with a known cold spot, a second cold spot lying very close to the southern end of the CMB dipole axis, and a hotspot lying close to the southern end of the ecliptic poles axis. In both analyses, the anomalies are observed at wavelet scales corresponding to angular sizes around 10° on the celestial sphere, with global significance levels around 1 per cent. Further investigation reveals that the alignment and signed-intensity anomalies are only very partially related. Instrumental noise, foreground emissions and some form of other systematics are strongly rejected as possible origins of the detections. An explanation might still be envisaged in terms of a global violation of the isotropy of the Universe, inducing an intrinsic statistical anisotropy of the CMB. 相似文献
16.
A variety of recent resurfacing features have been observed on Europa, which may produce thermal anomalies detectable by a future mission. However, the likelihood of such a detection depends on their size and lifetimes. The results of this numerical study suggest that the lifetime of a thermal anomaly associated with the emplacement of 100 m of water onto the surface of Europa is several hundred years, and ∼10 years for 10 m of water. If warm ice is emplaced on the surface instead of liquid water, these lifetimes decrease by up to a factor of two. Exploration of model parameters indicates that a thin insulating surface layer can double thermal anomaly lifetimes, anomalies emplaced at a latitude of 80° can remain detectable nearly a factor of two longer than those at equatorial latitudes, and anomalies on the night side can remain detectable for up to ∼20% longer than those on the day side. High temperatures are very short-lived as the surface ice cools very rapidly to below 200 K due to sublimation cooling. Assuming steady-state resurfacing, the number of detectable thermal anomalies associated with the emplacement of 100 m of water would be on the order of 10 if the typical resurfacing area is 15 km2. If recent resurfacing is dominated by chaos regions with typical areas of 100 to 1000 km2 and lifetimes of 1000 to 4000 years, the number of detectable thermal anomalies would be on the order of 1 to 10. 相似文献
17.
Peter Janle 《Earth, Moon, and Planets》1981,24(4):441-451
LOS Bouguer gravity anomalies have been calculated from a low altitude LOS free air Doppler gravity profile across northern Mare Fecunditatis, southern Mare Tranquillitatis and the Aridaeus Rille. The Hyginus-Triesnecker area has been included in model calculations, though here only free air anomalies are present. A crustal density model has been fitted to the Bouguer anomalies and to the free air anomalies in the case of the Hyginus-Triesnecker area.On a regional scale northern Fecunditatis has Bouguer anomalies up to 80 mgal and lithostatic stresses of 29 bar and thus is nearly in isostatic equilibrium. Tranquillitatis can be divided into three regions of different crustal structure: (1) northern Tranquillitatis with only minor free air gravity anomalies is more or less in isostatic balance, (2) the southeastern region with Bouguer anomalies to –100 mgal and lithostatic stresses of –73 bar has a considerable mass deficit, (3) the southwestern basin is dominated by the local structure Lamont with a Bouguer maximum of 200 mgal and extremely high lithostatic stresses of 285 bar.The Bouguer minimum of –180 mgal of the Aridaeus area has been modelled by two alternative models: (i) a crustal thickening of 33 km and associated lithostatic stresses of –164 bar, and (ii) a crustal thickening of 20 km plus a low density intrusion. The free air maximum of the Hyginus-Triesnecker area has been fitted by a mantle plug connected with stresses of 116 bar.As the old irregular maria could not sustain large mascon stresses, it has been concluded that the local high stresses of Lamont, Aridaeus, and Hyginus-Triesnecker have been evolved after the impacts of the circular maria. Intrusional activities in these areas could have proceeded to fault zones generated by the large impacts.Contribution No. 211, Institut für Geophysik der Universität Kiel, F.R.G. 相似文献
18.
I. S. Savanov 《Astrophysics》1996,39(2):107-111
The abundances of 12 elements in the atmosphere of the "F str 4077" star HD 177645 have been determined from new spectroscopic observations with the CCD camera and the model atmosphere method. The overabundance of nitrogen found for this star indicates its possible relation to barium dwarfs with anomalies in the chemical composition of their atmospheres due to mass transfer from the more evolved companion in a binary system. As an object related to Ba stars and CH subgiants, HD 177645 with an effective temperature Teff=7150K may also have anomalies in the chemical composition characteristic of diffusion processes in chemically peculiar stars of the upper main sequence, as may be indicated by the overabundance of sulfur in its atmosphere.Translated fromAstrofizika, Vol. 39, No. 2, pp. 201–209, April–June, 1996. 相似文献
19.
20.
East-west trending magnetic anomalies in the Southern Hemisphere of Mars: Modeling analysis and interpretation 总被引：1，自引：0，他引：1
Maps of the vector components of the martian crustal magnetic field over the strongly magnetized Terra Cimmeria/Sirenum region are constructed using Mars Global Surveyor magnetometer data. Although pronounced east-west trending anomalies are present on the radial and north field component maps at the mapping altitude (∼360-380 km), these trends are much less prominent at the lower aerobraking altitude (∼90-150 km). Comparisons with similar maps produced using artificial data at the aerobraking altitude indicate that elongated sources in this region may have maximum lengths along the martian surface of ∼500 km and maximum aspect ratios of ∼2. Iterative forward modeling of several relatively isolated anomalies in the mapped region yields paleomagnetic pole positions consistent with those estimated in previous studies of other anomalies using mapping phase and science phasing orbit data. On this basis, it is inferred that sources in the studied region are most probably magnetized primarily in northward or southward directions. Using this additional constraint, iterative forward modeling is then applied to determine a magnetization distribution that is consistent with data at both the aerobraking altitude and the mapping altitude. The model magnetization distribution, which includes 41 discrete sources, again indicates no highly elongated sources. An examination of surface geology in the region as well as a consideration of the global distribution of anomalies suggests that magmatic intrusions (e.g., subsurface dike swarms), cooling in the presence of water, are the most likely sources of the magnetic anomalies. 相似文献