Showing papers in "Earth Moon and Planets in 1991"
TL;DR: In this paper, chemical compositions of the constituent minerals of 13 mafic and ultramafic assemblages containing from one to five mineral components were analyzed with an electron microprobe, and the compositions were correlated with the reflectance spectra of the samples to determine the spectral-compositional relationships.
Abstract: Chemical compositions of the constituent minerals of 13 mafic and ultramafic assemblages containing from one to five mineral components were analyzed with an electron microprobe, and the compositions were correlated with the reflectance spectra of the samples to determine the spectral-compositional relationships of these assemblages. Results indicate that, as more components are added to a mixture, the quality and quantity of compositional information which can be derived from spectral analysis diminishes. It is shown that opaque minerals (such as magnetite for terrestrial occurrences and ilmenite in lunar assemblages) influence reflectance spectra out of proportion to their abundances, reducing overall reflectance and band depths of mafic silicates in small dispersed amounts.
84 citations
TL;DR: In this article, new radar images obtained from the Arecibo Observatory for portions of the southern hemisphere of Venus are reported, showing that the upland of Phoebe Region contains the southern extension of Devana Chasma, a rift zone extending 4200 km south from Theia Mons.
Abstract: Results of new radar images obtained from the Arecibo Observatory for portions of the southern hemisphere of Venus are reported. The images show that the upland of Phoebe Region contains the southern extension of Devana Chasma, a rift zone extending 4200 km south from Theia Mons and interpreted as a zone of extension. Alpha Regio, the only large region of tesserae within the imaged area, is found to be similar to tesserae mapped elsewhere on the planet; it covers a smaller percentage of the surface than that observed in the northern high latitudes. Themis Region is mapped as an ovoid chain of radar-bright arcuate single- and double-ring structures, edifices, and bright lineaments. On the basis of the present analysis, the southern hemisphere of Venus is interpreted to be characterized by regions of mantle upwelling on a variety of scales, upwelling and extension, and localized compression.
22 citations
TL;DR: Clark and Hawke as discussed by the authors investigated the nature and origin of geochemical variation in a portion of the farside highlands east of the Smythii basin using available lunar orbital data.
Abstract: Available lunar orbital data were studied in detail to determine the nature and origin of geochemical variation in a portion of the farside highlands east of the Smythii basin. Such data exist for the elements Al, Mg, Fe, Ti, and Th (Clark and Hawke, 1981; Davis, 1980; Metzger et al., 1977). As in our previous studies (Clarke and Hawke, 1981, 1987), averages and ranges of concentrations for these elements are calculated and correlated for photogeologically defined units associated with features such as Babcock, King, Al-Khwarezmi, Langemak, Pasteur, and Sklodowska and with the region as a whole. In addition, comparisons are made between this and other highland regions which have been investigated by other workers in a similar manner (Andre et al., 1977; Haines et al., 1978; Maxwell and Andre, 1981). The region is shown to be distinctively enriched in the anorthositic end-members of the ANT-suite. Anomalies which have been reported for this region (Hawke et al., 1985) are confirmed by this study. An area south of Pasteur shows enrichment in some mafic components, giving evidence for the presence of buried mare basalt, and lending support to the hypothesis that volcanic activity may be fairly widespread even in the farside highlands. The units just southeast of Mare Smythii appear to be geochemically related to the area partly surrounding the Smythii on the west (Clark and Hawke, 1987). Considerable geochemical heterogeneity exists in this area, as in areas of the nearside highlands (Clark and Hawke, 1981, 1982, 1987; Hawke et al., 1985).
20 citations
TL;DR: The Tharsis rise on Mars with a diameter of about 8000 km and an elevation up to 10 km shows extensive volcanism and an extensional fracture system as mentioned in this paper, which can be explained by a heated upper mantle, a chemically modified upper mantle or a combination of these three processes.
Abstract: The Tharsis rise on Mars with a diameter of about 8000 km and an elevation up to 10 km shows extensive volcanism and an extensional fracture system. Other authors explained this structure by (I) an uplift due to mantle processes and by (II) volcanic construction. Gravity models of four profiles are in accordance with a total Airy isostatic compensation of the whole rise with mean crustal thicknesses of 50 km and 100 km. But two regions exhibit significant mass deficits: (i) the area between Olympus Mons and the three large Tharsis volcanoes and (ii) central Tharsis. This can be explained by (1) a heated upper mantle, (2) a chemically modified upper mantle, (3) a crustal thickening, or (4) a combination of these three processes. Crustal thickening is mainly a constructional process, but the mass deficit should contribute to a certain degree of uplift causing the extensional area of Labyrinthus Noctis. Gravity modelling results in a different isostatic state of the three Tharsis volcanoes. Pavonis Mons is not compensated, Ascraeus Mons is highly or totally compensated, and Arsia Mons is medium or not compensated. The large, flat volcanic structure Alba Patera has been explained by a hot spot with an evolution of a mantle diapir.
20 citations
TL;DR: In this paper, high-resolution spectra of Jupiter's decametric S-storms are studied with an acousto-optical radio spectrograph operating over the frequency range 20-30 MHz.
Abstract: High-resolution spectra of Jupiter's decametric S-storms are studied with an acousto-optical radio spectrograph operating over the frequency range 20–30 MHz. In 1985–1989 20 S-storms were recorded in the Io-B region. There is only a slight average zoning effect of certain types of fine structure in the Io-B region, with sporadic S-bursts occurring most often in the early CML values, and S-trains in the late values. Emissions of type N and its variants occur at lower values of the Io phase than S-emissions and their variants. There is no exact storm-to-storm correspondence, nor any Io-B-centered zones in which the various types of fine structure could be accurately placed. Every storm is different and has a ‘signature’ of its own. An important exception is formed by the wide-range quasi-periodic FDS-S storms that occur at the edge of the Io-B region with Io phase values greater than 80 ‡. These are outstanding storms in which the individual bursts may extend across the full spectral width of 20–30 MHz and be repeated in rapid succession at quasi-periodic rates of 20–40 s−1. It is suggested that these be referred to as type Q storms. It is estimated that only 10% of the S-burst types are recorded so far.
19 citations
TL;DR: In this article, the authors adopt a thorough and more direct approach to error analysis, whereby known topography is compared with photoclinometric profiles derived from synthetic quantised reflectance scans.
Abstract: The technique of photoclinometry has frequently been used to determine planetary topography without proper consideration of possible sources of error. Previous studies of error sources have been limited in extent and have overlooked the importance of factors such as atmospheric scattering and the choice of a surface photometric function. This paper adopts a thorough and more direct approach to error analysis, whereby known topography is compared with photoclinometric profiles derived from synthetic quantised reflectance scans.
15 citations
TL;DR: The geology of a portion of the equatorial region of Venus (1 deg S to 45 deg N and from 270 deg eastward to 30 deg) is assessed on the basis of new radar images obtained from the Arecibo Observatory.
Abstract: The geology of a portion of the equatorial region of Venus (1 deg S to 45 deg N and from 270 deg eastward to 30 deg) is assessed on the basis of new radar images obtained from the Arecibo Observatory. Nine geologic units are mapped on the basis of their radar characteristics, and their distribution and correspondences with topography are examined. Plains are the most abundant unit, comprising 80 percent of the area imaged, and are divided into bright, dark, and mottled. Mottled plains contain abundant lava flows and domes, suggesting that volcanism forming planes is a significant process in the equatorial region of Venus. Tesserae are found primarily on Beta Regio and its eastern flank and are interpreted to be locally stratigraphically older units, predating episodes of faulting and plains formation. On the basis of spatial and temporal relationships between geologic units, the highlands of Beta Regio and Western Eistla Regio are interpreted to have formed in association with areas of mantle upwelling which uplift plains, cause rifting, and, in the case of Beta Regio, disrupt a large region of tesserae.
14 citations
TL;DR: In this paper, a simple model algorithm for simulating the solar ultaviolet radiation reaching the surface of the Earth is presented, which is capable of providing both the direct and diffuse solar ultraviolet radiation, for different atmospheric conditions, time, and geographic locations.
Abstract: The purpose of this study is to present a new simple model algorithm for simulating the solar ultaviolet radiation reaching the surface of the Earth. The algorithm is capable of providing both the direct and diffuse solar ultraviolet radiation, for different atmospheric conditions, time, and geographic locations. An application of the model relates to the calculation of the minimum energy input of ultraviolet radiation to be received by a human to allow an erythema development.
14 citations
TL;DR: The full recurrent power series solution is established for J2-gravity perturbed motion in terms of the Eulerian redundant parameters, and a final state of very high accuracy is obtained for each case study.
Abstract: In this paper the full recurrent power series solution is established for J2-gravity perturbed motion in terms of the Eulerian redundant parameters. Applications of the method for the problem of the final state prediction are illustrated by numerical examples of some typical ballistic missiles, a final state of very high accuracy is obtained for each case study.
14 citations
TL;DR: In this article, the authors considered the restricted problem of three rigid bodies (an axisymmetric satellite in the gravitation field of two triaxial primaries) and obtained collinear and triangular equilibrium solutions.
Abstract: In this paper we consider the restricted problem of three rigid bodies (an axisymmetric satellite in the gravitation field of two triaxial primaries). The collinear and triangular equilibrium solutions are obtained. The effect of the primaries on the location of the libration points of a spherical satellite has been studied numerically.
12 citations
TL;DR: In this article, the authors study how distribution of small NH3 ice particles over shapes affects the strength of resonant absorption features at 9.4 and 26 Μm. The results of their computations support the conclusion of West et al. (1989) that small NH 3 ice particles cannot be the principal component of the Jovian troposphere in the 300-to 500-mbar region.
Abstract: We study how distribution of small NH3 ice particles over shapes affects the strength of resonant absorption features at 9.4 and 26 Μm. The T-matrix approach is used to compute optical cross sections for shape distributions of 0.5- and 1-Μm volume-equivalent radius spheroids in random orientation. It is found that the maximum of the resonant absorption for the shape distributions is 1.5–2 times smaller than that for equal-volume spherical particles, the absorption peak being shifted towards longer wavelengths. The results of our computations support the conclusion of West et al. (1989) that, apparently, small NH3 ice particles cannot be the principal component of the Jovian troposphere in the 300- to 500-mbar region.
TL;DR: In this paper, the maximum possible acceleration due to out-gassing from cometary nuclei is calculated for H2O and CO(N2) molecules, and it is found that the maximum excess velocity at great distance is 0.18 km s−1.
Abstract: Maximum possible acceleration due to out-gassing from cometary nuclei is calculated for H2O and CO(N2) molecules. It is found that the maximum excess velocity at great distance is 0.18 km s−1 so that excess velocities less than this value are compatible with the non-gravitational acceleration due to non-symmetric out-gassing. On the other hand, Comet 1975q and comet 1955V have excess velocities 0.81 and 0.80 km s−1 respectively. These comets may be regarded as the candidates for possible interstellar comets.
TL;DR: In view of the elastic deformation of the Earth, this article performed a comparative study for the Earth's models 1066 A and PREM, calculated the static Love numbers from degree 2 to 30, and discussed the relative variations of the second degree Love numbers and their combinations due to the variation of the position of the core-mantle boundary, due to redistribution of Vp, Vs, and θ in the lower mantle, and due to possible rigidity in the outer core.
Abstract: In view of the elastic deformation of the Earth we performed the comparative study for the Earth's models 1066 A and PREM, calculated the static Love numbers from degree 2 to 30, and discussed the relative variations of the second degree Love numbers and their combinations due to the variation of the position of the core-mantle boundary, due to the redistribution of Vp, Vs, and θ in the lower mantle, and due to the possible rigidity in the outer core. From the above-mentioned discussions we recommended that the Standard Earth Model (SEM) should include two kinds of models—one is oceanless, and another has an oceanic surface. Finally, we calculated the astronomicgeodetic parameters, which are consistent with the primary constants in the IERS Standards, of the SEM.
TL;DR: In this paper, the effect of mixed convection flow in the liquid phase on the melting phenomenon is discussed. But the main focus is on determining the effect that mixed convective flow in a porous medium has on melting phenomenon.
Abstract: The problem of melting from a flat plate embedded in a porous medium is studied. The main focus is to determine the effect of mixed convection flow in the liquid phase on the melting phenomenon. It is discussed of the numerical considerations of boundary conditions and coupling between the governing equations through buyoyancy and melting parameters. Computations have been made for assisting flow over a horizontal flat plate at zero incident, and for stagnation point flow about a horizontal impermeable surface. It is found that the parameter governing mixed convection in porous media is % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOuaiaabg% gacaqGVaGaaeikaiaabkfacaqGLbGaaeiuaiaabkhacaqGPaWaaWba% aSqabeaacaqGZaGaae4laiaabkdaaaaaaa!3F7E!\[{\text{Ra/(RePr)}}^{{\text{3/2}}} \]. The effects of buoyance and melting parameters variations on heat transfer characteristics about a heated horizontal surfaces are examined. The melting phenomenon decreases the local Nusselt number at the solid-liquid interface.
TL;DR: In this paper, the authors investigated the dynamical evolution of globular clusters in the Large Magellanic Cloud (LMC) by means of N-body simulations; particular attention is paid to time evolution in the ellipticitical figure of Globular clusters.
Abstract: Dynamical evolution of globular clusters in the Large Magellanic Cloud (LMC) is investigated by means of N-body simulations; particular attention is paid to time evolution in the ellipticitical figure of globular clusters. The simulations were started with a binary globular cluster. It merged into a single cluster with ellipticity of about 0.3. The simulations were continued until the cluster became rounder due to the effects of two body relaxation and of tidal field of LMC. It is found that the outward angular momentum transport due to the gravothermal contraction makes the inner region rounder; the ellipticity at about the initial half-mass radius (rh) decreases with the e-folding time of 20 relaxation times. On the other hand, the outer region becomes rounder due to the stripping of stars by the tidal field; the ellipticity at about 3rh decreases with the e-folding time of 80 crossing times therein, though the time scale depends on the direction of the tidal field relative to the spin of the cluster. These two effects are comparable at about the half-mass radius. Taking account of such theoretical results we reanalyzed observed data for the ellipticity at about the half-mass radius of LMC clusters. We estimated the relaxation time and crossing time for each of the observed clusters, from which we calculated the effective time of getting round of the cluster. We plotted the observed ellipticity of the clusters against their non-dimensional age — i.e., the age normalized by the effective time. We found that observed ellipticity distribution is consistent with our picture.
TL;DR: In this paper, the authors analyzed the emission fluxes of carbon-bearing molecular species observed in the coma of comets Rudnicki (1967II), Ikeya-Seki (1968I), Whitaker-Thomas (1968V), and Honda (1968VI).
Abstract: Emission fluxes of CN, C2 and C3 carbon-bearing molecular species observed in the coma of comets Rudnicki (1967II), Ikeya-Seki (1968I), Whitaker-Thomas (1968V), and Honda (1968VI) are analysed in the framework of Haser model. CN, C3 and C3 production rates are determined using recently derived fluorescence efficiencies. The dependence of CN, C2 and C3 production rates on the heliocentric distance and the possible correlations among these radicals is studied. It is shown that comets Ikeya-Seki (1968I) and Honda (1968VI) have the same mean color indices (B-V) and (U-B).
TL;DR: In this article, the relation between the locations of L1, L2 Lagrangian points and the boundary to their respective satellite system is brought forth, in that, the Lagrangians points L 1, L 2 are seen to lie just on the boundary of their respective satellites.
Abstract: The relation between the locations of L1, L2 Lagrangian points and the boundary to their respective satellite system is brought forth, in that, the Lagrangian points L1, L2 are seen to lie just on the boundary to their respective satellite system.
TL;DR: In this article, the authors have observed an outburst of P/Schwassmann-Wachmann 1 (SW1) on 25-26 July 1987 using a CCD imager with R-band filter.
Abstract: We have observed an outburst of P/Schwassmann-Wachmann 1 (SW1) on 25–26 July 1987 using a CCD imager with R-band filter. The total brightness increased from 15.5 mg (25d) to 14.4 mag (26d) during tabout 24 hrs. The southward elongated coma of 25″ was detected. The radial surface brightness (B) profiles are plotted against apparent distance p from the nucleus. The logarithmic derivative k = d ln B/d ln p for the inner coma is found to have steepened from k = −1.40 (25d) to k = −1.69 (26d), whereas that for the outer coma showed no appreciable change (k = −1.19 ~ −1.22). The ellipticity of the isophotal contour of the inner coma increased about 15% fro 25d to 6d. It is concluded that the scale of this outburst was smaller than the typical ones whose magnitude change is 5–8 mag. From recent findings on the outburst natur eof SW1 including ours, a working model of the nuclues is proposed.
TL;DR: In this paper, a fifth-order with respect to masses Jupiter-Saturn theory by Hori-Lie canonical technique is constructed, and the influence of the 2:5 critical terms is taken into consideration.
Abstract: We construct a fifth-order with respect to masses Jupiter-Saturn secular theory by Hori-Lie canonical technique. The J-S Hamiltonian includes both parts of the perturbing function. The influence of the 2:5 critical terms is taken into consideration. The Jacobi-Radau system of origins is adopted and the theory is expressed in terms of the Poincare canonical variables.
TL;DR: In this paper, a new method is developed to determine the concentration profiles of chemical species from satellite measurements, which takes into account the interaction of photochemical and radiative processes in the stratosphere and is applied for chemical species (nitric oxide and nitrogen dioxide) experiencing large diurnal changes.
Abstract: A new method is developed to determine the concentration profiles of chemical species from satellite measurements. The method takes into account the interaction of photochemical and radiative processes in the stratosphere and is applied for chemical species (nitric oxide and nitrogen dioxide) experiencing large diurnal changes. It is found that if the interaction of the photochemical and radiative processes is neglected, that is if the temporal and spatial variations of NO and NO2 are not considered in the radiative transfer calculations, the resulting errors for the concentration profiles for altitudes less than 20 km reach 100 and 5% respectively, for both sunset and sunrise. A photochemical scheme is developed capable of providing the mixing ratio profiles of NO and NO2 for different latitudes, altitudes and seasons and a retrieval code combining an iterative inversion algorithm, working from top of the atmosphere downwards, and a parameterization of the variability of NO and NO2 is also constructed. The method is used to examine the accuracy of the retrieval of the vertical concentration profiles and the new results show that the recovered profiles are in good agreement (error 5–15%) with measured profiles (WMO, 1985) and reflect the trends of NO and NO2 at sunset and sunrise.
TL;DR: In this article, it was shown that the departures in the figure parameters of the tri-axial Saturnian satellites orbiting in 1 : 1 resonance, from equilibrium figure parameters are not large in general, and the tidal and centrifugal distorting forces can be responsible for the actual figures.
Abstract: It has been demonstrated that dynamically the Saturnian system is analogous to the Jovian system; however, it is not an analogue of the Solar system as a whole. The departures in the figure parameters of the tri-axial Saturnian satellites orbiting in 1 : 1 resonance, from equilibrium figure parameters are not large in general, and the tidal and centrifugal distorting forces can be supposed to be responsible for the actual figures. The estimates for different dynamical parameters of the system support the hypothesis that the tri-axial satellites in 1 : 1 resonance were formed from the same protoplanetary nebula that gave rise to Saturn.
TL;DR: In this article, it was shown that the short period comets, Apollo-Amor-Toro-asteroids and such other objects may be the relics of the Oort clouds that had existed surrounding the planets long ago.
Abstract: Although, we have no quantitative arguments to prove, but we have good reasoning to believe that the Oort clouds existed surrounding the planets. The short period comets, Apollo-Amor-Toro-asteroids and such other objects may be the relics of the Oort clouds that had existed surrounding the planets long ago.
TL;DR: The ridge belts of Ganiki Planitia on Venus (Laūma, Ahsonnutli and Pandrosos Dorsa) are part of the fan-shaped ridge belt complex along the 200 ‡ parallel of longitude as mentioned in this paper.
Abstract: The main major ridge belts of Ganiki Planitia on Venus (Laūma, Ahsonnutli and Pandrosos Dorsa) are part of the fan-shaped ridge belt complex along the 200 ‡ parallel of longitude. These ridge belts with evidence of crustal shortening support the idea of a large-scale E-W compression. The ridge belt patterns indicate a N-S shear component. These forces are explained by a triangular planitia area which compressed by surrounding terrains. The crustal shortening and ridge belt formation indicates compressional plate movement stresses in the uppermost lithosphere.
TL;DR: In this article, the energy deposition of secondary particles produced in matter antimatter annihilation interactions as a function of the dimensions of an antimatter meteor is described, where the secondary particles are formed by the passage of the annihilation secondaries penetrating throughout the meteor.
Abstract: Antimatter meteors, like ordinary ones, can be heated during their infall flight. However, this could happen by a completely different process than in the case of koinomatter meteors, since in the latter case the annihilation interactions mechanism is absent. In case of antimatter meteors, the temperature may be increased mainly due to the energy deposition effect, caused by the passage of the annihilation secondaries penetrating throughout the meteor. The energy deposition of the secondary particles produced in matter antimatter annihilation interactions as a function of the dimensions of an antimatter meteor is described in this paper.
TL;DR: In this article, the authors make the crucial assumption that the observed clustering of aphelion distances of intermediate-period comets in the 70-90 AU range is due to the influence of a tenth planet, called Planet X.
Abstract: The crucial assumption of this paper is, that the observed clustering of aphelion distances of intermediate-period comets in the 70–90 AU range is due to the influence of a tenth planet, called Planet X. We contribute to the search for Planet X a new and extended evaluation of a family of comets assumed to be Planet X's family of comets.
TL;DR: In this paper, the authors considered the problem of finding the maximum stable orbital elements corresponding to the stable equilibrium solutions of the restricted three bodies problem, where the three bodies are the Sun, the Jupiter and an asteroid.
Abstract: In this paper, we consider the secular variations in the restricted three bodies problem by implementing an explicit numerical technique for studying stability of equilibrium solutions. In the present case, the three bodies are the Sun, the Jupiter and an asteroid. Our results arise from studying some “maximum stable orbital elements” corresponding to the stable equilibrium solutions of the particular problem.
TL;DR: In this paper, a statistical analysis of the coefficient of atmospheric activity R of Jupiter for the time period 1910-1985 was performed and periodicities of 22, 8 and 6 years were found.
Abstract: Periodicities of 22, 8 and 6 years have been found by a statistical analysis of the coefficient of atmospheric activity R of Jupiter for the time period 1910–1985.
TL;DR: Inverness has some characteristics not explained by either the "raiser" or the "sinker" models, and which deserve further investigation as mentioned in this paper, as well as a comparison of Miranda coronae and the Earth ovoidal structures.
Abstract: A comparison of Venus and Miranda coronae, and the Earth ovoidal structures, suggests that Venusian coronae, thermal structures associated with important compressional stress fields, could be compared to Archaean gneiss domes. Among Miranda coronae, Inverness has some characteristics not explained by either the ‘raiser’ or the ‘sinker’ models, and which deserve further investigation.
TL;DR: In this article, a backscattered fraction of incident sunlight in backward directions that do not reach the Earth is calculated using Mie theory for a uniform distribution of particles distributed over a sunlit hemisphere.
Abstract: Small dielectric ice particles of radius ~0.25 Μm, which are known to be present in the mesophere, scatter a fraction of incident sunlight in backward directions that do not reach the Earth. This back-scattered fraction is rigorously calculated using Mie theory for a uniform distribution of particles distributed over a sunlit hemisphere. Such calculations provide necessary information for estimating equilibrium surface temperatures of the Earth under different conditions.
TL;DR: In this paper, the tidal effects on a fractured asteroid are considered and the necessary conditions for this motion are determined and amount of heat that can be generated is calculated for some cases.
Abstract: The tidal effects on a fractured asteroid are considered. The asteroid is assumed to consist of two parts. In gravitational field of another body the motion of one part of the asteroid in relation to second part may be initiated. The necessary conditions for this motion are determined and amount of heat that can be generated is calculated for some cases. It is suggested that metamorphic episodes found in some meteorites are the results of such heating.