Mercury: Internal structure and thermal evolution     

Robert W. Siegfried  Sean C. Solomon 《Icarus》1974,23(2):192-205

Astronomical observations and cosmochemical calculations suggest that the planet Mercury may be composed of materials which condensed at relatively high temperatures in the primitive solar nebula and may have a basaltic crust similar to parts of the moon. These findings, plus the long standing inference that Mercury is much richer in metallic iron than the other terrestrial planets, provide important constraints which we apply to models of the thermal evolution and density structure of the planet. The thermal history calculations include explicitly the differing thermal properties of iron and silicates and account for core segregation, melting and differentiation of heat sources, and simulated convection during melting. If the U and Th abundances of Mercury are taken from the cosmochemical model of Lewis, then the planet would have fully differentiated a metal core from the silicate mantle for all likely initial temperature distributions and heat transfer properties. Density distributions for the planet are calculated from the mean density and estimates of the present-day temperature. For the fully differentiated model, the moment of inertia C/MR² is 0.325 (J₂=0.302×10^?6). For models with lower heat source abundances, the planet may not yet have differentiated. The density profiles for such models give C/MR²=0.394 (J₂=0.487×10^?6). These results should be useful for preliminary interpretation of the Mariner 10 measurements of Mercury's gravitational field.  相似文献   

What Is Comga?     

Robert B. McNee 《The Professional geographer》1970,22(2):92-93

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RECENT GEOGRAPHY DISSERTATIONS AND THESES COMPLETED AND IN PREPARATION     

Robert H. Stoddard 《The Professional geographer》1973,25(1):52-77

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Theory of decametric radio emissions from Jupiter     

Ching S. Wu  Robert A. Smith  Jonas S. Zmuidzinas 《Icarus》1973,18(2):192-205

It is suggested that the Jovian decametric emissions (DAM) originate in a cyclotron instability of weakly relativistic electrons trapped in the Jovian magnetic field. The resulting radiation has a group velocity in the magnetosphheric plasma which may be of order 10²km/sec, and thus takes much more time to escape the magnetosphere than if the group velocity were at or near the speed of light. Therefore, the asymmetry of the Io phase with respect to sources east and west of the Earth-Jupiter line does not imply an asymmetric beaming of DAM; it is caused by the delay the waves experience in traversing the magnetosphere. The frequency drifts of milli- and decasecond bursts are also explained. It is found that the rotation of the magnetosphere can play an important role, since the observer views the propagation velocity of the waves as the sum of their group velocity and the velocity of the medium itself. The rotation velocity is in opposite directions, relative to the observer, for sources east and west of the Earth-Jupiter line; the resultant vector addition gives positive frequency drifts for decasecond bursts from the early and fourth sources, and negative drifts for bursts from the main and third sources. The negative drifts of millisecond bursts may be the result of large density gradients of plasma in a temporarily compressed magnetosphere.  相似文献   

Radio Astronomy Explorer (RAE)—I. Observations of terrestrial radio noise     

John R. Herman  Joseph A. Caruso  Robert G. Stone 《Planetary and Space Science》1973,21(3):443-461

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Annual General Meeting: February 5th, 1875     

Robert Etheridge 《Proceedings of the Geologists' Association. Geologists' Association》1875,4(4):205-212

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Faltenachsen in Überschiebungszonen     

Robert Balk 《International Journal of Earth Sciences》1953,41(1):90-103

English summary Near the eastern base of the Taconic Range, in extreme southwestern Vermont, a complex of chlorite slate is exposed in the position of the floor of a thrust along which a mass of dolomite-limestone has been pushed from the east against, and over, the slate. In addition to the common structure, exhibiting westward-overturned open folds, with slip cleavage dipping eastward, about parallel with the axial pianos, the slate displays a number of subsidiary shears or thrust zones having the same orientation as the principal thrust. In these zones, a strong lineation as well as axes of small folds plunge E—SE, parallel with the direction of propagation of the thrust blocks. The origin of the lineation and lamination is believed to be identical with that of corresponding structures in rolled steel and glass.However, the formation of folds with axes parallel to the direction of thrust requires an additional shear stress acting perpendicularly to the direction of thrusting. The inhomogeneous composition, strength, and mobility of the flooring rocks are pointed out, and it is suggested that unequal rates of yielding of local rock masses below the thrust block generated these supplementary stresses, producing slight movements of small masses sideways. That this is a reasonable explantation is shown by experiments on salt dome structure byEscher andKuenen, in which also axes of folds and lineation parallel with the direction of maximum forward propagation were produced.  相似文献   

The Transmission of Rayleigh Waves across an Ocean Floor with Two Surface Layers, Part II: Numerical     

Urs Hochstrasser  Robert Stoneley 《Geophysical Journal International》1937,4(S1):197-201

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On the geology of south-eastern Kincardineshire     

Robert Campbell 《Proceedings of the Geologists' Association. Geologists' Association》1912,23(5):295-298

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Geröllführende Schiefer und andere Trümmergesteine aus der Zentralzone der Ostalpen     

Schwinner  Robert 《International Journal of Earth Sciences》1929,20(3):211-244

Ohne Zusammenfassung  相似文献