共查询到20条相似文献，搜索用时 93 毫秒
1.
Sean C. Solomon 《Physics of the Earth and Planetary Interiors》1979,19(2):168-182
The cores of the terrestrial planets Earth, Moon, Mercury, Venus and Mars differ substantially in size and in history. Though no planet other than the Earth has a conclusively demonstrated core, the probable cores in Mercury and Mars and Earth's core show a decrease in relative core size with solar distance. The Moon does not fit this sequence and Venus may not. Core formation must have been early (prior to ～4 · 109 yr. ago) in the Earth, by virtue of the existence of ancient rock units and ancient paleomagnetism and from UPb partitioning arguments, and in Mercury, because the consequences of core infall would have included extensional tectonic features which are not observed even on Mercury's oldest terrain. If a small core exists in the Moon, still an open question, completion of core formation may be placed several hundred million years after the end of heavy bombardment on tectonic and thermal grounds. Core formation time on Mars is loosely constrained, but may have been substantially later than for the other terrestrial planets. The magnitude and extent of early heating to drive global differentiation appear to have decreased with distance from the sun for at least the smaller bodies Mercury, Moon and Mars.Energy sources to maintain a molten state and to fuel convection and magnetic dynamos in the cores of the terrestrial planets include principally gravitational energy, heat of fusion, and long-lived radioactivity. The gravitational energy of core infall is quantifiable and substantial for all bodies but the Moon, but was likely spent too early in the history of most planets to prove a significant residual heat source to drive a present dynamo. The energy from inner core freezing in the Earth and in Mercury is at best marginally able to match even the conductive heat loss along an outer core adiabat. Radioactive decay in the core offers an attractive but unproven energy source to maintain core convection. 相似文献
2.
Christiane Helling R. Giles Harrison Farideh Honary Declan A. Diver Karen Aplin Ian Dobbs-Dixon Ute Ebert Shu-ichiro Inutsuka Francisco J. Gordillo-Vazquez Stuart Littlefair 《Surveys in Geophysics》2016,37(4):705-756
Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. Instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) brown dwarfs which are amongst the oldest objects in the Universe. Despite this diversity, solar system planets, extrasolar planets and brown dwarfs have broadly similar global temperatures between 300 and 2500 K. In consequence, clouds of different chemical species form in their atmospheres. While the details of these clouds differ, the fundamental physical processes are the same. Further to this, all these objects were observed to produce radio and X-ray emissions. While both kinds of radiation are well studied on Earth and to a lesser extent on the solar system planets, the occurrence of emissions that potentially originate from accelerated electrons on brown dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. This paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation. 相似文献
3.
Fractionation between the metal and silicate components of objects in the inner solar system has long been recognized as a necessity in order to explain the observed density variations of the terrestrial planets and the H-group, L-group dichotomy of the ordinary chondrites. This paper discusses the densities of the terrestrial planets in light of current physical and chemical models of processes in the solar nebula. It is shown that the observed density trends in the inner solar system need not be the result of special fractionation processes, and that the densities of the planets may be direct results of simultaneous application of both physical and chemical restraints on the structure of the nebula, most notably the variation of temperature with heliocentric distance. The density of Mercury is easily attributed to accretion at temperatures so high that MgSiO3 is only partially retained but Fe metal is condensed. The densities of the other terrestrial planets are shown to be due to different degrees of retention of S, O and H as FeS, FeO and hydrous silicates produced in chemical equilibrium between condensates and solar-composition gases. It is proposed that Mercury and Venus Have cores of Fe0, Earth has a core of Fe0 containing substantial amounts of FeS, and Mars has a quite small core of FeS with more FeO in its mantle than in Earth's. Geophysical and geochemical consequences of these conclusions are discussed. 相似文献
4.
Karen L. Aplin 《Surveys in Geophysics》2006,27(1):63-108
Atmospheric electrification is not a purely terrestrial phenomenon: all Solar System planetary atmospheres become slightly
electrified by cosmic ray ionisation. There is evidence for lightning on Jupiter, Saturn, Uranus and Neptune, and it is possible
on Mars, Venus and Titan. Controversy surrounds the role of atmospheric electricity in physical climate processes on Earth;
here, a comparative approach is employed to review the role of electrification in the atmospheres of other planets and their
moons. This paper reviews the theory, and, where available, measurements, of planetary atmospheric electricity which is taken
to include ion production and ion–aerosol interactions. The conditions necessary for a planetary atmospheric electric circuit
similar to Earth’s, and the likelihood of meeting these conditions in other planetary atmospheres, are briefly discussed.
Atmospheric electrification could be important throughout the solar system, particularly at the outer planets which receive
little solar radiation, increasing the relative significance of electrical forces. Nucleation onto atmospheric ions has been
predicted to affect the evolution and lifetime of haze layers on Titan, Neptune and Triton. Atmospheric electrical processes
on Titan, before the arrival of the Huygens probe, are summarised. For planets closer to Earth, heating from solar radiation
dominates atmospheric circulations. However, Mars may have a global circuit analogous to the terrestrial model, but based
on electrical discharges from dust storms. There is an increasing need for direct measurements of planetary atmospheric electrification,
in particular on Mars, to assess the risk for future unmanned and manned missions. Theoretical understanding could be increased
by cross-disciplinary work to modify and update models and parameterisations initially developed for a specific atmosphere,
to make them more broadly applicable to other planetary atmospheres. 相似文献
5.
Mian Liu 《Pure and Applied Geophysics》1996,146(3-4):447-467
This paper examines the first-order dynamic interactions between crustal shortening, extension, and volcanism in tectonic evolution in the North American Cordillera. The protracted crustal compression in the Mesozoic and early Cenozoic (110–55 Ma) contributed to the subsequent Tertiary extension by thermally weakening the lithosphere and producing an overthickened (>50 km) and gravitationally unstable crust. In addition to post-kinematic burial heating, synkinematic thermal processes including conduction are shown significantly because of the long period of crustal contraction and the slow shortening rates (<4 mm/yr). The effects of shear heating were probably limited for the same reasons. Localized delamination of the lithospheric mantle may have contributed to the abundant plutonism and high crustal temperature in the southeastern Canadian Cordillera at the end of the orogeny. Most early-stage extension in the Cordillera, characterized by formation of metamorphic core complexes, resulted from gravitational collapse of the overthickened crust. Plutionism may have facilitated strain localization, causing widespread crustal extension at relatively low stress levels. Crustal collapse, however, was unlikely the direct cause of the Basin-Range extension, because the gravitational stresses induced by crustal thickening are limited to the crust; only a small fraction of the gravitational stresses may be transmitted to the lithospheric mantle. Nor could core complex formation induce the voluminous mid-Tertiary volcanism, which requires major upwelling of the asthenosphere. While the causes of the asthenospheric upwelling are not clear, such processes could provide the necessary conditions for the Basin-Range extension: the driving force from thermally induced gravitational potential and a thermally weakened lithosphere. The complicated spatial and temporal patterns of volcanism and extension in the Basin and Range province may be partially due to the time-dependent competing effects of thermal weakening and rheological hardening associated with intrusion and underplating of mantle-derived magmas. 相似文献
6.
Angioletta Coradini Costanzo Federico Pasquale Lanciano 《Physics of the Earth and Planetary Interiors》1983,31(2):145-160
The extent of formation heating for the Earth and Mars has been evaluated assuming that the terrestrial planets accumulated from planetesimals. The main result is that, even if a long accumulation time is assumed (τ ≥ 100 Ma), it is possible to obtain a planetary structure with a large melted shell taking into account the role played by massive projectiles, which, upon reaching depths of several kilometres, are able to deposit heat significantly below the planetary surface. Internal temperatures, sufficient for the downward migration of the liquid iron alloy, have been obtained. 相似文献
7.
George H. Shaw 《Physics of the Earth and Planetary Interiors》1979,20(1):42-47
Calculations of the radial distribution of the energy released in core formation indicate that the cores of all the terrestrial planets may be expected to receive a disproportionate share of the gravitational energy released. Since the model of the process used in these calculations favors transfer of energy to the mantle, it is likely that other reasonable models of the process will result in even more energy being deposited in the cores of the early planets. The calculations also show that it is necessary for a certain amount of core phase to separate and accumulate, before the energy released by gravitational settling is sufficient to supply the latent heat of fusion of the core phase. The amount of melting required to reach this point varies according to the total mass of the planet, and mass fraction of core, but is not particularly great (<5% for the Earth to ～ 37% for the Moon). In the case of the Moon, this amount of segregation, although large, amounts to a surface layer about 260 km thick, similar to the proposed depth of early wholesale melting. Core separation in terrestrial planets appears to be a self-sustaining process even for fairly small bodies, provided that a small amount of a dense potential core phase is present. Although it seems likely to occur rapidly (within 106–107 years) even for small (Moon-size) bodies, detailed kinetic models will be necessary to specify the time scale. 相似文献
8.
Acceleration of charged particles in magnetic field-aligned electric potential differences at Earth and at the outer planets in the solar system is summarized and its general importance in the Universe is briefly discussed.The role of field-aligned currents, driven by parallel electric fields, in causing filamentary structure in stellar atmospheres is briefly reviewed.The differences between auroral optical emissions at various planets are summarized.The important role of field-aligned potential differences in the generation of AKR and corresponding emissions from other objects is discussed.Finally, aurora-associated processes for ejection of planetary plasma into space are briefly reviewed. 相似文献
9.
The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth. 相似文献
10.
Silicate melts are very active in the interior of the Earth and other terrestrial planets, and are important carriers for the transport of material and energy. The determination of the equation of state(EOS) for silicate melts and the acquisition of a precise quantitative relationship between molar volume(or density) and temperature, pressure, and composition is essential for simulating the generation, migration, and eruption processes of magmas and the evolution of the magma ocean stage during the early formation of the Earth and other terrestrial planets, for calculating and modeling the phase equilibria involving silicate melts, and for revealing the variation of the microstructure of silicate melts with pressure. However, it is experimentally challenging to determine the volumetric properties of silicate melts and the accumulated density data at high pressure are still very limited due to a series of problems such as: the high liquidus temperature of silicate rocks; proneness for silicate melts to react with sample capsules to change the melt composition; and proneness for melts to flow and leak during the high pressure and high temperature experiments. In recent years, there is rapid progress in the high pressure and high temperature experimental techniques, in terms of not only the extension of temperature and pressure ranges but also the improvement on the accuracy of measurements, and the emergence of new methods for in-situ measurements. Here, we review the widely-used theoretical models of ambient-pressure and high-pressure EOS for silicate melts, and illustrate some problems that need to be solved urgently:(1) the room pressure EOS for iron-and titanium-bearing silicate melts needs to be improved;(2) the partial molar properties of the H2 O and CO2 components in silicate melts containing volatile components may vary markedly with the melt composition, which need to be addressed in high-pressure EOS;(3) how the formulation and applicable range of EOS correspond to changes in melt structure and compression mechanism requires further study. We highlight the basic principle and applicable range of various methods for determining the EOS for silicate melts, and compare the advantages and disadvantages of doublebob Archimedes method, fusion curve analysis, shock compression experiments, sink-float method, X-ray absorption, X-ray diffraction and ultrasonic interferometry. Future trends in this field are to develop experimental techniques for in situ measurements on melt density or sound velocity at high temperature and high pressure and to accumulate more experimental data,and on the other hand, to improve the theoretical models of the EOS for silicate melts by a combination of research on the microstructure and compression mechanisms of silicate melts. 相似文献
11.
Although vigorous mantle convection early in the thermal history of the Earth is shown to be capable of removing several times the latent heat content of the core, we are able to construct a thermal evolution model of the Earth in which the core does not solidify. The large amount of energy removed from the model Earth's core by mantle convection is supplied by the internal energy of the core which is assumed to cool from an initial high temperature given by the silicate melting temperature at the core-mantle boundary. For the smaller terrestrial planets, the iron and silicate melting temperatures at the core-mantle boundaries are more comparable than for the Earth, and the cores of these planets may not possess enough internal energy to prevent core solidification by mantle convection. Our models incorporate temperature-dependent mantle viscosity and radiogenic heat sources in the mantle. The Earth models are constrained by the present surface heat flux and mantle viscosity. Internal heat sources produce only about 55% of the Earth model's present surface heat flow. 相似文献
12.
《Astronomy& Geophysics》2008,49(1):1.06-1.06
Dust particles in a supernova remnant have been tracked to the supernova itself – an important step in understanding the formation of planets. 相似文献
13.
Megan K Pickett and Andrew J Lim examine the role of spirals in protoplanetary disks and the formation of gas giant planets, and find that slower may be better than faster, if planets are to endure. 相似文献
14.
The paper addresses the interpretation of the geochemical laboratory experiments aimed at studying the differentiation of partially molten rocks in the terrestrial planets. These experiments simulate the early stages of material differentiation when the layers with the different chemical and petrological composition are formed in the planets. Density inversion which may arise at a certain stage of this process leads to the emergence of the Rayleigh–Taylor instability. The lifetime of this instability is estimated, and the different phases of its evolution are explored. It is shown that the laboratory experiments do not always adequately reproduce the nature of the physical processes which occur in the interior of the planets. The suggested methods are also used for interpreting the evolution of intrusions during their differentiation. The obtained results can be helpful in analyzing the intrusions for minerals. 相似文献
15.
D. M. Pechersky D. M. Kuzina G. P. Markov V. A. Tsel’movich 《Izvestiya Physics of the Solid Earth》2017,53(5):658-676
Thermomagnetic and microprobe studies of native iron in the terrestrial upper-mantle hyperbasites (xenoliths in basalts), Siberian traps, and oceanic basalts are carried out. The results are compared to the previous data on native iron in sediments and meteorites. It is established that in terms of the composition and grain size and shape, the particles of native iron in the terrestrial rocks are close to each other and to the extraterrestrial iron particles from sediments and meteorites. This suggests that the sources of the origin of these particles were similar; i.e., the formation conditions in the Earth were close to the conditions in the meteorites’ parent bodies. This similarity is likely to be due to the homogeneity of the gas and dust cloud at the early stage of the solar system. The predominance of pure native iron in the sediments can probably be accounted for by the fact that interstellar dust is mostly contributed by the upper-mantle material of the planets, whereas the lower-mantle and core material falls on the Earth mainly in the form of meteorites. A model describing the structure of the planets in the solar system from the standpoint of the distribution of native iron and FeNi alloys is proposed. 相似文献
16.
V.E. Khain 《Journal of Geodynamics》1990,11(4)
The origin of the Central Asiatic mountain belt is treated nowadays from two opposing points of view. Some researchers believe that it is a consequence of the collision of the Indo-Australian and Eurasian lithospheric plates, starting from the Late Eocene; others consider the mountain edifices of this belt to be the product of low-density mantle uplift. Analysis of these concepts leads the author to the conclusion that they are not mutually exclusive, taking into account that both are based on actually observed facts: deformations connected with general compression in the first instance, and the elevated position of low-velocity rocks in the second. But the primary and main mechanism was the collision of the main tectonic plates, and heating of the lower part of the lithosphere and the formation of asthenospheric lenses represent a secondary effect. The processes of plate collision and mountain building were periodically repeated during the pre-Cenozoic history of Central Asia. 相似文献
17.
《Journal of Atmospheric and Solar》2007,69(14):1723-1738
Ion-cyclotron waves play important roles in planetary magnetospheres and are diagnostic of the processes operating in the magnetosphere and of the composition of the plasma producing the waves. At Jupiter, Io's exosphere interacts with the corotating magnetospheric plasma. At Saturn, the neutral torus around the E ring interacts with the corotating plasma. At the unmagnetized planets, Mars and Venus, the interaction is between the solar-wind flow and the planetary exosphere. A possible analog of these processes exists in the vicinity of the Earth's polar cusp where the shocked solar-wind plasma penetrates the Earth's exosphere. 相似文献
18.
A. B. Medvedev 《Izvestiya Physics of the Solid Earth》2008,44(4):303-315
A hypothetical possibility of a qualitative explanation of large crater formation on the surfaces of the Moon and Mercury is discussed in terms of the concept of thermal mantle plumes. Prerequisites to this hypothesis are revealed under the assumption that the model equation of state of SiO2 exhibiting an anomaly (a negative coefficient of thermal expansion) in the range of states approximately corresponding to average conditions typical of mantles of minor planets is applicable, in a first approximation, to mantle material. The anomaly reduces the buoyancy of hot plume material in such a way that, under conditions of moderate overheating, only relatively high columns comparable in size to the mantle are capable of ascending from the mantle bottom to the crust; allows cold peripheral material surrounding the hot column to be pushed away; causes compaction of the vertical zone of the contact of the column with the surrounding medium at the first stages after the plume ascent; and leads to compaction of the deep mantle due to the long-term heat supply. Such phenomena can lead to vertical craterlike deformations of the crust in areas of ascending large plumes whose presence can be supposed at early stages of the existence of minor planets. Significant implications of such an anomaly for geophysical processes can also be postulated. 相似文献
19.
Taylor SR 《AGSO journal of Australian geology & geophysics》1997,17(1):27-31
It is not possible to consider the formation of the Earth in isolation without reference to the formation of the rest of the solar system. A brief account is given of the current scientific consensus on that topic, explaining the origin of an inner solar system rocky planet depleted in most of the gaseous and icy components of the original solar nebula. Volatile element depletion occurred at a very early stage in the nebula, and was probably responsible for the formation of Jupiter before that of the inner planets. The Earth formed subsequently from accumulation of a hierarchy of planetesimals. Evidence of these remains in the ancient cratered surfaces and the obliquities (tilts) of most planets. Earth melting occurred during this process, as well as from the giant Moon-forming impact. The strange density and chemistry of the Moon are consistent with an origin from the mantle of the impactor. Core-mantle separation on the Earth was coeval with accretion. Some speculations are given on the origin of the hydrosphere. 相似文献
20.