共查询到20条相似文献，搜索用时 37 毫秒
1.
Eugster HP 《Science (New York, N.Y.)》1967,157(3793):1177-1180
Two new hydrous sodium silicates, NaSi(7)O(13)(OH)(3).3H(2)O (magadiite) and NaSi(11)O(20.5)(OH)(4).3H(2)O (kenyaite), were found in lake beds at Lake Magadi, Kenya. Both are well-crystallized layered silicates with large basal spacings. Concretions within the magadiite bed consist of kenyaite or quartz (chert) in the center, surrounded by kenyaite. In dilute acids magadiite and kenyaite are converted to 6SiO(2).H(2)O (SH), the first known crystalline hydrate of silica. The magadiite bed probably represents a chemical precipitate from alkaline brines. Percolating waters convert magadiite to kenyaite and eventually to chert. Thus a mechanism has been outlined for the formation of bedded chert deposits through inorganic precipitation. Alternations between silica-rich and iron-rich bands of iron formations may be due to concentration cycles in alkaline lakes. 相似文献
2.
Keller LP Bajt S Baratta GA Borg J Bradley JP Brownlee DE Busemann H Brucato JR Burchell M Colangeli L d'Hendecourt L Djouadi Z Ferrini G Flynn G Franchi IA Fries M Grady MM Graham GA Grossemy F Kearsley A Matrajt G Nakamura-Messenger K Mennella V Nittler L Palumbo ME Stadermann FJ Tsou P Rotundi A Sandford SA Snead C Steele A Wooden D Zolensky M 《Science (New York, N.Y.)》2006,314(5806):1728-1731
Infrared spectra of material captured from comet 81P/Wild 2 by the Stardust spacecraft reveal indigenous aliphatic hydrocarbons similar to those in interplanetary dust particles thought to be derived from comets, but with longer chain lengths than those observed in the diffuse interstellar medium. Similarly, the Stardust samples contain abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene. The presence of crystalline silicates in Wild 2 is consistent with mixing of solar system and interstellar matter. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust. 相似文献
3.
Pieters CM Head JW Pratt S Patterson W Garvin J Barsukov VL Basilevsky AT Khodakovsky IL Selivanov AS Panfilov AS Gektin YM Narayeva YM 《Science (New York, N.Y.)》1986,234(4782):1379-1383
Multispectral images of the basaltic surface of Venus obtained by Venera 13 were processed to remove the effects of orange-colored incident radiation resulting from interactions with the thick Venusian atmosphere. At visible wavelengths the surface of Venus appears dark and without significant color. High-temperature laboratory reflectance spectra of basaltic materials indicate that these results are consistent with mineral assemblages bearing either ferric or ferrous iron. A high reflectance in the near-infrared region observed at neighboring Venera 9 and 10 sites, however, suggests that the basaltic surface material contains ferric minerals and thus may be relatively oxidized. 相似文献
4.
Mueller RF 《Science (New York, N.Y.)》1969,163(3873):1322-1324
The high temperatures and chemical composition, as determined by space probe and terrestrial observation, suggest that the present atmosphere of Venus has formed by chemical interaction with the lithosphere. Although the precise reactions have not been identified, good theoretical approximations to the molecular abundance may be obtained from reactions applicable to terrestial rocks. The high temperatures and chemical reactivity create conditions on Venus which are fundamentally different from those on the cooler terrestrial planets where the attainment of equilibrium is prevented by kinetic barriers. 相似文献
5.
Mariner Stanford Group 《Science (New York, N.Y.)》1967,158(3809):1678-1683
Venus has daytime and nighttime ionospheres at the positions probed by radio occulation. The main layers are thin by terrestrial standards, with the nighttime peak concentration of electrons being about two orders of magnitude below that of the daytime peak. Above the nighttime peak were several scale-height regimes extending to a radius of at least 7500, and probably to 9700, kilometers from the center of Venus. Helium and hydrogen at plasma temperatures of 600 degrees to 1100 degrees K seem indicated in the regimes from 6300 to 7500 kilometers, with cooler molecular ions in lower regions. Above the daytime peak a sharp plasmapause was discovered, marking a sudden transition from appreciable ionization concentrations near Venus to the tenuous conditions of the solar wind. This may be indicative of a kind of interaction of the magnetized solar wind with a planetary body that differs from the two different kinds of interaction characterized by Earth and by Moon. For Venus and probably for Mars, the magnetic field of the solar wind may pile up in front of the conducting ionosphere, form an induced magnetosphere that ends at the plasmapause, above which any ionosphere that tends to form is swept away by the shocked solar wind that flows between the stand-off bow-shock and the magnetopause. The neutral atmosphere was also probed and a surface reflection may have been detected, but the data have not yet been studied in detail. Results are consistent with a super-refractive atmosphere, as expected from Soviet measurements near the surface. Thus, two unusual features of Venus can be described in terms of a light trap in the lower atmosphere, and a magnetic trap in the conducting ionosphere. 相似文献
6.
Bridge HS Lazarus AJ Snyder CW Smith EJ Davis L Coleman PJ Jones DE 《Science (New York, N.Y.)》1967,158(3809):1669-1673
Abrupt changes in the amplitude of the magnetic fluctuations, in the field strength, and in the plasma properties, were observed with Mariner V near Venus. They provide clear evidence for the presence of a bow shock around the planet, similar to, but much smaller than, that observed at Earth. The observations appear consistent with an interaction of the solar wind with the ionosphere of Venus. No planetary field could be detected, but a steady radial field and very low plasma density were found 10,000 to 20,000 kilometers behind Venus and 8,000 to 12,000 kilometers from the Sun-Venus line. These observations may be interpreted as relating to an expansion wave tending to fill the cavity produced by Venus in the solar wind. The upper limit to the magnetic dipole moment of Venus is estimated to be within a factor of 2 of 10(-3) items that of Earth. 相似文献
7.
Lewis JS 《Science (New York, N.Y.)》1971,172(3988):1127-1128
Steady-state thermal models for the large satellites of the outer planets strongly indicate that their interiors are currently maintained at temperatures well above the ice-ammonia eutectic temperature by the decay of long-lived radioisotopes of potassium, uranium, and thorium. The present-day steady-state thermal structure of a representative satellite, J IV (Callisto), is shown to be characterized by the presence of a thin icy crust over a deep liquid mantle, with a dense core of hydrous silicates and iron oxides. Some dynamical consequences of this model are briefly discussed. 相似文献
8.
The Pioneer Venus electric field detector observes significant effects of the interaction of the solar wind with the ionosphere of Venus all along the orbiter trajectory. Information is obtained on plasma oscillations emitted by suprathermal electrons beyond the bows shock, on sharp and diffuse shock structures, and on waveparticle interaction phenomena that are important near the boundary of the dayside ionosphere. 相似文献
9.
Zolensky ME Zega TJ Yano H Wirick S Westphal AJ Weisberg MK Weber I Warren JL Velbel MA Tsuchiyama A Tsou P Toppani A Tomioka N Tomeoka K Teslich N Taheri M Susini J Stroud R Stephan T Stadermann FJ Snead CJ Simon SB Simionovici A See TH Robert F Rietmeijer FJ Rao W Perronnet MC Papanastassiou DA Okudaira K Ohsumi K Ohnishi I Nakamura-Messenger K Nakamura T Mostefaoui S Mikouchi T Meibom A Matrajt G Marcus MA Leroux H Lemelle L Le L Lanzirotti A Langenhorst F Krot AN Keller LP Kearsley AT 《Science (New York, N.Y.)》2006,314(5806):1735-1739
The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk. 相似文献
10.
Annular moats and outer rises around large Venus coronae such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On Earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronae on Venus. Accordingly, it is proposed that retrograde lithospheric subduction may be occurring on the margins of the large Venus coronae while compensating back-arc extension is occurring in the expanding coronae interiors. Similar processes may be taking place at other deep arcuate trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of eastern Aphrodite Terra. 相似文献
11.
Hapke B 《Science (New York, N.Y.)》1972,175(4023):748-751
The spectral and polarization data for Venus are consistent with micrometer-sized aerosol cloud particles of hydrochloric acid with soluble and insoluble iron compounds, whose source could be volcanic or crustal dust. The yellow color of the clouds could be due to absorption bands in the near ultraviolet involving ferric iron and chlorine complexes. The ultraviolet features could arise from variations in the concentrations of iron and hydrochloric acid in the cloud particles. 相似文献
12.
Laboratory experiments document that liquid iron reacts chemically with silicates at high pressures (>/=2.4 x 10(10) Pascals) and temperatures. In particular, (Mg,Fe)SiO(3) perovskite, the most abundant mineral of Earth's lower mantle, is expected to react with liquid iron to produce metallic alloys (FeO and FeSi) and nonmetallic silicates (SiO(2) stishovite and MgSiO(3) perovskite) at the pressures of the core-mantle boundary, 14 x 10(10) Pascals. The experimental observations, in conjunction with seismological data, suggest that the lowermost 200 to 300 kilometers of Earth's mantle, the D" layer, may be an extremely heterogeneous region as a result of chemical reactions between the silicate mantle and the liquid iron alloy of Earth's core. The combined thermal-chemical-electrical boundary layer resulting from such reactions offers a plausible explanation for the complex behavior of seismic waves near the core-mantle boundary and could influence Earth's magnetic field observed at the surface. 相似文献
13.
Honey bees are sensitive to earth strength magnetic fields and are reported to contain magnetite (Fe3O4) in their abdomens. We report bands of cells around each abdominal segment that contain numerous electron-opaque, iron-containing granules. The iron is principally in the form of hydrous iron oxides. 相似文献
14.
Kaula WM 《Science (New York, N.Y.)》1990,247(4947):1191-1196
Of the planets, Venus and Earth are by far the most similar in primary properties, yet they differ markedly in secondary properties. A great impact into Earth is believed to have created its moon and removed its atmosphere; the lack of such an impact into Venus apparently led to a greatly differing atmospheric evolution. The lack of an ocean on Venus prevents the recycling of volatiles and inhibits subduction, so that its crust is probably more voluminous than Earth's, although distorted and quite variable in thickness. Venus's upper mantle appears to be depleted in both volatiles and energy sources because, in addition to the lack of volatile recycling, melts of mantle rocks are more dense than their solid matrix at pressures above 8 gigapascals and hence sink if they occur at depths below 250 kilometers. Appreciable energy sources persist at great depths to sustain the few great mountain complexes. The greatest current problem is reconciling the likelihood of a voluminous crust with indications of considerable strength at shallow depths of 20 to 100 kilometers. 相似文献
15.
Libby WF 《Science (New York, N.Y.)》1968,159(3819):1097-1098
The data on Venus obtained by Mariner V and Venera 4 are interpreted as evidence of giant polar ice caps holding the water that must have come out of the volcanoes with the observed carbon dioxide, on the assumption that Earth and Venus are of similar composition and volcanic history. The measurements by Venera 4 of the equatorial surface temperature indicate that the microwave readings were high, so that the polar ice caps may be allowed to exist in the face of the 10-centimeter readings of polar temperature. Life seems to be distinctly possible at the edges of the ice sheets. 相似文献
16.
It is shown that whistler mode waves from the ionosheath of Venus are absorbed by Landau damping at the dayside ionosphere boundary. This process heats the ionospheric electrons and it may provide an important energy input into the dayside ionosphere. Cyclotron damping of the waves does not occur in the same region. However, Landau damping of ionosheath waves is apparently not an important energy source in the nightside ionosphere. Impulsive events in the nightside ionosphere seem to fall into two classes: (i) lightning signals (near periapsis) and (ii) noise, which may be caused by gradient or current instabilities. 相似文献
17.
M?ssbauer absorption spectrography can be used to establish the presence of Fe(2)+ and Fe(3)+ in clay minerals. In the sheet structure silicates, octahedrally coordinated iron can be distinguished from tetrahedrally coordinated iron. Siderite and goethite, common contaminants of the clay minerals, can usually be detected. Goethite has a well-organized structure, though, owing to its fine grain size, it may appear to be amorphous to x-rays. The various families of clay minerals show minor differences in isomer shift and quadrupole splitting values, caused by variations in the character of the octahedral layer. 相似文献
18.
Nonbiological fractionation of iron isotopes 总被引：2，自引：0，他引：2
Laboratory experiments demonstrate that iron isotopes can be chemically fractionated in the absence of biology. Isotopic variations comparable to those seen during microbially mediated reduction of ferrihydrite are observed. Fractionation may occur in aqueous solution during equilibration between inorganic iron complexes. These findings provide insight into the mechanisms of iron isotope fractionation and suggest that nonbiological processes may contribute to iron isotope variations observed in sediments. 相似文献
19.
Pioneer Venus orbiter dual-frequency radio occultation measurements have produced many electron density profiles of the nightside ionosphere of Venus. Thirty-six of these profiles, measured at solar zenith angles (chi) from 90.60 degrees to 163.5 degrees , are discussed here. In the "deep" nightside ionosphere (chi > 110 degrees ), the structure and magnitude of the ionization peak are highly variable; the mean peak electron density is 16,700 +/- 7,200 (standard deviation) per cubic centimeter. In contrast, the altitude of the peak remains fairly constant with a mean of 142.2 +/- 4.1 kilometers, virtually identical to the altitude of the main peak of the dayside terminator ionosphere. The variations in the peak ionization are not directly related to contemporal variations in the solar wind speed. It is shown that electron density distributions similar to those observed in both magnitude and structure can be produced by the precipitation on the nightside of Venus of electron fluxes of about 108 per square centimeter per second with energies less than 100 electron volts. This mechanism could very likely be responsible for the maintenance of the persistent nightside ionosphere of Venus, although transport processes may also be important. 相似文献
20.
McClintock WE Izenberg NR Holsclaw GM Blewett DT Domingue DL Head JW Helbert J McCoy TJ Murchie SL Robinson MS Solomon SC Sprague AL Vilas F 《Science (New York, N.Y.)》2008,321(5885):62-65
During MESSENGER's first flyby of Mercury, the Mercury Atmospheric and Surface Composition Spectrometer made simultaneous mid-ultraviolet to near-infrared (wavelengths of 200 to 1300 nanometers) reflectance observations of the surface. An ultraviolet absorption (<280 nanometers) suggests that the ferrous oxide (Fe2+) content of silicates in average surface material is low (less than 2 to 3 weight percent). This result is supported by the lack of a detectable 1-micrometer Fe2+ absorption band in high-spatial-resolution spectra of mature surface materials as well as immature crater ejecta, which suggests that the ferrous iron content may be low both on the surface and at depth. Differences in absorption features and slope among the spectra are evidence for variations in composition and regolith maturation of Mercury's surface. 相似文献