共查询到20条相似文献,搜索用时 15 毫秒
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Titan's dense and cold nitrogen atmosphere contains a small amount of methane under conditions at least approaching those at which one or both constituents would condense. The possibility of methane and nitrogen rain clouds and global methane oceans has been discussed widely. From specific features of radio occultation and other Voyager results, however, it is concluded that nitrogen does not condense on Titan and that Titan has neither global methane oceans nor a global cloud of liquid methane droplets. Certain results indirectly support the conjecture that methane does not condense at any location. However, other considerations favor a methane ice haze high in the troposphere, and liquid and solid methane might exist on the surface and as low clouds at polar latitudes. 相似文献
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By use of observations of zodiacal light, the symmetry plane or plane of maximum density of interplanetary dust at elongations of 32 degrees to 50 degrees from the sun has been found to be closer to the orbital plane of Venus than to the invariable plane. This suggests that the plane of maximum density in this region is being gravitationally perturbed closer to the orbital plane of Venus. 相似文献
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Kerr RA 《Science (New York, N.Y.)》1982,215(4530):278-279
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Florensky CP Basilevsky AT Kryuchkov VP Kusmin RO Nikolaeva OV Pronin AA Chernaya IM Tyuflin YS Selivanov AS Naraeva MK Ronca LB 《Science (New York, N.Y.)》1983,221(4605):57-59
Venera 13 and Venera 14 transmitted almost complete panoramic views of their landing sites. Analyses of the photographs show the presence of rock formations undergoing geomorphic degradation. The formations display ripple marks, thin layering, differential erosion, and curvilinear fracturings. Some of them are interpreted as lithified clastic sediments. The lithification could have taken place at depth or at the surface, resulting in a type of duricrust. The origin of the sediments is unknown but could be aeolian, volcanic, or related to impacts or to turbidity currents. 相似文献
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Kerr RA 《Science (New York, N.Y.)》1982,215(4530):278
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Kerr RA 《Science (New York, N.Y.)》1993,259(5102):1696-1697
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Stone R 《Science (New York, N.Y.)》1991,253(5027):1488
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During the Archean, massive amounts of iron were deposited in the form of banded iron formations. It has been suggested that sedimenting particles of ferric oxyhydroxide may have stripped dissolved phosphate from the oceans, causing a reduction in phytoplankton productivity. However, that model does not take into account the high concentration of dissolved silica that was present in seawater at that time. We show experimentally that silica effectively competes with phosphate for sorption sites on ferrihydrite particles. Furthermore, coprecipitation of silica with ferrihydrite reduces particle reactivity toward phosphate. Hence, Archean oceans probably contained considerably more phosphate than previously predicted. 相似文献
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Kerr RA 《Science (New York, N.Y.)》1988,239(4841):729-730
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Broecker WS 《Science (New York, N.Y.)》2001,291(5508):1497-1499