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排序方式: 共有200条查询结果,搜索用时 31 毫秒
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A. Galli P. Wurz H. Lammer H. I. M. Lichtenegger R. Lundin S. Barabash A. Grigoriev M. Holmström H. Gunell 《Space Science Reviews》2006,126(1-4):447-467
We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m?3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity. 相似文献
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Björn J. R. Davidsson 《Space Science Reviews》2008,138(1-4):207-223
This paper reviews some important results about Knudsen layers obtained in theoretical gas kinetics research in the last few decades, focusing on the weak and strong evaporation problems in two-surface, half-space, and spherical geometries. Furthermore, the application of such results in cometary science is reviewed. In order to illustrate some properties of the half-space evaporation problem for water ice surfaces at temperatures relevant for active comets, a number of numerical Direct Simulation Monte Carlo calculations are presented. 相似文献
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P. Fabian R. Borchers D. Gömer S.A. Penkett 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(4):135-138
Stratospheric air samples collected between 10 and 35 km altitude my means of a cryogenic sampler were analyzed by gaschromatography. Thus vertical profiles of source gases for halogen radicals were derived, such as CCl4, CCl3F, CCl2F2, CClF3, CF4, C2F3Cl3, C2F4Cl2, C2F5Cl, C2F6, CH3Cl, CH3CCl3, CHF2Cl, CH3Br, CBrF3, and CBrCl2F. Systematic discrepancies between measured and modelled halocarbon profiles point to deficiencies of present one- and two-dimensional models. Measurements of fully halogenated hydrocarbons provide a tool for systematically studying these deficiencies and thus improving the models. 相似文献
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The COSAC (Cometary Sampling and Composition Experiment) onboard the Rosetta mission is a combined gas chromatograph (GC)-mass spectrometer (MS). It is situated on Philae, the lander of the mission, which is intended to land on the nucleus of comet 67P/Churyumov- Gerasimenko. The purpose of the experiment is to analyze the volatile fraction of soil samples retrieved by a drill. For investigation, the samples will be pyrolysed, and the emanating gases fed into a GC, into an MS, or the combination of both. In the first part of this paper, the bioastronomical relevance of such measurements is outlined. In the second part the details of the hardware and its performance are described. 相似文献
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C. Fröhlich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(4):191-198
The operating principles of modern absolute radiometers are discussed and the methods of their characterization, that is the accurate determination of the uncertainties, are described. In view of this analysis, the results of the solar constant determinations of the last 6 years are reviewed and an estimate of their uncertainties given. Procedures for the strategy of future experiments are recommended. 相似文献
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Merlin C. Köhnke Christian von Savigny Charles E. Robert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(10):2531-2539
Previous studies have identified solar 27-day signatures in several parameters in the Mesosphere/Lower thermosphere region, including temperature and Noctilucent cloud (NLC) occurrence frequency. In this study we report on a solar 27-day signature in NLC altitude with peak-to-peak variations of about 400?m. We use SCIAMACHY limb-scatter observations from 2002 to 2012 to detect NLCs. The superposed epoch analysis method is applied to extract solar 27-day signatures. A 27-day signature in NLC altitude can be identified in both hemispheres in the SCIAMACHY dataset, but the signature is more pronounced in the northern hemisphere. The solar signature in NLC altitude is found to be in phase with solar activity and temperature for latitudes N. We provide a qualitative explanation for the positive correlation between solar activity and NLC altitude based on published model simulations. 相似文献