Geology of the Selk crater region on Titan from Cassini VIMS observations     

Jason M. Soderblom  Robert H. Brown  Jason W. Barnes  Stéphane Le Mouélic  Katrin Stephan  Bonnie J. Buratti  Philip D. Nicholson 《Icarus》2010,208(2):905-912

Observations of Titan obtained by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) have revealed Selk crater, a geologically young, bright-rimmed, impact crater located ∼800 km north-northwest of the Huygens landing site. The crater rim-crest diameter is ∼90 km; its floor diameter is ∼60 km. A central pit/peak, 20-30 km in diameter, is seen; the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on Ganymede and Callisto, all of which are dome craters. The VIMS data, unfortunately, are not of sufficient resolution to detect such a dome. The inner rim of Selk crater is fluted, probably by eolian erosion, while the outer flank and presumed ejecta blanket appear dissected by drainages (particularly to the east), likely the result of fluvial erosion. Terracing is observed on the northern and western walls of Selk crater within a 10-15 km wide terrace zone identified in VIMS data; the terrace zone is bright in SAR data, consistent with it being a rough surface. The terrace zone is slightly wider than those observed on Ganymede and Callisto and may reflect differences in thermal structure and/or composition of the lithosphere. The polygonal appearance of the crater likely results from two preexisting planes of weakness (oriented at azimuths of 21° and 122° east of north). A unit of generally bright terrain that exhibits similar infrared-color variation and contrast to Selk crater extends east-southeast from the crater several hundred kilometers. We informally refer to this terrain as the Selk “bench.” Both Selk and the bench are surrounded by the infrared-dark Belet dune field. Hypotheses for the genesis of the optically bright terrain of the bench include: wind shadowing in the lee of Selk crater preventing the encroachment of dunes, impact-induced cryovolcanism, flow of a fluidized-ejecta blanket (similar to the bright crater outflows observed on Venus), and erosion of a streamlined upland formed in the lee of Selk crater by fluid flow. Vestigial circular outlines in this feature just east of Selk’s ejecta blanket suggest that this might be a remnant of an ancient, cratered crust. Evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the Belet dune field. We conclude that this feature either represents a relatively high-viscosity, fluidized-ejecta flow (a class intermediate to ejecta blankets and long venusian-style ejecta flows) or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west-northwest.  相似文献   

How to survive a Lunar night     

Stephan Ulamec  Jens Biele  Ed Trollope 《Planetary and Space Science》2010,58(14-15):1985-1995

In the frame of the recent worldwide activities of Lunar research, including various studies for surface stations, the aspect of longevity of such stations has been identified as a particular technical challenge. The reason for this lies in the long (about 14 days) and cold Lunar night during which it is non-trivial to keep spacecraft systems alive and sensitive equipment within an acceptable temperature range.The following paper analyzes and compares various concepts to survive Lunar night, both with and without radioisotope heater technology.The latter normally implies the use of highly toxic material (typically plutonium), which is politically problematic and a driver for cost and safety procedures.Concepts without radioisotope heating need to foresee special measures, like extremely efficient thermal insulation or sub-surface positioning of all temperature sensitive components.Special emphasis has been taken on the thermal analysis of a penetrator-type surface station. The relevant issues are discussed and results for day–night cycles are presented, assuming a typical set of engineering parameters. This concept appears to be the easiest to implement from a thermal point of view, if the use of radioisotope heaters has to be avoided.  相似文献   

Predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first-order controls   总被引：2，自引：1，他引：1  

Jens Hartmann  Nils Jansen  Hans H. Dürr  Akira Harashima  Kenji Okubo  Stephan Kempe 《International Journal of Earth Sciences》2010,99(1):207-230

Silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways. First by the uptake of atmospheric/soil CO₂ and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica (DSi). Previous work suggests that regions dominated by volcanics are hyperactive or even “hot spots” concerning DSi-mobilization. Here, we present a new approach for predicting DSi-fluxes to coastal zones, emphasizing “first-order” controlling factors (lithology, runoff, relief, land cover and temperature). This approach is applied to the Japanese Archipelago, a region characterized by a high percentage of volcanics (29.1% of surface area). The presented DSi-flux model is based on data of 516 catchments, covering approximately 56.7% of the area of the Japanese Archipelago. The spatial distribution of lithology—one of the most important first order controls—is taken from a new high resolution map of Japan. Results show that the Japanese Archipelago is a hyperactive region with a DSi-yield 6.6 times higher than the world average of 3.3 t SiO₂ km⁻² a⁻¹, but with large regional variations. Approximately 10% of its area exceeds 10 times the world average DSi-yield. Slope constitutes another important controlling factor on DSi-fluxes besides lithology and runoff, and can exceed the influence of runoff on DSi-yields. Even though the monitored area on the Japanese Archipelago stretches from about 31° to 46°N, temperature is not identified as a significant first-order model variable. This may be due to the fact that slope, runoff and lithology are correlated with temperature due to regional settings of the Archipelago, and temperature information is substituted to a certain extent by these factors. Land cover data also do not improve the prediction model. This may partly be attributed to misinterpreted land cover information from satellite images. Implications of results for Earth System and global carbon cycle modeling are discussed.  相似文献   

Comparison of atmospheric turbulence characteristics and turbulent fluxes from two urban sites in Essen, Germany     

Stephan Weber  Klaus Kordowski 《Theoretical and Applied Climatology》2010,102(1-2):61-74

From September 2006 to September 2007, the intersite variability of turbulence characteristics and turbulent heat fluxes was analysed at two urban stations in Essen, Germany. One site was situated within an urban residential setting while the other was located at the border of an urban park and suburban/urban residential housing. Therefore, the surroundings at both sites contributing to surface–atmosphere exchange differed in terms of surface cover and surface morphology. During the 1-year measurement period, 19% of data were characterised by stable atmospheric stratification. Since observations of urban turbulence characteristics under stable stratification are scarce, so far, this work adds additional input to this discussion. Turbulence characteristics, i.e. normalised standard deviations of wind components, were in agreement to empirical fits from other urban observations under both instable and stable atmospheric stratification. However, differences in magnitude of turbulence characteristics between sites were observable. Comparison of turbulent heat fluxes indicated typical urban features in the site located in the urban setting with increased surface heating and higher surface heat fluxes by about 30%. Also the temporal evolution of heat fluxes on the diurnal course was affected. Differences in momentum flux were of minor magnitude with about 6% variation on average between sites. Findings indicate that multiple urban flux measurements within one city may be characterised by general similarities in terms of turbulent characteristics but are still significantly influenced by differences in the surface cover of the flux footprint.  相似文献   

A BASIC-programme for the calculation of O-isotope temperatures     

Stephan Hoernes 《Contributions to Mineralogy and Petrology》1980,74(1):107-108

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Editors' note     

Giuliano F. Panza  Stephan Mueller  Erhard Wielandt 《Pure and Applied Geophysics》1980,118(2):1191-1191

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A crustal section across the Eastern Alps based on gravity and seismic refraction data     

Stephan Mueller  Manik Talwani 《Pure and Applied Geophysics》1971,85(1):226-239

Summary Existing gravity and seismic refraction data are used to deduce a crustal cross section across the Eastern Alps along the meridian 11°.4 East. The results suggest that a high density body of the Ivrea type is present under the southern margin of the Alps, that the Apennines do not have a crustal root extending to a depth of 50 km and that a profound discontinuity extending to the base of the crust exists between the Apennines and the Po Valley.Lamont-Doherty Contribution No. 1590.  相似文献   

Low-temperature heat capacity of magnesioferrite (MgFe2O4)     

Stephan Klemme  Martin Ahrens 《Physics and Chemistry of Minerals》2005,32(5-6):374-378

The low-temperature heat capacity of magnesioferrite (MgFe₂O₄) was measured between 1.5 K and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly was observed. From our data, we suggest a standard entropy (298.15 K) for magnesioferrite of 120.8±0.6 J mol⁻¹ K⁻¹, which is about 2.4 J mol⁻¹ K⁻¹ higher than previously reported calorimetric studies; but is in rough agreement with predictions from sets of internally consistent thermodynamic data.  相似文献   

Do clay mineral dissolution rates reach steady state?     

Stephan J. Köhler  Dirk Bosbach 《Geochimica et cosmochimica acta》2005,69(8):1997-2006

The temporal evolution of natural illite du Puy dissolution rates was measured from Si release rates in single-pass flow-through experiments lasting at least 100 days at 25°C and pH ranging from 2 to 12. Si release rates decreased by a factor of five and three at pH 12 and 2, respectively, during the experiments. These observations are interpreted to stem from changes in illite du Puy reactive surface area during these experiments. As the edges of clay minerals dissolve faster than the basal planes, dissolution tends to change clay mineral morphology decreasing the percentage of reactive edge sites. This continuously changing morphology prevents illite dissolution rates from attaining steady state during laboratory experiments lasting 100 to 200 days. A similar temporal decrease in dissolution rates is evident for many different sets of clay mineral dissolution rate data available in the literature. It seems reasonable, therefore, to expect that clay mineral dissolution does not attain steady state in nature, but rather their dissolution rates decrease continuously during their dissolution.  相似文献   

Moho depth and three-dimensional P and S structure of the crust and uppermost mantle in the Eastern Mediterranean and Middle East derived from tomographic inversion of local ISC data   总被引：1，自引：0，他引：1  

Ivan Koulakov  Stephan V. Sobolev 《Geophysical Journal International》2006,164(1):218-235

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