Noble gas record and cosmic‐ray exposure history of the new CO3 chondrite Moss––Comparison with Lancé and other CO chondrite falls     

Rainer BARTOSCHEWITZ  Ulrich OTT  Luitgard FRANKE  Siegfried HERRMANN  Yukio YAMAMOTO  Keisuke NAGAO  Morten BILET  Thomas GRAU 《Meteoritics & planetary science》2010,45(8):1380-1391

Abstract– The Moss meteorite is the first CO chondrite fall after a time period of 70 yr and the least terrestrially contaminated member of its group. Its cosmic‐ray exposure (CRE) age (T₃ ～ 13.5 Ma; T₂₁ ～ 14.6 Ma) is distinct among CO chondrites and, within witnessed falls is the shortest after Lancé, which we have reanalyzed. Gas retention ages are approximately 3.95 × 10⁹ yr (U/Th‐He) and approximately 4.43 × 10⁹ yr (K/Ar), respectively. Trapped Ar, Kr, and Xe are present in Moss in abundances typical for CO chondrites, with “planetary” elemental and isotopic compositions. Presence of HL‐xenon from presolar diamonds is observed in the stepwise release analysis of Lancé. It may also be present in Moss, but it is difficult to ascertain in single‐step bulk analyses. It follows from our new data combined with a survey of the literature that the abundance of trapped gases in CO chondrites is not a good indicator of their petrological subtype.  相似文献   

Radiative transfer in the atmosphere of Venus and application to surface emissivity retrieval from VIRTIS/VEX measurements     

Rainer Haus  Gabriele Arnold 《Planetary and Space Science》2010,58(12):1578-1598

The radiation measurements of VIRTIS-M-IR (1-5 μm) on Venus Express provide a valuable database for systematic studies of the atmosphere and surface of the Earth’s sister planet. The present paper focuses on the investigation of physical parameters that determine the retrieval accuracy of deep atmosphere and surface features of Venus including compositional conditions, continuum absorption effects, and spectroscopic input data required for radiative transfer simulations. The parameter discussion shall serve as a reference for ongoing and future work on methodical and simulation input data improvements.The high variability of the nightside atmospheric and surface emission window radiances with respect to cloud opacity and surface elevation is modeled and discussed in direct comparison with measurements performed over the northern hemisphere. Venus surface elevation is retrieved using the 1.18 and 1.02 μm emission windows where radiance ratios are well suited to de-cloud the measurement data. In general, the ratio-based VIRTIS topography is in good agreement with the Magellan topography, but differences occur in localized areas. The paper discusses possible origins of such differences including surface emissivity “anomalies”. Surface emissivity variations that may be due to changes in the chemical composition (mineralogy) and surface texture are important indicators of the nature of the surface material.Preliminary radiance retrievals along a number of complete northern orbits reveal a trend towards lower values of highland surface emissivity compared to the surrounding lowlands. Already the Magellan radar experiment suggested compositional variations at moderately high altitudes over the tesserae. They probably indicate a more felsic component giving a hint to older surface forming processes.  相似文献   

Periodic Variability of Visual Sporadic Meteor Rates     

Audrius Dubietis  Rainer Arlt 《Earth, Moon, and Planets》2010,106(2-4):105-111

A long-term variability of visual sporadic meteor hourly rates is studied in the period between 1984 and 2006. The present analysis involves four particular periods of visual sporadic meteor activity in January, March, July and September over two solar cycles, and the results reveal that the observed visual sporadic meteor rates vary periodically in the course of the solar cycle. It is found that the highest sporadic meteor rates are observed in the years near solar activity maxima, and their variability directly correlates with solar activity expressed by International sunspot numbers.  相似文献   

Thermodynamic properties and equation of state of fcc aluminum and bcc iron, derived from a lattice vibrational method     

Michel H. G. Jacobs  Rainer Schmid-Fetzer 《Physics and Chemistry of Minerals》2010,37(10):721-739

We use a lattice vibrational technique to derive thermophysical and thermochemical properties of the pure elements aluminum and iron in pressure–temperature space. This semi-empirical technique is based on either the Mie–Grüneisen–Debye (MGD) approach or an extension of Kieffer’s model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity, electronic effects based on the free electron gas model, and magnetic effects based on the Calphad approach. We show that Keane’s equation of state for the static lattice is better suitable to represent thermodynamic data for aluminum from 1 bar to pressures in the multi-megabar region relative to Vinet’s universal and the Birch–Murnaghan equation of state. It appears that the MGD and Mie–Grüneisen–Kieffer approach produce similar results, but that the last one better represents heat capacity below room temperature. For iron we show that the high temperature behavior of thermal expansivity can be explained within the Calphad approach by a pressure-dependent Curie temperature with a slope between –1 and 0 K/GPa.  相似文献   

Symplectite formation during decompression induced garnet breakdown in lower crustal mafic granulite xenoliths: mechanisms and rates     

Júlia Dégi  Rainer Abart  Kálmán Török  Enikő Bali  Richard Wirth  Dieter Rhede 《Contributions to Mineralogy and Petrology》2010,159(3):293-314

The complex microstructure of kelyphitic rims around garnet in lower crustal garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field, Central Pannonian Basin has been studied in order to identify controls on garnet breakdown. Symplectites comprised of a vermicular intergrowth of submicron sized anorthite, orthopyroxene and spinel replace garnet at a sharp reaction front. Based on element distribution maps the transformation of garnet to symplectite is isochemical. Phase diagram calculations indicate that this reaction was induced by a pressure decrease and/or a temperature increase. In site-specific TEM foils prepared by focused ion beam technique and oriented parallel and perpendicular to the reaction front 200 nm wide rods of anorthite and 20 nm wide rods of spinel are identified. The rods are oriented approximately perpendicular to the replacement front and are embedded in an orthopyroxene matrix. The regular spacing of the symplectite phases along the reaction front suggests that their growth is controlled by diffusion. The kinetics of symplectite formation has been modelled based on irreversible thermodynamics. During interaction of the xenolith with the host basalt the microstructure and chemistry of the An–Opx–Spl symplectite was significantly modified and it was partially replaced by an olivine bearing symplectite. In contrast to primary symplectite formation, these processes were metasomatic in nature including addition of sodium, titanium and some trace elements from the basaltic melt and can clearly be discerned from the garnet breakdown. Based on these observations it is inferred that symplectite formation took place within the deep crust during the extension of the Pannonian Basin between 15 and 30 km depth at high temperature (850–1,050°C) prior to the volcanic transport to the surface.  相似文献   

Comment on “Cosmogenic neon in grains separated from individual chondrules: Evidence of precompaction exposure in chondrules” by J. P. Das,J. N. Goswami,O. V. Pravdivtseva,A. P. Meshik,and C. M. Hohenberg     

U. Ott  R. Wieler  L. Huber 《Meteoritics & planetary science》2013,48(8):1524-1528

Das et al. (2012) claim that in several cases nominal cosmic ray exposure ages derived from concentrations of cosmogenic Ne in individual olivine grains separated from chondrules substantially exceed exposure ages of matrix samples. Some grains were also reported to show larger apparent exposure ages than other grains from the same chondrule. The authors conclude that the excesses were caused by an exposure of chondrules to high fluences of solar energetic particles and suggest that their data provide direct evidence for a highly active phase of the early Sun, similar to what is observed in X‐ray emissions of recent naked T‐Tauri stars. Here, we show that the production rates of cosmogenic Ne used by Das et al. (2012) to derive nominal cosmic ray exposure ages of their olivine grains are often much too low, as the reported major element concentrations in many cases sum up to considerably less than 100% even if converted to oxides. In contrast, adopted element concentrations for matrix samples are basically self‐consistent. A precompaction exposure of chondrules to a very high flux of solar energetic particles is thus not supported by the data presented by Das et al. (2012). Das et al. (2012) claim that in several cases nominal cosmic ray exposure ages derived from concentrations of cosmogenic Ne in individual olivine grains separated from chondrules substantially exceed exposure ages of matrix samples. Some grains were also reported to show larger apparent exposure ages than other grains from the same chondrule. The authors conclude that the excesses were caused by an exposure of chondrules to high fluences of solar energetic particles and suggest that their data provide direct evidence for a highly active phase of the early Sun, similar to what is observed in X‐ray emissions of recent naked T‐Tauri stars. Here, we show that the production rates of cosmogenic Ne used by Das et al. (2012) to derive nominal cosmic ray exposure ages of their olivine grains are often much too low, as the reported major element concentrations in many cases sum up to considerably less than 100% even if converted to oxides. In contrast, adopted element concentrations for matrix samples are basically self‐consistent. A precompaction exposure of chondrules to a very high flux of solar energetic particles is thus not supported by the data presented by Das et al. (2012).  相似文献   

The abundance and isotopic composition of Cd in iron meteorites     

Thomas S. Kruijer  Peter Sprung  Thorsten Kleine  Ingo Leya  Rainer Wieler 《Meteoritics & planetary science》2013,48(12):2597-2607

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility‐controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of ¹¹³Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd‐Pt‐W isotope results from this study thus demonstrate that the relative magnitude of neutron capture‐induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites.  相似文献   

Accretion and Early History of Planetesimals and Planets: The Noble Gas Record     

Rainer Wieler 《Earth, Moon, and Planets》2011,108(1):1-8

Some of the distinct noble gas “components” in meteorites represent a record of processes during and even before solar system formation. This record is difficult to interpret. Often, one of the major problems is to recognize whether a certain noble gas elemental and isotopic pattern has been established in a presolar epoch, later in the solar accretion disk, during meteorite parent body formation or finally as a result of metamorphism on a parent body. It would also appear that noble gases are a preferred tool to deduce the types of matter from which the Earth and other planets accreted—if the respective parent materials are present in our extraterrestrial sample collections at all. However, also this issue is unsettled. Noble gas isotopes originating from the decay of radioactive precursors allow us to study the early and later degassing history of terrestrial planets, although the interpretation often remains model-dependent. This contribution briefly reviews some of the fundamental aspects of the noble gas record in meteorites and planets.  相似文献   

Measured ion-molecule reaction rates for modelling Titan's atmosphere     

Seksan Dheandhanoo  Rainer Johnsen  Manfred A. Biondi 《Planetary and Space Science》1984,32(10):1301-1305

Rate coefficients for several two- and three-body ion-molecule reactions involving hydrocarbons have been determined at thermal energies and above using drift tube-mass spectrometer techniques. The measured rates for clustering and breakup reactions involving CH₅⁺ and C₂H₅⁺ ions in methane are found to be strongly temperature dependent in the range from 80 to 240 K. The equilibrium constants determined for these reactions differ somewhat from those of Hiraoka and Kebarle. Rate coefficients for two-body reactions of CH₅⁺, C₂H₅⁺, N⁺, H⁺ and D⁺ ions with methane and/or ethane have been measured. The results indicate that the product yields of several of the fast ion-molecule reactions depend strongly on ion energy (temperature), and therefore previous room-temperature results may be of limited value for model calculations of Titan's atmosphere.  相似文献   

Origin and history of chondrite regolith,fragmental and impact-melt breccias from Spain     

I. Casanova  K. Keil  R. Wieler  A. San Miguel  E. A. King 《Meteoritics & planetary science》1990,25(2):127-135

Abstract— Six ordinary chondrite breccias from the Museo Nacional de Ciencias Naturales, Madrid (Spain), are described and classified as follows: the solar gas-rich regolith breccia Oviedo (H5); the pre-metamorphic fragmental breccias Cabezo de Mayo (type 6, L-LL), and Sevilla (LL4); the fragmental breccias Cañellas (H4) and Gerona (H5); and the impact melt breccia, Madrid (L6). We confirm that chondrites with typical light-dark structures and petrographic properties typical of regolith breccias may (Oviedo) or may not (Cañellas) be solar gas-rich. Cabezo de Mayo and Sevilla show convincing evidence that they were assembled prior to peak metamorphism and were equilibrated during subsequent reheating. These meteorites contain small melt rock clasts that were incorporated into the host chondrite while still molten and/or plastic and cooled rapidly and, yet, are totally equilibrated with their hosts. Compositions of olivine and low-Ca pyroxene in host chondrite and breccia clasts in Cabezo de Mayo are transitional between groups L and LL. It is suggested, based on mineralogic and oxygen isotopic compositions of host and clasts, that the rock formed on the L parent body by mixing, prior to peak metamorphism. This was followed by partial equilibration of two different materials: the indigenous L chondrite host and exotic LL melt rock clasts.  相似文献