Nature of the Martian uplands: Effect on Martian meteorite age distribution and secondary cratering     

William K. Hartmann  Nadine G. Barlow 《Meteoritics & planetary science》2006,41(10):1453-1467

Abstract— Martian meteorites (MMs) have been launched from an estimated 5–9 sites on Mars within the last 20 Myr. Some 80–89% of these launch sites sampled igneous rock formations from only the last 29% of Martian time. We hypothesize that this imbalance arises not merely from poor statistics, but because the launch processes are dominated by two main phenomena: first, much of the older Martian surface is inefficient in launching rocks during impacts, and second, the volumetrically enormous reservoir of original cumulate crust enhances launch probability for 4.5 Gyr old rocks. There are four lines of evidence for the first point, not all of equal strength. First, impact theory implies that MM launch is favored by surface exposures of near‐surface coherent rock (≤10² m deep), whereas Noachian surfaces generally should have ≥10² m of loose or weakly cemented regolith with high ice content, reducing efficiency of rock launch. Second, similarly, both Mars Exploration Rovers found sedimentary strata, 1–2 orders of magnitude weaker than Martian igneous rocks, favoring low launch efficiency among some fluvial‐derived Hesperian and Noachian rocks. Even if launched, such rocks may be unrecognized as meteorites on Earth. Third, statistics of MM formation age versus cosmic‐ray exposure (CRE) age weakly suggest that older surfaces may need larger, deeper craters to launch rocks. Fourth, in direct confirmation, one of us (N. G. B.) has found that older surfaces need larger craters to produce secondary impact crater fields (cf. Barlow and Block 2004). In a survey of 200 craters, the smallest Noachian, Hesperian, and Amazonian craters with prominent fields of secondaries have diameters of ?45 km, ?19 km, and ?10 km, respectively. Because 40% of Mars is Noachian, and 74% is either Noachian or Hesperian, the subsurface geologic characteristics of the older areas probably affect statistics of recognized MMs and production rates of secondary crater populations, and the MM and secondary crater statistics may give us clues to those properties.  相似文献   

The planetary nebula K 1-2 and its binary central star VW Pyx     

K. M. Exter  D. L. Pollacco  S. A. Bell 《Monthly notices of the Royal Astronomical Society》2003,341(4):1349-1359

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Surface brightness profiles and structural parameters for 53 rich stellar clusters in the Large Magellanic Cloud     

A. D. Mackey  G. F. Gilmore 《Monthly notices of the Royal Astronomical Society》2003,338(1):85-119

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LU Vel (GJ 375): A M3.5Ve Flare and Double-Lined Spectroscopic Binary     

D. Montes  M. C. Gálvez  M. J. Fernández-Figueroa  I. Crespo-Chacón 《Astrophysics and Space Science》2006,304(1-4):367-369

High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D₁&D₂, He i D₃, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics.  相似文献   

Isotope hydrological study of mean transit time in the granitic Strengbach catchment (Vosges massif,France): application of the FlowPC model with modified input function     

D. Viville  B. Ladouche  T. Bariac 《水文研究》2006,20(8):1737-1751

Measurements of ¹⁸O concentrations in precipitation, soil solution, spring and runoff are used to determine water transit time in the small granitic Strengbach catchment (0·8 km²; 883–1146 m above sea level) located in the Vosges Mountains of northeastern France. Water transit times were calculated by applying the exponential, exponential piston and dispersion models of the FlowPC program to isotopic input (rainfall) and output (spring and stream water) data sets during the period 1989–95. The input function of the model was modified compared with the former version of the model and estimated by a deterministic approach based on a simplified hydrological balance. The fit between observed and calculated output data showed marked improvements compared with results obtained using the initial version of the model. An exponential piston version of the model applied to spring water indicates a 38·5 month mean transit time, which suggests that the volume in the aquifer, expressed in water depth, is 2·4 m. A considerable thickness (>45 m) of fractured bedrock may be involved for such a volume of water to be stored in the aquifer. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Morphological redshift estimates for galaxy clusters in a Sunyaev–Zel'dovich effect survey     

J. M. Diego  J. Mohr  J. Silk  G. Bryan 《Monthly notices of the Royal Astronomical Society》2003,341(2):599-608

We develop a new method to estimate the redshift of galaxy clusters through resolved images of the Sunyaev–Zel'dovich effect (SZE). Our method is based on morphological observables which can be measured by actual and future SZE experiments. We test the method with a set of high-resolution hydrodynamical simulations of galaxy clusters at different redshifts. Our method combines the observables in a principal component analysis. After calibrating the method with an independent redshift estimation for some of the clusters, we show – using a Bayesian approach – how the method can give an estimate of the redshift of the galaxy clusters. Although the error bars given by the morphological redshift estimation are large, it should be useful for future SZE surveys where thousands of clusters are expected to be detected; a first preselection of the high-redshift candidates could be done using our proposed morphological redshift estimator. Although not considered in this work, our method should also be useful to give an estimate of the redshift of clusters in X-ray and optical surveys.  相似文献   

A charge-coupled device study of high-latitude Galactic structure: testing the model parameters     

S. Karaali  S. G. Ak  S. Bilir  Y. Karata&#;  G. Gilmore † 《Monthly notices of the Royal Astronomical Society》2003,343(3):1013-1024

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The new model of a tidally disrupted star: further development and relativistic calculations     

P. B. Ivanov  M. A. Chernyakova  I. D. Novikov 《Monthly notices of the Royal Astronomical Society》2003,338(1):147-155

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Green Lake Landslide and other giant and very large postglacial landslides in Fiordland,New Zealand     

Graham T. Hancox  Nick D. Perrin 《Quaternary Science Reviews》2009,28(11-12):1020-1036

Green Lake Landslide is an ancient giant rock slide in gneiss and granodiorite located in the deeply glaciated Fiordland region of New Zealand. The landslide covers an area of 45 km² and has a volume of about 27 km³. It is believed to be New Zealand's largest landslide, and possibly the largest landslide of its type on Earth. It is one of 39 known very large (10⁶–10⁷ m³) and giant (≥10⁸ m³) postglacial landslides in Fiordland discussed in the paper. Green Lake Landslide resulted in the collapse of a 9 km segment of the southern Hunter Mountains. Slide debris moved up to 2.5 km laterally and 700 m vertically, and formed a landslide dam about 800 m high, impounding a lake about 11 km long that was eventually infilled with sediments. Geomorphic evidence supported by radiocarbon dating indicates that Green Lake Landslide probably occurred 12 000–13 000 years ago, near the end of the last (Otira) glaciation. The landslide is described, and its geomorphic significance, age, failure mechanism, cause, and relevance in the region are discussed, in relation to other large landslides and recent earthquake-induced landslides in Fiordland. The slope failure occurred on a low-angle fault zone undercut by glacial erosion, and was probably triggered by strong shaking (MM IX–X) associated with a large (≥ M 7.5–8) earthquake, on the Alpine Fault c. 80 km to the northwest. Geology was a major factor that controlled the style and size of Green Lake landslide, and in that respect it is significantly different from most other gigantic landslides. Future large earthquakes on the Alpine Fault in Fiordland are likely to trigger more very large and giant landslides across the region, causing ground damage and devastation on a scale that has not occurred during the last 160 years, with potentially disastrous effects on towns, tourist centres, roads, and infrastructure. The probability of such an event occurring within the next 50 years may be as high as 45%.  相似文献   

A mechanism of formation of globular clusters in the corona of a giant elliptical galaxy     

V. G. Gorbatskii 《Astrophysics》1990,32(2):149-154

Leningrad State University. Translated from Astrofizika, Vol. 32, No. 2, pp. 267–275, March–April, 1990.  相似文献