The OSIRIS‐REx target asteroid (101955) Bennu: Constraints on its physical,geological, and dynamical nature from astronomical observations          下载免费PDF全文

D. S. Lauretta  A. E. Bartels  M. A. Barucci  E. B. Bierhaus  R. P. Binzel  W. F. Bottke  H. Campins  S. R. Chesley  B. C. Clark  B. E. Clark  E. A. Cloutis  H. C. Connolly  M. K. Crombie  M. Delbó  J. P. Dworkin  J. P. Emery  D. P. Glavin  V. E. Hamilton  C. W. Hergenrother  C. L. Johnson  L. P. Keller  P. Michel  M. C. Nolan  S. A. Sandford  D. J. Scheeres  A. A. Simon  B. M. Sutter  D. Vokrouhlický  K. J. Walsh 《Meteoritics & planetary science》2015,50(4):834-849

We review the results of an extensive campaign to determine the physical, geological, and dynamical properties of asteroid (101955) Bennu. This investigation provides information on the orbit, shape, mass, rotation state, radar response, photometric, spectroscopic, thermal, regolith, and environmental properties of Bennu. We combine these data with cosmochemical and dynamical models to develop a hypothetical timeline for Bennu's formation and evolution. We infer that Bennu is an ancient object that has witnessed over 4.5 Gyr of solar system history. Its chemistry and mineralogy were established within the first 10 Myr of the solar system. It likely originated as a discrete asteroid in the inner Main Belt approximately 0.7–2 Gyr ago as a fragment from the catastrophic disruption of a large (approximately 100‐km), carbonaceous asteroid. It was delivered to near‐Earth space via a combination of Yarkovsky‐induced drift and interaction with giant‐planet resonances. During its journey, YORP processes and planetary close encounters modified Bennu's spin state, potentially reshaping and resurfacing the asteroid. We also review work on Bennu's future dynamical evolution and constrain its ultimate fate. It is one of the most Potentially Hazardous Asteroids with an approximately 1‐in‐2700 chance of impacting the Earth in the late 22nd century. It will most likely end its dynamical life by falling into the Sun. The highest probability for a planetary impact is with Venus, followed by the Earth. There is a chance that Bennu will be ejected from the inner solar system after a close encounter with Jupiter. OSIRIS‐REx will return samples from the surface of this intriguing asteroid in September 2023.  相似文献   

Amphibole as an archivist of magmatic crystallization conditions: problems,potential, and implications for inferring magma storage prior to the paroxysmal 2010 eruption of Mount Merapi,Indonesia     

Saskia?ErdmannEmail author  Caroline?Martel  Michel?Pichavant  Alexandra?Kushnir 《Contributions to Mineralogy and Petrology》2014,167(6):1016

Amphibole is widely employed to calculate crystallization temperature and pressure, although its potential as a geobarometer has always been debated. Recently, Ridolfi et al. (Contrib Mineral Petrol 160:45–66, 2010) and Ridolfi and Renzulli (Contrib Mineral Petrol 163:877–895, 2012) have presented calibrations for calculating temperature, pressure, fO₂, melt H₂O, and melt major and minor oxide composition from amphibole with a large compositional range. Using their calibrations, we have (i) calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations; and (ii) calculated crystallization conditions for amphibole from basaltic–andesitic pyroclasts erupted during the paroxysmal 2010 eruption of Mount Merapi in Java, Indonesia, to infer pre-eruptive conditions. Our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates. Calculated fO₂ and melt SiO₂ content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions. However, calculated crystallization pressure and melt H₂O content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters. Amphibole from Merapi’s pyroclasts yields calculated conditions of ~200–800 MPa, ~900–1,050 °C, ~NNO + 0.3–NNO + 1.1, ~3.7–7.2 wt% melt H₂O, and ~58–71 wt% melt SiO₂. We interpret the variations in calculated temperature, fO₂, and melt SiO₂ content as reasonable estimates, but conclude that the large calculated pressure variation for amphibole from Merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range. In contrast, bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas, respectively, and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth.  相似文献   

Dissolution–precipitation processes governing the carbonation and silicification of the serpentinite sole of the New Caledonia ophiolite     

Marc?UlrichEmail author  Manuel?Mu?oz  Stéphane?Guillot  Michel?Cathelineau  Christian?Picard  Benoit?Quesnel  Philippe?Boulvais  Clément?Couteau 《Contributions to Mineralogy and Petrology》2014,167(1):952

The weathering of mantle peridotite tectonically exposed to the atmosphere leads commonly to natural carbonation processes. Extensive cryptocrystalline magnesite veins and stock-work are widespread in the serpentinite sole of the New Caledonia ophiolite. Silica is systematically associated with magnesite. It is commonly admitted that Mg and Si are released during the laterization of overlying peridotites. Thus, the occurrence of these veins is generally attributed to a per descensum mechanism that involves the infiltration of meteoric waters enriched in dissolved atmospheric CO₂. In this study, we investigate serpentinite carbonation processes, and related silicification, based on a detailed petrographic and crystal chemical study of serpentinites. The relationships between serpentine and alteration products are described using an original method for the analysis of micro-X-ray fluorescence images performed at the centimeter scale. Our investigations highlight a carbonation mechanism, together with precipitation of amorphous silica and sepiolite, based on a dissolution–precipitation process. In contrast with the per descensum Mg/Si-enrichment model that is mainly concentrated in rock fractures, dissolution–precipitation process is much more pervasive. Thus, although the texture of rocks remains relatively preserved, this process extends more widely into the rock and may represent a major part of total carbonation of the ophiolite.  相似文献   

Field characterization and data integration to define the hydraulic heterogeneity of a shallow granular aquifer at a sub-watershed scale     

Daniel Paradis  Laurie Tremblay  René Lefebvre  Erwan Gloaguen  Alfonso Rivera  Michel Parent  Jean-Marc Ballard  Yves Michaud  Patrick Brunet 《Environmental Earth Sciences》2014,72(5):1325-1348

Providing a sound basis for aquifer management or remediation requires that hydrogeological investigations carried out to understand groundwater flow and contaminant transport be based on representative data that capture the heterogeneous spatial distribution of aquifer hydraulic properties. This paper describes a general workflow allowing the characterization of the heterogeneity of the hydraulic properties of granular aquifers at an intermediate scale of a few km². The workflow involves characterization and data integration steps that were applied on a 12-km² study area encompassing a decommissioned landfill emitting a leachate plume and its main surface water receptors. The sediments composing the aquifer were deposited in a littoral–sublittoral environment and show evidence of small-scale transitional heterogeneities. Cone penetrometer tests (CPT) combined with soil moisture and electrical resistivity (SMR) measurements were thus used to identify and characterize spatial heterogeneities in hydraulic properties over the study area. Site-specific statistical relationships were needed to infer hydrofacies units and to estimate hydraulic properties from high-resolution CPT/SMR soundings distributed all over the study area. A learning machine approach was used due to the complex statistical relationships between colocated hydraulic and CPT/SMR data covering the full range of aquifer materials. Application of this workflow allowed the identification of hydrofacies units and the estimation of horizontal hydraulic conductivity, vertical hydraulic conductivity and porosity over the study area. The paper describes and discusses data acquisition and integration methodologies that can be adapted to different field situations, while making the aquifer characterization process more time-efficient and less labor-intensive.  相似文献   

Machine Learning Feature Selection Methods for Landslide Susceptibility Mapping     

Natan Micheletti  Loris Foresti  Sylvain Robert  Michael Leuenberger  Andrea Pedrazzini  Michel Jaboyedoff  Mikhail Kanevski 《Mathematical Geosciences》2014,46(1):33-57

This paper explores the use of adaptive support vector machines, random forests and AdaBoost for landslide susceptibility mapping in three separated regions of Canton Vaud, Switzerland, based on a set of geological, hydrological and morphological features. The feature selection properties of the three algorithms are studied to analyze the relevance of features in controlling the spatial distribution of landslides. The elimination of irrelevant features gives simpler, lower dimensional models while keeping the classification performance high. An object-based sampling procedure is considered to reduce the spatial autocorrelation of data and to estimate more reliably generalization skills when applying the model to predict the occurrence of new unknown landslides. The accuracy of the models, the relevance of features and the quality of landslide susceptibility maps were found to be high in the regions characterized by shallow landslides and low in the ones with deep-seated landslides. Despite providing similar skill, random forests and AdaBoost were found to be more efficient in performing feature selection than adaptive support vector machines. The results of this study reveal the strengths of the classification algorithms, but evidence: (1) the need for relying on more than one method for the identification of relevant variables; (2) the weakness of the adaptive scaling algorithm when used with landslide data; and (3) the lack of additional features which characterize the spatial distribution of deep-seated landslides.  相似文献   

Influence of a hedge surrounding bottomland on seasonal soil‐water movement     

Virginie Caubel  Catherine Grimaldi  Philippe Merot  Michel Grimaldi 《水文研究》2003,17(9):1811-1821

The influence of a hedge surrounding bottomland on soil‐water movement along the hillslope was studied on a plot scale for 28 months. The study was based on the comparison of two transects, one with a hedge, the other without, using mainly a dense grid of tensiometers. The influence of the bottomland hedge was located in the area where tree roots were developed, several metres upslope from the hedge, and could be observed both in the saturated and non‐saturated zone, from May to December. The hedge induced a high rate of soil drying, because of the high evaporative capacity of the trees. We evaluated that water uptake by the hedge during the growing season was at least 100 mm higher than without a hedge. This increased drying rate led to a delayed rewetting of the soils upslope from the hedge in autumn, of about 1 month compared with the situation without a hedge. Several consequences of this delayed rewetting are expected: a delay in the return of subsurface transfer from the hillslope to the riparian zone, a buffering effect of hedges on floods, already observed at the catchment scale, and an increased residence time of pollutants. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

SHRIMP zircon U-Pb age, fitho- and biostratigraphic analyses of the Huaiyu Domain in South China,— Evidence for a Neoproterozoic orogen, not Late Paleozoic-Early Mesozoic collision     

Liangshu Shu Michel Faure Shaoyong Jiang Qun Yang Yujing Wang 《《幕》》2006,29(4):244-252

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Long-chain alkenones and U₃₇′ variability along a south–north transect in the Western Pacific Ocean     

Ilhem Bentaleb  Michel Fontugne  Luc Beaufort 《Global and Planetary Change》2002,34(3-4)

In this paper, we present 50 surface water samples collected during the IMAGES III cruise (June–July 1997) along a transect from New Zealand to the China Sea (42°S–178°E, 21°N–120°E) covering a temperature range from 13.3 to 30.4 °C. A very worthwhile aspect of this study is a coupling of both biomarker (alkenone) and coccolithophorid counting. We show that the U₃₇^k′–temperature relationship is very similar to the Prahl et al. [Geochim. Cosmochim. Acta 52 (1988) 2203] culture calibration and to the global core top calibration of Müller et al. [Geochim. Cosmochim. Acta 62 (1998) 1757]. However, in the warmest surface waters of the Western Pacific ocean (>26.4 °C) where Gephyrocapsa oceanica is likely the most widespread species, the associated U₃₇^k′ has a constant value of 1.0. The consequence is that above this temperature threshold, U₃₇^k′ cannot be used as an accurate paleothermometer.  相似文献   

Monte Carlo simulation of GCR neutron capture production of cosmogenic nuclides in stony meteorites and lunar surface     

D. Kollr  R. Michel  J. Masarik 《Meteoritics & planetary science》2006,41(3):375-389

Abstract— A purely physical model based on a Monte Carlo simulation of galactic cosmic ray (GCR) particle interaction with meteoroids is used to investigate neutron interactions down to thermal energies. Experimental and/or evaluated excitation functions are used to calculate neutron capture production rates as a function of the size of the meteoroid and the depth below its surface. Presented are the depth profiles of cosmogenic radionuclides ³⁶Cl, ⁴¹Ca, ⁶⁰Co, ⁵⁹Ni, and ¹²⁹I for meteoroid radii from 10 cm up to 500 cm and a 2π irradiation. Effects of bulk chemical composition on n‐capture processes are studied and discussed for various chondritic and lunar compositions. The mean GCR particle flux over the last 300 ka was determined from the comparison of simulations with measured ⁴¹Ca activities in the Apollo 15 drill core. The determined value significantly differs from that obtained using equivalent models of spallation residue production.  相似文献   

1999年8月11日日全食期间的重力吸引效应研究     

刘少明 《大地测量与地球动力学》2004,24(4):13-19

对1999年8月11日日全食阴影扫过欧洲期间,设在Annelles,Uccle,Walferdange和Bondy弹簧和超导重力仪的记录进行了分析.为了确定月亮对太阳万有引力可能的遮挡效应的极限,对超导和弹簧重力仪记录进行了比较.同时也对LCR和阿斯卡尼亚重力仪观测结果进行了讨论.结论是如果日食重力吸引效应存在,它应在超导重力仪±1 nm/s2(0.1×10-8ms-2)的观测精度范围之内.研究发现在以上情形下,弹簧和超导重力仪都在它们的精度范围内工作,并且日食引起的异常环境干扰可能使重力信号有重大的改变.  相似文献