Ultraviolet reflectivity and geometrical albedo of Titan     

Edwin S. Barker  Laurence M. Trafton 《Icarus》1973,20(4):444-454

Intermediate resolution (6Å) photoelectric spectral scans of Titan, Saturn, Saturn's Rings and the Moon appear in two forms: ratio spectra of Titan vs the Rings and of Saturn vs the Rings, and relative reflectivities, which are compared to previously published results. Titan's geometrical albedo of 0.094 ± 0.012 was measured at 4255Å with a 50Å bandpass. From this and the spectral measurements, we derived the geometrical albedo as a function of wavelength. We find that the wavelength dependences of Titan's uv spectrum and the spectrum of Saturn's Rings are remarkably similar. No trace of any absorption bands is apparent. These results imply that uv gaseous absorption and Rayleigh scattering play a strongly subdued role in Titan's atmosphere. Any homogeneous atmospheric model implies that the absorber responsible for Titan's uv spectral albedo varies strongly with wavelength. On the other hand, we find that the uv observations can be satisfied by an absorber having a relatively weak dependence upon wavelength if an inhomogeneous atmospheric model is employed. In particular, a fine dust, which absorbs as 1/λ, can explain the uv observations provided that it is preferentially distributed high up in Titan's atmosphere where the optical depth from Rayleigh scattering is low. The likely presence of such a dust in Jupiter's atmosphere and the difficulty in explaining the nature of a continuous uv absorber which varies rapidly with wavelength suggest that the gas and aerosol in Titan's atmosphere are inhomogeneously distributed.  相似文献   

Modern methods in the astrometry of double stars     

Laurence W. Fredrick 《Astrophysics and Space Science》1985,110(1):111-115

The techniques for studying double stars continue to evolve in a predictable way. The most recent major breakthroughs have been the area scanner and speckle interferometry. On the horizon looms the application of large format CCDs which will replace the photographic plate for many astrometric problems.Communication presented at the International Conference on Astrometric Binaries, held on 13–15 June, 1984, at the Remeis-Sternwarte Bamberg, Germany, to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel (1784–1846).  相似文献   

Possible fossil H₂O liquid-ice interfaces in the Martian crust     

Laurence A. Soderblom  David B. Wenner 《Icarus》1978,34(3):622-637

Throughout the northern equatorial region of Mars, extensive areas have been uniformly stripped, roughly to a constant depth. These terrains vary widely in their relative ages. A model is described here to explain this phenomenon as reflecting the vertical distribution of H₂O liquid and ice in the crust. Under present conditions the Martian equatorial regions are stratified in terms of the stability of water ice and liquid water. This arises because the temperature of the upper 1 or 2 km is below the melting point of ice and liquid is stable only at greater depth. It is suggested here that during planetary outgassing earlier in Martian history H₂O was injected into the upper few kilometers of the crust by subsurface and surface volcanic eruption and lateral migration of the liquid and vapor. As a result, a discontinuity in the physical state of materials developed in the Martian crust coincident with the depth of H₂O liquid-ice phase boundary. Material above the boundary remained pristine; material below underwent diagenetic alteration and cementation. Subsequently, sections of the ice-laden zone were erosionally stripped by processes including eolian deflation, gravitational slump and collapse, and fluvial transport due to geothermal heating and melting of the ice. The youngest plains which display this uniform stripping may provide a minimum stratigraphic age for the major period of outgassing of the planet. Viking results suggest that the total amount of H₂O outgassed is less than half that required to fill the ice layer, hence any residual liquid eventually found itself in the upper permafrost zone or stored in the polar regions. Erosion stopped at the old liquid-ice interface due to increased resistance of subjacent material and/or because melting of ice was required to mobilize the debris. Water ice may remain in uneroded regions, the overburden of debris preventing its escape to the atmosphere. Numerous morphological examples shown in Viking and Mariner 9 images suggest interaction of impact, volcanic, and gravitational processes with the ice-laden layer. Finally, volcanic eruptions into ice produces a highly oxidized friable amorphous rock, palagonite. Based on spectral reflectance properties, these materials may provide the best analog to Martian surface materials. They are easily eroded, providing vast amounts of eolian debris, and have been suggested (Toulmin et al., 1977) as possible source rocks for the materials observed at the Viking landing sites.  相似文献   

Assessing and monitoring local and long-range-transported hydrocarbons as potential stressors to fish stocks     

Arnfinn Skadsheim  Steinar Sanni  Laurence Pinturier  Ulf-Einar Moltu  Melania Buffagni  Laura Bracco   《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):2037

The Arctic is poorly described and understood compared to the North Sea and other boreal areas. We need to learn how knowledge obtained at boreal conditions may be applied at Arctic conditions. Increasing activity of the hydrocarbon industry may cause exposure stress from discharges. Within a joint industry research programme (Biosea) we studied how responses in fish from oil exposure may differ at North Sea boreal and Barents Sea Arctic conditions. Hydrocarbon uptake, metabolites, and enzymatic and genotoxic biomarker type of effect responses were measured in cod (Gadus morhua L.). Hydrocarbon metabolites remain longer in fish bile than original hydrocarbons, which are eliminated fast from tissues. The metabolites may be measured to background concentrations. They describe exposure and they constitute a link to other effects. Body burden, biliary polyaromatic hydrocarbon (PAH) metabolite concentration, and quantities of Cytochrome P-450 1A (CYP1A) and DNA adducts increased with oil in water concentration. The extent of biomarker expression was lower for some biomarkers and elimination was slower at the lowest temperature. The results show that several factors have to be accounted for if warm-water biomarker data are to be applied in cold water.  相似文献   

The Creston,California, meteorite fall and the origin of L chondrites     

Peter Jenniskens  Jason Utas  Qing‐Zhu Yin  Robert D. Matson  Marc Fries  J. Andreas Howell  Dwayne Free  Jim Albers  Hadrien Devillepoix  Phil Bland  Aaron Miller  Robert Verish  Laurence A. J. Garvie  Michael E. Zolensky  Karen Ziegler  Matthew E. Sanborn  Kenneth L. Verosub  Douglas J. Rowland  Daniel R. Ostrowski  Kathryn Bryson  Matthias Laubenstein  Qin Zhou  Qiu‐Li Li  Xian‐Hua Li  Yu Liu  Guo‐Qiang Tang  Kees Welten  Marc W. Caffee  Matthias M. M. Meier  Amy A. Plant  Colin Maden  Henner Busemann  Mikael Granvik   《Meteoritics & planetary science》2019,54(4):699-720

It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν₆ resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance.  相似文献   

The management of artisanal fishing within the Marine Protected Area of the Port-Cros National Park (northwest Mediterranean Sea): a success story?     

Cadiou  Gwenael; Boudouresque  Charles F.; Bonhomme  Patrick; Le Direach  Laurence 《ICES Journal of Marine Science》2009,66(1):41-49

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Stratigraphic simulations of the shelf of the Gulf of Lions: testing subsidence rates and sea‐level curves during the Pliocene and Quaternary     

Estelle Leroux  Marina Rabineau  Daniel Aslanian  Didier Granjeon  Laurence Droz  Christian Gorini 《地学学报》2014,26(3):230-238

Determining the relative importance of factors interacting to control stratigraphic organization is a key issue in sedimentology. The Pliocene‐Quaternary chronostratigraphy on the Gulf of Lions platform is still poorly constrained, giving rise to different interpretations of the evolution of its subsidence through time. This paper examines the Pliocene‐Quaternary sedimentary filling of the Gulf of Lion's shelf with Dionisos, a numerical stratigraphic model. Our results show that a constant subsidence rate accurately reproduces the observed geometries, whereas a varying subsidence rate reproduces them only if the acceleration of subsidence is limited. At this time‐scale, a third‐order eustatic curve is also reappraised: a higher resolution curve (built using δ¹⁸O measurements) gives a more realistic restitution of our stratigraphic markers. Finally, the constant subsidence rate and sediment fluxes implied in these modellings are discussed relative to climate and local factors of sedimentation.  相似文献   

Cl and Na Fluxes in an Andean Foreland Basin of the Peruvian Amazon: An Anthropogenic Impact Evidence     

Jean-Sébastien Moquet  Laurence Maurice  Alain Crave  Jérôme Viers  Nore Arevalo  Christelle Lagane  Waldo Lavado-Casimiro  Jean-Loup Guyot 《Aquatic Geochemistry》2014,20(6):613-637

The dissolved load of the Amazon River is generally considered to be lowly impacted by anthropogenic activities. In this work, based on the chemical and hydrological database of the Environmental Research Observatory—HYBAM (http://www.ore-hybam.org), we explore the importance of the Peruvian Foreland petroleum activity on the dissolved Na and Cl fluxes of the Amazon River. The main result of this study allows us suggesting that oil extraction activity, concentrated in the El Tigre River basin, a small foreland watershed in the Peruvian Amazon, influenced drastically the Na and Cl exportation of the Amazon River during the 2006–2007 period. During these years,  the dissolved exportations of this basin represented almost 20 % of the annual dissolved Cl Amazon flux and almost 12 % of the annual dissolved Na Amazon flux for a mean annual discharge <1 % of the Amazon River discharge. Since the last decades, the anthropogenic activities are increasing over the whole Amazon basin, especially in Andean countries. In this context, our results demonstrate that extractive activity cannot be considered as negligible on the hydro-chemistry of the Amazonian Rivers especially for the weathering budget estimation based on river-dissolved loads. Moreover, Cl and Na can be used to trace the formation waters derived from oil extraction at a large spatial scale. The environmental impacts of contaminants associated with deep water released to the hydrosystem (polycyclic aromatics hydrocarbons, metallic trace elements, etc.) at local and regional scales are still underestimated and should be monitored to map their local and regional influence and to prevent their risks on human health.  相似文献   

Organic Pollutants in Coastal Waters,Sediments, and Biota: A Relevant Driver for Ecosystems During the Anthropocene?     

Jordi Dachs  Laurence Méjanelle 《Estuaries and Coasts》2010,33(1):1-14

The total number of synthetic organic chemicals introduced to the environment by humans has never been quantified, but it is not lower than thousands. A fraction of these chemicals have toxic effects to coastal organisms and presumably affect ecosystems structure and function. During the last decades, some of the processes affecting the transport, degradation, and fate of a limited number of chemicals have been studied, and the rising concern for environmental risk of organic chemical has lead to the regulation of a few of them by national and international organisms. However, the environmental inventory of organic pollutants is far from being quantified, and current methodologies used in most toxicological tests only allow to determine effects of individual chemicals to organisms. There are major limitations on appropriate methodologies to assess the effects of organic pollutants at population and ecosystem levels and the effects induced by complex mixtures of organic pollutants present in natural environments. The modification of the composition of the biosphere by a myriad of organic pollutants at ultra-trace levels is not yet regarded as another vector of environmental change which is irreversible due to the persistent character of many of these chemicals and due to its global coverage. Here, we claim that the modification of the atmosphere, water, sediments, and biota composition is a factor to be taken into account in coastal ecosystems, and that its pressure on the environment has been exponentially increasing during the last six decades of the anthropocene.  相似文献   

On the water and energy cycles in the Tropics     

Rémy Roca  Jean-Claude Bergès  Hélène Brogniez  Michel Capderou  Philippe Chambon  Olivier Chomette  Sophie Cloché  Thomas Fiolleau  Isabelle Jobard  Julien Lémond  Mohamed Ly  Laurence Picon  Patrick Raberanto  André Szantai  Michel Viollier 《Comptes Rendus Geoscience》2010,342(4-5):390-402

The water and energy cycles are major elements of the Earth climate. These cycles are especially active in the intertropical belt where satellites provide the most suitable observational platform. The history of Earth observations of the water cycle and of the radiation budget viewed from space reveals that the fundamental questions from the early times are still relevant for today's research. The last 2 decades have seen a number of milestones regarding the documentation of rainfall, mesoscale convective systems (MCS), water vapour and radiation at the top of the atmosphere (TOA). Beyond dedicated missions that provided enhanced characterizations of some elements of the atmospheric water cycle and field campaigns that allowed the gathering of validation data, the advent of the long record of meteorological satellites lead to new questioning on the homogenisation of the data time series, etc. The use of this record to document the tropical climate brought new results of the distribution of humidity and reinforced the understanding of some robust features of the African monsoon. Challenges for the immediate future concerns the deepening of the understanding of the role of cloud systems in the monsoon circulation, the downscaling of the documentation of the water and energy cycle at the scale of these cloud systems, the research of better adequation between the users and the satellite estimate of rainfall and finally a much needed methodological effort to build exploitable time series for the estimation of climatic trends in the water and energy cycle in the Tropics. The required observations to address these challenges are rapidly presented with emphasis on the upcoming Megha-Tropiques (MT) mission.  相似文献