Titan's surface before Cassini     

Ralph D. Lorenz  Jonathan I. Lunine 《Planetary and Space Science》2005,53(5):557-576

We review current understanding of Titan's surface, synthesizing a paradigm from Earth-based radar observations and near-infrared surface maps, together with reanalysis of Voyager data and results from published theoretical models. Based on these we suggest that Titan has a varied landscape with a variety of tectonic and erosive features indicative of geologic activity, and an impact crater population reflective of the dense atmosphere.  相似文献   

Numerical calculations of the longevity of impact oases on Titan     

David P. O'Brien  Ralph D. Lorenz  Jonathan I. Lunine 《Icarus》2005,173(1):243-253

A promising setting for the formation of interesting prebiotic molecules on Titan is the transient liquid water environment formed by a comet impact, as originally suggested by Thompson and Sagan (1992, in: Symposium on Titan, ESA SP, vol. 338, p. 167). The impact melt (water or a water-ammonia mixture) generated in such an event can react with the abundant photochemical hydrocarbons and nitriles deposited on the surface of Titan to form more complex molecules such as purines and amino acids. We use a finite-difference thermal conduction code to calculate how long it takes for realistic liquid deposits in crater floors to freeze in the Titan environment. Our results suggest that 15 km diameter craters can sustain liquid water or water-ammonia environments for ∼¹⁰²-10³ yr and 150 km craters can sustain them for ∼¹⁰³-10⁴ yr. We discuss the implications of these timescales for organic chemistry on Titan.  相似文献   

Estimating the water content of hydrated minerals using reflectance spectroscopy: II. Effects of particle size     

Ralph E. Milliken  John F. Mustard 《Icarus》2007,189(2):574-588

Visible-near infrared reflectance spectra for five particle size fractions of a Hawaiian palagonite (HWMK101) and a nontronite (ferruginous smectite, Clay Minerals Society source clay SWa-1) were measured under ambient, purged, and heated conditions to characterize the effects of surface and volume scattering on the relationship between absolute H₂O content and the strength of the 3 μm absorption feature. Both materials were ground and dry sieved to particle sizes of <25, 25-45, 45-75, 75-125, and 125-250 μm. Particles of the bulk palagonite have an approximate bimodal distribution consisting of small, amorphous particles <5 μm in diameter mixed with crystalline and glass particles <1 mm in diameter, whereas the nontronite particles are polycrystalline aggregates. We find that band parameters value relating the strength of the 3 μm hydration feature to water content increase with particle size for a given water content, regardless of whether reflectance or single scattering albedo spectra are used. Spectra generally increase in reflectance as particle size decreases, a result of the relative increase in volume to surface scattering. Spectra of large particles are commonly saturated in the 3 μm region due to an increase in optical path length, making an accurate estimate of water content indeterminate until the samples dehydrate to the volume-scattering regime. We find that the presence of fines in several of the size fractions of palagonite cause their spectra to be representative of the finest fraction rather than the mean particle size. The nontronite spectra appear to be representative of an effective particle size within the range of the sieved size fractions. Many planetary surfaces are expected to have a large number of small particles which can dominate their spectral signature. Our results for particles <45 μm provide a reasonable model for estimating the H₂O content of hydrated asteroids and regions of Mars.  相似文献   

Body Wave Amplitude Calculations—II     

Ralph A. Wiggins 《Geophysical Journal International》1976,46(1):1-10

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Detecting rift basins in the Evans Ice Stream region of West Antarctica using airborne gravity data     

Philip C. Jones  Ashley C. Johnson  Ralph R. B. von Frese  Hugh Corr 《Tectonophysics》2002,347(1-3)

A total of 11,500 line km of aerogravity data have been used to construct an free-air gravity anomaly map for the Antarctic region that may contain the microplate boundary between the Haag Nunataks block and southern Antarctic Peninsula. Along-line free-air gravity anomaly data resolved wavelengths of 9 km or greater with better than 5 mGal accuracy. Coincident radio echo soundings provided data to construct a digital terrain model. The gravity effect of the terrain was calculated by Gauss–Legendre quadrature (GLQ) and spectrally correlated with the free-air gravity data. Terrain-correlated free-air anomalies related to possible isostatic imbalances of the crust were separated from terrain-decorrelated anomalies that may reflect intra-crustal density contrasts. Subtracting terrain-correlated free-air anomalies from the gravity effects of the terrain yielded compensated terrain gravity effects (CTGE) that were used to model the Moho by inversion. The results indicate moderate but significant crustal thinning below the Evans Ice Stream that is consistent with an extensional origin for the deep, wide, steep-sided trough that contains the ice stream as well as the continued elevation of the footwall flank of the basin. Changes along the axis of the rift, both in the gravity anomaly field and the distribution of Moho topography, can be explained by processes associated with continental lithospheric extension. Subsequently, many of the features produced by extension have been modified by glacial erosion and the sub-ice topography and gravity data reflect this.  相似文献   

Basement control on oblique thrust sheet evolution: seismic imaging of the active deformation front of the Central Andes in Bolivia     

Ralph Hinsch  Charlotte M. Krawczyk  Christoph Gaedicke  Raul Giraudo  Daniel Demuro 《Tectonophysics》2002,355(1-4)

In the area of the Bolivian Orocline, we examine the deformation pattern associated with the active development of a new thrust sheet. A dense grid of reprocessed 2-D seismic lines from hydrocarbon exploration industry is interpreted and a 3-D simplified structural and kinematic model is deduced. In the Boomerang Hills, onlapping Paleozoic and foredeep sediments are detached from the underlying S-dipping basement. They are thrust northeastwards by less than 2 km. Two zones can be differentiated along the Andean deformation front: (1) a W–E to NW–SE striking frontal segment of predominantly orthogonal shortening, comprising a thrust and anticline system; (2) a WSW–ENE striking lateral zone of oblique shortening within a complex system of thin-skinned strike–slip faults and minor folds. The deformation front always follows a pronounced edge in the topography of the top basement surface close to the boundary of the Paleozoic basin. The observed deformation pattern indicates intensified strain partitioning caused by the interaction of contraction direction and basement topography, which provides a near oblique ramp for the onlapping wedge of sediments. The SW–NE thrusting direction is divided into orthogonal and tangential components. These are accommodated by convergent and strike–slip structures, respectively, which sole into a common detachment horizon. The structural evolution of the new thrust sheet in the Bolivian Orocline is primarily controlled by the paleorelief of the Brazilian Shield because: (1) the shape of the basement affects the taper of the thrust wedge and localizes the deformation front and (2) small asperities in/close to the top of the basement promote fault localization. The coincidence of a relatively high basement position and a structural high of the Eastern Cordillera leads to the conclusion that the shape of the Brazilian Shield also controls the structural evolution of the pronounced eastern border of the Bolivian Orocline.  相似文献   

Questions and Answers for Environmental Professionals     

Daniel J. Gibby  Ralph E. Moon 《Ground Water Monitoring & Remediation》1997,17(2):56-58

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Spatial variation in delaware bay (U.S.A.) marsh creek fish assemblages     

Kenneth W. Able  David M. Nemerson  Ralph Bush  Phillip Light 《Estuaries and Coasts》2001,24(3):441-452

Delaware Bay is one of the largest estuaries on the U.S. eastern seaboard and is flanked by some of the most extensive salt marshes found in the northeastern U.S. While physicochemical and biotic gradients are known to occur along the long axis of the bay, no studies to date have investigated how the fish assemblage found in salt marsh creeks vary along this axis. The marshes of the lower portion of the bay, with higher salinity, are dominated bySpartina spp., while the marshes of the upper portion, with lower salinity, are currently composed primarily of common reed,Phragmites australis, S. alterniflora, or combinations of both. Extensive daytime sampling (n=815 tows) during May–November 1996 was conducted with otter trawls (4.9 m, 6 mm mesh) in six intertidal and subtidal marsh creek systems (upper and lower portions of each creek) where creek channel depths ranged from 1.4–2.8 m at high tide. The fish taxa of the marsh creeks was composed of 40 species that were dominated by demersal and pelagic forms including sciaenids (5 species), percichthyids (2), and clupeids (7), many of which are transients that spawn outside the bay but the early life history stages are abundant within the bay. The most abundant species wereMorone americana (24.3% of the total catch),Cynoscion regalis (15.4%),Micropogonias undulatus (15.3%),Anchoa mitchilli (12.0%), andTrinectes maculatus (10.8%). Non-metric Multi-Dimensional Scaling ordination of catch per unit effort (CPUE) data indicated two fish assemblages that were largely independent of the two major vegetation types, but generally corresponded with spatial variation in salinity. This relationship was more complex because some of the species for which we could discriminate different age classes by size had different patterns of distribution along the salinity gradient.  相似文献   

Computers In Geography     

Ralph E. Olson 《The Professional geographer》1970,22(3):161-161

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Spectral analysis in geophysics,M. Bath,Developments in Solid Earth Geophysics, 7, Elsevier,Amsterdam (1974), p. 563, U.S. $46.20     

Ralph A. Wiggins 《Earth》1976,12(1):79-80

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