Bright crater outflows: Possible emplacement mechanisms

Lobate features with a strong backscatter are associated with 43 percent of the impact craters cataloged in Magellan's cycle 1. Their apparent thinness and great lengths are consistent with a low-viscosity material. The longest outflow yet identified is about 600 km in length and flows from the 90-km-diameter crater Addams. There is strong evidence that the outflows are largely composed of impact melt, although the mechanisms of their emplacement are not clearly understood. High temperatures and pressures of target rocks on Venus allow for more melt to be produced than on other terrestrial planets because lower shock pressures are required for melting. The percentage of impact craters with outflows increases with increasing crater diameter. The mean diameter of craters without outflows is 14.4 km, compared with 27.8 km for craters with outflows. No craters smaller than 3 km, 43 percent of craters in the 10- to 30-km-diameter range, and 90 percent in the 80- to 100-km-diameter range have associated bright outflows. More melt is produced in the more energetic impact events that produce larger craters. However, three of the four largest craters have no outflows. We present four possible mechanisms for the emplacement of bright outflows. We believe this 'shotgun' approach is justified because all four mechanisms may indeed have operated to some degree

Application of multispectral radar and LANDSAT imagery to geologic mapping in death valley

Side-Looking Airborne Radar (SLAR) images, acquired by JPL and Strategic Air Command Systems, and visible and near-infrared LANDSAT imagery were applied to studies of the Quaternary alluvial and evaporite deposits in Death Valley, California. Unprocessed radar imagery revealed considerable variation in microwave backscatter, generally correlated with surface roughness. For Death Valley, LANDSAT imagery is of limited value in discriminating the Quaternary units except for alluvial units distinguishable by presence or absence of desert varnish or evaporite units whose extremely rough surfaces are strongly shadowed. In contrast, radar returns are most strongly dependent on surface roughness, a property more strongly correlated with surficial geology than is surface chemistry

Impact cratering and the surface age of Venus: The Pre-Magellan controversy

The average surface age of a planet is a major indicator of the level of its geologic activity and thus of the dynamics of its interior. Radar images obtained by Venera 15/16 from the northern quarter of the Venus (lat 30 to 90 degs) reveal about 150 features that resemble impact craters, and they were so interpreted by Soviet investigators B. A. Ivanov, A. T. Basilevsky, and their colleagues. These features range in diameter from about 10 to 145 km. Their areal density is remarkably similar to the density of impact structures found on the American and European continental shields. The basic difference between the Soviet and American estimates of the average surface age of Venus's northern quarter is due to which crater-production rate is used for the Venusian environment. Cratering rates based on the lunar and terrestrial cratering records, as well as statistical calculations based on observed and predicted Venus-crossing asteroids and comets, have been used in both the Soviet and American calculations. The single largest uncertainty in estimating the actual cratering rates near Venus involves the shielding effect of the atmosphere

Energy dissipation in sheared wet granular assemblies

Energy dissipation in sheared dry and wet granulates is considered in the presence of an externally applied confining pressure. Discrete element simulations reveal that for sufficiently small confining pressures, the energy dissipation is dominated by the effects related to the presence of cohesive forces between the particles. The residual resistance against shear can be quantitatively explained by a combination of two effects arising in a wet granulate: (i) enhanced friction at particle contacts in the presence of attractive capillary forces and (ii) energy dissipation due to the rupture and reformation of liquid bridges. Coulomb friction at grain contacts gives rise to an energy dissipation which grows linearly with increasing confining pressure for both dry and wet granulates. Because of a lower Coulomb friction coefficient in the case of wet grains, as the confining pressure increases the energy dissipation for dry systems is faster than for wet ones

Nuclear fusion and renewable energy forms: Are they compatible?

Nuclear fusion can be considered as a base-load power plant technology: High investment costs and limited operational flexibility require continuous operation. Wind and solar, on the other hand, as the putative main pillars of a future renewable energy system, are intermittent power sources. The resulting variations that occur on many different time scales require at first sight a rather flexible back-up system to balance this stochastic behavior. Fusion would appear not to be well suited for this task. The situation changes, however, if a large-scale renewable energy system is envisaged based on a transnational, or even transcontinental power grid. The present paper discusses a possible European power system in the year 2050 and beyond. A high percentage share of renewable energies and a strong power grid spanning the whole of Europe and involving neighboring countries, in particular those in North Africa, are assumed. The linear programming model URBS is used to describe the power system. The model optimizes the overall system costs and simulates power plant operation with an hourly resolution for one whole year. The geographical resolution is at least at the country level. The renewable technologies are modeled first on a more local level and then summed together at the country or regional level. The results indicate that the smoothing effects of the large-scale power grid transform the intermittent renewable supply, which is then more compatible with base-load power plants such as fusion reactors

Low-emissivity impact craters on Venus

An analysis of 144 impact craters on Venus has shown that 11 of these have floors with average emissivities lower than 0.8. The remaining craters have emissivities between 0.8 and 0.9, independent of the specific backscatter cross section of the crater floors. These 144 impact craters were chosen from a possible 164 craters with diameters greater than 30 km as identified by researchers for 89 percent of the surface of Venus. We have only looked at craters below 6053.5 km altitude because a mineralogical change causes high reflectivity/low emissivity above the altitude. We have also excluded all craters with diameters smaller than 30 km because the emissivity footprint at periapsis is 16 x 24 km and becomes larger at the poles

Documentation of Apollo 15 samples

A catalog is presented of the documentation of Apollo 15 samples using photographs and verbal descriptions returned from the lunar surface. Almost all of the Apollo 15 samples were correlated with lunar surface photographs, descriptions, and traverse locations. Where possible, the lunar orientations of rock samples were reconstructed in the lunar receiving laboratory, using a collimated light source to reproduce illumination and shadow characteristics of the same samples shown in lunar photographs. In several cases, samples were not recognized in lunar surface photographs, and their approximate locations are known only by association with numbered sample bags used during their collection. Tables, photographs, and maps included in this report are designed to aid in the understanding of the lunar setting of the Apollo 15 samples

The wetting state of water on a rose petal

The rose petal features surface structures that offer unique wetting properties. A water droplet placed on a rose petal forms a high contact angle but exhibits significant contact angle hysteresis, such that relatively large droplets remain stuck to the surface when it is tilted. Understanding this distinctive ‘parahydrophobic’ wetting behavior can provide insight into the design of highly nonwetting, yet highly adhesive, synthetic surfaces. Surface features of the rose petal are characterized via focused ion beam scanning electron microscopy, which reveals microscale papillae that are partially covered with nanoscale striae. The wetting state of water on a rose petal is directly visualized using confocal microscopy. This experimental evidence confirms the microscale wetting behavior on the papillae, but cannot resolve the wetting behavior on the nanoscale striae. To infer the wetting state on the striae, an energyminimization- based model is developed and the results from the model are compared to the experimental evidence. In combination, the experimental findings and the model results reveal the wetting state of water on the hierarchical surface structure and explain the macroscopic wetting behavior of the rose petal

Assessment of sweep net and suction sampling for evaluating pest insect populations in hay alfalfa

Insect populations in alfalfa grown for hay can be sampled using several methods. However, in a pest management program a relatively easy, quick, and reliable method of sampling is essential for making effective pest control decisions. A study was conducted to determine if two different sampling methods, sweepnet sampling and suction sampling, led to similar pest control decisions. Differences between sweepnet and D-Vac insect population estimates varied over sampling dates and years and were dependent on the insect species, their developmental stages, and abiotic factors. Our results indicate that, for many sampling dates, decisions on control of some pest insects would be similar for the two sampling methods.Keywords: Insecta; Medicago sativa; alfalfa weevil; pea aph