The possible effects of translationally excited nitrogen atoms on lower thermospheric odd nitrogen

In the quiet lower thermosphere, photolysis of N₂ produces translationally excited $\text{N}\text{(}{}^4\text{S}\text{)}$ and $\text{N}\text{(}{}^2\text{D}\text{)}$ atoms. A fraction of these $\text{N}\text{(}{}^4\text{S}\text{)}$ atoms may react rapidly with O₂ while still translationally hot. This results in substantially larger calculated NO densities than those obtained if translational excitation is not considered. The sensitivity of the calculated NO density in the lower thermosphere to this process is examined.     

Density within the moon and implications for lunar composition

Density models for the Moon, including the effects of temperature and pressure, can satisfy the mass and moment of inertia of the Moon and the presence of a low density crust indicated by the seismic refraction results only if the lunar mantle is chemically or mineralogically inhomogeneous. IfC/MR ² exceeds 0.400, the inferred density of the upper mantle must be greater than that of the lower mantle at similar conditions by at least 0.1 g cm^–3 for any of the temperature profiles proposed for the lunar interior. The average mantle density lies between 3.4 and 3.5 g cm^–3, though the density of the upper mantle may be greater. The suggested density inversion is gravitationally unstable, but the implied deviatoric stresses in the mantle need be no larger than those associated with lunar gravity anomalies. UsingC/MR ³=0.400 and the recent seismic evidence suggesting a thin, high density zone beneath the crust and a partially molten core, successful density models can be found for a range of temperature profiles. Temperature distributions as cool as several inferred from the lunar electrical conductivity profile would be excluded. The density and probable seismic velocity for the bulk of the mantle are consistent with a pyroxenite composition and a 100 MgO/(MgO+FeO) molecular ratio of less than 80.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.     

The impact of agronomic inputs on selected physicochemical features and their relationships with heavy metals levels in surface sediment and water in sugarcane farms in Nzoia,Kenya

Sugarcane farming is the most important cash crop cultivation activity in the Lake Victoria basin of Kenya practised in an area covering approximately 114,000 Ha in total. For better yields, various agronomic inputs including fertilizers and herbicides have been used intensively in the farms, causing serious concerns about their potential impacts on the aquatic ecosystems within the lake basin. In this study, the physicochemical features of surface sediment and water including pH, total organic carbon contents and heavy metal (Cd, Cu, Zn, Pb and Cr) loads in River Kuywa and in runoff canals in sugarcane farms in Nzoia nucleus estate within the lake basin were determined to assess the effects of agronomic activities including agronomic inputs in the form of nitrogenous fertilizers [urea and diammonium phosphate (DAP)], herbicides and sewage sludge used in farming on their levels. The results indicated significant differences (p ≤ 0.05) in the heavy metal levels in sediment and water samples taken before and after the farms, respectively, indicating a positive impact on the concentration levels. The canal water and sediment samples’ heavy metal levels were also significantly higher than those of the river samples showing that the influent sugarcane farm canal waters transfer these contaminants into River Kuywa. Although the levels of these parameters were significantly higher in the canals than in the controls obtained from outside the sugarcane farms, the heavy metal levels in soil samples from within the farms with similar agronomic activities did not differ significantly among the various plots. The turbidity, electrical conductivity, temperature, water and soil pH and total organic carbon values in samples obtained within the sugarcane farms showed significant seasonal variations and differed significantly from the values in the controls showing a significant negative impact of agronomic inputs on water quality.     

Community perceptions of forest–water relationships in the Blue Nile Basin of Ethiopia

Community perception of forest–water relationship was gathered using participatory rural appraisal tools in four watersheds of the Blue Nile River Basin in Ethiopia. These were compared and contrasted with the observational records of forest cover and water flow. Upstream and downstream communities were assessed separately to check for differences in perception based on location within a watershed. The key result of the study was that people in the study watersheds had a range of perceptions about the forest–water relationship which were watershed specific. The perceptions were generally consistent with observational evidence from the same watersheds. This study highlighted the need for locale-specific approaches to land and water management in the Basin, as well as the potential value of using community perceptions to complement the observational records which can have spatial and temporal limitations.     

Geochemistry of the Pegmatitic Rocks and Minerals in the Kenticha Belt, Southern Ethiopia: Implication to Geological Setting

Trace element distribution patterns are reported for whole rocks (granites, aplites, greisens, pegmatites, alaskites) and minerals from the Kenticha pegmatite field. The data shed light on the evolution, regional and local zonal pattern of the granitepegmatites and associated mineralization in the Kenticha belt. The complex mineralization of commercial concentrations of Ta, Nb, Hf, Zr, REE, U and Th is related to Be, Li, Cs, Rbbearing zones of pegmatites and is structurally controlled. Whole rock chemical signatures of the suite of felsic rocks of the Kenticha belt are predominantly similar to those generated by subduction in modern magmatic arcs and indicate a mantle derivation. Columbotantalite concentrates extracted from the pegmatitic ores represent the basic raw materials from which a number of possible byproducts can be recovered.     

Stereo topographic models of Mercury after three MESSENGER flybys

From photogrammetric analysis of stereo images of Mercury obtained during three MESSENGER flybys, we have produced three digital terrain models (DTMs) that have a grid spacing of 1 km and together cover 30% of the planet's surface. The terrain models provide a rich source of information on the morphology of Mercury's surface, including details of tectonic scarp systems as well as impact craters and basins. More than 400 craters larger than 15 km in diameter are included in the models. Additionally, the models provide important test cases for the analysis of stereo image data to be collected during MESSENGER's orbital mission phase. Small lateral offsets and differences in trends between stereo DTMs and laser altimeter profiles may be due to remaining errors in spacecraft position, instrument pointing, or Mercury coordinate knowledge. Such errors should be resolved during the orbital mission phase, when more joint analyses of data and detailed orbit modeling will be possible.     

Analysis of MESSENGER Gamma-Ray Spectrometer data from the Mercury flybys

During its three flybys of Mercury, the MESSENGER spacecraft made the first detection of gamma-ray emission from the planet's surface. With a closest approach distance of ∼200 km, the flybys provided an opportunity to measure elemental abundances of Mercury's near-equatorial regions, which will not be visited at low altitude during MESSENGER's orbital mission phase. Despite being limited by low planetary photon flux, sufficient counts were accumulated during the first two flybys to estimate bounds on abundances for some elements having relatively strong gamma-ray spectral peaks, including Si, Fe, Ti, K, and Th. Only for Si is the standard deviation σ sufficiently small to conclude that this element was detected with 99% confidence. Iron and potassium are detected at the 2−σ (95% confidence) level, whereas only upper bounds on Ti and Th can be determined. Relative to a Si abundance assumed to be 18 weight percent (wt%), 2−σ upper bounds have been estimated as 9.7 wt% for Fe, 7.0 wt% for Ti, 0.087 wt% for K, and 2.2 ppm for Th. The relatively low upper bound on K rules out some previously suggested models for surface composition for the regions sampled. Upper bounds on Fe/Si and Ti/Si ratios are generally consistent with Ti and Fe abundances estimated from the analysis of measurements by the MESSENGER Neutron Spectrometer during the flybys but are also permissive of much lower concentrations.     

Predictions of MESSENGER Neutron Spectrometer measurements for Mercury's north polar region

From radar images of Mercury's poles and MESSENGER Neutron Spectrometer (NS) measurements obtained during the spacecraft's flybys of Mercury, predictions of neutron count rates and their uncertainties are calculated for Mercury's north polar region as of the end of the MESSENGER primary orbital mission. If Mercury's poles contain large amounts of water ice, as has been suggested on the basis of the radar data, then during the one-year-long orbital mission the NS should detect signals indicative of excess polar hydrogen with a significance of at least 4σ, where σ is the standard deviation derived from Poisson counting statistics. If the polar deposits are not enriched with hydrogen, but are dominated by other elements, such as sulfur, then the MESSENGER neutron measurements should be able to confirm the absence of deposits having surface concentrations in excess of 50 wt% H₂O on permanently shadowed floors of craters near Mercury's north pole. Because of the large spatial footprint of the NS data, individual polar deposits will not be spatially resolved, but longitudinal asymmetries may be detected if residual systematic uncertainties are sufficiently low.     

Eminescu impact structure: Insight into the transition from complex crater to peak-ring basin on Mercury

Peak-ring basins represent an impact-crater morphology that is transitional between complex craters with central peaks and large multi-ring basins. Therefore, they can provide insight into the scale dependence of the impact process. Here the transition with increasing crater diameter from complex craters to peak-ring basins on Mercury is assessed through a detailed analysis of Eminescu, a geologically recent and well-preserved peak-ring basin. Eminescu has a diameter (∼125 km) close to the minimum for such crater forms and is thus representative of the transition. Impact crater size-frequency distributions and faint rays indicate that Eminescu is Kuiperian in age, geologically younger than most other basins on Mercury. Geologic mapping of basin interior units indicates a distinction between smooth plains and peak-ring units. Our mapping and crater retention ages favor plains formation by impact melt rather than post-impact volcanism, but a volcanic origin for the plains cannot be excluded if the time interval between basin formation and volcanic emplacement was less than the uncertainty in relative ages. The high-albedo peak ring of Eminescu is composed of bright crater-floor deposits (BCFDs, a distinct crustal unit seen elsewhere on Mercury) exposed by the impact. We use our observations to assess predictions of peak-ring formation models. We interpret the characteristics of Eminescu as consistent with basin formation models in which a melt cavity forms during the impact formation of craters at the transition to peak ring morphologies. We suggest that the smooth plains were emplaced via impact melt expulsion from the central melt cavity during uplift of a peak ring composed of BCFD-type material. In this scenario the ringed cluster of peaks resulted from the early development of the melt cavity, which modified the central uplift zone.