How much material do the radar-bright craters at the Mercurian poles contain?

The depth-to-diameter (d/D) ratios were determined for 12 craters located near the Mercurian north pole that were identified by Harmon et al. (2001, Icarus 149) as having strong depolarized radar echos. We find that the mean d/D value of these radar-bright craters is the mean d/D value of the general population of non-radar-bright craters in the surrounding north polar region. Previous studies, however, show no difference between d/D values of Mercurian polar and equatorial crater populations, suggesting that no terrain softening which could modify crater structure exists at the Mercurian poles (Barlow et al., 1999, 194, Icarus 141). Thus, the change in d/D is governed by a change in crater depth, probably due to deposition of material inside the crater. The volume of infilling material, including volatiles, in the radar-bright craters is significantly greater than predicted by proposed mechanisms for the emplacement of either water ice or sulfur.     

Cretaceous and Eocene lignite deposits, Jackson Purchase, Kentucky

Lignites occur in the Cretaceous McNairy Formation and the Eocene Claiborne Formation in the Jackson Purchase region of western Kentucky. The lone Cretaceous lignite sample has over 18 percent inertodetrinite and 32 percent humodetrinite which, along with the abundant mineral matter, suggests a possible allochthonous origin for the deposit. The Claiborne Formation lignites have higher humic maceral contents than the Cretaceous lignites. Palynology suggests that there was considerable variation in the plant communities responsible for the Claiborne deposits. Differences in the preservation of the various plants is also seen in the variations between the humic types, particularly in the ulminite and humodetrinite contents. Potter and Dilcher (1980) suggested that the Claiborne lignites in the Jackson Purchase and west Tennessee developed in the abandoned oxbows of Eocene rivers. Significant short-distance changes in the peat thickness, flora, and other depositional elements should be expected in such an environment and could easily account for the observed variations in composition.     

An attempt to separate out climatic and man‐induced causes of range degradation in Botswana using Landsat MSS imagery

Changes in natural vegetation cover comprising the Kalahari rangeland were undertaken using Landsat MSS imagery over a period of above average rainfall (1972–1982) and a period of drought (1982–1986). This and ancillary data were collected to determine whether changes in the range were related primarily to rainfall events or to man‐induced effects. Data from different orbits were made compatible digitally. Dark area subtraction was a problem because deep shadow and water were lacking in the Kalahari landscape. Eleven land‐use/land cover classes were derived for the 1984 base year. Additional signatures had to be obtained for the later drought years because of extreme increases in brightness. Broadly the south‐eastern Kalahari was divided into an interior, relatively uninhabited homogeneous area and a more diverse area containing fossil valleys and pans. Changes in vegetation cover in the interior appeared to be more related to rainfall events than anthropogenic factors. Changes in the fossil valley vegetation cover appeared to be more related to rainfall events during the period of above average rainfall and more related to cattle and smallstock densities during the drought period.     

Don’t Blame It on the Moonlight: Abiotic Drivers of Reproductive Development in an Estuarine-Dependent Prawn

Lunar phase is regarded as a key driver of reproductive development and spawning activity in prawns, but across smaller-temporal scales, other processes may have a significant influence. Here, we examined the effects of lunar phase and other abiotic variables on the reproductive development of an estuarine-dependent prawn, Metapenaeus bennettae Racek & Dall. We found that turbidity, salinity, water temperature and lunar phase each had a significant independent influence on the likelihood of female prawns being ripe throughout the spawning period. The likelihood of catching a ripe female increased on the new moon and first quarter of the moon and also during conditions of low turbidity, high salinity and high water temperature. For male prawns, however, significant interactions between salinity and lunar phase and also between turbidity and lunar phase were detected. These interactions indicated that salinity and turbidity have variable effects among the different lunar phases. Such complex relationships of reproductive timing and spawning success of M. bennettae, and potentially other aquatic species, are most likely adaptive responses to the highly variable conditions of estuarine environments.     

Local topographic effects on photometry and reflectance spectra of planetary surfaces: An example based on lunar photometry

Abstract— The photometric properties of the average lunar surface are characterized using Hapke's equations and whole disk observations ranging from 0.36 to 1.06 μm. Synthetic spectra across a crater topographic profile are created using the modeling results. The synthetic spectra are examined for spectral variations created by changes in lighting conditions induced by the topography. Changes above the modeling uncertainties are seen in both spectral slope and band depths, though the most pronounced change is in band depth. The data have insufficient spectral resolution to determine if there are any changes in band center due to photometric effects. No additional absorption features are introduced by the photometry. These results have serious implications on the interpretation of spectral observations in terms of abundance estimates and alteration processes as a function of location and association with geologic features.     

Spectrophotometry of Kuiper Belt Objects 20000 Varuna, 2000 Eb173 and Centaur 10199 Chariklo

Due to the distance, faintness, and very recent discovery ofKuiper Belt Objects (KBOs) and Centaurs, very little is knownabout the physical characteristics of these basic buildingblocks of the solar system. New intermediate-band photometryobservations of KBOs and Centaurs suggest that absorption bandsexist in the visible portion of their spectra, which could offerinsights into the surface composition of these objects.     

Iapetus dark and bright material:: giving compositional interpretation some latitude

Narrowband reflectance spectra (0.53-1.0 μm) of Iapetus' leading and trailing sides were obtained in 2000 to test the presence of an absorption feature located near 0.67 μm seen in reflectance spectra of Iapetus' dark material and Hyperion's surface material. No feature was observed. The difference in reflectance across the UV/VIS/NIR spectral region, and the dependence of the presence or absence of this absorption feature on angular separation from the apex of Iapetus in its orbit, phase angle, and heliocentric distance (affecting temperature), were examined. A trend of increased reddening, and the presence of the absorption feature, correlate with an angular separation from the apex of ? approximately 10°. Spectral information is lost when the contribution of the bright water ice signal to the reflectance spectrum increases sufficiently. In order to optimize compositional studies of Iapetus, we encourage future ground-based and space-based spectral observations to maximize the concentration of dark material in the instrumental field of view.     

Investigating the Vesta-vestoid-HED connection

We present spectral observations of Minor Planet 4 Vesta, of five V-type asteroids which are physically near Vesta, and of two V-type NEAs. We use these spectra to determine the presence or absence of a weak feature at 506.5 nm which is indicative of the presence of spin-forbidden Fe²⁺ in sixfold coordination. As with our earlier observations [Cochran and Vilas, Icarus 134 (1998) 207-212], we find this feature at all observed rotational phases of Vesta and again see the trend that spectra at longitudes between 240° and 360° have a smaller 506.5 nm feature equivalent width than spectra obtained at other longitudes. Additionally, we searched for this feature in V-class main-belt and NEA asteroids and positively detected the feature in main-belt Asteroid 2579 Spartacus and possibly in 3376 Armandhammer. The other objects lacked the feature. Our results are compared with previous observations of this feature by Vilas et al. [Icarus 147 (2000) 119-128]. The spatial distribution of the bodies as a function of the presence of this feature was investigated. We discuss the implication of the presence of this feature and the depth of the 0.9 μm pyroxene band for the scenario that pieces of Vesta were transported, via the 3:1 and ν₆ resonances, to the NEAs, and thence to inclusion in our meteorite collections as HED meteorites.     

Vulnerability to epidemic malaria in the highlands of Lake Victoria basin: the role of climate change/variability, hydrology and socio-economic factors

Endemic malaria in most of the hot and humid African climates is the leading cause of morbidity and mortality. In the last twenty or so years the incidence of malaria has been aggravated by the resurgence of highland malaria epidemics which hitherto had been rare. A close association between malaria epidemics and climate variability has been reported but not universally accepted. Similarly, the relationship between climate variability, intensity of disease mortality and morbidity coupled with socio-economic factors has been mooted. Analyses of past climate (temperature and precipitation), hydrological and health data (1961–2001), and socio-economics status of communities from the East African highlands confirm the link between climate variability and the incidence and severity of malaria epidemics. The communities in the highlands that have had less exposure to malaria are more vulnerable than their counterparts in the lowlands due to lack of clinical immunity. However, the vulnerability of human health to climate variability is influenced by the coping and adaptive capacities of an individual or community. Surveys conducted among three communities in the East African highlands reveal that the interplay of poverty and other socio-economic variables have intensified the vulnerability of these communities to the impacts of malaria.     

Note on Zoobotryon verticillatum (Bryozoa) in a solar saltfield

A study at the Penrice Soda Products Saltfields revealed that a “weed” blocking siphons in the lower salinity end of the fields was a bryozoan,Zoobotryon verticillatum (della Chiaje). Further observations showed that this bryozoan grows from early October to mid June, dying off for 3 months during winter, and that it was commonly found in salinities of up to 56 grams per litre.