Spectroscopic observations of Mercury's surface reflectance during MESSENGER's first Mercury flyby

During MESSENGER's first flyby of Mercury, the Mercury Atmospheric and Surface Composition Spectrometer made simultaneous mid-ultraviolet to near-infrared (wavelengths of 200 to 1300 nanometers) reflectance observations of the surface. An ultraviolet absorption (<280 nanometers) suggests that the ferrous oxide (Fe2+) content of silicates in average surface material is low (less than 2 to 3 weight percent). This result is supported by the lack of a detectable 1-micrometer Fe2+ absorption band in high-spatial-resolution spectra of mature surface materials as well as immature crater ejecta, which suggests that the ferrous iron content may be low both on the surface and at depth. Differences in absorption features and slope among the spectra are evidence for variations in composition and regolith maturation of Mercury's surface.     

Imaging the microscopic structure of shear thinning and thickening colloidal suspensions

The viscosity of colloidal suspensions varies with shear rate, an important effect encountered in many natural and industrial processes. Although this non-Newtonian behavior is believed to arise from the arrangement of suspended particles and their mutual interactions, microscopic particle dynamics are difficult to measure. By combining fast confocal microscopy with simultaneous force measurements, we systematically investigate a suspension's structure as it transitions through regimes of different flow signatures. Our measurements of the microscopic single-particle dynamics show that shear thinning results from the decreased relative contribution of entropic forces and that shear thickening arises from particle clustering induced by hydrodynamic lubrication forces. This combination of techniques illustrates an approach that complements current methods for determining the microscopic origins of non-Newtonian flow behavior in complex fluids.     

Mongolian Tree Rings and 20th-Century Warming

A 450-year tree-ring width chronology of Siberian pine (Pinus sibirica Du Tour) growing at timberline (2450 meters) in the Tarvagatay Mountains in west central Mongolia shows wide annual growth rings for the recent century. Ecological site observations and comparisons with instrumental temperature records indicate that the ring widths of these trees are sensitive to annual temperature variations. Low-frequency variations in the Tarvagatay tree-ring record are similar to those in a reconstruction of Arctic annual temperatures, which is based on 20 tree-ring width series from northern North America, Scandinavia, and western Russia. The results indicate that recent warming is unusual relative to temperatures of the past 450 years.     

Hollows on Mercury: MESSENGER evidence for geologically recent volatile-related activity

High-resolution images of Mercury's surface from orbit reveal that many bright deposits within impact craters exhibit fresh-appearing, irregular, shallow, rimless depressions. The depressions, or hollows, range from tens of meters to a few kilometers across, and many have high-reflectance interiors and halos. The host rocks, which are associated with crater central peaks, peak rings, floors, and walls, are interpreted to have been excavated from depth by the crater-forming process. The most likely formation mechanisms for the hollows involve recent loss of volatiles through some combination of sublimation, space weathering, outgassing, or pyroclastic volcanism. These features support the inference that Mercury's interior contains higher abundances of volatile materials than predicted by most scenarios for the formation of the solar system's innermost planet.     

Detection of silica-rich deposits on Mars

Mineral deposits on the martian surface can elucidate ancient environmental conditions on the planet. Opaline silica deposits (as much as 91 weight percent SiO2) have been found in association with volcanic materials by the Mars rover Spirit. The deposits are present both as light-toned soils and as bedrock. We interpret these materials to have formed under hydrothermal conditions and therefore to be strong indicators of a former aqueous environment. This discovery is important for understanding the past habitability of Mars because hydrothermal environments on Earth support thriving microbial ecosystems.     

The major-element composition of Mercury's surface from MESSENGER X-ray spectrometry

X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet's surface differs in composition from those of other terrestrial planets. Relatively high Mg/Si and low Al/Si and Ca/Si ratios rule out a lunarlike feldspar-rich crust. The sulfur abundance is at least 10 times higher than that of the silicate portion of Earth or the Moon, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles. Low Fe and Ti abundances do not support the proposal that opaque oxides of these elements contribute substantially to Mercury's low and variable surface reflectance.     

Time series forecast and soil characteristics-based simple and multivariate linear models for management of Diaprepes abbreviatus root weevil in citrus

Synthesis of insect and soil variable patterns in space and time via process models would be useful for reducing the cost of field monitoring and for achieving improved integrated pest management. During 2001-2003, we monitored the Diaprepes abbreviatus (L.) root weevil population in a flatwoods citrus grove containing a sandy Alfisol and a loamy Mollisol in Hendry County, South Florida. Our objectives were to examine the multi-year correlations of the Diaprepes root weevil with soil characteristics, and to develop a time series model and soil variable-based simple and multivariate linear models for predicting weevil patterns in space and time. Adult weevils were monitored weekly using 100 Tedders traps arranged in a 30×12 m grid. Gravimetric soil water content (SWC), time-domain-reflectory (TDR) volumetric SWC, soil organic matter content (SOM), clay, sand, silt, pH, and Mehlich-I extractable P, K, Ca, Mg, Fe and Mn concentrations were determined for each trap location. Adult weevil density was 0.023±0.018 weevils m⁻² across the 3 years, and the weevil population grew exponentially (R²=0.81). Each year, the weevil was positively related to SWC, TDR, clay, SOM, and soil Mg, Ca and K concentrations (0.32<r<0.65, P<0.05). High weevil density, SWC, SOM, and P, K, Mg and Ca levels matched the Mollisol boundary. The autocorrelation ranges for the weevil and soil variables were within the soil type unit. Time series moving average forecast of Diaprepes weevil development was related to the 3-year mean weevil density monitored in the field (R²=0.88). The SWC, TDR and SOM-based simple and multivariate linear models explained 45% of the variance in the weevil patterns (P<0.001). Time series and soil characteristics-based simple and multivariate linear models suggest a variable rate and less frequent spray for future management of the weevil in citrus production systems.