A Survey for Satellites of Venus

We present a systematic survey for satellites of Venus using the Baade-Magellan 6.5 meter telescope and IMACS wide-field CCD imager at Las Campanas observatory in Chile. In the outer portions of the Hill sphere the search was sensitive to a limiting red magnitude of about 20.4, which corresponds to satellites with radii of a few hundred meters when assuming an albedo of 0.1. In the very inner portions of the Hill sphere scattered light from Venus limited the detection to satellites of about a kilometer or larger. Although several main belt asteroids were found, no satellites (moons) of Venus were detected.Comment: Published in July 2009 (Sheppard, S. and Trujillo, C. 2009, Icarus, 202, 12-16.

Mercury's low-reflectance material: Constraints from hollows

Unusually low reflectance material, within which depressions known as hollows appear to be actively forming by sublimation, is a major component of Mercury's surface geology. The observation that this material is exhumed from depth by large impacts has the intriguing implication that the planet's lower crust or upper mantle contains a significant volatile-rich, low-reflectance layer, the composition of which will be key for developing our understanding of Mercury's geochemical evolution and bulk composition. Hollows provide a means by which the composition of both the volatile and non-volatile components of the low-reflectance material (LRM) can be constrained, as they result from the loss of the volatile component, and any remaining lag can be expected to be formed of the non-volatile component. However, previous work has approached this by investigating the spectral character of hollows as a whole, including that of bright deposits surrounding the hollows, a unit of uncertain character. Here we use high-resolution multispectral images, obtained as the MESSENGER spacecraft approached Mercury at lower altitudes in the latter part of its mission, to investigate reflectance spectra of inactive hollow floors where sublimation appears to have ceased, and compare this to those of the bright surrounding products and the parent material. This analysis reveals that the final lag after hollow-formation has a flatter spectral slope than that of any other unit on the planet and reflectance approaching that of more space-weathered parent material. This indicates firstly that the volatile material lost has a steeper spectral slope and higher reflectance than the parent material, consistent with (Ca,Mg) sulfides, and secondly, that the low-reflectance component of LRM is non-volatile and may be graphite

Constraints on Mercury’s surface composition from MESSENGER and ground-based spectroscopy

The composition and chemistry of Mercury’s regolith has been calculated from MESSENGER MASCS 0.3–1.3 μm spectra from the first flyby, using an implementation of Hapke’s radiative transfer-based photometric model for light scattering in semi-transparent porous media, and a linear spectral mixing algorithm. We combine this investigation with linear spectral fitting results from mid-infrared spectra and compare derived oxide abundances with mercurian formation models and lunar samples. Hapke modeling results indicate a regolith that is optically dominated by finely comminuted particles with average area weighted grain size near 20 lm. Mercury shows lunar-style space weathering, with maturation-produced microphase iron present at ~0.065 wt.% abundance, with only small variations between mature and immature sites, the amount of which is unable to explain Mercury’s low brightness relative to the Moon. The average modal mineralogies for the flyby 1 spectra derived from Hapke modeling are 35–70% Na-rich plagioclase or orthoclase, up to 30% Mg-rich clinopyroxene, <5% Mg-rich orthopyroxene, minute olivine, ~20–45% low-Fe, low-Ti agglutinitic glass, and <10% of one or more lunar-like opaque minerals. Mercurian average oxide abundances derived from Hapke models and mid-infrared linear fitting include 40–50 wt.% SiO2, 10–35 wt.% Al2O3, 1–8 wt.% FeO, and <25 wt.% TiO2; the inferred rock type is basalt. Lunar-like opaques or glasses with high Fe and/or Ti abundances cannot on their own, or in combination, explain Mercury’s low brightness. The linear mixing results indicate the presence of clinopyroxenes that contain up to 21 wt.% MnO and the presence of a Mn-rich hedenbergite. Mn in M1 crystalline lattice sites of hedenbergite suppresses the strong 1 and 2 lm crystal field absorption bands and may thus act as a strong darkening agent on Mercury. Also, one or more of thermally darkened silicates, Fepoor opaques and matured glasses, or Mercury-unique Ostwald-ripened microphase iron nickel may lower the albedo. A major part of the total microphase iron present in Mercury’s regolith is likely derived from FeO that is not intrinsic to the crust but has been subsequently delivered by exogenic sources

Conceptual Design of a Hydraulic Valve Train System

Variable valve train systems have been brought into focus during recent years as a means to decrease fuel consumption in tomorrow's combustion engines. In this paper an integrated approach, called simulation driven experiments, is utilised in order to aid the development of such highly dynamic systems. Through the use of systematic design methodology, a number of feasible concepts are developed. Critical components are subsequently identified using simulation. In this approach, component behaviour is simulated and validated by measurements on prototype components. These models are unified with complete system models of hydraulically actuated valve trains. In the case of the valve trains systems studied here component models could be validated using comparably simple test set-ups. These models enable the determination of non-critical design parameters in an optimal sense. This results in a number of optimised concepts facilitating an impartial functional concept selection

A Set of Laboratory Analogue Materials fort he MERTIS Instrument on the ESA BepiColombo Mission to Mercury

The MERTIS (Mercury Thermal Imaging Spectrometer) instrument on the ESA mission BepiColombo will study the surface of Mercury in the wavelength range from 7 to 14 μm. The analysis of the MERTIS data will be posing a number of significant challenges. To facilitate the development of analytic tools, support planned ground based observations and support a cross calibration with other instruments on BepiColombo and MESSENGER, a list of Mercury analogue materials was compiled [1]. This set of analogue materials is based on our current knowledge of the surface composition of Mercury and includes plagioclase and potassium feldspars, low Ca and high Ca pyroxenes, olivine, elemental sulfur and as an extraterrestrial analogue a lunar highland soil sample