In situ analysis of Europa ices by short-range melting probes

A key aspect for understanding the astrobiological potential of planets and moons in the Solar system is the analysis of material embedded in or underneath icy layers on the surface. In particular in case of the icy crust of Jupiters moon Europa such investigation would be of greatest interest. For a Europa lander to be launched in the 2020–2030 timeframe, we propose to use a simplified instrumented melting probe which is able to access and sample depths of a few meters without the necessity of heavy and complicated drilling equipment.     

Dominance in space — a new means of exercising global power?

Sustained criticism of the strategy of nuclear deterrence and technological developments in the military uses of space suggest that nuclear weapons may soon be replaced by control of outer space as the USA and USSR's primary instrument of global power. This article traces the change in perceptions of nuclear weapons policy and assesses the potential of outer space as a means of control, and the plans of the two superpowers for its exploitation, especially in the military sphere. The consequences for Western Europe of a shift from nuclear to space-based weapons as the primary guarantor of national security are also discussed.     

The Rosat mission

The primary scientific objective of the ROSAT mission is to perform the first all sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. Consequently a large number of new sources (> 10⁵) will be discovered and located with an accuracy of 1 arcmin. After completion of the survey which will take about half a year the instrument will be used for detailed observations of selected targets.The X-ray telescope consists of a fourfold nested Wolter type I mirror system with 80 cm aperture and 240 cm focal length, and three focal plane detectors. In the baseline version these will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 2⁰ × 2⁰.     

Calcification and silicification: fossilization potential of cyanobacteria from stromatolites of Niuafo'ou's Caldera Lakes (Tonga) and implications for the early fossil record

Calcification and silicification processes of cyanobacterial mats that form stromatolites in two caldera lakes of Niuafo'ou Island (Vai Lahi and Vai Si'i) were evaluated, and their importance as analogues for interpreting the early fossil record are discussed. It has been shown that the potential for morphological preservation of Niuafo'ou cyanobacteria is highly dependent on the timing and type of mineral phase involved in the fossilization process. Four main modes of mineralization of cyanobacteria organic parts have been recognized: (i) primary early postmortem calcification by aragonite nanograins that transform quickly into larger needle-like crystals and almost totally destroy the cellular structures, (ii) primary early postmortem silicification of almost intact cyanobacterial cells that leave a record of spectacularly well-preserved cellular structures, (iii) replacement by silica of primary aragonite that has already recrystallized and obliterated the cellular structures, (iv) occasional replacement of primary aragonite precipitated in the mucopolysaccharide sheaths and extracellular polymeric substances by Al-Mg-Fe silicates. These observations suggest that the extremely scarce earliest fossil record may, in part, be the result of (a) secondary replacement by silica of primary carbonate minerals (aragonite, calcite, siderite), which, due to recrystallization, had already annihilated the cellular morphology of the mineralized microbiota or (b) relatively late primary silicification of already highly degraded and no longer morphologically identifiable microbial remains.     

Assessing the elemental composition of comet 81P/Wild 2 by analyzing dust collected by Stardust

One of the prime objectives in the analysis of cometary dust collected by the Stardust space mission is to determine the elemental composition of comet 81P/Wild 2. For this analysis, samples captured by two sampling media, silica aerogel and Al foil, were available. While aerogel was qualified to sample the dust almost intact, particles impinging on Al foils produced hypervelocity impact craters with residual cometary matter. Both sample types delivered valuable information on the cometary inventory, even though a slight loss of volatiles was observed for impact residues on Al foils. Altogether an elemental composition close to solar elemental abundances was observed, indicating that the early solar system was chemically rather homogeneous from the innermost regions close to the sun to the outer edge of the solar system, the presumed region of cometary origin.     

Electromagnetic Induction Effects and Dynamo Action in the Hermean System

Embedded in a large mass density and strong interplanetary magnetic field solar wind environment and equipped with a magnetic field of minor strength, planet Mercury exhibits a small magnetosphere vulnerable to severe solar wind buffeting. This causes large variations in the size of the magnetosphere and its associated currents. External fields are of far more importance than in the terrestrial case and of a size comparable to any internal, dynamo-generated field. Induction effects in the planetary interior, dominated by its huge core, are thought to play a much more prominent role in the Hermean magnetosphere compared to any of its companions. Furthermore, the external fields may cause planetary dynamo amplification much as discussed for the Galilean moons Io and Ganymede, but with the ambient field generated by the dynamo and its magnetic field-solar wind interaction.     

Infrared Irradiance Calibration

Infrared astronomical measurements are calibrated against reference sources, usually primary standard stars that are, in turn, calibrated either by direct or indirect means. A direct calibration compares the star with a certified source, typically a blackbody. Indirect methods extrapolate a direct measurement of the flux at one wavelength to the flux at another. Historically, α Lyr (Vega) has been used as the primary standard as it is bright, easily accessible from the northern hemisphere, and is well calibrated in the visual. Until recently, the direct absolute infrared calibrations of α Lyr and those derived from the absolute solar flux scaled to the observed spectral energy distributions of solar type stars increasingly diverged with wavelength from those obtained using a model atmosphere to extrapolate the absolute visual flux of Vega into the infrared. The exception is the direct calibration by the 1996/97 Midcourse Space Experiment of the absolute fluxes for a number of the commonly used infrared standard stars, including Vega.In the mid-1980s, the Air Force Geophysics Laboratory began a program that led to the establishment of a network of stars with which to calibrate infrared space-based sensors. α Lyr and a CMa were adopted as the fundamental references and the absolute 1.2 to 35 µm infrared spectral energy distributions for the 616 secondary standard stars in the network were derived through spectral and photometric comparisons with the primary standards. The stars are also used for calibration at ground-based infrared observatories. For applications in which the network stars may not be bright enough, particularly at the longer infrared wavelengths, planets and the larger asteroids are used. Planets and asteroids move and rather sophisticated thermal modeling of the bodies is required to predict the disk-integrated brightness at a specific time with reasonable accuracy. The Infrared Space Observatory applied such a sophisticated ‘thermo-physical’ model to the largest asteroids to support calibration of the sensors to a claimed accuracy of within 5%. The AFRL program also created a spectral atlas of the brightest stars in the sky that, although they are variable, may be used for calibration if the large(r) attendant uncertainties are acceptable.