Asteroid Compositions: some evidence from polarimetry

Although it cannot provide direct and unambiguous information on the mineralogical composition of an asteroid surface, polarimetry is a very useful tool to get an improved understanding of parameters which are intimately related to surface composition and regolith structure. In recent times there has been a revival in the field of asteroid polarimetry, on the theoretical side, in relation to experimental simulations, and due to the activity of some teams who are engaged in extensive observational campaigns. Some new discoveries of objects exhibiting unprecedented polarimetric properties have been done. The above subjects are briefly reviewed.Fil: Cellino, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Di Martino, M.. Istituto Nazionale di Astrofisica; ItaliaFil: Levasseur Regourd, A. C.. Centre National de la Recherche Scientifique; Francia. Universidad Pierre y Marie Curie; FranciaFil: Belskaya, I. N.. Astronomical Institute of Kharkiv National University; UcraniaFil: Bendjoya, Ph.. Universite Nice; FranciaFil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin

Structure, bonding and morphology of hydrothermally synthesised xonotlite

The authors have systematically investigated the role of synthesis conditions upon the structure and morphology of xonotlite. Starting with a mechanochemically prepared, semicrystalline phase with Ca/Si=1, the authors have prepared a series of xonotlite samples hydrothermally, at temperatures between 200 and 250 degrees C. Analysis in each case was by X-ray photoelectron spectroscopy, environmental scanning electron microscopy and X-ray diffraction. The authors’ use of a much lower water/solid ratio has indirectly confirmed the ‘through solution’ mechanism of xonotlite formation, where silicate dissolution is a key precursor of xonotlite formation. Concerning the role of temperature, too low a temperature (~200 degrees C) fails to yield xonotlite or leads to increased number of structural defects in the silicate chains of xonotlite and too high a temperature (>250 degrees C) leads to degradation of the xonotlite structure, through leaching of interchain calcium. Synthesis duration meanwhile leads to increased silicate polymerisation due to diminishing of the defects in the silicate chains and more perfect crystal morphologies

Participation of women scientists in ESA solar system missions: A historical trend

We analyzed the participation of women scientists in 10 ESA (European Space Agency) Solar System missions over a period of 38 years. Being part of a spacecraft mission science team can be considered a proxy to measure the "success"in the field. Participation of women in PI (Principal Investigators) teams varied between 4% and 25 %, with several missions with no women as PI. The percentage of female scientists as Co-I (Co-Investigators) is always less than 16 %. This number is lower than the percentage of women in the International Astronomical Union from all ESA's Member State (24 %), which can give us an indication of the percentage of women in the field. We encountered many difficulties to gather the data for this study. The list of team members were not always easily accessible. An additional difficulty was to determine the percentage of female scientists in planetary science in Europe. We would like to encourage the planetary community as a whole, as well as international organizations, universities and societies to continuously gather statistics over many years. Detailed statistics are only the first step to closely monitor the development of achievement gaps and initiate measures to tackle potential causes of inequity, leading to gender inequalities in STEM careers

Rotation of an oblate satellite: Chaos control

Aims. This paper investigates the chaotic rotation of an oblate satellite in the context of chaos control. Methods. A model of planar oscillations, described with the Beletskii equation, was investigated. The Hamiltonian formalism was utilized to employ a control method for suppressing chaos. Results. An additive control term, which is an order of magnitude smaller than the potential, is constructed. This allows not only for significantly diminished diffusion of the trajectory in the phase space, but turns the purely chaotic motion into strictly periodic motion.Comment: 9 pages, 4 figures; accepted in A&

Palaeolithic extinctions and the Taurid Complex

Intersection with the debris of a large (50-100 km) short-period comet during the Upper Palaeolithic provides a satisfactory explanation for the catastrophe of celestial origin which has been postulated to have occurred around 12900 BP, and which presaged a return to ice age conditions of duration ~1300 years. The Taurid Complex appears to be the debris of this erstwhile comet; it includes at least 19 of the brightest near-Earth objects. Sub-kilometre bodies in meteor streams may present the greatest regional impact hazard on timescales of human concern.Comment: 7 pages, 3 figures; accepted for Monthly Notices of the Royal Astronomical Society (definitive version will be available at www.blackwell-synergy.com

Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs

Many high contrast coronagraph designs have recently been proposed. In this paper, their suitability for direct imaging of extrasolar terrestrial planets is reviewed. We also develop a linear-algebra based model of coronagraphy that can both explain the behavior of existing coronagraphs and quantify the coronagraphic performance limit imposed by fundamental physics. We find that the maximum theoretical throughput of a coronagraph is equal to one minus the non-aberrated non-coronagraphic PSF of the telescope. We describe how a coronagraph reaching this fundamental limit may be designed, and how much improvement over the best existing coronagraph design is still possible. Both the analytical model and numerical simulations of existing designs also show that this theoretical limit rapidly degrades as the source size is increased: the ``highest performance'' coronagraphs, those with the highest throughput and smallest Inner Working Angle (IWA), are the most sensitive to stellar angular diameter. This unfortunately rules out the possibility of using a small IWA (lambda/d) coronagraph for a terrestrial planet imaging mission. Finally, a detailed numerical simulation which accurately accounts for stellar angular size, zodiacal and exozodiacal light is used to quantify the efficiency of coronagraph designs for direct imaging of extrasolar terrestrial planets in a possible real observing program. We find that in the photon noise limited regime, a 4m telescope with a theoretically optimal coronagraph is able to detect Earth-like planets around 50 stars with 1hr exposure time per target (assuming 25% throughput and exozodi levels similar to our solar system). We also show that at least 2 existing coronagraph design can approach this level of performance in the ideal monochromatic case considered in this study.Comment: Accepted for publication to ApJ Sup

SMART-1 Impact Ground-based campaign

Based on predictions of impact magnitude and cloud ejecta dynamics, we organized a SMART-1 ground-based observation campaign to perform coordinated measurements of the impact. Results from the coordinated multi-site campaign will be discussed

An atmospheric radiation model for Cerro Paranal. I. The optical spectral range

The Earth's atmosphere affects ground-based astronomical observations. Scattering, absorption, and radiation processes deteriorate the signal-to-noise ratio of the data received. For scheduling astronomical observations it is, therefore, important to accurately estimate the wavelength-dependent effect of the Earth's atmosphere on the observed flux. In order to increase the accuracy of the exposure time calculator of the European Southern Observatory's (ESO) Very Large Telescope (VLT) at Cerro Paranal, an atmospheric model was developed as part of the Austrian ESO In-Kind contribution. It includes all relevant components, such as scattered moonlight, scattered starlight, zodiacal light, atmospheric thermal radiation and absorption, and non-thermal airglow emission. This paper focuses on atmospheric scattering processes that mostly affect the blue (< 0.55 mum) wavelength regime, and airglow emission lines and continuum that dominate the red (> 0.55 mum) wavelength regime. While the former is mainly investigated by means of radiative transfer models, the intensity and variability of the latter is studied with a sample of 1186 VLT FORS1 spectra. For a set of parameters such as the object altitude angle, Moon-object angular distance, ecliptic latitude, bimonthly period, and solar radio flux, our model predicts atmospheric radiation and transmission at a requested resolution. A comparison of our model with the FORS1 spectra and photometric data for the night-sky brightness from the literature, suggest a model accuracy of about 20%. This is a significant improvement with respect to existing predictive atmospheric models for astronomical exposure time calculators.Comment: 23 pages, 21 figures, accepted for publication in A&