Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Dust particles in interplanetary space are expected to charge up to an electrostatic potential of about +5 V mostly by the solar UV (Horányi, 1996, Annu. Rev. Astrophys. 34, 383). Since the dynamics of charged grains may be quite different from neutral particles, the knowledge of the grain charge Qd is highly desirable. In the last two decades, several detectors on spacecraft were flown to measure the dust charge in-situ, but the instrumentation was not capable of determining the dust charge unambiguously. The Cosmic Dust Analyser (CDA) on the Cassini spacecraft includes a charge sensitive entrance grid system (QP detector). While entering the instrument, sufficiently charged particles induce a characteristic charge feature onto the grid system, which allows a reliable determination of Qd as well as of the impact speed vd. Here we report the first successful in-situ measurement of charged interplanetary dust grains by CDA. Amongst 37 impacts by interplanetary grains registered between November 1999 and January 2000, we identified 6 impacts whose QP signals show a clear feature caused by charged grains, corresponding to Qd between 1.3 and 5.4 fC. Knowledge of Qd also allows us to estimate the grain mass md. Assuming a potential of φd~+5 V and spheroidal grain morphologies with ratios of the maximum size to the minimum size of less than 2 the masses derived from Qd were found to be in excess of 10-13 kg. The dynamics of such particles are dominated by the Sun's gravity. In the framework of the micro-meteoroid models of the Solar System these grains belong to the core population of interplanetary grains (Divine, 1993, J. Geophys. Res. 98, 17029). Furthermore, a rate of 6 impacts of grains with md>=10-13 kg during 107 days is in good agreement with the predictions of the interplanetary dust environment model by Staubach et al. (1997, Adv. Space Res. 19, 301). This result demonstrates that charge detectors as the CDA QP system offer a reliable in-situ technique for determining simultaneously both the mass and velocity of big interplanetary grains. The primary CDA subsystem to determine md and vd, however, is an impact ionisation detector. The majority of the 37 recorded dust impacts produced impact charges are well outside the calibrated range. Moreover, these impacts were usually characterised by impact ionisation signals which differ significantly from signals taken in calibration experiments. In this paper we took advantage of the fact that the measurement of Qd is not affected by the subsequent impact of the grain with the detector. By relating md and vd derived from Qd of the 6 QP impactors to their corresponding ionisation signals we show that in many cases even for energetic impacts outside the calibrated range meaningful values for the dust mass can be obtained. The observed deviations of the ionisation signals from the calibration measurements are likely due to the large amount of plasma generated by such impacts. We discuss the implications of these findings on a meaningful reduction of impact ionisation signals caused by big particle impacts. A new scheme to identify and to evaluate such signals is presented. These finding are of great importance for future Cassini measurements in the saturnian system

Le sortilège espagnol (Barbey d'Aurevilly)

Le dialogue de Barbey avec l Espagne ressemble à celui de deux amants. Fait de mille détails inexprimés, de sous-entendus, c est un soupir, un spasme, un râle d agonie. Tentons de crocheter le maléfice qui emprisonne Barbey à l Espagne. Subir l envoûtement de l Espagne, c est subir la charge du taureau. Qu en est-il de la confrontation de Barbey avec la fougueuse Vellini ? Le sortilège s organise autour de la corrida, et la trilogie Ouest peut être appréhendée comme un spectacle tauromachique. Il convient de cerner les modalités de l hispanisme aurevillien. Ce que Barbey a obtenu, c est une vibration, un halo de l événement. L usage du castillan n est-il pas constitutif, et à quel degré, d une Espagne barbeyenne ? Mais l essentiel est la restance , ce qui n entre dans aucune classe connue. Le paradoxe du sortilège espagnol réside dans la coexistence de signes fascinants et un dispositif voué à les maîtriser. L Espagne de Barbey n est nulle part parce qu on la respire partout.ST DENIS-BU PARIS8 (930662101) / SudocSudocFranceF

Cassini between Earth and asteroid belt: first in-situ charge measurements of interplanetary grains

Dust particles in interplanetary space are expected to charge up to an electrostatic potential of about +5 V mostly by the solar UV (Horányi, 1996, Annu. Rev. Astrophys. 34, 383). Since the dynamics of charged grains may be quite different from neutral particles, the knowledge of the grain charge Qd is highly desirable. In the last two decades, several detectors on spacecraft were flown to measure the dust charge in-situ, but the instrumentation was not capable of determining the dust charge unambiguously. The Cosmic Dust Analyser (CDA) on the Cassini spacecraft includes a charge sensitive entrance grid system (QP detector). While entering the instrument, sufficiently charged particles induce a characteristic charge feature onto the grid system, which allows a reliable determination of Qd as well as of the impact speed vd. Here we report the first successful in-situ measurement of charged interplanetary dust grains by CDA. Amongst 37 impacts by interplanetary grains registered between November 1999 and January 2000, we identified 6 impacts whose QP signals show a clear feature caused by charged grains, corresponding to Qd between 1.3 and 5.4 fC. Knowledge of Qd also allows us to estimate the grain mass md. Assuming a potential of φd~+5 V and spheroidal grain morphologies with ratios of the maximum size to the minimum size of less than 2 the masses derived from Qd were found to be in excess of 10-13 kg. The dynamics of such particles are dominated by the Sun's gravity. In the framework of the micro-meteoroid models of the Solar System these grains belong to the core population of interplanetary grains (Divine, 1993, J. Geophys. Res. 98, 17029). Furthermore, a rate of 6 impacts of grains with md>=10-13 kg during 107 days is in good agreement with the predictions of the interplanetary dust environment model by Staubach et al. (1997, Adv. Space Res. 19, 301). This result demonstrates that charge detectors as the CDA QP system offer a reliable in-situ technique for determining simultaneously both the mass and velocity of big interplanetary grains. The primary CDA subsystem to determine md and vd, however, is an impact ionisation detector. The majority of the 37 recorded dust impacts produced impact charges are well outside the calibrated range. Moreover, these impacts were usually characterised by impact ionisation signals which differ significantly from signals taken in calibration experiments. In this paper we took advantage of the fact that the measurement of Qd is not affected by the subsequent impact of the grain with the detector. By relating md and vd derived from Qd of the 6 QP impactors to their corresponding ionisation signals we show that in many cases even for energetic impacts outside the calibrated range meaningful values for the dust mass can be obtained. The observed deviations of the ionisation signals from the calibration measurements are likely due to the large amount of plasma generated by such impacts. We discuss the implications of these findings on a meaningful reduction of impact ionisation signals caused by big particle impacts. A new scheme to identify and to evaluate such signals is presented. These finding are of great importance for future Cassini measurements in the saturnian system

In situ dust measurements in the inner Saturnian system

Srama R, Kempf S, Moragas-Klostermeyer G, et al. In situ dust measurements in the inner Saturnian system. Planetary and Space Science. 2006;54(9-10):967-987.In July 2004 the Cassini-Huygens mission reached the Saturnian system and started its orbital tour. A total of 75 orbits will be carried out during the primary mission until August 2008. In these four years Cassini crosses the ring plane 150 times and spends approx. 400 h within Titan's orbit. The Cosmic Dust Analyser (CDA) onboard Cassini characterises the dust environment with its extended E ring and embedded moons. Here, we focus on the CDA results of the first year and we present the Dust Analyser (DA) data within Titan's orbit. This paper does investigate High Rate Detector data and dust composition measurements. The authors focus on the analysis of impact rates, which were strongly variable primarily due to changes of the spacecraft pointing. An overview is given about the ring plane crossings and the DA counter measurements. The DA dust impact rates are compared with the DA boresight configuration around all ring plane crossings between June 2004 and July 2005. Dust impacts were registered at altitudes as high as 100 000 km above the ring plane at distances from Saturn between 4 and 10 Saturn radii. In those regions the dust density of particles bigger than 0.5 mu m can reach values of 0.001 m(-3). (c) 2006 Published by Elsevier Ltd

The Cassini cosmic dust analyzer

The Cassini-Huygens Cosmic Dust Analyzer (CDA) is intended to provide direct observations of dust grains with masses between 10-19 and 10-9 kg in interplanetary space and in the jovian and saturnian systems, to investigate their physical, chemical and dynamical properties as functions of the distances to the Sun, to Jupiter and to Saturn and its satellites and rings, to study their interaction with the saturnian rings, satellites and magnetosphere. Chemical composition of interplanetary meteoroids will be compared with asteroidal and cometary dust, as well as with Saturn dust, ejecta from rings and satellites. Ring and satellites phenomena which might be effects of meteoroid impacts will be compared with the interplanetary dust environment. Electrical charges of particulate matter in the magnetosphere and its consequences will be studied, e.g. the effects of the ambient plasma and the magnetic field on the trajectories of dust particles as well as fragmentation of particles due to electrostatic disruption

The cosmic dust analyser onboard cassini: ten years of discoveries

The interplanetary space probe Cassini/Huygens reached Saturn in July 2004 after 7 years of cruise phase. The German cosmic dust analyser (CDA) was developed under the leadership of the Max Planck Institute for Nuclear Physics in Heidelberg under the support of the DLR e.V. This instrument measures the interplanetary, interstellar and planetary dust in our solar system since 1999 and provided unique discoveries. In 1999, CDA detected interstellar dust in the inner solar system followed by the detection of electrical charges of interplanetary dust grains during the cruise phase between Earth and Jupiter. The instrument determined the composition of interplanetary dust and the nanometre-sized dust streams originating from Jupiter’s moon Io. During the approach to Saturn in 2004, similar streams of submicron grains with speeds in the order of 100 km/s were detected from Saturn’s inner and outer ring system and are released to the interplanetary magnetic field. Since 2004 CDA measured more than one million dust impacts characterising the dust environment of Saturn. The instrument is one of the three experiments which discovered the active ice geysers located at the south pole of Saturn’s moon Enceladus in 2005. Later, a detailed compositional analysis of the water ice grains in Saturn’s E ring system led to the discovery of large reservoirs of liquid water (oceans) below the icy crust of Enceladus. Finally, the determination of the dust-magnetosphere interaction and the discovery of the extended E ring (at least twice as large as predicted) allowed the definition of a dynamical dust model of Saturn’s E ring describing the observed properties. This paper summarizes the discoveries of a 10-year story of success based on reliable measurements with the most advanced dust detector flown in space until today. This paper focuses on cruise results and findings achieved at Saturn with a focus on flux and density measurements. CDA discoveries related to the detailed dust stream dynamics, E ring dynamics, its vertical profile and E ring compositional analysis are published elsewhere (see Hus et al. in AIP Conference Proccedings 1216:510–513, 2010; Hsu et al. in Icarus 206:653–661, 2010; Kempf et al. in Icarus 193:420, 2008; 206(2):446, 2010; Postberg et al. in Icarus 193(2):438, 2008; Nature 459:1098, 2009; Nature, 2011, doi:10.1038/nature10175)

Chromoblastomycosis as an endemic disease in temperate Europe: first confirmed case and review of the literature

This study reports a case of a 56-year-old white male, retired coal-miner, diagnosed with chromoblastomycosis lasting 20 years. The infection site was the burnt skin of the back. For many years the patient had not undertaken any treatment believing that the lesion had been a burn scar. A gradual increase in lesion size prompted the patient to start therapy. The diagnosis was made by histopathological examination and mycological culture. Identification of the causative agent at the species level was achieved by sequence analysis of the internal transcribed spacer (ITS) region and D1/D2 domains of the 26S rDNA. To our knowledge, this is the first documented case of chromoblastomycosis caused by Fonsecaea monophora in temperate Europe, outside the endemic area for the disease. This finding is highly significant for understanding the routes of infection of chromoblastomycosis and radically revises the traditional view of the natural ecology of the etiological agents of the disease