Dust Measurements in the Outer Solar System

Dust measurements in the outer solar system are reviewed. Only the plasma wave instrument on board Voyagers 1 and 2 recorded impacts in the Edgeworth-Kuiper belt (EKB). Pioneers 10 and 11 measured a constant dust flux of 10-micron-sized particles out to 20 AU. Dust detectors on board Ulysses and Galileo uniquely identified micron-sized interstellar grains passing through the planetary system. Impacts of interstellar dust grains onto big EKB objects generate at least about a ton per second of micron-sized secondaries that are dispersed by Poynting-Robertson effect and Lorentz force. We conclude that impacts of interstellar particles are also responsible for the loss of dust grains at the inner edge of the EKB. While new dust measurements in the EKB are in an early planning stage, several missions (Cassini and STARDUST) are en route to analyze interstellar dust in much more detail.Comment: 10 pages, 5 figures, Proceedings of the ESO workshop on ``Minor bodies in the outer solar system'

Impact-Generated Dust Clouds Surrounding the Galilean Moons

Tenuous dust clouds of Jupiter's Galilean moons Io, Europa, Ganymede and Callisto have been detected with the in-situ dust detector on board the Galileo spacecraft. The majority of the dust particles have been sensed at altitudes below five radii of these lunar-sized satellites. We identify the particles in the dust clouds surrounding the moons by their impact direction, impact velocity, and mass distribution. Average particle sizes are 0.5 to $\rm 1 \mu m$, just above the detector threshold, indicating a size distribution with decreasing numbers towards bigger particles. Our results imply that the particles have been kicked up by hypervelocity impacts of micrometeoroids onto the satellites' surfaces. The measured radial dust density profiles are consistent with predictions by dynamical modeling for satellite ejecta produced by interplanetary impactors (Krivov et al., PSS, 2003, 51, 251--269), assuming yield, mass and velocity distributions of the ejecta from laboratory measurements. The dust clouds of the three outer Galilean moons have very similar properties and are in good agreement with the model predictions for solid ice-silicate surfaces. The dust density in the vicinity of Io, however, is more than an order of magnitude lower than expected from theory. This may be due to a softer, fluffier surface of Io (volcanic deposits) as compared to the other moons. The log-log slope of the dust number density in the clouds vs. distance from the satellite center ranges between --1.6 and --2.8. Appreciable variations of number densities obtained from individual flybys with varying geometry, especially at Callisto, might be indicative of leading-trailing asymmetries of the clouds due to the motion of the moons with respect to the field of impactors.Comment: Icarus, in press, 46 pages, 16 figures, 5 table

Jovian dust streams: Probes of the Io plasma torus

Jupiter was discovered to be a source of high speed dust particles by the Ulysses spacecraft in 1992. These dust particles originate from the volcanic plumes on Io. They collect electrostatic charges from the plasma environment, gain energy from the co-rotating electric field of the magnetosphere, and leave Jupiter with escape speeds over $\rm 200 km s^{-1}$. The dust streams were also observed by the Galileo and Cassini spacecraft. While Ulysses and Cassini only had a single encounter with Jupiter, Galileo has continuously monitored the dust streams in the Jovian magnetosphere since 1996. The observed dust fluxes exhibit large orbit-to-orbit variability due to both systematic and stochastic changes. By combining the entire data set, the variability due to stochatic processes can be approximately removed and a strong variation with Jovian local time is found. This result is consistent with theoretical expectations and confirms that the majority of the Jovian dust stream particles originate from Io rather than other potential sources.Comment: 4 pages, 1 b/w figure, 2 color figures, accepted for Geophysical Research Letter

Interstellar Dust in the Solar System: Model versus In-Situ Spacecraft Data

In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in-situ dust detector on board the Ulysses spacecraft. Later on, interstellar dust was also identified in the data sets measured with dust instruments on board Galileo, Cassini and Helios. Ulysses monitored the interstellar dust stream at high ecliptic latitudes for about 16 years. The three other spacecraft data sets were obtained in the ecliptic plane and cover much shorter time intervals.We compare in-situ interstellar dust measurements obtained with these four spacecrafts, published in the literature, with predictions of a state-of-the-art model for the dynamics of interstellar dust in the inner solar system (Interplanetary Meteoroid environment for EXploration, IMEX), in order to test the reliability of the model predictions. Micrometer and sub-micrometer sized dust particles are subject to solar gravity and radiation pressure as well as to the Lorentz force on a charged dust particle moving through the Interplanetary Magnetic Field. The IMEX model was calibrated with the Ulysses interstellar dust measurements and includes these relevant forces. We study the time-resolved flux and mass distribution of interstellar dust in the solar system. The IMEX model agrees with the spacecraft measurements within a factor of 2 to 3, also for time intervals and spatial regions not covered by the original model calibration with the Ulysses data set. It usually underestimates the dust fluxes measured by the space missions which were not used for the model calibration, i.e. Galileo, Cassini and Helios. IMEX is a unique time-dependent model for the prediction of interstellar dust fluxes and mass distributions for the inner and outer solar system. The model is suited to study dust detection conditions for past and future space missions.Comment: 24 pages, 7 figures, 1 tabl

Galileo In-Situ Dust Measurements in Jupiter's Gossamer Rings

During its late orbital mission at Jupiter the Galileo spacecraft made two passages through the giant planet's gossamer ring system. The impact-ionization dust detector on board successfully recorded dust impacts during both ring passages and provided the first in-situ measurements from a dusty planetary ring. In all, a few thousand dust impacts were counted with the instrument accumulators during both ring passages, but only a total of 110 complete data sets of dust impacts were transmitted to Earth. Detected particle sizes range from about 0.2 to 5 micron, extending the known size distribution by an order of magnitude towards smaller particles than previously derived from optical imaging (Showalter et al. 2008). The grain size distribution increases towards smaller particles and shows an excess of these tiny motes in the Amalthea gossamer ring compared to the Thebe ring. The size distribution for the Amalthea ring derived from our in-situ measurements for the small grains agrees very well with the one obtained from images for large grains. Our analysis shows that particles contributing most to the optical cross-section are about 5 micron in radius, in agreement with imaging results. The measurements indicate a large drop in particle flux immediately interior to Thebe's orbit and some detected particles seem to be on highly-tilted orbits with inclinations up to 20 deg.Comment: 13 figures, 4 tables, submitted to Icaru

Heliospheric modulation of the interstellar dust flow on to Earth

Aims. Based on measurements by the Ulysses spacecraft and high-resolution modelling of the motion of interstellar dust (ISD) through the heliosphere we predict the ISD flow in the inner planetary system and on to the Earth. This is the third paper in a series of three about the flow and filtering of the ISD. Methods. Micrometer- and sub-micrometer-sized dust particles are subject to solar gravity and radiation pressure as well as to interactions with the interplanetary magnetic field that result in a complex size-dependent flow pattern of ISD in the planetary system. With high-resolution dynamical modelling we study the time-resolved flux and mass distribution of ISD and the requirements for detection of ISD near the Earth. Results. Along the Earth orbit the density, speed, and flow direction of ISD depend strongly on the Earth's position and the size of the interstellar grains. A broad maximum of the ISD flux (2x10^{-4}/m^2/s of particles with radii >~0.3\mu m) occurs in March when the Earth moves against the ISD flow. During this time period the relative speed with respect to the Earth is highest (~60 km/s), whereas in September when the Earth moves with the ISD flow, both the flux and the speed are lowest (<~10 km/s). The mean ISD mass flow on to the Earth is ~100 kg/year with the highest flux of ~3.5kg/day occurring for about 2 weeks close to the end of the year when the Earth passes near the narrow gravitational focus region downstream from the Sun. The phase of the 22-year solar wind cycle has a strong effect on the number density and flow of sub-micrometer-sized ISD particles. During the years of maximum electromagnetic focussing (year 2031 +/- 3) there is a chance that ISD particles with sizes even below 0.1\mu m can reach the Earth. Conclusions. We demonstrate that ISD can be effectively detected, analysed, and collected by space probes at 1 AU distance from the Sun.Comment: 17 pages, 17 figure

Io revealed in the Jovian dust streams

The Jovian dust streams are high-speed bursts of submicron-sized particles traveling in the same direction from a source in the Jovian system. Since their discovery in 1992, they have been observed by three spacecraft: Ulysses, Galileo and Cassini. The source of the Jovian dust streams is dust from Io's volcanoes. The charged and traveling dust stream particles have particular signatures in frequency space and in real space. The frequency-transformed Galileo dust stream measurements show different signatures, varying orbit-to-orbit during Galileo's first 29 orbits around Jupiter. Time-frequency analysis demonstrates that Io is a localized source of charged dust particles. Aspects of the particles' dynamics can be seen in the December-2000 joint Galileo-Cassini dust stream measurements. To match the travel times, the smallest dust particles could have the following range of parameters: radius: 6nm, density: 1.35-1.75gr/cm$^3$, sulfur charging conditions, which produce dust stream speeds: 220|450km/sec (Galileo|Cassini) and charge potentials: 5.5|6.3Volt (Galileo|Cassini).Comment: 8 pages, 5 postscript figures, latex, uses esapub.cls, aa.bst. Version with high-resolution figures can be found at http://www.mpi-hd.mpg.de/dustgroup/~graps/thesis

Institute stellen sich vor: Die Forschungseinheit Maritime Meteorologie des Leibniz-Instituts für Meereswissenschaften IFM-GEOMAR an der Universität Kiel / The Research Unit Marine Meteorology at the Leibniz Institute of Marine Sciences at the University of Kiel (IFM-GEOMAR)

Die aktuelle thematische Ausrichtung der Maritimen Meteorologie trägt dem Sachverhalt Rechnung, dass der Zustand der Atmosphäre durch komplexe Wechselwirkungen mit dem Ozean, Land, Meereis und der Vegetation sowie durch den Einfluss äußerer Faktoren bestimmt wird. Zu letzteren gehören u.a. die Vulkane, die Sonne, aber auch anthropogene Faktoren wie etwa der Ausstoß von Treibhausgasen in die Atmosphäre. Die Intensität der Wechselwirkungen hängt stark von den betrachteten zeitlichen und räumlichen Skalen ab. Die Klimamodellierung unter Leitung von Mojib Latif bildet den Rahmen für die weiteren interagierenden Themenbereiche, die in der Maritimen Meteorologie bearbeitet werden. Hierzu gehören der globale und regionale Energieund Wasserkreislauf (Andreas Macke), die Analyse der Klimavariabiliät aus Modell und Beobachtung (Eberhard Ruprecht, Dietmar Dommenget) sowie die Rolle der ozeanischen Deckschicht (Dietmar Dommenget) und der mittleren Atmosphäre (Kirstin Krüger) im Wechselspiel mit Ozean und Atmosphäre. Present fields of research are based on the recognition that the current state of the atmosphere is a result of complex interactions with ocean, land surface, vegetation, and external influences such as volcanoes, the sun or anthropogenic factors, like the increasing atmospheric content of CO2, on all temporal and spatial scales. Climate modelling, headed by Mojib Latif, links all the Marine Meteorology research areas together. Andreas Macke is leading the working group of energy and water cycle, which comprises both, global and regional aspects. Climate variability is investigated on the basis of analyses and observations (Eberhard Ruprecht and Dietmar Dommenget). The role of the ocean’s mixed layer (Dietmar Dommenget) and of the middle atmosphere (Kirstin Krüger) on air-sea interaction are also subjects of research

PDGF and TGF-β contribute to the natural course of human IgA glomerulonephritis

PDGF and TGF-β contribute to the natural course of human Ig-A glomerulonephritis. PDGF and TGF-β are known mediators of mesangial cell proliferation and matrix expansion. The presence of these regulatory factors was examined in 30 renal biopsies from patients with IgA glomerulonephritis (IgA-GN) at the mRNA and protein level. Normal renal tissue served as control. The mRNA expression of PDGF A/B chains, PDGF-βR and TGF-β1 was evaluated by means of RT/PCR with subsequent Southern blot hybridization and/or non-radiactive in situ hybridization. In addition, PDGF-AB/BB, PDGF-βR, TGF-β isoforms (β1, β1+2, β2+3), the small TGF-β1 latency associated peptide (TGF-β1 LAP) and the extracellular matrix proteins tenascin and decorin were analyzed by immunocytochemistry. The expression of growth factors was correlated with light microscopic and clinical features. Compared to normal control kidneys, an increased expression of PDGF-BB/PDGF-βR mRNAs and the corresponding proteins was observed in all biopsies with IgA-GN. Up-regulation was related to the degree of glomerular proliferation and the extent of fibrosing interstitial lesions. In contrast, there was a discordance between TGF-β1 mRNA and protein expression (evaluated by immunocytochemistry). In all biopsies, irrespective of the stage of the disease, abundant TGF-β1 transcripts were detected, whereas TGF-β1 immunoreactivity was expressed to a lesser degree and disclosed a more variable staining pattern. In patients with significant proliferative glomerular lesions and minor tubulointerstitial alterations, TGF-β1 positivity was confined to areas of glomerular proliferation, whereas in cases with more severe histology including sclerosing lesions TGF-β1 immunoreactivity was less prominent. The distribution and the intensity of TGF-β1 LAP staining commonly exceeded the positivity noted for TGF-β1, indicating only limited TGF-β1 activation. A decreased reactivity for tenascin accompanied the morphological features of glomerular sclerosis. The staining patterns and the fact that only very few inflammatory cells, particularly CD68 positive monocytes/macrophages, were detected in glomeruli confirm that predominantly resident glomerular cells (mesangial and endothelial cells) are the major source of up-regulated growth factor production in IgA-GN. Since the expression of PDGF-AB/BB paralleled the severity of proliferative glomerular changes, PDGF seems to represent a potential indicator of activity in this condition. It is suggested that an imbalance between PDGF and TGF-β (by restricted translation and/or activation) production contribute to the progressive nature of IgA-GN