TY - JOUR A1 - Seiß, Martin A1 - Albers, Nicole A1 - Sremčević, Miodrag A1 - Schmidt, Jürgen A1 - Salo, Heikki A1 - Seiler, Michael A1 - Hoffmann, Holger A1 - Spahn, Frank T1 - Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn's Rings BT - Application to Bleriot JF - The astronomical journal N2 - One of the biggest successes of the Cassini mission is the detection of small moons (moonlets) embedded in Saturns rings that cause S-shaped density structures in their close vicinity, called propellers. Here, we present isothermal hydrodynamic simulations of moonlet-induced propellers in Saturn's A ring that denote a further development of the original model. We find excellent agreement between these new hydrodynamic and corresponding N-body simulations. Furthermore, the hydrodynamic simulations confirm the predicted scaling laws and the analytical solution for the density in the propeller gaps. Finally, this mean field approach allows us to simulate the pattern of the giant propeller Blériot, which is too large to be modeled by direct N-body simulations. Our results are compared to two stellar occultation observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS), which intersect the propeller Blériot. Best fits to the UVIS optical depth profiles are achieved for a Hill radius of 590 m, which implies a moonlet diameter of about 860 m. Furthermore, the model favors a kinematic shear viscosity of the surrounding ring material of ν0 = 340 cm2 s−1, a dispersion velocity in the range of 0.3 cm s−1 < c0 < 1.5 cm s−1, and a fairly high bulk viscosity 7 < ξ0/ν0 < 17. These large transport values might be overestimated by our isothermal ring model and should be reviewed by an extended model including thermal fluctuations. KW - diffusion KW - hydrodynamics KW - planets and satellites: rings Y1 - 2018 U6 - https://doi.org/10.3847/1538-3881/aaed44 SN - 0004-6256 SN - 1538-3881 VL - 157 IS - 1 PB - IOP Publishing Ltd. CY - Bristol ER - TY - GEN A1 - Grün, Eberhard A1 - de Pater, Imke A1 - Showalter, Mark A1 - Spahn, Frank A1 - Srama, Ralf T1 - Physics of dusty rings: History and perspective BT - Foreword T2 - Planetary and space science Y1 - 2006 U6 - https://doi.org/10.1016/j.pss.2006.05.005 SN - 0032-0633 VL - 54 IS - 9-10 SP - 837 EP - 843 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Makuch, Martin A1 - Brilliantov, Nikolai V. A1 - Sremcevic, Miodrag A1 - Spahn, Frank A1 - Krivov, Alexander V. T1 - Stochastic circumplanetary dynamics of rotating non-spherical dust particles JF - Planetary and space science N2 - We develop a model of stochastic radiation pressure for rotating non-spherical particles and apply the model to circumplanetary dynamics of dust grains. The stochastic properties of the radiation pressure are related to the ensemble-averaged characteristics of the rotating particles, which are given in terms of the rotational time-correlation function of a grain. We investigate the model analytically and show that an ensemble of particle trajectories demonstrates a diffusion-like behaviour. The analytical results are compared with numerical simulations, performed for the motion of the dusty ejecta from Deimos in orbit around Mars. We find that the theoretical predictions are in a good agreement with the simulation results. The agreement however deteriorates at later time, when the impact of non-linear terms, neglected in the analytic approach, becomes significant. Our results indicate that the stochastic modulation of the radiation pressure can play an important role in the circumplanetary dynamics of dust and may in case of some dusty systems noticeably alter an optical depth. (c) 2006 Elsevier Ltd. All rights reserved. KW - Mars KW - Deimos KW - ejecta KW - stochastics KW - radiation pressure Y1 - 2006 U6 - https://doi.org/10.1016/j.pss.2006.05.006 SN - 0032-0633 VL - 54 IS - 9-10 SP - 855 EP - 870 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Seiler, Michael A1 - Seiß, Martin A1 - Hoffmann, Holger A1 - Spahn, Frank T1 - Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn's Rings JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series N2 - The observation of the non-Keplerian behavior of propeller structures in Saturn's outer A ring raises the question: how does the propeller respond to the wandering of the central embedded moonlet? Here, we study numerically how the structural imprint of the propeller changes for a libration of the moonlet. It turns out that the libration induces an asymmetry in the propeller, which depends on the libration period and amplitude of the moonlet. Further, we study the dependence of the asymmetry on the libration period and amplitude for a moonlet with a 400 m Hill radius, which is located in the outer A ring. This allows us to apply our findings to the largest known propeller Blériot, which is expected to be of a similar size. For Blériot, we can conclude that, supposing the moonlet is librating with the largest observed period of 11.1 yr and an azimuthal amplitude of about 1845 km, a small asymmetry should be measurable but depends on the moonlet's libration phase at the observation time. The longitude residuals of other trans-Encke propellers (e.g., Earhart) show amplitudes similar to Blériot, which might allow us to observe larger asymmetries due to their smaller azimuthal extent, allowing us to scan the whole gap structure for asymmetries in one observation. Although the librational model of the moonlet is a simplification, our results are a first step toward the development of a consistent model for the description of the formation of asymmetric propellers caused by a freely moving moonlet. KW - Hydrodynamics KW - methods: data analysis KW - methods: numerical KW - planets and satellites: dynamical evolution and stability KW - planets and satellites: individual (Saturn) KW - planets and satellites: rings Y1 - 2019 U6 - https://doi.org/10.3847/1538-4365/ab26b0 SN - 0067-0049 SN - 1538-4365 VL - 243 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Hsu, Hsiang-Wen A1 - Schmidt, Jürgen A1 - Kempf, Sascha A1 - Postberg, Frank A1 - Moragas-Klostermeyer, Georg A1 - Seiss, Martin A1 - Hoffmann, Holger A1 - Burton, Marcia A1 - Ye, ShengYi A1 - Kurth, William S. A1 - Horanyi, Mihaly A1 - Khawaja, Nozair A1 - Spahn, Frank A1 - Schirdewahn, Daniel A1 - Moore, Luke A1 - Cuzzi, Jeff A1 - Jones, Geraint H. A1 - Srama, Ralf T1 - In situ collection of dust grains falling from Saturn’s rings into its atmosphere JF - Science N2 - Saturn’s main rings are composed of >95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft’s traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn’s dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred “ring rain.” Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings. Y1 - 2018 U6 - https://doi.org/10.1126/science.aat3185 SN - 0036-8075 SN - 1095-9203 VL - 362 IS - 6410 SP - 49 EP - + PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Albers, Nicole A1 - Spahn, Frank T1 - The influence of particle adhesion on the stability of agglomerates in Saturn's rings N2 - In planetary rings, binary collisions and mutual gravity are the predominant particle interactions. Based on a viscoelastic contact model we implement the concept of static adhesion. We discuss the collision dynamics and obtain a threshold velocity for restitution or agglomeration to occur. The latter takes place within a range of a few cm s(-1) for icy grains at low temperatures. The stability of such two-body agglomerates bound by adhesion and gravity in a tidal environment is discussed and applied to the saturnian system. A maximal agglomerate size for a given orbit location is obtained. In this way we are able to resolve the borderline of the zone where agglomerates can exist as a function of the agglomerate size and thus gain an alternative to the classical Roche limit. An increasing ring grain size with distance to Saturn as observed by the VIMS-experiment on board the Cassini spacecraft can be found by our estimates and implications for the saturnian system will be addressed. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/00191035 U6 - https://doi.org/10.1016/j.icarus.2005.10.011 SN - 0019-1035 ER - TY - JOUR A1 - Makuch, Martin A1 - Krivov, Alexander V. A1 - Spahn, Frank T1 - Long-term dynamical evolution of dusty ejecta from Deimos N2 - We re-assess expected properties of the presumed dust belt of Mars formed by impact ejecta from Deimos. Previous studies have shown that dynamics of Deimos particles are dominated by two perturbing forces: radiation pressure (RP) and Mars' oblateness (J2). At the same time, they have demonstrated that lifetimes of particles, especially of grains about ten of micrometers in size, may reach more than 10(4) years. On such timescales, the Poynting-Robertson drag (PR) becomes important. Here we provide a study of the dynamics under the combined action of all three perturbing forces. We show that a PR decay of the semimajor axes leads to an adiabatic decrease of amplitudes and periods of oscillations in orbital inclinations predicted in the framework of the underlying RP+J2 problem. Furthermore, we show that smallest of the long-lived Deimos grains (radius approximate to 5-10 mum) may reach a chaotic regime, resulting in unpredictable and abrupt changes of their dynamics. The particles just above that size (approximate to 10- 15 mum) should be the most abundant in the Deimos torus. Our dynamical analysis, combined with a more accurate study of the particle lifetimes, provides corrections to earlier predictions about the dimensions and geometry of the Deimos torus. In addition to a population, appreciably inclined and shifted towards the Sun, the torus should contain a more contracted, less asymmetric, and less tilted component between the orbits of Phobos and Deimos. (C) 2004 Elsevier Ltd. All rights reserved Y1 - 2005 SN - 0032-0633 ER - TY - JOUR A1 - Krivov, Alexander V. A1 - Sremcevic, Miodrag A1 - Spahn, Frank T1 - Evolution of a Keplerian disk of colliding and fragmenting particles: a kinetic model with application to the Edgeworth-Kuiper belt N2 - We present a kinetic model of a disk of solid particles, orbiting a primary and experiencing inelastic collisions. In distinction to other collisional models that use a 2D (mass-sernimajor axis) binning and perform a separate analysis of the velocity (eccentricity, inclination) evolution, we choose mass and orbital elements as independent variables of a phase space. The distribution function in this space contains full information on the combined mass, spatial, and velocity distributions of particles. A general kinetic equation for the distribution function is derived, valid for any set of orbital elements and for any collisional outcome, specified by a single kernel function. The first implementation of the model utilizes a 3D phase space (mass-semimajor axis-eccentricity) and involves averages over the inclination and all angular elements. We assume collisions to be destructive, simulate them with available material- and size-dependent scaling laws, and include collisional damping. A closed set of kinetic equations for a mass-semimajor axis-eccentricity distribution is written and transformation rules to usual mass and spatial distributions of the disk material are obtained. The kinetic "core" of our approach is generic. It is possible to add inclination as an additional phase space variable, to include cratering collisions and agglomeration, dynamical friction and viscous stirring, gravity of large perturbers, drag forces, and other effects into the model. As a specific application, we address the collisional evolution of the classical population in the Edgeworth-Kuiper belt (EKB). We run the model for different initial disk's masses and radial profiles and different impact strengths of objects. Our results for the size distribution, collisional timescales, and mass loss are in agreement with previous studies. In particular, collisional evolution is found to be most substantial in the inner part of the EKB, where the separation size between the survivors over EKB ' s age and fragments of earlier collisions lies between a few and several tens of km. The size distribution in the EKB is not a single Dohnanyi-type power law, reflecting the size dependence of the critical specific energy in both strength and gravity regimes. The net mass loss rate of an evolved disk is nearly constant and is dominated by disruption of larger objects. Finally, assuming an initially uniform distribution of orbital eccentricities, we show that an evolved disk contains more objects in orbits with intermediate eccentricities than in nearly circular or more eccentric orbits. This property holds for objects of any size and is explained in terms of collisional probabilities. The effect should modulate the eccentricity distribution shaped by dynamical mechanisms, such as resonances and truncation of perihelia by Neptune. (c) 2004 Elsevier Inc. All rights reserved Y1 - 2005 SN - 0019-1035 ER - TY - JOUR A1 - Sremcevic, Miodrag A1 - Krivov, Alexander V. A1 - Krüger, Harald A1 - Spahn, Frank T1 - Impact-generated dust clouds around planetary satellites : model versus Galileo N2 - This paper focuses on tenuous dust clouds of Jupiter's Galilean moons Europa, Ganymede and Callisto. In a companion paper (Sremcevic et al., Planet. Space Sci. 51 (2003) 455-471) an analytical model of impact-generated ejecta dust clouds surrounding planetary satellites has been developed. The main aim of the model is to predict the asymmetries in the dust clouds which may arise from the orbital motion of the parent body through a field of impactors. The Galileo dust detector data from flybys at Europa, Ganymede and Callisto are compatible with the model, assuming projectiles to be interplanetary micrometeoroids. The analysis of the data suggests that two interplanetary impactor populations are most likely the source of the measured dust clouds: impactors with isotropically distributed velocities and micrometeoroids in retrograde orbits. Other impactor populations, namely those originating in the Jovian system, or interplanetary projectiles with low orbital eccentricities and inclinations, or interstellar stream particles, can be ruled out by the statistical analysis of the data. The data analysis also suggests that the mean ejecta velocity angle to the normal at the satellite surface is around 30°, which is in agreement with laboratory studies of the hypervelocity impacts. © 2004 Elsevier Ltd. All rights reserved Y1 - 2005 SN - 0032-0633 ER - TY - JOUR A1 - Spahn, Frank A1 - Schmidt, Jürgen A1 - Albers, Nicole A1 - Hörning, Marcel A1 - Makuch, Martin A1 - Seiß, Martin A1 - Kempf, Sascha A1 - Srama, Ralf A1 - Dikarev, Valeri A1 - Helfert, Stefan A1 - Moragas-Klostermeyer, Georg A1 - Krivov, Alexander V. A1 - Sremcevic, Miodrag A1 - Tuzzolino, Anthony J. A1 - Economou, Thanasis A1 - Grün, Eberhard T1 - Cassini dust measurements at Enceladus and implications for the origin of the E ring Y1 - 2006 UR - http://www.sciencemag.org/content/311/5766/1416.full U6 - https://doi.org/10.1126/science.1121375 ER - TY - JOUR A1 - Seiss, Martin A1 - Spahn, Frank A1 - Sremcevic, Miodrag A1 - Salo, H. T1 - Structures induced by small moonlets in Saturn's rings : implications for the Cassini Mission N2 - Particle simulations are carried out to study density features caused by small moonlets embedded in a dense planetary ring. The creation of a "propeller" like structure is found together with adjacent density wakes. Both features are clear indications for the existence of moonlets in the rings. We confirmed that the propeller scales with the Hill-radius in radial direction whereas its azimuthal extent is determined by the ratio between the moonlet-mass and the ring-viscosity. Our findings bear direct implications for the analysis of the Cassini imaging (ISS) and occultation (UVIS) data: (i) for the detection of embedded larger bodies (>30 m) in Saturn's rings, and (ii) for remotely probing transport properties of the rings. The existence of a moonlet population may point to a catastrophic disruption of a parent body as a formation scenario for rings Y1 - 2005 SN - 0094-8276 ER - TY - JOUR A1 - Seiß, Martin A1 - Spahn, Frank A1 - Schmidt, Jürgen T1 - Moonlet induced wakes in planetary rings : analytical model including eccentric orbits of moon and ring particles N2 - Saturn's rings host two known moons, Pan and Daphnis, which are massive enough to clear circumferential gaps in the ring around their orbits. Both moons create wake patterns at the gap edges by gravitational deflection of the ring material (Cuzzi, J.N., Scargle, J.D. [1985]. Astrophys. J. 292, 276-290; Showalter, MR., Cuzzi, J.N., Marouf, E.A., Esposito, LW. [1986]. Icarus 66, 297-323). New Cassini observations revealed that these wavy edges deviate from the sinusoidal waveform, which one would expect from a theory that assumes a circular orbit of the perturbing moon and neglects particle interactions. Resonant perturbations of the edges by moons outside the ring system, as well as an eccentric orbit of the embedded moon, may partly explain this behavior (Porco, CC., and 34 colleagues [2005]. Science 307, 1226-1236; Tiscareno, M.S., Burns, J.A., Hedman, MM., Spitale, J.N., Porco, CC., Murray, C.D., and the Cassini Imaging team [2005]. Bull. Am. Astron. Soc. 37, 767; Weiss, J.W., Porco, CC., Tiscareno, M.S., Burns, J.A., Dones, L [2005]. Bull. Am. Astron. Soc. 37, 767; Weiss, J.W., Porco, CC., Tiscareno, M.S. [2009]. Astron. J. 138, 272-286). Here we present an extended non-collisional streamline model which accounts for both effects. We describe the resulting variations of the density structure and the modification of the nonlinearity parameter q. Furthermore, an estimate is given for the applicability of the model. We use the streamwire model introduced by Stewart (Stewart, G.R. [1991]. Icarus 94, 436-450) to plot the perturbed ring density at the gap edges. We apply our model to the Keeler gap edges undulated by Daphnis and to a faint ringlet in the Encke gap close to the orbit of Pan. The modulations of the latter ringlet, induced by the perturbations of Pan (Burns, J.A., Hedman, M.M., Tiscareno, M.S., Nicholson, P.D., Streetman, B.J., Colwell, J.E., Showalter, M.R., Murray, C.D., Cuzzi, J.N., Porco, CC., and the Cassini ISS team [2005]. Bull. Am. Astron. Soc. 37, 766), can be well described by our analytical model. Our analysis yields a Hill radius of Pan of 17.5 km, which is 9% smaller than the value presented by Porco (Porco, CC., and 34 colleagues [2005]. Science 307, 1226- 1236), but fits well to the radial semi-axis of Pan of 17.4 km. This supports the idea that Pan has filled its Hill sphere with accreted material (Porco, C.C., Thomas, P.C., Weiss, J.W., Richardson, D.C. [2007]. Science 318, 1602-1607). A numerical solution of a streamline is used to estimate the parameters of the Daphnis-Keeler gap system, since the close proximity of the gap edge to the moon induces strong perturbations, not allowing an application of the analytic streamline model. We obtain a Hill radius of 5.1 km for Daphnis, an inner edge variation of 8 km, and an eccentricity for Daphnis of 1.5 x 10(-5). The latter two quantities deviate by a factor of two from values gained by direct observations (Jacobson, R.A., Spitale, J., Porco, C.C., Beurle, K., Cooper, N.J., Evans, M.W., Murray, C.D. [2008]. Astron. J. 135, 261-263; Tiscareno, M.S., Burns, J.A., Hedman, M.M., Spitale, J.N., Porco, C.C., Murray, C.D., and the Cassini Imaging team [2005]. Bull. Am. Astron. Soc. 37, 767), which might be attributed to the neglect of particle interactions and vertical motion in our model. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/00191035 U6 - https://doi.org/10.1016/j.icarus.2010.06.013 SN - 0019-1035 ER - TY - JOUR A1 - Spahn, Frank A1 - Albers, Nicole A1 - Sremcevic, Miodrag A1 - Thornton, C. T1 - Kinetic description of coagulation and fragmentation in dilute granular particle ensembles N2 - We derive kinetic equations covering coagulation and fragmentation of granular gases including a combined dynamics of the mass spectrum and the velocity distribution. We will focus on coagulation; that can only occur at low impact velocities where attractive forces and dissipation prevent a post-collisional separation. We calculate an impact speed-dependent threshold velocity g(c) for coagulation to occur based on binary collision dynamics of viscoelastic Iranular particles including adhesive forces and determined by the masses, and the material of the colliding particles. Growth processes are immensely slowed down due to g(c) and the resulting restriction in phase space, and do furthermore depend on the ratio of threshold and thermal velocity of a considered particle ensemble. The Smoluchowski equation emerges from the general kinetic approach as a special case Y1 - 2004 SN - 0295-5075 ER - TY - JOUR A1 - Srama, Ralf A1 - Ahrens, Thomas J. A1 - Altobelli, Nicolas A1 - Auer, S. A1 - Bradley, J. G. A1 - Burton, M. A1 - Dikarev, V. V. A1 - Economou, T. A1 - Fechtig, Hugo A1 - Görlich, M. A1 - Grande, M. A1 - Graps, Amara A1 - Grün, Eberhard A1 - Havnes, Ove A1 - Helfert, Stefan A1 - Horanyi, Mihaly A1 - Igenbergs, E. A1 - Jessberger, Elmar K. A1 - Johnson, T. V. A1 - Kempf, Sascha A1 - Krivov, Alexander v. A1 - Krüger, Harald A1 - Mocker-Ahlreep, Anna A1 - Moragas-Klostermeyer, Georg A1 - Lamy, Philippe A1 - Landgraf, Markus A1 - Linkert, Dietmar A1 - Linkert, G. A1 - Lura, F. A1 - McDonnell, J. A. M. A1 - Moehlmann, Dirk A1 - Morfill, Gregory E. A1 - Muller, M. A1 - Roy, M. A1 - Schafer, G. A1 - Schlotzhauer, G. A1 - Schwehm, Gerhard H. A1 - Spahn, Frank A1 - Stübig, M. A1 - Svestka, Jiri A1 - Tschernjawski, V T1 - The Cassini Cosmic Dust Analyzer N2 - 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 held on the trajectories of dust particles as well as fragmentation of particles due to electrostatic disruption. The investigation will be performed with an instrument that measures the mass, composition, electric charge, speed, and flight direction of individual dust particles. It is a highly reliable and versatile instrument with a mass sensitivity 106 times higher than that of the Pioneer 10 and I I dust detectors which measured dust in the saturnian system. The Cosmic Dust Analyzer has significant inheritance from former space instrumentation developed for the VEGA, Giotto, Galileo, and Ulysses missions. It will reliably measure impacts from as low as I impact per month up to 104 impacts per second. The instrument weighs 17 kg and consumes 12 W, the integrated time-of-flight mass spectrometer has a mass resolution of up to 50. The nominal data transmission rate is 524 bits/s and varies between 50 and 4192 bps Y1 - 2004 SN - 0038-6308 ER - TY - JOUR A1 - Spahn, Frank A1 - Krivov, Alexander V. A1 - Sremcevic, Miodrag A1 - Schwarz, U. A1 - Kurths, Jürgen T1 - Stochastic forces in circumplanetary dust dynamics N2 - Charged dust grains in circumplanetary environments experience, beyond various deterministic forces, also stochastic perturbations caused, by fluctuations of the magnetic field, the charge of the grains, by chaotic rotation of aspherical grains, etc. Here we investigate the dynamics of a dust population in a circular orbit around a planet which is perturbed by a stochastic planetary magnetic field B', modeled by an isotropically Gaussian white noise. The resulting perturbation equations give rise to a modified diffusion of the inclinations i and eccentricities e. The diffusion coefficient is found to be D proportional to w^2 O /n^2 , where the gyrofrequency, the Kepler frequency, and the synodic frequency are denoted by w , O, and n, respectively. This behavior has been checked against numerical simulations. We have chosen dust grains (1 m in radius) ejected from Jupiter's satellite Europa in circular equatorial orbits around Jupiter and integrated numerically their trajectories over their typical lifetimes (100 years). The particles were exposed to a Gaussian fluctuating magnetic field B' with the same statistical properties as in the analytical treatment. These simulations have confirmed the analytical results. The theoretical studies showed the statistical properties of B' to be of decisive importance. To estimate them, we analyzed the magnetic field data obtained by the Galileo spacecraft magnetometer at Jupiter and found almost Gaussian fluctuations of about 5% of the mean field and exponentially decaying correlations. This results in a diffusion of orbital inclinations and eccentricities of the dust grains of about ten percent over the lifetime of the particles. For smaller dusty motes or for close-in particles (e.g., in Jovian gossamer rings) stochastics might well dominate the dynamics. Y1 - 2003 UR - http://www.agu.org/pubs/current/je/ ER - TY - JOUR A1 - Kirvov, Alexander V. A1 - Wardinski, Ingo A1 - Spahn, Frank A1 - Krüger, Harald A1 - Grün, Eberhard T1 - Dust on the outskirts of the Jovian System Y1 - 2002 UR - http://www.idealibrary.com/links/doi/10.1006/icar.2002.6848 ER - TY - JOUR A1 - Gordon, M. K. A1 - Krivov, Alexander V. A1 - Schmidt, Jürgen A1 - Spahn, Frank T1 - Planetary rings Y1 - 2002 ER - TY - INPR A1 - Thiessenhusen, Kai-Uwe A1 - Esposito, Larry W. A1 - Kurths, Jürgen A1 - Spahn, Frank T1 - Detection of hidden resonances in Saturn's B-ring N2 - The Voyager 2 Photopolarimeter experiment has yielded the highest resolved data of Saturn's rings, exhibiting a wide variety of features. The B-ring region between 105000 km and 110000 km distance from Saturn has been investigated. It has a high matter density and contains no significance features visible by eye. Analysis with statistical methods has let us to the detection of two significant events. These features are correlated with the inner 3:2 resonances of the F-ring shepherd satellites Pandora and Prometheus, and may be evidence of large ring paricles caught in the corotation resonances. T3 - NLD Preprints - 13 KW - Planetary Rings Y1 - 1995 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13618 ER - TY - JOUR A1 - Grätz, Fabio M. A1 - Seiss, Martin A1 - Spahn, Frank T1 - Formation of moon-induced gaps in dense planetary rings BT - application to the rings of saturn JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We develop an axisymmetric diffusion model to describe radial density profiles in the vicinity of tiny moons embedded in planetary rings. Our diffusion model accounts for the gravitational scattering of the ring particles by an embedded moon and for the viscous diffusion of the ring matter back into the gap. With test particle simulations, we show that the scattering of the ring particles passing the moon is larger for small impact parameters than estimated by Goldreich & Tremaine and Namouni. This is significant for modeling the Keeler gap. We apply our model to the gaps of the moons Pan and Daphnis embedded in the outer A ring of Saturn with the aim to estimate the shear viscosity of the ring in the vicinity of the Encke and Keeler gap. In addition, we analyze whether tiny icy moons whose dimensions lie below Cassini's resolution capabilities would be able to explain the gap structure of the C ring and the Cassini division. KW - diffusion KW - planets and satellites: rings KW - scattering Y1 - 2018 U6 - https://doi.org/10.3847/1538-4357/aace00 SN - 0004-637X SN - 1538-4357 VL - 862 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Szalay, J. R. A1 - Poppe, A. R. A1 - Agarwal, J. A1 - Britt, D. A1 - Belskaya, I. A1 - Horanyi, M. A1 - Nakamura, T. A1 - Sachse, M. A1 - Spahn, Frank T1 - Dust Phenomena Relating to Airless Bodies JF - Space science reviews N2 - Airless bodies are directly exposed to ambient plasma and meteoroid fluxes, making them characteristically different from bodies whose dense atmospheres protect their surfaces from such fluxes. Direct exposure to plasma and meteoroids has important consequences for the formation and evolution of planetary surfaces, including altering chemical makeup and optical properties, generating neutral gas and/or dust exospheres, and leading to the generation of circumplanetary and interplanetary dust grain populations. In the past two decades, there have been many advancements in our understanding of airless bodies and their interaction with various dust populations. In this paper, we describe relevant dust phenomena on the surface and in the vicinity of airless bodies over a broad range of scale sizes from to , with a focus on recent developments in this field. KW - Dust KW - Airless bodies KW - Interplanetary dust Y1 - 2018 U6 - https://doi.org/10.1007/s11214-018-0527-0 SN - 0038-6308 SN - 1572-9672 VL - 214 IS - 5 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Buratti, Bonnie J. A1 - Thomas, P. C. A1 - Roussos, E. A1 - Howett, Carly A1 - Seiss, Martin A1 - Hendrix, A. R. A1 - Helfenstein, Paul A1 - Brown, R. H. A1 - Clark, R. N. A1 - Denk, Tilmann A1 - Filacchione, Gianrico A1 - Hoffmann, Holger A1 - Jones, Geraint H. A1 - Khawaja, N. A1 - Kollmann, Peter A1 - Krupp, Norbert A1 - Lunine, Jonathan A1 - Momary, T. W. A1 - Paranicas, Christopher A1 - Postberg, Frank A1 - Sachse, Manuel A1 - Spahn, Frank A1 - Spencer, John A1 - Srama, Ralf A1 - Albin, T. A1 - Baines, K. H. A1 - Ciarniello, Mauro A1 - Economou, Thanasis A1 - Hsu, Hsiang-Wen A1 - Kempf, Sascha A1 - Krimigis, Stamatios M. A1 - Mitchell, Donald A1 - Moragas-Klostermeyer, Georg A1 - Nicholson, Philip D. A1 - Porco, C. C. A1 - Rosenberg, Heike A1 - Simolka, Jonas A1 - Soderblom, Laurence A. T1 - Close Cassini flybys of Saturn’s ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus JF - Science N2 - Saturn’s main ring system is associated with a set of small moons that either are embedded within it or interact with the rings to alter their shape and composition. Five close flybys of the moons Pan, Daphnis, Atlas, Pandora, and Epimetheus were performed between December 2016 and April 2017 during the ring-grazing orbits of the Cassini mission. Data on the moons’ morphology, structure, particle environment, and composition were returned, along with images in the ultraviolet and thermal infrared. We find that the optical properties of the moons’ surfaces are determined by two competing processes: contamination by a red material formed in Saturn’s main ring system and accretion of bright icy particles or water vapor from volcanic plumes originating on the moon Enceladus. Y1 - 2019 U6 - https://doi.org/10.1126/science.aat2349 SN - 0036-8075 SN - 1095-9203 VL - 364 IS - 6445 SP - 1053 PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Grätz, Fabio M. A1 - Seiß, Martin A1 - Schmidt, Jürgen A1 - Colwell, Joshua A1 - Spahn, Frank T1 - Sharp Gap Edges in Dense Planetary Rings BT - an Axisymmetric Diffusion Model JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - One of the most intriguing facets of Saturn's rings are the sharp edges of gaps in the rings where the surface density abruptly drops to zero. This is despite of the fact that the range over which a moon transfers angular momentum onto the ring material is much larger. Recent UVIS-scans of the edges of the Encke and Keeler gap show that this drop occurs over a range approximately equal to the rings' thickness. Borderies et al. show that this striking feature is likely related to the local reversal of the usually outward directed viscous transport of angular momentum in strongly perturbed regions. In this article we revise the Borderies et al. model using a granular flow model to define the shear and bulk viscosities, ν and ζ, and incorporate the angular momentum flux reversal effect into the axisymmetric diffusion model we developed for gaps in dense planetary rings. Finally, we apply our model to the Encke and Keeler division in order to estimate the shear and bulk viscosities in the vicinity of both gaps KW - celestial mechanics KW - diffusion KW - hydrodynamics KW - planets and satellites: rings KW - scattering Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/ab007e SN - 0004-637X SN - 1538-4357 VL - 872 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Spahn, Frank A1 - Sachse, Manuel A1 - Seiss, Martin A1 - Hsu, Hsiang-Wen A1 - Kempf, Sascha A1 - Horanyi, Mihaly T1 - Circumplanetary Dust Populations JF - Space science reviews N2 - We summarize the current state of observations of circumplanetary dust populations, including both dilute and dense rings and tori around the giant planets, ejecta clouds engulfing airless moons, and rings around smaller planetary bodies throughout the Solar System. We also discuss the theoretical models that enable these observations to be understood in terms of the sources, sinks and transport of various dust populations. The dynamics and resulting transport of the particles can be quite complex, due to the fact that their motion is influenced by neutral and plasma drag, radiation pressure, and electromagnetic forcesall in addition to gravity. The relative importance of these forces depends on the environment, as well as the makeup and size of the particles. Possible dust sources include the generation of ejecta particles by impacts, active volcanoes and geysers, and the capture of exogenous particles. Possible dust sinks include collisions with moons, rings, or the central planet, erosion due to sublimation and sputtering, even ejection and escape from the circumplanetary environment. KW - Circumplanetary dust KW - Planetary rings and tori KW - Dust sources and sinks KW - Dust dynamics Y1 - 2019 U6 - https://doi.org/10.1007/s11214-018-0577-3 SN - 0038-6308 SN - 1572-9672 VL - 215 IS - 1 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Hoffmann, H. A1 - Seiß, Martin A1 - Spahn, Frank T1 - Vertical relaxation of a moonlet propeller in Saturn's a ring JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - Two images, taken by the Cassini spacecraft near Saturn's equinox in 2009 August, show the Earhart propeller casting a 350 km long shadow, offering the opportunity to watch how the ring height, excited by the propeller moonlet, relaxes to an equilibrium state. From the shape of the shadow cast and a model of the azimuthal propeller height relaxation, we determine the exponential cooling constant of this process to be lambda = 0.07 +/- 0.02 km(-1), and thereby determine the collision frequency of the ring particles in the vertically excited region of the propeller to be omega(c)/Omega = 0.9 +/- 0.2. KW - planets and satellites: individual (Saturn) KW - planets and satellites: rings Y1 - 2013 U6 - https://doi.org/10.1088/2041-8205/765/1/L4 SN - 2041-8205 VL - 765 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Petzschmann, Olaf A1 - Thiessenhusen, Kai-Uwe A1 - Spahn, Frank A1 - Schmidt, Jürgen T1 - Inelastic collisions in planetary rings : thickness and satellite-induced structures Y1 - 1998 SN - 0-7923-5102-9 ER - TY - JOUR A1 - Schwarz, Udo A1 - Kurths, Jürgen A1 - Spahn, Frank A1 - Petzschmann, Olaf T1 - Reply on the comment of "Clustering of granular assemblies with temperature dependent restitution and under differential rotation" Y1 - 1998 ER - TY - JOUR A1 - Spahn, Frank A1 - Schmidt, Jürgen T1 - Planetary science : Saturn's bared mini-moons Y1 - 2006 UR - http://www.nature.com/nature/journal/v440/n7084/full/440614a.html U6 - https://doi.org/10.1038/440614a ER - TY - BOOK A1 - Spahn, Frank A1 - Hertzsch, Jan-Martin A1 - Brilliantov, Nikolai V. T1 - The role of particle collisions for the dynamics in planetary rings T3 - Preprint NLD Y1 - 1995 VL - 14 PB - Univ. CY - Potsdam ER - TY - JOUR A1 - Spahn, Frank A1 - Katzorke, Ines A1 - Petzschmann, Olaf A1 - Schwarz, Udo A1 - Kurths, Jürgen T1 - Cluster instabiliy of granular assemblies Y1 - 1997 ER - TY - JOUR A1 - Spahn, Frank T1 - Planetary rings : nonequilibrium systems in space Y1 - 1997 ER - TY - JOUR A1 - Spahn, Frank A1 - Schwarz, Udo A1 - Kurths, Jürgen T1 - Clustering of granular assemblies with temperature dependent restitution under Keplerian differential rotation Y1 - 1997 ER - TY - JOUR A1 - Scholl, H. A1 - Spahn, Frank A1 - Hertzsch, Jan-Martin A1 - Katzorke, Ines T1 - Simulation of collisions in planetary rings Y1 - 1997 ER - TY - THES A1 - Spahn, Frank T1 - Einfluß von Satelliten auf die Dynamik planetarer Ringe Y1 - 1994 ER - TY - JOUR A1 - Bodrova, Anna A1 - Schmidt, Jürgen A1 - Spahn, Frank A1 - Brilliantov, Nikolai V. T1 - Adhesion and collisional release of particles in dense planetary rings JF - Icarus : international journal of solar system studies N2 - We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn's dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn's rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for "Saturn after Cassini-Huygens" Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system. KW - Planetary rings KW - Saturn, Rings KW - Collisional physics Y1 - 2012 U6 - https://doi.org/10.1016/j.icarus.2011.11.011 SN - 0019-1035 SN - 1090-2643 VL - 218 IS - 1 SP - 60 EP - 68 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Srama, Ralf A1 - Krueger, H. A1 - Yamaguchi, T. A1 - Stephan, T. A1 - Burchell, M. A1 - Kearsley, A. T. A1 - Sterken, V. A1 - Postberg, F. A1 - Kempf, S. A1 - Grün, Eberhard A1 - Altobelli, Nicolas A1 - Ehrenfreund, P. A1 - Dikarev, V. A1 - Horanyi, M. A1 - Sternovsky, Zoltan A1 - Carpenter, J. D. A1 - Westphal, A. A1 - Gainsforth, Z. A1 - Krabbe, A. A1 - Agarwal, Jessica A1 - Yano, H. A1 - Blum, J. A1 - Henkel, H. A1 - Hillier, J. A1 - Hoppe, P. A1 - Trieloff, M. A1 - Hsu, S. A1 - Mocker, A. A1 - Fiege, K. A1 - Green, S. F. A1 - Bischoff, A. A1 - Esposito, F. A1 - Laufer, R. A1 - Hyde, T. W. A1 - Herdrich, G. A1 - Fasoulas, S. A1 - Jaeckel, A. A1 - Jones, G. A1 - Jenniskens, P. A1 - Khalisi, E. A1 - Moragas-Klostermeyer, Georg A1 - Spahn, Frank A1 - Keller, H. U. A1 - Frisch, P. A1 - Levasseur-Regourd, A. C. A1 - Pailer, N. A1 - Altwegg, K. A1 - Engrand, C. A1 - Auer, S. A1 - Silen, J. A1 - Sasaki, S. A1 - Kobayashi, M. A1 - Schmidt, J. A1 - Kissel, J. A1 - Marty, B. A1 - Michel, P. A1 - Palumbo, P. A1 - Vaisberg, O. A1 - Baggaley, J. A1 - Rotundi, A. A1 - Roeser, H. P. T1 - SARIM PLUS-sample return of comet 67P/CG and of interstellar matter JF - EXPERIMENTAL ASTRONOMY N2 - The Stardust mission returned cometary, interplanetary and (probably) interstellar dust in 2006 to Earth that have been analysed in Earth laboratories worldwide. Results of this mission have changed our view and knowledge on the early solar nebula. The Rosetta mission is on its way to land on comet 67P/Churyumov-Gerasimenko and will investigate for the first time in great detail the comet nucleus and its environment starting in 2014. Additional astronomy and planetary space missions will further contribute to our understanding of dust generation, evolution and destruction in interstellar and interplanetary space and provide constraints on solar system formation and processes that led to the origin of life on Earth. One of these missions, SARIM-PLUS, will provide a unique perspective by measuring interplanetary and interstellar dust with high accuracy and sensitivity in our inner solar system between 1 and 2 AU. SARIM-PLUS employs latest in-situ techniques for a full characterisation of individual micrometeoroids (flux, mass, charge, trajectory, composition()) and collects and returns these samples to Earth for a detailed analysis. The opportunity to visit again the target comet of the Rosetta mission 67P/Churyumov-Gerasimeenternko, and to investigate its dusty environment six years after Rosetta with complementary methods is unique and strongly enhances and supports the scientific exploration of this target and the entire Rosetta mission. Launch opportunities are in 2020 with a backup window starting early 2026. The comet encounter occurs in September 2021 and the reentry takes place in early 2024. An encounter speed of 6 km/s ensures comparable results to the Stardust mission. KW - Interstellar dust KW - Cometary dust KW - Churyumov Gerasimenko KW - Interplanetary dust KW - IMF KW - Cosmic vision KW - Sample return KW - Dust collector KW - Mass spectrometry Y1 - 2012 U6 - https://doi.org/10.1007/s10686-011-9285-7 SN - 0922-6435 SN - 1572-9508 VL - 33 IS - 2-3 SP - 723 EP - 751 PB - SPRINGER CY - DORDRECHT ER - TY - JOUR A1 - Baibolatov, Yernur A1 - Spahn, Frank T1 - The role of adhesion for ensembles of mesoscopic particles JF - Granular matter N2 - We present a toy-model for an ensemble of adhering mesoscopic constituents in order to estimate the effect of the granular temperature on the sizes of embedded aggregates. The major goal is to illustrate the relation between the mean aggregate size and the granular temperature in dense planetary rings. For sake of simplicity we describe the collective behavior of the ensemble by means of equilibrium statistical mechanics, motivated by the stationary temperature established by the balance between a Kepler-shear driven viscous heating and inelastic cooling in these cosmic granular disks. The ensemble consists of N' equal constituents which can form cluster(s) or move like a gas-or both phases may coexist-depending on the (granular) temperature of the system. We assume the binding energy levels of a cluster E-c = -N-c gamma a to be determined by a certain contact number N-c, given by the configuration of N constituents of the aggregate (energy per contact: -gamma a). By applying canonical and grand-canonical ensembles, we show that the granular temperature T of a gas of constituents (their mean kinetic energy) controls the size distribution of the aggregates. They are the smaller the higher the granular temperature T is. A mere gas of single constituents is sustained for T >> gamma a. In the case of large clusters (low temperatures T << gamma a) the size distribution becomes a Poissonian. KW - Adhesion KW - Statistical mechanics KW - Planetary rings Y1 - 2012 U6 - https://doi.org/10.1007/s10035-012-0325-4 SN - 1434-5021 VL - 14 IS - 2 SP - 197 EP - 202 PB - Springer CY - New York ER - TY - JOUR A1 - Spahn, Frank A1 - Vieira Neto, E. A1 - Guimaraes, A. H. F. A1 - Gorban, A. N. A1 - Brilliantov, Nikolai V. T1 - A statistical model of aggregate fragmentation JF - New journal of physics : the open-access journal for physics N2 - A statistical model of fragmentation of aggregates is proposed, based on the stochastic propagation of cracks through the body. The propagation rules are formulated on a lattice and mimic two important features of the process-a crack moves against the stress gradient while dissipating energy during its growth. We perform numerical simulations of the model for two-dimensional lattice and reveal that the mass distribution for small-and intermediate-size fragments obeys a power law, F(m) proportional to m(-3/2), in agreement with experimental observations. We develop an analytical theory which explains the detected power law and demonstrate that the overall fragment mass distribution in our model agrees qualitatively with that one observed in experiments. Y1 - 2014 U6 - https://doi.org/10.1088/1367-2630/16/1/013031 SN - 1367-2630 VL - 16 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kempf, Sascha A1 - Srama, Ralf A1 - Grün, Eberhard A1 - Mocker, Anna A1 - Postberg, Frank A1 - Hillier, Jon K. A1 - Horanyi, Mihaly A1 - Sternovsky, Zoltan A1 - Abel, Bernd A1 - Beinsen, Alexander A1 - Thissen, Roland A1 - Schmidt, Jürgen A1 - Spahn, Frank A1 - Altobelli, Nicolas T1 - Linear high resolution dust mass spectrometer for a mission to the Galilean satellites JF - Planetary and space science N2 - The discovery of volcanic activity on Enceladus stands out amongst the long list of findings by the Cassini mission to Saturn. In particular the compositional analysis of Enceladus ice particles by Cassini's Cosmic Dust Analyser (CDA) (Srama et al., 2004) has proven to be a powerful technique for obtaining information about processes below the moon's ice crust. Small amounts of sodium salts embedded in the particles' ice matrices provide direct evidence for a subsurface liquid water reservoir, which is, or has been, in contact with the moon's rocky core (Postberg et al., 2009, 2011b). Jupiter's Galilean satellites Ganymede, Europa, and Callisto are also believed to have subsurface oceans and are therefore prime targets for future NASA and ESA outer Solar System missions. The Galilean moons are engulfed in tenuous dust clouds consisting of tiny pieces of the moons' surfaces (Kruger et al., 1999), released by hypervelocity impacts of micrometeoroids, which steadily bombard the surfaces of the moons. In situ chemical analysis of these grains by a high resolution dust spectrometer will provide spatially resolved mapping of the surface composition of Europa. Ganymede, and Callisto, meeting key scientific objectives of the planned missions. However, novel high-resolution reflectron-type dust mass spectrometers (Sternovsky et al., 2007; Srama et al., 2007) developed for dust astronomy missions (Gran et al., 2009) are probably not robust enough to be operated in the energetic radiation environment of the inner Jovian system. In contrast, CDA's linear spectrometer is much less affected by harsh radiation conditions because its ion detector is not directly facing out into space. The instrument has been continuously operated on Cassini for 11 years. In this paper we investigate the possibility of operating a CDA-like instrument as a high resolution impact mass spectrometer. We show that such an instrument is capable of reliably identifying traces of organic and inorganic materials in the ice matrix of ejecta expected to be generated from the surfaces of the Galilean moons. These measurements are complementary, and in some cases superior, compared to other traditional techniques such as infrared remote sensing or in situ ion or neutral mass spectrometers. KW - Europa KW - Ganymede KW - Callisto KW - Surface composition KW - Mass spectroscopy KW - Dust Y1 - 2012 U6 - https://doi.org/10.1016/j.pss.2011.12.019 SN - 0032-0633 VL - 65 IS - 1 SP - 10 EP - 20 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Hoffmann, Holger A1 - Seiss, Martin A1 - Salo, Heikki A1 - Spahn, Frank T1 - Vertical structures induced by embedded moonlets in Saturn's rings JF - Icarus : international journal of solar system studies N2 - We study the vertical extent of propeller structures in Saturn's rings (i) by extending the model of Spahn and Sremcevic (Spahn, F., Sremcevic, M. [2000]. Astron. Astrophys., 358, 368-372) to include the vertical direction and (ii) by performing N-body box simulations of a perturbing moonlet embedded into the rings. We find that the gravitational interaction of ring particles with a non-inclined moonlet does not induce considerable vertical excursions of ring particles, but causes a considerable thermal motion in the ring plane. We expect ring particle collisions to partly convert the lateral induced thermal motion into vertical excursions of ring particles in the course of a quasi-thermalization. The N-body box simulations lead to maximal propeller heights of about 0.6-0.8 Hill radii of the embedded perturbing moonlet. Moonlet sizes estimated by this relation are in good agreement with size estimates from radial propeller scalings for the propellers Bleriot and Earhart. For large propellers, the extended hydrodynamical propeller model predicts an exponential propeller height relaxation, confirmed by N-body box simulations of non-self gravitating ring particles. Exponential cooling constants, calculated from the hydrodynamical propeller model agree fairly well with values from fits to the tail of the azimuthal height decay of the N-body box simulations. From exponential cooling constants, determined from shadows cast by the propeller Earhart and imaged by the Cassini spacecraft, we estimate collision frequencies of about 6 collisions per particle per orbit in the propeller gap region and about 11 collisions per particle per orbit in the propeller wake region. (C) 2015 Elsevier Inc. All rights reserved. KW - Planetary rings KW - Saturn, rings KW - Saturn, satellites KW - Disks Y1 - 2015 U6 - https://doi.org/10.1016/j.icarus.2015.02.003 SN - 0019-1035 SN - 1090-2643 VL - 252 SP - 400 EP - 414 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Guimaraes, Ana H. F. A1 - Albers, Nicole A1 - Spahn, Frank A1 - Seiss, Martin A1 - Vieira-Neto, Ernesto A1 - Brilliantov, Nikolai V. T1 - Aggregates in the strength and gravity regime Particles sizes in Saturn's rings JF - Icarus : international journal of solar system studies N2 - Particles in Saturn's main rings range in size from dust to kilometer-sized objects. Their size distribution is thought to be a result of competing accretion and fragmentation processes. While growth is naturally limited in tidal environments, frequent collisions among these objects may contribute to both accretion and fragmentation. As ring particles are primarily made of water ice attractive surface forces like adhesion could significantly influence these processes, finally determining the resulting size distribution. Here, we derive analytic expressions for the specific self-energy Q and related specific break-up energy Q(star) of aggregates. These expressions can be used for any aggregate type composed of monomeric constituents. We compare these expressions to numerical experiments where we create aggregates of various types including: regular packings like the face-centered cubic (fcc), Ballistic Particle Cluster Aggregates (BPCA), and modified BPCAs including e.g. different constituent size distributions. We show that accounting for attractive surface forces such as adhesion a simple approach is able to: (a) generally account for the size dependence of the specific break-up energy for fragmentation to occur reported in the literature, namely the division into "strength" and "gravity" regimes and (b) estimate the maximum aggregate size in a collisional ensemble to be on the order of a few tens of meters, consistent with the maximum particle size observed in Saturn's rings of about 10 m. KW - Collisional physics KW - Accretion KW - Planetary rings KW - Saturn, Rings Y1 - 2012 U6 - https://doi.org/10.1016/j.icarus.2012.06.005 SN - 0019-1035 SN - 1090-2643 VL - 220 IS - 2 SP - 660 EP - 678 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Dzhanoev, Arsen R. A1 - Spahn, Frank A1 - Yaroshenko, Victoriya A1 - Lühr, Hermann A1 - Schmidt, Jürgen T1 - Secondary electron emission from surfaces with small structure JF - Physical review : B, Condensed matter and materials physics N2 - It is found that for objects possessing small surface structures with differing radii of curvature the secondary electron emission (SEE) yield may be significantly higher than for objects with smooth surfaces of the same material. The effect is highly pronounced for surface structures of nanometer scale, often providing a more than 100% increase of the SEE yield. The results also show that the SEE yield from surfaces with structure does not show a universal dependence on the energy of the primary, incident electrons as it is found for flat surfaces in experiments. We derive conditions for the applicability of the conventional formulation of SEE using the simplifying assumption of universal dependence. Our analysis provides a basis for studying low-energy electron emission from nanometer structured surfaces under a penetrating electron beam important in many technological applications. Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevB.92.125430 SN - 1098-0121 SN - 1550-235X VL - 92 IS - 12 PB - American Physical Society CY - College Park ER - TY - GEN A1 - Spahn, Frank A1 - Seiss, Martin T1 - Charges dropped T2 - Nature physics Y1 - 2015 SN - 1745-2473 SN - 1745-2481 VL - 11 IS - 9 SP - 709 EP - 710 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Brilliantov, Nikolai V. A1 - Krapivsky, P. L. A1 - Bodrova, Anna A1 - Spahn, Frank A1 - Hayakawa, Hisao A1 - Stadnichuk, Vladimir A1 - Schmidt, Jurgen T1 - Size distribution of particles in Saturn's rings from aggregation and fragmentation JF - Proceedings of the National Academy of Sciences of the United States of America N2 - Saturn's rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative interparticle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, similar to r(-q) with q approximate to 3, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent q to be constrained to the interval 2.75 <= q <= 3.5. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of microstructures seen in Saturn's rings. KW - planetary rings KW - kinetic theory KW - coagulation-fragmentation Y1 - 2015 U6 - https://doi.org/10.1073/pnas.1503957112 SN - 0027-8424 VL - 112 IS - 31 SP - 9536 EP - 9541 PB - National Acad. of Sciences CY - Washington ER - TY - JOUR A1 - Postberg, Frank A1 - Grün, Eberhard A1 - Horanyi, Mihaly A1 - Kempf, Sascha A1 - Krueger, Harald A1 - Schmidt, Jürgen A1 - Spahn, Frank A1 - Srama, Ralf A1 - Sternovsky, Zoltan A1 - Trieloff, Mario T1 - Compositional mapping of planetary moons by mass spectrometry of dust ejecta JF - Planetary and space science N2 - Classical methods to analyze the surface composition of atmosphereless planetary objects from an orbiter are IR and gamma ray spectroscopy and neutron backscatter measurements. The idea to analyze surface properties with an in-situ instrument has been proposed by Johnson et al. (1998). There, it was suggested to analyze Europa's thin atmosphere with an ion and neutral gas spectrometer. Since the atmospheric components are released by sputtering of the moon's surface, they provide a link to surface composition. Here we present an improved, complementary method to analyze rocky or icy dust particles as samples of planetary objects from which they were ejected. Such particles, generated by the ambient meteoroid bombardment that erodes the surface, are naturally present on all atmosphereless moons and planets. The planetary bodies are enshrouded in clouds of ballistic dust particles, which are characteristic samples of their surfaces. In situ mass spectroscopic analysis of these dust particles impacting onto a detector of an orbiting spacecraft reveals their composition. Recent instrumental developments and tests allow the chemical characterization of ice and dust particles encountered at speeds as low as 1 km/s and an accurate reconstruction of their trajectories. Depending on the sampling altitude, a dust trajectory sensor can trace back the origin of each analyzed grain with about 10 km accuracy at the surface. Since the detection rates are of the order of thousand per orbit, a spatially resolved mapping of the surface composition can be achieved. Certain bodies (e.g., Europa) with particularly dense dust clouds, could provide impact statistics that allow for compositional mapping even on single flybys. Dust impact velocities are in general sufficiently high at orbiters about planetary objects with a radius > 1000 km and with only a thin or no atmosphere. In this work we focus on the scientific benefit of a dust spectrometer on a spacecraft orbiting Earth's Moon as well as Jupiter's Galilean satellites. This 'dust spectrometer' approach provides key chemical and isotopic constraints for varying provinces or geological formations on the surfaces, leading to better understanding of the body's geological evolution. KW - Moon KW - Europa KW - Ganymede KW - Dust KW - Surface composition KW - Spectrometry Y1 - 2011 U6 - https://doi.org/10.1016/j.pss.2011.05.001 SN - 0032-0633 VL - 59 IS - 14 SP - 1815 EP - 1825 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Meier, Patrick A1 - Kriegel, Hendrik A1 - Motschmann, Uwe A1 - Schmidt, Jürgen A1 - Spahn, Frank A1 - Hill, Thomas W. A1 - Dong, Yaxue A1 - Jones, Geraint H. T1 - A model of the spatial and size distribution of Enceladus' dust plume JF - Planetary and space science KW - Enceladus KW - Plume KW - Nanograins KW - Cassini KW - Tail Y1 - 2014 U6 - https://doi.org/10.1016/j.pss.2014.09.016 SN - 0032-0633 VL - 104 SP - 216 EP - 233 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Arridge, Christopher S. A1 - Achilleos, N. A1 - Agarwal, Jessica A1 - Agnor, C. B. A1 - Ambrosi, R. A1 - Andre, N. A1 - Badman, S. V. A1 - Baines, K. A1 - Banfield, D. A1 - Barthelemy, M. A1 - Bisi, M. M. A1 - Blum, J. A1 - Bocanegra-Bahamon, T. A1 - Bonfond, B. A1 - Bracken, C. A1 - Brandt, P. A1 - Briand, C. A1 - Briois, C. A1 - Brooks, S. A1 - Castillo-Rogez, J. A1 - Cavalie, T. A1 - Christophe, B. A1 - Coates, Andrew J. A1 - Collinson, G. A1 - Cooper, J. F. A1 - Costa-Sitja, M. A1 - Courtin, R. A1 - Daglis, I. A. A1 - De Pater, Imke A1 - Desai, M. A1 - Dirkx, D. A1 - Dougherty, M. K. A1 - Ebert, R. W. A1 - Filacchione, Gianrico A1 - Fletcher, Leigh N. A1 - Fortney, J. A1 - Gerth, I. A1 - Grassi, D. A1 - Grodent, D. A1 - Grün, Eberhard A1 - Gustin, J. A1 - Hedman, M. A1 - Helled, R. A1 - Henri, P. A1 - Hess, Sebastien A1 - Hillier, J. K. A1 - Hofstadter, M. H. A1 - Holme, R. A1 - Horanyi, M. A1 - Hospodarsky, George B. A1 - Hsu, S. A1 - Irwin, P. A1 - Jackman, C. M. A1 - Karatekin, O. A1 - Kempf, Sascha A1 - Khalisi, E. A1 - Konstantinidis, K. A1 - Kruger, H. A1 - Kurth, William S. A1 - Labrianidis, C. A1 - Lainey, V. A1 - Lamy, L. L. A1 - Laneuville, Matthieu A1 - Lucchesi, D. A1 - Luntzer, A. A1 - MacArthur, J. A1 - Maier, A. A1 - Masters, A. A1 - McKenna-Lawlor, S. A1 - Melin, H. A1 - Milillo, A. A1 - Moragas-Klostermeyer, Georg A1 - Morschhauser, Achim A1 - Moses, J. I. A1 - Mousis, O. A1 - Nettelmann, N. A1 - Neubauer, F. M. A1 - Nordheim, T. A1 - Noyelles, B. A1 - Orton, G. S. A1 - Owens, Mathew A1 - Peron, R. A1 - Plainaki, C. A1 - Postberg, F. A1 - Rambaux, N. A1 - Retherford, K. A1 - Reynaud, Serge A1 - Roussos, E. A1 - Russell, C. T. A1 - Rymer, Am. A1 - Sallantin, R. A1 - Sanchez-Lavega, A. A1 - Santolik, O. A1 - Saur, J. A1 - Sayanagi, Km. A1 - Schenk, P. A1 - Schubert, J. A1 - Sergis, N. A1 - Sittler, E. C. A1 - Smith, A. A1 - Spahn, Frank A1 - Srama, Ralf A1 - Stallard, T. A1 - Sterken, V. A1 - Sternovsky, Zoltan A1 - Tiscareno, M. A1 - Tobie, G. A1 - Tosi, F. A1 - Trieloff, M. A1 - Turrini, D. A1 - Turtle, E. P. A1 - Vinatier, S. A1 - Wilson, R. A1 - Zarkat, P. T1 - The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets JF - Planetary and space science N2 - Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun's planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus' atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency's call for science themes for its large-class mission programme in 2013. KW - Uranus KW - Magnetosphere KW - Atmosphere KW - Natural satellites KW - Rings KW - Planetary interior Y1 - 2014 U6 - https://doi.org/10.1016/j.pss.2014.08.009 SN - 0032-0633 VL - 104 SP - 122 EP - 140 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Seiss, Martin A1 - Spahn, Frank T1 - Hydrodynamics of saturn's dense rings JF - Mathematical modelling of natural phenomena N2 - The space missions Voyager and Cassini together with earthbound observations revealed a wealth of structures in Saturn's rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn's moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Furthermore, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn's dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves. KW - granular gas KW - instabilities KW - hydrodynamics KW - planetary rings Y1 - 2011 U6 - https://doi.org/10.1051/mmnp/20116409 SN - 0973-5348 SN - 1760-6101 VL - 6 IS - 4 SP - 191 EP - 218 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Meier, Patrick A1 - Motschmann, Uwe A1 - Schmidt, Jurgen A1 - Spahn, Frank A1 - Hill, Thomas W. A1 - Dong, Yaxue A1 - Jones, Geraint H. A1 - Kriegel, Hendrik T1 - Modeling the total dust production of Enceladus from stochastic charge equilibrium and simulations JF - Planetary and space science KW - Enceladus KW - Plume KW - Nanograin charge KW - CAPS Y1 - 2015 U6 - https://doi.org/10.1016/j.pss.2015.10.002 SN - 0032-0633 VL - 119 SP - 208 EP - 221 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Dzhanoev, Arsen R. A1 - Schmidt, J. A1 - Liu, X. A1 - Spahn, Frank T1 - Charging of small grains in a space plasma: Application to Jovian stream particles JF - International psychogeriatrics N2 - Context. Most theoretical investigations of dust charging processes in space have treated the current balance condition as independent of grain size. However, for small grains, since they are often observed in space environments, a dependence on grain size is expected owing to secondary electron emission (SEE). Here, by the term "small" we mean a particle size comparable to the typical penetration depth for given primary electron energy. The results are relevant for the dynamics of small, charged dust particles emitted by the volcanic moon Io, which forms the Jovian dust streams. Aims. We revise the theory of charging of small (submicron sized) micrometeoroids to take into account a high production of secondary electrons for small grains immersed in an isotropic flux of electrons. We apply our model to obtain an improved estimate for the charge of the dust streams leaving the Jovian system, detected by several spacecraft. Methods. We apply a continuum model to describe the penetration of primary electrons in a grain and the emission of secondary electrons along the path. Averaging over an isotropic flux of primaries, we derive a new expression for the secondary electron yield, which can be used to express the secondary electron current on a grain. Results. For the Jupiter plasma environment we derive the surface potential of grains composed of NaCl (believed to be the major constituent of Jovian dust stream particles) or silicates. For small particles, the potential depends on grain size and the secondary electron current induces a sensitivity to material properties. As a result of the small particle effect, the estimates for the charging times and for the fractional charge fluctuations of NaCl grains obtained using our general approach to SEE give results qualitatively different from the analogous estimates derived from the traditional approach to SEE. We find that for the charging environment considered in this paper field emission does not limit the charging of NaCl grains. KW - plasmas KW - planets and satellites: individual: Jupiter Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527891 SN - 1432-0746 VL - 591 SP - 647 EP - 684 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Liu, Xiaodong A1 - Sachse, Manuel A1 - Spahn, Frank A1 - Schmidt, Jurgen T1 - Dynamics and distribution of Jovian dust ejected from the Galilean satellites JF - Journal of geophysical research, Planets N2 - In this paper, the dynamical analysis of the Jovian dust originating from the four Galilean moons is presented. High-accuracy orbital integrations of dust particles are used to determine their dynamical evolution. A variety of forces are taken into account, including the Lorentz force, solar radiation pressure, Poynting-Robertson drag, solar gravity, the satellites' gravity, plasma drag, and gravitational effects due to nonsphericity of Jupiter. More than 20,000 dust particles from each source moon in the size range from 0.05 μm to 1 cm are simulated over 8000 (Earth) years until each dust grain hits a sink (moons, Jupiter, or escape from the system). Configurations of dust number density in the Jovicentric equatorial inertial frame are calculated and shown. In a Jovicentric frame rotating with the Sun the dust distributions are found to be asymmetric. For certain small particle sizes, the dust population is displaced towards the Sun, while for certain larger sizes, the dust population is displaced away from the Sun. The average lifetime as a function of particle size for ejecta from each source moon is derived, and two sharp jumps in the average lifetime are analyzed. Transport of dust between the Galilean moons and to Jupiter is investigated. Most of the orbits for dust particles from Galilean moons are prograde, while, surprisingly, a small fraction of orbits are found to become retrograde mainly due to solar radiation pressure and Lorentz force. The distribution of orbital elements is also analyzed. Y1 - 2016 U6 - https://doi.org/10.1002/2016JE004999 SN - 2169-9097 SN - 2169-9100 VL - 121 SP - 1141 EP - 1173 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Salo, H. A1 - Schmidt, Jürgen A1 - Spahn, Frank T1 - Viscous overstability in Saturn's B ring : I. Direct simulations and measurements of transport coefficients Y1 - 2001 ER - TY - JOUR A1 - Schmidt, Jürgen A1 - Salo, H. A1 - Spahn, Frank T1 - Viscous overstability in Saturn's B ring : II. Hydrodynamic theory and comparison to simulations Y1 - 2001 ER - TY - JOUR A1 - Spahn, Frank A1 - Petzschmann, Olaf A1 - Schmidt, Jürgen A1 - Sremcevic, Miodrag A1 - Hertzsch, Jan-Martin T1 - About the viscosity of granular gases : the force-free case versus granular gases under Keplarian differential rotation Y1 - 2001 SN - 3-540-41458-4 ER - TY - JOUR A1 - Spahn, Frank A1 - Schmidt, Jürgen A1 - Petzschmann, Olaf A1 - Salo, H. T1 - Stability analysis of a Keplarian disk of granular grains : influence of thermal diffusion Y1 - 2000 ER - TY - JOUR A1 - Thiessenhusen, Kai-Uwe A1 - Krueger, Harald A1 - Spahn, Frank A1 - Grün, Eberhard T1 - Large dust grains around Jupiter : the observations of the Galileo dust detector Y1 - 2000 ER - TY - JOUR A1 - Spahn, Frank A1 - Sremcevic, Miodrag T1 - Density Patterns induced by small Moonlets in Saturn's Rings? Y1 - 2000 ER - TY - JOUR A1 - Spahn, Frank A1 - Schmidt, Jürgen A1 - Sremcevic, Miodrag T1 - Structures in planetary rings : stability and gravitational scattering Y1 - 2000 SN - 3-540-41074-0 ER - TY - JOUR A1 - Salo, H. A1 - Petzschmann, Olaf A1 - Spahn, Frank A1 - Schmidt, Jürgen T1 - Vertical distribution of temperature and density in a planetary ring Y1 - 1999 ER - TY - JOUR A1 - Thiessenhusen, Kai-Uwe A1 - Colwell, Josh E. A1 - Srama, Ralf A1 - Grün, Eberhard A1 - Spahn, Frank T1 - Dynamics of dust ejected from enceladus : application to the cassini dust detector Y1 - 1999 ER - TY - JOUR A1 - Schwarz, Udo A1 - Spahn, Frank A1 - Grebogi, Celso A1 - Kurths, Jürgen A1 - Petzschmann, Olaf T1 - Length scales of clustering in granular gases Y1 - 1999 ER - TY - JOUR A1 - Seiler, Martin A1 - Sremcevic, Miodrag A1 - Seiss, Martin A1 - Hoffmann, Holger A1 - Spahn, Frank T1 - A Librational Model for the Propeller Bleriot in the Saturnian Ring System JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters KW - planets and satellites: individual (Saturn) KW - planets and satellites: rings Y1 - 2017 U6 - https://doi.org/10.3847/2041-8213/aa6d73 SN - 2041-8205 SN - 2041-8213 VL - 840 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Srama, Ralf A1 - Kempf, S. A1 - Moragas-Klostermeyer, Georg A1 - Helfert, S. A1 - Ahrens, T. J. A1 - Altobelli, N. A1 - Auer, S. A1 - Beckmann, U. A1 - Bradley, J. G. A1 - Burton, M. A1 - Dikarev, V. V. A1 - Economou, T. A1 - Fechtig, H. A1 - Green, S. F. A1 - Grande, M. A1 - Havnes, O. A1 - Hillierf, J.K. A1 - Horanyii, M. A1 - Igenbergsj, E. A1 - Jessberger, E. K. A1 - Johnson, T. V. A1 - Krüger, H. A1 - Matt, G. A1 - McBride, N. A1 - Mocker, A. A1 - Lamy, P. A1 - Linkert, D. A1 - Linkert, G. A1 - Lura, F. A1 - McDonnell, J.A.M. A1 - Möhlmann, D. A1 - Morfill, G. E. A1 - Postberg, F. A1 - Roy, M. A1 - Schwehm, G.H. A1 - Spahn, Frank A1 - Svestka, J. A1 - Tschernjawski, V. A1 - Tuzzolino, A. J. A1 - Wäsch, R. A1 - Grün, E. T1 - In situ dust measurements in the inner Saturnian system JF - Planetary and space science N2 - 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 can reach values of 0.001m-3. KW - Cassini KW - dust KW - CDA KW - E-ring KW - water ice Y1 - 2006 U6 - https://doi.org/10.1016/j.pss.2006.05.021 SN - 0032-0633 VL - 54 IS - 9-10 SP - 967 EP - 987 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Kurths, Jürgen A1 - Seehafer, Norbert A1 - Spahn, Frank T1 - Nichtlineare Dynamik in der Physik : Forschungsbeispiele und Forschungstrends Y1 - 1999 UR - http://www.phil.uni-augsburg.de/dgksnd SN - 3-540-65329- 5 ER - TY - JOUR A1 - Otto, Katharina Alexandra A1 - Jaumann, R. A1 - Krohn, K. A1 - Spahn, Frank A1 - Raymond, C. A. A1 - Russell, C. T. T1 - The Coriolis effect on mass wasting during the Rheasilvia impact on asteroid Vesta JF - Geophysical research letters N2 - We investigate the influence of the Coriolis force on mass motion related to the Rheasilvia impact on asteroid Vesta. Observations by the NASA Dawn mission revealed a pattern of curved radial ridges, which are related to Coriolis-deflected mass-wasting during the initial modification stage of the crater. Utilizing the projected curvature of the mass-wasting trajectories, we developed a method that enabled investigation of the initial mass wasting of the Rheasilvia impact by observational means. We demonstrate that the Coriolis force can strongly affect the crater formation processes on rapidly rotating objects, and we derive the material's velocities (28.9 ± 22.5 m/s), viscosities (1.5–9.0 × 106 Pa s) and coefficients of friction (0.02–0.81) during the impact modification stage. The duration of the impact modification stage could be estimated to (1.1 ± 0.5) h. By analyzing the velocity distribution with respect to the topography, we deduce that the Rheasilvia impactor hit a heterogeneous target and that the initial crater walls were significantly steeper during the modification stage. Y1 - 2016 U6 - https://doi.org/10.1002/2016GL071539 SN - 0094-8276 SN - 1944-8007 VL - 43 SP - 12340 EP - 12347 PB - American Geophysical Union CY - Washington ER - TY - GEN A1 - Seiß, Martin A1 - Spahn, Frank T1 - Hydrodynamics of Saturn’s dense rings T2 - Postprints der Universität Potsdam : Postprint Mathematisch Naturwissenschaftliche Reihe N2 - The space missions Voyager and Cassini together with earthbound observations re-vealed a wealth of structures in Saturn’s rings. There are, for example, waves being excited at ring positions which are in orbital resonance with Saturn’s moons. Other structures can be assigned to embedded moons like empty gaps, moon induced wakes or S-shaped propeller features. Further-more, irregular radial structures are observed in the range from 10 meters until kilometers. Here some of these structures will be discussed in the frame of hydrodynamical modeling of Saturn’s dense rings. For this purpose we will characterize the physical properties of the ring particle ensemble by mean field quantities and point to the special behavior of the transport coefficients. We show that unperturbed rings can become unstable and how diffusion acts in the rings. Additionally, the alternative streamline formalism is introduced to describe perturbed regions of dense rings with applications to the wake damping and the dispersion relation of the density waves. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 574 KW - granular gas KW - instabilities KW - hydrodynamics KW - planetary rings Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413139 SP - 191 EP - 218 ER - TY - JOUR A1 - Shepelyansky, Dima L. A1 - Pikovskij, Arkadij A1 - Schmidt, Jürgen A1 - Spahn, Frank T1 - Synchronization mechanism of sharp edges in rings of Saturn N2 - We propose a new mechanism which explains the existence of enormously sharp edges in the rings of Saturn. This mechanism is based on the synchronization phenomenon due to which the epicycle rotational phases of particles in the ring, under certain conditions, become synchronized with the phase of external satellite, e. g. with the phase of Mimas in the case of the outer B ring edge. This synchronization eliminates collisions between particles and suppresses the diffusion induced by collisions by orders of magnitude. The minimum of the diffusion is reached at the centre of the synchronization regime corresponding to the ratio 2:1 between the orbital frequency at the edge of B ring and the orbital frequency of Mimas. The synchronization theory gives the sharpness of the edge in a few tens of meters that is in agreement with available observations. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0035-8711 U6 - https://doi.org/10.1111/j.1365-2966.2009.14719.x SN - 0035-8711 ER -