@article{SeilerSremcevicSeissetal.2017, author = {Seiler, Martin and Sremcevic, Miodrag and Seiss, Martin and Hoffmann, Holger and Spahn, Frank}, title = {A Librational Model for the Propeller Bleriot in the Saturnian Ring System}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {840}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.3847/2041-8213/aa6d73}, pages = {6}, year = {2017}, language = {en} } @article{MakuchBrilliantovSremcevicetal.2006, author = {Makuch, Martin and Brilliantov, Nikolai V. and Sremcevic, Miodrag and Spahn, Frank and Krivov, Alexander V.}, title = {Stochastic circumplanetary dynamics of rotating non-spherical dust particles}, series = {Planetary and space science}, volume = {54}, journal = {Planetary and space science}, number = {9-10}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-0633}, doi = {10.1016/j.pss.2006.05.006}, pages = {855 -- 870}, year = {2006}, abstract = {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.}, language = {en} } @article{SpahnSchmidtAlbersetal.2006, author = {Spahn, Frank and Schmidt, J{\"u}rgen and Albers, Nicole and H{\"o}rning, Marcel and Makuch, Martin and Seiß, Martin and Kempf, Sascha and Srama, Ralf and Dikarev, Valeri and Helfert, Stefan and Moragas-Klostermeyer, Georg and Krivov, Alexander V. and Sremcevic, Miodrag and Tuzzolino, Anthony J. and Economou, Thanasis and Gr{\"u}n, Eberhard}, title = {Cassini dust measurements at Enceladus and implications for the origin of the E ring}, doi = {10.1126/science.1121375}, year = {2006}, language = {en} } @article{KrivovSremcevicSpahn2005, author = {Krivov, Alexander V. and Sremcevic, Miodrag and Spahn, Frank}, title = {Evolution of a Keplerian disk of colliding and fragmenting particles: a kinetic model with application to the Edgeworth-Kuiper belt}, issn = {0019-1035}, year = {2005}, abstract = {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}, language = {en} } @article{SremcevicKrivovKruegeretal.2005, author = {Sremcevic, Miodrag and Krivov, Alexander V. and Kr{\"u}ger, Harald and Spahn, Frank}, title = {Impact-generated dust clouds around planetary satellites : model versus Galileo}, issn = {0032-0633}, year = {2005}, abstract = {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}, language = {en} } @article{SeissSpahnSremcevicetal.2005, author = {Seiss, Martin and Spahn, Frank and Sremcevic, Miodrag and Salo, H.}, title = {Structures induced by small moonlets in Saturn's rings : implications for the Cassini Mission}, issn = {0094-8276}, year = {2005}, abstract = {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}, language = {en} } @article{SpahnAlbersSremcevicetal.2004, author = {Spahn, Frank and Albers, Nicole and Sremcevic, Miodrag and Thornton, C.}, title = {Kinetic description of coagulation and fragmentation in dilute granular particle ensembles}, issn = {0295-5075}, year = {2004}, abstract = {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}, language = {en} } @article{SpahnKrivovSremcevicetal.2003, author = {Spahn, Frank and Krivov, Alexander V. and Sremcevic, Miodrag and Schwarz, U. and Kurths, J{\"u}rgen}, title = {Stochastic forces in circumplanetary dust dynamics}, year = {2003}, abstract = {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.}, language = {en} } @article{SpahnPetzschmannSchmidtetal.2001, author = {Spahn, Frank and Petzschmann, Olaf and Schmidt, J{\"u}rgen and Sremcevic, Miodrag and Hertzsch, Jan-Martin}, title = {About the viscosity of granular gases : the force-free case versus granular gases under Keplarian differential rotation}, isbn = {3-540-41458-4}, year = {2001}, language = {en} } @article{SpahnSremcevic2000, author = {Spahn, Frank and Sremcevic, Miodrag}, title = {Density Patterns induced by small Moonlets in Saturn's Rings?}, year = {2000}, language = {en} }