TY - JOUR A1 - Sachse, Manuel T1 - A planetary dust ring generated by impact-ejection from the Galilean satellites JF - Icarus : international journal of solar system studies N2 - All outer planets in the Solar System are surrounded by a ring system. Many of these rings are dust rings or they contain at least a high proportion of dust. They are often formed by impacts of micro-meteoroids onto embedded bodies. The ejected material typically consists of micron-sized charged particles, which are susceptible to gravitational and non-gravitational forces. Generally, detailed information on the dynamics and distribution of the dust requires expensive numerical simulations of a large number of particles. Here we develop a relatively simple and fast, semi-analytical model for an impact-generated planetary dust ring governed by the planet’s gravity and the relevant perturbation forces for the dynamics of small charged particles. The most important parameter of the model is the dust production rate, which is a linear factor in the calculation of the dust densities. We apply our model to dust ejected from the Galilean satellites using production rates obtained from flybys of the dust sources. The dust densities predicted by our model are in good agreement with numerical simulations and with in situ measurements by the Galileo spacecraft. The lifetimes of large particles are about two orders of magnitude greater than those of small ones, which implies a flattening of the size distribution in circumplanetary space. Information about the distribution of circumplanetary dust is also important for the risk assessment of spacecraft orbits in the respective regions. Y1 - 0207 U6 - https://doi.org/10.1016/j.icarus.2017.10.011 SN - 0019-1035 SN - 1090-2643 VL - 303 SP - 166 EP - 180 PB - Elsevier CY - San Diego 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 - 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 - THES A1 - Sachse, Manuel T1 - Dynamics and distribution of dust ejected from the Galilean moons of Jupiter Y1 - 2017 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 - Kappel, David A1 - Sachse, Manuel A1 - Haack, David A1 - Otto, Katharina A. T1 - Discrete element modeling of boulder and cliff morphologies on comet 67P/Churyumov-Gerasimenko JF - Astronomy and astrophysics : an international weekly journal N2 - Context: Even after the Rosetta mission, some of the mechanical parameters of comet 67P/Churyumov-Gerasimenko's surface material are not yet well constrained. These parameters are needed to improve our understanding of cometary activity or for planning sample return missions. Aims: We study some of the physical processes involved in the formation of selected surface features and investigate the mechanical and geometrical parameters involved. Methods: Applying the discrete element method (DEM) in a low-gravity environment, we numerically simulated the surface layer particle dynamics involved in the formation of selected morphological features. The material considered is a mixture of polydisperse ice and dust spheres with inter-particle forces given by the Hertz contact model, translational friction, rolling friction, cohesion from unsintered contacts, and optionally due to bonds from ice sintering. We determined a working set of parameters that enables the simulations to be reasonably realistic and investigated morphological changes due to modifications thereof. Results: The selected morphological features are reasonably well reproduced using model materials with a tensile strength on the order of 1-10 Pa. Increasing the diameters of the spherical particles decreases the material strength, and increasing the friction leads to a more brittle but somewhat stronger material. High friction is required to make the material sufficiently brittle to match observations, which points to the presence of very rough, even angular particles. Reasonable seismic activity does not suffice to trigger the collapses of cliffs without material heterogeneities or structural defects. Conclusions: DEM modeling can be a powerful tool to investigate mechanical parameters of cometary surface material. However, many uncertainties arise from our limited understanding of particle shapes, spatial configurations, and size distributions, all on multiple length scales. Further numerical work, in situ measurements, and sample return missions are needed to better understand the mechanics of cometary material and cometary activity. KW - comets: general KW - comets: individual: 67P KW - Churyumov-Gerasimenko KW - methods: numerical Y1 - 2020 U6 - https://doi.org/10.1051/0004-6361/201937152 SN - 0004-6361 SN - 1432-0746 VL - 641 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Sachse, Manuel A1 - Kappel, David A1 - Tirsch, Daniela A1 - Otto, Katharina A. T1 - Discrete element modeling of aeolian-like morphologies on comet 67P/Churyumov-Gerasimenko JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Even after the Rosetta mission, some of the mechanical parameters of comet 67P/Churyumov-Gerasimenko's surface material are still not well constrained. They are needed to improve our understanding of cometary activity or for planning sample return procedures. Aims. We discuss the physical process dominating the formation of aeolian-like surface features in the form of moats and wind taillike bedforms around obstacles and investigate the mechanical and geometrical parameters involved. Methods. By applying the discrete element method (DEM) in a low-gravity environment, we numerically simulated the dynamics of the surface layer particles and the particle stream involved in the formation of aeolian-like morphological features. The material is composed of polydisperse spherical particles that consist of a mixture of dust and water ice, with interparticle forces given by the Hertz contact model, cohesion, friction, and rolling friction. We determined a working set of parameters that enables simulations to be reasonably realistic and investigated morphological changes when modifying these parameters. Results. The aeolian-like surface features are reasonably well reproduced using model materials with a tensile strength on the order of 0.1-1 Pa. Stronger materials and obstacles with round shapes impede the formation of a moat and a wind tail. The integrated dust flux required for the formation of moats and wind tails is on the order of 100 kg m(-2), which, based on the timescale of morphological changes inferred from Rosetta images, translates to a near-surface particle density on the order of 10(-6)-10(-4) kg m(-3). Conclusions. DEM modeling of the aeolian-like surface features reveals complex formation mechanisms that involve both deposition of ejected material and surface erosion. More numerical work and additional in situ measurements or sample return missions are needed to better investigate mechanical parameters of cometary surface material and to understand the mechanics of cometary activity. KW - comets: general KW - comets: individual: 67P/Churyumov-Gerasimenko KW - methods: numerical Y1 - 2022 U6 - https://doi.org/10.1051/0004-6361/202141296 SN - 0004-6361 SN - 1432-0746 VL - 662 PB - EDP Sciences CY - Les Ulis ER -