TY - JOUR A1 - Ye, Shengyi A1 - Kurth, William S. A1 - Hospodarsky, George B. A1 - Persoon, Ann M. A1 - Sulaiman, Ali H. A1 - Gurnett, Don A. A1 - Morooka, Michiko A1 - Wahlund, Jan-Erik A1 - Hsu, Hsiang-Wen A1 - Sternovsky, Zoltan A1 - Wang, Xu A1 - Horanyi, M. A1 - Seiss, Martin A1 - Srama, Ralf T1 - Dust Observations by the Radio and Plasma Wave Science Instrument During JF - Geophysical research letters N2 - Plain Language Summary Cassini flew through the gap between Saturn and its rings for 22 times before plunging into the atmosphere of Saturn, ending its 20-year mission. The radio and plasma waves instrument on board Cassini helped quantify the dust hazard in this previously unexplored region. The measured density of large dust particles was much lower than expected, allowing high-value science observations during the subsequent Grand Finale orbits. Y1 - 2018 U6 - https://doi.org/10.1029/2018GL078059 SN - 0094-8276 SN - 1944-8007 VL - 45 IS - 19 SP - 10101 EP - 10109 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Ye, S. -Y. A1 - Kurth, William S. A1 - Hospodarsky, George B. A1 - Persoon, Ann M. A1 - Gurnett, Don A. A1 - Morooka, Michiko A1 - Wahlund, Jan-Erik A1 - Hsu, Hsiang-Wen A1 - Seiss, Martin A1 - Srama, Ralf T1 - Cassini RPWS dust observation near the Janus/Epimetheus orbit JF - Journal of geophysical research : Space physics N2 - During the Ring Grazing orbits near the end of Cassini mission, the spacecraft crossed the equatorial plane near the orbit of Janus/Epimetheus (similar to 2.5 Rs). This region is populated with dust particles that can be detected by the Radio and Plasma Wave Science (RPWS) instrument via an electric field antenna signal. Analysis of the voltage waveforms recorded on the RPWS antennas provides estimations of the density and size distribution of the dust particles. Measured RPWS profiles, fitted with Lorentzian functions, are shown to be mostly consistent with the Cosmic Dust Analyzer, the dedicated dust instrument on board Cassini. The thickness of the dusty ring varies between 600 and 1,000 km. The peak location shifts north and south within 100 km of the ring plane, likely a function of the precession phase of Janus orbit. KW - Saturn KW - dust KW - ring Y1 - 2018 U6 - https://doi.org/10.1029/2017JA025112 SN - 2169-9380 SN - 2169-9402 VL - 123 IS - 6 SP - 4952 EP - 4960 PB - American Geophysical Union CY - Washington 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 - 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 - 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 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 - 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 - 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 - 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 -