@article{YeKurthHospodarskyetal.2018, author = {Ye, Shengyi and Kurth, William S. and Hospodarsky, George B. and Persoon, Ann M. and Sulaiman, Ali H. and Gurnett, Don A. and Morooka, Michiko and Wahlund, Jan-Erik and Hsu, Hsiang-Wen and Sternovsky, Zoltan and Wang, Xu and Horanyi, M. and Seiss, Martin and Srama, Ralf}, title = {Dust Observations by the Radio and Plasma Wave Science Instrument During}, series = {Geophysical research letters}, volume = {45}, journal = {Geophysical research letters}, number = {19}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1029/2018GL078059}, pages = {10101 -- 10109}, year = {2018}, abstract = {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.}, language = {en} } @article{YeKurthHospodarskyetal.2018, author = {Ye, S. -Y. and Kurth, William S. and Hospodarsky, George B. and Persoon, Ann M. and Gurnett, Don A. and Morooka, Michiko and Wahlund, Jan-Erik and Hsu, Hsiang-Wen and Seiss, Martin and Srama, Ralf}, title = {Cassini RPWS dust observation near the Janus/Epimetheus orbit}, series = {Journal of geophysical research : Space physics}, volume = {123}, journal = {Journal of geophysical research : Space physics}, number = {6}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1029/2017JA025112}, pages = {4952 -- 4960}, year = {2018}, abstract = {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.}, 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{SeissSpahn2011, author = {Seiss, Martin and Spahn, Frank}, title = {Hydrodynamics of saturn's dense rings}, series = {Mathematical modelling of natural phenomena}, volume = {6}, journal = {Mathematical modelling of natural phenomena}, number = {4}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0973-5348}, doi = {10.1051/mmnp/20116409}, pages = {191 -- 218}, year = {2011}, abstract = {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.}, language = {en} } @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{HsuSchmidtKempfetal.2018, author = {Hsu, Hsiang-Wen and Schmidt, J{\"u}rgen and Kempf, Sascha and Postberg, Frank and Moragas-Klostermeyer, Georg and Seiss, Martin and Hoffmann, Holger and Burton, Marcia and Ye, ShengYi and Kurth, William S. and Horanyi, Mihaly and Khawaja, Nozair and Spahn, Frank and Schirdewahn, Daniel and Moore, Luke and Cuzzi, Jeff and Jones, Geraint H. and Srama, Ralf}, title = {In situ collection of dust grains falling from Saturn's rings into its atmosphere}, series = {Science}, volume = {362}, journal = {Science}, number = {6410}, publisher = {American Assoc. for the Advancement of Science}, address = {Washington}, issn = {0036-8075}, doi = {10.1126/science.aat3185}, pages = {49 -- +}, year = {2018}, abstract = {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.}, language = {en} } @article{HoffmannSeissSaloetal.2015, author = {Hoffmann, Holger and Seiss, Martin and Salo, Heikki and Spahn, Frank}, title = {Vertical structures induced by embedded moonlets in Saturn's rings}, series = {Icarus : international journal of solar system studies}, volume = {252}, journal = {Icarus : international journal of solar system studies}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2015.02.003}, pages = {400 -- 414}, year = {2015}, abstract = {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.}, language = {en} } @article{GuimaraesAlbersSpahnetal.2012, author = {Guimaraes, Ana H. F. and Albers, Nicole and Spahn, Frank and Seiss, Martin and Vieira-Neto, Ernesto and Brilliantov, Nikolai V.}, title = {Aggregates in the strength and gravity regime Particles sizes in Saturn's rings}, series = {Icarus : international journal of solar system studies}, volume = {220}, journal = {Icarus : international journal of solar system studies}, number = {2}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2012.06.005}, pages = {660 -- 678}, year = {2012}, abstract = {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.}, language = {en} } @article{GraetzSeissSpahn2018, author = {Gr{\"a}tz, Fabio M. and Seiss, Martin and Spahn, Frank}, title = {Formation of moon-induced gaps in dense planetary rings}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {862}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/1538-4357/aace00}, pages = {9}, year = {2018}, abstract = {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.}, language = {en} } @article{BurattiThomasRoussosetal.2019, author = {Buratti, Bonnie J. and Thomas, P. C. and Roussos, E. and Howett, Carly and Seiss, Martin and Hendrix, A. R. and Helfenstein, Paul and Brown, R. H. and Clark, R. N. and Denk, Tilmann and Filacchione, Gianrico and Hoffmann, Holger and Jones, Geraint H. and Khawaja, N. and Kollmann, Peter and Krupp, Norbert and Lunine, Jonathan and Momary, T. W. and Paranicas, Christopher and Postberg, Frank and Sachse, Manuel and Spahn, Frank and Spencer, John and Srama, Ralf and Albin, T. and Baines, K. H. and Ciarniello, Mauro and Economou, Thanasis and Hsu, Hsiang-Wen and Kempf, Sascha and Krimigis, Stamatios M. and Mitchell, Donald and Moragas-Klostermeyer, Georg and Nicholson, Philip D. and Porco, C. C. and Rosenberg, Heike and Simolka, Jonas and Soderblom, Laurence A.}, title = {Close Cassini flybys of Saturn's ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus}, series = {Science}, volume = {364}, journal = {Science}, number = {6445}, publisher = {American Assoc. for the Advancement of Science}, address = {Washington}, issn = {0036-8075}, doi = {10.1126/science.aat2349}, pages = {1053}, year = {2019}, abstract = {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.}, language = {en} }