@article{SeissAlbersSremčevićetal.2019,
  author    = {Seiß, Martin and Albers, Nicole and Sremčević, Miodrag and Schmidt, J{\"u}rgen and Salo, Heikki and Seiler, Michael and Hoffmann, Holger and Spahn, Frank},
  title     = {Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn's Rings},
  series = {The astronomical journal},
  volume    = {157},
  journal   = {The astronomical journal},
  number    = {1},
  publisher = {IOP Publishing Ltd.},
  address   = {Bristol},
  issn      = {0004-6256},
  doi       = {10.3847/1538-3881/aaed44},
  pages     = {11},
  year      = {2019},
  abstract  = {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 Bl{\´e}riot, 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 Bl{\´e}riot. 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.},
  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}
}
@article{SeilerSeissHoffmannetal.2019,
  author    = {Seiler, Michael and Seiß, Martin and Hoffmann, Holger and Spahn, Frank},
  title     = {Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn's Rings},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series},
  volume    = {243},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series},
  number    = {2},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {0067-0049},
  doi       = {10.3847/1538-4365/ab26b0},
  pages     = {16},
  year      = {2019},
  abstract  = {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 Bl{\´e}riot, which is expected to be of a similar size. For Bl{\´e}riot, 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 Bl{\´e}riot, 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.},
  language  = {en}
}