TY - JOUR A1 - Seiler, Michael A1 - Seiß, Martin A1 - Hoffmann, Holger A1 - Spahn, Frank T1 - Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn's Rings JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series N2 - 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 Blériot, which is expected to be of a similar size. For Blériot, 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 Blériot, 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. KW - Hydrodynamics KW - methods: data analysis KW - methods: numerical KW - planets and satellites: dynamical evolution and stability KW - planets and satellites: individual (Saturn) KW - planets and satellites: rings Y1 - 2019 U6 - https://doi.org/10.3847/1538-4365/ab26b0 SN - 0067-0049 SN - 1538-4365 VL - 243 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Seiß, Martin A1 - Albers, Nicole A1 - Sremčević, Miodrag A1 - Schmidt, Jürgen A1 - Salo, Heikki A1 - Seiler, Michael A1 - Hoffmann, Holger A1 - Spahn, Frank T1 - Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn's Rings BT - Application to Bleriot JF - The astronomical journal N2 - 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 Blériot, 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 Blériot. 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. KW - diffusion KW - hydrodynamics KW - planets and satellites: rings Y1 - 2018 U6 - https://doi.org/10.3847/1538-3881/aaed44 SN - 0004-6256 SN - 1538-3881 VL - 157 IS - 1 PB - IOP Publishing Ltd. CY - Bristol ER -