@phdthesis{Seiler2020,
  author    = {Seiler, Michael},
  title     = {The Non-Keplerian Motion of Propeller Moons in the Saturnian Ring System},
  school      = {Universit{\"a}t Potsdam},
  pages     = {127},
  year      = {2020},
  abstract  = {One of the tremendous discoveries by the Cassini spacecraft has been the detection of propeller structures in Saturn's A ring. Although the generating moonlet is too small to be resolved by the cameras aboard Cassini, its produced density structure within the rings, caused by its gravity can be well observed. The largest observed propeller is called Bl{\´e}riot and has an azimuthal extent over several thousand kilometers. Thanks to its large size, Bl{\´e}riot could be identified in different images over a time span of over 10 years, allowing the reconstruction of its orbital evolution. It turns out that Bl{\´e}riot deviates considerably from its expected Keplerian orbit in azimuthal direction by several thousand kilometers. This excess motion can be well reconstructed by a superposition of three harmonics, and therefore resembles the typical fingerprint of a resonantly perturbed body. This PhD thesis is directed to the excess motion of Bl{\´e}riot. Resonant perturbations are a known for some of the outer satellites of Saturn. Thus, in the first part of this thesis, we seek for suiting resonance candidates nearby the propeller, which might explain the observed periods and amplitudes. In numeric simulations, we show that indeed resonances by Prometheus, Pandora and Mimas can explain the libration periods in good agreement, but not the amplitudes. The amplitude problem is solved by the introduction of a propeller-moonlet interaction model, where we assume a broken symmetry of the propeller by a small displacement of the moonlet. This results in a librating motion the moonlet around the propeller's symmetry center due to the non-vanishing accelerations. The retardation of the reaction of the propeller structure to the motion of the moonlet causes the propeller to become asymmetric. Hydrodynamic simulations to test our analytical model confirm our predictions. In the second part of this thesis, we consider a stochastic migration of the moonlet, which is an alternative hypothesis to explain the observed excess motion of Bl{\´e}riot. The mean-longitude is a time-integrated quantity and thus introduces a correlation between the independent kicks of a random walk, smoothing the noise and thus makes the residual look similar to the observed one for Bl{\´e}riot. We apply a diagonalization test to decorrelated the observed residuals for the propellers Bl{\´e}riot and Earhart and the ring-moon Daphnis. It turns out that the decorrelated distributions do not strictly follow the expected Gaussian distribution. The decorrelation method fails to distinguish a correlated random walk from a noisy libration and thus we provide an alternative study. Assuming the three-harmonic fit to be a valid representation of the excess motion for Bl{\´e}riot, independently from its origin, we test the likelihood that this excess motion can be created by a random walk. It turns out that a non-correlated and correlated random walk is unlikely to explain the observed excess motion.},
  language  = {en}
}
@article{ArridgeAchilleosAgarwaletal.2014,
  author    = {Arridge, Christopher S. and Achilleos, N. and Agarwal, Jessica and Agnor, C. B. and Ambrosi, R. and Andre, N. and Badman, S. V. and Baines, K. and Banfield, D. and Barthelemy, M. and Bisi, M. M. and Blum, J. and Bocanegra-Bahamon, T. and Bonfond, B. and Bracken, C. and Brandt, P. and Briand, C. and Briois, C. and Brooks, S. and Castillo-Rogez, J. and Cavalie, T. and Christophe, B. and Coates, Andrew J. and Collinson, G. and Cooper, J. F. and Costa-Sitja, M. and Courtin, R. and Daglis, I. A. and De Pater, Imke and Desai, M. and Dirkx, D. and Dougherty, M. K. and Ebert, R. W. and Filacchione, Gianrico and Fletcher, Leigh N. and Fortney, J. and Gerth, I. and Grassi, D. and Grodent, D. and Gr{\"u}n, Eberhard and Gustin, J. and Hedman, M. and Helled, R. and Henri, P. and Hess, Sebastien and Hillier, J. K. and Hofstadter, M. H. and Holme, R. and Horanyi, M. and Hospodarsky, George B. and Hsu, S. and Irwin, P. and Jackman, C. M. and Karatekin, O. and Kempf, Sascha and Khalisi, E. and Konstantinidis, K. and Kruger, H. and Kurth, William S. and Labrianidis, C. and Lainey, V. and Lamy, L. L. and Laneuville, Matthieu and Lucchesi, D. and Luntzer, A. and MacArthur, J. and Maier, A. and Masters, A. and McKenna-Lawlor, S. and Melin, H. and Milillo, A. and Moragas-Klostermeyer, Georg and Morschhauser, Achim and Moses, J. I. and Mousis, O. and Nettelmann, N. and Neubauer, F. M. and Nordheim, T. and Noyelles, B. and Orton, G. S. and Owens, Mathew and Peron, R. and Plainaki, C. and Postberg, F. and Rambaux, N. and Retherford, K. and Reynaud, Serge and Roussos, E. and Russell, C. T. and Rymer, Am. and Sallantin, R. and Sanchez-Lavega, A. and Santolik, O. and Saur, J. and Sayanagi, Km. and Schenk, P. and Schubert, J. and Sergis, N. and Sittler, E. C. and Smith, A. and Spahn, Frank and Srama, Ralf and Stallard, T. and Sterken, V. and Sternovsky, Zoltan and Tiscareno, M. and Tobie, G. and Tosi, F. and Trieloff, M. and Turrini, D. and Turtle, E. P. and Vinatier, S. and Wilson, R. and Zarkat, P.},
  title     = {The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets},
  series = {Planetary and space science},
  volume    = {104},
  journal   = {Planetary and space science},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0032-0633},
  doi       = {10.1016/j.pss.2014.08.009},
  pages     = {122 -- 140},
  year      = {2014},
  abstract  = {Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99\% of the mass of the Sun's planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus' atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency's call for science themes for its large-class mission programme in 2013.},
  language  = {en}
}