Libration and migration of propeller moons in Saturns dense rings

• Applicant: Professor Frank Spahn, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 252107923

• Final Report Year: 2020

Final Report Abstract

Our prediction of propeller-structures – caused by “sky-scraper”-sized moonlets embedded in Saturn’s dense rings – has been confirmed by detections of the Cassini-mission. The largest of those moonlet-propellers have been rediscovered in a series subsequent images over more than a decade, in this way tracking their orbits. Surprisingly, it has been found that the moonlets perform a considerable deviation from their expected Keplerian motion, called excess motion! There have been two approaches in order to explain this deviation: (i) a moonlet-ring interaction (physical- or gravitational collisions), (ii) resonant excitations by the gravity of outer satellites. Here, we have been able to show that both ingredients are needed to describe the excess motion of, for instance, the moonlet Blériot: While the external gravitational-resonant excitations by outer moons [(ii)] set the observed frequencies, the moonlet-ring interaction [(i)] constitutes an oscillator where a few modes are amplified by resonances with the outer gravitational driving! As a result of our studies, our modeling has been able to explain fairly well the frequencies and amplitudes of the excess motion of the moonlet Blériot.

Publications

• (2012), Librating Propeller Moonlets in Saturn’s A-Ring, European Planetary Science Congress / Madrid, Spain
  M. Seiler, M. Seiß, and F. Spahn
  
• (2016), Simulating the librational behaviour of propeller moons in Saturn’s rings, AAS, Division Planetary Sciences (DPS) / JPL-Pasadena, U.S.A.
  M. Seiler, M. Seiß, H. Hoffmann, and F. Spahn
  
• (2017), A Librational Model for the Propeller Bl´ riot in the Saturnian Ring System, Astrophys. J. Lett., 840
  M. Seiler, M. Sremčević, M. Seiß, H. Hoffmann, and F. Spahn
  
• (2017), Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn’s Rings: Application to Blériot, Astron. J., 252
  M. Seiß, N. Albers, M. Sremčević, J. Schmidt, H. Salo, M. Seiler, H. Hoffmann, and F. Spahn
  
• (2017), Studies of asymmetric propeller structures in Saturn’s rings, European Planetary Science Congress / Riga, Latvia
  M. Seiler, M. Seiß, and F. Spahn
  
• (2018), Hydrodynamic Simulations of Asymmetric Propeller Structures in the Saturnian Ring System, European Planetary Science Congress / Berlin, Germany
  M. Seiler, M. Seiß, H. Hoffmann, and F. Spahn
  
• (2019), Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn’s Rings, Astrophys. J. Supp. Series, 243,
  M. Seiler, M. Seiß, H. Hoffmann, and F. Spahn
  
• (2019), The non-Keplerian motion of propeller-moons in the Saturnian ring system., PhD-thesis
  M. Seiler