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Universität Potsdam
Institut für Physik und Astronomie
Innenhof des Physikgebäudes bei Nacht
Bild: David Gruner

Institut / Details zur Veranstaltung

05.07.: Kolloquium des Instituts: Prof. Larry Esposito (Univ. Colorado/LASP), Non-Linear Dynamics of Saturn's Rings

They are systems of granular material: where particle-to-particle collisions dominate; thus a kinetic, not a fluid description is needed. Stresses are strikingly inhomogeneous and fluctuations are large compared to equilibrium. 1) They are strongly forced by resonances: which drive a non-linear response, and push the system across thresholds that lead to persistent states. 2) Periodic forcing from the moon causes streamline crowding, downstream from the forcing and outside of the resonance; Collisions damp the relative velocity. About a quarter phase later, the aggregates stir the system to higher relative velocity and the limit cycle repeats each orbit, with relative velocity ranging from nearly zero to a multiple of the orbit average. Aggregates that form are thus out of phase with the moon forcing. These can tear apart the ring material downstream. Solitary Waves: Created when Janus moves inward every 8 years, they move through the density waves. Maintaining their morphology requires a dispersion relation that depends on amplitude. Ring Structure: Gaps explain the azimuthal brightness variations, indicating 'self-gravity wakes'. These are found between the strong density wave crests. Rapid growth implies Disk Instability. Binary accretion and sweep up is too slow to create the structures seen in occultation statistics and blotchy structure that have time scales of an orbital period. F ring kittens: Show a broken power-law size distribution, and are found preferentially opposite the shepherd moons.
Raum 0.108, Haus 28 (Institut fuer Physik)
16:15 Uhr
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