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Title: CARE AND FEEDING OF FROGS

Abstract

'Propellers' are features in Saturn's A ring associated with moonlets that open partial gaps. They exhibit non-Keplerian motion (Tiscareno et al.); the longitude residuals of the best-observed propeller, 'Bleriot', appear consistent with a sinusoid of period {approx}4 years. Pan and Chiang proposed that propeller moonlets librate in 'frog resonances' with co-orbiting ring material. By analogy with the restricted three-body problem, they treated the co-orbital material as stationary in the rotating frame and neglected non-co-orbital material. Here we use simple numerical experiments to extend the frog model, including feedback due to the gap's motion, and drag associated with the Lindblad disk torques that cause Type I migration. Because the moonlet creates the gap, we expect the gap centroid to track the moonlet, but only after a time delay t{sub delay}, the time for a ring particle to travel from conjunction with the moonlet to the end of the gap. We find that frog librations can persist only if t{sub delay} exceeds the frog libration period P{sub lib}, and if damping from Lindblad torques balances driving from co-orbital torques. If t{sub delay} << Pl{sub ib}, then the libration amplitude damps to zero. In the case of Bleriot, the frog resonance model canmore » reproduce the observed libration period P{sub lib} {approx_equal} 4 yr. However, our simple feedback prescription suggests that Bleriot's t{sub delay} {approx} 0.01P{sub lib}, which is inconsistent with the observed libration amplitude of 260 km. We urge more accurate treatments of feedback to test the assumptions of our toy models.« less

Authors:
;  [1]
  1. Department of Astronomy, University of California, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22034314
Resource Type:
Journal Article
Journal Name:
Astronomical Journal (New York, N.Y. Online)
Additional Journal Information:
Journal Volume: 143; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1538-3881
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; ASTRONOMY; ASTROPHYSICS; DAMPING; DRAG; EVOLUTION; FEEDBACK; PARTICLES; RESONANCE; RINGS; SATELLITES; SATURN PLANET; STABILITY; THREE-BODY PROBLEM; TIME DELAY; TORQUE

Citation Formats

Pan, Margaret, and Chiang, Eugene. CARE AND FEEDING OF FROGS. United States: N. p., 2012. Web. doi:10.1088/0004-6256/143/1/9.
Pan, Margaret, & Chiang, Eugene. CARE AND FEEDING OF FROGS. United States. https://doi.org/10.1088/0004-6256/143/1/9
Pan, Margaret, and Chiang, Eugene. 2012. "CARE AND FEEDING OF FROGS". United States. https://doi.org/10.1088/0004-6256/143/1/9.
@article{osti_22034314,
title = {CARE AND FEEDING OF FROGS},
author = {Pan, Margaret and Chiang, Eugene},
abstractNote = {'Propellers' are features in Saturn's A ring associated with moonlets that open partial gaps. They exhibit non-Keplerian motion (Tiscareno et al.); the longitude residuals of the best-observed propeller, 'Bleriot', appear consistent with a sinusoid of period {approx}4 years. Pan and Chiang proposed that propeller moonlets librate in 'frog resonances' with co-orbiting ring material. By analogy with the restricted three-body problem, they treated the co-orbital material as stationary in the rotating frame and neglected non-co-orbital material. Here we use simple numerical experiments to extend the frog model, including feedback due to the gap's motion, and drag associated with the Lindblad disk torques that cause Type I migration. Because the moonlet creates the gap, we expect the gap centroid to track the moonlet, but only after a time delay t{sub delay}, the time for a ring particle to travel from conjunction with the moonlet to the end of the gap. We find that frog librations can persist only if t{sub delay} exceeds the frog libration period P{sub lib}, and if damping from Lindblad torques balances driving from co-orbital torques. If t{sub delay} << Pl{sub ib}, then the libration amplitude damps to zero. In the case of Bleriot, the frog resonance model can reproduce the observed libration period P{sub lib} {approx_equal} 4 yr. However, our simple feedback prescription suggests that Bleriot's t{sub delay} {approx} 0.01P{sub lib}, which is inconsistent with the observed libration amplitude of 260 km. We urge more accurate treatments of feedback to test the assumptions of our toy models.},
doi = {10.1088/0004-6256/143/1/9},
url = {https://www.osti.gov/biblio/22034314}, journal = {Astronomical Journal (New York, N.Y. Online)},
issn = {1538-3881},
number = 1,
volume = 143,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2012},
month = {Sun Jan 15 00:00:00 EST 2012}
}