CARE AND FEEDING OF FROGS
Open accessAbstract
"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, "Blériot," appear consistent with a sinusoid of period ∼4 years. Pan & 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 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 delay exceeds the frog libration period P lib , and if damping from Lindblad torques balances driving from co-orbital torques. If t delay ≪ P lib , then the libration amplitude damps to zero. In the case of Blériot, the frog resonance model can reproduce the observed libration period P lib ≃ 4 yr. However, our simple feedback prescription suggests that Blériot's t delay ∼ 0.01 P 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.
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The observed non-Keplerian radial motions of propeller moonlets may result from interactions between moonlets and stochastic density fluctuations in the disk or between moonlets and ring particles on loosely bound frog orbits.
“These motions may result from interactions between moonlets and stochastic density fluctuations in the disk (Crida et al. 2010;Rein & Papaloizou 2010;Pan et al. 2012) or between moonlets and ring particles on loosely bound”
From MIGRATION OF SMALL MOONS IN SATURN's RINGS (2013) · cites this paper as Pan et al. 2012
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Cites
The Dynamics of Planetary Rings
Goldreich, P., & Tremaine, S. D. (1982) · Annual Review of Astronomy and Astrophysics · doi:10.1146/annurev.aa.20.090182.001341 · Cited by 393 · see citing works
Ring Particle Composition and Size Distribution
Cuzzi, J., Clark, R., Filacchione, G., French, R., Johnson, R. E., Marouf, E., & Spilker, L. (2009) · Springer eBooks · doi:10.1007/978-1-4020-9217-6_15 · Cited by 124 · see citing works
The Structure of Saturn's Rings
Colwell, J. E., Nicholson, P. D., Tiscareno, M. S., Murray, C. D., French, R. G., & Marouf, E. A. (2009) · Springer eBooks · doi:10.1007/978-1-4020-9217-6_13 · Cited by 114 · see citing works
100-metre-diameter moonlets in Saturn's A ring from observations of 'propeller' structures
Tiscareno, M., Burns, J., Hedman, M., Porco, C., Weiss, J. W., Dones, L., Richardson, D., & Murray, C. (2006) · Nature · doi:10.1038/nature04581 · Cited by 105 · see citing works
A belt of moonlets in Saturn’s A ring
Srem̌cevíc, M., Schmidt, J., Salo, H., Seiß, M., Spahn, F., & Albers, N. (2007) · Nature · doi:10.1038/nature06224 · Cited by 76 · see citing works
THE POPULATION OF PROPELLERS IN SATURN'S A RING
Tiscareno, M. S., Burns, J. A., Hedman, M. M., & C. Porco, C. (2008) · The Astronomical Journal · doi:10.1088/0004-6256/135/3/1083 · Cited by 73 · see citing works
Tiscareno, M. S., Burns, J. A., Sremčević, M., Beurle, K., Hedman, M. M., Cooper, N. J., Milano, A. J., Evans, M. W., Porco, C. C., Spitale, J. N., et al. (2010) · The Astrophysical Journal · doi:10.1088/2041-8205/718/2/l92 · Cited by 71 · see citing works
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MIGRATION OF A MOONLET IN A RING OF SOLID PARTICLES: THEORY AND APPLICATION TO SATURN'S PROPELLERS
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Research works printed but not linked: 2
- Colwell, J. E., Nicholson, P. D., Tiscareno, M. S., et al. 2009, in Saturn from Cassini-Huygens, ed. M. Dougherty, L. Esposito, & T. Krimigis (Heidelberg: Springer), 375
- Cuzzi, J., Clark, R., Filacchione, G., et al. 2009, in Saturn from Cassini-Huygens, ed. M. K. Dougherty, L. W. Esposito, & S. M. Krimigis (Heidelberg: Springer), 459
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MIGRATION OF SMALL MOONS IN SATURN's RINGS
Bromley, B. C., & Kenyon, S. J. (2013) · The Astrophysical Journal · doi:10.1088/0004-637x/764/2/192 · Cited by 29 · see citing works
- Authors
- Pan, M., & Chiang, E.
- Affiliations
- University of California, Berkeley (US)
- Corresponding author
- Pan, Margaret
- ORCID
- Chiang, Eugene
- Venue
- The Astronomical Journal
- Publisher
- American Astronomical Society
- Published
- 2011-12-08
- Volume
- 143
- Issue
- 1
- Pages
- 9
- ISSN
- 0004-6256 (ISSN-L)
- 1538-3881
- OpenAlex
- W2002945171
- Cited by
- 31
- References
- 13
- Citations by year
- 2019: 1 · 2018: 21 · 2017: 1 · 2013: 2 · 2012: 3
- FWCI
- 1.36
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- The Astronomical Journal (publishedVersion)
- arXiv (Cornell University) (submittedVersion)
- arXiv (Cornell University)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
- Physical Sciences › Engineering › Aerospace Engineering › Space Satellite Systems and Control
- Keywords
- ring gaps, Lindblad torque, type I migration, restricted three-body problem
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