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Age and Evolution of Saturn’s Rings

Age and Evolution of Saturn’s Rings. Larry W. Esposito, Bonnie K. Meinke, Nicole Albers and Miodrag Sremcevic LASP Third Moscow Symposium 11 October 2012. Key Cassini Observations.

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Age and Evolution of Saturn’s Rings

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  1. Age and Evolution of Saturn’s Rings Larry W. Esposito, Bonnie K. Meinke, Nicole Albers and Miodrag Sremcevic LASP Third Moscow Symposium 11 October 2012

  2. Key Cassini Observations • High resolution images of propellers, straw, embedded moons, F ring objects. These show aggregation in the rings! • Occ’s confirm structure, self-gravity wakes, B ring propellers, ghosts. More evidence for aggregates. • Equinox images: embedded objects • Key question: Are Saturn’s rings young or old?

  3. Sub-km structure seen in wavelet analysis varies with longitude • Wavelet analysis from multiple UVIS occultations is co-added to give a significance estimate • For the B ring edge, the significance of features with sizes 200-2000m shows maxima at 90 and 270 degrees ahead of Mimas. Same distance where objects are seen in the images!

  4. We identify this structure as temporary clumps

  5. Edges also show structure • Some of this can be explained by multiple modes • Other sharp features appear stochastic, likely caused by local aggregates

  6. From Albers etal 2012

  7. F ring Observations • 27 significant features in F ring: ‘Kittens’ from 22m to 3.7km, likely they are elongated and transient • They have weak correlation to Prometheus, may evolve into moonlets

  8. New Features

  9. I Gatti di Roma: temporary features in an ancient structure

  10. We identify our ‘kittens’ as transient clumps

  11. Prometheus excites F ring structures

  12. Buerleetal 2010: Bright spots cast shadows.

  13. Predator-Prey Equations for Ring Clumping M= ∫ n(m) m2 dm / <M>; Vrel2= ∫ n(m) Vrel2dm / N dM/dt= M/Tacc – Vrel2/vth2 M/Tcoll [accretion] [fragmentation/erosion] dVrel2/dt= -(1-ε2)Vrel2/Tcoll + (M/M0)2 Vesc2/Tstir [dissipation] [gravitational stirring] - A0 cos(ωt) [forcing by streamline crowding]

  14. Predator-Prey model of Moon-triggered Accretion?

  15. Phase plane trajectory V2 M

  16. Rare accretion can renew rings • Solid aggregates are persistent , like the absorbing states in a Markov chain • Even low transition probabilities can populate the states: e.g., 10-9 per collision to an absorbing state • These aggregates can renew the rings: • shield their interiors from meteoritic dust pollution • release pristine material when disrupted by an external impact

  17. Analogy: Coast Redwoods 1 in 104 seeds grows to a tree!

  18. Like Beijing, rings contain both new and ancient structures!

  19. Conclusions • Although rings show youthful features, this may imply renewal instead • Changes since Voyager and abundant embedded objects indicate accretion • A predator-prey model shows how moons can trigger accretion today • Are rings young or old? Yes, maybe both! • Key measurement: Ring mass in 2017.

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