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Saturn’s Rings
• Axis tilted 27° • Orbits 9.5AU from
sun in 29.5 years • Ears to Galileo
1609, explained by Huygens 1659
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Saturn’s Rings • Can not be gas, liquid, solid rings Maxwell 1859 • Billions of particles icy boulders- snow; 95% H2O • Stars seen thru rings
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Rings Have Structure • A ring separated from B ring by Cassini division • Cassini division opened by 2:1 resonance of ring
particle in gap with Saturn’s moon, Mimas
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Ringlets • Ring particles orbit Saturn, but where their period
resonates with a moon, they are disturbed • A-ring composed of thousands of very fine ringlets • Enke gap caused by moonlet=Pan sweeps material
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Shepherd Satellites • Over time the rings particles should collide and spread out • But ring particles closer to Saturn orbit faster so • Shepherd Satellites confine the narrow F-ring and others?
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Formation of Rings? • Sum all ring particles=small moon. Bright, White, 95%H2O • Rings formed from moon breakup ~50Million years ? • Or clumps which form & then break apart ~4Billion yrs.
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Roche Limit • Tidal force exceeds self-gravitational force • Small moons & spaceships can survive
inside Roche limit because they’re held together by electromagnetic force not gravity
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Saturn’s Moons • From right to left: Titan’s shadow,
Titan, Mimas, Dione & Enceladas
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More of Saturn’s Moons • Dione: ice cliffs & Tethys: craters & faults • Many are captured KBO’s?, asteroids?, formed with Saturn? • Sometimes 2 or 3 moons in one orbit???
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Lagrangian Points • Restricted 3-body problem solved: Lagrange 1772 • Gravitational forces balance at L1 • Add rotation=centrifugal force and get L2,L3,L4,L5 • L1,L2,L3 unstable but handy for satellites • L4&L5 stable–Tethys + Telesto@L4 and Calypso@L5
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Medium Sized: Iapetus • Leading hemisphere is dark and the
trailing hemisphere is white • Maybe from dust kicked off Phobe by
micrometeorites • Big equatorial ridge and scarp
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Small Moon:Methone (me-thoh-nee) • Discovered by Cassini
2004 & Orbit=24 hour • 3km diameter moon • Has no craters!?!?!? • Denisity=0.3gm/cc • Rubble pile or Fluff?? • Slight color markings
on surface
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Hyperion • 370km diameter • Very low density 0.5gm/cm3:
caves ~sponge • Rotates chaotically
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Enceladus • 90% albedo =snow • Embedded in the E ring • Orbital resonance with
Dione gives tidal heating • Tiger Stripes – are warm
as seen in Infrared • Lack of craters: resurfaced
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Enceladus - Volcanoes
• Water vapor ejected from warm ocean
• Geysers more active when far from Saturn
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Titan- Atmosphere • Temp94K, Density1.9Xwater, Pressure 1.5Earths • Atmosphere 98%nitrogen,1.6% methane • Totally obscured by clouds of smog. Methane rain • Cassini launched1997; arrived 2004; Huygens probe 2005 • Core decoupled by ocean
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Titan- Surface • Radar observations show liquid
methane/ethane ocean/lake & streams • Ground has consistency of mud • Ice rocks show signs of weathering
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Titan-RADAR • Dunes on Earth & Titan’s huge
dunes of hydrocarbon chemicals • Only body other than Earth with
liquid on surface • Crater on Titan • Cryovolcano
Doom Mons
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Magic Island
• 20 km Island? Not visible and then appears
• Bubbles?, waves? Something floating????
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Upcoming Missions 2020-2029 • Missions to Europa-Jupiter? and/or/nor • Enceladus-Titan-Saturn ?
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Every 15 years Saturn’s rings seem to disappear because:
a) They move within the Roche limit & are torn apart b) Orbital resonance with Saturn’s moons causes the
ringlets to grow so large they cover the ring c) Earth crosses the ring plane & we see them edge on d) The spokes become so large that the rings are in
shadow e) The Cassini division divides the shepherd satellites
dispersing the rings
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Spokes in Saturn’s Ring • Linear features rotating with magnetic field • Discovered by Voyager and initially not seen by Cassini • Probably micrometeorites hit ring particles making dust
which cast shadows??
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Cryovolcano
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Medium Sized :Dione • Why does Dione have its trailing hemisphere more
cratered than the leading one??