Saturn’s Rings

•  Axis tilted 27° •  Orbits 9.5AU from

sun in 29.5 years •  Ears to Galileo

1609, explained by Huygens 1659

Saturn’s Rings •  Can not be gas, liquid, solid rings Maxwell 1859 •  Billions of particles icy boulders- snow; 95% H2O •  Stars seen thru rings

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

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

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?

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.

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

Saturn’s Moons •  From right to left: Titan’s shadow,

Titan, Mimas, Dione & Enceladas

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???

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

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

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

Hyperion •  370km diameter •  Very low density 0.5gm/cm3:

caves ~sponge •  Rotates chaotically

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

Enceladus - Volcanoes

•  Water vapor ejected from warm ocean

•  Geysers more active when far from Saturn

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

Titan- Surface •  Radar observations show liquid

methane/ethane ocean/lake & streams •  Ground has consistency of mud •  Ice rocks show signs of weathering

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

Magic Island

•  20 km Island? Not visible and then appears

•  Bubbles?, waves? Something floating????

Upcoming Missions 2020-2029 •  Missions to Europa-Jupiter? and/or/nor •  Enceladus-Titan-Saturn ?

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

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??

Cryovolcano

Medium Sized :Dione •  Why does Dione have its trailing hemisphere more

cratered than the leading one??