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Saturn = Cronus • • • • God of Harvest, Agriculture. Saturnday Father of Jupiter, Neptune, Pluto. Son of Uranus and Gaia. Faintest + Farthest of planets visible to naked eye Saturn’s Physical Properties • • • • Mass=59Earths; Diameter 9Earths~Jupiter Density 0.7water; implies lots of gas & little rock Rotation 10h14m to 10h46m –Differential Rotation Oblate Saturn’s Atmosphere • Composed of Hydrogen 92% & Helium 7.4% - missing Helium! • Temperature of 100 Kelvin • Thick methane haze covers/mutes clouds: ammonia, ammonium hydrosulfide, water clouds Spots/Storms on Saturn • IR image: Dragon Storm“ produced lightning & radio static • Super storm wrapped around Saturn by zonal flow faster than Jupiter’s Polar Vortex • Spring in North allows Cassini probe to see North pole surrounded by hexagon • Centered on Pole is hurricane (Vortex) with low clouds in red & high clouds in green (infrared) Internal Energy Source • Radiates 2 times energy it receives from sun • Infrared picture shows hot spot at south pole • Helium precipitation: Helium & Neon “Rain” falling on core releases heat Aurora on Saturn • Magnetic field aligned with rotational axis • Smaller mass means smaller amount of liquid metallic hydrogen so a smaller magnetic field • Saturn’s radio noise in AM band – reflected by ionosphere 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 solid rings Maxwell 1859 • Billions of particles icy boulders-golf ball- dust • Stars seen thru rings Rings Have Structure • A ring separated from B ring by Cassini division • Encke gap part way thru A Ring Ringlets • Ring particles orbit Saturn, but where their period resonates with a moon they are disturbed • Cassini division opened by resonance with Mimas • 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 • Ring particles closer to Saturn orbit faster so • Shepherd Satellites confine the narrow F-ring and others? Spokes in Saturn’s Ring • Linear features rotating with magnetic field • Probably micrometeorites hit ring particles making dust which cast shadows?? Roche Limit • Tidal force exceeds self gravitational force • Moons and spaceships can survive inside Roche limit because they’re held together by electromagnetic not gravitational forces Formation of Rings • Sum ring particles=small moon. And bright/white • Rings formed from moon breakup ~50Million yrs ? • Or clumps which form & then break apart ~4Billion Saturn’s Moons • From right to left: Titan’s shadow, Titan, Mimas, Dione and Enceladas More of Saturn’s Moons • Rhea has white streaks and Mimas has huge crater • Many are captured KBO’s?, asteroids?, formed with Saturn • Some have 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 –dust asteroids… 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 Medium Sized :Dione • Why does Dione have its trailing hemisphere more cratered than the leading one?? Small Moon:Methone (me-thoh-nee) • Discovered by Cassini 2004 & Orbit=24 hour • 3km diameter moon • Has no craters!?!?!? • Rubble pile?? • Slight color markings on surface 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 etc. is being ejected from warm ocean Titan- Atmosphere • • • • • Temp94K, Density1.9Xwater, Press1.5Earth Atmosphere 98%nitrogen,1.6% methane Totally obscured by clouds of smog. Methane rain? Cassini launched 1997; 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 • Crater on Titan • Cryovolcano • Clouds & Lakes Doom Mons? Cryovolcano Upcoming Missions 2020-2029 • Missions to Europa-Jupiter? and/or/nor • Enceladus-Titan-Saturn ? Free-floating Planet • Part of AB Doradus moving group gives age=400million yr & distance=100ly • IR color & spectra give temperature=430K • Escaped from star or born from small dust cloud? • How many of these are there???
