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 10 h 14 m to 10 h 46 m –Differential Rotation• Oblate
Saturn’s Atmosphere• Composed of Hydrogen 92% &Helium 7.4% - missing Helium!• Temperature of 100 Kelvin• Thick methane haze covers/mutesclouds: ammonia, ammoniumhydrosulfide, water clouds
Spots/Storms on Saturn• IR image: Dragon Storm“ producedlightning & radio static• Super storm wrapped around Saturnby zonal flow faster than Jupiter’s
Polar Vortex• Spring in North allows Cassini probe to seeNorth pole surrounded by hexagon• Centered on Pole is hurricane (Vortex) withlow 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 metallichydrogen so a smaller magnetic field• Saturn’s radio noise in AM band – reflected by ionosphere
Saturn’sRings• Axis tilted 27°• Orbits 9.5AU fromsun in 29.5 years• Ears to Galileo 1609,explained by Huygens1659
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 periodresonates 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 dustwhich cast shadows??
Roche Limit• Tidal force exceeds self gravitational force• Moons and spaceships can survive insideRoche limit because they’re held togetherby 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 ofSaturn’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 thetrailing hemisphere is white• Maybe from dust kicked off Phobe bymicrometeorites• Big equatorial ridge and scarp
Medium Sized :Dione• Why does Dione have its trailing hemisphere morecratered than the leading one??
Small Moon:Methone (me-thoh-nee)• Discovered by Cassini2004 & Orbit=24 hour• 3km diameter moon• Has no craters!?!?!?• Rubble pile??• Slight color markingson surface
Enceladus• 90% albedo =snow• Embedded in the E ring• Orbital resonance withDione gives tidal heating• Tiger Stripes – are warmas seen in Infrared• Lack of craters: resurfaced
Enceladus -Volcanoes• Water vapor etc. isbeing ejected fromwarm 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 liquidmethane/ethane ocean/lake & streams• Ground has consistency of mud• Ice rocks show signs of weathering
Titan-RADAR• Dunes on Earth & Titan’s hugedunes of hydrocarbon chemicals• Crater on Titan• Cryovolcano• Clouds & LakesDoom Mons?
Upcoming Missions 2020-2029• Missions to Europa-Jupiter? and/or/nor• Enceladus-Titan-Saturn ?
Free-floating Planet• Part of AB Doradus moving group givesage=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???