Transcript Document
Rotation period as fast as Jupiter, as well as differential rotation rates at poles and equator Saturn • Second largest planet – with rings • Atmosphere composition similar to Jupiter, but less metallic H2 • Density ~ 0.69 g/cc (could float on water!) • Twice as far from the Sun as Jupiter • Surface Temp = 95 K • Deep clouds, strong winds (1700 Km/hr) • Intrinsic magnetic field is 1000 x Earth’s (but because of its size it is only 70% of Earth’s just outside the atmosphere) Rings of Saturn: Highly structured and stable formations Polar caps are illuminated due to electrical activity at the two magnetic poles Orientation of rings and different views of Saturn Distances of Rings (How many?) 2.5 times radius of planet The Ring systems lie within about 2.5 x Saturn’s radius. i.e. within Roche limit Rings and Gaps: Thousands of rings interspersed with gaps Voyager view: Before that there were thought to be only a few Main ring formations and divisions Rings and Moons • What are the rings made up of ? • What keeps the rings stable and in orbit ? • Saturn has 62 moons, more than any other planet (Titan and Enceladus most interesting !) • All Jovian planets are now known to have rings • Saturn’s rings are most shiny: made of icy rocks, in independent Keplerian orbits, above the equator Composition of Rings • Dirty, icy, snowballs from about 1/1000 of an inch (dust particles) to 10 yards; most about a foot • Origin: (i) breakup of satellite(s), (ii) incomplete formation (a la asteroid belt !) • Orbits are stable and particles do not collide • Rings are stable due to gravitational interaction with small Shepherding Moons that lie among the ring structures The Roche Limit • Gravitational stability limit, out to about 2.5 times the radius of the planet • Any object without intrinsic gravity (such as a pile of gravel) will break up inside the Roche limit due to tidal effects; a moon with sufficient mass and under its own gravity need not break up • All rings, and small shepherding moons, lie within the Roche limit; larger moons are outside Gaps in rings contain shepherding moons Moons and rings: Shepherding moons within rings Shepherding moons and a ring Ring particles in ‘orbital resonance’ with the moons are ejected due to periodic gravitational interaction, i.e. only particles whose periods are NOT multiples of moon’s orbital periods survive in the rings Asteriod Ripped Apart By Star Into Ring-like Structures http://www.ibtimes.com/november-astronomy-findings-unprecedented-image-asteroid-ripped-apart-dead-star-2179852 TITAN • Titan is one of several large moons beyond the Roche limit • Titan is most interesting, about 1.5 times the size of Earth’s moon and a density of 1.9 g/cc • Second largest moon in the solar system TITAN: Moon with (heavy) Atmosphere Infrared (heat) map of Titan Infrared reflectivity indicates composition of atmosphere Atmosphere of Titan • • • • Mostly nitrogen (80%), argon, methane (CH4) Pressure: 1.6 x Earth’s atmosphere Surface Temperature: -300 F (95 K) CH4 and C2H6 (ethane: ethyl alcohol) oceans, (half-mile deep) clouds, rain, ice, snow • Orangish color due to smog • Oxygen locked in ice Titan and Origin of Life ? • Many organic, hydrocarbon compounds HCN, C3H8, etc. • Present conditions similar to primordial conditions on Earth in the first billion years • Slow evolution because of cold • NASA probe Cassini is now studying Titan • Terraforming Titan!! Heat up to release Oxygen, which would covert methane to CO2 (like Mars): CH4 + O2 CO2 + 2H; plant life to follow CASSINI Enceladus – Water ! Other moons: heavily cratered Data on Some Saturn Moons