Transcript Document

Rotation period as fast as Jupiter, as well as differential rotation rates at
poles and equator
• 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
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
• 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
• 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
• All rings, and small shepherding moons, lie
within the Roche limit; larger moons are outside
Gaps in rings contain shepherding
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
• 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)
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
• Terraforming Titan!!  Heat up to release
Oxygen, which would covert methane to
CO2 (like Mars): CH4 + O2  CO2 + 2H;
plant life to follow
Enceladus – Water !
Other moons: heavily cratered
Data on Some Saturn Moons