Saturn Astronomy 311 Professor Lee Carkner Lecture 18

Saturn -- King of the Titans   He was overthrown by Jupiter who became king of the gods  Saturn’s symbol is the sickle

Viewing Saturn from Earth   First viewed through a telescope by Galileo   Modern telescopes reveal a series of rings and cloud patterns in Saturn’s atmosphere

Saturn Facts  Size: 9.5 Earth diameters   Orbit: 9.5 AU   Description: smaller, more distant Jupiter with rings

Viewing Saturn from Space   Hubble Space Telescope has provided many images   Orbiting Saturn to study it long term  Dropped a probe (Huygens) into Titan’s atmosphere

Path of Cassini

Saturn’s Atmosphere  Saturn has belts, zones, ovals and storms, but they are less distinct than on Jupiter   Nothing like the Great Red Spot   Saturn sometimes has storms that burst up from below

Composition of Atmosphere  We believe that Saturn has an atmospheric structure similar to Jupiter’s   Middle layer of Ammonium Hydrosulfide (NH 4 SH)   We don’t see all of the layers as clearly as we do on Jupiter

Saturn’s Dullness  The temperature of Saturn’s atmosphere increases more slowly with depth than Jupiter because:   Due to weaker gravity the layers are more spread out   Clouds form deeper in atmosphere   Upper layers obscure the deeper layers

Saturn and Jupiter’s Atmospheric Structure

Saturn’s Heat   Saturn is smaller than Jupiter and should have radiated much of its heat away by now   Theory: the helium condensed into droplets and fell towards the core liberating gravitational energy   Calculations seem to support this

Saturn’s Interior  Saturn has a very low density (690 kg/m 3 )   This means it must have a large core (26% of the mass)   Saturn is much less massive than Jupiter so there is less gravity to compress the hydrogen   Due to slower rotation, less liquid hydrogen and blocking of charged particles by the rings

Internal Structure of Jupiter and Saturn

Saturn’s Rings  Saturn’s rings appear very bright but very thin from Earth   Rings reflect 80% of light that hits them   The inner rings moves faster than the outer rings   Size = 1cm to 5m (average ~10 cm)

Rings and Tides  Imagine a ball of material near a planet   The tidal force from the planet wants to pull it apart  tidal force self gravity force

Roche Limit  The region where the tidal force pulling the material apart is stronger than the gravitational force holding it together is called Roche limit   Outside Roche limit, material forms moons Saturn R Roche Moon Ring

Structure of the Rings   Rings are separated by gaps or divisions with relatively few particles   The size and composition of particles vary from ring to ring  B ring has many large, icy bright particles  F ring has many small, dark particles

Diagram of Saturn’s Rings

Moons and the Rings  Several moons have orbits within the rings   Moons may also be a source of ring material   Cassini division is formed by gravitational resonance with Mimas   F ring is contained by two small moons, one on either side

Saturn’s Moons  Cassini has shown that some of Saturn’s moons are active   Internal liquid water  Something is providing energy to some moons   Outgassing of Enceladus contains salts 

Next Time  Read Chapter

Summary  Saturn is the second largest planet and the second closest gas giant to Earth  Saturn is similar to Jupiter with key exceptions mostly due to less mass and smaller gravity  cloud layers are more spread out in depth  less distinct cloud bands  larger core  less liquid metallic hydrogen

Summary: Rings  Made up of many distinct rings and ringlets  Composed mostly of icy particles of various sizes and reflectivity  Ring structure shaped by moons  Rings cannot form a larger body due to tidal forces