Astronomy 161
Introduction to Solar System Astronomy
Prof. Paul Martini

Lecture 37: Moons of Saturn

Key Ideas:

Most diverse moon system of any planet
Trojan and co-orbital moons
Large moons: Cratered Hyperion; Two-toned Iapetus; Cryo-geysers on Enceladus
Saturn's Giant Moon Titan: Only moon with a thick atmosphere
Prospects for Life

Trojan Moons

Co-orbital Moons

Large Moons

Tethys, Dione, and Rhea: Densities of ~1 g/cc; Spherical due to gravity; Flattened craters
Mimas: Responsible for the Cassini Division; Herschel Crater is 140km across; Egg-shaped by tidal forces

Hyperion

Covered in deep, sharp-edged craters
Main constituent is dirty water ice
Porosity is about 40%
Craters may form by melting around darker material or compression upon impact

Iapetus

Leading hemisphere has a 3-5% albedo
Trailing hemisphere has a 50-60% albedo
Has a 1300 km equatorial ridge that rises 20 km above the surface
Likely the leading surface is polluted by Phoebe, which may be an object captured from the Kuiper Belt

Titan: Saturn's Giant Moon

Huygens Lander

Part of the Cassini mission to Saturn
The Huygens probed separated from Cassini and parachuted to the surface of Titan on January 14, 2005
Goal to measure surface composition and conditions

Titan's Atmosphere

Composition:: 98% N₂ (Nitrogen); 2% CH₄ (Methane); Argon, hydrocarbons like Ethane
Cold, dense atmosphere:: Temperature: 94 K (-290 F); Pressure: ~1.6 Earth atmospheres; Clouds of Nitrogen and methane ices; Hydrocarbon "smog"

Titan's Surface

Young surface with very few impact craters
Varied terrain:: Smooth, dark plains (methane mud flats?); Rugged highlands; Drainage channels; Impact basins

Is Methane Titan's "Water?"

Methane (CH₄) may play the same role on Titan that water does on the Earth:: 94 K is between the boiling and freezing points of Methane; Get gaseous methane in the atmosphere
Methane condenses into clouds that rain liquid methane: Signs of drainage flows; Huygens landed in soft methane/water ice mud; Water ice is like sand on Titan

Life in the Outer Solar System?

Europa and Titan are considered the most promising sites to search for life in the Solar System after Mars
Jupiter's Giant Moon Europa: Liquid ocean under the ice?; Life could be present
Saturn's Giant Moon Titan: Methane-based, rather than water-based, life could be present
Enceladus may also harbor microbial life

See A Note about Graphics to learn why some of the graphics shown in the lectures are not reproduced with these notes.