The Revolution is like Saturn, It eats its own children Georg Buchner, Danton's Death

Assignment: Problem Set #8 is due Thursday at 1 pm. Sign up for Observing Lab #3

In Class: Question to Ponder Which of the Galilean moons of Jupiter is least affected by tidal heating? a) Callisto b) Io c) Europa d) Ganymede Saturn Not quite as big as Jupiter, and a lot less massive. density = 700 kg/m3 -- less than that of water ice. Because of lower mass, Saturn's interior is not compressed as much; thus the average density is lower. Interior heat generation via "helium rain," where helium condenses into droplets and falls with in the mostly hydrogen interior, releasing gravitational energy. Less colorful upper atmosphere banding than in Jupiter, probably because temperautres are considerably lower. Saturn's Rings Leftover stuff that didn't fall into the planet or form into moons. Material is inside the Roche Limit, region where tidal forces are sufficiently large to prevent gravitational accretion. Material cannot hold itself together purely via graviational attraction. Region extends outward approximately 2.5 times the radius of Saturn. Makes it very difficult for it to collect together into a moon. Instead, the material spreads out into a thin orbiting disk. Extends ~100,000 km, but is less than 100 m thick. Probably dynamically unstable, e.g., material falls into the planet on ~100 MYr timescales. That means that either 1) the rings are continually fed, perhaps by moon collisions, or 2) the rings are ephemeral, and have not always been present around Saturn. If 2) is correct, then we're just lucky enough to live when a large amount of material is present in the rings; come back in 100 MYr and there might be no ring. Divisions in the rings -- major ones labeled "Cassini" and "Encke" for their discoverers.