## Monday, November 8, 2010

### Homework 9

--- PROBLEM 1 ---

Io experiences tidal heating primarily because __________.
 Io is located very close to Jupiter Io's elliptical orbit causes the tidal force on Io to vary as it orbits Jupiter Io has an unusually elongated shape that makes it look more like an egg than a sphere Io is made of relatively soft materials that deform quite easily

From Part A, Io's elliptical orbit is necessary to its tidal heating. This elliptical orbit, in turn, is a result of the orbital resonance among Io, Europa, and Ganymede. This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because __________.

 all three moons orbit with the same period, staying aligned at all times Europa and Ganymede always pull on Io from the same direction as Jupiter pulls on Io Io periodically passes Europa and Ganymede in the same orbital position Europa and Ganymede are unusually large moons

We cannot see tidal forces or tidal heating; rather, we predict that they must occur based on the orbital characteristics of the moons. What observational evidence confirms that tidal heating is important on Io?

 Io's unusual, egg-like shape Io's surprisingly elliptical orbit the orbital resonance between Io, Europa, and Ganymede active volcanoes on Io

The orbital resonance also gives Europa an elliptical orbit, so it also experiences tidal heating. However, Europa experiences less tidal heating than Io, because Europa __________ than Io.

 is more perfectly spherical in shape contains much more ice is much smaller is farther from Jupiter

We now know of many Jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating?

 We need to know whether the planet also has a third moon. We need to know their orbital periods. We need to know whether either moon is volcanically active. No other information is needed: With two moons, there is sure to be tidal heating. No other information is needed: With two moons, there is no chance of any tidal heating.

--- PROBLEM 2 ---
Listed following are some of the distinguishing geological characteristics of the moons orbiting Jupiter. Match each characteristic to the appropriate moon.
Io: heavily cratered terrain adjacent to much younger terrain; volcanoes currently erupting; hot, glowing lava visible in some photos
Europa: surface features provide evidence of a subsurface liquid ocean; ice covered surface with few impact craters
Ganymede: source of ionized gas in the donut-shaped charged particle belt around Jupiter; largest moon in the solar system