Astronomy 3 - Solution Set 7

1. Why are Phobos and Deimos non-spherical? Why is Earth's moon much more spherical?

   The most important fact is that Phobos and Deimos are very small. Their gravitational pull is too weak for the moons to pull themselves into spheres.

2. Why is Jupiter oblate? Do you expect all Jovian planets to be oblate? Why or why not?

   There are three important facts. The first is that Jupiter rotates very quickly (it rotates once every 10 hours). The second is that Jupiter is composed almost entirely of liquid and gas, making it very easy to deform. Finally, Jupiter is physically very big, which makes the fast rotation have a larger effect. (If you stand far from the center of a merry-go-round, you'll feel a larger outward force than if you stand near the center.)

3. Describe two theories to explain the persistence of the Jovian belts and zones.

   The debate centers around what provides the energy source for the belt-zone circulation. One theory says that energy deposited in the upper part of the atmosphere by the Sun provides the energy. Another theory holds that the energy is provided by the flow patterns deep inside the planet.

4. Why are there no craters on Io and few on Europa? Why should we expect Io to suffer more impacts per square kilometer than Callisto?

   Io has no craters because it has many active volcanos which resurface the moon very quickly.

   Europa's surface is ice, which is much easier to melt than rock. Therefore it requires less energy to melt Europa's surface and erase the craters than it does for a typical rocky moon.

   To correct a common misconception: Europa is not younger than Io, Callisto, or Ganymede! When the text refers to Europa as ``youthful,'' it's talking about Europa's surface, not the moon itself.

5. What is the status of our understanding of the Jovian moon Europa? This moon was studied extensively be the Galileo mission. Visit Galileo -related Web sites to find the results of this exploration, and discuss our current ideas regarding the possibility of liquid water beneath Europa's crust. How might future missions to Europa probe such an underground ocean?

   Studies of the tides Jupiter raises on Europa led to the conclusion that Europa may have a liquid water ocean hidden beneath it's icy surface.

   Some people speculate that geologic activity on Europa could provide the energy needed to sustain bacterial life in the layer of water.

   One way to study study Europa's ocean it to simply send a probe that will melt its way through the ice and directly study the ocean beneath.

6. Check on Cassini. What is the latest news from this spacecraft? What has it photographed most recently?

   There's lots of information available about Cassini at:

   http://saturn.jpl.nasa.gov/cassini/index.shtml