Part II. SHORT ANSWER [100 pts]: Answer each question with at least five complete sentences or more.

11. [20 pts] Describe what evidence exists that there was liquid water on the surface of Mars in the past and what happened to that water.

12. [20 pts] Describe two major observational methods for detecting extrasolar planets indirectly? For each method explain what planetary properties can be measured from each method.

13. [20 pts] What is tidal heating? Describe what evidence exists that there is tidal heating on Europa and discuss the type of habitable conditions that would be present if life did exist on this moon.

14. [20 pts] A common theme in science fiction is “leaving home” to find a new planet for humans to live on. Now that we know about thousands of exoplanets, we can start imagining how to choose one. Describe the characteristics that we would look for in a planetary system that would make for a good home for humans. [Hint: think about life’s prerequisites and planetary system properties.] 

15. [20 pts] Make your own estimate of the Drake Equation. Please explain your reasoning about the values selected for each of the variables of the Drake Equation. Does your estimate of N match your view of the probability of Life and Civilizations in the Universe? Why or why not?