Astro 120 Fall 2003
Essay Question for Exam 3
You will be asked to answer this question during Exam
3 on Tuesday, December 16. Please think about how you will answer this
question before the exam, and write your answer during the exam time.
PART II: ESSAY (20 points): Answer the question on this
sheet only
We discussed the Drake Equation at the end of this course. Please answer the
following questions about the Drake Equation in terms of what you learned in
Astro 120 this semester.

(15 points)
The term f_{L} is the fraction of planets that have suitable
conditions for life to develop that do, indeed, develop life on their
surfaces. Before discussing this term, though, earlier terms in the
Drake Equation considered other factors are that provide approrpriate
conditions for life to develop. In a single brief essay,
describe how the terms leading to f_{L} restrict stars and planets
to those that can support life. In your essay be sure to address the
following questions:
 What are the considerations that go into deciding if a planet can
develop life? In other words, what are the restrictions on stars and on
planets that need to be made before we can consider if life could develop
there?
 Which terms in the Drake Equation take these into account?
 How do those terms take the life question into account?

(5 pts)
Make your own estimates for each of the terms of the Drake Equation (feel
free to use those determined in class if you agree with them, or use
different values if you prefer) and briefly discuss (in a complete sentence
or two) your reasons for adopting each value.
What is your final value of N?