Astro 250: Astronomy Bizarre
Spring 2008

Assignment #4
Due: Monday, April 14, 2008

Name: ______________________________________

1. (5 points) Do you think the implications of discovering microbial life beyond Earth would be more, less, or equally profound than those of discovering extraterrestrial intelligence? Explain your reasoning.

    

    

    

    

2. (15 points) Some scientists suggest that the current Earth may have be the fourtnate result of several kinds of cosmic "luck" - i.e. the specific circumstances that made it possible for evolution to progress beyond microbes to produce intelligent beings might be so rare that ours might be the only inhabited planet in the Milky Way that harbors anything but the simplest life. This idea is known as the "Rare Earth hypothesis." Rare Earth proponents include many mainstream scientists with a range of specialties and interests.

   On the other hand, we know that our planet is not the center of the Universe, or even of our solar system. This realization took millenia to form; this so-called "Copernican Principle" jump-started modern science in the 16th and 17th centuries. The same principle has been borne out many times since, as we learned that we are not in the center of the Galaxy (in the 1920s) that the Universe has no center at all (in the 1950s and 60s). In other fields, it has parallels - for example, in the discovery in the 1990s that we share much of the same genetic code as most other creatures on Earth, and that other planetary systems appear to be quite common.

   Do you consider the Copernican Principle to be in conflict with the Rare Earth hypothesis? If so, does this make the Rare Earth hypothesis any less scientific? Please explain your opinions. In doing so, you should look through the following sources for more details and various opionions about the Rare Earth idea:
   

   • An article on the Rare Earth hypothesis
   • A summary of the Rare Earth arguments
   • A more thorough, critical review of the book Rare Earth written by James F. Kasting - you need to access this page from an ISU computer.
   • Here's a one-hour radio show from the "Are We Alone" folks about possible life forms - including a debate with Peter Ward twoards the end of the show.
   • Text of a debate between a scientist who is a principal Rare Earth proponent and a SETI Institute scientist
   • Part 1 of a 5 part debate on the Rare Earth idea - links to further parts lie within.

    

    

3. (5 points) We're working through the Drake equation in class, and you've seen and read about the reasoning behind the various factors. Here, I'd like you to "solve" the Drake equation by coming up with your own estimates for each of the factors. Do not hesitate to make estimates that differ from the ones you've heard in class... as I hope you realize, the factors beyond f_p involve limited data and therefore require significant subjective judgement.

   List each factor in the equation and your adopted value, and be sure to write one or more sentences explaining why you chose the value you chose. For simplicity, lets assume that R_*=3/year and f_p=0.3 are not controversial. This way, you need only talk about n_e, f_l, f_i, f_c and L. With your estimates, compute your best guess at the value of N.