A decade ago, scientists who spent time thinking about life elsewhere in the universe were considered somewhere between eccentric and crackpots --- not because the idea was outlandish, but because there seemed to be nothing for a scientist to do but speculate wildly on the topic. Today, over a hundred planets outside our solar system are known; and even as they continue to be detected, new and more powerful techniques for their discovery are being developed. At the same time, our knowledge of planetary science and elementary biology is growing by leaps and bounds. It is becoming more and more reasonable to carefully examine the question of whether any of those other planets could be inhabited. `Astrobiology' is becoming a respectable discipline, and Caltech students can even major in it.

This course will cover the Astronomy, Geoscience, and Biology that underlies the current search, and take a look at how the search is being performed, both directly in our Solar System, and by observations of stars far distant.