The Big Questions:Does life exist on other planets? If so, how similar might it be to life on Earth? Would it use DNA or something completely different? What common features would there be among living things that have arisen independently on different planets, and what features of life on Earth are merely due to our own particular circumstances or to historical accident?
The recent "Life on Mars" debate has certainly renewed interest in questions such as these. Here are a few pointers to relevant sites:
Life on Mars