Rare Earth: Why Complex Life Is Uncommon in the Universe : why complex life is uncommon in the universe

n November 12, 2002, Dr. John Chambers of the NASA Ames - search Center gave a seminar to the Astrobiology Group at the OUniversity of Washington. The audience of about 100 listened with rapt attention as Chambers described results from a computer study of how planetary systems form. The goal of his research was to answer a dec- tively simple question: How often would newly forming planetary systems produce Earth-like planets, given a star the size of our own sun? By "e;Ear- like"e; Chambers meant a rocky planet with water on its surface, orbiting within a star's "e;habitable zone. "e; This not-too-hot and not-too-cold inner - gion, relatively close to the star, supports the presence of liquid water on a planet surface for hundreds of million of years-the time-span probably n- essary for the evolution of life. To answer the question of just how many Earth-like planets might be spawned in such a planetary system, Chambers had spent thousands of hours running highly sophisticated modeling p- grams through arrays of powerful computers. x Preface to the Paperback Edition The results presented at the meeting were startling. The simulations showed that rocky planets orbiting at the "e;right"e; distances from the central star are easily formed, but they can end up with a wide range of water c- tent.