This past year there have been hundreds of news reports about the discovery of so-called “Earth-like” planets: GJ667C, Kepler-22b, … There could be billions of Earth-like planets in the universe but a great majority of them may have a totally different internal and atmospheric structure. … life is capable of far more diversity and adapatation than we can imagine. Self-replicating matter might evolve to feel right at home on some of these exotic worlds. However, recognizing such bizarre life forms would probably be impossible without directly visiting the planets where they live. On carbon planets there might be creatures that eat silicates or oxides, and use carbon instead of oxygen for metabolism.