‘Are we alone?’ This is the question that may come to predominate the science of our new century, as is evident from the vigour of the nascent discipline of astrobiology (or, if you prefer, bioastronomy, or even xenobiology). A cynical definition of this area is ‘the study of things that do not exist’, but even if the question of extra-terrestrial life, and especially intelligence, is never satisfactorily answered, the theme of astrobiology has the immediate benefit of drawing upon strands of science as diverse as infra-red astronomy, microbial ecology and molecular biology, not to mention planetary missions and palaeontology.

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