There has been a flurry of books published to mark the fiftieth anniversary of the start of the Search for Extraterrestrial Intelligence (SETI), but James Kasting’s offering stands out from the pack. He is not so much concerned with the prospects for communicating with ET, but with assessing the likelihood that ET exists. His approach is to consider the way in which a habitable planet is ‘built’, using the Earth, the only example of a habitable planet that we have, as a case study.

The danger of this approach is that it involves extrapolating from what may be a special case – even a unique example – to make broad generalisations. But that situation may be about to change dramatically, since, as Kasting makes clear, we are probably on the brink of