WHAT is the biggest question in science? The origin of consciousness? How to combine quantum mechanics with general relativity? These are big, but arguably there's a bigger one: is there anyone out there?

Understanding exactly what life is, how it began and whether it exists beyond our planet is, I believe, the greatest challenge of our time. Finding alien life would be the most important discovery in history, and the search for it is more likely than anything else to maintain public support for space research. Given this, you'd think space agencies would be devoting pretty much all their resources to it. Oddly, they are not.

t is time to refocus public space programmes on answering the biggest question of all. That means funding big, expensive, ambitious exploration projects on Mars, Titan, Europa and any other promising places, and flying telescope arrays to spot extrasolar Earths. Cancel everything else, if necessary.