If we find life of any kind out there – whether it be Martian microbes (we have several probes prodding the Martian surface and observing it from orbit) or a signal from super-intelligent (or even mildly brainy) aliens – it will change everything. ET will force us to confront a deep truth; that humans are not the only game in town, that we live in a possibly crowded (and quite probably threatening) universe.

But here’s the thing. What if they don’t find anything? What if, 10 years, a 100 years, a 1,000 years hence, endless sky-surveys, proddings and pokings of Mars and elsewhere, turn up nothing, save rocks, gas, ice and vacuum. We had better be prepared for this because, I am beginning to believe, this seems to be the most likely result.

ET should be out there. As the physicist Enrico Fermi famously pointed out more than 60 years ago, in a universe of great antiquity and size such as ours, there ought to be many, many civilisations in space, some of which will be far in advance of our own. It is, he said, a paradox that we have not seen any evidence of this.