Just like Alexei Sayle, I have always wondered this too. These books try to find an answer.

The Possibility of Life: Searching for Kinship in the Cosmos
Jaime Green
304 pages including notes and index
published in 2023
If you know anything about SETI, the Search for Extra Terrestrial Intelligence, you probably know the Drake Equation:
The equation calculates the number of possible civilisations we might be able to talk to based on a number of variables, most of which currently unknown. It starts with the average rate of stars forming in the Galaxy, the fraction of stars having planets, the number of planets that could support life and the actual fraction that do have life on them, the fraction of planets with intelligent life, then with civilisations that actually develop technology that enables them to send messages and finally, their average life span. Because we have no evidence for any of these numbers, except barely the first two, you can reach whatever conclusion you want by plugging in the right numbers. Make them low enough and it’s likely we’re the only civilisation in the Galaxy, make them high and it’s a miracle we haven’t been contacted yet.
But that’s not what the equation is intended to do. It’s not meant to provide an answer, but to get you thinking about the possibilities: what if… Which is exactly what Jaime Green has done in The Possibility of Life: Searching for Kinship in the Cosmos: asking questions, rather than wanting to find answers, using the Drake Equation as a rough guideline. If you are looking fora history of SETI, this is not it, nor is it a guide to what an extraterrestrial intelligence should be like for us to be able to contact it. Rather, this is as much about what asking those questions means for our own life here on Earth as well as for the possibilities of life elsewhere. What I liked about this is that Green did not hesitate to bring science fiction into the subject. And modern science fiction at that, not just the obligatory Clarke or Asimov references. Science fiction after all has more freedom to imagine the possibilities of intelligent life unfettered by concerns about whether or not these aliens e.g. use the same parts of the electromagnetic spectrum as us.
The Possibility of Life is a book that if I had read it age twelve, it would’ve blown m,y mind just like Carl Sagan’s Cosmos did. Taking that freedom to imagine the possibilities of what alien life might be, unencumbered by what we need it to be to be able to communicate with it is liberating. This gave me a genuine sense of wonder few books on SETI manage to.

Civilizations Beyond Earth: Extraterrestrial Life and Society
Douglas A. Vakoch & Albert A. Harrison (editors)
250 pages including notes and index
published in 2011
Civilizations Beyond Earth: Extraterrestrial Life and Society is very different from Jaime Green’s book, far more narrow in its focus on possible Extraterrestrial Intelligences we could communicate with. Its underlying assumption is that it will be a civilisation, a species remarkably like ourselves. Not necessarily because that’s the only sort of intelligence that could be out there, more because it’s the only sort of intelligence we currently could recognise let alone communicate with. This assumption is not explicitly stated in this anthology of course, but it is clear from the assumptions the individual authors make in their essays.
Rather, this anthology is more interested in the actual contact and what this would entail. It tries to provide answers to the following three questions: does extraterrestrial life exists in the first place? If so, how would we react to its discovery? Finally, could we actually communicate with them if an extraterrestrial civilisation was discovered? These are not questions that can be answered by just astronomers or astrobiologists, which is why this is an interdisciplinary study, with participants also including sociologists, archaeologists and even journalists.
Each of these questions has about a third of the book devoted to it, after an introduction that provides a brief history of SETI. Considering the limited room in the book and the individual essays, there are no real answers given to any of these three questions, rather more than indications in which direction an answer may be found. In any case too we have such limited data on even the possibility of extraterrestrial life that answering these questions is neigh-impossible anyway. It’s only been a few decades since we’ve even been able to detect planets outside our own solar system after all; only the last decade or so that we could make any predictions about their habitability. Having this little data on the possibility of extraterrestrial life makes answering the question of how we would react and communicate even more difficult to answer. For the first question the best we can do is look at people’s current attitudes towards the idea and extrapolate from that. For the second we can look at historical examples of two human civilisations coming into contact, but that isn’t quite the same thing either, at best an analogy, not an example.
The combination of lack of space to dive deeper into possibilities together with a lack of hard data to grapple with makes this a more frustrating book than Jaime Green’s one. There are some interesting ideas here, but the need to ground them into something approximating reality when we have no clue if we are actually being realistic meant none of them really captivated me. The one thing that did intrigue me was the idea that we could evolve out of intelligence as a species similar to how we evolved into it. Not a new idea; several classic sf stories are about post-intelligent humans or other species, but here Alan Penny postulates that this evolution into an intelligent species happened much more recently than you’d assume. He argues that this happened somewhere between the Ancient Egyptians, who knew some math but didn’t systemise it and the Ancient Greeks, who did. So if this indeed happened so recently, the idea that we could evolve out of it as suddenly isn’t so farfetched. Colour me sceptical though.

Alien Oceans: The search for Life in the Depths of Space
Kevin Peter Hand
281 pages including notes and index
published in 2020
Alien Oceans looks at the possibility of extraterrestrial life from an entirely different point of view. What if, instead of expecting life on the usual Earth like worlds, we instead look for specific type of moon orbiting gas giants? What if we look at worlds like Europa or Enceladus for life instead? It may sound strange to look for life on moons orbiting gas giants much farther out from our Sun than we are, which are covered in thick ice and, like Europa, exposed to a hell of a lot of radiation from their mother planet, but it actually make sense. Because below those icy surfaces these worlds have worldwide liquid water oceans and an active molten rocky core that could create hydrothermal vents. The same sort of vents that also exist in our oceans and have given rise to life forms not dependent on photosynthesis for their survival.
Alien Oceans then has a much more narrow focus than the first two books; unlike them it’s looking at a question that can be solved. Finding out if there’s life on Europa or Enceladus is bluntly speaking, an engineering problem now. As the book shows, the probability of there being underground oceans on either of these two moons is very high. All the evidence we can get from here on Earth seems to point to it. What’s needed to prove it beyond doubt therefore is ‘just’ getting a probe there with the technology to drill down to them and take samples. This is not an easy problem, but not an unsolvable problem either. A NASA or ESA could do this mission with enough political will and enough budget.
Alien Oceans describes how this point, in parallel looking at the discovery of these alien ecosystems in our own oceans and the possibilities of similar ecosystems elsewhere. It looks at the evidence for the existence of these oceans on Jupiter’s moons and at how life might’ve started there, before discussing what the next steps could be to find a definitive answer. Any real exploration of Europa or Enceladus would be a decades long mission, but finding any answer, even a negative one, would be worthwhile.

Packing for Mars: The curious Science of Life in the Void
Mary Roach
334 pages including notes and index
published in 2010
The last book I want to talk about is not about the search for extraterrestrial intelligence, but rather the challenges for humans to actually live in space. Space it turns out is not really a place suitable for humans. We tend to be squishy, our bodies are not built for zero gravity and tend to react annoyingly badly to minor irritations like excess radiation. What’s more, the only way to get into space is to stick you on top of what’s basically a big exploding firework and hope it explodes in such a way it launches you into orbit but not explodes you. Finally, once you do reach orbit without being killed you are confronted with the reality that all sorts of everyday activities just became a lot more difficult, up to and including the simple art of defecation.
Packing for Mars is a gleeful, humorous look at all these difficulties and how NASA and other space agencies set out to tackle them. I knew Mary Roach writing already from Stiff, her book on what happens to your body if you’ve donated it to science after you died, which is why I picked up this book in the first place. It doesn’t disappoint and I especially like her use of footnotes to put in irrelevant but interesting asides.
The title is a bit misleading, as the focus is not really on the extra challenges a Mars expedition brings, but rather on the general dangers and discomforts of being in space. The dangers of traveling to space are less discussed; Roach is more interested in what happens to you once you’re there. As an introduction the book therefore starts with a look at what sort of people are selected to be astronauts in the first place, what qualities a space agency looks for, before looking at the psychological aspects of being in space. Because for all its vastness, the reality is that you’re stuck in a tin can with a few other people for days, weeks or months and you can’t get away. You need people who can deal with that. Fortunately the idea that being in space itself could make you crazy has largely been disproven.
Physically though being in space, or rather being in zero gravity is also dangerous. Your inner ear doesn’t like it so you tend to get seasick. Your skeleton really doesn’t like it, so you’ll lose bone mass and density. But these problems are peanuts compared to the real dangers of interplanetary flight. Astronauts in orbit around the Earth are still protected by its magnetic field; venture outside it, on a journey to Mars e.g. and you will be exposed to cosmic radiation and the like, drastically increasing your cancer risk. Get caught in the path of a solar flare and you’re screwed.
Packing for Mars therefore is sobering and eye opening on how difficult crewed space travel truly is. For somebody who grew up on science fiction that took for granted that space travel would’ve become routine once he was an adult it’s rather a bit of a disappointment to be confronted by the realities of it.