Searching for ET in the exoplanet revolution

Are aliens real? Why haven’t we found them? And what happens if we do? Those are a few of the questions that the astrophysicist Adam Frank has set out to answer in his excellent new book: A Brief Guide to Aliens. Chris Smith has been speaking to him…

Adam - I certainly am very optimistic about the possibilities of at least microbial life. I think it's going to be pretty hard to imagine that microbial life hasn't evolved elsewhere in the universe, probably quite often. Now, animals, and then intelligence, that may be difficult for evolution to achieve looking at Earth's own history. But I certainly think that life in general is going to be quite common in the universe.

Chris - The odds do look good, don't they? If we look at the statistical calculations people have done in the past, looking at how many stars there are in the billions and billions of galaxies that we have and so on, it does look odds on that there are going to be other Earth-like entities out there where the conditions we judge to be ideal for the same sorts of coincidences to line up like they did on Earth.

Adam - Well, that is really something that is recent, that statistical understanding, because it comes from what I call the exoplanet revolution. We discovered our first planet orbiting another star only in 1995. Before that, some people thought that planets were very, very rare. Now we understand that every star that you see in the night sky hosts a family of worlds. And if you count up five of those stars, one of them has a planet in the right place for life to form, meaning that liquid water could form. Now, of course, until you look and you find it, statistics is still just a guess. But in terms of at least having places to look, there's been an explosion of possibilities.

Chris - Where in the pecking order of life's evolutionary timeline across the universe would we sit? In terms of, we are in the Milky Way, so how old does that make us and the rate at which life has evolved here and when it got started, versus are there older aliens and younger aliens than us out there somewhere?

Adam - That's a great question. So the universe is about 13 or 14 billion years old. The Milky Way galaxy is 10 billion years old. The Sun and the Earth are around four and a half billion years old. Earth life is somewhere around 3 and a half to 4 billion years old. So what that means is there's absolutely the possibility of younger life, planets that have formed more recently. But it also means that there may be stars and planets that formed when the galaxy formed 10 billion years ago that have had life on them for quite a long time. The interesting thing is, though, that the habitable lifetime of a planet is not infinite, right? That actually on Earth, at some point, the Sun in about a billion years if going to get hot enough that it will boil the oceans away. So, unless we get on spaceships and leave, Earth will become uninhabitable in about a billion years. So there is sort of a finite lifetime for how long a planet can support life.

Chris - The big question about aliens, given the timeline you've given us is, well, where are they? But if space poses such an obstacle, maybe we are all confined to our own cosmic neighbourhoods and we're not ever destined to say hello to ET.

Adam - I think that's a real possibility. I think solar systems can certainly be inhabited. In another thousand years, if we make it through climate change and everything, I could imagine billions of human beings spread throughout the solar system, but travel between the stars, it's maybe something that's very difficult and is not done very much; for economic reasons, for timeline reasons, for lots of different reasons. That may be one answer to what's called the Fermi paradox, which is the, 'Why aren't they here now?' question.

Chris - It was Frank Drake who was one of the people who sent that famous message out into space inviting ET to recognise that humans are here. Not many people expect we're going to hear back from anyone anytime soon, of course, but if we did, do you devote some column inches in the book to how we should have first contact, what should be done, if anything?

Adam - So I do talk about METI: messaging extraterrestrial intelligence. In general, I'm not a big fan of it because really we don't know what's out there. It may be that the best decision is to lay low. Don't stick your head above the grass and be like, 'Hey, we're here, we're tasty.'

Chris - Isn't it a bit late to lay low, though? We've got a hundred years plus of us beaming stuff into outer space and anyone who's eavesdropping, it's there emerging as a bubble radiating away from Earth at the speed of light. It's there, a hundred years away from Earth now, isn't it? So we can't get it back.

Adam - Well, except that that is very low power. Unless somebody knew exactly where to look, they wouldn't hear us. There's all kinds of radio transmissions in the galaxy. The thing about everything that we've pumped out there, it's true that we've been putting out emissions, but it's been like a low hum, a barely audible hum. So there is really, I think, a difference in terms of how noticeable the message would be. When you do METI, you are really screaming into the void.

Chris - Do you think, Adam, before you finish your career and write your last book, that we'll have evidence of extraterrestrial life somewhere?

Adam - I tell you what I'm certain of, I'm certain we will have data relevant to the question, and that's new, right? It may be that we search and we don't find anything, that's already important information because we will have searched through the nearby stars and planets and if we really don't find anything that's already telling us something. For the first time, we are really going to have data that is going to take us beyond just yelling our opinions at each other and that's going to be really exciting. I'm optimistic. I do believe we're going to get some really interesting data from staring at these planets. What exactly it's going tell us, I can't tell you, but I can tell you that it will be groundbreaking either way.