Humanity’s Fifth Copernican Moment

It looks increasingly likely that we will find extraterrestrial life

I expect to see the existence of extraterrestrial life confirmed within the next few years. When it happens, put down your phone, look up from your work, walk away from your computer, and let the moment sink in. Then we can go back to arguing about pronouns and tariffs.

It looks increasingly likely that we will find alien life. We are not there yet, but the discovery announced this week by Nikku Madhusudhan and his colleagues at Cambridge University, of what looks suspiciously like a ‘biosignature’ of life in the atmosphere of a planet called K2-18b orbiting a star 124 light-years away, may prove to be a key moment event in the history of human understanding.

It will be a fifth ‘Copernican moment’ when extra-terrestrial life is finally discovered: scientists putting yet another dent in human self-importance. They showed that the earth orbits the sun, not vice versa (Nikolaus Copernicus, 1543); that we are just another species of animal (Charles Darwin, 1859); that we use the very same genetic code as a cabbage (Francis Crick, 1953); that far from being sophisticated creatures, we have the same number of genes, indeed mostly the very same genes, as a mouse (the Human Genome Project, 2003).

Now evidence has come from the James Webb Space Telescope, which a couple of years ago started looking at distant planets with sufficient resolution to identify the chemicals in their atmospheres. In this case, they have found fairly strong hints of dimethyl sulphide and/or dimethyl disulphide, neither of which are generated on Earth except by marine plankton.

It was my old friend James Lovelock, the Gaia theorist, who first suggested that dimethyl sulphide, also known as DMS, would be something to look for as a characteristic signature of life. Oceanic algae belch the stuff out with gusto on Earth – it is one of the reasons sea breezes have their distinctive smell - while volcanoes, which can exist on lifeless planets, don’t.

Of course, it does not follow that the same is true on K2-18b. DMS has also been detected on a sterile comet, as well as created by chemical reactions in a laboratory experiment designed to replicate a planetary atmosphere. But if the science is right, there’s an awful lot of it in K2-18b’s ‘air’. So, the burden of proof is perhaps on those who think it is not a bio-signature rather than those who think it is.

K2-18b is about eight times as large and probably somewhat hotter than Earth, but it does seem to be a rock, rather than a Jupiter-like ball of gas. It lies in what astronomers call the ‘Goldilocks zone’ with respect to its sun, not too hot and not too cold for liquid water, and therefore perhaps perfect for life.

Its atmosphere contains some carbon dioxide and methane but not carbon monoxide and ammonia, a combination which suggests it has a big ocean of liquid water but a hydrogen-rich atmosphere. Hence the astronomers are calling it a ‘Hycean’ planet.

Given the scale of the universe, it would be more surprising if life did not exist in it. Do the maths: so far, it looks like planets orbit every fifth star. There are 200 billion stars in our own galaxy, the Milky Way; and there are about 200 billion such galaxies. If there are, say, five planets per solar system that would mean 200,000,000,000,000,000,000,000 (two hundred quintillion CHK) planets in all.

Even supposing just one planet in a billion is suitable for life, that’s still 200,000,000,000,000 (two hundred trillion) life-capable worlds. It would be fairly bizarre if ours were the only one that had life.

Many of these exoplanets will be much older than Earth, because our solar system formed when the universe was already nine billion years old. So, others are bound to have had more time to spawn life and get evolution going.

Activity emerged here fairly soon after Earth cooled down, suggesting that if the conditions are right, it is all but inevitable life will emerge.

If it started billions of years earlier on other planets, then it is probable that it has had time to generate not just microbes and algae, but technology-generating beings too, and probably super-intelligent ones.

Hence the question that the physicist Enrico Fermi famously posed over lunch one day in 1950: ‘But where is everybody?’ Aliens should be dropping by regularly in their warp-drive spaceships, or at least seeding us with microbes from time to time. And no, UFO reports don’t count as evidence. If they really were alien spacecraft we would have got decent photographs by now and certainly not kept the secret inside the notoriously leaky American government.

We can be fairly confident that they have not dropped by. We have never found a living creature on this planet that fails to use DNA or RNA, let alone our highly idiosyncratic and apparently arbitrary genetic code by which we earthlings construct protein molecules. Life here – we now know for sure – is just one big family. Nor has fossilised evidence of a crashed spaceship turned up in any ancient rocks (except in the bad novel I started drafting once).

One worrying answer to Fermi’s question, proposed by the economist Robin Hanson in the 1990s, is that perhaps every time life reaches the point somewhere in the universe when it can start doing interstellar travel, it blows itself up. In this scenario, known as the Great Filter, billions of planets may have reached our stage of technology, including things like nuclear weapons, and none have got past it without annihilation.

An even nastier possibility, the Berserker Hypothesis, is that somewhere out there are ‘von Neumann probes’ – spacecraft capable of replicating themselves. These effectively seek out and consume or destroy any planets before they can start colonising other worlds. Which is why perhaps we should keep quiet and not let the aliens know we exist.

Too late: our radio signals are already more than 120 light-years out – and will soon reach K2-18b. In any case, our own dimethyl sulphide biosignature has been readable by aliens for billions of years.

When we do find unequivocal evidence of life elsewhere, it is almost bound to be odder than we can imagine, with a very different genetic code and very different metabolism. Will we even recognise it or figure out how it works? Its two characteristic features, I think, will be that it uses information to harness energy and create complexity, and that it experiences evolution by natural selection. But there could be some very peculiar ways to do this.

If it’s intelligent, then we face an all-too-mundane dilemma: whom do we put up to represent us in the greeting ceremony? Donald Trump? Xi Jinping? The head of the United Nations? Please no! I reckon we should hold a grand global lottery and hand the microphone to whichever random person wins the lucky ticket.

The last word should go to Monty Python’s Eric Idle, from the Galaxy song in the film The Meaning of Life: ‘So remember, when you’re feeling very small and insecure/How amazingly unlikely is your birth/And pray that there’s intelligent life somewhere up in space/’Cause there’s bugger-all down here on Earth!’

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Matt Ridley is a science writer, businessman, and NY Times bestselling author. His books include The Rational Optimist: How Prosperity Evolves and most recently, Birds, Sex & Beauty: The Extraordinary Implications of Charles Darwin’s Strangest Idea.

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