‘We live in a golden time of exploration’: astronomer Lisa Kaltenegger on the hunt for signs of extraterrestrial life

Staring into the abyss… Am I really reaching anyone out there?” Lisa Kaltenegger is laughing about the unsatisfactory experience of teaching astrophysics over Zoom during Covid lockdowns, but she could be talking about her vocation: trying to discover if there’s life beyond our solar system.

Kaltenegger founded the Carl Sagan Institute in 2015 to investigate just that. A burst of sunny energy and infectious enthusiasm on a grey day, she’s speaking to me from the legendary extraterrestrial life researcher’s old office, now hers, overlooking the leafy Cornell campus in upstate New York. The institute brings together researchers across a range of disciplines to work out what signs of life on other planets might look like from here, so that we recognise them if (or when) we find them.

It’s a big job at the forefront of exceptionally hard science. Kaltenegger collaborates with Nasa, has won multiple awards and published extensively over two decades. But her latest project is no peer-reviewed paper: it’s a pop science book about the search for life. Alien Earths – at least the UK edition – has a cover of brightly coloured orbs; inside there are cartoonish line drawings and a bookmark with planet stickers, which Kaltenegger mentions delightedly. It’s not a kids’ book (though interested teens and younger enthusiasts will love it), some of the concepts are necessarily complex, but it’s a joyful, eye-opening introduction to a topic many are too intimidated to tackle.

That includes me. I’ve always considered the universe – terrifying, unknowable, probably hostile – none of my business, but reading Alien Earths, several surprising things happened. Initially, it made me cry: overwhelmed at the vastness, the age, the mystery, of the universe. But gradually, as I began to grasp the basics, I started seeking out, not avoiding, news stories about space. Within weeks, my husband, my son and I had were enthusiastically debating the possibility of alien life. It’s exactly the kind of conversation I would previously have checked out of entirely, but Alien Earths left me both empowered to believe I can grasp the basics of the cosmos, and truly curious to know more.

Sagan was a great populariser of cosmic exploration, but what pushed Kaltenegger to follow in his footsteps? She wanted to step back and think about the big picture to see if there was anything she was missing in the search for life, she says, and realised the best way to do so was “telling a friend”: (a nice description: that’s just how the book’s chatty tone feels). But she was also keen to communicate something she thinks gets lost in the general pessimism of the age. “We live in this incredible golden time of exploration. We are so close to a change in our understanding of the cosmos. We are living it, and we are explorers.”

If, like me, this has passed you by, let me explain, thanks to my newfound Alien Earths confidence. For life to exist, you need a rocky planet with an atmosphere in the “habitable zone”: neither too hot nor too cold. One in five of the stars you see in the night sky (around 20bn in the Milky Way) has a planet in the habitable zone, but learning anything about them is exceptionally hard, because they are so distant. Even detecting planets outside our solar system (exoplanets) requires a sort of educated guesswork, based on observing how light from a star changes.

The first exoplanet was detected in 1995; now more than 5,000 have been identified. In Alien Earths, Kaltenegger’s excitement is infectious as she relates how she discovered that the Kepler telescope had detected two potential candidates for life; it’s even more palpable as she talks. “We had no idea how long we’d have to wait for planets that are rocks within the habitable zone. And then Kepler found them and they found two. I was like, if they already found two…”

The next leap forward was the James Webb Space Telescope (JWST), launched on Christmas Day 2021. Kaltenegger explains: “With this big telescope, for the first time in history we have the chance to figure out what’s in the air of other planets that could be Earths.” That means we could soon know if we’re not alone. “If life is everywhere and it leaves signs in the atmosphere, then we will find it,” she says. Among the candidates she has her eye on is our closest neighbour, the Proxima Centauri system. “Even the next star over has a planet that could potentially be another Earth; it’s just on our doorstep.” I find myself getting goosebumps when she talks about how close we might actually be. “I think about it like a history book. There are going to be two sections of this history book in the long run – the time before humankind knew whether or not they were alone and the time after. We are on that edge.”

Of course, plenty of people believe we already know, and last year’s claims at a Congressional hearing relating to alien crafts and “non-human” life have only fanned the flames (despite Pentagon denials). The book makes extremely short shrift of UFO sightings (“The subject is full of poor observations”), but what does Kaltenegger make of our enduring obsession? “To me, the fascination is based on an excitement and hope that we might not be alone in the cosmos. But now we have entered a completely new golden era of exploration where we don’t have to stake all our hopes on supposed top-secret government programmes or phenomena that could be created by a variety of events, like weather patterns. Instead, we have now found planets circling other stars and can actually read their light fingerprint.”

Preparing for what the JWST might find is at the heart of Kaltenegger’s work. Using biology, geology, astronomy, astrophysics and the knowledge of how life on Earth evolved, her team models how the atmospheres of other habitable planets might look. They “melt rocks” and grow microorganisms, explore all the possible colours of life. “I wonder if our imagination can cover even a fraction of the possibilities,” she says at one point and I’m struck by how much of her work is speculative, imaginative, creative. That’s not how I imagined astrophysics, I say. “I agree. I think this is also why a lot of people don’t want to go into science. They think it’s stifling, it’s rigid, it’s dry and, at least at the forefront of science, it’s not that way, because you have to imagine – it’s an educated guess.”

Reaching the best educated guess involves casting the net as widely and diversely as possible. That’s one of the guiding principles of the institute. Experts from different disciplines bring specific expertise and insight and so do people from different backgrounds. “If you have six people with exactly the same training, same ethnicity, same gender, they will probably produce six times the same solution for a problem. The more diverse you can make it, the more solutions you will find.” The launch of the JWST, she says, involved “people from everywhere, literally the whole globe. I think sometimes it’s not so visible how it takes an international village – or a huge city! – to get these space telescopes going. But that village exists.”

Kaltenegger’s career and philosophy defy the historic view of science – “an ivory tower, a white male in a white coat” – but that hasn’t been without challenges. A brilliant student growing up in Austria, she was advised against studying science, then as an engineering undergraduate (she took her physics degree simultaneously, only possible, she laughs, because the city of Graz was small enough to bike between campuses), she and the only other female student were sometimes ignored by “Stone Age” teachers. There’s an anecdote in Alien Earths about men grousing she only got a job “because I was a woman”; another about a hiring committee quizzing her on whether she had kids (her daughter actually features proudly in one of the book’s illustrations – she shows me). Mostly her professional experiences have been supportive – one early boss firmly stopped her doing the photocopying – but she’s obviously no pushover either. In her first job, she tells me: “The first time I made the coffee, I made it so bad. It was super funny, they were like, ‘Oh, you know what, you don’t have to!’ It was a little bit devious.”

Speaking of coffee, it is almost a character in its own right in Alien Earths, it features so heavily. One of the most important purchases setting up the institute, Kaltenegger says, were “two really good espresso machines”. She truly loves coffee, but the real purpose was to stimulate connection. “If you have really good coffee, people will congregate and talk about what they’re doing. And there are always cookies and dark chocolate in my office – not even a question, there’s always food.”

Kaltenegger must be an incredible teacher, not just because of the snacks, or the lecture on impostor syndrome she casually mentions giving students (“I know you’re good enough. You’re great! Come back to my office whenever you’re in doubt.”) In Alien Earths, she conveys complex concepts and numbers too big to comprehend in a way anyone – even me – can grasp, using imagery. If our solar system were a cookie, our nearest planetary neighbour is nearly 9,000 cookies (four football fields) away, for example. There’s a thought experiment where she invites readers to wonder whether a banana is an alien; the expansion of the universe after the big bang is like “raisins in raisin-bread dough” and explaining how little of the cosmos we can see or grasp, she says we’re “like a piece of pepperoni on a pizza trying to imagine the whole pizza’s shape” (still with the snacks). There’s something very generous about her desire to bring us along for the “amazing ride we’ve all been on”, and are still on.

I notice, too, how often she describes movement in the universe as a dance; it’s quite poetic. “Actually, being Austrian, I went to dance school,” she laughs (Latin was her speciality). “This kind of influenced my thinking about gravity, because it is basically a dance, give and take. It’s really funny how the thing I did such a long time ago – and I still love to dance! – also shaped my perception. You want to have as diverse a team as you humanly can, because you never know what actually brings the idea that might solve a problem.”

Kaltenegger is optimistic we’ll soon solve enough of those problems to move from the first to the second half of that history book she imagines. But even if life proves elusive, and getting an answer takes longer and is harder than predicted, she’s happy imagining her work “will allow somebody to do it in the future”. It was important to show in the book how collaborative and interconnected the search for life is, “not just globally, but through time. Ideas vibrate through time and are still influencing what we do and see.” On tough days, she says, she imagines a future cosmonaut on their first mission.“They have this very old, funky star map, as a memento. And the first couple of dots, I made those.”

Alien Earths: Planet Hunting in the Cosmos by Lisa Kaltenegger is published by Penguin at £25. Buy it for £22 at guardianbookshop.com