In the wake of Kupe, Zheng He and Cook, a new breed of mostly deskbound adventurers are making incredible breakthroughs in the search for life-supporting planets.
We live in the middle of a golden age of space exploration – most of it by people sitting over computers in their offices, analysing data downloaded from telescopes on Earth or in the far reaches of the galaxy.
Technology has enabled our knowledge of the universe to expand at a rate undreamt of even 50 years ago. There’s every chance that many people who witnessed the first moon landing in 1969 will live to see the discovery of life on another planet. As computing power and the number of techniques for finding planets continue to grow, so does the number of exoplanets – planets outside our solar system – that have been identified.
First, a little arithmetic to give some perspective. It is estimated there are between 200 billion trillion stars, in between 200 billion and 2 trillion galaxies in the observable universe. That’s 200,000,000,000,000,000,000,000 stars. Most of these have planets. In the years since the first exoplanet was confirmed in 1992, we have discovered 5500 planets at last count. If, therefore, there are 200 billion trillion stars, then 5500 is at best 0.00000000000000000275% of the planets that probably exist. So, even though we haven’t yet discovered one capable of supporting life, there are still plenty left to check out.
Out of the past
To understand planets beyond the solar system, we first need to know a lot about this one. Lisa Kaltenegger is an astrophysicist, astrobiologist, and co-founder of the Carl Sagan Institute at Cornell University in Ithaca, New York. Her bio describes her as a pioneer and world-leading expert in modelling habitable worlds and their light fingerprints. She is also the author of more than 100 peer-reviewed research papers, and her recently published book, Alien Earths, is an approachable and inspiring introduction to the search for alien life.
One of Kaltenegger’s main focuses is astrobiology and the history of our own planet. When she began considering the problem of identifying alien Earths, she discovered it was necessary to learn a lot about how this one developed, because that tells us what signs to look for out there.
“When I was working on the Darwin mission at the European Space Agency to find life in the universe,” says Kaltenegger, “it was clear that if we looked for modern Earths, we would miss signs of life. When you look at the Earth through time, life has changed our planet. And that’s the only way I can find life on another planet – if the biosphere didn’t change it, I wouldn’t have anything to look for.”
Which, she explains, is why there is so much about life on Earth in her book. “If you are looking for a carbon copy of modern Earth, even if you have billions of options, you’re probably going to miss it because you are looking for something specifically that went through all the same evolutionary steps.”
If we restricted our search for evidence of life to identifying radio signals from other planets – as was once the case –that could exclude other technologies. In the case of our own planet, for instance, radio signals reflect less than 200 years of our existence.
But if we allow ourselves to look for other signs, such as those in the biosphere, we widen our search to billions of years in a planet’s history. Kaltenegger points out that single-celled organisms have been on this planet for two billion years, “and we have no idea what the evolutionary scale is on other planets”.
“Some planets are younger than us, some planets older than us, because their stars are younger and older. So, it could be that evolution is in different stages. By wanting to find only civilisations we can communicate with, you have bias in your sample from the get-go. But by looking at a wide scale of possibilities, you get a better view of what is out there, and then you can still pick and choose the ones that have more oxygen and thus have a higher chance of having higher advanced multicellular life.”
No time like the present
Daniel Bayliss grew up on a sheep farm in the Wairarapa: clear skies, lots of stars. Now, he’s an assistant professor in the astronomy and astrophysics group of the department of physics at the University of Warwick in the UK. Not so clear skies, still lots of stars. “Most of the research I’m doing is related to a mission called TESS, which is the Transiting Exoplanet Survey Satellite, that’s scanning the whole sky, basically looking for transiting planets,” he says.
“I’m also heavily involved in the NGTS project [Next-Generation Transit Survey] here, in which we have 12 telescopes in the Paranal Observatory in Chile that we use to follow up the discoveries from TESS to catch the next transit.”
At the start of his career, Bayliss kept a ring binder to which he would add a new page of data every time a new exoplanet was found. He doesn’t do that any more.
He is also preparing for Plato (Planetary Transits and Oscillations of stars), which is TESS with higher precision. “Plato’s goal is to find an Earth 2.0, like an Earth-size planet around a sun-like star.”
Bayliss says it has a very good chance of doing that. “It’s not going to be affected by scattered light from the Earth. It’s got a lot of cameras on it, so you build up a lot of signal. It will be able to pick up the dip in the light that you get from an Earth-sized planet passing in front of a sun-like star. But, of course, that only happens once every year. So, that’ll be the hard bit.”
Some planets are very close to their stars and have very short orbits, meaning they can pass in front of them as often as every two days. This makes them much easier to spot than planets like ours that transit once a year.
Bayliss is that rare New Zealander who has actually discovered not just another planet, but a kind of planet that was not believed possible. In 2017, “we found a giant planet orbiting a very low-mass star. NGTS-1b is the planet. That was quite an exciting moment for me, because people didn’t think these low-mass stars could have giant planets like this.”
NGTS-1b is not the only planet Bayliss has caught behaving in ways that planets shouldn’t. Such as an early planet going retrograde, meaning “the star’s spinning one way, the planet’s going the opposite way, [which] doesn’t happen in our solar system where all the planets go in the same direction that the sun spins”.
Then there are recently discovered solivagant, or “rogue”, planets, unattached to any star, and found using “a technique called microlensing, which is probably the New Zealand exoplanet community’s biggest contribution. They’ve done a lot of it at Mt John Observatory in Canterbury. It’s possible that the galaxy is full of these free-floating planets that have got kicked out of their birth environments and are floating through the galaxy without orbiting a star.”
All of which leads Bayliss to observe: “If I had a one-line summary about exoplanets, I would say there’s a huge diversity of them, far more diversity than we see in our solar system. And our solar system is quite diverse.”
Back to the future
Kaltenegger and Bayliss both work from major science centres overseas. Nick Rattenbury explores space from the University of Auckland’s physics department, but has equally far-sighted ambitions.
Unusually for his field, Rattenbury gained his qualifications up to PhD level here before taking up a post-doctoral position as research associate at the University of Manchester. His career rather gives the lie to the notion that you have to get away to get ahead.
Now, he is back where he started. “I came here on a promise that I would work within this field of exoplanets, which is the topic of the research I was doing in Manchester,” says Rattenbury. “Then it became very obvious that New Zealand was suddenly about to become a space nation, one of the very few nations that can produce a Peter Beck, and can then produce a US rocket company operating in New Zealand.”
He has used the example of Beck and Rocket Lab to inspire students, helping to develop a programme for undergraduates to design, build and test-launch a little satellite. The Auckland Programme for Space Systems started in 2016, and the first launch of a satellite was in 2020.
Now, “I want to build New Zealand’s first space telescope for astronomy. This is not a particularly new idea, but it’s something which is just doable. And that telescope would be able to look for atmospheres around exoplanets.”
Advances across the field are supporting Rattenbury’s aim. “When I was an undergraduate, we had nine planets in the solar system. Now we have eight, because we killed Pluto. But we also now have 5000 planets known in our galaxy, which allows us to make statements like there is at least one planet per normal star in our galaxy, which means there are billions of planets out there.”
Which leads to asking what the chances are that life will take hold on a world.
“We can find worlds that are roughly the same size as the Earth, the same mass, possibly even orbiting away from their star at just the right distance, in the so-called Goldilocks zone with just the right temperature. For life to exist on a planet like Earth, we need an atmosphere.” So far as we know, water is still essential for life to develop. Without an atmosphere, there would be no water, because it would burn off.
Spectroscopy lets observers see markers in the spectrum that indicate the presence of particular gases in an atmosphere. It’s hard, he admits. “You have to have a very specialised machine, or be very lucky and choose the right planet.”
But Rattenbury thinks it has great potential because of an experiment being conducted at the University of Colorado. “They’re flying a telescope that is operating in the ultraviolet area of the wavelength spectrum, which is quite hard to work in. But in the ultraviolet, there are interesting lines, which could be caused by interesting atmospheres. The challenge is you have to do that from space, because our atmosphere blocks a lot of the ultraviolet light.
“What we [here in Auckland] can do is put a good enough telescope in a CubeSat – a standardised satellite.” (For more on telescopes and techniques, see Star power below.)
The Colorado project has done this, but Rattenbury thinks he can improve on that. “I noticed the way that they had built their optics was of a particular type where they had to put a round thing into a square box. How do you do that? Well, they cut things off the telescope. And I thought, I’m sure we can do something better. So I started thinking about how we design optics that work in the ultraviolet and which maximise the throughput.”
He’s working on it. “And Peter Beck has said publicly, ‘If the students build it, we’ll launch it.’ That’s one of the advantages that we have as New Zealanders – that we have a patron of space science who says, ‘You do it. I’ll send it.’”
Another, albeit unwitting, contributor to Rattenbury’s thinking is the late American engineer Thomas Midgley Jr, who had more than 100 patents over his career and is notorious for two of them. “One was CFCs, and one was lead in petrol. One guy did two things that managed to screw up the Earth’s atmosphere. But you can detect those things in the atmosphere, and they are not made by nature. They would be made by a technological society that hasn’t worked out that this is a terrible idea.”
Saving planet earth
The kind of telescope Rattenbury envisages launching could detect those chemical signatures, at which point we would have evidence of another technological civilisation in the galaxy. Remembering that the further away we are looking in space, the further back we are looking in time, the question then would be – did the civilisation that, like ours, made these potentially fatal errors find a solution before it was too late? That seems a question well worth asking.
Lisa Kaltenegger agrees that what we learn about other planets could save our own. For instance, if all the older Earth-like planets turn out to have atmospheres full of sulphur dioxide, which comes out of volcanoes, “that does not mean that this will happen to the Earth, but it means that it would be a smart idea to develop a technology to filter it out, just in case it happens to every Earth.”
And there could be an existential message from the aliens themselves: “If you find advanced civilisations everywhere, that will mean we have a high chance to survive as a species”, and might get through our development without destroying ourselves.
Surely all this thinking about a universe of so many possibilities affects how one thinks about the day-to-day? Kaltenegger finds looking at the stars keeps her feet on the ground.
“Sometimes I get grumpy, sometimes things are stressful. But because of this big-picture thinking that I do at work, I make myself stop and look up at the sky and appreciate what an exciting time we are living in. And that makes some of these worries smaller. I’m like, ‘Look over there, there’s actually a star exploding; over there, there’s actually planets being formed.’”
It gives her hope for the future. “I can’t believe we’ve figured this out – all of us together through time. Even if I don’t get to find life on other planets – and I hope I do, but even if not – I’ll build the foundation for the next people to try to do that.
“I find that beautiful sometimes, when life gets so stressed, just to realise that we are here because of everyone who came before us. Before the finals come up, I usually have a lecture where I tell my students: remember, it took the whole universe to make you. You are ancient stardust. I hope the big-picture thinking is actually something I can also give to other people.”
Alien Earths: Planet Hunting in the Cosmos, by Lisa Kaltenegger (Allen Lane, $65) is out now.
Space for both
When there are so many problems that need fixing here on Earth, how can anyone justify investing in planets so far away? It’s the question everyone who works in space exploration faces constantly.
“I usually talk about the fact that sometimes scientists find things that don’t first appear to you, and then, years later, become why your phone works or why GPS works,” says the University of Warwick’s Daniel Bayliss. “People often say, ‘We’d be better to spend our money researching something that saves lives. I agree we should spend money doing that as well. So it’s not an either/or.”
Auckland’s Nick Rattenbury agrees: “Why should we be giving astronomers money when we should be looking for cures for cancer? Why not both? There are already huge pharmaceutical companies funding armies of scientists looking for cancer cures. But people can get excited by big ideas, like how a star is made, how a galaxy has been built up. And these are discoveries that we have made as a weird bag of thinking water on a tiny grain of goop-covered rock around a very ordinary star out of billions in our galaxy.
“If you can capture people’s attention and expand their minds to the point where they fine-tune their ability to query the universe around them, then that person may not end up going and discovering planets, that person might be the person who goes into one of these massive teams and discovers that cure for cancer.”
Easy Acronyms
MOA (Microlensing Observations in Astrophysics), Plato (Planetary Transits and Oscillations of stars), Cute (Colorado University Ultraviolet Transit Experiment), – the exoplanet community has a reputation for being good at coming up with easy-to-use acronyms. Undeserved, according to Rattenbury.
“It really isn’t,” he demurs. “Let me give you an example. One of the principal observatories in the world is in Chile, and it has four unit telescopes that are part of the Very Large Telescope. That’s its name: the Very Large Telescope. The projects coming up next are the ELT, which is the Extremely Large Telescope. And then there’s a proposed one, which is the Overwhelmingly Large Telescope.”
Trust an astrophysicist to keep things in perspective.
Star power
The microlensing technique depends on two stars aligning in such a way that they effectively act like a lens through which we can see planets. “The chance of two stars aligning sufficiently well for this to occur is about one in a million,” says Rattenbury.
In the 1930s, “[Albert] Einstein was asked by a Czech engineer, Rudy W Mandel, who was into this stuff, if it was possible.” Mandel thought Einstein’s theory of relativity meant that it was. “Einstein fobbed him off again and again. And again and again, the engineer just kept on going, saying, ‘Isn’t this true?’ And Einstein eventually admitted, that, yes, it was true, but the chances of it happening were so infinitesimally small as to be practically impossible.
He wrote a paper just to basically shut this guy up. But what he didn’t know then, and we know now, was that we would be able, thanks to advances in computing, to routinely image millions of stars, night after night. So, that makes it very possible, and that is what we are doing.”
lava RAIN
Within the short time we have known that exoplanets exist, we have learnt a lot about some of them. According to Nasa, for instance, on exoplanet HD 189733b, it rains glass (from lava) sideways.
“We have found a lot of planets around two stars, because most stars are not alone,” says astrobiologist Lisa Kaltenegger. “So, there’s two sunsets and sunrises.” And anyone standing on one of those planets would have two shadows.
Then there are the planets where it rains lava. Kaltenegger explains how this works and how we know it: “We know the star, and we know where the planet is in respect to the star. It’s so close, every rock will melt at those temperatures. So, that means there are huge lava oceans on this world. And if that evaporates because it’s so hot, at a certain distance from the surface it will get colder, because you have space around you, so it will form rocks that rain back down on you.”