Ever since humans first looked at the stars and contemplated the existence of other worlds we have asked the question, “Are we alone in the Universe?”
Now, with the discovery of thousands of exoplanets orbiting alien stars and a new generation of huge, Earth- and space-based telescopes coming online, this generation might just be the first that is able to answer that question once and for all.
Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University, is in town to give two lectures at the Adler Planetarium on the search for alien life. The lectures will be simulcast to museums and planetariums around the world.
Below, an edited Q&A with Kaltenegger.
Talk a little bit about the work of the Carl Sagan Institute, where you serve as director. What is the mission?
The Carl Sagan Institute is looking and trying to find signs of life inside the Solar System and out. So we are at this connection between planetary science and everything we know about our Solar System and trying to use that to find signs of life on planets that are not orbiting our sun but others. It is an interdisciplinary institute so currently we have about 27 faculty in 14 different departments and that means we have biologists, chemists, astronomers, physicists, engineers and also science communication professors. And the idea is to generate a forensic tool kit to spot life, if it exists, inside the Solar System and outside.
In terms of the ways that we can search for and hopefully one day identify signs of extraterrestrial life, what are the most promising tools to help you identify those signs?
The most promising method we have right now is when we collect the light from a planet outside our Solar System orbiting an alien sun we can actually see what the atmosphere or the air there is made out of. And if you look at the Earth and you see oxygen with gas like methane at the same time, that indicates that something is producing oxygen in huge amounts and that tells you that there is life on our planet. So we are looking for the exact same thing on another planet. That’s our most robust bio-signature that we have so far—looking at the Earth as a Rosetta Stone and taking what we know of our home planet and then applying it to other ones.
And then we have other interesting bio-signatures—and what we mean by that is that when you look at life on Earth it is not just the plants you see outside on the window, but it’s also some kind of extreme life forms or some algae, things like that. So the color of the planet—and that is a harder measurement to take—but the color of a planet can also indicate what kind of life is on that planet. Of course, under the assumption that life is pretty similar to what we have here, and that’s another whole, really interesting can of worms that you open up. Other people at the Carl Sagan Institute are actually looking at that and asking if you have a place like Titan (Saturn’s largest moon) that is incredibly cold and where you don’t have a water ocean but a methane ocean, how would life have to be to survive there? And so we have a biochemist, with an astronomer and an engineer to try to figure out how that could work.
What do scientists now believe are the prerequisites of life? Water?
I think the current scientific thought is that generally we want to look for water because on the Earth we don’t know of any kind of life that doesn’t need water. That’s our first clue. So we are saying that if we look at all the life on Earth and all of it needs water so that’s what we are looking for. However, having said that, we do understand that life could also be different. But of course we haven’t found life. We haven’t found life on Titan. So we haven’t found any life that doesn’t need water. We can speculate what life could be like in these other conditions, what it could look like ... so in a way it’s in the realm of being a little bit like science fiction but having a lot of science in the fiction.
We are trying to figure out what alternative types of life could look like so that we don’t miss it. So we are trying to make a better tool kit so that it doesn’t just spot the obvious kinds of life but that it can also spot things that are may be not as obvious. The big idea is to try to figure out what kind of environment you need to get life in the first place. We don’t know that. We know roughly what the conditions were on the Earth but it could be that life could actually start under very different conditions or maybe it needs exactly the conditions of the Earth. And that is why we are looking.
It seems like there has never been a better time to be in your line of work. The James Webb Space Telescope is going to be coming online which will be able to surpass even what Hubble was able to achieve. There’s also the discovery of thousands of exoplanets
We are nearly at 4,000.
Remind me. When did we discover the first exoplanet?
The first exoplanet detected around a satellite star was 1995. But the first exoplanet to be a rock around a satellite star was in 2013 with Kepler 62e and f—but people will debate that. From everything that we know, Kepler 62e and f should be smaller enough that they could be (rocky planets) and they are the right distance from there star.
With the next generation of telescopes are we going to be able to directly image planets around other stars?
Absolutely. Basically, with this 40-meter telescope (the Very Large Telescope or VLT being built in Chile) we will be able to actually image planets like the one next to our neighboring star. The planet around Proxima B will be within the limit of what we can image with the VLT. But even if we can’t, even if the light from the star is overshadowing and the planet and the star are too close together, we can actually read what is in the air of that planet by looking at the planet as it transits its star—when it goes in front of its star and part of the light gets filtered through the planet’s atmosphere.
What I usually say is that light travels through the universe and when sunlight hits your hand it’s warm—so light is energy. And so if that energy hits a molecule in the air of another world like oxygen or methane or water—and that specific energy, that color of light, is then missing in the light that gets to our telescope. And by seeing what is missing in the light, I can tell you what molecule it hit in the atmosphere of another planet before getting to me. And this is how I can read the spectral fingerprint of the planet. The missing light is telling me what that light encountered as it travelled to me.
So far we have talked about life. How about intelligent life? What are the most promising ways of detecting signs of intelligent life?
I think the most promising way to do this is to go one step forward. We are looking at these gases in the atmosphere. And with bigger telescopes we can find gases that are less abundant like technological gases. For example Freon that is coming out of our fridges. I think that is probably a straightforward way to go. To finds signs of technologies and if there is enough technology signs of intelligent civilization.
The other way we can do this of course is we can look for radio signals. The trade-off that you are making (if you focus on radio signals) is that we have used radio for a bit less than 100 years and we are already actually moving away from radio. We are using Bluetooth, internet cables, etc., so it seems to be an incredibly short time in the evolution of a species—if they are like ours—where you actually use significant radio signals. It’s very interesting approach. I wish my colleagues the best of luck because I think it’s also courageous. And there’s no dispute, if a signal were to come in that says ‘Hello, my name is blah blah blah’—there’s no dispute, you would say that’s a sign of intelligent life. But if you do it via gases, my view is that you can find life and then you can build bigger telescopes to learn more about it whether or not they have graduated to the stage of being technology ready.
Your talk at the Adler Planetarium, which is being simulcast to museums and planetariums all over the world, is about the search for life in the universe. The question of whether we are alone in the universe is really an age-old question that has existed since we first looked up at the stars. Do you think we will finally be the generation that is able to answer that question definitely?
Absolutely! If life exists everywhere it can it’s just going to be a couple of years out for us to figure that out. If life is very rare, or it doesn’t produce a unique signature, and what I mean by that is the Earth had life for about 3.5 billion years at least. But in the first 1.5 to 2 billion years it produced methane and carbon dioxide—the problem is that those signatures are not unique because they could also be produced geologically. So if life exists everywhere it can we will be able to spot it with the telescopes we are building.
I don’t think people always appreciate the amazing age of scientific discovery that we are living in.
I completely agree. There are so many bad things in the news but then we are also living in this golden age of discovery where we are figuring out our place in the universe.
If you look at history books in the future, there’s going to be the time before humans learned they were not alone, and after. And we might just live exactly in that generation—there are a lot of indications that say we are because of the discovery of so many exoplanets—we might just be the generation that actually figures that out. That is amazing.
Oct. 26: Viewers on four continents will watch a virtual presentation hosted by Adler Planetarium in early November to learn about the possibility of life on other planets.
Oct. 17: An international team that includes Chicago astronomers recently observed the collision of two high-density neutron stars, a historic discovery that confirms decades of scientific work.
Aug. 25, 2016: A planet that could potentially host life has been discovered orbiting Proxima Centauri, the star closest to our solar system, according to a report published Wednesday by more than 30 international scientists.