Yes, exoplanets found me before I found them.
My personal opinion about life that could traverse the galaxy or travel to a distant star system is that it probably has to be nonbiological.
—Sara Seager
Sara Seager is Professor of Planetary Science and Physics, astrophysicist, and planetary scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. She is known for her work on extrasolar planets and their atmospheres.
Seager earned a doctorate in astronomy at Harvard University, at a time when the first reports of exoplanets around Sun-like stars began appearing, and she studied the atmospheres of these so-called hot Jupiter planets. She then joined the cadre of postdoctoral fellows at the Institute for Advanced Study at Princeton University, followed by a stint on the senior research staff at the Carnegie Institution of Washington before making her way back to Harvard.
Her research focuses on the theory, computation, and data analysis of exoplanets. She is Co-Investigator on the MIT-led TESS, a NASA Explorer Mission to be launched in 2017, and chairs the NASA Science and Technology Definition Team for a Probe-class Starshade and telescope system for direct imaging discovery and characterization of Earth analogues. She is a 2013 MacArthur Fellow, the 2012 recipient of the Raymond and Beverly Sackler Prize in the Physical Sciences, and the 2007 recipient of the American Astronomical Society’s Helen B. Warner Prize.
Adolfo Plasencia:
Thank you for having me, Sara.
To start with, I have two questions. The first one is about your education. I read that when you were a child, someone put you in front of a telescope and you looked at the Moon through it for the first time.
Was it a turning point in your life?
Do you remember?
Sara Seager:
Adolfo, I just want to tell you a story. I was teaching astrophysics at a winter school in Guatemala, and many of these students come from all sorts of backgrounds, but they’re not as privileged as we are in North America. I told them a personal story about the Moon. It was a slightly different story but it was amazing because it resonated with all those students, many of whom had had a very similar experience, so the very fascinating thing is that such experience with the Moon is common with people who love astronomy.
Yes, at first I felt like I had nothing in common with the students. It was more the story of the Moon following me and I couldn’t figure out why. And every student just had a huge smile because they realized that the MIT professor from far away is really just like them.
A.P.:
You earned a BSc in mathematics and physics and later a PhD in astronomy. What is your relationship to mathematics? Is it a rational or a logical thing, or is it more related to emotions and passion?
Is it the same with physics?
S.S.:
Well, math for me is just a tool. I use it just as an application to help solve problems; although I know there’s an aesthetic beauty, it’s a challenge for me to reach that level. Physics, on the other hand, is fascinating to me, very phenomenal, because it describes the world around us, and although it’s somewhat disappointing that you have to make many approximations, physics I see as both a tool and a beautiful way to describe the universe.
A.P.:
After completing your undergraduate degree in mathematics and physics, you earned a PhD in astronomy from Harvard University. At that time, exoplanet astronomy was developing very quickly: in 1995 researchers found the first known planet orbiting a Sun-like star. Named 51 Pegasi b, it was about as massive as Jupiter but orbited its star so closely that its surface temperature must have been almost 2,000° Fahrenheit. In 1996 Geoff Marcy, an astronomer at the University of California, Berkeley, along with his collaborator, Paul Butler, discovered six more exoplanets, three of which were also big and broiling. Humanity finally had hard proof that the universe is full of other solar systems, something that until then had been an act of faith in science fiction. You followed these discoveries very closely. Apparently, you—and you later devoted your life to finding them—were found by them, by the exoplanets.
Was it like that? As far as I know, you were doing your PhD work when the first exoplanet was discovered. So exoplanets entered your life even before you made the decision to find them. Is that right?
S.S.:
Yes, that’s a fascinating way of looking at it. In fact, nobody has ever described it in that way. You’re very right: the exoplanets found me. It’s a little bit more like you’re hiking in the forest and you come across a huge mountain. Do you climb the mountain or not? So exoplanets presented me with an opportunity, which I took. Yes, they did indeed interrupt my life, but I had to make a conscious choice to follow the path of exoplanets.
A.P.:
Let’s talk about the “what.” Which features must a celestial object have for us to call it an exoplanet? Can this concept be understood by schoolchildren? I understand there are “gas dwarfs” (mini-Neptunes), up to “super-Earth” planets, with a large mass—ones that predominantly consist of hydrogen and helium, like exoplanet Gliese 581 c. But the term gas dwarves has also been used for planets smaller than gas giants, with hydrogen or helium atmospheres. It sounds complicated, doesn’t it?
S.S.:
The simple way to look at it is that every star in the sky is a sun, and the planets of our Solar System orbit our Sun, just as exoplanets orbit other stars or other suns. We could leave it at that, but I think that what you’re trying to explain is that exoplanets come in all masses and all sizes and there’s literally a continuum from a small rocky planet to a bigger rocky planet, to a small planet with gas, to a bigger planet with gas—and it is, I agree, somewhat complicated. We are struggling a little bit to decide how to define planets, but I think it’s just better to see the bigger picture; that there are planets of all sizes and masses and that nature forms many kinds of planets, and we just simply call an exoplanet a planet that orbits a star other than our Sun.
A.P.:
According to the May 2014 Smithsonian Magazine,
Kepler space telescope scientists announced the discovery of 715 new planets orbiting other stars; the current total is 1,693. (In the 4,000 years from the emergence of Mesopotamian astronomy until the 1990s, scientists found a total of three new planets—two if you are a Grinch and don’t count Pluto.) There may be tens of billions of Earth-sized worlds in our galaxy alone. NASA recently approved TESS, the Transiting Exoplanet Survey Satellite, to identify other worlds around the nearest stars. You [Sara] are involved as a project scientist.1
All this really seemed unimaginable not too long ago.
How can you convince people responsible for budgets that really remote things like exoplanets are relevant to all of us?
S.S.:
It’s not hard to convince anyone in the world at any level how exciting and compelling the search for rocky exoplanets is. In fact, people hardly need convincing to understand how exciting the search for exoplanets actually is. When it comes to a mission like TESS, there’s a competition that unfolds over many years, and one has to have a very compelling scientific case and an airtight technical case, so that’s why TESS was selected by the higher officials at NASA. In general, though, the astronomy community gets together and decides what its priorities are. It’s sort of like a wave passing through matter: more and more astronomers want to work on exoplanets. And it’s a kind of democratic process at some level, deciding which science of which mission gets chosen. However, I think the science of exoplanets is very special because, unlike most fields in astronomy or in science, it generally captures the world’s fascination—and that includes the general public and the higher-level officials managing the budget—like almost no other topic we’ve ever seen before.
A.P.:
Sara, there are many assumptions about the universe: some argue there is just one universe, while others say there are several universes connected to each other.2 The last theory I read describes the universe as being some sort of depiction or a huge hologram. What do you think?
S.S.:
Adolfo, exoplanets used to be like science fiction, but now they’re scientific fact, and their study seems almost practical in comparison to thinking about multiple universes. So my personal opinion is that the multiple-universe study and that of extra dimensions are really more math and philosophy rather than actual astronomy. I think it will be some time, if ever, before we have a way to find real evidence for any universe beyond our own or even what our universe really is.
A.P.:
Is this type of deliberation really worthwhile since it all seems so unreal and impossible?
S.S.:
Yes, absolutely; it is something that should be discussed. I think a great analogy is inflation: we believe that our universe initially had to rapidly expand by something called inflation, which for some was just an idea, a concept worked out mathematically through physics, and recently we’ve begun to think there’s actual evidence in the echoes of the Big Bang. Therefore, some idea today that seems a little crazy needs to be worked through because whatever we think of, nature is always smarter than we are and it may actually have implemented something that is at the limits of our creativity. This said, there may be a time downstream in the future when we can actually prove it so. Yes, definitely, it must be worked on.
A.P.:
And now let’s talk about the “how.” The way some exoplanets were found is incredible. I don’t know if this is right, but it seems that some exoplanets were found without our actually being able to see them. They are celestial bodies with no light and therefore difficult to see with a telescope, yet they were detected thanks to the apparent small oscillation of some star resulting from that planet’s gravitational force. Is this a way used by science to find them?
Can a remote planet that can’t be seen be found?
S.S.:
Well, Adolfo, most planets are seen indirectly. A planet is so small, so less in mass and so faint compared to the big star that it is right next to that it’s nearly impossible to see a planet directly. So, as for most planets that have been discovered, we only see them indirectly, by their effects on their host star. We’ve kind of accepted this to such a degree that we barely even talk about it, so I’m really glad that you asked about that.
A.P.:
You said (please correct me if I’m wrong): “I’m dedicated to finding another Earth, other Earth-like planets or planets that can support life.” Based on this, you are convinced there is life elsewhere in the universe. I have a few questions on this:
What type of life can there be far away from us in the universe?
Michail Bletsas told me he is convinced that in this century there will be nonbiological intelligence, intelligence not based on Homo sapiens.3
Could life on remote planets already be intelligent life? Would it compare to human life as we know it? Would it be biological or nonbiological life?
S.S.:
That’s such a great question and concept. I have to start out by saying that in astronomy, we’re more focused on what we can see and find, and remotely, all we can see are chemicals; we can see the atmospheres of other planets. With future space telescopes we’ll be able to look at the atmospheres of planets the size of Earth and see what chemicals are there; here on Earth, plants and photosynthetic bacteria produce oxygen, and oxygen is a very reactive gas and shouldn’t be in our atmosphere at all, so if we can see oxygen on a planet far away we have a clue that there may be biological life that uses chemistry, that uses chemical reactions to release and store energy. From astronomy we can only search for life that makes some kind of by-product that is chemical, so I think in astronomy we can only look for biological life. My personal opinion about life that could traverse the galaxy, if we are now talking about life that could come to Earth, or in the future, if we’re able to travel to a distant star system, it probably has to be nonbiological because space is very harmful for people. We can barely survive on Earth, if you think about it, and Earth is a very safe, well-designed place for us, or rather we are adapted to our environment. So I think for us initially as human beings to find life elsewhere, it’s bound to be biological, since that’s all we can see; it’s all we know how to do. But if we ever think of traveling through the galaxy or of alien life coming here, then I believe on a personal level that it will be nonbiological.
A.P.:
I’d like to talk to you about a long-term matter. Whatever the case, humankind’s mission to find life is really a very long-term goal. You said it could take “more than a generation, as happened with the construction of the Great Wall of China or Europe’s great cathedrals.” You also said that “we are now fully prepared for it.”4
I suppose you meant scientists and human beings, because some pessimistic voices said that NASA no longer has a long-term mission, a mission that can live up to the challenges that made it necessary.
And there is another corollary: your projects are obviously long-term projects. Young people today need to have instant satisfaction.
Do we live in a world of immediacy? Are today’s young people patient enough to be astronomers?
S.S.:
I’ll answer that question in a couple of different ways. The first is that we have a wonderful new thing happening in the United States. We call it the “private commercial spaceflight world”; there are companies like SpaceX and several others that are going off and doing their own thing, since NASA, as you mentioned, is big, engages in big projects, and has a lot of bureaucracy and risk aversion, so these smaller companies are making access to space cheaper and easier. They want to reduce the cost of going to space by a factor of 100 or 1,000, and that will enable even NASA, for example, to launch much larger telescopes to carry out surveys to find other Earths. So it may actually be easier to go into space sooner than it has been in the last couple of decades.
But now let’s turn to the notion that finding signs of life on another planet could be a project lasting over many generations. I think that we are all hard-wired in a certain way, and even though young people may seem less patient, I believe that there are enough talented, dedicated people out there to carry on the search for other Earths. The way I actually describe this to my students goes like this—and I’m sure it’s true for yourself and others. You have many things going on; it’s the pie chart of investment. Some of them give short-term satisfaction; we all must have these or we can’t get up every day and do our job. Then you have much longer-term tasks that you know are going to take a very long time, so I think that as long as these younger people have a better balanced way of doing things, it will definitely be possible for them to continue.
A.P.:
I’ve been involved in a twelve-year project with 4,600 students. That’s why I see young people this way.
S.S.:
Hopefully they can balance that immediacy. I’m going to have to think about that too, because it’s incredible, really. I mean, I have two children of my own, aged nine and eleven. I got each of my two boys an iPhone because I leave them alone now for short periods of time. I was surprised at the direction things took. For example, they maintain friendships with adults now; they mostly see my friends or my students. When you’re nine, do you have a series of adult friends you can message with? I’m just trying to put that in context. When you think of moving to a technological, biological life—you sort of see that happening now—in one or two generations, kids are practically born with their brains connected, they’re with their friends in constant communication. We have to think about that more. … I’ll be thinking about these questions after you leave.
We see through people like Elon Musk and the SpaceX Corporation that the younger generation thinks differently. It may seem negative but it has huge positives, and they’re able to get things done in a way that prior generations were not, so perhaps their sense for immediacy may fold over into getting things done more quickly. It’s certainly possible.
A.P.:
It takes less and less time to discover a new exoplanet. Are some of them more exciting than others as far as the possibility of finding life is concerned?
I have been told Kepler-62f is a good candidate in this respect, as it ranks among the top twenty. At 1,200 light-years from Earth, it is one of five planets orbiting the same star. Are you excited about such a remote possibility?
S.S.:
I’d like to backtrack a little and say that, initially, I and others used to know every single exoplanet by its name and features when there were only ten of them; we knew them all. Then, as the years went by, there were too many to remember. If you have one or two children, you remember them, but perhaps if you have so many great-grandchildren it’s as though there are just too many of them to recall. So it’s true that now we have less emotional connection. As for these new planets that are found and are supposedly habitable—we actually don’t know for sure whether they’re habitable—we only know their size and the amount of energy they’re receiving at the upper limit of their atmosphere. We don’t really know what they’re like, we don’t have enough information on them to know if they’re habitable; that’s probably why I wouldn’t get emotional. On the whole, it’s not so much the distance; it’s the idea that our universe and our galaxy are full of small rocky planets. We know it for a fact, they are so common—every star must have a handful of them—and it’s emotional to think that every time you look in the sky those stars probably have a rocky planet, whether or not it’s habitable. Some of them actually will be, so the very fact that we’re finding a few of them makes it exciting to think how many of them are actually out there.
A.P.:
You are known for your determination, among many other positive things. I read a very nice story about you in the Smithsonian Magazine article by Corey S. Powell. It was about your very unconventional birthday party thrown at MIT, at the new, elegant extension of the MIT Media Lab, Building E15. You invited a few dozen colleagues, including a prestigious former astronaut and the director of the Space Telescope Science Institute.
You told them you did not want any presents. Well, just one: you asked them to respond to a challenge: to help you “plot a winning strategy to find another Earth,” and do it within your lifetime.
A huge challenge, isn’t it? What a present!
What was the party like? And what was that challenge like? I suppose it is the challenge of your life.
S.S.:
The occasion was my fortieth birthday, which I kind of see as the halfway point in my life, although I do expect to live to be a hundred or older. I did invite all my so-called famous friends. And I asked them to be bold, not like at a regular conference. I gave them a short amount of time to say something important, and I would say that not a single specific thing came out of the conference. It was more a question of momentum building; you had all these people stand up there and say how important it is to find a planet, how they believed that we need to work harder, that we need to focus our efforts. I think it made an important mark on the world, and I had each talk videotaped. You didn’t see the part afterward where we celebrated! That part was not filmed, but the actual talks are filmed so people can go back and look at them. So yes, I have had a growing sense that it is the biggest challenge of my life, you’re correct, to try to find another Earth with signs of life on it. However, I already know that all these people are with me. It wasn’t just the scientists who came and talked at the meeting, it’s also about people like you who are writing about us, the viewers who are listening to us, everybody in the world who wants us to succeed. So although it’s a challenge, we believe it’s one that we can meet and for which we have the help of the entire world.
A.P.:
Sara, thank you for your words.
S.S.:
Thanks, Adolfo, for this great conversation.