What does the discovery of the possibly habitable exoplanets around Trappist-1 mean? What could we be seeing out there when we look at the night sky? And how might this change our idea of our existence in the grand scheme of things?
We spoke with Professor Sara Seager, astrophysicist and planetary scientist at MIT about how to explore the night sky and what possibilities that might bring.
This program is part of the project “Science Education for Jewish Professionals,” a series of webinars run by in partnership the American Association for the Advancement of Science Program of Dialogue on Science, Ethics and Religion, in partnership with Sinai and Synapses, hosted by Clal – The National Jewish Center for Learning and Leadership, and funded by the John Templeton Foundation.Read Transcript
Rabbi Geoff Mitelman: Welcome, everyone, to the first of three webinars for Science Education for Jewish Professionals. My name is Rabbi Geoff Mitelman, I am the founding director of Sinai and Synapses, which is an organization that bridges the worlds of religion and science. We are incubated at CLAL, the National Jewish Center for Learning and Leadership, and they are our fiscal sponsors and also the hosts of these series of webinars, where we will be looking at a variety of different exciting and important topics from both the scientific world and the religious world, starting today with a question of “Are We Still Special If We Are Not Alone?”
I now want to actually, of course, turn it over to Professor Sara Seager, who is an astrophysicist and a planetary scientist at MIT. When I was doing a little bit of research and making sure that we were up to speed on all these exoplanets, particularly Trappist-1, this new series of exoplanets, that we discovered, if you read the New York Times article about this a couple of weeks ago, Professor Seager was the astrophysicist interviewed there.
She is, as she said in her research, she is trying to find another Earth, and that raises all sorts of fascinating cosmological theological questions. She is a MacArthur Fellow, and so I want to be able to turn it over to her, because she is a brilliant scholar and brilliant presenter and has some very exciting things to be able to share with us this afternoon. So Professor Seager, I’m going to mute myself and turn it over to you right now.
Professor Sara Seager: Thanks Rabbi Mitelman, and I’d like to thank you and Curtis Baxter and Rachel for helping us to be here together today.
So the group asked me to come to you today and to talk about exoplanets. I just want to start out by reminding all of us that every star in our sky is a sun, and so if our sun has planets, Mercury, Venus, Earth, Mars, et cetera, surely those other stars should have them.
So every star in the sky is a sun. And did you know that astronomers believe that every each of those stars has planets? So the next time you go out to the night sky, and I know even in New York City you can see a handful of stars, you should be able to wonder, like, what kind of planet is around that star? And that’s what I wonder when I look at the night sky, and I wonder, do any of those stars have planets around them? And might there even be intelligent beings there, looking out at their night sky and wondering the same about us?
So to get started, I have this software here, it is called Eyes on Exoplanets, and Rabbi Mitelman said that you can download the talk later or you can access the webinar archive, and you can, each of you, can download this. You can pass it on to your friends and family in your congregation. And I have a video clip from this website. It’s not mine, it’s made by NASA, so it’s available for everybody, and I’m going to walk you through a little bit of it.
So here it’s showing you – this is just an artist’s conception right now – but the software rapidly takes you to a real map of the sky. Each one of these little white points is a known star, and each of these other highlights are stars with no planets. And each of these stars that are highlighted, either yellow, red or white, are just different star types. So this software actually has shown you each of the highlighted stars are stars with known planets.
Now at the top, you can’t see it because it may be blocked, but you can go to Earth and go to any point on Earth and see what the night sky looks like from that point. And here it’s showing you how the sky would look from the west coast of North America. Now admittedly, you’d need binoculars to be able to see all of these stars, the constellations are overlaid here, but I just wanted you to appreciate how many stars have planets. On any given night, you can look out in the night sky, and you can be sure that some of those have known planets and the rest of the stars likely have planets as well.
Now there’s one very special patch of our sky, I wonder if any of you know what this patch is. It’s not really special in any way other than that a space telescope called Kepler, the Kepler space telescope, stared at this patch of sky for four years. And there’d literally be that many known stars with known planets. So in fact, we use the software and download it, if you happen to know the name of the star of the planet you can type it in, and the person who made this little animation clip for me typed in Kepler- 186, and the software will take us to that particular star system. And yeah, you can see all the planets that orbit it.
Here it’s showing you, there are five planets orbiting this star system. There’s another little button here, which shows you the so-called Goldilocks Zone, a region around a star that is heated by a star. A planet will have the right temperature to be not too hot, not too cold, but just right for life. Is this going a little quickly here? Can you read the bottom of my screen, the fine print? Hypothetical visualization of planet. We actually can’t see the planets, like that, that was just simply an artist’s conception to take this animation a little farther.
But my takeaway from here is that you can download this software yourself, go to Earth, go to any position on Earth, and see what types of stars are in the night sky. And these highlighted stars are stars with known planets. And I just wanted you to get a sense of what astronomers know. We know that there are just so many planets out there. Thousands that we know about, and probably billions more.
So out of all these planets, the ones we’re most interested in are the ones that are rocky worlds that are the right temperature to support life. Now, we don’t know of any planets that have signs of life on them. We have not, obviously, met aliens, despite all the Hollywood films that keep cropping up about them. We do know that rocky planets are common, and that there’s a number of planets that are at just the right distance from their star. They’re not too close that they’re so hot, they’re not too far that they’re too cold, but they’re kind of in this just right special zone.
And I’m going to move on to a couple of slides that are a little more technical because I wanted to capture for you the main way that astronomers find planets today. Now you can see at the top, it’s an illustration of the sun, we don’t see any stars like that except our own sun, and do you see the little planet in front of it? That planet is representative of the size of our earth compared to the size of our sun. We can’t resolve the star. All the stars, even to our biggest telescopes, are just a point of light.
Instead, we see what the graph is showing you. If we can monitor the brightness of a star as a function of time, like taking an image every minute, or every few seconds, and we do that day after day, like minute after minute, night after night, day after day, we can sometimes see a little tiny drop in brightness. That little star is just dimmed a tiny, tiny amount by the planet going in front of it. And believe it or not, in this light curve, we call it a light curve, a transit light curve, when the planet transits the star, there is an unbelievable amount of information encoded in that light curve. And there’s been entire – maybe a dozen or two dozen different PhD theses in astronomy written only on the light curve and what you can learn from it. There’s a lot there, but for our purposes today I just wanted you to know, that’s the main way we find planets.
Now I think, I hope that you’ve all heard in the news a couple weeks ago there was a giant, rightly hyped-up exoplanet news announcement about the Trappist-1 planetary system. But I’m going to walk you through it, just in case you hadn’t heard about it. This is like – I just have a couple of technical slides because I wanted you to appreciate what the data looks like. In this particular case, it’s showing you 23 days of data. So if you read across the bottom of the plot, it shows you day one, two, three, four etc all the way to day 23, about. This is a special space telescope called Spitzer which looked at the star that had known planets around it for 20 days in a row.
And if you look now, you can see the relative brightness of star and there are these lines pointing down. Can you see them? They each have a different letter, like C, B, G, D, E. Those are that transit light curve, that little drop in brightness as the planet’s going in front of the star. It looks different than the previous plot, the one I showed you on this page, because this page here, it’s kind of just a three hour, four hour kind of plot. This other one’s 20 days, so it’s getting scrunched together.
But look at all these drops in brightness. Did you know each one of these is some kind of planet? If you see B, this particular planet B, it went around 1-2-3-4-5-6-7-8-9-10-11-12… wow, it went around 14 times in 20 days. That planet has a period of like, one and a half days. Its year is one and a half days. You can look at some other ones, like this planet G here, it has this big drop in brightness, it dropped there, there I guess it drops again here, so maybe that went twice, maybe that has a period of about ten days. But believe it or not, a lot of people stare at these light curves. They use their computers to try to find planets, and a lot more work has to be done other than this graph. Finding that drop in brightness is just a first step, we need a lot of corroborating evidence to see what’s there.
Here’s a little schematic, you didn’t have to understand this plot to understand the rest of my talk, but this particular planet’s star that was in the news, it’s called Trappist-1, and I just wanted you to know that Trappist-1 is nothing like our own sun. It is a star, so it creates energy by fusion, but other than that, it’s so small. This schematic is showing you our sun. If you see our sun in the bottom right, just the little tiny corner of it, just imagine how big our sun is on this to scale here. It’s just giant, right? Like it would probably not fill the room you’re in, but maybe go from like, your floor to your ceiling. That’s how big our sun is according to this plot that’s just showing a corner of it.
Trappist-1 is shown here in orange. It’s so small, it’s almost the same size as Jupiter. It’s a tiny, tiny star, and the reason astronomers focused on this star is because it’s so small. It’s easier to find planets around small stars. And the technical reason in this case is they just block out more light. It’s easier to see that little drop in brightness.
And it’s showing you here in the boxes – can you see my notes here by the way? OK great. So here it’s showing you Mercury, Venus, Earth, Mars, and this little plot here, it’s showing you the Trappist planets. We don’t know anything about them, that’s why they’re all white. Trappist B, C, D, E, F, G, H. Not too inventive naming system. But there you go, there’s a bunch of planets, all about the same size.
And it’s amazing, really, that this one particular star, a very, small, very, very cold, very dim star, has seven planets. It’s huge for us to find that. It’s actually quite unique at the moment. We don’t have any other systems like that. But typically in astronomy or in exoplanets, when we find one type of system, it’s just the tip of the iceberg. There’s likely many more like this out there.
Now the reason this got in all the news all around the world was because a few of these planets, we think, are the right temperature to host life. That a few of them, depending on who you talk to or what your theory is, actually could be in the so-called Goldilocks Zone. And these are a prime candidate for astronomers to look at the atmospheres and to look for signs of life on the planet.
And so the second half of my talk is to tell you how, in the traditional astronomy sense, we are going to search for life on other worlds. And so bear with me here, because we’re not talking about little green aliens, like, waving to us or sending us a radio signal, broadcasting. Anyway, we’re probably talking about bacteria, some kind of life, we won’t know if it’s animal or just bacteria or plants or intelligent aliens, we don’t know. But all it has to do with is looking at the atmosphere.
On our own Earth, actually – we have, our Earth has oxygen in the atmosphere to 20% by volume. That’s a lot. That means every parcel of air you could grab in a box, 20% of that would be oxygen. But did you know that without any life, without photosynthesis from plants or photosynthetic bacteria, we would have basically zero oxygen. So, you know, that’s one of the things we’re looking for. We want to see an atmosphere that has gases in it that shouldn’t belong, like oxygen, ozone, we have actually a whole list of these gases, and that’s primarily what we’re doing. The second thing we want to look for in the atmosphere is water, because all life as we know it needs liquid water. And water vapor in a planet atmosphere, a small rocky planet atmosphere, is actually a sign of liquid water oceans.
So I have just two or three slides now to explain to you how we’re going to look for these signs of life by way of gases that don’t belong. And if you see this figure, this artist’s conception on the left, you see how the atmosphere around this fake planet illustrated is glowing. It’s supposed to illustrate to you that these planets that go in front of the star, not all of them do this, but the ones that are lined up, the star light can shine through the atmosphere. And actually, when that light goes through the atmosphere, the planet atmosphere gases get imprinted on the light itself. They’re actually absorbing light.
And to try to explain that concept further, I’m starting with the rainbow, because hopefully everyone has seen a rainbow. But what you probably don’t know is if you look at the rainbow more closely, if you could look at it in great detail, you would see that tiny parts of the rainbow are missing. And this is a picture of a rainbow, actually it’s our sun’s light, but it’s not broken up, it’s not split up by a raindrop, it’s split up with a special instrument called a spectrograph.
And look at this, in this beautiful rainbow there are all these little pieces missing, little tiny colors are missing. See, some of them are really fat, some are so thin you can barely see it, there’s some here in the blue, some in the red, and each of these actually is a gas, either in the sun itself or in Earth’s atmosphere, absorbing. And when the gas is absorbed, It’s like, I call it colloquially like they’re taking a bite out of the spectrum. You just take the light away.
And astronomers and physicists, we actually literally know not every single line but pretty much every line, we know where it comes from. Each atom or molecule, each gas, has a special fingerprint of lines. And so this is like a whole field of research in many different areas. In fact, most of astronomy relies on spectra to tell us what kind of gases are there and what the gases are actually doing. So on exoplanets, it’s no different. But I’m going to stop short of showing you real data because it would take me a very long time to explain the data and it’s very noisy. We get data from the Hubble space telescope, we get it from ground based telescopes. So far, we haven’t been able to look at small rocky planets.
So here is what I just am going to tell you in this “atmosphere summary” slide: that we need these spectra to learn about the atmosphere. You know, on our Earth, we’re worried about parts per million of carbon dioxide for our climate change here on Earth. But another world may have ten times the carbon dioxide, not just a part per million or 100 parts per million million different, could have a thousand times or double or triple or way more or less, actually. So we feel that we need to see the atmosphere to understand what’s going on.
So for example, if there happened to be intelligent life on the Trappist worlds and they’re looking at our system, they would probably say, you know what, they would have their own press release and they would say look, there’s three habitable planets, Venus, Earth and Mars, because they’re about the same size, at least Venus and Earth are about the same size, the same mass. But we already know they’re very different. Venus is hot enough to melt lead, but our Earth is just a beautiful oasis. So we’d like to be able to see and to identify gases that might be produced by life, such as oxygen, methane and other gases. We can do this in the future with new telescopes that are being built right now and that will launch in the future.
So now just to end up, before we get to our conversation, both technical and theological, I actually wanted to share some of these travel posters with you. So we can’t go there yet, we don’t know what they’re really like, we try to piece things together so NASA made these beautiful travel posters. This one says “Kepler 186f, where the grass is always redder on the other side.” So you are all muted but hopefully you’re smiling or laughing a little, and that’s because, remember, I told you about Trappist-1. It’s a small, very cool, very red star. There’s no sunlight, yellow sunlight, on that planet – those planets would be red light. So people like to speculate – this is not very scientific, but just speculation – are the plants red? Instead of having, you know, plants that are harvesting yellow light, they have to harvest red or infrared light?
This one says, “Experience the gravity of HD 40307g, a super earth.” And here it’s imagining a planet named 40307-G. It has a higher surface gravity than Earth. And maybe you could imagine going there and, you know, skydiving.
“Relax on Kepler-16b, the land of two suns, where your shadow always has company.” And this particular planet, and at least a dozen like it, are known to have two suns. That means they actually orbit two stars, and you would literally see two sunsets.
And finally my last slide and my last poster, this is a little less humorous, but really, “Planet-hop from Trappist-1e.” And they’re imagining that in this new system that was announced last week, where there are seven planets there’s imagine that, look, there’s this child looking out this window and you’re just cruising by, taking a look at the other worlds. It says at the bottom, “voted best ‘hab zone’ vacation within 12 parsecs of Earth.”
So just to summarize, I started out with a software that you could download and look at yourself to try to convey to you that there are thousands of stars with known planets. We call them exoplanets. We don’t know much about them, typically their masses and orbits, and out of all of these we have more evidence that every star in our sky and in our galaxy should have planets.
I then talked about the big announcement from two weeks ago, Trappist-1, a brand new system with seven worlds, seven Earth-sized planets. Then I went on to say we don’t know if they’re Earth-like, we don’t know much about them. But I explain to you how we try to study atmospheres trancing planets, and try to give you hope that for the future, we’ll see things like water vapor on those planets and we might be able to infer that there’s water oceans.
Looking for signs of life is, even though I said it with a very serious face, it’s more sketchy, it’s more challenging, but we may live in a in a world here on earth where, a decade from now, we’ve found many terrestrial worlds with water, and we maybe have some signs of life. So thank you for your attention, I’m going to stop there and turn it back to you, Rabbi Mitelman.
Rabbi Geoff Mitelman: And thank you very much, Professor Seager. Thank you to Curtis, and Se is on as well, from the AAAS. Thank you to the John Templeton Foundation. And thank you to all of you for such a fascinating and inspiring conversation. I got a lot to think about, and hopefully everyone has something to be able to use in their communities, to be able to use science as a Jewish professional. So again, my name is is Rabbi Geoff Mitelman, and thank you again for taking the afternoon with us.