Paul Rand: The search for alien life is by design the search for habitable planets. That search recently got very, very interesting.

Tape: K2-18b, no, it’s not a character from Star Wars. It’s a planet two and a half times the size of earth and 700 trillion miles away and it could be home to living organisms.

Tape: In a distant corner of our own galaxy, a planet that could have an atmosphere with molecules that on earth only come from life.

Paul Rand: Uncovering science of life in the atmosphere of distant planets is far from easy. It’s an intricate cosmic detective story. Who better to guide us through this interstellar mystery than someone that Chicago magazine dubbed the Planet Hunter. In this article, this Planet Hunter is pictured wearing a rugged coat looking like an Indiana Jones for outer space.

Jacob Bean: I felt a little strange about that. I showed up for that photo shoot wearing just a normal button-down shirt thinking this would be a regular day at work, but instead the artistic directors of the article, they had something very different in mind.

Paul Rand: Well, it worked because it was memorable, and I’m sure you got no end of grief to that from everybody in your world. That probably gave them a lot to play with too.

Jacob Bean: A year later, it still hasn’t ended.

Paul Rand: Okay, well here I am bringing it up again. We’ll keep calling you the Planet Hunter, but in accuracy, you’re not really a planet hunter. You’re more like an exoplanet hunter.

Jacob Bean: Yeah, that’s right.

Paul Rand: Jacob Bean is an astrophysicist at the University of Chicago who spends his time studying the atmospheres of exoplanets.

What is an exoplanet?

Jacob Bean: Exoplanet is just a shortened word, meaning extrasolar planet. What does extrasolar mean? It means outside our solar system. I like to find and study planets that orbit stars other than our sun.

Paul Rand: Bean already has several planet discoveries under his belt, but his name appeared on many people’s radars when he led a team that was the first to detect carbon dioxide on a distant planet,

Jacob Bean: It was the first observation of an exoplanet and boom, just right there, we saw something that we’d never seen before. We saw it at an extraordinary level of confidence that was no ambiguity. Carbon dioxide is a normal gas that’s produced in the atmospheres of terrestrial planets. Seeing that has really, it doesn’t indicate life at all. In fact, it could be quite the opposite, but it shows how this technique works. It was just kind of like this toehold onto these planets, atmospheres that’s like, yes, this is a route that we can follow and we can make these kinds of measurements and deduce what’s in these planets atmospheres in a really unambiguous way.

Paul Rand: This discovery was more than just the first time we had detected carbon dioxide on a distant planet. It was proof of concept that we could use the brand new James Webb Space Telescope to study the atmosphere of the other 5,000 exoplanets that we know of, and possibly many more.

Jacob Bean: I think the question of life on other planets and even in our solar system and beyond, that just goes at that root human desire to understand our place, to provide that sort of meaning. In this day and age when truth is under assault, I would say that truth matters and what we’re doing in astrophysics to learn about the universe is part of that pursuit of truth that enriches our lives and teaches us to see the world in a rational way.

Paul Rand: From the University of Chicago Podcast Network, welcome to Big Brains, the show where we explore the groundbreaking research and discoveries that are transforming our world. I’m your host, Paul Rand. Join me as we meet the minds behind the breakthroughs. On today’s episode, The Search for Alien Life Through the Atmospheres of Exoplanets.

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How does a person become one of the world’s most renowned exoplanet hunters? Well, Bean’s origin story isn’t too dissimilar from many astronomers and cosmologists.

Jacob Bean: Well, like a lot of kids in the eighties and nineties, I grew up with Star Wars and Star Trek. I was interested in math and science. As an undergraduate, finishing my physics degree, I thought I want to go on to graduate school. I think I want to do astrophysics. I’m really interested in this topic called cosmology, which is understanding the formation, origin, evolution of our own universe, big question. I went to my first professional astronomical society meeting and I saw something really unexpected, which were talks about extrasolar planets, about exoplanets. From that moment, it just caught my attention and I really didn’t want to do work on anything else. I forgot about cosmology in a heartbeat.

Paul Rand: While at this point, you’re now seen as, if it’s not being too modest, to say that you’re really considered one of the world leaders in exoplanets. When you first got into the field, there weren’t a lot of folks vying for that title.

Jacob Bean: Yeah and actually I found that a really exciting thing. It was a very new topic. The first exoplanet around a sun-like star was found in 1995 and the field, it had a slow takeoff. Exoplanets are very difficult to discover or were at that time, given technology and what we knew about our observational techniques. Over time, it’s become a real large part of the field of astronomy, but at the time it was not. It was very much outsiders trying to do something really strange and kind of bucking the trend and bucking the conventional wisdom.

Paul Rand: Studying planets light years away takes a fair amount of trend, bucking and crafting of creative ways to find and interpret data. One of the instruments Bean is most famous for inventing is called MAROON-X.

Jacob Bean: MAROON-X is an instrument that was built at the University of Chicago. It’s a planet finding instrument. It’s an instrument that allows us to measure actually the speeds of stars and over time, if a star is orbited by an unseen planet, the speed of the star will change. MAROON-X is installed on an eight-meter telescope on the summit of Mauna Kea, which is an extinct volcano in Hawaii. MAROON-X is exciting because it’s broken a new barrier in terms of precision of making these measurements, which opens up finding smaller planets and planets more distant from their host stars than previous techniques. We’ve made a few initial discoveries with the instrument and we’re looking for planets around the nearest stars that are actually great targets to observe with the James Webb Space Telescope to study them in more detail. It’s really a planet finding machine that sets up James Webb, which is a planet characterization machine.

Paul Rand: When it comes to characterizing planets, the James Webb Telescope has blown away everyone’s expectations.

Is there extraterrestrial life on other planets?

Jacob Bean: Right. The James Webb Space Telescope or JWST for short was the largest space telescope ever built. It can do a lot of different things for astronomy but for the study of exoplanets, its main strength lies in its an ability to characterize the atmospheres of planets. From the standpoint of searching for extraterrestrial life and looking for life on these exoplanets, characterizing the atmosphere is the really key thing that we have to be able to do.

Paul Rand: Okay, can you explain that? Why is the atmosphere the it?

Jacob Bean: If you take a planet like the Earth, if you didn’t have Earth’s atmosphere, the surface of the earth would actually be freezing cold. It would not be suitable for liquid water. If the earth had a different kind of atmosphere, the surface of the earth could be way too hot for surface liquid water. The atmosphere through the impact of the greenhouse effect modulates what the surface temperature is. The composition and the thickness of the atmosphere tells you whether you could actually have life on the planet. Beyond that, the atmosphere can encode what kind of life exists on the planet. For example, oxygen in Earth’s atmosphere is a sign that there’s photosynthetic life here on the earth. That’s something that remote observers with enough precision and sensitivity could see that in Earth’s atmosphere and deduce the presence of life.

For these exoplanets, that’s the thing that we want to be able to do. We want to be able to see the composition and thickness of those atmospheres. We want to be able to calculate what the surface temperature would be on these planets, given the amount of energy they get from their own host stars. Then we want to look at the different chemical species are in the atmosphere and we want to be able to see is there a smoking gun evidence for life among those chemical species.

Paul Rand: When the JWST was first launched, Bean and his team were able to detect for the first time in history, carbon dioxide around a distant star.

Jacob Bean: The way that James Webb Space Telescope explores the atmospheres of exoplanets is by a technique called spectroscopy, which is just spreading the light out into its different wavelengths and seeing which chemical species are absorbing at different wavelengths of light. James Webb was the first telescope that we could use to search for the signature of CO₂ in a planet’s atmosphere. We saw this specific chemical spectral fingerprint of CO₂ in the planet’s atmosphere that we were looking at. That was really exciting because just first of all, it showed the discovery power of the telescope. In the very first data set that we took for an exoplanet, we discovered something new that we had never seen before.

Now on top of that CO₂, even though we detected it in a gas giant-type planet atmosphere, it’s actually a really important gas in the atmospheres of terrestrial planets. The terrestrial planets of our solar system that have atmospheres, so Venus, Earth, Mars, they all have CO₂ in them. They’re real interesting molecule to look for in terrestrial planets. We could see it in this gas giant-type planet really easily. From just extrapolating how sensitive our measurements were, we thought yes, if it exists in terrestrial exoplanets, we could see it in their atmospheres as well. If we can do it for CO₂, we could probably do it for oxygen, we could do it for water.

What is the habitable zone?

Paul Rand: Tell us about what a habitable zone is and why it’s so important.

Jacob Bean: Right. The habitable zone is really the hunting ground for looking for life. It’s based on the concept that the ideal form of life that an astronomer could find, this life that exists on the surface of a planet and for life to exist on the surface, we think it needs liquid water. All life on Earth needs liquid water. Every kind of life, no matter how different it looks, that’s one of the unifying principles of all life on Earth, it uses liquid water. The habitable zone concept is what range of distances can a planet be from a star if it had some conceivable atmosphere such that it would have surface liquid water?

There’s obviously a distance that’s too close to the star, it’s too hot. You could remove the whole atmosphere so there’s no greenhouse effect and it would still be too hot, so no surface liquid water. Then you could be too far away that no matter how thick that you make the atmosphere, you also could not have liquid water. It’s just too cold. It’s this range of distance, this Goldilocks zone if you want, where if you had a terrestrial planet and it had the right kind of atmosphere, boom, surface liquid water would be there and that’s where you could expect to find life.

It’s not to say that life can’t exist in other environments. In our own solar system there are icy moons in the outer parts around Jupiter and Saturn that have subsurface liquid water oceans. We can conceivably explore those, right? We could send a mission there, we could land, we could drill down. Some of them have big cracks in the surface and liquid water spewing out and tidal forces are pumping that water out and geysers are spewing out, and we can chemically analyze those geysers, right? That’s the solar system. Beyond our solar system for extrasolar planets, we can’t study objects in that great of detail. We can’t go there so we need remote observations. It’s a very simple story. We want to look at the atmosphere of a terrestrial planet that has liquid water, and we want to see if there’s a gas in the atmosphere that’s indicative of life.

Paul Rand: What would your reaction be if number one, you found the atmosphere and then actually you found oxygen in that atmosphere?

Jacob Bean: That would be a really exciting discovery because I would have pretty high confidence that that was coming from life. Oxygen in Earth’s atmosphere is created by photosynthetic life. Oxygen is highly reactive. If all photosynthetic life, God forbid, on Earth ceased to exist in this moment, the oxygen would be pulled out of the atmosphere by chemical reactions with surface rocks in just a few 10,000 years. Oxygen is something that has to be continually replenished by life here on the Earth. It’s a type of gas that we call a biosignature gas, something that’s caused by life. If I saw oxygen in the atmosphere of a planet, my questions would be is this a terrestrial planet? Is it a planet in the habitable zone? What other chemical species are present in the atmosphere? What do we know about the star and its history and how it’s irradiated the planet over several billion years more than likely? If we could put all that together, we could have a credible picture of life being on that planet.

Simply the detection of oxygen would already be pretty exciting. Even though there are false positive scenarios for oxygen not being caused by life, those are sort of edge cases. The most likely explanation if we see oxygen in the atmosphere of a terrestrial planet orbiting another star is, there’s life there. I would, at that point, I’d push my chips across the table and say, “I’m all in. This planet’s got life. I’ll bet the house on it.”

Paul Rand: Now, when we talk about there being life, that may not actually be the type of extraterrestrial humanoid-like life that I think people jump to in their imagination, it could be a cellular level of life. Is that right?

Jacob Bean: I think that’s actually most likely. In fact, the presence of oxygen in an atmosphere doesn’t indicate the presence of complex animal life. The oxygen in Earth’s atmosphere is created by fairly simple photosynthetic life. The oxygen in Earth’s atmosphere about 2 billion years ago was first put into the atmosphere by cyanobacteria. Now, oxygen being in the atmosphere makes it possible for complex animal life. We couldn’t have complex animal life here on the Earth without all that oxygen in the atmosphere that’s caused by cyanobacteria, first of all, and then slightly more complex photosynthetic life right now. That would be a really interesting thing would be, okay if we could identify that there’s any kind of life on the planet, what sort of evolutionary stage and level of complexity is it at? We could start asking and answering those questions as well.

Paul Rand: We have already discovered more than 5,000 exoplanets, and the James Webb Telescope is allowing Bean and other astronomers to learn what their atmospheres really look like. There are a number of fascinating planets to explore. That’s after the break.

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One of the successes that came up was when you started looking at the atmosphere of an exoplanet, if I have this right, of GJ 1214 b.

Jacob Bean: Right. It really rolls off the tongue, right?

Paul Rand: It does.

Jacob Bean: It should. You really should know this planet.

Paul Rand: Okay, tell me about this. It is bigger than Earth, but smaller than Neptune. Is that right?

Jacob Bean: That’s right. It sounds like it’s sort of this in-between sized planet that maybe is not very interesting, but it turns out it’s representative of a class of planets that’s the most common kind of planet in our galaxy. 50% of stars, like the sun in our galaxy, have a planet like this, that does not exist in our solar system. The discovery of these objects, which happened around 2010, was a shock. The theorists who calculate models for planet formation did not predict their existence. When they showed up, it’s like, who ordered this? Why this? Then it became like, gosh, they’re so common and they’re really enigmatic because we don’t have a template in the solar system. Since they’re between the Earth and Neptune, you could imagine, well, maybe it’s a smaller Neptune or a bigger Earth. We’ve really been struggling to understand these objects and use pieces of information from a lot of different types of exoplanet research to try to piece together a story of what these objects are and how they form.

Paul Rand: If we talk about all the discoveries that came out, and I’m probably not pronouncing this right, but one of the others stood out was, is it Gliese 486 b?

Jacob Bean: Come on, that’s another one that should just roll off the tongue. Gliese 486 b, everyone knows that, right?

Paul Rand: They will now.

Jacob Bean: Right. That’s a rocky extrasolar planet that I actually helped discover, and it’s become a key target for the James Webb Space Telescope because it’s a terrestrial planet orbiting a very nearby star. It’s very favorable for atmospheric characterization. We’ve been trying to answer this question about whether it has an atmosphere or not.

There were some first observations with the James Webb Telescope indicated that this planet did have an atmosphere and it had a water vapor in its atmosphere. That’d be really exciting. That’s exactly what we’re looking for, but there was speculation that the signal that JWST was measuring for this planet was not from the planet itself. It was actually contamination of the signal from the star. Stars, unfortunately are variable. The measurement technique that we use to probe these planets atmospheres, depends on a certain level of stability and time. My team has done some observations though using a technique that’s much less sensitive to stellar variability. Our observations suggest, unfortunately, this planet is a bare rock, that it doesn’t have any atmosphere at all.

We developed a technique about five, six years ago before the James Webb Space Telescope launched. We asked ourselves what would be the simplest, most robust way for seeing a planet doesn’t have an atmosphere? The first rocky planets that we’re going to look at with JWST, to be honest, we picked the easiest ones. The easiest ones are less likely to have an atmosphere. Let’s start there because it takes less telescope time to do those and then work our way towards cooler objects, less irradiated objects that may have atmosphere.

If your expectation is the planet doesn’t have an atmosphere, the best way to figure that out and to confirm that hypothesis is actually look at the temperature on the day side of the planet. If you measure that, you can do an energy balance calculation that says what’s the maximum possible temperature, and then what’s the cooler temperature that you would get if the planet has an atmosphere that’s reflecting some starlight back out into space and absorbing some of that starlight and distributing it evenly over the planet.

If you go measure the temperature of a rocky planet and it has its maximum possible day side temperature, the feeling is that there’s no atmosphere. That’s what we did for this planet. We measured the temperature, we got about 700 Kelvin. That’s as hot as the planet could be, which means the planet is a bare rock, it’s not going to an atmosphere for reflecting starlight. It’s not transporting heat, it’s just absorbing all the incident starlight and then remitting it back towards us. That’s the infrared light that we see from the planet. We deduce this temperature, it’s very hot. Unfortunately, this planet doesn’t have its atmosphere.

Does Mars have an atmosphere?

Paul Rand: When you find a planet and it doesn’t have atmosphere, are you let down and you say, “Let’s go find the next one,” or how do you think about that?

Jacob Bean: Well, so first of all, it informs just our general understanding of how planets form and retain atmospheres. This retaining the atmosphere is a really key element here because we take for granted that terrestrial planets can have atmospheres. We’re existing here on the Earth. We have a beautiful atmosphere. Our next door neighbor, Venus, also has an atmosphere. If you look farther afield, Mars has a very thin atmosphere. Mercury has no atmosphere at all. The Moon, which is the same distance from the sun as the Earth is, also has no atmosphere. Terrestrial bodies can and can’t have atmospheres. We want to understand what sets that dichotomy between the haves and the have-nots.

The theory that we have is this idea called the cosmic shoreline, which relates how much energy the star puts out that’s incident on the object, on the planet, versus its gravity, which is its ability to hold onto an atmosphere. You’ve got this competition between ability to blast off an atmosphere from high radiation from the star or high gravity, the ability to hold onto an atmosphere. That sets up this dichotomy. That’s our working hypothesis about what separates the haves and have-nots in the solar system. We want to see if that applies to extrasolar planets.

On one hand, it’s disappointing because if the planet Gliese 486 b that we looked at had an atmosphere, that would’ve made all of this so much easier. We’d be like, great, we’re going to start looking for life like today because there it is, it could be there. Our expectation under this cosmic shoreline hypothesis was that it didn’t have an atmosphere based on what we knew about its properties and what its star is. We didn’t actually expect that. It fits this hypothesis. It’s not upsetting from that standpoint. Then it guides us to what we should do next. We should push on to planets that would be on the other side of the shoreline, and there’s where we would expect them, but that will be harder. The reason we did this planet first was it was easy. We did just one little JWST observation with a few hours of telescope time and we could say, “No atmosphere, move on.”

Paul Rand: I was going to ask you about another planet, but I know I’m going to get mocked. Before I do, I want to ask you, how in the world do you guys come up with these names? I’ve going to ask you about K2-18b.

Jacob Bean: Right.

Paul Rand: Let’s start with how in the world do these planets get their names?

Jacob Bean: In a way, it’s very simple. It’s usually a combination of two components. One is the catalog of stars that it is in, and the other is just a number. It’s just a line and a table. For example, to go back to GJ 1214, that’s a catalog named after two German guys who made a catalog of nearby stars almost a hundred years ago now.

Paul Rand: Okay.

Jacob Bean: JG are their initials, and then 1214 is just where it was in this list. It’s just as random as a telephone number.

Paul Rand: Got it.

Jacob Bean: Why do you have the telephone number you have? It’s just random chance. There’s some system, but you don’t know what it is. It’s really unimaginative. As you can tell, it’s orderly. Those of us who studied them, we know these phone numbers to these planets as well as you would know your mom’s phone number, for example, or your home phone number when you’re a kid or your best friend’s phone number.

Paul Rand: Yeah, tell me what was so impressive about K2-18b then?

How far away is k2-18b?

Jacob Bean: K2-18b is an interesting planet.

Tape: In a world more than 120 light years away, scientists say they found the strongest signs yet of extraterrestrial life using the James Webb Space Telescope. The team has detected specific gases on a planet known as K2-18b. Now on Earth, the gases are only produced by living organisms, mainly algae and other microbes. The discovery suggests that the planet may be teeming with microbial life.

Jacob Bean: It’s bigger than the Earth. It’s one of these intermediate-sized planets between the Earth and Neptune. Its amount of radiation it gets from its host star, depending on what its whole structure is, what its atmosphere is, what its interior is, it could have liquid water below a deep atmosphere. As I said, liquid water is that precondition for life. Anywhere in our solar system or in the broader universe where we could find liquid water, that automatically becomes an interesting place for astrobiology. The thing about K2-18b where some chemical species were detected in the atmosphere, that were somewhat indicative that there was this liquid water ocean below the atmosphere.

Paul Rand: An ocean?

Jacob Bean: An ocean, liquid water.

Paul Rand: Wow.

Jacob Bean: It was somewhat indicative of that. There’s two things to remember about this though. One is not everyone agreed that the detection of these certain molecules that were seen, actually indicated in ocean. There were chemical pathways for creating those molecules that didn’t involve liquid water at all. Not everyone agreed on that. The other thing is these measurements were sort of down near the level of the noise, and not everyone agrees that all of these molecules that were initially claimed are actually present there. That’s okay. Nobody should be discouraged or think, oh gosh, these astronomers don’t know what they’re doing. This is a normal part of the scientific process just unfolding.

We found this planet, we started studying it, we saw something interesting, let’s keep studying it. We’ll get more data. Those data have already been obtained. I’m sure people are analyzing them. We’ll increase the signal-to-noise, our sensitivity of our measurements, we’ll see if those molecules are there. At the same time, we’re developing more sophisticated follows that will tell us which molecules that we see in the atmosphere are indicative of a sub-atmosphere, liquid water ocean or not.

What’s really exciting is this is all just unfolding, and the general public honestly can follow it in near real time. This is not science in a textbook that somebody discovered a hundred years ago and you read it and you take it as fact. This is the scientific process unfolding before our eyes with an amazing telescope that our engineers built and our governments with its decades of foresight decided to fund. I think the whole world is part of this story that’s playing out here, and we’re having the fun of seeing does this planet have a liquid water ocean? Could we imagine life existing there? If life is existing, what sort of more subtle molecules is it putting in the atmosphere that we could detect? I think it’s just a fantastic story, but there’s a lot of controversy. Like any interesting scientific discovery, there’s going to be controversy. That’s just playing out right now, and I think it’s a really fun thing to watch.

Paul Rand: Do you look at where you are because James Webb is just a few years old at this point, do you look at it and say, in your lifetime and your team’s lifetime, this is going to be as good as it gets? Do you look at it and say, actually there’s another iteration coming and that next iteration is going to help us do even more?

Jacob Bean: We hope that there’s a next iteration. We hope there’s a few different next iterations.

Paul Rand: Okay.

Jacob Bean: For example, the University of Chicago and other institutions are working to build the next generation of large ground-based telescopes, even bigger than the ones that we have now. Those will be able to advance this field. Then ultimately, another space telescope-

Paul Rand: And the name of that one again is?

Jacob Bean: ... The University of Chicago is involved in the Giant Magellan Telescope project, and there are a couple of other projects also of similar size telescope that other people are working on. Those would really advance this topic. Then ultimately, we want a telescope in space of the similar size of JWST, but that can use a different kind of observational technique and actually image planets. That’s kind of the ultimate goal in the sort of vision that I could have for my lifetime. Having that kind of telescope, imaging planets like the Earth around sun-like stars now, different kinds of stars, and seeing if they have atmospheres, what their atmospheres are made out of, and being able to detect oxygen for those planets that do have atmospheres. That telescope would launch in say, the 2040s. That would sort of round out my own personal career and put a capstone on this journey that I’ve started when I was in my twenties.

Paul Rand: In the meantime, Bean is just excited to continue adding to the growing list of exoplanets left to explore.

Jacob Bean: There’s really two paths for this field discovery of more planets. In my classes that I teach, almost every lecture I show this one two-dimensional plot of planet mass versus separation from the star. You can put all the planets that we know of in one part of that diagram, but there’s vast parts of that diagram they’re just white space because we can’t find planets with our existing technology there. That would be really informative to understand just what’s out there and to understand how planetary systems form and evolve. There’s a constant push to improve planet detection technology, to push into those unexplored parts of the map where there be dragons part of the map. That would give us a more complete picture.

The other is just trying to learn more about these objects because of these 5,000 plus exoplanets that we know of, we only know things like mass, maybe radius, distance from the star. We don’t know these objects’ real worlds. They’re just like point masses to us at this point. For me, the really interesting thing is to get to know these objects and to characterize them in more detail. I see infinite possibilities there, to be honest, in both of these, pushing towards the detection of more planets, characterizing the ones that we’ve been able to find. The study of the solar system planets continues,

Paul Rand: All of this staring up into the stars certainly has an effect on the people looking through these telescopes. Bean himself says it gives him a unique perspective on life that we all should pay more attention to.

Jacob Bean: Well, being an astronomer, it’s unavoidable to not have this sort of cosmic perspective. When we look for planets around other stars, we’re really kind of looking at ourselves reflected in the data. We’re trying to understand place in the universe better. There’s a very famous essay by Carl Sagan called the Pale Blue Dot. This essay was motivated by an image taken by the Voyager 1 spacecraft, where instead of looking at the planets in the outer part of the solar system that it was supposed to be looking at, instead it turned around and took a picture of the Earth. Earth is this blue speck of dust in this vast cosmic landscape.

Carl Sagan: From this distant vantage point, the Earth might not seem of any particular interest, but for us, it’s different.

Jacob Bean: He says it in such eloquent language.

Carl Sagan: That’s here, that’s home, that’s us,

Jacob Bean: It was timely when it was written decades ago, it’s timely today.

Carl Sagan: On it, everyone you love, everyone you know, everyone you ever heard of, every human being who ever was lived out their lives.

Jacob Bean: All the hopes and dreams of humanity.

Carl Sagan: Every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species lived there on the mode of dust, suspended in a sunbeam.

Jacob Bean: All the kind things that we’ve done to each other, all the awful things that we’ve done to each other.

Carl Sagan: Think of the rivers of blood spilled by all those generals and emperors so that in glory and triumph, they could become the momentary masters of a fraction of a dot.

Jacob Bean: It’s all happened there on that speck of dust flying through space in a fraction of the age of the universe.

Carl Sagan: Earth is a very small stage in a vast cosmic arena.

Jacob Bean: The world is always at odds with itself, but we have so much more common with each other than our differences. Our differences are so minor in the vast cosmic landscape that I do wish that more people would come to grips with astronomy and what that’s telling us about our place and about how fragile our place in the universe is, how fleeting it is, and how close we are to each other relative to what’s out there and what’s so different from us. Maybe that’s the perspective that it gives me that I’m confronted with that on a daily basis. It’s not like once a year, I just decide to go to a lecture on astronomy, and I’m like, “Look at all the galaxies.” Every day I’m faced with this.

Matt Hodapp: Big Brains is a production of the University of Chicago Podcast Network. We’re sponsored by the Graham School. Are you a lifelong learner with an insatiable curiosity? Access more than 50 open enrollment courses every quarter. Learn more at graham.uchicago.edu/bigbrains. If you like what you heard on our podcast, please leave us a rating and review. The show is hosted by Paul M. Rand, and produced by Lea Ceasrine and me, Matt Hodapp. Thanks for listening.