SPEAKER_00: 0:15

Welcome to the Where Shall We Me podcast. Our guest this week is Natalie Batalia. Natalie is a professor of astronomy and astrophysics at UC Santa Cruz, where she received her PhD. Previously, she was a research astronomer in the Space Scientist division of NASA Ames Research Center. She held the position of science team lead on the Kepler mission, the first mission capable of finding Earth-sized planets around other stars. This mission revolutionized our understanding of planetary systems.

SPEAKER_03: 0:42

The Kepler mission discovered thousands of exoplanets, revealing that planets are common in the galaxy, not rare, and many even lie within the habitable zone. Natalie is a member of the American Academy of Arts and Sciences, and she was listed as one of Time magazine's 100 most influential people in the world in 2017. We talk about where is everyone? aka the Fermi Paradox. What is an exoplanet? The Drake equation, in simple terms.

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The revelation that planets like ours are more common than ever imagined.

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What was the KEP commission? And what did it achieve? Who owns space? Will our alien friends be receptive?

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Can we be trusted to become multiplanetary?

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Unfortunately, we had a couple of technical issues on this recording, but we've done our very best to iron them out, so please bear with us.

SPEAKER_00: 1:35

Let's look through the telescope. Hi, this is Amida Stari.

SPEAKER_03: 1:42

I'm Natasha McElhone, and with us today is Natalie Batalia.

SPEAKER_01: 1:47

Hello.

SPEAKER_00: 1:48

Hi, Natalie. Thanks for taking the time. Hi.

SPEAKER_01: 1:52

So good to have you here. My pleasure. Thank you so much for the invitation.

SPEAKER_00: 1:56

So we're going to talk about exoplanets today and peering into the universe and finding our place within it. To do that, we felt a good starting point would be talking about the Fermi paradox. Where is everyone? Is the question. Maybe you want to talk to us a little bit about the paradox and then tell us what you think about it.

SPEAKER_01: 2:14

Yeah, absolutely. So first a little bit of history. Enrico Fermi was a physicist. In the 1930s, 40s, he was quite well known. He won a Nobel Prize in 1938 for induced radioactivity, his studies on radioactivity. And he worked on the Manhattan Project. So he was at Los Alamos National Lab. And then after the war, he went back to the University of Chicago. But he around 1950, he was visiting Los Alamos National Labs again, and he was walking with a couple colleagues on their way to lunch. And they were talking about recent UFO reportings. And so they were musing about UFOs and they keep walking and they get to lunch and they sit around a table and they're with a bigger group of colleagues and talking about different things now. And in the middle of the discussion, Enrico interrupts and says, But where is everybody? And of course, everybody knew exactly what he was talking about. So they they laughed and the discussion ensued, and he did these back of the envelope calculations there at the lunch table. Say, well, you know, if life is common, then he concludes aliens should have visited us already. And that's how the story came about. And Carl Sagan later published it in one of his books, and it became what we know today as the Fermi Paradox. But I I actually don't think it is a paradox because you know it's pointing out the apparent contradiction that if alien life is common, then where is everybody? But it presupposes that aliens are engaged in this activity of interstellar travel. Or it presupposes that aliens are involved with, you know, trying to communicate with life elsewhere in the galaxy. And I don't think that's a fair assumption. So I don't think we know yet if it's a paradox. Um we are very early in our human endeavor of trying to find evidence of life beyond the solar system. So I think time will tell.

SPEAKER_03: 4:22

I heard you once delineate to two groups. I found it quite helpful, um the pluralists and the rare earthers. Yes.

SPEAKER_01: 4:30

Yeah, this is two opposite ends of a philosophical spectrum. So on the one hand, you know, we don't think that we humans are special. We've had that idea pounded into our brains over and over again as we make mistake after mistake in our scientific pursuits. Uh we are not at the center of everything or of anything, and there is nothing special about our existence. And if you accept that as fact, then you conclude that there must be life elsewhere, especially when you consider that there are hundreds of billions of stars in our galaxy, um, and you know, hundreds of billions of galaxies in the universe. So it would be uh somebody once wrote, a ridiculous waste of real estate if there were not life elsewhere. And so those are what I would call the pluralists, and they would say that yes, certainly there must be life. But on the other hand, on the other end of the spectrum, you have the rare earthers who say, well, that's fine, and certainly here on earth, life got a toehold very early on in its evolution. But life was the evolution of life, and maybe all of these amazing innovations that have occurred along the millennia, along the eons, were enabled by having exactly the right conditions. You had a rock made of exactly the right proportions of elements that led to magnetism and plate tectonics and outgassing and you know, all of the things that make our atmosphere breathable, that make temperatures quite stable, and and make life make this a living world, a world where life could get a global tollhold. And where where this planet could actually become a living world in a global sense. And so the rare earthers, uh I mean, uh Don Brownlee wrote a book on this. He invokes other arguments like our position in the galaxy, or the fact that we have a moon that stabilizes our orbit, or the fact that we have Jupiter out there that's deflecting asteroids from huge collisions with Earth. So, you know, you can go through a lot of different arguments to say that perhaps this is a fluke.

SPEAKER_00: 6:50

If you have a sample of one out of one, really, where you see that life has occurred, obviously everything looks like it was just meant to be, right? There's a way that uh to think about this, and I think Nick Bostrom brought this argument about a great filter, right? If I'm not mistaken, it was him. And so the notion being that maybe it's really rare that bacterial life forms to begin with, or that multicellular forms, or that intelligent life forms, or that actually all civilizations, great filters still being in front of us, actually self-destruct. Where do you find yourself on the spectrum if you have to take an educated guess?

SPEAKER_01: 7:22

Oh goodness. I al I always uh try to take maybe the more hopeful perspective. I I often contemplate that maybe the heyday of life in the Milky Way is in the future.

SPEAKER_02: 7:33

Right.

SPEAKER_01: 7:33

I mean, for example, 70% of the stars in the Milky Way are actually what we call M-type stars. These are very low-mass stars, but they live, they can fuse hydrogen into helium in their cores and remain as stable stars, not for billions of years, but for trillions of years. And they host a lot of planets, we have found. So, you know, maybe there are other interesting things about the M-dwarfs. They are magnetic stars, they have very high magnetic fields, maybe more intense than the magnetic fields we have on our own sun. So they create a lot of charged particles in their solar winds, and people speculate that maybe that has an uh deleterious impact on life, causes a lot of mutations, maybe even you know, gives cancers or destroys life somehow. But you could take the other perspective that maybe those mutations cause evolution to proceed more quickly.

SPEAKER_02: 8:32

Faster, yeah.

SPEAKER_01: 8:33

So yeah, faster, and maybe more innovations, and maybe over trillions of years of doing that, maybe you end up creating things that are more robust, more innovative, more who knows. Right. Um so I find that idea very exciting. Um and it's a more little slightly more positive uh spin on the Great Filter.

SPEAKER_03: 8:57

Unless this is really exhaustive for for you and maybe listeners, I just wondered you've described that kind of a star. What about the other most commonly occurring stars? Is is it worth just telling us they all seem to begin with a letter, the ones that I've heard you mention?

SPEAKER_01: 9:14

Yeah, um stellar classification is uh has a great history. Um, but it results you know, humans like to put things in drawers. We like to classify things. And what we've learned is that nature, in almost all cases, nature is quite continuous. It's it's not discrete. You can't neatly put things in drawers. Um, nevertheless, we try because it helps to give us um insights into what's out there. And what the astronomers in the early 1900s were doing were looking at the light from stars, um, splitting that light up into a rainbow and looking at different characteristics of the light. How much red light, how much blue light, what light's missing? And they see patterns in what that's called a spectrum. I'll use that word instead of the word rainbow. And so by looking at these spectra, you can see patterns, and you can start to put stars into drawers, and they were assigning letters to these different stars. And they started, of course, with the letter A. And that star had the strongest hydrogen absorption, so an absence of light that was due to hydrogen atoms eating away the photons. And then they went to B, etc., and they started to put stars into drawers like this. Fast forward another 10 years or so, an astronomer named Cecilia Pain Gapotchkin came along and she was analyzing that data together with the latest physics on statistical mechanics and thermodynamics, and she was and quantum mechanics, and she was putting all these equations into a model to simulate the details about the colors that we get from stars. Why do we see these different absences of colors or or presence of colors? Um, and her models came up with the amazing conclusion that the most common element in a star is hydrogen itself, not the not the heavy elements that are so prevalent in the spectrum. Um, and so she reshuffled all of the drawers. And instead of having A stars and B stars, etc., she said actually the hottest stars are the O type stars. And then you have the B type stars, and then you have the A-type stars, and then the Fs and the Gs and the Ks and the M's. So this is her scrambled sequence of drawers that she had put these that they had put these stars into. And so we have this spectral sequence, which is a temperature sequence, which is O B A F G K M, M's being the smallest, coolest, faintest of the stars, but the most populous in the galaxy. Um yeah, and it turned out to be a temperature sequence. So um our Sun is a G-type star. We're kind of in the middle, but in the galaxy, only about 20% of the stars are G-type stars. And if you go to the O's and the Bs, those are the most massive stars. They're very bright, they're very hot. They fuse hydrogen furiously in their cores and they extinguish themselves relatively quickly. They only live for some tens of thousands, hundreds of thousands, maybe a million years at most. Um, and those stars are actually quite rare. And so this is a theme that we actually see in nature quite frequently, that nature makes small things more easily, more readily, more numerous. And as you go to larger and larger things, there are fewer and fewer. We see that with stars, we see that with objects in the solar system, and uh we tend to extrapolate that idea as we're thinking about the occurrence or the frequency of other things in nature as well.

SPEAKER_00: 13:00

And what's the lifespan of our star, the sun?

SPEAKER_01: 13:04

Yeah, it's about 10 or 11 billion years.

SPEAKER_00: 13:07

Got it. So it's 10 or 11 billion years. Earth has been around for four and a half, so we're kind of at the halfway mark for for for this one, right?

SPEAKER_01: 13:15

We are middle-aged, yes.

SPEAKER_00: 13:17

Middle-aged, okay. And when you say you feel like we may be in the early innings of uh the story of life in the universe, and you mentioned that these M stars stick around for like a trillion of years, right? What does that say about the age of the universe right now being what we estimate to be 13.7 billion years? Like we're basically saying we're still babies and we're just really early as life in this universe.

SPEAKER_03: 13:44

Just for the Joe Blogs like me, am I correct in thinking that it's the M stars that are likely to have planets with possible life on them because they're cooler or or no?

SPEAKER_01: 13:54

Well, it turns out that M stars make small rocky planets quite easily. So we have been observing with our space telescopes um quite a high frequency of small rocky planets orbiting M dwarfs. But whether or not something, a planet, a world is potentially habitable depends on the energy equilibrium, like how much how much warmth is it getting from its central star. The idea of the habitable zone that it's orbiting at just the right distance where liquid water could potentially pool and be in liquid form on its surface, on the surface of that planet. So you can have that situation around a G star too. You'd but its G stars are a brighter campfire, so you have to back away. Yeah, an M star is a tiny weak little campfire. You cozy up next to it to be potentially habitable.

SPEAKER_00: 14:51

Yeah. And so in in terms of the age of the universe, you're thinking we're just like a fluke because we're really early and life popped up here at the earliest possible time. Because I, as far as I understand, uh um the elements have been around since uh a billion years into the existence of the universe that that make us up, more or less, right?

SPEAKER_01: 15:10

Well, this is an interesting question. Um and and was a puzzle to me when Kepler first launched. Right. So keep in mind that our galaxy is about 11 billion years old. Okay, and the sun is four and a half billion years old. So, you know, we're not the earliest star. The Milky Way had a burst of star formation in the very earliest stages. And and but the thing is that the heavy elements that are necessary for life, and that's elements like carbon, nitrogen, oxygen, phosphorus, sulfur, those elements are forged through fusion in the cores of stars. So the idea is that the very first generations of stars had a lot of hydrogen and helium from the Big Bang, but not a lot of the heavier elements because those require fusion. Okay. So now so in my thinking, I was expecting our spacecraft, Kepler at the time, to find planets orbiting stars kind of like our sun. But one of the first discoveries we made was a rocky planet orbiting a star that is the age of the galaxy itself. So that and that implied that that blew my mind. I I was very surprised. Um now astronomers studying the fusion processes, the rate of star formation, how galaxies form, etc., are telling us that those very first supernovae that go off in the very earliest moments, you're building very massive stars. You've got a lot of gas and dust that's available, and it builds very massive stars, and they they fuse and they die out very quickly, and they enrich the interstellar medium almost immediately. So that the subsequent smaller stars that are forming are already from almost T equals zero, already enriched with enough heavy elements to create a rocky planet. Now, it gets very interesting as you start to look at the small tweaks that can be made. So supernovae that go off produce certain types of, you know, they enrich the interstellar medium with certain types of elements. But there are other violent processes in the galaxy, like the collision of two neutron stars, that can also produce these giant explosions and spew a bunch of heavy elements out into the into the galaxy, they produce slightly different heavy elements. And so the ratio of these abundances can actually have a huge impact on how a planet forms and evolves, it turns out. So if you dial up just a little bit, for example, elements like thorium, which is radioactive and produces a lot of internal heat inside of a planet. But if you turn turn that down a little bit, it's not going to produce as much heat. A planet's not going to be geologically active for for as long. So there's all kinds of really interesting questions about this interplay, this feedback between stellar birth and death and fusion and all of these violent processes and how it enriches the galaxy and what those subsequent generations of planets are going to be like. That's changing.

SPEAKER_00: 18:25

Right. I think you already introduced a lot of terminology here that I find familiar by looking at the Drake equation. Uh, I I think it's maybe a great place to introduce the notion of the Drake equation because you spoke about rate of um star creation, and then obviously you have dedicated your life to figuring out some of those variables of that Drake equation. So it's it's a good guide.

SPEAKER_01: 18:45

The Drake equation is is a wonderful conversation starter. You know, it generates discussion, it generates ideas. And if I can, let me talk a little bit about the history of the Drake Equation as well. So um in the 1950s, like mid-1950s, there was a radio telescope that was constructed in in West Virginia. This is the Green Bank Observatory, an 85-foot dish radio um telescope. And around that time, right after it opened its eyes for the first time, around a year later, there was a paper that was written by two physicists, um, Phil Morrison and Giuseppe Coccone. And the title of the paper was Searching for Interstellar Communication. And so they put forward this idea that with this new technology, we could potentially detect radio transmissions similar to the ones that Earth itself was spewing out into interstellar space. We were transmitting shows like I Love Lucy, for example, and that and the honeymooners, right? And so they turned it around and said, wow, with a big radio telescope, we might be able to hear another civilization transmitting similar signals. So meanwhile, at around the same time that the Green Bank Observatory was opening, there was a young astronomer who had just gotten his PhD named Frank Drake. And he got a faculty position at Cornell University, where Carl Sagan was as well. And he read this paper and he decided to create a project to detect or to listen or to detect radio transmissions, and he observed two stars, Tau Seti and Epsilon Eridoni. These are two relatively nearby stars. And the idea was to see if he could detect any transmissions, which he did not. But he showed that the surge was at least technically feasible and maybe even worthwhile to do. Well, the National Academy of Sciences got wind of this, and as they often do, they convened small think tanks to say, oh, look at this interesting thing that's happening. And they they asked somebody to organize a small workshop to get all of these experts in the same room to talk about this in more earnestness. And this young astronomer Frank Drake was one of the people that was on this organizing committee, and he had to come up with the agenda for this meeting. Um but this had never been done before. This was like the first meeting that was going to talk about SETI searches or the search for extraterrestrial intelligence. And we can circle back to that later. Um so he had to kind of think, well, how am I even going to start the discussion? And so he started writing down all of the different variables that might contribute to whether or not there is life, intelligent life that you can communicate with in the galaxy. Like how many stars are there? How many planets might there be? How many of those planets could be amenable to life or have a suitable environment? How many of those planets actually gave life? Right? Where where life actually got a toehold? Um, and then of course, how what fraction of those are uh intelligent, evolved intelligent life? And then finally he asked himself the question, all right, well, if you do create intelligence, how long does it last? Or if you do create technology, how long does it last? And so he just kind of scribbled this down on a piece of paper and used this as fodder for discussion. And this is actually what became the infamous Drake equation. And I keep wondering, I mean, Frank Drake was um an astronomer here at UC Santa Cruz, and I was a graduate student here at UC Santa Cruz way back when. Now I'm faculty here at UC Santa Cruz, but back then Frank was on the faculty, and he so he was around. He was one of our former deans of science, and he was on my uh qualifying exam committee, which was pretty terrifying, actually. Even though he's a very nice man, I've came to know him very quite well. But I think you know, he would be a little bit amused, probably mostly amused, but also maybe a little chagrined to know that astronomers and the public are using his equation in such a serious way, like writing papers about how it's wrong or how it could be better. But, you know, I say amused because it does it does uh point out that it just stimulates discussion. It gets the conversation going, right? Um, and I think in a way it does catalyze new research pathways. And maybe NASA's Kepler mission is an example of that.

SPEAKER_00: 23:41

We talked about the rate of star formation is the first element, right, of the variables that we want to look at. The second one is how many planets per star, right? And I think these are the two wheelhouses that we're gonna start off with. Maybe you want to comment on that and then we can take a look at it.

SPEAKER_01: 23:59

Yeah, absolutely. Um so an exoplanet is really just a planet, but it's orbiting another star. So exo means outside of, and in this case it means outside the solar system. So um we have been searching using various techniques to find these planets orbiting other stars, and most of those techniques are indirect. That is, we're not taking a telescope like you see in a cartoon and pointing it around, looking around the sky to try and find, you know, aha, there is a planet. Um they are very tiny. They are literally the crumbs dropped on the floor. They're they're the leftovers, they're the detritus, there's like the crumbs that you sweep under the rug. It's the leftovers of of star formation. Um and it's quite poetic, I think, that these little crumbs are where complexity in the universe arises and life and intelligence. Okay, so those are exoplanets. And the first exoplanet orbiting a normal star like our sun was discovered in 1995 at a conference in Florence, and I was a third-year graduate student at the time, and the Keck Teneter telescope in Hawaii had just been commissioned. And my advisor, Steve Vogt, is the person who built the spectrometer, the instrument that spreads light out into its constituent colors for that telescope. And we had this commissioning data that was collected during the engineering run, and it was very interesting, and everybody wanted to see this brand new data that was coming from you know now the world's largest telescope. And so he got invited to go to that conference to give a talk, but he couldn't attend, so he sent me instant. So I was there when Michelle Mayor announced the discovery of the very first exoplanet orbiting a normal star. That was 51 Peg B. Um, but it was a giant planet, you know, like a Jupiter-sized planet. But it was very odd because the planet was orbiting like thirty times closer to its star than Mercury is to our own sun. Mercury being the very closest planet to the sun in our solar system. So it it catalyzed this whole new branch of science. And me sitting in the audience at the time studying stars, because that's what we did, in order to find the planets, you have to observe something weird about the star itself that reveals the presence of an orbiting planet indirectly.

unknown: 26:40

Right.

SPEAKER_01: 26:41

So, in fact, the title of the conference was Cool Stars, Stellar Systems, and the Sun. The planet was not in the title at all. So um so a lot of us were studying stars at that time, and and I had no idea how that discovery was going to change the course of my own life, my pathway and and and the science that it was going to yield over the next couple decades. Uh in fact, we just celebrated the 30th anniversary of that discovery. And you know, that was the first. And today we have about six thousand discoveries, yeah, that have been that have been um identified. Whenever you have big discoveries like this, you can expect that the discourse is going to change, just like it did. Just like it did when Frank Drake pointed his radio dish out. You know, the National Academy of Sciences, oh, what's happening? You know, and it changes the discourse. And or you you have a major new discovery and it changes the way we we think about the next steps. And and so that certainly happened. But but again, that first discovery was a giant planet. And so, you know, a decade goes by and you've got a smattering of new planet discoveries.

SPEAKER_00: 27:59

And how would were they discovered? Um, maybe tell us a little bit about the method then and how the methods changed.

SPEAKER_03: 28:04

The transit method then. Oh yeah. Yeah, yeah, yeah. So is that what is that what started um this new way of trying to measure?

SPEAKER_01: 28:12

Uh so uh no, the very first discovery was um made through a method called the Doppler technique. Uh so uh now again, you're you're looking at the stars. You just there's lots of starlight streaming into your telescope. So you collect this starlight and you can analyze the light. And what they were doing was they were spreading that light out into a rainbow of colors. They were looking at the missing colors, what we call absorption lines, due to the elements that are in the atmosphere that are eating up photons of very specific colors. And for decades before that, they had been playing this game for stars that are in binary systems. So when you have two stars that are gravitationally bound, they are orbiting around their common center of mass. And that means relative to you, they are moving towards you and away from you, towards you and away from you as this orbit proceeds. And if you look at the spectrum, you split up the light into its constituent colors, you see something called the Doppler effect, where these missing colors are actually swaying back and forth to slightly bluer colors, slightly redder colors, slightly bluer colors, slightly redder colors. And the idea is exactly analogous to a fire truck that is driving past you. When it's driving towards you, the frequency is high, you know, and it goes by you, and the tone drops to a lower frequency. The starlight is doing the exact same thing for these binary star systems. Astronomers had been doing this game for decades. And so all we wanted to do in the 1990s was push that down to smaller masses. So you now you imagine you've got a big star and A tiny planet, they're still gravitationally bound. The planet is gravitationally bound to the star. And we know that the planet is orbiting the star, but the star is also orbiting the planet. And in fact, they are orbiting their common center of mass. So the planet is whipping around, but the star is wobbling ever so slightly because the center of mass of that system is very close to the star. And so the Doppler method sought to detect this Doppler motion of the star due to the gravitational tug of the planet in orbit. And that's the same thing.

SPEAKER_00: 30:37

So that's why presumably you only found the big ones first.

SPEAKER_01: 30:41

Exactly. Because the velocity, the star is moving at a velocity that's like a car driving down a freeway. Okay? It's a not a huge velocity, but it's it's detectable quite readily. Not sorry, that was really hard. Like achieving that milestone in the 1990s was extremely challenging. But they were able with modern CCD detectors like what we have in our cell phones that had come online and that was an enabling technology to make all of this possible.

SPEAKER_00: 31:13

Ingenious.

SPEAKER_01: 31:14

So yeah, but yes, you're exactly right. The larger planets were easier to see, the more massive planets, because they torque around the star with a greater force. Um so, you know, we started making more and more discoveries as the decade ensued, and it was kind of felt like stamp collecting, you know. Every new discovery was celebrated, it was in the news, it was a big deal. Um, and most all of these were these very short period Jupiter-sized planets. But it wetted our appetite for finding a planet as small as an Earth. Like, okay, if we can do that, why not push it down to even smaller planets? Like we really wanted to find something that reminded us at least of an Earth. The problem is that an Earth-sized planet orbiting in the habitable zone of a G-type star, it's also inducing a small wobble, but that wobble is the speed of a ladybug crawling on my desk. It's it's really small. So we don't currently I mean, we actually have the technology, we're close to having the technology to do that. The problem is that everything that's going on on the surface of the sun, all the broiling. Yeah, it's causing variations in the Doppler signal that we measure that are larger than the signal of an Earth. So it's it's been very tricky to push the Doppler method down to that precision.

SPEAKER_00: 32:41

So you needed to find a new way.

SPEAKER_01: 32:43

We needed to have a new technique. So now fast forward to um, I guess it was 1999, I get this email from a colleague, Deborah Fisher, who was doing Doppler detection. We were graduate students together. She ended up to be a professor at Yale. And she sends me an email and she says, you know, there's this guy at NASA Ames who is trying a new detection technique. You should give him a call because I think you would be helpful to his team. And so this was Bill Barucki that she was talking about, and Bill Barucki was he was proposing a new method called the transit method. And the idea again, you're collecting light from the star. You bring all that light into your telescope, but in this case, you're measuring the brightness of the star very, very precisely, and you're measuring it every some minutes or you know, two minutes, every thirty minutes, whatever it is, without blinking for a very long time. Just waiting for the small probability that the orbit of a planet around that star will be inclined exactly perfectly. So this planet passes in front of the disk of the star and blocks out some of the light. So in that situ in that scenario, the brightness of the star will momentarily dim and then come back up. And it'll happen again every single time that planet orbits back around. And this is called the transit method. And what Bill Baruchy claimed at the time was that modern instrumentation or detectors, these C C Ds, were able to reach the precision necessary to detect a planet as small as an Earth in that eclipse geometry. Okay.

SPEAKER_02: 34:37

Right.

SPEAKER_01: 34:38

It's very small. Very, very small. It's like a part per 10,000 in brightness. You know, imagine you had 10,000 light bulbs and you just chip one away. Right? That's the change in brightness that you are trying to measure.

SPEAKER_03: 34:51

Uh so is it it's measuring the dips in the dips in lightness then that that happen when a planet passes in front of it. Yeah.

SPEAKER_01: 35:01

Yep, exactly. That's right. And and so that gives us uh a measure of how big the planet is. Because if you have a Jupiter-sized planet, it's gonna take away 1% of the light. But a planet like Earth is a part per 10,000. So it gives us a direct measure of the radius of the planet and we can measure the orbital period of the planet. If we have the orbital period, Johannes Kepler in the 1600s taught us that we can then get the semi-major axis, we know the size of the orbit. And if we know the size of the orbit and we know the temperature of the star, we know what kind of campfire we're we're sitting around and how far away we are from that campfire. And so then we know if a planet is potentially habitable.

SPEAKER_00: 35:44

And do we see, you know, as they pass through, I assume you see the light potentially that comes through the atmosphere of the planet as well. This is also something that leads us to the third variable on the Greg equation.

SPEAKER_01: 35:57

That's right. That's right. And that's what we're doing right now with the James Webb Space Telescope, um, is that second part. These planets that have this very special geometry in their orbits are quite valuable to us. They're teaching us a lot about the diversity of planets in the galaxy.

SPEAKER_03: 36:14

Are they also teaching us about how life on Earth could have begun or or we're not there?

SPEAKER_01: 36:20

Um indirectly, yeah. I mean, I I think that you have the biologists on one side who are thinking, you know, they're really down in the weeds. How did life originate on Earth? Was it RNA? Did you know, did we develop the genetic code first, or did we did we develop the metabolism first? You know, how to harness energy to do work? And where did that happen? Was it in the deep sea thermal vents, or was it in shallow pools on land? You know, they're they're really down in the weeds studying this. They're studying evolution. How did multicellularity start? How do you regulate genes? How do you create limbs or an eyeball or you know, they're they're studying all of these major transitions in the evolution of life on Earth? And then we astronomers, we have our heads in the clouds. We're over there studying the big picture about the cosmos from the Big Bang and the origin of the first atoms to the first molecules and how you can see amino acids in the solar system, you can see nucleic acids in a comet's tail, and you can see, you know, all of these basic building blocks of life that are evolving. Um, and now we're finding planets and um we see how common they are, we see their diversity, we're starting to understand, thanks to NASA's Kepler mission, um, we're starting to understand a lot of the physical processes that lead to that diversity. And so we're kind of working towards the middle to some of these questions that the biologists are starting or are thinking about. Like how how does ecology, how does the ecological environment drive these major evolutionary innovations? And then we're over here saying, oh, look, we've got a lot of different ecological environments that are out there in the galaxy, right? So can you, who's studying the life on Earth, this one example of life that we have, how can you um generalize that to other extreme environments that are out there in the galaxy? And that's kind of where we're meeting in the middle and starting to cross, talk across the aisle to one another.

SPEAKER_03: 38:34

Just to uh pull the lens out for a second, because you were talking about oceans and where life began and it is there a responsibility? Is there you know that propensity of human beings, because we are explorers and we get excited about new frontiers, our ethics always seem to come after or lag behind our, you know, inventions and expansion first, ethics later. Do you have any thoughts about cosmic ecology or stewardship around what we're doing in space? You you know where I'm going.

SPEAKER_01: 39:07

I mean, absolutely. I think about it every day. Well, oh gosh, there's so many stories to tell. Um, so I was at NASA for 20 years working on NASA's Kepler mission, and towards the end of it, as we we determined that planets like Earth are very common. Like on average, you know, the average number of potentially habitable the average number of stars that host potentially habitable planets is like um 0.5. It's like 50% probability of having um a habitable planet based on uh these results. And perhaps the better way to communicate that is um given the number of stars that are in the Milky Way galaxy, given the commonality of Earth-sized planets orbiting in the habitable zone, I can ask the question all right, how far out in the galaxy do I need to look before finding a potentially habitable planet? Okay, how far would I have to go? Or how far is it? Where where is our nearest neighbor? Exactly. And so the way to communicate this to you, so I have those numbers and I can make that calculation. And the way I like to communicate it is to say, all right, let's imagine that we take the Milky Way galaxy and we shrink it down to the size of the continental United States. Okay? And here I am in California, standing with my back against the Pacific Ocean, and I look out across the continent, and I ask myself, where is my nearest neighbor? Where is the nearest potentially habitable planet going to be? And the answer is, I'm here at the UC Santa Cruz campus. The answer is right over here at McHenry Library on campus. Like it's it's like a quarter of a mile away or or less.

SPEAKER_03: 40:55

So that's within still 175,000 years away or something, right?

SPEAKER_01: 41:00

I mean, I don't know what it is, but it's still it's it's going to be less than 10 light years. And in fact, we now know of a planet like that orbiting Proxima Centauri B, which is only four light years away. So well, maybe the number you're giving is like how long it would take us to reach. Yeah, something like that.

SPEAKER_03: 41:19

I mean, I guess what I'm saying is is it our business? I'm just I'm curious about that bigger question of yes. I I want to do both, and I want to zoom go, I know I'm zooming out for a second. What right do we have? Do we have a right? Does our curiosity? I mean, probably we're just looking. I don't know.

SPEAKER_00: 41:35

I don't feel like it's a it's a big deal to just look. We're not doing anything yet.

SPEAKER_01: 41:39

Well, okay, but hold on, hold on. I totally but I'm I hear what Natasha is saying. Yeah, okay. And and that's what I was trying to get at. I I got a little sidetracked, but yeah, but basically that's the what Kepler told us, taught us, and it changed the national discourse in such a fundamental way that I was starting to be contacted by venture capitalists, by you know, people like Yuri Milner, who was creating the breakthrough, breakthrough initiatives. But the one that really impressed me was the venture capitalist. He wanted to do a fintech financial technology thing where every time somebody went to the gas pump, a little bit of the money would be filtered into the search for Earth 2.0. You know, Earth's backup plan. And this just set off all kinds of alarms in my head as I was going through this mental exercise. And so as I was thinking about what to do after Kepler, like what would my legacy be? How would I how would I carry forward the legacy of Kepler? The ethics question was front and center. Like what I wanted to do was to go someplace, do something where everything we learn about the propensity for life in the galaxy circled back to teach us something about the sustainability of life on Earth. You know, I wanted to go someplace where this idea of decolonizing science was at least being talked about. That's the idea that if we do find life, we factor in ethics and we move forward with the premise of doing the least harm. I I think that it has to be part of the dialogue. And so when I decided to come back to UC Santa Cruz and create an astrobiology institute, it was with the understanding that I could spend some of that money on an ethics of space sciences group. And so we have such a group here, we meet every Friday and we read essays, books, philosophy, science fiction, speculative fiction, all kinds of things to just kind of wrap our head around that question that you have raised, Natasha, which I think is very important.

SPEAKER_00: 43:54

Okay, so then let me flip this around. There's this notion of the dark forest theory, right? So we're we're not trying to be all ethical about listening to the universe or the way we're we're looking at these planets and say we would detect a signal on one of those planets. How how would you feel about that? Should we reach out to them? Should we not reach out to them? Uh can could we reach out to them? Um the dark forest theory is something I'm sure you know about. Maybe you can explain that to the listeners briefly.

SPEAKER_01: 44:22

Um I know that it's a reference to the uh three-body problem. Three-body problem, exactly. That's that's the one.

SPEAKER_00: 44:28

Yeah.

SPEAKER_01: 44:28

I I read the first book, not the second. Um yeah, so but but I get the gist of what you're saying. Another question that's similar to that is should we be broadcasting our presence?

SPEAKER_00: 44:42

Correct.

SPEAKER_01: 44:42

Um, you know, I and Stephen Hawking was very famous for instilling fear, saying that we should be afraid of alien species that might want to colonize our planet or or whatever. And there are many, even Octavia Butler has referenced to this, you know, I think in her Xenophobia series, or um, you know, there there are many books that broach this subject as well and and really get into the nuance, the gray area about the ethics, about not just not doing harm, but like minimizing harm. And how do you approach this when it's about your own survival or you know, whatever questions come up? So it's it is very nuanced. Um my personal opinion is that first and foremost we seek knowledge. Like that's the to me is the end all be all. It's the purpose of my existence, it's it's why I'm here. It's Carl Sagan saying, you know, understanding is a form of ecstasy. If I don't have that, what am I doing here?

SPEAKER_02: 45:48

Right.

SPEAKER_01: 45:48

Wha wh why am I here? So I think we are here to seek knowledge, and I think that sometimes that's dangerous. I think that um there's another couple of books that were written by Lubatu, a Chilean author, who explores this, you know, every time, whether it's the Manhattan Project or Th there's so many examples in history where science, I mean AI now or gene editing. Genomics, exactly. All of those things are fraught and and scary and and we can't always predict what's going to happen. And I think that we need to have conversations and it needs to be but I think we have to bring the humanists on board. That's what I think. I think they have to be part of the dialogue. Because you know, our job is to seek knowledge and we don't always think about the implications. So bring the humanists on board, have the conversations, but at the end of the day we keep exploring. And when I think about alien life, it is probably naively, but it's never from a position of fear. I I just I never have that feeling. Um again, maybe it's my naivete, but um, you know, why I I have very Buddhist perspectives about, you know, why worry about something that hasn't happened? Um that said, you yeah, you have as much knowledge and as as you can and you learn from experience. That's that's the other part. You know, we've been there, done that with colonialism, like we learn from our experience and do a little bit better. Yeah, sorry, but I interrupted you.

SPEAKER_03: 47:33

No, no, I was just gonna say, but it's so clear that you are coming from a place of wanting to fill in the gaps of your knowledge base and learn more as you say, that it's a form of ecstasy. I think I don't know if it was Carstagen or someone else, but that thing about curiosity, even he identified humans can be guilty of having curiosity without care from everything you've said and everything I've heard you say before, your curiosity is with um a bucket load of care built in. And I suppose it's months.

SPEAKER_00: 48:03

This is the question whether we can make the same assumption about the aliens. It's very abundantly clear to me that Athlete has that. And so the question is really um, if they weren't able to travel through interstellar space, for instance, they're so advanced, why would they even care? Right? Like, why would they even consider us a threat? And obviously the universe has abundant resources. Why would they want to come here and take our resources away or somehow enslave us or all that is like a naive way for me to think about it, right? Yeah, I think.

SPEAKER_01: 48:34

Do you remember the feeling when social media first came online?

SPEAKER_00: 48:38

Yeah, sure.

SPEAKER_01: 48:39

Like there is something innate in us that drives us to connect. Maybe it's maybe it's related to endosymbiosis, maybe it's related to multicellularity, maybe, maybe in the whole story of the evolution on of life there is some kind of drive to come together knowing that we can do more together than we can do alone. I don't know if that's some there's some kind of evolutionary driver, but there seems to be something there that we can we have more innovations, we can do more if we work together. And and I loved those early days of social media. I loved connecting with other people. Yeah, the early days of social media. It was a really exhilarating feeling, and I have that feeling about extant life. So I think that there is a very fundamental draw to want to connect with whoever else is out there, like ah, we're in this together. We're all it changes our sense of otherness, it's it's profound, it it's so many different deep implications. But you have to consider the energetics of it.

SPEAKER_00: 49:52

Yeah, yeah, exactly.

SPEAKER_01: 49:53

The whole the whole thing that life does is harness energy to do work, to sustain our existence, to work against the second law of thermodynamics, to you know, to stay alive and to do all the interesting things that we do, and we're always inventing new interesting things that we want to do. And so you have to kind of weigh that against that survival and all of those things that you want to do with the cost, the energy cost of like making an interstellar voyage. That said, I think we're going to do it. Like break through breakthrough initiatives is already, you know, supporting the idea of a small sending a postage stamp-sized detector to Proxima Centauri to take a picture using light sales. And you know, uh people are always thinking about innovative. We can already get to the next star within a couple generations.

SPEAKER_00: 50:45

Yeah, yeah. Right?

SPEAKER_01: 50:46

It won't be me who who ends up analyzing the data, but it could be my daughter or her my granddaughter. So um, you know, that's quite feasible, but actually sending humans even to Mars is a whole different question.

SPEAKER_00: 51:01

Yeah, exactly. And so I also don't know if frankly humans, if we were to travel there in our current state, would be taking uh the ethical path and that in first contact interaction, frankly. And so maybe we need a couple more generations to get to the place where we want to put contact.

SPEAKER_03: 51:21

Yeah, I think that's what it is.

SPEAKER_00: 51:23

Yeah, I mean I can't trust another human being. Can I trust an alien?

SPEAKER_03: 51:28

Yeah, I well, it's to your point about colonization, just yeah, it it that we damage other worlds before we even understand them. We push to a frontier because we just have that aspiration, we have that ambition before thinking about the consequences of it. And I wonder now, with all the tools that we have at our disposal, whether we might approach this differently.

SPEAKER_00: 51:52

And that was really killing billions of chickens every year, right? They're uh a species that is like below us and you know they they seem to have some sort of emotional life as well. So it's it's just I don't know if I trust us fully to be super ethical in these circumstances, depending on what we encounter.

SPEAKER_01: 52:11

Right. Yeah, so that that seems clear that we cannot be trusted yet. And I don't see these kinds of conversations happening really at the national level or e let alone the international level. Like I'd love us to be uh, you know, Star Trek prime directive kind of civilization, but we are so I mean, who listens to the United Nations, let alone But NASA does have a guideline from the era that you were talking about, the 90s, where some of your work was beginning.

SPEAKER_03: 52:41

My next question was going to be if if indeed they do, and I don't know how strict those guidelines are or how um international they are, how on earth would you enforce something like that?

SPEAKER_01: 52:51

So NASA has a planetary protection branch that thinks about um solar system exploration, the idea of you know not having forward or backward contamination. So they think very carefully about that. But then I guess I felt really good about that for a long time. But then I saw a car traveling through inner solar space, interplanetary space, with a dummy sitting in the driver's seat and you know, talking about the SpaceX. The Tesla. The Tesla, the red Tesla, yeah. I mean, I felt a certain childlike excitement watching that because it was really amazing to see something earth-made in space like that.

SPEAKER_02: 53:40

Yeah.

SPEAKER_01: 53:40

Um, something so familiar to me. But at the same time, I it was so cringy. Um but but I'm just saying that now we have the corporate sector who's talking about interplanetary exploration, mining asteroids. That was a big one. Um, you know, back in the day, 2013, I went to the to DC to be on a committee or a think tank that was um talking about grand challenges, like what would be the next grand big grand challenge that could be done. We did we did the human genome, for example, that was a grand challenge. Like, what would the next one be? And this is like right after Kepler came up with all of these results about potentially habitable planets. And so I was on the team that was thinking about how to find evidence of life now that we know that it's relatively nearby. But what emerged from that was asteroid menu. That is what emerged as the next big challenge. And it was around the time that the that the politics were that that NASA was trying to foster public private partnerships. Like with SpaceX and you know, all of that. It was when Yuri Milner was creating breakthrough initiatives, like there was so much interest that they were leveraging it. And to be fair, I like the balance of having a government agency that can rally its entire scientific community to think carefully about what the next big questions are and how to get there. And and they do that through the National Academy of Sciences, and it's all peer-reviewed and it's thoughtful, and and you know, you spend the tax dollars very carefully because you don't want to waste and and all of that. I like to have that balanced with an arm that is can take more risks, you know, that can drive innovation, that can do it for different reasons. I mean, but it's it's gone amuck, in my opinion. Um, and it's lost the ethical arm, which is what started this conversation. Like I don't see the ethical arm in the corporate sector. It's all seems to be, at least from where I'm sitting, driven by commercial needs, etc. So that worries me.

SPEAKER_00: 55:59

Yeah, no, understandably so. And I think actually three-body problem has a good point there. It was just one rogue scientist that in the book is using some device. It's a radio dish. Radio dish, yeah, exactly. A radio dish to send a signal to the sun and amplify it and then send it out to the universe and say, hey, look, come and help us. We're not gonna help ourselves. Like, and so you send that message out to aliens out there. Obviously, they're gonna come with some sort of intention and can't trust you. So people can can do interesting things, and uh, you know, depending on what the message is that goes out that is amplified, it could lead to many different outcomes.

SPEAKER_01: 56:33

But we don't want it to be in the hands of just one person.

SPEAKER_00: 56:37

Exactly, exactly. Yeah, yeah. A rogue scientist should not be able to do that. But let me actually kind of take us to a more positive way um of closing up. Look, I on a daily basis try to remind myself of my place in this universe. I kind of fail on most days um to take steps back from the canvas and understand that we're just like floating around on this mode of dust suspended in a sunbeam on the arm of you know, the Milky Way somewhere in the outer on the cheap seats, basically. Um and and you are looking at this every single day. And I wonder how that makes you feel because you have a very different awareness of our place than I do, or most people do on this planet, and what there is for us to take away from that.

SPEAKER_01: 57:19

Oh, that's a big, big question, Omid. Um I do think about it every day. I think about how I got here, I think about my purpose, I think about the rise of complexity in the universe from the Big Bang to intelligent life. Um studying this really makes me feel like the rise of complexity is just a natural outcome of the laws of physics and that it's you know, it's logical. Stars make exactly the elements that life on earth utilizes for its existence. And, you know, there's so much beauty to that. Um I mean that that knowledge gives the meaning to my life mostly that you know, I'm not religious, but I say that with almost a little bit of um irony because I have faith. I have faith that everything is exactly as it should be. And that's even things like the negative things, the loneliness or the the violence or the illness, or you know, everything is exactly as it should be, and I kind of embrace that. You know, both sides of the coin, the joy and the suffering, all of that. Um I also have a very deep, deep reverence. So I'm using purposely two religious words, yeah. So I also have a very deep reverence for mystery. It's it's everything. It's the mystery is everything. And and I'll just tie that back to the pursuit of knowledge because I think I I live myself with an intentionality that all mystery is ultimately knowable. And I recognize that that assumption might be false. But I choose I live my life as if everything is knowable. And I have that deep reverence for the mystery, and so I I seek knowledge as that my meaning. I mean, we all make our own meaning, that that is my meaning. Um and the the flip side of that is that I have to also embrace the discomfort of not knowing. And this is well, and and the certainty that I'm going to leave this world with more questions left unanswered than answered. And this was really driven home to me one day when I was at a meeting sitting around the conference table was just. Jill Tarter. In fact, she was sitting next to me. Jill Tarter is the woman who was the m inspiration for Carl Sagan's Ellie Arrowway in the movie Contact and his book Contact. She she was a SETI researcher. And um she this was around 20, I don't know, 2013 or so. And we were talking about the future of Kepler and the future of science funding in the country and how we were going to keep the mission going and fulfill its its meet its objective, its science objectives. And she whispered under her breath We didn't find anything. And she was talking about the SETI searches. Like she'd been this was her life's work. Was creating the SETI Institute and and promoting the search for intelligent life, which is a slightly different way of finding life. Um and she was just lamenting the fact under her breath privately, it wasn't meant to be heard. Oh, we didn't find anything. And and I think she, if I remember correctly, she announced her retirement very shortly thereafter. And it it just what I took away from that was, I mean, it was kind of beautiful in a way. I didn't feel a sadness. I felt this recognition that that yes, I am going to all despite everything I'm doing to make all of this science happen, I am going to leave this world with more questions left unanswered than answered. And that's that's like not easy to live with.

SPEAKER_03: 1:01:35

Um it's strange though, because the quality of the questions that she would have been trying to answer mean that the life that she's lived is just so rich.

SPEAKER_01: 1:01:47

Yes, exactly. Yes, absolutely. And that's enough. That that's very meaningful for me because um, you know, I'm getting up in years, I'm starting to think about retirement. My elderly father, who has advanced Parkinson's dementia, lives with us, and we have decided to accompany his unraveling, his returning his stardust to the universe, metaphorically, as Maria Popova would like to say. Um, you know, we're we're there every day watching this, and I think about death all the time. But but you know, I have a daughter who is also working at NASA doing astrophysics, also searching for evidence of life. And so I see this like thread of continuity, and I know that she will oh now I'm gonna tear up, that she will continue to do this work and that it moves forward and that everything you're doing is kind of a chain in the in the one one link in the chain of knowledge. And so it it matters and somehow that mystery and and the knowledge is kind of well, I won't say it's all because I think love is mixed in there some somewhere. But love is all or knowledge is all and I think there you can't have one without the other. Like you need that understanding to have the capability of being a species that loves. Right? The two go hand in hand.

SPEAKER_03: 1:03:15

And not knowing and having mystery and mystery some parts of life, let's say always being mysterious and unanswerable, to me is is the beauty of everything and the balance I'd love to retain, to continue to ask why, but kind of secretly know I'll never find out. It makes it more exciting.

SPEAKER_01: 1:03:36

An endless reservoir of mystery.

SPEAKER_00: 1:03:39

Yeah, there's plenty still to do. Natalie, it was uh pleasure to have you on the podcast. Thanks so much for you playing your role and being that link in the chain that is continuing to do this work. Um, and hopefully your daughter, the generation afterwards, will know a little bit more and all be able to find out more about the meaning of of our lives on this little planet here that we uh call home.

SPEAKER_01: 1:04:05

Thank you for uh for ending on that now.

SPEAKER_03: 1:04:07

Thank you for having me, all the work you do. Yeah, really such a joy to talk to you. Thank you.

SPEAKER_01: 1:04:12

My pleasure.