David Kipping: Alien Civilizations and Habitable Worlds | Lex Fridman Podcast #355

1. 0:00 – 1:41

   Introduction

   1. DKDavid Kipping0:00

      I think it's actually not that hard to imagine we are the only civilization in the galaxy right now.

   2. LFLex Fridman0:04

      Living.

   3. DKDavid Kipping0:05

      Yeah, that's currently extant. But there may be very many extinct civilizations. If each civilization has a typical lifetime comparable to, let's say, AI is the demise of our own, that's only a few hundred years of technological development, or maybe 10,000 years if you go back to the Neolithic re- revolution, the dawn of agriculture, you know, hardly anything in cosmic time span. Um, that- that's nothing. That's the blink of an eye. And so it's not surprising at all that we would happen not to co-exist with anyone else.

   4. LFLex Fridman0:34

      Mm-hmm.

   5. DKDavid Kipping0:34

      But that doesn't mean nobody else was ever here. And if other civilizations come to that same conclusion and realization, maybe they scour the galaxy around them, don't find any evidence for intelligence, then they have two options. They can either give up on communication and just say, "Well, it's never gonna happen, uh, we just, may as well just, you know, worry about what's happening here on our own planet," or they could attempt communication, but communication through time.

   6. LFLex Fridman1:03

      The following is a conversation with David Kipping, an astronomer and astrophysicist at Columbia University, Director of the Cool Worlds Lab, and he's an amazing educator about the most fascinating scientific phenomena in our universe. I highly recommend you check out his videos on the Cool Worlds YouTube channel. David quickly became one of my favorite human beings. I hope to talk to him, uh, many more times in the future. This is a Lex Friedman podcast. To support it, please check out our sponsors in the description. And now, dear friends, here's David Kipping.

2. 1:41 – 12:01

   Habitable exoplanets

   1. LFLex Fridman1:41

      Your research at Columbia is in part focused on what you call cool worlds, or worlds outside our solar system where temperature is sufficiently cool to allow for moons, rings, and life to form, and for us humans to observe it. So can you tell me more about this idea, this place of cool worlds?

   2. DKDavid Kipping2:00

      Yeah. The history of discovering planets outside our solar system was really dominated by these hot planets. And that's just because of the fact they're easier to find. When the very first methods came online, these were primarily the Doppler spectroscopy method, looking for wobbling stars, um, and also the transit method. And these two both have a really strong bias towards finding these hot planets. Now, hot planets are interesting. The chemistry in their atmosphere is fascinating. It's very alien. Um, an example of one that's particularly close to my heart is TrES-2b, whose atmosphere is so dark it's less reflective than coal. And so they have really bizarre photometric properties, yet at the same time, they resemble nothing like our own home. And so, they said there's two types of astrophysicists, the astrophysicists who care about how the universe works, they wanna understand the mechanics of the machinery of this universe, why did the Big Bang happen, why is the universe expanding, how are galaxies formed, and there's another type of astrophysicist which perhaps, um, speaks to me a little bit more, it whispers into your ear, and that is, why are we here, are we alone, are there others out there? And ultimately along this journey, the hot planets aren't gonna get us there. We- when we're looking for life in the universe, seems to make perfect sense that there should be planets like our own out there, maybe even moons like our own planet around gas giants that could be habitable. And so my research has been driven by trying to find these more treacherous globes that might resemble our own planet.

   3. LFLex Fridman3:35

      So they're the ones that lurk more in the shadows, in terms of how difficult it is to detect?

   4. DKDavid Kipping3:39

      They're much harder. Uh, they're harder for several reasons. The method we primarily use is the transit method, so this is really eclipses. As the planet passes in front of the star, it blocks out some starlight. The problem with that is that not all planets pass in front of their star. They have to be aligned correctly from your line of sight. And so the further away the planet is from the star, the cooler it is, the less likely it is that you're gonna get that geometric alignment. So whereas a hot Jupiter, about 1% of hot Jupiters will transit in front of their star, only about, uh, 0.5%, maybe even a quarter of a percent of Earth-like planets will have the right geometry to transit. And so that makes it much, much harder for us.

   5. LFLex Fridman4:19

      What's the connection between temperature of the planet and geometric alignment, probability of geometric alignment?

   6. DKDavid Kipping4:23

      There's not a direct connection, but they're connected via an intermediate parameter, which is their separation from the star. So-

   7. LFLex Fridman4:29

      Oh, got it.

   8. DKDavid Kipping4:30

      ... the, the planet will be cooler if it's further away from the star, which in turn means that the probability of getting that alignment correct is going to be less. On top of that, they also transit their star less frequently. So if you go to the telescope and you wanted to discover a hot Jupiter, you could probably do it in a week or so, because their orbital period is of the order of one, two, three days. So you can actually get the full orbit two or three times over, whereas if you wanted to detect an Earth-like planet, you have to observe that star for three, four years. And that's actually one of the problems with, uh, Kepler. Kepler was this very successful mission that NASA launched, um, over a decade ago now, I think, and it discovered thousands of planets. It's still the dominant source of exoplanets that we know about. But unfortunately, it didn't last as long as we would have liked it to. It died after about 4.35 years, I think it was. And so for an Earth-like planet, that's just enough to catch four transits. And four transits was kind of seen as the minimum. But of course, the more transits you see, the easier it is to detect it, because you build up signal to noise. If you see the same thing, tick, tick, tick, tick, tick, the more ticks you get, the easier it is to find it. And so it was really a shame that Kepler was just at the limit of where we were expecting it to start to see Earth-like planets. And in fact, it really found zero, zero planets that are around stars like the Sun, their orbits similar to the Earth around the Sun, and could potentially be similar to our own planet in terms of its composition. And so it's a great shame, but, um, that's why it gives astronomers more to do in the future.

   9. LFLex Fridman6:02

      Just to clarify, the transit method-

   10. DKDavid Kipping6:04

       Mm-hmm.

   11. LFLex Fridman6:05

       ... is our primary way of detecting these things.... and what it is, is, uh, when the object passes, occludes the source of light just a tiny bit, a few pixels, and from that we can infer something about its mass and size and distance and geometry and all- all of that.

   12. DKDavid Kipping6:24

       Mm-hmm.

   13. LFLex Fridman6:25

       That's like trying to tell, what? Uh, (laughs) at a party, you can't see anything about a- a person, but you can just see by the way they occlude others. So this is the method.

   14. DKDavid Kipping6:38

       Yeah.

   15. LFLex Fridman6:38

       But this is super far away. How many pixels of information do we have? Basically, how high resolution is the signal that we, um, that we can get about these occlusions?

   16. DKDavid Kipping6:50

       You're right in your description. I- I think, just to build upon that a little bit more, it might be almost like your vision's completely blurry. Like, you have an extreme, you know, eye prescription and so you can't resolve anything, everything just blurs, and – but you can tell that something was there 'cause it just got fainter for a short amount of time. Something- someone passed in front of a light.

   17. LFLex Fridman7:09

       Yeah.

   18. DKDavid Kipping7:09

       And so that light, in your eyes, would just dim for a short moment. Now, the reason we have that problem with blurriness or resolution is just because the stars are so far away. I mean, these are- the closest stars are four light years away, but most of the stars Kepler looked at were thousands of light years away. And so you- there's absolutely no chance that the telescope can physically resolve the star or even the separation between a planet and the star, is- it's too small, especially for a telescope like Kepler. It's only a meter across. In principle, you can make those detections, but you need a different kind of telescope. We call that direct imaging. And direct imaging is a very exciting distinct way of detecting planets, but it, as you can imagine, is going to be far easier to detect planets which are really far away from their star to do that, because that's gonna make that separation really big, and then you also want the star to be really close to us, so the nearest stars. Not only that, but you would prefer that planet to be really hot, because the hotter it is, the brighter it is, and so that tends to buy us direct imaging towards planets which are in the process of forming.

   19. LFLex Fridman8:11

       Mm-hmm.

   20. DKDavid Kipping8:12

       So things which have just formed and the planet's still got all of its primordial heat embedded within it, and it's glowing, we can see those quite easily. But for the planets more like the Earth, of course they've cooled down and so we can't see that. The light is pitiful compared to a newly formed planet. We would like to get there with direct imaging. That's the dream, is to have the pale blue dot, an actual photograph of it, maybe even just a one pixel photograph of it. But for now, the entire solar system is one pixel, with- certainly with the transit method of most other telescopes. And so all you can do is see where that one pixel, which contains potentially dozens of planets, and the star, maybe even multiple stars, dims for a short amount of time.

   21. LFLex Fridman8:51

       It dims just a little bit, and from that you can infer something.

   22. DKDavid Kipping8:54

       Yeah, I mean, it's- it's like being a detective in the scene, right? It's very- it's indirect clues-

   23. LFLex Fridman8:59

       Yeah.

   24. DKDavid Kipping9:00

       ... of the existence of the planet.

   25. LFLex Fridman9:01

       It's amazing that humans can do that. We're just looking out in these immense distances, and looking, you know, if there's alien civilizations out there, like let's say one exactly like our own, we're like, would we even be able to see an Earth that passes-

   26. DKDavid Kipping9:19

       Mm-hmm.

   27. LFLex Fridman9:19

       ... in the way of its sun and slightly dims? And that's the only sign we have of that- of that alien human-like civilization out there, is it's just a little bit of a dimming?

   28. DKDavid Kipping9:29

       Yeah. I mean, depends on the- on the type of star we're talking about. If it is a star truly like the Sun, the dip that that causes is- is 84 parts per million. I mean, that's just- it's like the same as a, um, as like a firefly flying in front of like a giant floodlight at a stadium or something. That's the- kind of the brightness contrast that you're trying to compare to. So it's- it's extremely difficult detection, and in the very, very best cases we can get down to that, but as I said, we don't really have any true Earth analogs that have been in the exoplanet candidate yet. Unless you relax that definition, you say, "It's not- just doesn't have to be a star just like the Sun." It could be a star that's smaller than the Sun, it could be these orange dwarfs or even the red dwarf stars, and the fact those stars are smaller means that, for the same size planet passing in front of it, more light is blocked out. And so a very exciting system, for example, is TRAPPIST-1, which has seven planets which are smaller than the Earth, and those are quite easily detectable, not with a space-based telescope, but even from the ground. And that's just 'cause the star is so much smaller that the relative increase in or decrease in brightness is enhanced significantly, 'cause that smaller size. So TRAPPIST-1E, it's a planet which is in the right distance for liquid water. It has a slightly smaller size than the Earth. Um, it's about 90% the size of the Earth, about 80% the mass. And it's one of the top targets right now for potentially having life. Um, and yet it raises many questions about, um, what would that environment be like? This is a star which is one eighth the mass of the Sun. Its, um... Stars like that take a long time to come off their adolescence.

   29. LFLex Fridman11:08

       Mm-hmm.

   30. DKDavid Kipping11:08

       When stars first form, like the Sun, it takes them maybe 10, 100 million years to sort of settle into that main sequence lifetime. But for stars like these late M dwarfs, as we call them, they can take up to a billion years or more to calm down. And during that period, they're producing huge amounts of X-rays, ultraviolet radiation, that could potentially rip off the entire atmosphere, it may desiccate the planets in the system, and so even if water arrived by comets or something, it may have lost all that water due to this prolonged period of high activity. So we have lots of open-ended questions about these M dwarf planets, but they are the most accessible. And so in the near term, if we detect anything in terms of biosignatures, it's gonna be for one of these red dwarf stars. It's not gonna be a true Earth twin, as we would recognize it as having a yellow star.

3. 12:01 – 23:51

   Alien life in our Solar System

   1. DKDavid Kipping12:01

   2. LFLex Fridman12:01

      Well, let me ask you, I mean, there's a million ways to ask this question, I'm sure I'll ask it, uh, about habitable worlds. Let's just go to our- our own solar system. What can we learn about the planets and moons in our solar system that...... might contain life, whether it's Mars or some of the moons of Jupiter and Saturn. What kind of characteristics, 'cause you said it might not need to be Earth-like-

   3. DKDavid Kipping12:28

      Mm-hmm.

   4. LFLex Fridman12:28

      ... what kind of characteristics might be, we'd be looking for?

   5. DKDavid Kipping12:31

      When we look for life, it's hard to define even what life is. Um, but we can maybe do a better job in defining the sorts of things that life does, and that provides, um, some aspects to, some avenue for looking for them. Um, in the classically, conventionally, I think we thought the way to look for life was to look for oxygen. Oxygen is a byproduct of photosynthesis on this planet. Um, we didn't always have it. Certainly if you go back to the Archean period, um, there was, you know, you have this period called the Great Oxidation Event where the Earth floods with oxygen for the first time and starts to saturate the oceans and then into the atmosphere. And so that oxygen, if we detect it on another planet, whether it be Mars, Venus, or an exoplanet, whatever it is, um, that was long thought to be evidence for something doing photosynthesis. Because if you took away all the plant life on the Earth, the oxygen wouldn't just hang around here. It's a highly reactive molecule. It would oxidize things. And so within about a million years, you would probably lose all the oxygen on planet Earth. So that was, uh, conventionally how we thought we could look for life. And then we started to realize that it's not so simple because, A, there might be other things that life does apart from photosynthesis. Um, certainly the vast majority of the Earth's history had no oxygen, and yet there was living things on it. So that doesn't seem like a complete test. Um, and secondly, could there be other things that produce oxygen besides from life? Um, a growing concern has been these false positives in biosignature work. And so one example of that would be photolysis. That happens in the atmosphere. When ultraviolet light hits the upper atmosphere, it can break up water vapor. The hydrogen splits off to the oxygen, the hydrogen is a much lighter atomic species, and so it can actually escape certainly planets like the Earth's gravity. That's why we don't have any hydrogen or, or very little helium. And so that leaves you with the oxygen, which then oxidizes the surface. And so, um, there could be a residual oxygen signature just due to this photolysis process. So we've been trying to generalize, and, um, certainly in recent years there's been other suggestions of things we could look for in the solar system beyond. Uh, nitrous oxide, basically laughing gas, is a product of microbes. Um, that's something that we're starting to get more interest in looking for. Methane gas in combination with other gases can be an important biosignature, uh, phosphine as well. And phosphine is particularly relevant to the solar system because there was a lot of interest for Venus recently. Um, you may have heard that there was a claim of a biosignature in Venus's atmosphere, I think it was like two years ago now, and the, the judge and jury are still out on that. Um, there was a very provocative claim and signature of a phosphine-like spectral absorption. Um, but it could have also have been some other molecule, in particular sulfur dioxide, which is not a biosignature. Uh-

   6. LFLex Fridman15:24

      So this is a detection of a gas in the atmosphere-

   7. DKDavid Kipping15:27

      Yeah.

   8. LFLex Fridman15:27

      ... of Venus. And, and, uh, it might be controversial on several dimensions. So one, how to interpret that, two, is this the right gas, and three, is this even the right detection? Is this, is, is there an error in the detection?

   9. DKDavid Kipping15:41

      Yeah. I mean, how much do we believe the detection in the first place? If you do believe it, does that necessarily mean there's life there? And, um, what gives, how can you have life in Venus's atmosphere in the first place because that's, you know, been seen as like a hell hole place for imagining life, but I guess the, the, the counter to that has been that, okay, yes, the surface is a horrendous place to imagine life thriving. Um, but as you go up in altitude, the very dense atmosphere means that there is a cloud layer, um, where the temperature and the pressure become actually fairly similar to the surface of the Earth. And so maybe there are microbes stirring around in the clouds which are producing phosphine.

   10. LFLex Fridman16:19

       Mm-hmm.

   11. DKDavid Kipping16:20

       Um, at the moment this is fascinating. It's got a lot of us reinvigorated about the prospects of going back to Venus and doing another mission there. In fact, there's now two NASA missions, VERITAS and DAVINCI, which are gonna be going back in, before 2030 or the 2030s. Um, and then we have a European mission, I think that's slated now, and even a Chinese mission might be coming along the way as well. So we might have multiple missions going to Venus, which has long been overlooked. I mean, apart from the Soviets, there really has been very little in the way of exploration of Venus. That's certainly as compared to Mars. Mars has enjoyed most of the activity from NASA's rovers and surveys. Um, and Mars is certainly fascinating. There's, you know, the signature of methane that has been seen there before. Um, again, there the discussion is whether that methane is a product of biology, which is possible, something that happens on the Earth, or whether it's some geological process that we are yet to fully understand. Could be a, you know, for example, a reservoir of methane that's trapped under the surface and it's leaking out seasonally.

   12. LFLex Fridman17:24

       So the nice thing about Venus is if there's a giant living civilization there, it'll be airborne so you can just fly through and collect samples.

   13. DKDavid Kipping17:34

       Yeah.

   14. LFLex Fridman17:34

       With Mars and, uh, moons of, uh, Saturn and Jupiter, you're gonna have to dig, dig under to find the civilizations...

   15. DKDavid Kipping17:42

       Right.

   16. LFLex Fridman17:42

       ... de- dead or living.

   17. DKDavid Kipping17:43

       Right. And so, yeah, maybe it's easier than for Venus because certainly you can imagine just a balloon floating through the atmosphere, um, that, or a drone or something, that would have the capability of just scooping up and sampling. Um, to, to dig under the surface of Mars is maybe feasible-ish with, you know, especially with something like Starship that could launch, you know, a huge digger basically to the surface and you could just excavate away at the surface. But for something like Europa, um, we really are still unclear about how thick the ice layer is, um, how you would melt through that huge, th- thick layer to get to the ocean. And then potentially also discussions about contamination.... the problem with looking for life in the solar system, which is different from looking for life with exoplanets, is that you always run the risk of, especially if you visit there, of introducing the life yourself. Right? It's very difficult to completely exterminate every single microbe and spore on the surface of your, of your rover or the surface of your lander, and so there's always a risk of introducing something. I mean, to some extent there is continuous exchange of material between these planets naturally on top of that as well, and now we're sort of accelerating that process to some degree. Um, and so if you dig into Europa's surface, which probably is completely pristine, it's very unlikely there has been much exchange with the outside world for, for its subsurface ocean, you are for the first time potentially introducing bacterial spores into that environment that may compete or may introduce spurious signatures for the life you're looking for. And so it's, it's almost an ethical question as to how to proceed with looking for life on, on those subsurface oceans. And I don't think one we really have a good resolution for at this point.

   18. LFLex Fridman19:32

       Ethical. So you mean ethical in terms of concern for the, like, for preserving life elsewhere?

   19. DKDavid Kipping19:40

       Right. Yeah. Yeah.

   20. LFLex Fridman19:40

       Not, not to murder it? As opposed to a scientific one?

   21. DKDavid Kipping19:43

       I mean, we always worry about a space virus, right? Coming, coming here, or, or, you know, some kind of external source, and that we would be the source of that potential contamination.

   22. LFLex Fridman19:51

       Or the other direction.

   23. DKDavid Kipping19:52

       Yeah.

   24. LFLex Fridman19:52

       I mean, they, that, you know, the whatever, whatever survives in such harsh conditions might be pretty good at, uh, surviving all conditions. It might be a little bit more resilient and robust, so it might actually take a ride on us back home.

   25. DKDavid Kipping20:08

       Possibly. I mean, I'm sure, I'm sure that some people would be concerned about that. I think we would, we would hopefully have some containment, uh, procedures, as if, well, if we did sample return. Or, I mean, you don't even really need a sample return. These days you can pretty much send, like, a little micro laboratory to the, the planet to do all the experiments in s- you know, in situ, and then just send them back to your planet, the data. And so I don't think there's, it's necessary, the, especially for a case like that where you might have contamination concerns, that you have to bring samples back. Um, although probably if you brought back Europan sushi, it would probably sell for quite a bit with the billionaires (laughs) in New York City.

   26. LFLex Fridman20:43

       (laughs) S- sushi?

   27. DKDavid Kipping20:45

       Yeah.

   28. LFLex Fridman20:45

       Um, I, I would love from an engineering perspective just to see all the different candidates and designs for, like, the scooper for Venus and the scooper for Europa and, and Mars. I haven't really looked deeply into how they actually, like the actual engineering of collecting the samples, because that's, the engineering of that is probably essential for not either destroying life or, or, uh, polluting it with our own microbes and so on.

   29. DKDavid Kipping21:13

       Mm-hmm.

   30. LFLex Fridman21:13

       Th- that's like an eng- interesting engineering challenge. I usually, for rovers and stuff, focus on the, on the robo- on the sort of the mobility aspect of it, on the robotics, the perception, uh, and the movement and the planning and the control.
4. 23:51 – 27:59

   Starship

   1. DKDavid Kipping23:51

   2. LFLex Fridman23:51

      Yes. The unfortunate fact about physics is the takeoff is easier than the landing.

   3. DKDavid Kipping23:55

      (laughs) Yes. Yes.

   4. LFLex Fridman23:57

      It's easy. And you mentioned Starship. One of the incredible engineering feats that you get to see is the reusable rockets that take off, but they land, and they land, uh, using control, and they do so perfectly, and sometimes when it's synchronous, it's, it's just, it's beautiful to see. And then with Starship, you see the, the chopsticks that catch the ship. I mean, there's just so much incredible engineering. But you mentioned, uh, Starships is somehow helpful here. So what's your hope with Starship? What kind of science might it enable?... possibly.

   5. DKDavid Kipping24:28

      Mm-hmm. There's two things. I mean, it's the launch cost itself, which is hopefully gonna be in per kilograms, gonna dramatically reduce the cost if it's s- sort of the lev- even if it's a factor of 10 higher than what Elon originally promised, this is gonna be a revolution for the cost to launch. That means you could do all sorts of things. You could launch, um, large telescopes, which could be basically like JWST, but you don't even have to fold them up. JWST had this whole issue with its design that it's six and a half meters across, and so you have to, there's no fuselage which is that large. At the time, Aries4 wasn't large enough for that, and so they had to fold it up into this kind of complicated origami, and so a large part of the cost was figuring out how to fold it up, testing that it unfolded correctly, repeated testing, and, you know, the n- there was something like 130 fail points or something during this unfolding mechanism, and so all of us were holding our breath during that process. But if you have the ability to just launch, you know, arbitrarily large masses, um, at least comparatively, compared to JWST, and very large mirrors into space, you can more or less repurpose ground-based mirrors. Um, the Hubble Space Telescope mirror and the JWST mirrors are designed to be extremely lightweight.

   6. LFLex Fridman25:38

      Mm-hmm.

   7. DKDavid Kipping25:39

      And that increased their cost significantly. Um, they have this kind of honeycomb design on the back to try and minimize the, the weight. If you don't really care about weight, because it's so cheap, then you could just literally grab s- many of the existing ground-based mirrors across telescopes across the world, four meter, five meter t- mirrors, and just pretty much attach them to a chassis and have your own space-based telescope. Um, I think the Breakthrough Foundation, for instance, uh, is an entity that has been interested in doing this sort of thing. Um, and so that raises the prospects of having not just one JWST that just, you know, JWST is a fantastic resource, but it's split between all of us, cosmologists, star formation, uh, astronomers, those of us studying exoplanets, those of us wanting to study, you know, the ultra-deep fields and the origin of the first galaxies, the expansionary of the universe. Everyone has to share this resource, but we could potentially each have, (laughs) you know, one, uh, JWST each that is, uh, maybe just studying a handful of the brightest exoplanet stars-

   8. LFLex Fridman26:42

      Mm-hmm.

   9. DKDavid Kipping26:42

      ... and measuring their atmospheres. This is important because if you, you know, we talked about this planet Trappist-1e earlier. That planet, if JWST studied it and tried to look for biosignatures, by which I mean oxygen, um, nitrous oxide, methane, it would take it of order of 200 transits to get even a very marginal what we'd call two-and-a-half sigma detection of those, which basically nobody would believe with, with that, and 100 transits, I mean, this thing transits once every six days, so you're talking about sort of four years of staring at the same star with one telescope. There'd be some breaks, but it'd be hard to schedule much else, because you have to continuously catch each one of these transits to build up your sig- signal to noise. And so JWST is never gonna do that. In principle, technically, JWST could technically have the capability of just about detecting a biosignature on an Earth-like planet around a s- around a non-sunlike star, but still, impressively, we have basically the technology to do that, but we simply cannot dedicate all of its time practically to that one resource. And so Starship opens up opportunities like that, of mass-producing these kinds of telescopes, which will allow us to survey for life in the universe, which of course is one of the grand goals of astronomy.

5. 27:59 – 41:18

   James Webb Space Telescope

   1. DKDavid Kipping27:59

   2. LFLex Fridman27:59

      I wonder if you can speak to the, the bureaucracy, the political battles, the scientific battles for s- for time on the James Webb Telescope.

   3. DKDavid Kipping28:09

      Hm.

   4. LFLex Fridman28:09

      Is n- I, is there a, uh, there must be a fascinating, it's process of scheduling that. All scientists, they're trying to collaborate and figure out what the most important problems are, and there's an interesting network of interfering scientific experiments probably they have to somehow optimize over.

   5. DKDavid Kipping28:26

      It's, it's a really difficult process. I don't envy the TAC that are gonna have to make this decision. We call it the TAC, the Time Allocation Committee, that, that make this decision. Um, and I've served on these before. And it's very difficult. I mean, typically for Hubble, we, we were seeing at least 10, sometimes 20 times the number of proposals for telescope time versus available telescope time. For JWST, there has been one call already that has gone out. We call it cycle one. And that was oversubscribed by I think something like six to one, seven to one. And, uh, the cycle two, which has just been announced, uh, fairly recently, and the deadline is actually end of this month, so my team are totally laser focused on-

   6. LFLex Fridman29:07

      Yes.

   7. DKDavid Kipping29:07

      ... writing our proposals right now. Um, that is expected to be much more competitive, probably more comparable to what Hubble saw. And so it's hard.

   8. LFLex Fridman29:16

      More competitive than the cycle one, you said, already? 'Cause that's already super high.

   9. DKDavid Kipping29:19

      More, more, more competitive in the first cycle.

   10. LFLex Fridman29:20

       Yeah.

   11. DKDavid Kipping29:20

       So I said the first cycle of James Webb was about six to one.

   12. LFLex Fridman29:23

       (laughs)

   13. DKDavid Kipping29:23

       Um, and this will probably be more like 20 to one-

   14. LFLex Fridman29:26

       (laughs)

   15. DKDavid Kipping29:26

       ... I would expect.

   16. LFLex Fridman29:26

       So these are all proposals by scientists and so on, and it's not like you can schedule at any time. 'Cause if you're looking for transit times-

   17. DKDavid Kipping29:34

       Yeah.

   18. LFLex Fridman29:34

       ... uh-

   19. DKDavid Kipping29:34

       You, you ha- you have a, a time critical element.

   20. LFLex Fridman29:36

       Yes. Time critical element.

   21. DKDavid Kipping29:37

       If you're scheduling. Yeah.

   22. LFLex Fridman29:38

       And they're conflicting in non, like, non-obvious ways, 'cause they're, the, the frequency is different, the, the duration is different.

   23. DKDavid Kipping29:44

       Right.

   24. LFLex Fridman29:44

       There's the co- there's probably computational needs-

   25. DKDavid Kipping29:46

       Yeah.

   26. LFLex Fridman29:46

       ... that are different. Uh, the ty- there's the type of sensors, the direction pointing, all that.

   27. DKDavid Kipping29:51

       Yeah. It, it's hard. And there are certain programs like doing a deep field study, where you just more or less point the telescope, and that's pretty open. I mean, you're just accumulating photons. You can just point at that, at that patch of the sky, um, whenever the telescope is not doing anything else, and just get to your month, let's say a month of integration time is your, is your goal over the lifetime of JWST. So that's m- maybe a little bit easier to schedule. It's harder, especially for us looking at cool worlds, um, because as I said earlier, these, these planets transit very infrequently.

   28. LFLex Fridman30:20

       Mm-hmm.

   29. DKDavid Kipping30:21

       ... so we have to wait, if you're looking at the Earth transiting the Sun, an alien watching us, they, they would only get one opportunity per year to do that observation. The transit lasts for about 12 hours, um, and so if they don't get that time, it's hard. You, you, that's it, uh, if it conflicted with another proposal that wants to do, use the, uh, another time-critical element. It's much easier for planets like, uh, these hot, these hot planets or these close-in planets, um, because they transit so frequently there's maybe 100 opportunities, and so then the TAC can say, "Okay, they want 10 transits. There's 100 opportunities here." It's easier for us, to give us ti- to give them time. Um, we're almost in the worst-case scenario. We're proposing to look for exomoons around two cool planets.

   30. LFLex Fridman31:04

       Mm-hmm.
6. 41:18 – 51:34

   Binary planets

   1. LFLex Fridman41:18

      uh, you've written about, uh, binary planets.

   2. DKDavid Kipping41:21

      Yeah.

   3. LFLex Fridman41:21

      What, what's... And that they're surprisingly common. Or they might be surprisingly common. What's the difference between a large moon and binary planets? What, what, what are binary planets? What, uh, what, what's interesting to say here about giant rocks flying through space-

   4. DKDavid Kipping41:38

      (laughs)

   5. LFLex Fridman41:38

      ... and, and orbiting each other?

   6. DKDavid Kipping41:40

      The thing that's interesting about binary objects is that they're very common in the universe. Binary stars are everywhere. In fact, the majority of stars seem to live in binary systems. Um, when we look at the outer edges of the solar system, we see binary Kuiper belt objects all the time, asteroids basically bound to one another. Pluto-Charon is kind of an example of that. It's a 10% mass ratio system. It almost is, by many definitions, a binary planet, but now it's a dwarf planet. So-

   7. LFLex Fridman42:08

      Yeah, it's not-

   8. DKDavid Kipping42:09

      ... I don't know-

   9. LFLex Fridman42:09

      Yeah.

   10. DKDavid Kipping42:10

       ... what you'd call that now. But the... We kn- we know that these... You know, the universe likes to make things in pairs.

   11. LFLex Fridman42:15

       Yeah.

   12. DKDavid Kipping42:15

       Um...

   13. LFLex Fridman42:16

       So you're saying our sun is an incel.

   14. DKDavid Kipping42:19

       (laughs)

   15. LFLex Fridman42:20

       It's, it's looking... So most things are dating, they're in relationships, and our- ours is, is alone.

   16. DKDavid Kipping42:25

       ... it, it's not a complete freak of the universe to be alone, but it is, um... It's more common for Sun-like stars. If you count up all the Sun-like stars in the universe, about half of the Sun-like star systems are in binary or trinary systems, and the other half are single. But because those binaries are two or three stars, then cumulatively, maybe like a third of all Sun-like stars are single ?

   17. LFLex Fridman42:46

       I'm trying hard to not anthropomorphize the relationship-

   18. DKDavid Kipping42:50

       (laughs)

   19. LFLex Fridman42:50

       ... that stars have with each other. But yeah-

   20. DKDavid Kipping42:53

       The triplet, the triplets (laughs)

   21. LFLex Fridman42:54

       Yeah. That's... Yeah. I've, I've met those folks also.

   22. DKDavid Kipping42:57

       (laughs)

   23. LFLex Fridman42:58

       Um, so is there something interesting to learn about the habitability, the... How that affects the probability of habitable worlds when they kind of couple up like that in those different ways?

   24. DKDavid Kipping43:08

       Uh, well, it depends on if we're talking about the stars or the planets. Certainly if stars couple up, that has a big influence on the habitability. Um, of course, this is very famous from Star Wars, Tattooine in Star Wars is a binary star system, and you have Luke Skywalker looking at the sunset and seeing two stars come down. And, uh, for years we thought that was purely a product of George Lucas' incredibly creative mind, and we didn't think that planets would exist around binary star systems. It seems like too tumultuous an environment for a quiescent planetary disk, circumstellar disk, to form planets from. And yet, uh, one of the astounding discoveries from Kepler was that these appear to be quite common. In fact, as far as we can tell, uh, they're just as common around binary stars as single stars. The only, uh, caveat to that is that you don't get planets close in to binary stars. They have like a clearance region in, on the inside, where planets, maybe they form there, but they, they don't last.

   25. LFLex Fridman44:06

       Mm-hmm.

   26. DKDavid Kipping44:07

       They are dynamically unstable in that zone. But once they get out to about the distance that the Earth orbits the Sun, or even a little bit closer in, you start to find planets emerging. And so that's the right distance for liquid water, it's the right distance for potentially life on those planets. And so there may very well be plenty of habitable planets around the binary stars. Binary planets is a little bit different. Um, binary planets, I don't think we have, um, any serious connection of planet binarity to habitability. Certainly when we investigated it, that wasn't our drive, that this is somehow the solution to life in the universe or anything. It was really just a, like all good science questions, a curiosity-driven question.

   27. LFLex Fridman44:48

       What's the dynamic? Are they legit orbiting each other-

   28. DKDavid Kipping44:51

       Yes.

   29. LFLex Fridman44:51

       ... as they orbit the s- uh, uh, the star?

   30. DKDavid Kipping44:53

       So the formation mechanism proposed here, um, 'cause it is very difficult to form two proto-planets close to each other like this. They would generally merge within the disk, and so that's why you normally get single planets. But you could have something like Jupiter and Saturn form at separate distances. They could dynamically be scattered in towards one another-
7. 51:34 – 1:05:04

   Exomoons and Kepler-1625b

   1. LFLex Fridman51:34

      more. But can we step back to Kepler-1625b?

   2. DKDavid Kipping51:38

      Mm.

   3. LFLex Fridman51:38

      What is it? And you, you've talked about this kind of journey, this effort to discover, uh, exomoons, so moons out there.

   4. DKDavid Kipping51:49

      Mm-hmm.

   5. LFLex Fridman51:49

      Uh, or small cool objects out there. Uh, where does that effort stand? And what is Kepler-1625b?

   6. DKDavid Kipping51:56

      Yeah. We... I mean, I've been searching for exomoons for most of my professional career. And I think a lot of my colleagues think I'm kind of, uh, crazy to, to still be doing it. You know, after, after five years of not finding anything, I think most people would probably try doing something else. I even had people say that to me, they said, um, you know, professors, and I remember at a par- a cocktail party took me to the side, an MIT professor, and he said, "Um, you know, you should just look, look for hot Jupiters. They're everywhere. It's really... You can write papers." (laughs)

   7. LFLex Fridman52:25

      (laughs)

   8. DKDavid Kipping52:25

      "They're so easy to find." (laughs) And I was like, "Yeah, but hot Jupiters, just, they're not interesting to me. I want to do something that I feel intellectually pushes me to the edge, and, and is maybe a contribution that not no one else could do, but maybe, um, is not certainly the thing that anybody could do. I don't want to just be the first to something for the sake of being first. I want to do something that feels like a meaningful intellectual contribution to our society." And so, you know, this exomoon problem has been haunting me for years to try and solve this. Now, as I said, we looked for years and years using Kepler. And the closest we ever got was just a hint for this one star, Kepler-1625 has a Jupiter-like planet in orbit of it. And that Jupiter-like planet is on a 287 day period. So it's l- it's almost the same distance as the Earth around the Sun, but for Jupiter. Um, so that was already unusual. I don't think people realize that Jupiter-like planets are quite rare in the universe. Certainly mini Neptunes and Neptunes are extremely common, but Jupiter's... Only about 10% of Sun-like stars have Jupiters around them, as far as we can tell.

   9. LFLex Fridman53:33

      When you say Jupiter, which aspect of Jupiter?

   10. DKDavid Kipping53:36

       In terms of its mass and, uh, its major axis. So anything beyond about half an AU, so half the distance of the Earth and the Sun, and something of order of, um, a tenth of a Jupiter mass, so that's the mass of Saturn, up to, say, 10 Jupiter masses, which is basically where you start to get to brown dwarfs. Those types of objects appear to be somewhat unusual. Most solar systems do not have Jupiters, which is really interesting, because Jupiter, again, like the Moon, seems to have been a pivotal character in the story of the development of our solar system, perhaps especially having a large influence with the development of, um, the Late Heavy Bombardment and the rate of asteroid impacts that we receive and things like this. Anyway, to come back to 1625, this, this Jupiter-like planet, um, had a hint of, of something in the data. But what I mean by that is when we looked at the transit, we got the familiar decrease in light that we always see when a planet tracks in front of the star. But we saw something extra, just on the edges, we saw some extra dips around the outside.

   11. LFLex Fridman54:36

       Hm.

   12. DKDavid Kipping54:36

       ... it was right at the hairy edge of detectability. We didn't believe it, because, um, I think one of the challenges of looking for something for 10 years is that you become your own greatest skeptic. And no matter what you're shown, you're always thinking, "I've been..." It's like falling in love so many times and it, and it not working out.

   13. LFLex Fridman54:56

       Right.

   14. DKDavid Kipping54:57

       You, you convince yourself it's never gonna be, it's never gonna happen. "Not for me." You know, "This just isn't, this isn't gonna happen." And so I saw that, and I, I didn't really believe it, 'cause I didn't dare let myself believe it. But being a good scientist, we knew we had an obligation to publish it, to talk about the result, and to follow it up, and to try and resolve what was going on. So we asked for Hubble Space Telescope time, which was awarded in that case, so we were one of those lucky 20 that got telescope time, and we stared at it, uh, for about 40 hours continuously. And, um, the, to provide some context, the dip that we saw in the Kepler data corresponded to a Neptune-sized moon-

   15. LFLex Fridman55:38

       Mm-hmm.

   16. DKDavid Kipping55:39

       ... around a Jupiter-sized planet, which was another reason why I was skeptical. I was like, that... We don't have that in the solar system. That seems so strange. And then when we got the Hubble data, it seemed to confirm exactly that. There was two really striking pieces of evidence in the data that suggested this moon was there. Another was a fairly clear second dip in light, pretty clearly resolved by Hubble. It was about a five sigma detection. And on top of that, we could see the planet didn't transit when it should've done. It actually transited earlier than we expected it to, by about 20 minutes or so. And so that's a hallmark of a gravitation interaction between the planet and the moon. We actually expected that. You can also expect that if the moon transits after the planet, then the planet should come in earlier than expected-

   17. LFLex Fridman56:25

       Mm-hmm.

   18. DKDavid Kipping56:25

       ... because the barycenter, the center of mass, lives between the two of them. They're kind of like on a, on a balancing arm between them. And so we saw that as well. So the phase signature matched up. The mass of the moon was measured to be Neptune-mass, and the size of the moon was measured to be Neptune-radius. And so everything just really lined up, and, um, we spent months and months trying to kill it.

   19. LFLex Fridman56:50

       Mm-hmm.

   20. DKDavid Kipping56:50

       This is my strategy for anything interesting. We just try and throw the kitchen sink at it and say, "We must be tricked by something." And so we tried looking at the, you know, the centroid motion of the telescope, at the, um, the different-

   21. LFLex Fridman57:02

       (laughs)

   22. DKDavid Kipping57:02

       ... wavelength channels of, that have been observed, the pixel level information. And no matter what we did, we just couldn't get rid of it. And so, uh, we submitted to Science, and I think at the time, Science, which is one of the top journals, said to us, "Um, would you mind calling your paper 'Discovery of an Exomoon'?" And I had to push back, and we said, "No, we're not calling it that. I don't... Even despite (laughs) everything we've done, we're not calling it a discovery. We're calling it evidence for an exomoon."

   23. LFLex Fridman57:29

       Mm-hmm.

   24. DKDavid Kipping57:29

       Because for me, I would wanna see this repeat, two times, three times, four times-

   25. LFLex Fridman57:33

       Mm-hmm.

   26. DKDavid Kipping57:34

       ... before I really would bet my house that this is the real deal. And maybe, and I, I do worry, as I said, that perhaps that's my own skepticism, self-skepticism going too far, but, um, I think it was the right decision. And, uh, since that paper came out, there has been continuous interest in the subject. Um, another team independently analyzed that star and recovered actually pretty much exactly the same results as us, the same dip, the same, the same wobble of the planet, and a third team looked at it and they actually got something different. They saw the dip was diminished compared to what we saw. They saw a little hint of a dip, but not as pronounced as what we saw. And they saw the wobble as well. So there's been a little bit of tension about analyzing the reduction of the Hubble data. Um, and so the only way in my mind to resolve this is just to look again. Uh, we actually did propose to Hubble straight after that, and we said, "Look, if our model is right, if the moon is there, it came in late last time. It transited after the planet. Because of the orbit, we can calculate that it should transit before the planet next time. If it's not there, if it doesn't transit before, and if we, even if we see a dip afterwards, we know that's not our moon. It's obviously some instrumental effect with the data." We had a causal prediction as to where the moon should be. And so I was really excited about that. But we didn't get the telescope time, and unfortunately, if you go further into the future, we no longer have the predictive capability, because it's like predicting the weather. You might be able to predict the weather next week to some level of accuracy, but predicting the weather next year becomes incredibly hard. The uncertainties just grow and compound as you go forward into the future more and more.

   27. LFLex Fridman59:15

       H- how were you able to know where, where the moon would be positioned? So you're able to tell the, the, the orbiting, like, geometry, and, and, and frequency?

   28. DKDavid Kipping59:26

       Yeah, so from the, uh, basically from the wobbles of the planet itself, that tells us the orbital motion of the moon. It's the reflex motion of the moon upon the planet.

   29. LFLex Fridman59:36

       But isn't, isn't it just an estimate to where... Like, I'm concerned about you making a strong prediction here, because like if you don't get, if you don't, uh, get the moon where the moon leads on the next time around, if you did get Hubble time, w- couldn't that mean something else if you didn't see that? Like, 'cause you said it, it would be an instrumental... (laughs) I feel, I, I, I feel, um, the strong urge to disprove your, your own... (laughs)

   30. DKDavid Kipping1:00:01

       (laughs)
8. 1:05:04 – 1:18:46

   Discoveries of alien life

   1. DKDavid Kipping1:05:04

      yeah, as I've alluded to, exomoons is, is kind of a niche topic within the discipline of exoplanets, and that's largely because there are people like, I think, are waiting for those slam dunks. And it was like the... If you go back to the first exoplanet discovery that was made in 1995 by Michel Mayor and Didier Queloz, um, I think it was true at the time that they were seen as mavericks, that the idea of looking for planets around stars was considered fringe science. And, you know, I'm sure many colleagues told them, "Why don't you do something more safe like study eclipsing stars, two binary star systems? We know those exist. So why are you wasting your time looking for planets? You're gonna get this, um, alien moniker or something and you'll be, you'll be seen as a fringe maverick scientist." And so I think it was quite difficult for those early planet hunters to get legitimacy and be taken seriously. And so very few people risked their careers to do it, except for those that were either emboldened to try or had maybe the career, uh, maybe like a tenure or something, so they didn't have to necessarily worry about the implications of failure. And so once that happened, once they made the first discoveries, overnight, you know, everyone and their dog was getting into exoplanets, and all of a sudden, the whole, you know, the whole astronomy community shifted and huge numbers of people that were once upon a time studying eclipsing binaries, you know, changed to becoming exoplanet scientists.

   2. LFLex Fridman1:06:28

      Mm-hmm.

   3. DKDavid Kipping1:06:28

      And so that was the first wave of exoplanet scientists. We're now in a kind of a second wave or even third wave where people like me, to some degree, kind of grew up with the idea of exoplanets as being normal. You know, I was 11 years old, I guess, when the first exoplanet was discovered. And so to me, it was a fairly, uh, normal idea to grow up with. Um, and so we've been trained in exoplanets from the very beginning. And so that brings...... a different perspective to those who have maybe transitioned from a different career path. Um, and so I suspect with exomoons and probably technosignatures, uh, astrobiology, many of the topics which are seen at the, the fringes of what's possible, they will all open up into becoming mainstream one day. But every, there's a lot of people who are just waiting, uh, waiting for that, that assuredness that there is a secure career net (laughs) ahead of them before they commit.

   4. LFLex Fridman1:07:28

      Yeah. It, it does seem to me that exomoons open wider or open for the first time the door to, to aliens, so s- more seriously academically studying, all right, let's, let's look at, like alien worlds. Like-

   5. DKDavid Kipping1:07:42

      Mm-hmm.

   6. LFLex Fridman1:07:42

      So, um, I think it's still pretty fringe to talk about alien life, even on like on Mars and the moons and so on. You're kind of like, you know, it would be nice, but imagine the first time you disc- discover a living organism. That's gonna change, then, then everybody will look like an idiot for not focusing everything on this.

   7. DKDavid Kipping1:08:01

      (laughs) . Yeah.

   8. LFLex Fridman1:08:01

      'Cause the, the possibility of the things we'll... It, it's possible it might, it might be super boring, it might be very boring bacteria, but even the existence of life elsewhere-

   9. DKDavid Kipping1:08:10

      Yeah.

   10. LFLex Fridman1:08:10

       ... some, I mean, that changes everything. That means life is everywhere.

   11. DKDavid Kipping1:08:14

       Yeah. If you knew now that in five years, 10 years, the first life would be discovered elsewhere, you knew that in advance, it would surely affect the way you approach your entire career. As a-

   12. LFLex Fridman1:08:25

       Yeah.

   13. DKDavid Kipping1:08:25

       ... especially someone junior in astronomy, you would surely be like, "Well, this is clearly going to be the direction I have to dedicate my classes and my training and my education towards that direction."

   14. LFLex Fridman1:08:34

       All the new textbooks, all the... (laughs)

   15. DKDavid Kipping1:08:36

       Yeah, right. (laughs)

   16. LFLex Fridman1:08:36

       ... ............................ And I mean, uh, and I, I think there's a lot of value to hedging, like allocating some of the time to that possibility-

   17. DKDavid Kipping1:08:45

       Mm-hmm.

   18. LFLex Fridman1:08:45

       ... because the, the kind of discovery we'll, the kind of discoveries we might get in the next few decades, um, it feels what, like we're on the verge of a lot of, um, uh, getting a lot of really good data and having better and better tools that can process that data. So there's just going to be a continuous increase of the kind of discoveries that will open. Like, but a slam dunk, that's hard to come by.

   19. DKDavid Kipping1:09:09

       Yeah, I think a lot of us are anticipating, I mean, we're already seeing it to some degree with Venus and the phosphine incident, um, but we've seen it before with Bill Clinton standing on the White House lawn announcing life from Mars. And there, there are inevitably gonna be spurious claims, or at least claims which are, um, ambiguous to some degree. There will be, for sure, a high profile journal like Nature or Science that will one day publish a paper saying, "Biosignature discovered," or something like that on TRAPPIST-1 or some other planet, and then there will be years of back and forth in the, in the literature. And that might seem frustrating, but that's how science works. It's in a... That's the mechanism of science at play, of people scrutinizing the results to intense skepticism. And it's like a crucible, you know, you burn away all the relevances until whatever is left is the truth, and so you're left with this, this product, which is that, okay, we either believe or don't believe that biosignatures are there. So there's inevitably gonna be a lot of controversy and debate and argument about it. We just have to anticipate that. And so I think you have to basically have a thick skin, to some degree, academically, to dive into that world. And you're seeing that with, um, with phosphine. It's been, uh, it's, it's been uncomfortable to watch from the outside, the kind of dialogue that some of the scientists have been having with each other about that, because, um-

   20. LFLex Fridman1:10:35

       They get a little aggressive.

   21. DKDavid Kipping1:10:37

       Yeah.

   22. LFLex Fridman1:10:37

       (laughs)

   23. DKDavid Kipping1:10:37

       And you can under- you can, you can understand why, because-

   24. LFLex Fridman1:10:41

       Jealousy? I don't know.

   25. DKDavid Kipping1:10:42

       I- (laughs)

   26. LFLex Fridman1:10:43

       That's me saying, not you. That's me talking. (laughs)

   27. DKDavid Kipping1:10:46

       It, the... I'm sure there's, I'm sure there's some envy and jealousy involved, um, on the, on the behalf of those who are not part of the original discovery.

   28. LFLex Fridman1:10:56

       Sure.

   29. DKDavid Kipping1:10:56

       But there's also, in any case, just leave, you know, the particular people of ve- involved in Venus alone, in any case of making it a claim of that magnitude-

   30. LFLex Fridman1:11:05

       Yeah.

Episode duration: 3:47:09