Planet 9 Evidence Revealed by Caltech Expert [Ep. 481]

Visit Consensus.app and Enter code KEATING at checkout for 40% off Consensus Premium for 2 Years or visit this link 👉 https://bit.ly/ConsensusApp Please join my mailing list here 👉 https://briankeating.com/list to win a meteorite 💥 Astronomers have detected strange gravitational forces pulling at objects beyond Neptune. Some believe these forces could be caused by an undiscovered ninth planet—but if Planet 9 is real, why haven’t we found it yet? And if it doesn’t exist, what else could be shaping the outer edge of our solar system? Here today to explore this issue and reveal extraordinary new evidence of Planet 9, is none other than Konstantin Batygin, one of the world’s foremost experts in this field. A professor at Caltech, Konstantin specializes in planetary astrophysics, the formation and evolution of the solar system, orbital dynamics, exoplanet behavior, and the physics of planetary interiors and atmospheres. In this episode, he not only breaks down the latest evidence for Planet Nine but also shares insights from his research on Jupiter’s magnetic field. Plus, Konstantin gave us exclusive permission to feature his lecture on these topics—an unmissable opportunity to learn from one of the best in the field! — Key Takeaways: 00:00:00 Audio essay 00:03:08 What is Planet 9 and why it matters 00:12:47 Perihelion distribution dynamics 00:14:17 The most unstable component of the Kuiper Belt 00:16:46 Why is it so hard to prove Planet 9? 00:20:29 The Three-Body Problem 00:26:57 Rubin Observatory and the search for TNOs 00:30:42 Konstantin’s lecture on Planet 9 00:43:32 The importance of Jupiter 00:52:41 The role of entropy on planetary formation 00:56:04 Konstantin’s lecture on Jupiter 01:37:39 Outro  — Additional resources: ➡️ Learn more about Konstantin Batygin: 💻 Website: https://www.konstantinbatygin.com/ 📚 Publications: https://www.konstantinbatygin.com/publications ➡️ Follow me on your fav platforms: ✖️ Twitter: https://twitter.com/DrBrianKeating 🔔 YouTube: https://www.youtube.com/DrBrianKeating?sub_confirmation=1 📝 Join my mailing list: https://briankeating.com/list ✍️ Check out my blog: https://briankeating.com/cosmic-musings/ 🎙️ Follow my podcast: https://briankeating.com/podcast — Into the Impossible with Brian Keating is a podcast dedicated to all those who want to explore the universe within and beyond the known. Make sure to follow/subscribe so you never miss an episode! Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Brian Keating?

  Hey everybody. It's a great pleasure to welcome you to the special in-person episode of the Into the Impossible podcast, featuring two-time guest Konstantin Batijan. Konstantin's a renowned astrophysicist, planetary scientist at Caltech, a professor. It's the second time on the podcast, and he is one of my favorite guests, and especially infectious enthusiasm to experience him in person. You'll hear all about the quest to uncover Planet Nine, what the critics are saying in their attempts to assail and perhaps disprove Konstantin. How does he handle that? New research that will be coming up involving LSST, or the Vera Rubin Observatory in Chile, where the next frontier in planetary research, not just in exoplanets, as we've talked about

• 0:46Brian Keating?

  way more than this topic. This is inner planets, planets in our own solar system, beyond the orbit of Neptune. And last but not least, you're going to hear a deep dive into the physics behind Jupiter's past history. How can we do archaeology on planets in our own solar system? Will Konstantin figure out a way to do that? And it involves, of all things, its magnetic field. You'll hear about that, see the latest research into the planetary dynamics of our own solar system. Konstantin's no stranger to attention. You'll see him featured in 60 Minutes. Now, I want you to sit back, relax, and enjoy this episode of Into the Impossible with the irrepressible Professor Konstantin Batijan.

• 1:27Speaker 01

  Any sufficiently advanced technology is indistinguishable from magic.

• 1:34Speaker 01

  Open the pod bay doors, Hal.

• 1:36Brian Keating?

  Welcome back, everybody, to an episode that promises to be out of this world with a friend, a two-time guest on the Into the Impossible podcast, Professor Konstantin Batijan. Welcome, my friend. You survive fires, and floods, and mudslide potential to be here. Thank you so much.

• 1:55Speaker 02

  We're not even talking about the drink.

• 1:58Brian Keating?

  That was just to get down here. I always thought it was a good day to come down to San Diego. Whenever I'd leave Caltech's confines and come down here, I always felt that it was a good day. We're so happy you're here. Going to be talking about-

• 2:08Speaker 02

  Good to be here, man.

• 2:09Brian Keating?

  The Hebrew planet, as I call it, Jupiter.

• 2:11Speaker 02

  Hmm.

• 2:11Brian Keating?

  Jupiter.

• 2:12Speaker 02

  Yes.

• 2:12Brian Keating?

  Uh, we'll be talking about that. We'll learn about how it got its size. Collaborate with Fred Adams, I think, on that.

• 2:18Speaker 02

  I sure do.

• 2:18Brian Keating?

  Recent paper. Uh, he's been a guest a long time ago. I gotta get him back. And I'll use this as an opportunity to do that. But first, we gotta talk about updates to the most important topic, your band. How's your band doing?

• 2:29Speaker 02

  Man, I'm, my band is doing awesome. So we, you know, we played a couple of gigs. I think it was in November and December, and it's been a tremendous amount of fun. Like, uh, the club we play at most often now, the mix has this like huge screen behind the stage. And so, you know, we've been kind of incorporating that uh into the show and also just because like AI video production is now so easy.

• 2:58Brian Keating?

  So good.

• 2:59Speaker 02

  It's been kind of adding an extra element. We've, we're, uh, we're working on a new album. So things are going, you know, knock on wood, things are going well.

• 3:08Brian Keating?

  That's awesome. Okay, let's get to some of the meat of the conversation because we're gonna talk about lots of things involving planets. Uh, I have some planetary swag. You'll find out about that in just a bit.

• 3:18Speaker 02

  Good.

• 3:18Brian Keating?

  But the first thing is, you know, for someone who's not familiar, Planet Nine, we used to have Planet Nine. Actually, this asteroid up here, you can barely see it's called asteroid sixty-six eighteen Jim Simons. Got that named after Jim Simons.

• 3:30Speaker 02

  Mm-hmm.

• 3:30Brian Keating?

  And it was discovered by, see the discoverer, can you read that?

• 3:34Speaker 02

  Clyde Tombaugh.

• 3:34Brian Keating?

  Yeah. Now, what's the importance of Clyde Tombaugh in the world of planetary discoveries?

• 3:39Speaker 02

  Clyde Tombaugh famously discovered Pluto, of course, right? Pluto was the original Planet X, right? If you go back in history about a century ago, right? Um, there was all of this discussion about there being an additional planet, which was largely driven by Lowell, right? Uh, and like Lowell Observatory was in part constructed in order to look for this elusive, you know, planet. Um, and Lowell died, I think in nineteen sixteen, but the search kept going and Clyde Tombaugh, who was employed at Lowell Observatory in nineteen thirty, discovers Pluto. Now, one of the things that I think many people don't realize, when you just discover- Or something up in the night sky. You don't know how massive it is.

• 4:22Speaker 02

  And so you kind of say, well, I was looking for a thing that was supposed to be seven earth masses. So it's probably seven earth masses. But Clyde Tomba immediately realized that, well, if it was something that big, you should be able to resolve the disk. And instead it looked kind of like a point source. So he was like, probably one earth mass? Like, you know, there's no way to calculate it if it doesn't have a satellite. And, uh, you know, you can watch Pluto's mass kind of decrease through the out, through the literature. And there's even some joke paper, uh, from like the eighties that makes a plot of Pluto's mass as a function of time between nineteen thirty and like nineteen eighty something.

• 5:03Speaker 02

  And predicts how Pluto would disappear, right? It would cross zero in like two thousand five or something like that.

• 5:10Brian Keating?

  Anti-matter.

• 5:10Speaker 02

  Yeah. And so, you know, it was, it was really realized only in the seventies when, when Sharon, the satellite of Pluto was discovered, just how miniscule the mass of Pluto is. And so that was the kind of story that led to the demotion of Pluto. You know, Mike, of course, my partner in crime had a lot to do with that back, you know, twenty years ago. Um, but the thing we're looking for now is not some miniscule thing, right? The thing we're looking for is the legitimate planet night.

• 5:43Brian Keating?

  Mm hmm. And it would be far beyond the orbit of even Pluto, correct?

• 5:47Speaker 02

  About, uh, you know, about factor of ten, fifteen further away.

• 5:52Brian Keating?

  Wow. Nowadays, we don't use, you know, pencil and paper like Lowell or even Le Verrier did, right? I recently discussed, uh, with Davis Sobel, who wrote a lot of wonderful books, including a book called Galileo's Daughter. She talks about that. And we were just musing on how many, you know, amazing discoveries Galileo made, but he also discovered Neptune. He didn't realize he discovered it, but he discovered it. So I aspire to be like that. I aspire that my blunders, you know, like Einstein's cosmology should be as, as good as that. But, um, nowadays we have N body simulations and so forth. And to me, as a scientist, that opens up, you know, a whole new realm, including AI, machine learning. But also potential pitfalls. And I wonder if you could respond, you know, some of the critics say when you're talking about this object, um, which we call planet nine,

• 6:37Brian Keating?

  and that you are at the very, very forefront of its of its investigation, that, you know, there could be artifacts introduced because these in-body simulations. So can you explain why it's so important to discover this? And what are the new tools and new pitfalls of those new tools?

• 6:53Speaker 02

  Yeah. Okay. So first of all, the in-body simulation as a thing, right? Is in effect a numerical experiment, right? It is a realization of the solar system as it unfolds over its lifetime. You start off with a reasonable initial condition and you say, I've gotten to the point where we are now at four and a half billion years after the formation of the sun. Does the solar system that I've created in my numerical experiment look like the one that we see? What are the pitfalls? Well, the pitfalls, the simplest one is just in the method, right? You can, if you're not careful, you can screw up and you can introduce like fictitious dynamics into your simulations.

• 7:35Speaker 02

  That's pretty easy to get like at this point, that's almost never a question, right? Think much of the discussion, right, has been, you know, related to planet nine has been, okay, you do this numerical experiment. How do you then compare the output, like the what we see at the end to what you really see on the night sky? And this is where I think my collaboration with Mike has been the thing that has, uh, you know, for a change, made us greater than the sum of the parts, not less than the sum of the parts. Because, you know, Mike is an observational astronomer. He isn't, he's a ninja when it comes to understanding, right?

• 8:13Speaker 02

  What the night sky is telling us. And we've been, I think, between through the kind of back and forth, uh, which sometimes gets kind of loud, but it's all fun. You know, we've been able to kind of challenge each other and really get down to the question of how do we take this output? And compare it meaningfully with what we see on the night sky because of course, when you're observing stuff, you don't just have access to the entire solar system, you just have access to what you can see. You know, that leads to a well-defined number, which is the false alarm probability of this entire.

• 8:51Speaker 02

  You know, story and there are different lines of evidence for Planet Nine and like the two that I think people like to talk about because they're kind of the easiest to imagine is that if you go far enough away, all the orbits are all facing, they're all kind of like swinging out in the same direction and that has a well-defined false alarm probability of about 0.2%, right? There are other lines of evidence, like they're somewhat higher, like five sigma. Well, so you can do all this in a pretty rigorous way, but the point I think is that you, you have, you can't just, you know, do a simulation and say, well, here's what I got, you know, and, you know.

• 9:31Brian Keating?

  So when Galileo turned his telescope, here he is there, not this actual, you know, guy, but he turned his telescope to the skies in 1609. He saw, looked at the moon. He saw it was flawed, full of craters, mountains. He measured the height of the mountains. The guy's incredible. And, oh, and speaking of the moon, this is actually, you get to choose which, which one of these do you think is more valuable, actually?

• 9:53Speaker 02

  Oh, well, definitely the smaller one.

• 9:54Brian Keating?

  The smaller one? Yeah. This is from your former home country. You don't get this one. This is, I'm keeping this one, but you'll, you'll probably like this one better. This is a piece of the moon. So this was delivered not by the NASA astronaut. This is Chelyabinsk meteorite from your former.

• 10:07Speaker 02

  Chelyabinsk.

• 10:08Brian Keating?

  Chelyabinsk.

• 10:09Speaker 02

  Yeah. Yeah, say again.

• 10:11Brian Keating?

  Chelyabinsk. Chelyabinsk, pasiva. This is a piece of the moon. Okay. And the reason I'm giving that to you is I'm so grateful that you're here for your second appearance and that is real and you'll get also a piece of the Proto Solar System. This is a meteorite. So this is a chunk of.

• 10:24Speaker 02

  Oh, this is an iron meteor.

• 10:25Brian Keating?

  Yeah, this is from the Campo de Cielo in Argentina, which you will win too guaranteed if you're out there and you have a dot edu email address and you live in the United States, briankeating.com/edu, or you can take your chances if you don't have one, unlike Konstantin and me, at briankeating.com/list and you can join up there. But the reason I give this to you is because when Galileo discovered these four little stars, he called them after his funding agency, not the NSF, but the Cosmo Medici family, he called them after them. Now we call them the Galen. What I'm getting at is that then, you know, added four new moons to the retinue of moons that we knew about. In the in the solar system alone, to what extent if we found planet nine, would that essentially imply planet ten, planet eleven, planet twelve?

• 11:10Brian Keating?

  Would there be many, many more to come essentially?

• 11:12Speaker 02

  Yeah, so the solar system has quite a bit of real estate, right? You can keep moving out. Eventually, though, you run out of real estate that's stable. Because eventually you start to see the galactic tide, right? And the galactic tide, you know, functionally, basically just takes your orbital inclination with respect to the plane of the galaxy and trades that for eccentricity. And through something akin to what's called the Cozy Effect. And in in any case, you know, there is sort of half of an order of magnitude left still in semi major axis. But once you go well beyond that, passing stars, the galactic tides start to really mess you up.

• 11:55Speaker 02

  That's why, you know, kind of where planet nine is, or where we infer it to be. So in the region we called the inner Oort Cloud, right? Where it's material that could have been trapped there by interacting with the solar system's birth environment, like the cluster of stars in which the sun formed. Now that that's gone, there isn't really a way to trap material there anymore. And well beyond that, you're in the Oort Cloud. And the fact that we have Oort Cloud comets, right? That come in is just a manifestation of the fact that if you're in the Oort Cloud, you're not just sitting there forever orbiting. You know, happily, there are dynamics that that unfold.

• 12:36Brian Keating?

  It will cause you to be much more elliptical and then eccentric and then eventually trans out of the Kuiper Belt, right?

• 12:42Speaker 02

  So I'm not saying it's impossible.

• 12:45Brian Keating?

  Right now.

• 12:45Speaker 02

  I'm saying it's into the impossible.

• 12:46Brian Keating?

  Mm hmm. And you talk about this thing, which I I think is very interesting, at least the names of it. I love these names that you give the perihelion distribution dynamics. You talk about this planet nine inclusive model being relatively flat. This is some distribution function in your most recent paper that the graduate students will be quizzed on later on today after your wonderful talk. Talk about that. What is a a flat distribution to me? I mean, wow, there's got to be many, many of these things and and and yet I. I can understand because of your, the clarity of your, you know, presentation just now, that actually may not be the case that there's sort of an infinite number of planets left to come. I mean, planets that we would say are honest to goodness planets, not chunks of Pluto or asteroids.

• 13:25Speaker 02

  Yeah. So the, the most recent paper is something that we were inspired to do. And this is work that, you know, I did with Mike, but also with my close collaborators, you know, Sandra Morbidelli, Nice, and also David Nisworny at Boulder. It's a Southwest Research Institute. So, you know, for about a, you know, eight years or whatever, however long it's been, I guess now nine years that we've been working on this planet nine shtick. We have always been focusing on the most distant, the most kind of untouched orbits possible. Because Neptune messes stuff up. There's a subset of the Kuiper belt, which we kind of ignore because we say at close approach,

• 14:09Speaker 02

  it hugs the orbit of Neptune and the chaotic dynamics that ensue from interacting with Neptune make that.

• 14:17Brian Keating?

  Just to set the stage, for the listener might not be familiar, the solar system goes out to Neptune, the classic planets, then the Kuiper belt, then the Oort cloud, then the heliopaws.

• 14:26Speaker 02

  Yeah, then the end.

• 14:27Brian Keating?

  Whatever.

• 14:29Brian Keating?

  Okay. So you were saying Neptune tugs on it.

• 14:31Speaker 02

  Right. So stuff that is kind of in the outer solar system, whose evolution is chaotic and stuff that's out, like it's kind of, it's kind of being thrown out of the solar system as we speak. So we kind of tend to ignore that and only focus on the orbits that are sufficiently detached, sufficiently calm, that we know that kind of gravitational footprint of planet nine has a chance of being seen in these orbits. And so what we thought about a couple of years ago, I guess a year and a half ago now, was we're like, well, let's now look at the opposite extreme. Let's now look at the most unstable component of the Kuiper belt. And these are things that orbit in the plane of the solar system, that physically cross the orbit of Neptune.

• 15:17Speaker 02

  And so they're being actively scattered around. Now, if you reason through. A question of like, should such objects exist in the first place? The answer is basically no, because their lifetime in the solar system is 10, maybe 100 million years at most. So Neptune should clear the solar system out.

• 15:36Brian Keating?

  Right.

• 15:37Speaker 02

  But if Planet 9 is there, then Planet 9 should be systematically injecting these things back into the solar system interior to Neptune.

• 15:46Brian Keating?

  And it would have to clear out its orbit, right? To be consistent with our friends of the only union I'm a member of, the International Astronomical Union.

• 15:53Speaker 02

  Yeah. And so what we did, yeah, so what we did is we, you know, conducted numerical simulations, which I think are the most kind of encompassing and body simulations of the solar system of evolution that, you know, have been done perhaps. And, you know, we asked the question of looking at this highly unstable component of the Kuiper Belt, right? Can we rule out, rule in a solar system with, without Planet 9? And what we found is that the solar system without Planet 9 is five sigma ruled out. And the solar system with Planet 9 is indistinguishable from the data. So that, even though it's kind of a surprising, you know, it's surprising that the most unstable,

• 16:35Speaker 02

  kind of boring part of the Kuiper Belt gives you the most statistically significant thread, that's the most stringent evidence we have that Planet 9 is really out there.

• 16:45Brian Keating?

  So that's when, you know, we hear things like, yeah, the five sigma confidence, that's saying that ruling out the null hypothesis that Planet 9 does not exist. Very good, very good. Now, how much of this, you know, depends on data? When Le Verrier predicted the existence of Neptune, and then it was found the same day or something like that, the legend goes, or very soon after. And then, of course, he went on to blunder and predict Vulcan, right? So, you know, sometimes if you only have a hammer, you hit yourself in the head too many times. Why is it so hard? I mean, you know, no offense, but, you know, you told me I have to look in this area of the sky to see the CMB's beam mode polarization. I'd be out there tomorrow with the Simons Observatory, be looking for it, right? So why so hard? If you know exactly, or if you know, if you're so confident that it exists, five sigma is

• 17:30Brian Keating?

  the level of evidence. For the Higgs boson to be awarded Nobel Prize. So why, why is this so hard?

• 17:35Speaker 02

  Yeah, well, I'm glad you bring up the Laverrier discovery of Neptune as a kind of counterpart. Because what Laverrier was able to calculate very precisely was the acceleration is coming from there. Okay. And this, this had to be, this had to do with the fact that he was doing the calculation in 1846. And Uranus and Neptune happened to be close to conjunction. And so the information that was stored in the Iranian residuals was actually not the mass of Neptune, not the orbit, but like, where is it on the night sky? We're in precisely the opposite regime. What we can calculate from the orbits, like the orbital distribution of the Kuiper ball is the orbit and the mass of planet nine. We don't know the phase.

• 18:21Speaker 02

  And so, you know, you can draw orbits on the night sky all day long, all night long, right? And you can say, well, that leaves a lot of sky there to be, to be searched. But I'm optimistic because the LSST is coming online this summer and that's going to be a game changer.

• 18:37Brian Keating?

  It's always seemed to me can be surprising that, you know, it'd be so controversial. Is it because there's so much pride associated with discovering a planet? Because there's so few of them that is so, so hotly debated. You know, they say about academics like us, you know, the stakes are so, you know, the, the stakes are so low that we have these incredibly passionate battles. But here the stakes are high. Is that because of the pride? Is it ego? Is it swag? What is it?

• 18:59Speaker 02

  I sometimes think about it this way, like if I was sitting at home, whatever, drinking wine, reading the archive. And I read, like I saw a posting that some rando is like, I'm thinking there's a planet beyond Neptune. I, I were like, okay, moving on. Right? Like, you know, there's a natural skepticism that, that you kind of gravitate to. And, you know, I think another component to this is that planets beyond Neptune have been predicted by everyone and their brother between 1846 and now. And it's always been wrong. Like there was this one guy Pickering who predicted, I don't know, like 30 of them.

• 19:36Brian Keating?

  He was at Harvard though, right?

• 19:37Speaker 02

  Yeah. You know, I think there's a, there's a basic. And prior, if you will, to this story being wrong. But I think it's important to simply follow the data, right? And just say, okay, what is the data telling us, right? Meaningfully, like, yeah, we know that the data is biased, right? We like, let's account for that, like, does it look promising? And sometimes when, as you say, the stakes are high, that when the problem is important, I think it's, it's important to take a bit of a leap. And even if the, you know, your initial kind of significance is only, you know, whatever, to sigma, right? Something that we're not, something to write home about.

• 20:18Speaker 02

  Like, I think it's important to pursue those things because the worst thing that's going to happen is you're going to be wrong. And like, no one's going to die, right? It's going to be okay.

• 20:29Brian Keating?

  So I have to, I have to always interject. Whenever my guests, like Konstantin just did, or I've had, you know, five Nobel laureates sit right where you are, whenever they make a point that's really crucial to the development of good scientific habits, I like to double click on that and, and really enforce that for, you know, half my audience is, you know, young people in academia, not half, but more of my audience has PhDs than only has high school degrees. And these are people that are easily going to be influenced for good or bad. Uh, and, and so when Konstantin said just now that the stakes aren't life or death, like you just survived a fuck. At the same time, the, the stakes for kind of what makes us, you know, enriched as a species is exploration. And so what you're doing has to be balanced, that, that tempered, you know, notion of

• 21:12Brian Keating?

  not only accepting what you want to be true, because it would be great, but also to realize, yes, it's important, but there are other things that are important too. So I, I wanted to highlight that. One, one question I've had as a layperson in this field, I mean, I love looking at planets and, and whatever planets, planets and the moon got me into astronomy and, um, but now what I do is so far away from it.

• 21:32Speaker 02

  Isn't that as young?

• 21:33Brian Keating?

  What's that? Yeah, I know, I could become your graduate. So that's one thing I'm going to return to Caltech to be a student. No, my, one of my kids wants to, wants to go there, maybe he'll end up with you. But tell me, Konstantin, the three body problem. It's seemingly the most complicated thing in the world. Like, how can you predict with how many things could be, there could be a trillion objects in the Kuiper belt in the Oort Cloud? How can you possibly predict anything? I mean, it's remarkable that you even have, forget about the phase that's unknown currently, but that you have this, you know, five sigma confidence bound on something that is a localized, you know, probability cloud, however you want to describe it. How is it even possible when the three body problem says you can't even do that with three bodies, let alone trillions?

• 22:09Speaker 02

  Just because something is chaotic does not mean it cannot be understood, right? I mean, think about weather. Okay. Weather is chaotic, right? And the lap of time is whatever, a couple of days, right? So the time for weather to forget about its own initial conditions. And just because that's true, doesn't mean the weather forecast is going to be horribly wrong, right? And so similarly, when we're dealing with the outer solar system, the dynamics instilled upon the Kuiper belt, right? Kind of manifest tells you what's going on, not because each particular orbit is super important. Like you should never obsess over one particular KBO. Is there cumulative statistical nature that points to what's going on?

• 22:54Speaker 02

  So yeah, the each one is kind of doing its own, you know, stochastic thing, but cumulatively, there's an there, there's a merge. There's patterns, right? Similar with like the stock market, right? You each stock might be quite stochastic. The cumulative behavior actually embeds some information about what's going on.

• 23:11Brian Keating?

  It's a complex system and a complicated system. I would say like building a seven eighty seven is really complicated. But if you do it with the right parts, the same time, every time you get the same results. Not so with a sand pile or with, you know, the weather in San Diego or Pasadena, but that doesn't stop people, right? So in my field, when we come up with an anomaly, which is very exciting and it should herald, you know, joy on the part of scientists, not like depression or I was wrong. No, you need, I always say, when you encounter a flaw, it could be a new law, right? So in the context of what I do in cosmology, we have something that's unknown, like dark matter. Okay. So there'll be millions of alternative conjectures, whether it's a different particle, it's a field, or in fact, it could be. A new modification to Newtonian dynamics.

• 23:54Speaker 02

  Sure.

• 23:54Brian Keating?

  Does that come into play? Are there, I'm sure there are those, but, but where do you rank these in terms of, you know, Mond equivalents for planetary science? And in particular, things that aren't as, as abstract, like they call them rogue planets, you know, other trans-Neptunian object. How, how do you rank the alternative explanations? Put up the, the straw man and then burn it down for the.

• 24:15Speaker 02

  Okay, no, I mean, I, uh, this is an easy exercise to do because when an alternative explanation comes out, right? I try to, uh, not just, you know, believe it, but I tried to go through and, and simulate it better. Okay. An example is, uh, you know, there, there've been, okay, so, uh, example, Mond, this is not my simulation, but, uh, David Nisworny, who I mentioned was, is my collaborator.

• 24:44Brian Keating?

  Yeah.

• 24:44Speaker 02

  When like Mond was proposed as a, uh, as a replacement for Planet 9 to create all of these structures in the outer solar system. And of course, because Mond has this tunable parameter of where you transition from the, you know, Newtonian to the non-Newtonian regime, right? Uh, there were a couple of papers that pointed towards this and, uh, this got tested with very, very high fidelity numerical simulations. And the simulations showed that if that was the explanation, then the Oort spike of comets, which we see very well, would just go away. So it's ruled out. Uh, could it be self-gravity of the Kuiper belt? This has been an idea that kind of floated around. We looked into this with and dedicated a lot of, you know, GPU time to actually studying

• 25:29Speaker 02

  this and convinced ourselves, no, and this is all published, like this cannot work actually because of Neptune scattering, et cetera. So each of these alternative, um, explanations are interesting and I've been interested in them and I've dedicated time to, to kind of studying them. And I think it's really important not to be religious about your own.

• 25:52Brian Keating?

  Yeah.

• 25:52Speaker 02

  You know, your own.

• 25:53Brian Keating?

  Confirmation bias is a hell of a drug.

• 25:54Speaker 02

  Hell of a drug, yeah. And so, yeah, that's what we've been doing so far. There is no theoretical, uh, there's no theoretical alternative model that I think is able to explain the data nearly as well as Planet 9.

• 26:10Brian Keating?

  Hey, if you're enjoying this, I hope that you'll also subscribe to my Monday Magic mailing list. We'll get to hear some behind the scenes info. About this interview that I did with Konstantin and many, many more subjects that I like to share with you around the universe, the multiverse of minds that I get exposed to. And I love to take you for a ride. Once you subscribe, it's free. And if you have a .edu email address, you're guaranteed to win one of these beauties, a meteorite, a fragment of the solar system before Jupiter, before Planet Nine, before they were all even glimmers in the cosmic eye. So please subscribe. If you don't have a .edu email address, that's okay. You are entered to win automatically a competition each month. I give away several of these to

• 26:51Brian Keating?

  people that aren't blessed to live with .edu email addresses. But for now, let's get back to the episode. You mentioned you deadnamed, you know, the Vera, not you mentioned LSST. Talk about that. What is the excitement all about there? What are you gonna? I've heard everything from, you know, Avi Loeb, who's been a many time guest on the show, talking about how they're going to discover an Amumuua every night. Are you going to discover, you know, a TNO or Planet Nine? Every other? How is it going to revolutionize what you do and what Mike does? And, you know, your collaboration is a ritual.

• 27:22Speaker 02

  Right. Well, look, fundamentally, finding TNOs is, you know, conceptually, not that hard. You take a picture of the night sky, and then the next day, you also take a picture of the night sky, and you look for what has moved. And the third day, you do that again, and you say, did that move in a consistent manner with this being a TNO? Well, I've just like, found one. Okay. And for the first year or so, all you know is how far away it is and where it is on the night sky. You have some constraint and inclination, but like, you don't really have a good handle on the orbit first. So you need this, this string of three consecutive observations to tie together.

• 28:02Brian Keating?

  Try again.

• 28:03Speaker 02

  Exactly. And, you know, LSST is going to do that very, very efficiently, because its entire job is to wake up every night and kind of look up and down the sky, record what it saw. So it, it's going to do a lot of things for many different fields. But I think for the outer solar system, in a way, it's a, it's a really good survey. It might not go deep enough, or it might not go north enough to. Find Planet Nine directly, but even if it doesn't, it will still provide an independent check on all of the predictions that Planet Nine.

• 28:36Brian Keating?

  Okay, so think big. Sixty Minutes calls you up again. They got a bag of cash. What's the Batijan Observatory look like? If you could build whatever you want, you know, money's not an object. Where would it be? What would it look like? Design it for me.

• 28:48Speaker 02

  Oh, it's just like my laptop in my office and the door closed.

• 28:54Brian Keating?

  And an infinite supply of the impossible coffee, right?

• 28:57Speaker 02

  Yeah, you know, I mean, I think, you know, instruments, right? You don't need to, you know, really dream here, right? Instruments like Subaru, like the Japanese National Observatory. Yeah, they're out there, but you know, the thing that has prevented us from conducting a search that's really nailing down the northern hemisphere is really the efficiency. It's the fact that you only get a few nights per year. You know, and you're dominated by the worst night that you have of the of this sequence. And, you know, I wasn't an observer and I'm still not an observer, you know, and I'm happy about that, but.

• 29:38Brian Keating?

  Keep you out of my life.

• 29:39Speaker 02

  But like, I do now, having started this, you know, observing about a decade ago, I now have this deep appreciation and gratitude for each data point that comes up because for especially for all the Planet Nine stuff, that stuff is up in December, like January, a little November sky. And the weather in the northern hemisphere is actually not that good. And so that's like something I learned is that it's actually not that good. Yeah, you were like, the fog down, there's snow, the seeing is crap. So it's really tough. It's really tough. It's not as much fun as theory because with theory, as you as you know very well, right? You were, you know.

• 30:24Speaker 02

  Like you're creating the world from scratch, so to speak, from from axioms. It's so much, there's so much joy in doing that.

• 30:32Brian Keating?

  Instant gratification.

• 30:33Speaker 02

  Yeah, with with observations, you're just kind of at the mercy of the telescope, the the conditions, and also what exists in the solar system.

• 30:41Brian Keating?

  Yeah, that's right. We're taking a little break from the in person episode. I need to fold in the actual lecture that Konstantin gave. He gave me permission to share the lecture on Planet Nine, and you'll see later Jupiter's magnetic field. This is a deep dive, it's a little technical, but it's captivated the imagination. So watch this deep dive where he's going to take us through what I call an office hour, an actual presentation by a top scientist, perhaps the top scientist in this field. And he's going to walk us through the evidence that we have for Planet Nine. It's fascinating. I don't want you to miss it, and I'm so grateful that Konstantin gave us permission to share this little nugget of wisdom. Then we'll come back to the follow up of that in person interview, where I discuss the fascinating aspects of how we know what Jupiter's mass and size were some four billion years ago.

• 31:26Brian Keating?

  So stay tuned for that. Now into Planet Nine, and stay tuned.

• 31:29Speaker 02

  This is the solar system. Okay, this blue thing here is the orbit of Neptune. Back about a decade ago, me and my friend Mike, inspired by work that some of our colleagues, Chetra Hu and Scott Shepherd, did, noticed that if you look at the most distant orbits in the solar system, they all swing out into sort of the same direction, and they all are inclined with respect to the ecliptic plane by about 20 degrees. And we thought this was kind of a big deal. Now, the data set has evolved over the decade. It's sort of expanded by about a factor of three.

• 32:09Speaker 02

  This is from a paper I wrote with my friend Morby in 2017. Then you can sort of see in 2019, there's a little bit more objects. In 2021, more objects still. And that's more or less what the data set looks like right now. So looking at this, I think you can just like kind of tell there are more orbits swinging out this way than another way. And so why is that? Well, can we invoke that something bad happened to the solar system when it was forming? Maybe a star flew by and kind of aligned all of these objects and we're seeing this relic?

• 32:49Speaker 02

  The answer is no, because if you leave the solar system alone, all of these objects will differentially process and that differential procession time, right? The time scale over which this structure would become fully axisymmetric is a few hundred million years. Okay, so no. Moreover, you see a strong correlation with orbital stability in this plot. Objects that are very strongly interacting with Neptune, and in fact Neptune is in the process of kicking them out of the solar system altogether, here as shown in green. Objects that are dynamically stable, whose perihelion are well enough removed from the orbit of Neptune that nothing happens to them are shown in purple.

• 33:33Speaker 02

  And again, without being an awesome statistician, you can see by eye that the purple orbits cluster together much better than the green ones, which basically don't cluster at all. There is a much more sophisticated way to measure orbital diffusion. That's something that's work that Gabrielle Picari, who's a postdoc in my group, just submitted, but maybe I will not spend too much time on this in interest of time. Okay, so if you see, you believe what you see and you see these orbits and you're like, wow, they really are clustered together. How can that be?

• 34:13Speaker 02

  Well, you need something exterior, intrinsic to perturb them, to keep them confined, and it has to be eccentric to break axial symmetry. And the rest you can compute from these types of forward models that are just numerical and body simulations. So what you're seeing here is an evolutionary model where you're starting off with, and for scale, this is about 30 AU, the orbit of Neptune, you're introducing a new planet on some highly eccentric orbit and you're starting Starting off with a rather axysymmetric disk of Kuiper belt objects.

• 34:53Speaker 02

  And the blue orbits here represent long-period things, right? Because, well, they have long period. And these, these golden orbits are things that are too short period to be strongly affected by Planet Nine-induced dynamics. So it takes a couple billion years for a pattern to emerge. But right about now, we're starting to see how the anti-aligned direction with respect to the orbit of the introduced perturber is kind of starting to get preferred, right? There are more objects hanging out here. You guys also see this, right? Like, I'm not alone. Okay, that's good. Problem if I was the only one. Okay, uh, why is this happening, right?

• 35:38Speaker 02

  Why anti-aligned? Well, as you can see, occasionally, objects will process through orbital alignment. And when they process through orbital alignment, their eccentricity reaches a peak. And their orbits get jammed into the orbit of Neptune, which then scatters them out of the solar system. Okay, so this is kind of a, a survival technique, if you will, of long-period Kuiper belt objects. Okay? And the same thing largely remains true also for the, for the plane. Okay, so if we go into 3D, we'll find that the surviving objects also get tilted away from the plane, the ecliptic plane, um, by, you know,

• 36:22Speaker 02

  effectively bending of the Laplace plane by gravity of, of Planet Nine. Okay, uh, there's also very high inclination, uh, dynamics that gets excited. Okay, good. So. If you believe that this is the case, right? Then you can compute what the best kind of fit Planet Nine parameters are. And they turn out to be about five Earth masses with an orbital period of about 10,000 to 20,000 years. Let's think 500 AU in terms of semi-major axis and an eccentricity of about 0.3, an inclination of about 20 degrees. That's kind of what you get from here.

• 37:04Speaker 02

  Now, there's been some discussion in the literature about whether or not this is actually real, right? People talk about, well, you know, what if all of this is a conspiracy of observational biases that together make this pattern? And we've, you know, participated in that debate. I would argue that the false alarm probability here is 0.2%. But that's not what I want to talk about, okay? Because I want to leave that question for Vera Rubin. Instead, what I want to think about is a distinct, you know, a distinct process, namely, up until now, right?

• 37:46Speaker 02

  I've been asking you to focus on these objects that are very, very stable, right? These things that are removed from the orbit of Neptune, so they have, they're corralled by Planet Nine's gravity, they hold the footprint or thumbprint of secular interactions with Planet Nine. And also, if you were paying attention to the previous slide, you saw how we started out with lots and lots of objects, and then many of them disappeared, right? Because they got jammed into the orbit of Neptune. So what these calculations tell you is that if Planet Nine really exists, it should also,

• 38:25Speaker 02

  in addition to doing this confining business, drive a steady flux of long-period objects that cross the orbit of Neptune. Okay? And, well, here are some numerical simulations of the chaotic evolution of the perihelion distances, for example, where you see that happening, where perihelia dip below Neptune, right? And then at the end of, you know, as the solar system, at the moment when we're observing now, they're being just like jammed into the space in between the giant planets.

• 39:04Speaker 02

  All, all successful planet nines will do this, okay? Even the unsuccessful ones, okay? Every single planet nine, unless it's like pathetic. And yeah, pathetic is probably like point seven earth masses, okay? I'm making that up, but like, that sounds right. So anyway, all successful planet nines will do this, okay? So we ran a couple simulations. And these are actually the most detailed simulations of solar system evolution ever, because they go through first the process of forming the Kuiper belt, all self-consistently, right?

• 39:49Speaker 02

  The expansion of the planet, giant planet orbits, they self-consistently capture the effects of the birth cluster in which the solar system was born, et cetera, et cetera. They include, you know, perturbations from the galactic tide, passing stars. Uh, the only thing they don't have is like a simulation of me simulating. Right? Like that's the level at which we, we decided we didn't want to see too deep into the matrix, okay? So, um, okay, so we did two simulations, because these are rather computationally heavy, one with and one without planet nine. And here's the answer.

• 40:32Speaker 02

  Okay, this is the, at the end of the day, kind of as today's solar system. This is the distribution of perihelion distance, or closest approach distance of objects with semi-major axes presented on the x-axis. And what you see is that if you don't have planet nine, then Neptune forms a barrier.

• 40:57Speaker 02

  Okay, in other words, as objects try to get penetrated kind of interior to the orbit of Neptune, that process is so slow, because the galactic tide is actually a painfully slow process, that Neptune scatters them out before they can get, you know, well beyond 28 AU. If Planet 9 is there, on the other hand, it creates a rather flat distribution, right? Populates all the way from 30 to 15. So what does the data look like? Well, the data for Neptune crossers looks like this, right?

• 41:35Speaker 02

  And I think you can look at this and say, yeah, these are not all sitting at 28 AU. But before you hype 5 yourself, okay, you have to be careful, because there's of course a strong observational bias towards discovering things with smaller perihelio. So you have to account for that. The good news is, it's very easy to account for that. Like, we know that stuff becomes less bright as 1 over r to the fourth. We know how to account for the amount of time spent in a Keplerian orbit. It's a trivial calculation of the bias. So after accounting for the bias, what we find is that the P9 free solar system is

• 42:20Speaker 02

  ruled out at more than 5 sigma by the existing dataset of Neptune crossers, and the Planet 9 inclusive solar system is like 0.2 sigma away. So it's basically indistinguishable from the data. I am out of time, and so I will just leave with this image of optimism here as my last slide, because LSST, the Verarubin Observatory, is coming online this year, and all of this stuff Planet 9 related will be tested independently. And I think, you know, we'll be well on our way either to proving all of this wrong, which would be kind of a bummer, but, you know, that would be okay, or well on our

• 43:04Speaker 02

  way back to a full-up, you know, 9-planet, make the solar system great again level of Planet membership.

• 43:13Brian Keating?

  So that was just awesome, learning about the... Evidence for or maybe against the existence of planet nine from the world's foremost expert in it. I mean, how often do we get a treat like that? I needed to expose you to it because I want you to see how good science is done. And this is science at the cutting edge. You're hearing it first. These are brand new results from Constantine. But even fresher results than on planet nine have to do with planet five, which is Jupiter. And Jupiter is the most important planet in our solar system by far, except for the earth. I mean, I'm kind of partial to the earth. But besides that, we might not even exist if it weren't for Jupiter, having the properties that it has. And yet we don't know that much about it. There were no videotapes, no Tik Tok, uh, four billion years ago when it formed. How did it get to be the size it is now?

• 43:56Brian Keating?

  Well, it turns out it went on a cosmic version of Ozempic, some kind of slimming down process to get to the size that it is now. One Jupiter radius. You'll find out why in this discussion, we think that Jupiter was much more massive. Constantine does and his collaborators, including upcoming guest, Mike Brown, author of How I Killed Pluto and Why It Had It Coming. He's also an upcoming guest, I said. So now listen to this conversation with Constantine describing how they know what they know about Jupiter's former size and mass. It's fascinating. Another cosmic detective story. I couldn't resist discussing this with Constantine. And after that, we're going to go to the lecture where he describes it in great detail. And it's just a fascinating and once in a lifetime kind of exposure for you out there, my brilliant audience,

• 44:41Brian Keating?

  to get an insight into how astronomers really think and work. Okay, here we go. Let's move on to your topic of today's talk, uh, which is on the, um, the formation of Jupiter and it's the relationship between the magnetic field. This doesn't immediately strike me as, you know, kind of in your research portfolio. Are you branching out or are you moving out into, you know, purely looking for, you know, these, these Neptunian transits, trans-Neptunian and planet nine? Does this complement it in some way? Talk about the research. Why is it so important? Did Jupiter look different, you know? And if so, how long ago could, you know, could Galileo have seen a different Jupiter than we see to this, uh, to this day?

• 45:19Speaker 02

  Well, so to answer your first question, you know, I did my thesis on planetary interiors, actually, and magnetohydrodynamics. So orbital dynamics has always been an interest of mine, but, um, I've always done that in parallel. And when it comes to Jupiter, the planet Jupiter, the planet. In a way is the most important planet of the solar system. No, uh, you know, I hope Planet Nine didn't hear this and didn't go into hiding. Uh, but Jupiter is uh, is the great architect of of our solar system. There there are things that would not like.

• 45:52Brian Keating?

  Yeah, we would be here.

• 45:53Speaker 02

  Yeah, we would be here. Yeah. And so

• 45:54Brian Keating?

  Bodyguard.

• 45:55Speaker 02

  It's critical to understand how Jupiter, the great architect of the solar system arose, right? And we have a pretty good kind of theoretically, you know, self-consistent, but nevertheless vague picture of first you form a core, then this core slowly accretes an atmosphere that's hydrostatic. And once the mass of the atmosphere becomes as big as the core itself, then you enter a runaway phase of accretion where the planet grows very fast to Jupiter mass. Okay. So when did that take place exactly? Like how, what was the state of Jupiter like, you know, at some point after the sun's formation other than now?

• 46:35Brian Keating?

  Yeah.

• 46:35Speaker 02

  We don't know. And so what this new work demonstrates is that there's actually a record of how Jupiter evolved about four million years after formation of the first solids in the solar system that's embedded within the orbits of the tiny satellites that live inside of Io. Okay. So there's

• 46:55Brian Keating?

  Sorry, satellites inside of Io?

• 46:57Speaker 02

  Uh, no.

• 46:57Brian Keating?

  Oh, inside the orbit of Io.

• 46:58Speaker 02

  Yeah, inside the orbit of Io.

• 46:59Brian Keating?

  Oh, there are satellites, there are

• 47:00Speaker 02

  Yeah, everybody, everybody always forgets that these exist, but actually the first one, Amalthea, was discovered by Barnard.

• 47:06Brian Keating?

  Really?

• 47:06Speaker 02

  Yeah, and like

• 47:07Brian Keating?

  Eighteen twenty-six.

• 47:08Speaker 02

  Eighteen ninety, maybe ninety, but like, he must have had crazy good vision, right? Because this satellite's like eighty kilometers across and it orbits at only a couple, two and a half or so jovian radii. And uh, there's another one called Thebe that's that's slightly further out. And as it turns out, the orbital inclinations of these moons store a record of where Io started out, how it migrated out tidally. And from this, you can infer a lot.

• 47:39Brian Keating?

  I have a little shameful detail, a secret, a metric to reveal to you, which is that only about a third of you that are watching, enjoying, or listening to this podcast, or watching it on YouTube, are actually subscribed and following me on those platforms. And it's quite a shame, because we have so many cool episodes coming up with the actual man who killed Pluto, Mike Brown, it's coming up. You don't want to miss it. So please do subscribe, follow it wherever you're watching or listening to it. I guarantee you it's worth your while. And if you wouldn't mind doing me a favor, an astronomical favor, you can't have your own constellation. Those are set. There's only 88 of those. But you could make your own asterism, a collection of five stars, hopefully, where you can review the podcast if you're listening on audio. So please do that on Apple or Spotify. It really means a lot to me, and it really does help us boost the

• 48:22Brian Keating?

  visibility. In the constellation of over 3 million podcasts, you know, this is in the top 0.01% of all podcasts, but I think we're criminally under subscribed. I hope you will do that and help me boost the ratings visibility and quality and caliber of the productions. I'm really up to it. Better cameras, better sound, better lighting. And I know that you'll appreciate it. So please do do that. And I hope you will see it will pay off. Of course, it's free. So it doesn't really cost you anything. Please do that. Now, back to the episode.

• 48:51Speaker 02

  The basic idea is that from Io's orbital record, right, you can also use, you know, conservation laws, conservation of angular momentum of the spin of Jupiter, etc., to read off what was it like when the gas just evaporated? And the answer is, it was twice as big as it is now. Okay. And it glowed at about 1,200 Kelvin.

• 49:15Brian Keating?

  So it's almost brown dwarf, or even hotter than a brown dwarf?

• 49:18Speaker 02

  Oh, yeah. Initially, yeah. Yeah, absolutely. And so

• 49:21Brian Keating?

  Was there fusion? I mean, could it have fusion at that scale?

• 49:24Speaker 02

  No.

• 49:24Brian Keating?

  Because it didn't have that much.

• 49:25Speaker 02

  Yeah. Yeah. And so like the interior temperature, even like DT fusion requires 70,000 Kelvin. It's like at 50 at the, so, close, but no cigar. But once you know the interior state, then you can infer the magnetic field. Why? Because as it turns out, right, rapidly spinning, spherical, fully convective Physical dynamos all fall in this regime of having a equal partition like behavior where the kinetic energy of the convection is so like rho V squared of convective, you know, motion within the planet is balanced by the magnetic energy density B squared over two mu naught. And that comes from the fact that convection is the thing that's generating the field and

• 50:10Speaker 02

  there's kind of, there's a bucket to put the energy in. And so

• 50:13Brian Keating?

  Unlike the solid rocky planets, right?

• 50:15Speaker 02

  Right, right. Well, and so that gives you a couple hundred gauss as the field of the primordial Jupiter. And once you know the radius and the field and you know where Io was parked, you can actually also infer from that the accretion rate of gas that Jupiter was experiencing right before the gas went away. And that turns out to be a Jupiter mass per million years.

• 50:36Brian Keating?

  Holy cow.

• 50:37Speaker 02

  So all of these things are actually not surprising numbers, but it is a model independent way to infer them. And it's like stored in the orbits of these tiny

• 50:46Brian Keating?

  And are there implications for the survival? I'm just thinking right now about Earth. And as you said, Jupiter is the architect, but it's also like a bodyguard. We saw Shoemaker Levy, you probably weren't even born, but I saw it 1994 smash into Jupiter.

• 50:57Speaker 02

  I was born.

• 50:59Brian Keating?

  Babyface Batijan, they call you. You know, there's this notion of as a bodyguard absorbing stuff. So if it was eight times bigger, you know, volume, it was eight times more massive, roughly, it's just, you know, whatever, I'm a experimentalist, right? Does that mean it was even more efficient soaking up the meteorites, the meteors that would have impacted Earth, comets, trans-Neptunian objects, planet 27? Could it have been more, you know, of a bodyguard than it already was? Allowed life? I'm trying to get to, yeah.

• 51:23Speaker 02

  Yeah, I think certainly, certainly compared to the work it does now, like right now, the load is low because there's not that much stuff coming in from the outer solar system. So just the flux of trans-Neptunian objects, you know, becoming centaurs and being kicked around by the giant planets and then eventually reaching Jupiter to become Jupiter famicomis, that flux is nothing compared to what it was immediately after the gas went away in the primordial solar system. Because when that happened, the solar system was encircled by 20 Earth masses of planetesimals.

• 51:57Brian Keating?

  Right.

• 51:58Speaker 02

  All had to get scattered out. So Jupiter was kind of working overtime for the in the in the first.

• 52:04Brian Keating?

  Will these Europa Clipper, JUICE, all these other missions, will they tell you anything? Are they more the outer moons? They don't tell you as much about Io.

• 52:11Speaker 02

  They they will tell us a lot about the composition, the geophysics and the and the geochemistry of the satellites. You know, I I work a little bit on satellite formation. I have a couple of papers. And I'm really excited because that's going to kind of take the real constraints of just being there and kind of taking a look at what this looks like to the next level. Um, for this problem, I don't think it will matter that much. But, you know, I always don't think things matter that much until they do. So, you know.

• 52:42Brian Keating?

  And then Leslie, whatever his name is, shows up on your doorstep. Uh, her name is, talk about the calculations that surprised me in this paper, the consequences of thermodynamics. I didn't initially see that there'd be any connection between the entropy, what you call the cold star and the hot star. What are they first explain? How is entropy relevant to, you know, these calculations? And what bearing does the calculation from thermodynamics even have on a planetary system?

• 53:05Speaker 02

  Okay, so can I tell you, tell a quick?

• 53:07Brian Keating?

  Yeah.

• 53:08Speaker 02

  Story that's like one of my favorite moments from undergrad is I had a, I had a professor uh, in in Thermo who said on lecture one, he's like, you have been all misled about entropy. You've been told that entropy is a measure of disorder in the universe or in in your system. And that's just like, that's just like, forget that. Okay, in this class, we're going to really learn what it is. But before you do, you have to first learn quantum statistics, then from it, you're going to get to classical statistics. So there's like kind of three weeks of prep that you have to do before you really understand what entropy is. And then came the day when it was like, today you will learn what entropy really is. And you, it'll finally make full sense to you. Everyone's, you know, super excited.

• 53:51Speaker 02

  He's like, okay, entropy is the Boltzmann constant times the log of the partition function. Do you understand? Right? So that's my answer. That's how it's all connected.

• 54:03Speaker 02

  But to maybe bring it back to something a little bit more practical, right? Jupiter by virtue. Of being a convective planet, okay, is also very nearly isentropic. Okay, even though temperature, of course, goes up as you go into the deep interior. If you were to grab a patch of gas from, I don't know, halfway into Jupiter's radius. And slowly move it back up to the surface, it would have the same temperature as the surface. Right, or as the convective, very convective boundary, effectively speaking, right? And so the entropy is a much better number than temperature. Because it's the thing that defines the entire kind of curve of the interior profile.

• 54:47Brian Keating?

  Record of the trace of the path.

• 54:48Speaker 02

  Exactly, exactly. And so quoting a number like whatever, ten point five, right? KB per baryon, right? That tells you how hot Jupiter is, not just at the surface, but how hot it is in the interior. It kind of gives you the full picture. Now, this hot start versus cold start problem is ultimately comes down to the problem of the shock. Okay, so when you're forming the planet, okay, and the planet is accreting, and gas is falling on it, right? If you imagine, you know, taking a balloon of gas and smacking it against another balloon of gas. If you do it slowly, it just absorbs, right? If you do it much faster than the speed of sound, it bounces. And so you get some energy release.

• 55:31Speaker 02

  So there's this question, which is not a, this is theoretically difficult question to answer of how much energy is actually injected into Jupiter when it accretes mass? And how much of it just bounces off and radiates away? What this new paper suggests is that actually most of it gets injected into Jupiter. As you accrete, the, a, a large fraction of the luminosity that the planet it, uh, you know, exudes is coming from material that's being injected, accreted.

• 56:05Brian Keating?

  So that was awesome. That was a kind of grand overview of what we know about Jupiter and how we know it. Now here's a deep dive from the slides from the presentation that we heard Konstantin just give to us here in person at UCSD. This is again, a real and rare treat for you and me to experience the top performer in this field. It's like having Steph Curry, you know, teach you how to do jump shots. This is a masterclass from an expert, perhaps again, the foremost expert in the world, on the properties of our early solar system, including the second most important planet. Okay, fine, Jupiter. So now we're going to go into that slide and then we'll come back to the very end of the interview. And then we'll have homework and takeaways for you.

• 56:43Speaker 02

  So we've got all of these circles, right? These are all planets color-coded by the type of star that they orbit. And what I've done here is on the Y-axis, I've done a slight variation. Usually people just to show the mass, I've normalized the mass by the mass of the central object so that I could also overplot the population of solar system satellites as these rectangles. So naively, just like without knowing anything, you can kind of tell that the population of giant planet satellites fits nicely with this cloud of sub-Jovian extrasolar planets

• 57:25Speaker 02

  that, as it turns out, is the dominant outcome of planet formation in the galaxy. Now, there are many patterns that are being studied about this population day. And I would say one of the most striking things is that they're all kind of right here. Okay, now this is a log scale, so it's easy to say right here and kind of cover a lot of space. But if you focus on this histogram here, it shows you a histogram of the shortest orbital period of a planet in a given system.

• 58:05Speaker 02

  And there is clearly some peak, right, that lives between a period of one day and 10 days. How do we understand this? Like, why should this be? Where does this come from? Well, In general, we think these planets, when they form, interact with the protoplanetary disk where they form, right? And they do so principally by raising wakes, right? Within the gas and these wakes, sorry, gravitationally pulled back on the planet. And so if you put a planet somewhere within the disk through this interaction, which is creatively called type one migration, there's also type two.

• 58:50Speaker 02

  Uh, so through type one migration, the orbit just decays and it decays all the way down to the place where the disk ends, right? And the disk, right? The protoplanetary disk has a cavity because magnetospheres of stars tend to carve out this cavity. And this is sort of a well-known and well-appreciated feature of protoplanetary disks. It shouldn't be a selection effect. Could it be a selection effect? Let's go back. It's easier to find stuff this way. Okay? So.

• 59:30Speaker 02

  No, no, it's easier to find stuff this way. So the fact that there's, there's a, there's a drop off here, here is, is real. Out here is there selection effect? Absolutely. And people do very careful modeling of, of asking the question of like, is this fall off real? And the short answer is it's real. There's really a turnover in the knee of the occurrence distribution. Okay. So there's, if you kind of accept that protoplanetary disks are truncated by magnetospheres, like people generally accept that to be true. And if you accept that this interaction leads you to decay to the inner disk, then you're presented with a bit of a puzzle.

• 1:00:12Speaker 02

  And this puzzle, um, I can highlight by going to ran three systems which orbit three different types of stars. Kepler 256 has some planets, they orbit a star of a solar mass and the innermost period is one and a half days. Then if you go an order of magnitude down, the Trappist I system, which is a very famous exoplanet system, in part because it's called Trappist. And you ask, what is the innermost orbital period? It's also a half, well, one and a half days. If you go another two orders of magnitude down and ask, what was Jupiter, like where's Io orbit?

• 1:00:56Speaker 02

  It's sort of also one and a half days. So I don't want to make the impression that one and a half days is, you know, absolutely the critical number. But the order of magnitude is kind of conserved, even though the mass of the central body changes by orders of magnitude. So how can this be, right? How can there be, within this context, a deep level, deep like state level of conspiracy, where all discs get truncated at an orbital period of only a few days? So let's think about how this can be. Well, first of all, the physics of truncation of protoplanetary discs has been understood since at least 1979.

• 1:01:41Speaker 02

  Like, literature in neutron stars by Gosch and Lamb was the, really the first to point out that you can compute this radius of the magnetospheric cavity by equating the magnetic pressure scale to the accretionary ram pressure scale. So you can do that, assuming a dipole field. You know, magnetic pressure as usual is B squared over 2 mu naught. And for kind of spherical free fall, ram pressure, rho B squared, can be re-expressed in terms of the disk M dot. Okay, so these two things, where the radius

• 1:02:26Speaker 02

  at which these two things equal is where you cut the disk. Okay, so somehow, right, the radius changes with.

• 1:02:35Speaker 02

  The central mass, right? But the frequency remains the same. So how can we have this? Well, let's, let's compute, let's construct a very simple model. So the simplest thing, the simplest scaling that you can imagine for the accretion rate of protoplanetary or just like disk astrophysical disks is that the rate of accretion will scale with the mass of the central body. The data is actually quite fuzzy. This might be to the one power, this might be to the two power. Both are consistent with the available data, but for, for the simplicity, let's, let's choose this linear relationship.

• 1:03:18Speaker 02

  Okay, so then we'll replace the M dot here with something that goes as M. Okay, what about the magnetic field? Well, for rapidly rotating, fully convective astrophysical dynamos, there exists a important scaling law that tells you that magnetic energy density B squared over two mu naught goes roughly as the kinetic energy density of convection, right? And then through mixing length theory, you can relate this in the usual way to the heat flux. Okay, there's a reason, by the way, I'm telling you all this. I'm not just randomly making stuff up.

• 1:04:00Speaker 02

  This is all going to connect back to Jupiter momentarily, but I'm having fun first with extrasolar planets. Okay, so this scaling law between the field strength and the luminosity of stars is a pretty well-established thing, and it connects, you can actually connect the geodynamic, the jovian dynamo, M dwarfs, all on the same curve.

• 1:04:27Speaker 02

  Now, what about the radius? Well, remember, early on, while things are encircled by protoplanets, by discs, stars are contracting roughly as just Kelvin-Helmholt's contraction. And this is a well-known result that the radius then is also just expressed in terms of the heat flux. And as it turns out, if you put all of these things together, right? You can derive an equation for the frequency, orbital frequency, at which the disk will be truncated, and all of the dependence on the mass goes away. Okay, and all of these various constants that appear in the scaling laws are there,

• 1:05:11Speaker 02

  but they come in at a sublinear power. Okay, so you kind of get this 2 pi over 3 days orbital frequency as a relatively universal outcome of disk truncation. And I would argue that the fact that Io and Trappist 1 and all the usual Kepler exoplanets all orbit in a matter of a few days, it's just a reflection of the interplay of these mechanisms, right? Convective dynamo generation, just regular disk accretion, and Kelvin-Helmholt's contraction.

• 1:05:46Speaker 02

  So as we enter the age of characterization of circumplanetary discs for which PDS70C is the poster child, here's the poster, here's PDS70C, there's clearly a circumplanetary disk here. If you don't see it, look again. Okay, it's there. Okay, this blob is a disk. Okay, so I would argue that as we, you know, enter, discover more of these things in the age of Alma, you know, we will find that these two will be truncated at a period of, on the order of a few days. And that's the preamble. And the reason I wanted to tell you this is because much of the same physics that I

• 1:06:30Speaker 02

  just mentioned will come back momentarily when we talk about Jupiter.

• 1:06:36Speaker 02

  Okay, so why do we care about Jupiter? First of all, every person interested in celestial mechanics to have ever lived has concluded that the solar system is composed of the Sun, Jupiter, and other things, okay? In fact, if you read like the textbook of Arnold, not Arnold Schwarzenegger, but a different Arnold, like the mathematician, he kind of says this, and he says, okay, so everything else we'll do in this textbook is basically going to be in this framework of the restricted circular three-body problem.

• 1:07:16Speaker 02

  Also, you know, as our understanding of how the solar system came into existence has sharpened up, it's become clear that actually the formation of Jupiter played a great, you know, maybe defining role in setting the large-scale architecture of our solar system. Perhaps even the fact that the terrestrial planets are solo mass is connected to the fact that Jupiter formed. And these days, and by the way, Jupiter-like planets are not a given, right? Jupiter-like planets occur at around 10 to 15% of Sun-like stars, much less common for lower metallicity, lower-mass stars.

• 1:08:00Speaker 02

  So by virtue of having giant planets in the first place, our solar system kind of already scores at least a B+. Okay, so it's a pretty good planetary system, yes?

• 1:08:22Speaker 02

  15 to...

• 1:08:36Speaker 02

  Oh, yeah. Good question. So is it simply an observational bias? I would say at this point, no, because some of the, I mean, that number at this point comes from the California Legacy Survey, which has been going on for nearly 40 years, right? So of course, with ever increasing precision, but yeah, at this point, in terms of period, we kind of go beyond Saturn. And there appears to be a drop off in the occurrence rate before the bias really sets in. So there seems to be like a couple AU is the peak of where giant planets occur, and they're much more rare interior and exterior to that.

• 1:09:19Speaker 02

  So it's kind of this log Gaussian distribution. Okay, so today, we know quite a bit about Jupiter itself. We've got the Juno mission, which orbits Jupiter. One of the goals of the Juno mission was to measure the gravitational harmonics out to degree like 12,000. It's not really 12,000, but it's some very, very high degree. I think they had like a Le genre polynomial out to J14, right? So just crazy, crazy good understanding of the Jovian, you know, the Jovian gravitational field. There's all this understanding of what's

• 1:10:01Speaker 02

  in the Jovian atmosphere. And I would argue that by comparison, our understanding of how Jupiter formed can be summarized in this plot from 1996. And this is still more or less the state of the art. So let's go through this plot. What is it? What is it showing us? Well, first of all, on the X axis, it's showing us time in millions of years. Okay. And on the Y axis, it's showing us mass. So this plot can be separated out into three distinct phases, which are named Phase 1, Phase 2, and Phase 3. Okay, Phase 1, which is this phase,

• 1:10:44Speaker 02

  corresponds to the formation of the core of Jupiter. It's like from Jupiter gravity data, we know that there's about 25 Earth masses of heavy elements inside Jupiter. They're not concentrated in a straight up solid core. They're kind of distributed in a fuzzy core, but we know that the core is relatively deep seated. Okay, so once this core forms, then we have a protracted period of steady gas accretion, where this core acquires a hydrostatic envelope. Okay, that slowly grows in mass. Okay, it grows simply by cooling down. In fact, Eve has a paper about this, right? It's just like cools down.

• 1:11:28Speaker 02

  So when it cools down, it contracts a little bit, letting in more gas into the Hill sphere. That's the basic mechanism. And once the gas accretion allows the atmosphere to become as massive as the core itself, this process accelerates into a phase of runaway accretion, during which you grow up and graduate from sort of 20, 30 Earth masses all the way up to the 300 Earth masses, that is Jupiter, in a short amount of time. In fact, in these 1D models, the accretion rate goes as something like mass to the 4 thirds power. And so you reach infinite mass in finite time.

• 1:12:11Speaker 02

  Okay, and the way that you'd explain that Jupiter is not infinitely massive is at some point, you just have to turn off the code. Right, like when it goes through Jupiter mass, you're gonna shut that sucker down. Okay, shut off the gas. Um, so this is from 1996. Okay, right, Nickelback hadn't even made it big. Okay, like that's how old this plot is. Uh, right, this is from 2019, and modern kind of 3D calculations more or less look like this. And they have had a Illuminating effect in quantifying how the hydrodynamics of gas occurs when you have

• 1:12:55Speaker 02

  a young planet and that is embedded within a protoplanetary disk. And it's very, very interesting. But when it comes to answering the question of like, what happens to the, what's going on at the planetary scale, they, these models basically have no resolving power, in part because their softening length is about this big. Okay. About point one hill spheres. And, and it's frustrating because like, I would like to know how Jupiter formed. Now, uh, I'm not in the astronomy department at Caltech. I'm in planetary science, which is part of geological and planetary sciences. There are a lot, a lot of my colleagues are geologists.

• 1:13:37Speaker 02

  And one of the things that you learn about a geologist is like, if you go out into a field with a geologist, a geologist will kind of walk around for a while, pick up a rock, kind of look at it, put it back down, pick up another one to kind of smell it and be like, that mountain definitely felt like formed 50 million years ago. Like, I just know it. And it's like, how did you know? It's like, you just know. Okay. So I always kind of feel jealous that I can't just like, look at a rock and just know how Jupiter formed. Except for, I think you, that there is a chance. Okay. There is a chance. So Jupiter, and this is by the way, a beautiful JWST image of Jupiter. So Io is, uh, it's not in the image, it's further out.

• 1:14:20Speaker 02

  If you look at Jupiter close in, it's orbited by a series of rocks. And these are rocks that are maybe 80 kilometers across. And people always forget that these rocks exist. Okay. In fact, this one, Amalthea, was discovered by Barnard of the Barnard star fame. In his paper, he speculated about the kinds of aliens that live on Amalthea, uh, which is pretty fun to read. Uh, but there's now, as it turns out, there's four of them. There's Amalthea here, there's Stevie, which is off the image, but you can see some of the light there. And there's a couple, um, couple of other really, really tiny rocks that actually create the Jovian rings. And these rocks.

• 1:15:08Speaker 02

  Even though, you know, by the looks of it, they orbit exactly in the plane, in the kind of equatorial plane of Jupiter, that correspondence is in fact not precisely exact, okay? Amalthea is inclined with respect to the Jovian plane by 0.39 degrees, and Thebe is inclined with respect to the Jovian equatorial plane by 1.1 degrees.

• 1:15:37Speaker 02

  Uh, people in astronomy would like to say, what's 1.1 degrees among friends? That's like zero. Uh, but I would argue that these are in fact very, very meaningful numbers. Why are they meaningful numbers? They're meaningful numbers because they in fact hold the record of Io's tidal regression. Okay?

• 1:16:05Speaker 02

  Where do you see Io's footprint?

• 1:16:08Speaker 02

  Oh, this? Oh, okay, so Io is heavily volcanic, right? And so it's always like the plasma torus is, part of the plasma torus is accreting onto, uh, they're following the, the Jovian, uh, field lines.

• 1:16:24Speaker 02

  Um, okay. So, given what I've told you in the first few slides about extrasolar planets, and the fact that almost certainly qualitatively the same thing unfolded in the Jovian system, namely, the satellites formed somewhere by type 1 torques. They migrated and parked near the inner edge of the circum-Jovian disk. And that's actually why they're in a 4 to 2 to 1 resonance. Okay? So at the time when the disk is right about ready to dissipate, the picture is as follows. You have Io, Europa, Ganymede, Callisto somewhere here,

• 1:17:09Speaker 02

  and the two rocks, um, Amalthea and Thebe are inside the magnetospheric cavity. Why are they inside the magnetospheric cavity? It's because, well, they're too massless to experience meaningful type 1 torques. They are just shepherded inwards by resonances with, with Io. Um, I can dwell on that a little bit longer, but for now... Just trust me, they were inside the inner edge. Okay, now, then the disk photo evaporates at some point. Typical disks live for about 3 million years. Or I would argue that the solar system's disk lived a little bit longer.

• 1:17:53Speaker 02

  We'll again touch on this in a bit, but the disk photo evaporates. And then, for the remainder of time, since disk evaporation, Io, Europa, and Ganymede have been slowly migrating out by tides raised on Jupiter. This is the same process as why the moon is receding, right? The moon is receding at about a centimeter per year. You have to enjoy it while it's there, okay? Because it's taken off, like it has had enough, okay? So the same thing is happening. And naively, we don't know, right? Where Io started, right? We know that it's moving out right now. We can sort of do astrometry.

• 1:18:39Speaker 02

  But in fact, I would argue that by knowing the orbital inclinations of Amalthea and Thibi, you can very well constrain where Io started. Why? Because as Io, Europa, and Ganymede all move out in concert, they sweep a series of interior orbital resonances. Orbital resonances are configurations where the gravitational perturbations between these bodies become coherent. They correspond to integer period ratios. And as these resonances sweep, every time you cross one, you get a slight kick, both in the eccentricity and the inclination. Okay?

• 1:19:22Speaker 02

  The convergent encounters with resonances lead to capture. That's how Io, Europa, and Ganymede all locked into a 4 to 2 to 1 period ratio. Divergent encounters lead to kind of impulsive kicks. This has been understood since at least the 1980s, but probably even well before that. Okay, how does that work?

• 1:19:48Speaker 02

  When I was a grad student, I started first working on celestial mechanics. I was encountering these types of diagrams. And this looks like the Eye of Mordor, just like staring you deep into your soul. But then, once you understand what's going on, it's super clear. Okay, the keys to get there. So, these are phase space coordinates. And you can think of the radius away from the origin as the orbital inclination of one of the tiny satellites, say Amalthea. As Io migrates, this homoclinic curve slowly contracts

• 1:20:30Speaker 02

  upon this equilibrium where you sit originally at zero inclination. And because this process is adiabatic, phase space area occupied by your equilibrium is conserved until you encounter the separatrix. Now, the separatrix is an orbit of infinite period. So adiabaticity is briefly broken and you acquire some phase space area. And then, as this process continues, this deforms back into a circle. And you have a very deterministic kick in orbital inclination that you can compute, associated with each passage of each resonance. Okay.

• 1:21:12Speaker 02

  So, in practice, what does this mean? This means that, to explain Amalthea's inclination, you can calculate that it must have crossed the 3 to 1 orbital period ratio with Io. If you started out, if you basically start Io too far away from Jupiter, then the inclination would be too small. But, you can't start Io too close to Jupiter because then it would sweep too many resonances and the inclination would be too high. The same argument applies to the inclination of Thebe. This is the one with the 1.1. To explain its inclination,

• 1:21:53Speaker 02

  you have to have sweep the 6 to 4, 5 to 3, and 4 to 2 resonances across this satellite. So, Amalthea offers a lower bound on where Io started out, namely 4.02 Jovian radii. And Thebe provides an upper bound, which is 4.06 Jovian radii. So...

• 1:22:19Speaker 02

  The craters on Amalthea. Yeah, okay, great question. So yeah, they're heavily cratered. They don't impact because you can, uh, so they would impact rather if the reaccretion time was slower than the differential procession time. Okay. So imagine you come in, you shoot one of these things, it breaks apart into a bunch of pieces, right? Those pieces are all occupying the same orbit, but those orbits can differentially process, right? If the differential procession takes them away, then that. But as it is, the reaccretion is basically instant.

• 1:22:57Speaker 02

  Okay, so by measuring the inclinations, right, and matching them to Io's outward migration, you can constrain where Io originated pretty well. I was super happy when I figured this out because I thought it was kind of a big deal. But turns out I was not the first person to figure this out at all. And my undergrad advisor, Greg Loughlin, used to tell me, never fully solve a problem. Like, if you fully solve a problem, just get the full answer, then you won't get cited ever because there's no one left to work on this problem. So just be like, get like halfway, maybe 70% of the way there, but don't ever fully

• 1:23:42Speaker 02

  solve the problem. Okay, uh, so here is an abstract that actually fully solved the problem in 2001 by Doug Hamilton. It was never published as a full paper because the abstract already says everything that needs to be said. Okay, it basically said everything I just told you. And it's got a whopping three citations, okay? Because they fully solved the problem. And, um, this was kind of a cool discovery. And by going into the Wayback Machine, which is like the best website ever, uh, you can, you can go and find slides from a talk that Doug Hamilton gave in 2001. And like, there it is, right?

• 1:24:27Speaker 02

  This is the inclination history of Amalthea. You can see how its inclination grows in this step-like fashion, very deterministic, as Io migrates out. And the same is true for Thebe, where it grows as kind of a multitude of additional steps. Really cool. Okay, good. So now that we know where Io is, so what? Well, let's go back to this figure where I told you early in the talk that satellites and planets will stop at the inner edge of the disk. And in fact, these types of simulations have been done by everyone and their brother over the last 25 years.

• 1:25:11Speaker 02

  And they all conclude that there exists a factor of where you park and where the disk is truncated, and this factor is close to unity but slightly bigger. It's 1.13, okay? The basic dynamics, by the way, of what's happening here is, once you are close to, um, close to the inner edge, then you have this trailing arm of the spiral density wake, right? And so this is a density enhancement in the disk. And that's basically always pulling back on the satellite. And so it's sapping angular momentum away from the satellite. So the torque associated with this arm, which is called the limbblad torque, is causing the satellite to go in.

• 1:25:57Speaker 02

  But, once you go close to the inner edge, there's also, um, horseshoe dynamics, okay, which is, you can almost see the, the outlines of the horseshoe dynamics, which is basically just taking gas and throwing it into the, into the void, where it then gets picked up by the magnetic field and accreted. So that process of throwing gas in creates a torque that gives the planet angular momentum, and they cancel out when you park the, uh, the satellite, sorry, not the planet's satellite, a factor of 1.12, 1.13 away from the inner edge.

• 1:26:38Speaker 02

  Okay, so if you know where Jupiter was, you can then divide the, oh shit, not Jupiter, I'm sorry. If you know where Io was, you can divide Io's primordial orbit by 1.13 and understand where the disk was truncated. And 4.04 divided by 1.13 is 3.6. Okay, this is where the Circumjovian Nebula ended, okay? By the process of magnetospheric truncation. Okay.

• 1:27:13Speaker 02

  You had a question? No, very cool. Oh, it's cool. Yeah, well, it's actually pretty hot. Okay, right around, next to Jupiter, it was, it was, it was like 1,500 degrees. And I have no artistic skill, okay? But, uh, but I did, um, I did have a grant that I could do whatever I wanted with. So I paid a guy to draw this picture. And this picture basically shows everything I just said. This is, um, this is where the circumjovian nebula is truncated, right? It's truncated by the magnetic fields. You've got some meridional flow. You've got the thermally ionized disk.

• 1:27:53Speaker 02

  And a critical, uh, consequence of this truncation is that it also tells you how Jupiter was rotating at this time. Because in fact, all of this business with circum, uh, stellar disk truncation came from the realization that like T Tauri stars do not spin at breakup, right? They spin at a period of a few days. And that's because they spin at almost co-rotation with the, um, with the truncation period of the nebula. Let's think about how this works. If you write down the equation for the spin angular momentum evolution of Jupiter,

• 1:28:38Speaker 02

  you've got a whole bunch of terms, okay? Plus magnetic braking, right? This is just Lorentz torques of the field coupling to the disk. And because the disk is going Keplerian, so slowly compared to say the spin of the, of the planet, the field lines sap angular momentum away from the planet. You also have accretion of angular momentum along the magnetic field lines, which is this term. Now, I took some plasma physics classes as a grad student and my professor used to tell me, in plasma physics, you have equations with lots and lots of terms in them, okay?

• 1:29:20Speaker 02

  But never worry, because always, like, two of them cancel out and the rest just don't matter. And in fact, that's the case here as well. All of this first line is like a 10 to the minus 4 correction to the balance of these two terms, okay? So if you were to solve this, what you would find quickly is that J dot, the spin angular momentum evolution would go to zero, balanced by Lorentz torques breaking the spin and accretionary torque spinning up the planet. And when you plug in the numbers for a dipole field, what you get is that the equilibrium

• 1:29:59Speaker 02

  rotation, very quickly, in like 10 to the 3, 10 to the 4 years, approaches 0.88 of the orbital frequency at which the disk is truncated. So if you know the mass of Jupiter, which I do, it's 300 Earth masses, and I know where Jupiter was truncated, it's 3.6 Jupiter radii, I also know the period with which it was spinning at this time, and it turns out to be about a day. Now, then, the disk photo evaporates, right? The photoevaporation front comes, reaches Jupiter, and it's gone. What happens after?

• 1:30:42Speaker 02

  Well, what happens after is that the spin angular momentum of Jupiter is conserved to a great approximation, because the satellites are actually tiny compared to Jupiter, so their tidal migration extracts a negligible amount of angular momentum. And so, if you know how it was spinning to start with, and you know the angular momentum now, right, and you know the moment of inertia now, and in general, moments of inertia can be computed as a single valued function of the radius with standard planetary structure.

• 1:31:17Speaker 02

  Evolution calculations like, you know, those you can do with Mesa code. Then you can just plug in the the numbers. And it gives you what the radius of Jupiter was when the disk went away. Okay, turns out to be two. Jupiter was twice as big as it is now when the Circumjovian Nebula evaporated. This is a highly boring answer. Okay, because before I did the calculation. I I guessed what it was, and I guessed two. Because, you know, people know that like T Tauri stars are two times the radius of the sun. Uh, and I was like, yeah, it's probably two Jupiter radii. And this is indeed a literature that people guess.

• 1:32:01Speaker 02

  Uh, sorry, a number that people guess in the literature already. But this is kind of a model independent way, I would argue, at getting at this. Okay, so, uh, what else does this tell you? Well, if you have the radius and you have the mass for a giant planet. That gives you what the interior entropy of the planet was. And, uh, the numbers clock in at a little bit higher than 10 K B per baryon. So this corresponds to a pretty hot start of giant planet, which means that, um, most of the energy of the accretionary infall was not radiated away as a shock.

• 1:32:46Speaker 02

  Most of it went contributed to the deep interior. Okay, uh, the entropy is a subtle point, it's kind of fun. But let's get back to, uh, something Brian said I would tell you, which is the magnetic field. Okay, remember how early in the talk I said that for all astrophysical spherical rapidly spinning dynamos, there exists a, uh, scaling law between flux, like luminosity and the field. You can apply that same scaling law here and deduce that to the extent that that scaling law is correct.

• 1:33:26Speaker 02

  The magnetic field of Jupiter when the disk went away was about 200 gauss. And that's a factor of, uh, like 50 higher than it is today.

• 1:33:40Speaker 02

  And finally, once you have the field, you can go back to the formula of the ram pressure equals magnetic pressure to deduce what the accretion rate through the disk was right as it went away. And that gives you about one Jupiter mass per million years. So what do we know now? Well, now we know that this quasi-universal three-day pileup of planets and satellites is a natural consequence of the interplay between disk accretion, Kelvin-Helmholtz contraction, and just dynamo generation in a fully convective object.

• 1:34:25Speaker 02

  And in the jovian system specifically, you can read off what the Io initial starting position was. And from this, you can deduce that Jupiter was twice as big as it is now when the disk went away. It had a field of a couple hundred gauss and was accretion matter at one Jupiter mass per million years. But like, I kept saying that this is at the time when the disk goes away, right? There's a terminal stage of the circumjovian nebula. So when is that, right? Is that 1 million years after CAI formation, 5 million years?

• 1:35:07Speaker 02

  Like, what's the number? Turns out it's 3.98. And this is a well-known number because of something called angrites, okay? Angrites, I always assumed just stood for angry meteorites. Turns out, it's not the case. It's named after some basin in Brazil. But angrites are meteorites that came from a parent body that was volcanic, okay? And the parent body lived for, you know, something like 12 million years. So you can date them, and you can tell each one what time after calcium aluminum inclusion formation each of these meteorites erupted. But because they erupt and then cool down, they go through the Curie temperature, right?

• 1:35:51Speaker 02

  So they record the magnetic field that they see. And you can see that at 3.98 million years, the field goes from a couple gauss to like a zero, okay? And that's interpreted by people in the Kind of that paleomag world kind of agree that what's going on is they were interpreting the field of the circumstellar nebula. And then, once the nebula is gone, they don't see a field anymore. Okay, so the lifetime of the nebula is in the solar system, actually, pretty well constrained to about four million years after C A I formation. So all of this stuff, all of this, the the measurement of the entropy, the field, the

• 1:36:31Speaker 02

  radius, all of this puts a point on Jupiter's formation at four million years after C A I. Now, like, is this a complete history of how Jupiter formed? Of course not. But I'm actually working with a with a student in Switzerland right now, who is doing evolutionary calculations, and he's showing that there's actually a lot of information that can be deduced by matching this point and today's state. Right? So forward modeling can actually rule out a lot of, a lot of things.

• 1:37:14Speaker 02

  Actually, yeah, so, once you let go of the of the nebula, its Kelvin Helmholtz contraction time is like a million years. So in a million years, its radius is now down to 1.5, something like this. Then, that that contraction slows down, but it's, you know, instant compared to the age of the solar system, right? It's sort of tens of millions of years.

• 1:37:39Brian Keating?

  Well, all this talk about entropy has made me hungry to fill up my, I'm running dangerously low on calories, you know, the experts saying, you should know this after your harrowing escape from from L A, that, you know, they say to have six months worth of food, you know, on hand at all times, you know, for instance, I keep it on my body. I just keep the food on my body at all times, calories are there, it's close.

• 1:37:59Speaker 02

  I only have the beer.

• 1:38:00Brian Keating?

  Constantine, I love talking to you, one of the most exciting and interesting minds in this whole field. I'm grateful that you came down. Other than that, we'll be sure to get you back on when we get that that five sigma becomes six, seven, eight sigma, hopefully, in the future. And I just can't wait to see where these investigations go. I love, I love what you do, and it's so different from what I do, that it it really is kind of like a hobby that that's it's like appreciating fine art, you know, it's like something that another expert does, that's just so gratifying to know that there are people like you out there, because I couldn't do what you do.

• 1:38:32Speaker 02

  Well, right back at you.

• 1:38:34Brian Keating?

  All right, my friend. Thank you so much. Let's go grab some lunch at the factory. Let's do it.