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Dr. Konstantin Batygin, professor of Planetary Science at Caltech, made a joke that turned out to be true. In 2014, another Caltech professor, Mike Brown, brought an intriguing  to Batygin's attention. The paper described a peculiar planetary alignment in the outer solar system. While developing theoretical models to explain the paper's assertions, Brown and Batygin had a running gag, "We were like, okay, as a joke, let's put a planet in the outer solar system just to see what would happen." In this episode of Looking Up, Dean Regas chats with Dr. Batygin and gets the full story.

Send us your thoughts at lookingup@wvxu.org or post them on social media using #lookinguppodcast

Additional resources referenced in this episode:

• The Pluto Killer (with Mike Brown)

EPISODE TRANSCRIPT:

Looking Up is transcribed using a combination of AI speech recognition and human editors. It may contain errors. Please check the corresponding audio before quoting in print. This transcript may include additional material from the conversation, not featured in the audio.

Dean Regas: Pluto鈥檚 not a planet, right? I think we are all in agreement about that. So that leaves us with eight planets in our solar system. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Thanks for not turning off the episode, by the way. Stay with me because what, what if I were to tell you that there was another planet out there - lurking in the farthest reaches of our solar system, way beyond Pluto?

It鈥檚 so distant and so dark that no telescopes on Earth are yet powerful enough to detect it. Yet. A ninth planet. Let鈥檚 call it Planet Nine.  Sure, you say. Actually, I say the same thing. If we can鈥檛 see it, how do we know it鈥檚 there?

Math! And math found a planet before. Can it do it again?

 From the studios of 91制片厂, I鈥檓 your host Dean Regas and this is Looking Up! The show that takes you deep into the cosmos or just to the telescope in your backyard to learn more about what makes this amazing universe of ours so great. My guest today is astronomer and mathematician Konstantin Batygin, Professor of Planetary Science at Caltech.

Dean Regas: I鈥檓 excited to talk with Konstantin Batygin about Planet Nine. He is one of the main people who have predicted its existence, and I got him to almost bet it will be found soon.

[Dr. Konstantin Batygin Interviewer]: You think planet 9 exists with 99% probability?

[Dr. Konstantin Batygin]: Something like that. Yeah, maybe I鈥檒l push it higher, 99.9% probability.

Dean Regas: And many Planet 9 believers cite precedence. Neptune, or as I may call Planet 8, was discovered in 1846 when it was first spotted in a telescope.  But two mathematicians found Neptune on paper long before then.

A new planet discovered without the use of a telescope or any distant instrument, solely with the help of paper and pen.

Dean Regas: Astronomers were watching Uranus, discovered in 1781, and it moved in a funny way. It was AS IF an unseen object was perturbing (or affecting) its orbit ever so slightly. When John Couch Adams in England and Urbain Le Verrier in France looked at the problem, they computed a mass that would cause such perturbations, unseen to that point, and its possible location in space. Le Verrier went so far as to write to astronomers and in essence claim, 鈥減oint your telescope there, and you鈥檒l find it.鈥�
On the night of September 23, 1846, an astronomer at the Berlin Observatory, Johann Gottfried Galle, following Le Verrier鈥檚 instructions, aimed the telescope. And within 1 degree, 1 degree of where Le Verrier predicted鈥�

2.8 billion miles from the sun, a lonely blue world drifts in the darkness.

Dean Regas: There it was. A deep blue disc. It was Neptune. Galle must鈥檝e been shocked and awed when he wrote to Le Verrier later: "The planet whose place you have computed really exists!" This was math鈥檚 day in astronomy. Could history repeat itself? Could the mathematicians be right about Planet 9?

Dr. Konstantin Batygin: Hi, my name is Konstantin Batygin and I鈥檓 a professor of Planetary Science at Caltech.

Dean Regas: Well, Konstantin, thanks so much for joining me today.

Dr. Konstantin Batygin: Thanks so much, Dean. Pleasure to be here.

Dean Regas: Back in 2016, you worked with Astronomer Mike Brown to try to mathematically prove the existence of a ninth planet, an unseen planet far beyond the orbits of Neptune and Pluto.
So, first question. Mike, of course, is famous for discovering many dwarf planets that contributed to Pluto's getting kicked out the Planet Club. Did Mike come to you because he felt bad about what he did to Pluto, and he wanted to make up for it?

Dr. Konstantin Batygin: Well, that's sort of like a joke story that he likes to tell, but the answer is no, actually. The answer, the real story is more interesting.

He came to me because, I I had just returned to Caltech, just started my faculty job and Mike was like, listen, there's this remarkable paper by these guys, Trujillo and Shepherd, Chad Trujillo and Scott Shepherd, and they are talking about this like alignment of the arguments of perihelion and like, what the hell is that? And like, we should kind of look into this. It looks kind of interesting.
And then we sort of, over the course of a year, I mean, started kind of developing theoretical models to try and explain some of this.

And we would routinely make fun of the idea. Like, you know, what would be hilarious is if we wrote a paper about how this is caused by an extra planet in the outer solar system.
And, as we kind of work through the various sorts of explanations and like our takeout blooper reel is full of ideas that didn't work, we were like, okay. As a joke, let's try and put a planet in the outer solar system just to see what would happen. Like the worst thing that's gonna happen is it's gonna be ridiculous, and then like suddenly all of these patterns that we were seeing in the outer solar system started to crystallize and come together.

And, you know, even going beyond what the original motivation was like, there was, there's this alignment that I mentioned in this peculiar parameter called argument of perihelion, but along the way we discovered there were other patterns as well. And, and so it was this slow crystallization where we went from an idea that we would just make fun of and joke around about to being like, wait, like this is the only thing that works.

And so, yeah, it was a really fun first year and a half when we kind of led up to that first paper. And of course we've, over the last decade, worked quite a bit on improving the theory and kind of understanding the mechanisms through which these patterns are shaped much better and discovering new ones along the way.

Dean Regas: It鈥檚 so great to see the collaboration between an observational and a theoretical astronomer, it鈥檚 a beautiful thing putting you two together.

Dr. Konstantin Batygin: Well, putting the two of us together was hilarious because we spent most of our time just making dumb jokes and not really getting anything done. But I do have to say I don鈥檛 think I would鈥檝e had the expertise of really understanding the observation, bias, and how these data are collected in the data. What it all means. I think reciprocal is true for Mike. I mean he鈥檚 not really a theorist by training but putting us together really led to the challenge of trying to push one another a little bit. That鈥檚 where I think it鈥檚 been really fun and the institution where we are encourages crazy things so it鈥檚 fun to do it here at Caltech.

Dean Regas: Can you talk more about the moment you realize that this joke about Planet Nine was actually looking to be possibly true? Like was there this aha moment where you look at each other and you鈥檙e like, oh my gosh, this could actually be something?

Dr. Konstantin Batygin: There really was an aha moment! It was kind of a slow build towards an aha moment because we were trying to explain what we were seeing in the outer solar system but it鈥檚 much easier to explain what you already know to be true than to predict something. And then kind of go test it.
So, one of the things that I kept seeing in the simulations was that the eccentric orbit of Planet 9 was twisting some of the distant bodies out of alignment with the plane of the solar system. And I鈥檓 turning them onto these perpendicular orbits. And I thought to myself, well this would be a good prediction, we could say, all right here鈥檚 what we鈥檝e explained but if this is true, then if you go out and look, you should see these perpendicular long period orbits.

And we would kind of have our daily chats with Mike and he was in his office. And I walked over to him like, I think I found something like that could be an awesome prediction. And he was like, okay, I think Doctor 14 is like this? And you know Kuiper Belt objects have these license plates that are usually a year and then followed by two letters and then some more numbers. And he鈥檚 like Doctor, I forget exactly, he kept referring to some object that a 鈥淒R鈥� was in the license plate. And we looked indeed there had been one of these bodies detected that looked exactly like something that was coming out of the simulation.

Of course, I was completely unaware of it, right? I鈥檓 just doing my theoretical world. Of course, Mike, the observer of the two of us had his eye on the pulse of what鈥檚 in the data. And then we鈥檙e like, okay, let鈥檚 dig some more in the data and it turned out there had been consensus of such bodies already detected.
And we said, alright, let鈥檚 do this right now. Let鈥檚 overplot the simulation, kind of outcome, the synthetic expectation of where these things should be according to the model. And let鈥檚 just overplot where the real objects are. And seeing them appear on the screen where the clouds of simulated data were, we鈥檙e like oh my God, I think this might be for real. It kind of graduated in our minds from just something that we sort of make fun of and speculate and are in no rush to get done, so to speak, to this might actually be there, you know?

Dean Regas: Well, I gotta be the skeptic here partially, you know, because it's been nine years since you proposed Planet Nine and it's still remaining undetected. So, from your point of view, is it just like we're waiting for a technology to advance far enough?

Or are you having any doubts, you know, as a mathematician, what percentage of certainty are you that Planet Nine exists? If you wanted to be a betting person.

Dr. Konstantin Batygin: So, let me answer maybe the first question first of like, yeah, it's been nine years. Where the hell is Planet Nine? Well, first of all, in 2016, I said this is gonna take at least a decade because, and I'm on record all over the place saying that, because you're looking for one thing.
This is a very strange, astronomical search. Usually in astronomy you look for a population of bodies and you hope to capture some fraction of it. Here there's one, one little dim star and it's dim as hell. I mean, its visual magnitude, probably 24. It's right at the edge of what can be done with sort of the best telescopes.

And critically, we don't know where to look for it. Like, we can compute the orbit and the mass.
Being a theorist, I really didn鈥檛 appreciate the extent to which you are not in control when you're observing. When you're doing theory and the weather鈥檚 bad鈥攇reat! You sit at home, drink some wine, do some math, relax.

But when you're observing, you're completely at the mercy of the environment. Suddenly the atmosphere becomes turbulent, and your seeing is way down. Or suddenly the telescope breaks. Or the fog rolls in. Or someone goes hiking nearby, gets hurt, and now there's an ambulance at the observatory鈥攕trobing red lights obscuring all the observations.

All of this stuff meant that our search efficiency was probably around 20%, maybe 25%. So, we said, 鈥淎lright, we鈥檙e just going to wait for LSST鈥攖he Vera C. Rubin Observatory鈥攖o come online.鈥� And it just did, last month.

As they start collecting real data, I think that will be a real turning point for this whole business. I think the observational story has been on hold for four or five years now鈥攁nd that鈥檚 about to change.
Dean Regas: Well, I want to go a little farther afield, we鈥檝e had some very interesting interstellar visitors come through our solar system lately. I think the object 鈥極umuamua made headlines, and now we鈥檝e got 3I/ATLAS passing through our solar system.

How exciting are these for someone in your field? To see these interstellar interlopers come through our solar system?

Dr. Konstantin Batygin: Well, look鈥攆irst and foremost, their existence is not at all a surprise.
Now, what was quite strange about 鈥極umuamua was the absence of a coma and the presence of non-gravitational acceleration. That鈥檚 the thing that fed so much of the excitement鈥攖rying to figure that out. Because usually comets have non-gravitational acceleration galore. But they also show a coma.
So, after the detection of 鈥極umuamua there鈥檚 still this lingering question: are all interstellar comets gonna be this weird? And then when the next one comes in, I don鈥檛 remember exactly what year it was, and it was just the most normal looking solar system comet ever. And that really, I think, adds to the mystery of the first objects.

Dean Regas: Konstantin thanks so much for joining me today this has been a lot of fun.

Dr. Konstantin Batygin: Thanks so much Dean, appreciate it.

Dean Regas: Konstantin mentioned 3 Interstellar visitors we have had so far to come to our solar system. These are objects whose journey originated from distant stars and have only recently wandered into our neighborhood.

They are 1I/驶Oumuamua. That鈥檚 the object that sparked curiosity not only because it was first but because it behaved so strangely. And鈥� sparked alien ideas. Ugh, don鈥檛 worry, we鈥檒l do a whole episode on that soon.

The second one was 2I/Borisov. This looked to be a typical but was in fact a rogue comet - on a trajectory that will just pass through. Some astronomers believe Borisov was ejected from a star system about 13 light years away.

And that leaves 3I/Atlas the third of its kind passing through. The thing with interstellar interlopers is that we only recently have the technology to detect them. And the telescope that can help, the telescope I may have a crush on, the Vera Rubin Telescope could unlock and discover so many objects that it will keep people like Konstantin busy for the rest of our lives. But come on, let鈥檚 find the 9th planet already鈥� Again!

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