In a couple of weeks, Caltech astronomers Mike Brown and Konstantin Batygin will be staying up late over six autumn nights, scanning part of the sky via the great Subaru telescope in Hawaii. They'll be looking for something their data tell them is there, but which they have to see with their own eyes: a newfound ninth planet in the solar system. They hadn't gone looking for a planet — they went looking for explanations for why space debris behaves so weirdly, out beyond Neptune, in what's called the Kuiper Belt. But now they're convinced it's a planet out there, one that's 10 times the mass of Earth, with a 15,000-year orbit around our sun, and 30 times farther away than Pluto. It has no name because it is not yet an official planet, but for now they're calling it Planet Nine — yes, not unlike the cult movie "Plan 9 from Outer Space." And, how's this for synchronicity? Brown is the man whose research wound up demoting Pluto, which is actually smaller than Australia, down to a dwarf planet — yes, he killed off Planet Pluto.
I have to ask the first question of Mike Brown: is this all about penance for being the assassin of Pluto?
MB: If you were to ask my daughter, she would say yes. She is the one who told me that I need to go find a new planet to make up for everybody hating me about the old ninth planet. I would say no. I would say it would require much more foresight to have known that this was going to go on.
Konstantin Batygin, what is it exactly that you found?
KB: What we have is a gravitational signature of the existence of this planet. This planet, just like every other major planet in the solar system, shepherds the small bodies that surround it. And the particular way in which the orbits of this debris are arranged can only be explained by existence of a planet. So it's a little bit like being downtown and hearing an ambulance — you know it's there, but you haven't seen it yet. You even know the overall direction the sounds are coming from, but you haven't seen what color the ambulance is.
Mike came to my office a couple of years ago and said, There's something really strange going on in the Kuiper belt and we should figure out what's going on. And that was kind of the beginning of this whole Planet Nine adventure that we've been on.
Because all the stuff that's out there — all the material or matter that's out there — behaves differently when there's a planet in the neighborhood. What was your eureka moment with this?
KB: That's a great question. The eureka moment was at first a kind of slow eureka creep. We spent the first year trying desperately to demonstrate that there is no planet.
MB: People have been saying, Oh, maybe there's a planet, for 150 years. And they're always wrong. And it makes anyone who says, Oh I think there's a planet, generally is crazy or turns out to have been crazy or just wrong. And we wanted to be more careful and show that it does not have to be a planet. Usually when people say, There's a planet, it's based on something that turns out not to be true.
Or wishful thinking.
MB: Or wishful thinking, or misinterpretation, or something. If you stand up as an astronomer and say, There's a planet out there, all the other astronomers just look at you and roll their eyes and, Oh, you're one of THOSE people — fine. We didn't want to be one of those people unless we were really sure.
So how did you persuade yourselves?
KB: That was the hardest part, actually. We ruled out systematically every other option. No, it's not a passing star, no, it's none of these things. And I think at first rather reluctantly we started playing around with the idea of, OK, what if we introduce a planet into the distant solar system?
MB: Just for discussion.
KB: If we were to imagine that a planetary body could potentially exist, then what would it do? Even the first kind of simple models we constructed, you could see that there was something there.
To get back to your original question about the eureka moment, the moment when we really believed ourselves, for the first time, was about October 2015. We were sitting right here.
MB: We had done what Konstantin said and we had proved to ourselves that a planet could work. And we had tried very hard to rule out everything else. We're both like, yeah, a planet works, but it might be some other idea we haven't thought of yet.
KB: I brought my laptop over here, transferred the theoretical prediction that our model was making onto Mike's computer. We said, all right, we're going right now to plot the entire outer solar system data set on top of the model and let's see what happens. That was the moment of truth where we just — Mike hits the button and on top of these streams of theoretical prediction are our few points and they're aligned, and exactly where they're supposed to be.
What did you do?
MB: We didn't do anything at that point except stare. I think that was one of the few times when we were both silent. Up until that point, it was a cute story. The math was nice, the modeling that Konstantin had done was really elegant, and we had a great story. And we could have written a paper and said, Here's a great story. And everyone would have been, Oh, a very nice story.
And at that moment it went from great story to, holy crap, there's a planet out there. Which I never — I don't think until that moment it had ever actually been real in my mind.
So now what is the protocol to go forward?
KB: Now we're at the stage where we go to the telescope and we just find it, we catch the photons that have been reflected of its surface.
MB: We have done a pretty good job of narrowing down where in the sky it should be. It's pretty close to the constellation Orion, which is kind of fun because that's a constellation everybody knows. If people get up early in the morning this time of year, they can see Orion coming up and they can think, Planet Nine is right around there somewhere.
We're waiting for another couple of weeks before it's up high enough in the sky that we can start observing it and then we're going to start systematically sweeping that area until we find it.
It makes me think of the solar system differently than I did before. There's the inner solar system, and now we are some of the only people in the world who consider everything from Neptune interior to be the inner solar system, which seems a little crazy.
So it would redefine the sense of the acreage of the solar system?
MB: Oh yeah — dramatically.
KBL: It's as if we've all been living in Monaco and mapping out different parts of Monaco, and then we discovered Russia. Or if the sun is the size of a dime, and you walk across Caltech, you reach Planet Nine.
How did it end up being, prosaically, Planet Nine?
MB: We haven't found it yet so it does not yet deserve a real name. And we've actually studiously avoided thinking about names because mostly because I'm superstitious and I feel like that would jinx it. So we can't think of names yet. We stick our fingers in our ears when people suggest things, although everybody seems to suggest David Bowie anyway.
KB: Good name.
MB: Good name.
Is it up to you?
MB: It's funny because there are rules for naming everything in the solar system. Craters on Mercury have to be named after poets. Moons of Uranus are Shakespearean characters. There are no rules for naming planets because there aren't supposed to be any [new] planets.
KB: In the history of humanity, only two planets have been discovered astronomically, and in both cases, the names that the astronomers chose were not the names that we know now. Uranus was originally called George.
KB: George, yes. That was in honor of King George.
MB: Like George's Star.
KB: George's Star, yes.
MB: That sounds like a good country band, too.
Are people hanging on this? Are you starting to get interest?
MB: Yes. A lot of people are convinced that it's going to destroy the world. How many emails do you get a day from people that are scared Planet Nine is going to? There has been this crazy Internet conspiracy, maybe pre-Internet conspiracy, of planets on big looping orbits— ridiculous things, they're going to flip the magnetic fields of the Earth as if, A, that even makes sense, and, B, that would actually do anything.
Nibiru — have you heard of Nibiru? This is apparently, allegedly predicted by this guy from the Sumerian texts. And they've always put it on an orbit, a very eccentric orbit, but of course it crosses the Earth's orbit and that's why it destroys the Earth. So as soon as we found something on eccentric orbit, clearly we have proved that Nibiru is real.
KB: There is one thing I noticed, which is a pattern. When you get crackpot emails, they're always signed not simply with the name of the person, but also the location where that person is from. It's not just, Thanks for discovering Nibiru, I will punch you in the face — Pavel. It's not just Pavel, it's always Pavel from.
Why do people care so much about this?
MB: Ignoring the crazy parts, many other people are excited for real reasons. This is part of our basic exploration of the universe around us. This is changing the way that we look at where we live by expanding it by such a huge amount. And as Konstantin said, it's only happened twice in human history that these new planets have been discovered.
KB: We live in a very special time for planetary science. We have Rovers on Mars taking pictures, we have a sort of exoplanet revolution happening within the last two decades. There are just new things that are out there that have led to some of the renewed interest.
MB: Even 10 years ago, if there was a Rover on Mars, you would eventually see the pictures in a magazine. Now you get them the day the scientists get them. You can look at them and put them together.
The same thing is happening with Planet Nine. Konstantin and I write a lot about it on our blog, about what's going on. People can follow along. People just feel they're more part of the scientific endeavor than they were ever allowed to be before.
What is the definition of a planet?
KB: It's a big thing.
That's so technical!
KB: I think that's as good an explanation as you can — it's a big thing that orbits the sun and dominates its neighborhood gravitationally.
You make it sound like a bully.
MB: It is. I've actually often described it this way. There are eight, maybe nine now, planets that are on these very, very stable orbits. They go around and around the sun, the don't care about anybody else, they don't care about what anybody else does. It's as if you have nine huge boulders in a field of gravel and the gravel is just moving around wherever the boulders say they should, and the boulders don't care how much gravel you thrown at them.
What has to happen next?
MB: We've got to find it. That's the only answer. We are on the telescope at the end of September for six nights. We need about 20 nights on the telescope to survey the region where we think we need to look.
Unless you get lucky.
MB: Well, yes, we need 20 nights to do the full region and it's entirely possible we find it on the very first night.
KB: Neptune was found on the very first night of its observational search, so that's what we're hoping for.
MB: Yeah — I don't think we're that good.