The discovery of Planet 9 has caused a wonderful, confusing uproar and a flood of misinformation in the news and social media. We’ll sort out what we actually know, what things just aren’t true, and what things might be possible!
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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest-running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser: Astronomy Cast, episode 410. Planet Nine: Facts and Fiction. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos where we help you understand not only what we now but how we know what we know. My name is Fraser Cain. I’m the publisher the universe today. With me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville, and the Director of Cosmo Quest. Hey Pamela. How you doing?
Pamela: I’m going well. How are you doing Fraser?
Fraser: Great. Done for like three weeks of travel, looking forward to kind of getting my life back in order. I still, once again, I have no idea how you travel so much without just everything falling apart. I just can’t do it.
Pamela: I can generally work on airplanes as long as the airplanes are not vibrating so hard that it’s impossible to focus on my device. I had that last night, but next week I fly off to the Czech Republic, and I’ll be at the Academic Film Festival at Alamoke. But other than that, I’m mostly home until May.
Fraser: So good. I’m mostly home until the beginning of June, and then there’s an astronomy festival happening in New Mexico that I’m gonna be speaking at.
Pamela: That’s awesome.
Fraser: Which I will give you more information as we get closer to it.
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Fraser: So the discovery of Planet nine has caused a wonderful confusing uproar, and a flood of misinformation in the news and social media. So we’ll sort out what we actually know, what things just aren’t true, and what things might be possible. Now, when we started Astronomy Cast, so many years ago, our first episode was about how we lost a planet.
Pamela: It was, yes. We lost Pluto, thanks to Michael Brown.
Fraser: Thanks to Michael Brown. But Mike Brown taketh, but Mike Brown also giveth. And so here we are, lo these many years later, and Mike Brown and team have potentially delivered us a new planet, Planet Nine, which needs a new name. But I guess it won’t get a new name until it actually gets discovered. And this is the part that’s kind of weird, right? People are really a little confused. Does this thing exist? Does this thing not exist? Does this have anything to do with Nibiru? Are the conspiracy nut jobs right? Should I not be defending science anymore? It’s a topsy turvy world. So, Pamela, first let’s go back and sort of talk about what has actually been discovered so far?
Pamela: So what has been observationally determined? These are things that you can point a telescope at the sky, point the telescope at a few more places in the sky, and after looking at all of these different places in the sky go, “Okay. That chunk of ice is acting in this weird way. This chunk of ice is acting in this weird way. And when you start putting together all of the weird things that we’re seeing, they can all be explained by one roughly ten earth mass object that is on a highly elliptical orbit, tilted to the plane of the rest of the solar system, and hanging out yanking things around.
Fraser: And so we’re seeing objects move in their orbits in ways that you would not predict. Based on the calculations, look at the gravity, try and figure out where it should be moving in its orbit, and these things are all – and a bunch of these objects are all just a little askew from where they’re supposed to be. And so, they are inferring that this object exists, not that they’ve actually observed it yet.
Pamela: And it’s not just a few chunks of ice misbehaving. So first of all, we do see a variety of different Kuiper belt objects that have highly elongated orbits that are all kind of pointing in the same way out of the solar system, so they all come in closest to the sun on roughly the same side of the solar system, and then they stick out at a weird angle out the other side of the solar system. So you have this family of Kuiper belt objects that are in aligned orbits pointed in the same way. Then we also have Sedna, this giant chunk of ice in the outer solar system, not quite as big as Pluto, but pretty big, with a highly elongated orbit, and it actually is also totally explained by this object.
And then we also find that there are what we call centaurs, these families of things orbiting in small clouds that would have resonance pockets where their orbits are stable, and then the rest of the orbit would be cleared out. So you have these clouds of objects predicted by the theorized orbit of Planet nine. And when we look we find those centaurs. Okay! That’s kind of awesome. And then there’s other things with unusual orbits that just seem to make sense. And so when you can explain so many different observable things by a single object with very predictable attributes, you start to think, “That thing probably exists.”
And when you look at the predictions they’ve made for Planet nine, they’re extremely precise. They’re able to say what its orbit likely is in terms of how it’s tilted relative to the rest of the solar system. They’re able to say what is the variation with nine error bars for its orbit distance from the sun. They can say even what is its theorized brightness, and given that brightness would we have seen it already? So there’s a whole bunch of beautifully aligned stuff that tell us the bugger is probably out there and currently sitting in front of the Milky way refusing to be detected.
Fraser: Right, so let’s get on to that second part, which is like why haven’t they found it? I mean, do they know where it is, roughly where it is? Or specifically where it is?
Pamela: They know what its orbit would be. We don’t have sufficient data to say based on how things are orbiting to say exactly where in that orbit it would be. But if you look at the WISE satellite’s survey of the sky and start saying, “Okay. Where can we rule out using WISE data that there would have been things here or there at this other place?” You look at that part of the sky and WISE doesn’t see anything. So using WISE, you can say it’s probably not on its closest approach to the sun. It’s not at 200 AU. It’s gotta be further out. Okay, fine. So we used WISE.
Then what other data is out there? And we have the Catalina sky survey, which is year after year working to map out all of the asteroids that are potentially hazardous to us here on earth. But the data they use to try and detect all of those asteroids can be re-processed to try and recover slowly-moving objects in the outer solar system. And this is something that Mike Brown and collaborators did going through. And they didn’t just do it to try and look for Planet nine, but they also said, “Okay, let’s take a blind look at all of this data from the Catalina sky surveys, and they called this the serendipitous all sky survey.
Looking at it blind, they recovered all of the Kuiper belt objects in those parts of the sky at that magnitudes that we would have expected to find except for one that was hanging out in front of the Milky Way, refusing to be seen against all of the background objects. So they know that this technique works. They know they can look at this data. They can recover objects, and they know down to what magnitude they can recover objects. And they believe that it’s down to about 19.1 V magnitude in the north, and 18.6 in the south. And so that tells us that this is a faint sucker, but it’s still something that you could recover with a good 30 inch telescope.
Fraser: A good 30 inch, that we’ve all got kicking around.
Pamela: A good 3 inch. Well, but this means that you don’t have to be using the VLT. You don’t have to be using one of the hardest to get times on telescopes in the world. You need a good standard university telescope. A lot of universities have these in a dome somewhere on their campus.
Fraser: Right, right. But it’s about knowing where to point the telescope to really catch it.
Pamela: So using Catalina, they’ve ruled out a whole chunk of the sky. Now Catalina didn’t allow them to rule out the entire sky. So they also looked at the Pan-STARRS transit survey, the Pan-STARRS moving objects survey. That got them fainter. So –
Fraser: They tried. They really tried.
Pamela: The tried. So now they’ve gotten down to about 22.5 magnitudes, and this is where you really starting to go, “Oy. I need a multi-meter telescope now. Please give me a bigger telescope.” So they ruled it out except, annoyingly, for that part of the sky that probably, yeah, means it’s hiding in the Milky Way. So it turns out that this sucker – and there’s amazing plots that help understand just how bad the situation is – it is probably out beyond 600 AU right now. It is probably at a visual V magnitude of 22nd magnitude or fainter, and it is probably because it’s so far out, moving so slowly, less than two-tenths of an arcsecond per hour, which most stars, when you look at them, with a good sight, would be one arc second across. So to get the planet to move five diameters of what it would appear like, you’re looking at like five times five, 25 hours, just to get it to move a couple of diameters. And that’s not going to be something you can detect easily.
Fraser: Right. So you’re gonna need a world class telescope, one of the big guns, and you’re gonna need to know precisely where to point it so that you’re gonna get the resolution. And then you’re gonna have to leave that thing collecting light for hours to be able to get a pretty good observation of this object moving at the right speed.
Pamela: And they don’t have to be contiguous hours. So you can look at it –
Fraser: Right, yeah go ahead and –
Pamela: come back.
Fraser: Sure, but that’s what you’re looking at what you’re gonna need. And so this is just one of those things that they just don’t have. All those telescopes are busy, and no one’s gonna give up space in one of the big guns just to examine the sky one arc second at a time.
Pamela: And it’s a pretty big chunk of the sky that it’s predicted to be in. So while we can say it’s over there somewhere, over there somewhere is still several tens of degrees. And that’s not the whole sky but, yeah, it’s a bit difficult.
Fraser: So you got into some of the facts about what we know. You talked about like we know it’s about 600 AU. What’s that? That’s like Pluto’s 100 AUish?
Pamela: No, it’s not that far out. It’s in the 20s I believe.
Fraser: Oh, okay. So much, much further than –
Pamela: So we’re looking –
Fraser: Pluto, okay.
Pamela: Yeah. This is a very distant system. And it’s just not the kind of thing that we’re used to dealing with even thinking about. And this is starting to trigger some interesting rumors floating around the internet.
Fraser: Right. Okay, well we’ll get on to the rumors then. So what are some of the rumors that people are proposing is going on here?
Pamela: One of my favorites is – I love how people don’t know how to use units sometimes. People are trying to say that the every 20 to 30 million year extinction cycles, which we do kind of sort of see here on earth are caused by Planet nine. Now the problem with this is that estimates on the orbital time for this new planet are on the scale of 20,000 years which means any cycle that’s we’d be looking for should be a 20,000 year cycle, and people are now trying to blame a 20 million year cycle on the object. And million and thousand are not the same thing. If they were, my bank account would be better.
Fraser: Right. So right, this idea of – it’s the nemesis theory, right, that there is something out there. And it’s not like there’s anything wrong with the nemesis theory itself, right? This idea that there is a brown dwarf or maybe some kind of red dwarf that is actually, that the sun is actually a binary star. It has this binary companion, and this object moves closer into the solar system every 20 million years, 30 million years, and lets out a cascade objects, interactions from the ork cloud, throws comets, move the asteroid belts around a little bit, and causes some damage. And it is super interesting that the mass extinctions do seem to happen on this fairly regular intervals. This is absolutely science.
Pamela: Yeah. Not related science.
Fraser: Yeah. But as you said, yeah. So there’s nothing wrong with the nemesis theory, just that Planet nine wouldn’t account for the nemesis interval.
Pamela: And I do wanna make a correction. I was fact-checking while we go. Pluto is about 40 AUs away, so we’re looking at Pluto 39.44 AUs. This object we’re looking at currently, it’s around 600 AUs, so huge difference in distance.
Fraser: Right. What else are some theories that are coming around and what we’re looking at here?
Pamela: So one of the things that’s happening is people are striving to read as much into every physics paper as they can. And there were some scientists who were working quite hard to try and figure out is there any way we can narrow down on where this sucker is in its orbit using data that we have, any of it. And one of the ideas that was put forward was if we had enough data from the Cassini space probe that would, as it orbits Saturn, give us more precise information on Saturn’s orbit, maybe that would help us learn more about where planet nine is
Because planet nine would be plugging away, pulling on Saturn gravitationally, creating small anomalies that we may not be able to see from the planet Earth, but we might be able to detect, given the fullness of time, in Cassini’s orbital data. And somehow between that research paper and the internet, it became, “There are anomalies in Cassini’s orbit that no one had heard of before. There are anomalies that have been observed and Cassini’s orbit, and they tell us exactly where Planet nine is. No.
And poor NASA had to actually come out with a press release saying, “No. There are no anomalies in Cassini’s orbit. And if we were able to keep the spacecraft orbiting until 2020, then we might have enough information on Saturn’s orbit that has been refined, thank to Cassini, that we might know something. But Cassini’s almost out of fuel, so we’re crashing it in 2017, and so we don’t get to do this, and we’re really sorry, but really, there’s no anomalies in Cassini’s orbit. And it’s just one of those press releases that you read it and I’m like, “Wow. Someone had a really bad day.” Because you can just image some orbital person is being like, “You never told us there were anomalies.” And the person’s like, “There aren’t anomalies.” Yeah, no. There aren’t anomalies in Cassini’s orbit.
Fraser: Okay . So then let’s talk about the big elephant in the room, which is this idea of Nibiru, right, which you and I and Phil Plait have been debunking you this thing since, I’m not kidding you, 1997 I think is when Phil Plait was starting to write articles about how this is not a thing. And people are like showing pictures from their camera and they show two sons, and they’re like, “See, the planet’s on its way!”
Pamela: Yeah, no.
Fraser: Yeah, and so could there be a planet careening towards earth in the center of the solar system –
Fraser: that’s on a really long elliptical orbit and we just haven’t seen it, and it’s on its way? Maybe, it would have to be –
Pamela: But it’s not this one.
Fraser: But it’s not this one, because once again, we can see Pluto, which is 40 astronomical units away, and it’s teeny tiny, and it’s not very bright. And we can detect it with big telescopes. So anything that would be coming our way that would interact with us or impact us in any way would need to be, with a very powerful telescope, it would be very bright in the sky. We would be able to see it. And we just don’t see it. And Mike Brown, one of the best astronomers in the world, can’t find it. He’s found all the others. He can’t find this one yet.
Pamela: And the thing about the theorized Nibiru is first of all, it gets us back to that 27 million year orbit, because they like to use it to explain mass extinctions. This we know would have a tens of thousands of year orbit. So orbital time doesn’t work. The other thing is people are like, “Is it going to kill us next month?” Well, think about how long it took Pluto to get visited by New Horizons. We launched that spacecraft when Pluto was still a planet. And it was traveling really expletive fast for a solar system object. And if you think about how long it takes for comets that get detected out by Jupiter to make it into the inner solar system, if something was gonna wipe us out next month, we’d see that sucker, and it would be way closer than even Mars is by now.
Fraser: Yeah, yeah, absolutely. So, again, nemesis, perfectly reasonable theory. A planet that gets close to the inner solar system – it’s possible, although you would wonder why all of the rest of the solar system wasn’t all messed up from this planet coming by every few thousand years. So, but the point is is that it would be detectable, and it just isn’t. So there goes that theory. So, were there any other sort of nutty theories that you think need to be quashed here.
Pamela: Well, it wasn’t a nutty theory so much as an intriguing Twitter exchange. So this weekend, poor innocent Mike Brown ended up having to stick his head in and say, “No, Planet nine is not going to destroy the earth.” And I believe it was either Ian O’Neill or Dr. Matthew Francis – they’re both doctors, but their Twitter accounts, it’s @astroengine or @drmrfrancis, and I don’t remember which of the two it was said, “What I want to know is if Planet nine is going to destroy Pluto.” And Mike Brown basically responded, “We’re working to figure that out, because I want to know that, too.” So it sounds like there’s some interesting outer-solar system dynamic calculations going on to figure out what it is the long-term perturbations that this object is going to cause? What are the long-time bad things that it might trigger by throwing different icy bodies around over the fullness of time? We’re not talking next month –
Fraser: Yeah, over billions of years.
Pamela: So, yeah. It’s – follow @plutokiller, @astroengine, and @drmrfrancis. They all have these great exchanges on a fairly regular basis.
Fraser: Right, right. So I guess the point here is that when you look at Pluto, it has this really strange elliptical inclined orbit, very different from the rest of the planets. And so one of the possibilities is that Planet nine helped it get into that weird orbit, and it’s gonna help it get out of that weird orbit right out of the solar system, maybe, way down the road. One thing – this is a little unrelated, right – is that don’t astronomers sort of have odds on whether Jupiter will eventually throw Earth out of the solar system? Weren’t there – right?
Pamela: I think it’s been pretty much figured out that isn’t gonna happen. But looking at the other side of this problem, there have been a few people kicking around the idea that whether than Planet nine flinging things out of our solar system, maybe our solar system, early on, ate Planet nine from another solar system. So perhaps in the earliest days, when our solar system was right butted up against a bunch of other solar systems in that open cluster that we formed in, maybe we just happened to have stolen Planet nine. It’s that – no one knows even what the probability of that is.
Most likely my thinking, based on not having done a Monte Carlo simulation, is it probably formed here, because it actually makes us more normal of a solar system. If you look around, most solar systems have a few oddballs in them, and they have things that are in weird places. We’re far too normal. This is why all of our solar system formation models are just not sophisticated enough to deal with the rest of the galaxy. This finally makes us a little bit less explainable, and thus more normal.
Fraser: Helps us fit in. So if we could get out to Planet nine, what would it look like? You said it’s maybe 10 to 12 times the mass of the earth. Is it an ice giant? Is it rocky? Is it ice? What is it?
Pamela: There’s actually some really neat work being done where they’re actually starting to come out, and this isn’t Michael Brown and Konstantin Batygin. This is a different team over in Europe. I believe one of the author’s names is Esther, and I wish I could remember the rest of their names, because that’s not useful information. Anyways, there’s teams that are currently working to model if you had a ten mass object, and we know ten mass objects are going to be basically ice giants like Neptune.
If we had a ten earth mass object in the outer solar system, how would the materials inside it have settled out? And you basically end up with an icy, rocky core, surrounded by various layers of very cold gas. You’re looking at something that was in the mid 200s of degrees Kelvin. It’s cold. And potentially quite shiny – that’s what we’re hoping for. But that’s just models. Reality has a tendency to surprise us.
Fraser: Right. An object that big is gonna still have a tremendous amount of heat and pressure in its core, and that’s gonna go pretty far out into its outer layers and atmosphere before it really starts to cool down to that minus 200 degrees that the upper upper atmosphere. So but definitely gas, like made of the same stuff as Neptune.
Pamela: So we’re looking at something that’s basically four times, maybe not quite that big, roughly four times the radius of earth. So, yeah – cold.
Fraser: Let’s say that we did get a fix on it, and we wanted to send a fly by to it. What kind of scale would it take to actually reach out and put an object into – just a flyby, like New Horizons?
Pamela: It’s not that it’s hard to do. You just need to know its orbit, and then be very patient across multiple generations. It’s just time. It takes time to get that far out, and if it’s at 600 AU, while it probably is on its way sooner rather than later, it’s not moving very fast.
Fraser: Yeah, I’m just doing the math in my head, right, about 150 yearsish. One hundred plus years for sure, depending on how many gravity assists you can get going. And an I N drive would help somewhat, because you’d have constant acceleration, but still. Still.
Pamela: And one of the kind of really interesting things is that this could just be one of a whole class of objects out there. This is the one that we can kind of detect, but it’s entirely possible there’s just more of these out there, even bigger ones, just the further out you go.
Fraser: Well, so mathematically, we have a few different things that point to maybe having some other larger earth-like sized things out there. So there’s a cliff in the Kuiper belt as near as we can tell out around 55 AU, and one way to explain that cliff in the Kuiper belt, where it’s just like suddenly, we have no more objects out there – one way to get there is to say maybe we have an earth-like object that’s resonance is causing things to get knocked out of that particular band of orbits.
But mathematically, we’re not seeing any evidence for anything other than maybe something that’s weeding out the Kuiper belt at that 55 AU cliff, and then evidence for this. Now there could be further things out, but you start to run into problems that they’re not going to be gravitationally attached all that firmly. So how did they get there, and why did they stay?
Pamela: Well, so I guess we’ll have to wait until Brown and team actually get some photographs of this object before we can come back around and give an update. Everything is still so theoretical right now.
Fraser: And I am gonna make one more correction. We have people pointing out that I made a unit flaw. It’s the temperature of this theoretical object would be 47 Kelvin or minus 226 Celsius, not mid 200s Kelvin. That would be death.
Pamela: Right. That would be –
Fraser: So thank you for your patience, because this is all new stuff that we’re learning as we go. So, it’s not often that we get new worlds, and so basically it’s once every very long lifetime. So the last time this happened was in the early 1900s. Now we’re in the early 2000s. So you and I will be dead the next time a planet is found, should history prove itself forward.
Pamela: Right. Right, and just it’s good to know that you are here as the science is getting figured out. It’s just like the same thing that we say about dark matter and dark energy. We’ve got the slightest hint that something is going on, and now the telescopes of the world are turning to try and piece in this puzzle. And it might be that it’s a dead end, and it might be that the math was wrong, and it might be that there’s a whole new planet out there, and we’re within a couple of decades of having some images of it. Of course, we just need to wait for the large synoptic sky survey, and it should find it.
Fraser: Gaia. Gaia will do this one.
Pamela: Gaia will do it, okay. If it’s pointed in the right place. But what’s so amazing about this is you have Michael Brown and Constantine who always gets left off of absolutely everything, and we really need to stop doing that. It’s Konstantin Batygin. I may be mispronouncing it, but you need to remember his name. It’s not just Michael Brown on this. They said, “Hey, we have this notion there’s this world out here. Let us show you why we think this.” And now scientists all over the world are looking to try and understand all they can as the entire astronomical community goes, “Well, how do we find this sucker?” And that’s kind of awesome to watch.
Fraser: All right. Well stay tuned. To be continued.
Pamela: To be continued.
Fraser: Thanks Pamela.
Pamela: Thank you.
Fraser: Thanks for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astonomycast.com. You can email us at firstname.lastname@example.org. Tweet us @astronomycast. Like us on Facebook, or circle us on Google Plus. We record our show live on Google Plus every Monday at 12:00 pm Pacific, 3:00 pm Eastern, or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at cosmoquest.org.
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