Thursday, May 4, 2017

Planet Nine: the score card


Last year, just after Konstantin and I announced our hypothesis that a distant massive planet in an eccentric orbit was corralling distant Kuiper belt objects into peculiar orbits, I wrote a post explaining why it might all be wrong. Not that it I thought was all wrong – I was and still am quite convinced that Planet Nine is out there waiting to be found – but it’s always good to understand how a hypothesis might be wrong, particularly when it’s one of your own.

The biggest worry with the original evidence for Planet Nine was that we might have stared at our own data for so long that patterns were appearing out of the randomness. This sort of pattern finding is what leads to people discovering faces on Mars or deities in burnt toast or, sometimes, giant planets in the void of space. As you remember, the evidence for the existence of Planet Nine was that the six most distant know objects in the Kuiper belt were all swept off in one direction and also systematically tilted in the same direction (see the top of this page!), contrary to how they should be. We calculated a probability that such an alignment should occur due to chance, and we came up with something like one-in-a-million. This calculation is one place our hypothesis could go wrong. Though I think we did this calculation in a sensible way, these sorts of after-the-fact calculations should always be looked at a little suspiciously.  A much better approach is to use your hypothesis to predict what will happen in new data. We did exactly this when we predicted the presence of objects with orbits perpendicular to the solar system and then realized these objects indeed existed. For Konstantin and I this prediction was what changed Planet Nine from being a cute idea to a solid and viable hypothesis. Even that successful prediction, however, was less central to the main observation of an aligned set of distant objects. What I really wanted to see was whether or not future discoveries would live up to our specific predictions.

It’s been a year now. How has the hypothesis fared?

First, let’s review the specific predictions.

(1) Newly discovered distant Kuiper belt objects (specifically those with semimajor axis beyond 230 AU, for the sticklers out there) will continue to have orbits the sweep off in the opposite direction of the hypothesized orbit of Planet Nine

(2) These objects will be systematically tilted the same way as the original 6 objects.

Our second paper, a few months later, made a third prediction:

(3) In addition to all of the distant objects swept in the opposite direction, there should be a small population of distant objects with orbits in the same direction as Planet Nine. No such objects were known but they must also exist in the Planet Nine hypothesis is true.

Finally, in a talk at a scientific conference in October, after some even more detailed computer simulations, we made one last prediction, or perhaps we should call it a modification of the second prediction:

(4) Newly discovered objects will have orbital planes that are, on average, tilted in the same direction, but there will be a systematic spread in that tilt.

This last prediction is difficult to explain but easy to show. Every object orbiting the sun has an orbital north pole. Objects which are tilted exactly the same will all have the same north pole. We can represent the tilt of the orbit of an object by the position of its north pole on a top-down view of its latitude and longitude. In this plot, the degree of the tilt of the orbit of the object is the distance from the center of the plot, which the direct of the tilt of the orbit of the object is the direction from center to the point. Any objects in the exact orbit plane of the solar system will have a pole latitude of 90 degrees, and will plot right in the center of the plot. Our latest round of computer simulations showed us to expect a cluster of pole positions all tilted off in one direction, but with a larger spread than we had anticipated in prediction (2). The comparison of the computer simulations of the expected pole positions with the real pole positions of the six distant objects was good, but that’s not surprising, as we designed the computer simulations to match the known objects. The question will be: where do future discoveries lie? Note that it is pretty easy for any one object to satisfy this prediction, as the predicted pole positions cover a pretty wide swatch of the sky, but in general they cluster more strongly off in one direction.
Poles of distant Kuiper belt objects. The original six objects all had poles tilted approximately in the same direction, as can be seen by the red points. The small black dots show the poles found in computer simulations. While they concentrate near where the red dots are, they cover a much wider range of space.


Since then we’ve been waiting to see what might be discovered. It’s slow going. From 2000 until 2013 only six distant objects had been found. Happily, astronomers have been busy, and 4 new distant objects have been announced just in the past nine months. Where are they? Let’s take a look.

The most interesting set of objects came from Scott Sheppard and Chad Trujillo – the same group that realized early on that something fishy was going on in the outer solar system and that inspired us to try to figure it out. Sheppard and Trujillo found 3 distant objects. Two of them fit right into the pattern of the previous 6 objects. They are both swept off in the correct direction, and their orbital poles fit within the range of our computer simulations (again, though, this is a large range to fit into. Sorry. Blame Planet Nine). The third new distant object, though, is my favorite. It is swept into an orbit exactly opposite of all of the rest. This object was precisely the type predicted for the new population we had predicted, and it was in exactly the right spot. How exciting was it to see this newly predicted population? Let’s just say I did a little dance in my office when I saw the orbit.
The orbits of the most distant Kuiper belt objects. The red objects are the original six, the green are the Sheppard & Trujillo discoveries, while the blue is the OSSOS discovery.


Most recently, the OSSOS team announced the discovery of a single distant object. If you look where its orbit lies and then you look at its pole, you will not be surprised to learn that the announcement of this discovery again had me doing a little dance in my office. Four for four! But then you might also be surprised that the astronomers making the announcement claimed that it showed that there was probably no Planet Nine, partially based on the fact that the pole is not tilted enough. What? Ah, it’s because they’re looking at the rather simple prediction (2) and not taking into account the refined understanding that led to prediction (4). That’s OK. The discussion of prediction (4) took place at a scientific conference, and the paper describing it, though submitted for publication, has not yet come out.  It’s always hard for scientific authors to know how to acknowledge these sorts of things, and so, though the authors knew about the prediction, they hadn’t had the opportunity to read a detailed paper describing it, so they chose to not mention it. We’ll still count it.
The newly discovered objects (green = Sheppard & Trujillo, blue = OSSOS) fit nicely into the predicted pole positions.


We now have a score card! Originally there were six objects. Now there are ten. That’s a 66% increase, which is good work, mostly thanks to Sheppard & Trujillo’s efforts. And every single discovery fits a true prediction perfectly. By “true prediction” I mean an authentic prediction about something not yet seen, rather than an after-the-fact explanation. Those are hard. Those are the things that we give serious credence to, as a fun idea turns into a compelling hypothesis turns into a rigorous theory.

Are we there yet? No. I would put us about halfway between compelling hypothesis and rigorous theory. There are still a few details about Planet Nine and its effect on the outer solar system that we can’t yet explain. But we’re close. When (or, to be fair, I should say “if”) those details are nailed down, I will be happy to put Planet Nine into the category of rigorous theory. Of course, we might get lucky and actually find it first. Then it will simply be confirmed fact.

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The season for hunting Planet Nine is coming upon us soon (we predict that Planet Nine will most likely be discovered near the constellation Taurus, which starts to rise in the fall). With all of these new discoveries and, significantly, with our improved understanding of the way in which Planet Nine gravitationally effects the objects of the outer solar system, it’s time to update our predicted positions for all of those searching for Planet Nine. The next two posts will be a bit technical, but will give the most detailed information for anyone out there trying hard to find Planet Nine. Good luck, and, um, tell me if you find it.

36 comments:

  1. Just curious, the day you discover it in the Subaru images, what will be your next steps other than a few dance moves? Get a Hubble shot and gather more info before making public? Can't wait, we need this planet found sooner than later. The cultural impact it will have, thinking about it gives me goose bumps.

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    1. What about starting the push for a NASA (or private) probe mission? I imagine it would be magnificent to be the first discoverer of a large object in the outer solar system to be alive at the time the discovery is flown-past. I should think the opportunity to examine a 10 earth-mass body at close quarters would garner plenty of support from the exoplanet community, given we're finding objects of that size class in other systems but have rather limited remote-sensing options. Great opportunity for trialing new propulsion technologies, as well.

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  2. Thanks for the excellent explainer, Mike.
    Is one of the Sheppard&Trujillo objects missing in the last picture (green dot)?

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    1. By my calcutations the missing one should be at ~10 o'clock and 17 degrees.

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    2. The anti-aligned objects don't share the same poles as the aligned, so I didn't put that one on the plot.

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  3. Are the new constraints hard in the sense that they say "Judging from the gravitational influence on visible objects' orbits, Planet 9 is most likely in Area X"?

    Or would they rather say "Planet 9 is most likely in Area X, Y, Z, A or B, but if it was in Y, Z, A or B, we'd already have seen it"?

    I ask that because I think it's highly likely that if we eventually find and identify Planet 9, we will find we had actually seen it many times before, but didn't recognize it.

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    1. No, we don't yet have those hard constraints.

      Your suggestion about having seen it many times may well be right. If it is at the brighter end of our predictions it definitely has been. If at the fainter end it's less likely, though.

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    2. So we don't really know about Planet 9's position in its orbit, but the predictions based on the assumption of the orbit itself we supported by the new observations (within error margins)?

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  4. Urbain Le Verrier would be so proud! I hope your eyes are the first to find your Planet Nine.

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  5. If Planet Nine had a mass of 10 M_earth and a semimajor axis of 600 AU the Sun's orbit about the Solar System's barycenter due to Planet Nine would be a few times larger than that due to Jupiter. Would this have any interesting effects?

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    1. It would only look like that from outside the Solar System. Planet 9 would cause a gravitational acceleration for every object in the Solar System, but the differences between those accelerations in direction and value would be tiny. Most likely, they would only be noticable if objects got anywhere near Planet 9.

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  6. If the existence of Planet 9 is true, would the models predicting the likelihood of a significant asteroid impact with Earth need to be adjusted or the search area and inclination of potentially hazardous objects?

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  7. One presumes that if dark matter really exists, that dark matter planets would be a thing also, no?

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    1. Regular matter reacts to all kinds of forces, which makes it able to clump together and form stars and planets. Dark matter only reacts to gravity and is spread out very thinly in space. So there won't be any dark matter planets.

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  8. "The season for hunting for Planet Nine is coming upon us soon."
    If P9 is near Taurus, and Taurus is approach the sun, it seems like the season for hunting is soon over, unless "Fall" is soon by astronomical standards!

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  9. "If the existence of Planet 9 is true, would the models predicting the likelihood of a significant asteroid impact with Earth need to be adjusted or the search area and inclination of potentially hazardous objects?"

    Probably wouldn't make much difference. Planet Nine is *very* far out there (waaay beyond Pluto), and most of the asteroids at risk of hitting Earth are much closer in.

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  10. Is the clustering of the poles in one direction combined with the anti-alignment of their perihelia enough to account for the clustering of the arguments of perihelion?

    What does the darkness of the of the various streaks indicate? Is there one 'dot' per unit time, are they darker when the perihelion is lower and the object is more visible, or something else?

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    1. yes about argument of perihelion.

      and the dots are one per time, so they are darker where the poles spend more time.

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  11. Which way do the poles travel along the arcs, is it clockwise like in the normal parts of the solar system (IIRC) or counter-clockwise.

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  12. I think there are 19 Objects, 10 or 11 have been alraidy found, the rest are going to be found soon.
    be carefull, planet nine is very dangerous...!

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  13. In the beginning you calculated a very small probability of the first six KBOs having this anomality by chance instead of it being caused by P9. By how much has this probability changed considering the newly found objects?

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  14. Pluto is a planet (a dwarf planet) and is planet number 9. Planet X aka The 10th Planet aka Nibiru aka Wormwood aka The Red Karachi aka ERIS is real and I see it with my telescope every morning and night. The fact that this object wasn't discovered until 2005 by Mike Brown and put into the laps of NASA whom immediately acting like pros on the entire subject tells me EVERYTHING I need to know. This planet was discussed by the ancient Egyptians, Sumerians, Greeks, Romans, Theologians, Hobie, Aztecs, Incas, Mayans and the Bible. This was before telescopes and "modern science." How much more proof do you need? They were all in harmony about it's 3600 year rotation around our sun and that is brought nothing but doom. If you count back by intervals of 3600 years you find the great flood, the disappearance of the Incas, the Mayans and the Egyptians. I'm sure if you roll back far enough you will find it was responsible for the freezing of Antarctica and the disappearance of the dinosaurs. The bible has never been wrong and refers to Eris as "The Destroyer." Chem Trails are consistently placed in the east during the morning hours and in the west during the evening hours. The Department of Defense is hiding something in the sky and you don't have to be a wizard to figure out what it is. You can sit here and debate about it's existence all you want but I think it wise to place your money on the ancient texts. The Sumerians were NOT the cavemen we were lead to believe they were. They knew about Saturn's' rings, the moons of Jupiter, Earth being the 3rd planet from the sun and they knew about the existence of a 10th planet thousands of years before the telescope. That is all the proof I need. We need to protect ourselves, our families and one another. If you believe 9-11 was an inside job, the JFK assassination was an inside job or that the moon landing video was a hoax then you have NO reason to believe our government and the shit they are spoon feeding us. "We the Sheeple" can only depend on ourselves and need to start making the necessary arrangements to ensure our existence on this planet. Switch yourself out of auto-pilot, listen to the voice of reason, look up in the sky passed the chem trails and realize this is real. Nobody is going to save you, but you.

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  15. If the sun once had a distant companion like Proxima Centauri could it have caused Planet Nine's orbit to vary enough to create the Kuiper cliff without completely destabilizing Planet Nine's orbit?

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    1. interesting question! I don't know the answer right off hand.

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  16. What you call planet 9, was called Nibiru/Marduk by ancient civilizations as far back as the Summerian culture. Researcher Zechariah Stichin has written extensively about this planet, gleaning his information from a very scholarly translating of ancient texts, tablets and engravings. If you were to check his nonfiction book, The 12th Planet , on page 239 in figure 111, you will see a representation of the orbit of this planet that is exceedingly similar to yours. It seems that nothing is new under the sun. Perhaps his research can help you find your 9th planet. It won't be passing by the sun for another 1300 years

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  17. So has the search actually begun? If so, how much of the target area has been scanned so far?

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  18. One of the more fun speculations I've engaged in re planet 9 is the possibility that it is actually a binary planet. If the mass ratio were close to that of Pluto-Charon, that would make the smaller of the two planets roughly Earth mass...

    If the orbit was substantially elliptical (presumably as a result of whatever event ejected it from the inner solar system), that might create enough geothermal energy for Enceladus/Io-style eruptions, or perhaps a Titan-style atmosphere, or Europa style liquid-water oceans, or perhaps all of the above ;)

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  19. This Mike's theory is nice, but If we put on orbit of Planet 9 (10) much more massive object than 10 Neptunes,..everything is much clear and more possible. I made it more than 10 years ago in agreement with what pre-ancient astronomical maps let us know. Simply p9(10) if cca 35Jupiters mass causes, that we see objects far enough beyond Pluto in prooper direction on very elongated eliptical orbits because they have other speeds than real(from our point of wiew, our place in our Solar system) due to opposite motion of Sun,...toward Planet9(10).
    senmut.beep.com
    http://www.lulu.com/shop/pavel-smutny/ancient-egypt-and-2012/paperback/product-16951885.html
    Pavel Smutny

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  20. If predictions on orbit are correct, would P9 have been visible to ancient Chinese and Arabic astronomers? Not talking Nibiru nonsense, but could there be info "back dated" 2000-3000 years ago? Something that scholars have noticed as a mystery that has not yet been answered...

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    1. If P9 had Neptune's size and albedo, and a perihelion at 200 AU as Brown and Batygin predict, then it would have 16th magnitude at perihelion... so no, it wouldn't have been visible without modern telescopes. (Jupiter's size and albedo at 200 AU would still only return about 13th magnitude)

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  21. Yes,..there are infos, ancient , pre-ancient astronomical maps with P9(10) orbital,...depictions,..2, .3,5, ..more than 11,5 ,..thousands years old,but so called modern science ignore these informations. Pavel Smutny

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