Planet Nine from Outer Space ▸ KITP Colloquium by Konstantin Batygin

all right well thanks very much it's my pleasure to be here thanks for inviting me out just before we start like if I can make a suggestion for the future like we might consider doing these outside you know I'm just saying but up to you all right so you know of course I'm sure everybody here is aware of the fact that the last two decades have been revolutionary in terms of detection of planets around other stars so our count I've lost count to be completely honest of how many exoplanets there are now it's four thousand or something like that so we have been clearly winning on the exoplanet front and in the meantime in the solar system we have been losing okay and in 2006 we went from nine planets to eight planets with the demotion of Pluto so today I want to talk about how to make the solar system great again and return it to its former or nine planet glory right so what is staggering is that this solar system has had literally two additions to planetary additions to legitimate planetary additions in its entire in the entire history of humankind right because everything out to Saturn you can just see with the naked eye so the Greeks and Romans just knew about everything out to Saturn and the first addition of a planet to the solar system came right around 1776 towards the end of the Revolutionary War when Herschel announced the discovery of of an object which was very very slowly moving across the night sky so Herschel was exceedingly meticulous in the way that he observed he just observed every night and drew everything he saw every night right so it was it was because of that consistency that he was able to note that this particular dim star was slowly moving across the night sky and so he said oh wow this this has got to be this has got to be a planet and what was immediately realized is that the the particular star he was referring to had been observed before many many times including by Galileo himself so the year the orbit of this new new object was immediately reconstructed right so they knew what was going on by the way Herschel you know being a English character decided to kind of cheer up the king who was kind of depressed at the time because he's kind of losing and said we'll name this planet George okay so we'll have Jupiter Saturn and George you know and that actually persisted for about fifty years after which just like they whatever the equivalent of IAU you know at the time said there's a terrible name for a planet right let's instead call it Uranus so that was the story of how George was was discovered now what was interesting is that almost immediately astronomers realized that something was wrong with orbit and this is a slide from the memoirs of from 1821 of Alexis Bovard alexis brevard was the director of the persian observatory and he took it upon himself to kind of collect all the legacy observations of uranus and put them together in a table and point out kind of you know compile the data set so to speak and I don't speak French but you can clearly tell that something is wrong with the orbit because they're they're sines and cosines right over here and there's a table over there with pluses and minuses so it's cool and also I've highlighted the word Uranus to just demonstrate that I'm on the right page if it what evidently Rivard writes about and here is that Uranus is not where it should have been right the perturbation theories of I mean they're like thing to do if you were a mathematician at the time was to construct kind of perturbative you know solutions for the motions of planets and you know Uranus was not observed where it was supposed to be right so in here on this page Lavar it speculates that there's two solutions being a good theorist he proposed number one that the data is crappy and should not be believed right is that on the off chance that the data is right then what this suggests is that there exists an additional object beyond the orbit of Uranus which is result which is causing the perturbation causing yunus to veer off course so the promise of that data set and remember that was 1821 took a couple decades for it to really come to fruition and the character which is typically credited with the mathematical discovery of Neptune is upon the very a solar very a did a extremely careful and just remarkably complicated calculation to demonstrate that you could explain the anomalies in the Iranian motion with the existence of an additional planet in the solar system when I was an undergrad I lived I was went to UC Santa Cruz and I lived in kind of shaky part of town so I can spot a gangsta from from far away so I kind of know to not make eye contact and this is I mean live area as clearly it has all the signs because he's got his bling right always wearing on outside his stage name is urban right it's yeah what a guy so I like to you know you can download the various manuscript online and it is totally unreadable but it is interesting to just scroll through because it's it's staggering just how much calculation went into that discovery what is even more intriguing perhaps is that when live area was done with this calculation which was in 1846 he went to the Parisian observatory and gave this talk where basically he provided the coordinates for this elusive you know invisible planet to try and cheer up the observers to get them to come out and confirm his calculations and it was very warmly received in fact airy of course it was a very famous geophysicist at the time said I cannot attempt to convey the impression which was made on me by the author's undoubting confidence but the firmness with which he proclaimed to the observing astronomers quote look into the place which I have indicated and you will see the planet well so he was exceedingly confident of his calculations and what's interesting is that the observers were like yeah it's cool math bro but like you realized we have to stay up at night for this and that's kind of a big commitment you're asking us to make so they did nothing ok there's no he in the end drummed up very little enthusiasm among the French observers to go out and find Neptune and the end it was a German observer by the last name gal who found it and Galvez was very meticulous as well he they had this campaign planned on how they were going to search for you know the predicted planet on first night of the observation run you know sky wind dark they opened up the dome found Neptune was what in one hour okay that was so that was that was it it was it was remarkable right how well it worked and what is even more in my view staggering is that it all worked out because it was 1846 okay so like the timing here was everything here's a plot of the real orbit of Neptune and a predicted orbit of Neptune by levira a his contemporary Adams at Cambridge did similar calculations it has recently turned out that Adams so for a long time people believed that they were truly contemporaries it has recently turned out by the discovery of some set of letters I the details are murky to me but that Adams basically was late to the game he presented his theoretical prediction after the planet was already discovered so he was working on this but he didn't have the right coordinates one way or another both of them predicted this orbit that was the head a period that was too long and a mass for Neptune that was too big okay and the reason they got it wrong was because they assumed that the planetary semi-major axes have to follow a geometric sequence it is now known as their tadeas bode law which is not really a law so they got the orbit wrong but they got the location in the night sky right and the reason is that in 1846 Uranus and Neptune were close to conjunction so you could basically do that problem in a shearing sheet and you would get the same answer right so what's interesting is that Neptune has gone around the Sun approximately one time since then if you were to repeat this calculation in 2011 when Neptune returned to where it started from the very a would have predicted Neptune to be here and Adams here so it's like show business right you got to be in the right place at the right time we've got to be in Paris 1846 a place to be nevertheless this discovery made a huge impression on everyone not everyone was impressed a hipster from Cambridge Massachusetts said that this calculation was nothing but a happy accident and Benjamin peers in fact was was highly influential in in getting kind of American astronomers interested in continuing the Stasi said that whatever live area did was kind of worked out coincidentally let's do the real calculation find the next planet over using the same technique and the reason interestingly the reason he thought you could do is because even though Neptune had cleansed most of the errors from the Iranian data set it didn't cleanse all of them that was because they didn't have the mass of Neptune down you know to the exact correctly correct value so he said look there's still some anomalies in the data that we can go after and he strongly influenced a parse of a Lowell who founded the Lowell Observatory and was came from an exceedingly wealthy family in Massachusetts basically at one point asked his dad for a telescopes and so Lowell spent that spent the rest of his life looking for Planet X and in fact he came up with the would the word Planet X didn't find it died in 1916 his last published work was called memoirs on the search for Planet X where he provided a set of coordinates he actually didn't do any calculations himself he took the kind of like Ford production line approach to to finding planets so he hired computers right to just carry out the calculations for him and he kind of in the time that he spent working on this here it's at one point doubled the number of computers so long story short Planet X the old died without having found Planet X then at X was eventually discovered by Clyde Tombaugh here's a real-life picture of him you can also buy his biography in children's book format a little little faster to read so Clyde Tombaugh was employed by the Lowell Observatory after the death of lower himself to just search for the night sky followed the predictions and indeed he found Planet X if you read the frontpage the New York Times on March 14 1930 okay it's it's actually pretty interesting there's a lot of interesting stuff here but if you zoom in to right over here it says that astronomer is hail finding the sphere possibly larger than Jupiter remember Jupiter's 300 Earth masses and four billion miles away meets predictions all right so you know looks like Lowell was right after all of course today we know that that's not true what they found was Pluto man Pluto if you put Pluto on top of Australia it fits right that's how small Pluto really is so really the Pluto's planetary status was derived entirely from this legacy of trying to predict additional objects mathematically its mass wasn't measured until the 70s when it was discovered that it has a satellite and then people were like what this thing is tiny it's five thousand times less massive than the earth so that's kind of the story of the failure of finding new planets in throughout the 20th century so even though no additional planetary objects were discovered in the distant solar system at the turn of the century what astronomers did find who was the Kuiper belt so if there's the solar system viewed from top that blue circle is is the earth orbit so my house is right there okay the Jupiter Saturn years in Neptune this is the orbit of Pluto note by the way that the orbit of Pluto overlaps the orbit of Neptune the reason they stay stable is because they're locked in a mean motion resonance so for every three orbits that Pluto completes sorry Neptune completes Pluto completes two and in a second we'll see all the Kuiper belt objects with well-defined orbits that are known at the moment so there's about a couple thousand of them each one is not very mass at all cumulatively the Kuiper belt is only about 0.1 masses maybe even less than that so they they don't they're basically test particles orbiting outside of Neptune and we've derived a lot of knowledge about how the solar system formed by studying the Kuiper belt but there's one thing I guess I want you to focus on is the fact that if you look at the orbits and the dynamical structure of the Kuiper belt is exceedingly interesting by the way there's there subsets of Kuiper belt objects that are rapidly chaotic Pluto is actually one of them Pluto loses memory of its own initial conditions 20 million years so it's lapin of times or 20 million years and there's other interesting stuff but for the purposes of what I'm gonna talk about it's only relevant to note that all the orbits more or less hug the orbit of Neptune physically okay and this is because this entire population of icy debris was emplaced into their current orbits through scattering off of Neptune and gravity being conservative you know and requires you to come back to where you started from so the orbits change chaotically on long timescales but they remained gravitationally tethered to Neptune this is something that is shared across all essentially all dynamical classes within the Kuiper belt so that's fine and there's no if you just look at this there's no evidence of there being anything wrong with the solar system except for in 2003 my partner in crime Mike Brown was my co-author on this work discovered Sedna together with Chad Trujillo and Scott Shepard so you don't have to be an expert in the Kuiper belt to note that something is horrific Allah wrong with Sedna right first of all at aphelion over here it's about a thousand astronomical units right it's it's kind of in a logarithmic sense it is it is flirting with being an inner Oort cloud if that's all it was I would say that's not really a big deal I'd say well it's just scattered off of Neptune and acquired an energy of almost zero just slightly negative so it's almost on an unbound orbit but but no the the really interesting thing about Sedna is that it's not elliptical enough okay so I had perihelion it never comes up comes to hug the orbit of Neptune and you can integrate you know the n-body problem with Sedna forever and they all it'll do is a its orbit will just slowly process right nothing will change it never comes in its eccentricity doesn't doesn't vary it just doesn't hug Neptune so what this means is that Neptune could not have him placed Sedna into its current orbit something other than interactions with Neptune are responsible for the orbit for a long time for about a decade this was the example of a detached Kuiper belt object and people said yeah right because that's kind of how it was in 2013 however Joe Biden who was discovered orbiting the Sun okay bye again yeah writes they they found Joe Biden on an orbit like this and even at closest approach right Joe Biden comes in only at 80 astronomical units nowhere near the 30 which is the semi-major axis of Neptune and it's like if you have two data points like you've got to make a theory right if you have one ignore if two is hands down you can draw a line through them so this was actually our starting point right we were just like pretty interesting and you know the first thing that we did was we you know we studied carefully the paper of true hero and Shepard and we in there they they pointed out that if you look at the arguments of perihelion which are the arguments of perihelion our weird angle they are the angle that an orbit makes when it crosses the ecliptic in between where it crosses the ecliptic plane and where it comes to perihelion so it's an angle which is actually dependent on which plane you measure it from and they noted that they all kind of if you look in the distant orbits they're all close to zero but if you actually look at the graph they're close to like minus 53 you know there's some spread I was just like what is that so that was our starting point and upon looking at the data the first thing that we immediately noted is that simply if you restrict yourself to orbits that are orbital periods 4,000 years and greater than all the orbits of distant Kuiper belt objects more or less lie in the same plane so if we translate ourselves to the ecliptic we'd almost imagine putting a piece of paper that is about 21 degrees inclined through that group of bodies moreover the all point towards me right and I know I'm gravitationally attractive right but it's just like this is this is odd it's odd that beyond a certain critical semi-major axis all of a sudden the Laplace plane of the solar system if you will tilts and all the orbits point towards me what can I say you can say well hold on there there's six objects right this is like don't be a king of small data but you can ask yourself the following question if you were to just randomly select among the known Kuiper belt objects right which are discovered a similar radial separation six objects how often will you get grouping of the angles this good and the answer is about zero point zero zero seven percent of the time okay so the false alarm probability if you will that this is due to chance it's quite low okay the good news is since then this data set has tripled more or less and to leading order everything is still very much intact I mean this cluster has gotten much stronger so what is happening right strange things are happening beyond 250 astronomical units and by the way in 2016 I met Alex winter and he has aged exactly zero days which makes sense because in the plot of Bill & Ted's Excellent Adventure they have a time machine so I never never understood that that movie was a documentary okay so we mike and i are firm believers that crazy people proposed planets beyond neptune right it's just like if you type in Planet X into Google before 2000 before 2016 it was just crazy people on like a VIX row you know screaming at each other and just blogs and stuff so it's it's a very it's a very uncomfortable thing to do the problem is that literally no other explanation works the the first model we actually could developed was was one where I thought well there's this cluster of orbits and they're far enough away that the orbits of the giant planets just look more or less like a quadrupole moment of the Sun right you can phase average them just replace them with massive rings maybe there's just enough mass in the distant Kuiper belt that itself modulates and that kind of forms this eccentric you know lobe structure so you can work through the calculations turns out that works rather well there was about 10,000 times more mass in the Kuiper belt and we know there is so that the Kuiper belt would simply be brighter we would observe a lot more objects in that explanation so that can't be right I thought maybe is it's due to a passing star right maybe a passing star created some pattern and we're now seeing the legacy of that turns out that that's very uncomfortable as well because each one of these objects has a distinct semi-major axis so it's their precession rates are very very different from one another so within a geologically short period of time only about a hundred million years this pattern would disperse right see so something extant is needed to explain the orbits so the problem is that you can basically come up with whatever you want okay when you introduce a planet you just we've got seven parameters to choose and that's a lot of parameters so the first thing that I did is I thought okay well what would live vary I do write live area would would write be able to write this down and like a piece of paper and figure it out and turns out the only configuration you can write down on a piece of paper and solve the problem in a more or less analytic way is that if you introduce a planet into that cluster and say well secular via secular interactions this this configuration of orbits is kept together by by a planet indeed you can write down you can actually write down an integrable hamiltonian that approximates that problem and you can demonstrate with this integrable hamiltonian that if you if the planet is the answer then the planet has to be of order ten earth masses and its orbit has to be eccentric okay so it's it requires eccentricities above 0.3 preferably above 0.5 something like that so just a simple perturbative calculation can give you some insight into what the planetary parameters should be oh wait I've since revisited this approach with with Alessandra morbid le who's a mathematician in Nice France and we've came up with a different integrable hamiltonian which which handles the opposite case where if you anti align the planet with respect to the instead of cluster of the orbits turns out in both cases you get roughly the same constraints the good news is despite what you may derive from the news cycle it is no longer 1846 right it truly is not and so the good news is that at the end of they were not limited to just doing things on the board and we can do in the miracle experiments so the numerical experiments that we carried out are as follows quite simple you start the solar system in its nascent state four billion years ago when the Kuiper belt just formed and here you have all of the giant planets right in this little circle this is the orbit of Planet nine of the parameters of which you set and you basically let it go let it gravitational e evolve in gold orbits shown in gold are those with semi-major axes smaller than 250 au so they are representative of the conventional Kuiper belt that doesn't have coherent structure and all of the blue orbits are those with orbital periods greater than 4000 years so they are the ones that show this weird clustering and you can do these calculations relatively cheaply they only take about a week each so you can iterate over the parameters of Planet nine a lot and for a long time just nothing happens in these calculations it's only about two billion years in which is right around now that some structure begins to emerge and the structure I think you will join me or either I'm crazy or you will join me in agreeing that there's more orbits pointing that way then there are together with finite so the dynamics here is actually beautifully intricate all of these orbits that are long-term stable started out by coincidence locked into a mean motion resonance with planet 9 so just by virtue of being scattered out by Neptune and acquiring a random set of orbital parameters they were locked by coincidence into a commensurability just like pluto and neptune itself but the so that that is the mechanism that allows them to remain stable for long periods of time that's what keeps them from being flowing out whereas all these guys weren't the actual confinement of the major axes is a secular effect that's a mean field in order to understand that you have to average over the orbital motions under the resonant condition so all of this stuff is now worked out in that new paper I just mentioned and we understand this pretty well so long story short you can iterate over the parameters of plane at night numerically and find that the best fit more or less lies in indeed a 10 earth mass object with a semi-major axis of order 700 astronomical units right so similar size to two like the orbits of Sedna and these these other guys and a highly eccentric orbit sorry eccentricity of 0.6 gives you a good match and note that it also lies roughly in the same plane as the as the observed Kuiper belt objects themselves so that's kind of what is responsible for the tilting of the Laplace plane of the solar system so this is great I I typically tell my students that if you have a theory right that explains the data you were aiming to explain then you should give yourself a B okay I should get it that's at best a B+ like if you're feeling good right about your theory it should be a b-plus and the reason it's not an A is because you haven't made if you just explain the data that you have at hand and you propose something with adjustable parameters and you've been parameters you haven't made any predictions right you haven't there's there's an it's difficult to confirm or refute that model looking forward and so while writing this up this is something that was lingering in my mind that that planet 9 that simply explains what we see and it's kind of uncomfortable until I noticed this okay and this is really something that at the like end of of writing up the paper noted that every successful simulation that we have right there's a population of objects that get gets produced that start out at low orbital inclinations as the inclinations with respect to the plane of the solar system and get taken up to a very high inclination factor retrograde one and then come back down and Wow through this cycle they become visible or right around over here where the lines have color okay and so I thought now this would be a really interesting prediction nobody ever observes outside of the ecliptic plane okay because you don't to be wasting telescope time looking into empty space right so when you look for Kuiper belt objects you don't look for things on highly inclined orbits and printed out this exact page went down the hall to Mike's office I said this would be an actual observational prediction right that we could make that you know if planet nine is really there it would entail the existence of objects that orbit the solar system in essentially perpendicular sense and Michael's like wait I think I think dr. 30 does that I was like what so he was like yeah doctor 30 is an object that was discovered by accident by a near-earth asteroid survey I was just looking for stuff and when you look for near-earth asteroids you don't discriminate on the night sky you just look everywhere because you're gonna have a pretty embarrassing last couple hours of your life right as you try to explain to the president that well you know we didn't see the killer asteroid coming from an inclined orbit because we only looked in the ecliptic plane right so so Mike was like yeah there's there's this object I remember it from 2014 or whatever it was discovered and then nobody thought it was a big deal but it had an inclination of order 90 degrees and so you know just dug through kind of dumpster dived into this into this data set and noted that there had been about five of these objects already discovered okay we had no idea that they were there but they are more or less exactly where them where the model predicts them to be and if you look at what they look would they appear like in physical space they kind of look like the wings of the solar system and they're totally wild I can't believe we missed them we like weren't aware because they're totally crazy I mean this guy has a semi-major axis of like 1,500 au so they're much more staggering than Sedna for example and again since since this original discovery they found another one which is right about here so in my view this picture actually is the kind of is the refute ability and of the model if if this pattern where we have a set of clustered orbits pointing opposite way from Planet nine goes away and if these wings become better-looking and more excess symmetrically distributed around the solar system then we're just wrong but so far it's holding up very well where this nearly orthogonal set of orbits which is like I said a prediction of the model it said it's really a retro addiction actually because the data was already there but that's something that that is dear to us okay so this was so there was those three lines of evidence cumulative li was what we published back in 2016 so we said number one planet nine confines these distant orbits into a cluster number two as they rattle around within that cluster via secular interactions their eccentricities go up and down so that is a process to remove the perihelion from Neptune so some of the initially attached Kuiper belt objects become detached and then reattach back to Nancy so we're observing Sedna and Joe Biden in a state at the moment when they are at the detach part of their cycle if we wait a couple hundred million years they will reattach back to Neptune and some of the more garden-variety Kuiper belt objects will become like Sedna and Joe Biden and then this this set of the set of wings this sort of highly inclined bodies that we didn't know were there these three lines of evidence are what we believe makes up a compelling story for the existence of Planet nine and then about a year later maybe six months theater I was on a run go ahead my iphone with me and I got a call was from a reporter I said and the reporter said okay so this huge news in the Kuiper belt okay they found an object which is orbiting the Sun the wrong way and I said what do you mean is orbiting the Sun the wrong way like there's no right way or wrong way to orbit the Sun and kind of an astronomer are you you didn't know that there's a right way in a wrong way yeah I said well it's like I think I think where you're getting at is there is there like retrograde it's like going opposite from everywhere else yeah and then I sort of told the same this exact story that I just presents to you I said oh yeah planet nine bebebe died and takes orbits and puts them on to retrograde orbits and then I you know ran back to my office and opened the email and found that I was completely off right so what they had what they had discovered is an object parked right next to Neptune okay on a nearly circular orbit it was a little bit retrograde but you should never you know give up right just because logic tells you to so it's like okay this is this is odd I looked at through the literature on solar system formation there's no way to make Kuiper belt objects like these right so I thought what about all the objects we threw away right because as you saw in that movie from a few slides ago we started out with a lot more blue ellipses then we ended with and that's because a lot of these blue ellipses got scattered out or got scattered in okay so Neptune you know basically is a is a machine of perturbing things out and in and for things that just went into the inner solar system but to me everything inside of Neptune is the inner solar system right everything that went inside Neptune I just deleted or just didn't keep track of because I figured doesn't matter right these things go in and become Jupiter family comments or whatever that's not they're not interesting but then I went back and revisited all the objects that were thrown away and found that actually a lot of them do really interesting cool stuff right so here's again planet 9 here's a body that started out on some random orbits as you can see it's kind of flipping upside down chaotically its orbit is changing but every time it comes to hug the orbit of Neptune it gets scattered right so it gets whipped around and it's semi-major axes changes in a in a random way and so eventually this guy comes down and becomes parked right outside of Neptune on a nearly circular orbits if you if you liked it and you should have put a ring on it okay that's that's the moral of the story here and so this was four billion years and I chose this particular particle because it starts out on some random orbit and it ends exactly as this new object that was discovered after the fact so the two orbits are truly within you know 1% of one another and this is not because there's something you know special about that or they actually go all over the place mm-hmm it's just that you know we we found one that really represent yeah so sure absolutely so Planet nine itself is ten earth masses in this simulation ten earth masses ten earth masses is is a strange range because it's between the earth and Neptune Uranus which are 17 or 18 respectively right it's considerably smaller than Jupiter and Saturn which are 390 but what is remarkable is if you look at the catalog of extrasolar planets ten earth masses is the most common type of object you will find maybe eight but something around there kind of in between the earth and Neptune is the most common type of body what about the Kuiper belt objects the Kuiper belt objects are the biggest ones well the biggest ones are of course Pluto and there's a few of the other they're about a thousand kilometers across that's of order 10 to the 9 and minus 9 solar masses the remainder of them vast majority of them are the size of LA ok maybe size of Santa Barbara so they're really yeah they're their test particles well the planet 9 if maybe if they were observing the Sun within the first million years when it was still forming because you can I mean all of the distant extrasolar planets that we've found the direct imaging are those that are still in the process of emitting their their heat so through gravitational contraction so they're effective temperatures are you know a thousand degrees planet nines effective temperature is 40 Kelvin right so you would need a very remarkable infrared instrument plus a very nice coronagraph to detect Planet nine in fact the wise mission which is was which was our premier infrared survey of the night sky barely detected a Neptune okay so Neptune was detected with a signal-to-noise of order six if I remember correctly so if you put a Neptune a factor of two far away further away it disappears okay so this prompted us to look deeper into the data set right we thought okay so are there more objects turns out there are a lot more objects on retrograde orbits that are placed that are parked right next to Neptune and it's not actually clear why that discovery was a big deal and the news because there's a few more of them okay and so the one that made the big time is like this one right but it's not particularly more special than this and it's definitely not as interesting as this guy which is in the plane of the solar system more or less but is truly going the wrong way so I also drew a line here because everything out to about 45 degrees you can manage to generate during solar system formation everything above you're just completely hopeless so weirdness Planet nine in place objects from afar turns out there's a intriguing pattern to how it in places objects it this region over here is devoid of bodies and that has to do with the specific resonance that that tilts the orbits and and where it comes to low perihelion during the inclination cycle so there's kind of a large popular we expect a large population above 90 and they somewhat smaller population which is almost retrograde I should have updated this plot with the new there's there's been a couple more discoveries there's one here and another one here which both fit very nicely final thing about Planet nine that I'll mention today so you guys all know about the Sun right no I'm sure your parents at some point told you not to look directly at the Sun sir Carrington in 1859 did not follow that advice okay and instead and measured the Sun directly it was the first person to measure the spin axis of the Sun and pointed out that if you look at how star sports move you will note that the spin axis of the Sun is six degrees offset with respect to the plane of the solar system and in that paper which you can download on a dias right he said he knows that gee it's this is weird the planets are coplanar to less than a degree all right whereas the Sun is off by six and I actually knew about this like before Planet nine and we've talked to like my office mates about this and we all concluded that it doesn't matter because six it's just not that many degrees right and it's it's true like six is not its small compared to ninety but six is also big compared to one you see like that's the kind of math that I'm into so you know it's like what's going on with the six degrees so actually to be to be completely fair I I thought the six degrees was a big deal back in 2012 I'm like a six degrees hipster I was like into the six degrees before was popular and in 2012 I wrote a paper about how well if the solar system formed as a binary star which many sun-like stars do then the binary could have perturbed the disk of the solar system out of alignment with the host star and and then the binary gets stripped by just binary binary interactions in the cluster so I kind of knew how to do this calculation at I'm Elizabeth Bailey who's my grad student it was just starting and so why don't you calculate you know given the torque but we know the orbit of Planet nine what torque does it exert upon not the port of planetary disc of the solar system but the planets themselves right as if planet nine in you know torques the rest of the solar system by twenty five degrees and four billion years we're in trouble because 25 is bigger than six if it's zero degrees then it just doesn't matter and you know she did the calculation right and demonstrated that in four and a half billion years planet nine torques the solar system by six degrees okay and moreover it's not just six degrees it torques them towards this well tilts the solar system in such a way that the longitude into which the Sun is tilted is the correct one so you can by knowing you know the orbit of Planet nine and the tilt of the Sun compute the plane of the distant Kuiper belt objects and vice versa right so this doesn't have to be right okay at the end of the day you know maybe you know this planet 9 contributed not the full six degrees maybe there are other explanations like I said with the binary star whatever for for generating this obliquity but the fact that it fits as well as it does I think is kind of staggering when I said I think this is not I wouldn't jump if this was the only a line of evidence with the existence of Planet nine I would I would you know it would be laughable but the fact that it's it works as well as it does is pretty interesting in my view okay so we're getting close to the end here as I said there's a lot more objects now the cluster gets better there's a few now that were found which are exactly diametrically aligned with Planet nine these guys are in are interesting these guys are also something that comes out of the model naturally these are locked in a secular librarian cycle where their librarian amplitudes are so low that they're protected from collisions in a different way they just simply never hug never touch the orbit of planet nine so the the picture continues to kind of refine and get better so I think that we are in in good shape as we you know conduct the observational search which is what we are into at the moment so let me quickly summarize what do we think we know about Planet nine we think that tenet nine has an orbital period of about twenty thousand years it's about seven hundred astronomical units a mass about ten times that of the earth of course we haven't seen it it could be a dark matter black hole right so it could have a which is interesting because that's the same as a regular black hole but you know if you just don't go into again crazy land planets of this type if you look at the extrasolar catalog typically have radii of between two and four times that of the earth and it's on an eccentric orbit it's not quite commentary right it's not like a comet but it's halfway in between having a comet-like orbit and typical planet like orbit if we assume that it's got a radius of about three Earth masses we expect and an albedo similar to that of Neptune it would be visual 2:24 I'm not an observing person but I recently learned that that means really dim okay but the the good news about magnitude 24s that there is a telescope with a large field of view which which does the job and then this so this is the top of Mauna Kea on the Big Island this is the Subaru telescope which which is incredible here's a picture of Mike and I inside the telescope so it is kind of you know fully in line with with my Japanese you know background this looks like a Mechagodzilla right and it is truly staggering right when you when the picture doesn't do it justice just how big it is and I think the camera was the CCD is actually the the largest CCD ever commissioned because it was commissioned to bail out a fraction of the engineers during the economic recession in the 90s so this was a an incredible telescope so we are conducting our search at the moment we have covered I'll tell you how much we've covered we we're at the telescope in late September and we we had five nights were five half nights and for the first two nights the weather was supposed to be bad and we were groggy but then by you know chaotically s own weather does you know a bubble of warm air appeared on top of Hawaii and so there was all this rain that was in circulation around the island we could sort of see the clouds declare you know kind of going around us but we had beautiful you know seeing on the first two nights and then this the final three nights were really really great so we covered about this much sky which is about 20% of what we need in total so we have the the orbit and the location the night sky constrained to about five times what I'm showing at the moment we're going back to the telescope in mid-december fully the same exact thing will happen right and will have awesome nights but because you know cuz you guys have been good to me I'll just tell you where a plane at 9 is just so that you know and you can be planted 9 hipsters and so to say yeah well other than you where was no find it so this is the Orion constellation okay I noticed named my cat Brian back in 2008 and so this is the one constellation that I actually know and over here Orion is holding usually a shield or bow people tell me that this star is not Planet nine and I tend to believe them but our best estimates put Planet nine very close to it so it's probably somewhere in Orion shield alright so I'll stop here and take any questions thank you different color yeah sure yeah thank you and to be to give credit to my grad student Chris Spaulding he has instructed me to never show that plot because he said it looks at best like modern art so what that plot is showing it on the y-axis is the inclination on the x-axis is the up Seidel direction of the orbits so the point there being is that as the orbits come up and execute a very well-defined kind of pattern and that in that space right there's a there's a well-defined just having a bunch of inclined orbits is not consistent with the model right they need to follow what they predict and then you may have noted that the the lines had different opacity or the dots had different opacity so where the objects have perihelion greater than 80 astronomical units which is kind of as far as we are current observational horizon stretches I plotted them in gray and we're in where they are where they have color they are in not gray so the point being is that they're most readily observable at about 90 degrees and they disappear from sight over here the highest inclination they are also not very well not very observable in this part of the flow yesterday they come to perihelion and almost 90 degrees I should also caution that the observed objects even though they fall right so right where they should be are the freaks of this population they're the freaks of this population because they were discovered by this near asteroid survey which is not very sensitive to the Kuiper belt so it picked out the things with perihelion distances inside the solar system their perihelion distances are 11 au 90 years of these these things are things that are hugging the giant planets so they have been more or less perturbed out of this perfect so the fact that they're kind of on the edges is is because they've been kicked by the giant planets already part of the survey that we're doing in is done in hopes of discovering more of these guys with perihelion well beyond Neptune that should map much better to these lines that's a great question and yes it can so we are the way that we are doing the observational search is so it turns out like I voted last year was my first time observing turns out it's super easy right you just upload a set of targets and then you just occasionally press up up enter just just to make sure that you know is doing well and yeah so it's I thought it was much more magical than what it really is so what we're doing is we're taking a stamp of the night skies a two-minute exposure which on a clear night so seeing kind of below one arcsecond gets you down to about twenty-fifth okay so there are objects in fact discovered that our twenty-fifth magnitude and then we just follow that down we just stamp down down down down down and then kind of cold the night sky that way yeah and that's that's all it is it's very it's very simplistic and that all we're looking for is just reflected light we their theoretical calculations of the atmosphere and what happens at when you're at 40 K which suggests that everything should condense out and you should just have Rayleigh scattering so the atmosphere should be should light up like a mirror and it should have a albedo of 0.9 or something like that which would be great I am cautious to you know jump up and down about this just because I always worry I always want like to be on the pessimistic side so there's a there's a chance that planet 9 is actually brighter than 24 there's also a good chance that it's in the Galactic plane which would be very difficult yeah if well if only we could just remove the galaxy right I mean do I have any any supporters in this room that's a great yeah it's a great question you complete the so with but these things there's always kind of your best one Sigma set of orbits you can keep expanding that after a while you you do run out of a reasonable sky if you the way you research for so the way we search for planet is very simple it's basically not moving right so it's all parallax okay and if we find an object that bright at a distance of a thousand au it has got to be big then so suppose you know in December when we go back we find an object that is that that is that big what's the next step the next step is to get Hubble time to try to resolve it if we have satellites then we know the mass for free if it doesn't it's gonna have satellites don't don't even go there okay the other thing you can do is of course observe it with something like Keck and get a spectrum of the atmosphere you immediately learn something about the composition I I'm almost certain that an object of 10 Earth masses must have a hydrogen helium envelope right it's not a ball it's not it's not like the earth it's more like Neptune yeah so then the question is if we don't find it what does it mean well you know unfortunately it's not super clear cut because of this the galaxy that's in the way if a large fraction of the aphelion part of the orbit covers the galaxies and galaxies you just get confusion so then you have to and it's actually not even clear if with the current generation of telescopes we can solve that problem so we have some more time in February and in February we're going to do our first experiment with observing kind of the edge of the galaxy to see if to see what we get because nobody nobody looks at the galaxy when looking for solar system stuff you just plot all the observed fields the galaxy is a chunk that is completely missing right so so there's not even you know good reference to go to to understand what that would that does right so that's dude hopefully that answer is a fraction of your question yes yeah fantastic question so the the latest one is of New Horizons which went to visit Pluto fortunately Pluto is exactly the opposite or so it's going the wrong way the voyagers that are at a hundred astronomical units each they I don't know much about the voyagers because I think that their telemetry is actually not that good right they were launched yeah that's right what the spacecraft was great telemetry is Cassini and Cassini has been in orbit around Saturn for a decade before we smashed it into Saturn there was a group in France led by Agnes Bianca and Jacques Lascar who pointed out that if if you park planet nine at perihelion where where it's clearly not because it would be observable anyway then Cassini's orbit would be totally messed up if it's at aphelion you just don't have any signal there is however a point in the orbit where you park it which is about halfway to aphelion where you get the residuals of the Cassini orbit become smaller in fact they go away right so there's some there's some residuals in the Cassini telemetry which can be solved with Planet nine it's very intriguing actually that there's this potential additional yeah that's right discrepancy between what you predict with JPL you know an ephemeris model the the problem might lie in the fact that we also don't know the masses of all asteroids okay so what they have actually the only constraint they have is the distance between Earth and Cassini itself the distance between Earth and Saturn all right and so because we don't have all the masses of the asteroids down right earth is a little bit easy to move around if what would be the ideal experiment is to put an object around Jupiter and our object around this Saturn and then just measure the title field on exerted on the solar system right I think that's something that can be done there are some hints of it might be yeah of the fact that it might be sure yeah yeah and you know yeah everybody that don't find what we find is doing it wrong thank you you

Channel: Kavli Institute for Theoretical Physics

Views: 124,012

Rating: 4.4340835 out of 5

Keywords: planet nine, planet 9, kavli institute for theoretical physics, kitp, ucsb, uc santa barbara, physics

Id: 3kQwzEIP-pY

Length: 65min 15sec (3915 seconds)

Published: Wed Jan 03 2018