Alumni Seminar Day Keynote - K. Batygin - 5/21/16

presented by Caltech earlier this year Caltech scientists announced a probable presence of a ninth planet we are lucky to have one of the papers authors as our general session speaker today dr. Betty Ann was born in Russia but received his education in multiple places but he got his undergraduate degree at UC Santa Cruz but he got his master's degree and his PhD here at Caltech and I think he's never left in 2015 constantine landed a spot on Forbes list of 30 under 30 young scientists who in addition are changing the world the magazine called him the next physics rock star it is a most apt description since in addition to spending time with his wife and young daughter he moonlights as the lead singer in the band the 7th season it has been my great pleasure to get to know this very engaging young man and to introduce them to him today he will be addressing why he and his colleagues think there is probably a ninth planet in our solar system dr. petit all right how do I turn the Sun can you hear me Oh excellent all right well it's a it's my true pleasure to be here today I'm delighted and frankly starstruck and humbled to be talking to this group of people so today I'd like to take a few minutes to talk about well maybe a few tens of minutes to talk about a subject for which I've developed quite an affection which is the orbital architecture of our own solar system in particular its most distant realms now astronomy of course being sort of one of the oldest forms of natural science has enjoyed a long and dramatic history but it was only kicked into high gear astronomy as we know it in current form really 400 years ago when Galileo adopted the telescope and we became no longer limited by the resolving power of the human eye and what's further fascinating is that despite the kind of breaking down this limitation the search for you know additional faint wandering stars that walk around the night sky has been pretty unproductive in the solar system in the last 400 years sheer numbers wise we've only discovered two planets that the ancient civilizations were not aware of and the first such planet was discovered actually during the American Revolutionary War in 1781 by Sir William Herschel and she called it George so you could have Jupiter Saturn George and the International Astronomical community of the time said that's a bad name for a planet so let's call it Uranus cuz that's a better name and what yeah so the fascinating thing is that almost immediately astronomers and mathematicians of the time notice that George was not behaving correctly if a juror was was doing the wrong thing its orbit was reconstructed upon discovery so from previous kind of serendipitous observations when astronomers drew it but didn't recognize that it was a an actual moving star and they noticed immediately that it was deviating from its a purely envisioned capillary in orbit and alexis Bovard who was the observer director of the observatory Perry in 1821 published a set of astronomical tables which I'm sure as a parent from this slide there is cosines and sines on the left-hand side and a table on the right-hand side and what he pointed out was that look it's just you know if you combine all of the observations of the time together you there's no way to reconcile here this is orbit with just the two perturbed being big planets Jupiter and Saturn so as a good theorist he didn't rule out the possibility that the data is crappy but he also speculated somewhere in here I don't speak French that's I'm only guessing that it's in overall this slide that you know perhaps there's a different additional massive planet that lives beyond the orbit of Neptune and it wasn't for an additional two decades before the promise of Bovard data really came to fruition and it was it was really worked out by this guy or bangla varier who lived between 1811 1877 who you know took took this idea right that you know there's there's a different additional perturb er residing in the solar system and worked it out so by probably with a lot of wine and a lot of papers and his Parisian apartment he just worked out and predicted the existence of Neptune and beyond beyond Uranus no when I was an undergrad in Santa Cruz I lived in sort of a shady part of town so I can spot a gangsta from afar and this guy's clearly a gangster you can tell because he's wearing his bling on the outside right important his stage name is urban urban live area underneath some gangster so this is actually part of the manuscript where he details the the derivation of how to resolve the Iranian irregularities with introduction of of Neptune and what he also proved was that I don't have the worst handwriting in astronomy in history so what's remarkable is that after this discovery which took place in 1846 and by the way Neptune when it was finally observational II confirmed it was confirmed in just a single night of observation gal who was an observational astronomer in Berlin sort of mapped made this multi-year plan campaign to look for live areas predicted planet and opened up the telescope and said oh well there it is so it was kind of one of the most remarkable examples of you know where Theory meets observations but in the last 170 years despite numerous attempts to relive and reconstruct these types of calculations the solar system has failed to produce additional planets what we have found however is a field of debris that lives beyond the orbit of Neptune so there is Mercury Venus there's earth and blew my house right here is Mars Jupiter Saturn Uranus George Neptune this big blue thing is the orbit of Pluto I don't know why it's there it's you know P for Pluto P and Pluto stands for not a planet you know Pluto really is is smaller than the moon so I think it's it's correct that my my friend and colleague Mike Brown really pulled the plug on its planetary status but what's interesting is Pluto it turns out is just one fragment in this big belt of debris which we now collectively call the Kuiper belt what we will see shortly are all of the orbits of the Kuiper belt and when we turn our viewing angle back to to sort of a top view you'll see that the Kuiper belt has this unifying feature and this unifying feature is that most of these orbits can be well most of these orbits virtually all of them are tethered to the orbit of Neptune right they physically hug the orbit of Neptune the reason this is the case is that Neptune was the thing that produced the Kuiper belt right the gravitational potential is conservative so if you're a neptune and you kick an object it's going to go out on its elliptical orbit but it's gonna come back to exactly where it started from so that's why all of these orbits hug the orbit of Neptune so when the Kuiper belt was first discovered one of the kind of key elements key things that we learned was that it totally makes perfect sense right it's its orbital structure is complicated but it can all be understood within the framework of our a planet solar system we even learned things about how our solar system formed from mapping out this structure of the Kuiper belt except for one object and this one object was discovered by my friend Mike Brown back in 2003 object called Sedna 2003 VB 112 was our BVB 12 and so you can immediately I mean you don't have to be an expert in the Kuiper belt to understand that this is different from this right Sedna at its farthest point goes out to almost a thousand times different distance between the Earth and the Sun so it's got this exceptionally elongated orbit was even more remarkable about its orbit is that it's not elongated enough right at perihelion it doesn't hug the orbit of Neptune Neptune could not have by itself produced this object so back in 2003 you with data point of one there's quite a bit of speculation maybe this was an object that was dropped off by a by a passing star maybe there's a earth-mass planet over here or no or over here you know with with one data point it's hard to say anything useful but it was really two years ago when I just started here as as a professor as was already mentioned I was a grad student here before that so when I came back as a faculty member you know Mike and I sort of got back to work together and really he he was the one who pointed me to this and said let's do let's figure out what's going on in the in the distant solar system so really the first thing we noticed was that if you just look at the most distant orbits in the solar system of which there are now six now six Sedna like orbits they all kind of point to the left okay and moreover they all sort of lie in the same planes if we put ourselves in the ecliptic plane you can almost envision putting a piece of paper through that collection of orbits and you know if you've ever done an open water swim right you you have good intuition for isotropy right there's no reason why all of these orbits should point in one direction right in fact you know this is it's surprising to me that this point had eluded the field for as long as it had so we thought okay well maybe just maybe this is just observational bias maybe your mom observers you know only looked in that part of the sky and somehow picked out orbits that all point to the same direction turns out each one of these guys was discovered by a different survey different telescope even with different observational biases maybe we got lucky maybe we just happen to pick out six orbits and you know they all sort of happened to point in the same direction and by you can evaluate the statistical significance of that you can evaluate the probability that this is all by chance and that clocks in at zero point zero zero seven percent so it's not a great gamble some of the the quantitative investors will you know and it can make can comment further on this and importantly this could not be some relic from the past but if you invoke some stellar encounter in during the sun's birth you would not see this observed structure because if you just leave these orbits alone under the influence of the known giant planets in a few hundred million years they will randomize so something is keeping them together right now so in the next couple hours I want to go through this derivation and you know I usually put up this slide as a joke you know but I guess this is this is the wrong audience to be joking about this because it's a guys might actually enjoy but the point here is that you know you can get started in virtually the same way that laverre EA had you can do perturbation theory and come up with a with a Hamiltonian which provides a pretty good approximation to the long term evolution of these orbits and you can learn just by doing stuff on the board is that if there is indeed a planet it has to be pretty massive it's got to be at least a few times more massive than the earth more like 10 and its orbit will be unlike the orbits of the planets that we have grown to know and love it will be highly eccentric so despite the feeling you might get at times watching the news it is no longer 1846 so we don't have to do the entire calculation on paper we can resort to the to the vast and awesome computational resources that we have here at Caltech so we decided to do a bunch of evolutionary calculations right let's start the solar system in the configuration that it had four and a half billion years ago when the Kuiper belt just formed as this axi-symmetric collection of eccentric orbits and evolved it forward in time under the influence of the known planets plus a putative planet planet 9 so we ended up doing just a ton of these calculations so so there's no shortage of bad results if you guys are ever in need of bad results I can provide you with bad results but what we've began well we began to notice is that much like what the would those analytic calculations had suggested if you put eight an earth-mass planet on an eccentric orbit whose perihelion closest approach to the Sun is at about 250 au 250 times the distance between the Earth and Sun over a period of 4 billion years what this planet will do is it will start carving out a population of orbits which will in the end resemble the ones that we we really have and it's it's a fascinating thing because it actually does take 4 billion years for this - for the structure to emerge it's right around now which is about 2 and 1/2 billion years into the evolution that you begin to see that only the orbits that are anti-aligned with respect to the orbit of the planet are surviving and there's still some stragglers over here so you know every time I watch this I know what the final answer is but I'm still like what will it really happen you know will it really happened yeah so to quote Kanye you know I'm gonna let you finish so yeah in the end you know the thing it produces is that these gold orbits are like the conventional Kuiper belt right there they're evenly distributed and these distant guys are our ante aligned one of the things that surprised us right away both Mike and I said how the heck are these things stable and all of these orbits intersect how do you how do they avoid suffering close encounters with planet 9 and getting ejected in the end that's how the rest of the orbits got ejected what's keeping these guys confined and the the answer as it turns out can be deduced from our insignificant friend Pluto Pluto also crosses the orbit of Neptune but is protected from ever coming too close to it suffering close encounters by a mean motion resonance meaning that or Pluto's orbit and Neptune's orbit are nice share this clockwork like a relationship where for every three orbits that Pluto completes Neptune completes now sorry for every two that Pluto completes Neptune completes exactly three and so they they're kind of avoid seeing each other and as it turns out all of these orbits are resonant with planet nine only this time the resonances are much more exotic and are in fact chaotic so if you leave this system alone they maintain the overall orientation but the orbits are changing in and up for the unpredictable matter all the time so at this point we had a pretty good pretty good sense for what the orbit of planet 9 would look like based on the real objects we'd around it's got to be like this we know that it's not in the closer half maybe closer two-thirds of its orbit presently at it's closer to AB helium that's what you would expect anyway from a capillary in orbit because by Kepler's second law you spend most of your time far away from the Sun so we felt pretty good about ourselves and then we ran into this total total block which was which which is nicely summarized in this slide you know this is a huge problem right well we have here is on the x-axis this is basically the azimuthal orientation of the orbits on the y-axis is the orbital inclination and what we noticed is that every time we represent things in the solar system we also produce a population of orbits that had been twisted on their side orbit the Sun in an almost perpendicular sense compared to the disk of the solar system and I'm just a simple theorist but I remember learning in elementary school that in the solar system things go roughly like this they don't go they don't go like that so I was I was really stumped and Mike was stumped for a little bit and then Mike said you forgot about 2012 dr 30 and i had indeed well i've never heard of 2012 dr 30 but i thought maybe that was an experimental drug or something and what Mike said I remember learning that 2012 dr 30 has an inclination of 78 degrees okay so what we did one afternoon in his office we said okay let's let's put all of the model predictions and just you know do they do the honest thing not look at the data and then let's plot not just a Kuiper belt data but all of the data that we have in the solar system small body catalog and what we found is that indeed there exists these little guys these tiny pieces of debris that orbit the Sun in an almost perpendicular sense and they had all been discovered only within the last couple years entirely by accident it had been discovered by a near-earth asteroid survey because the near-earth asteroid survey does not discriminate based upon where in the sky the killer asteroid will come from but it's gonna be a very embarrassing last couple hours of your life when you kind of try to explain to the world you know we well we we searched over there and there was no killer asteroid but it came from over there right so this is at Starcom chest with Kuiper belt surveys Kuiper belt surveys only look in the ecliptic plane which is why these objects had had eluded observation so as it turns out what our model was predicting this population of or perpendicular orbits it really is out there and I think this is actually the strongest line of evidence for the existence of Planet 9 because there's no other way in hell to produce orbits in the solar system that are that are twisted up so this is what they look like in in real space these are the real objects notice that this guy over here is even more extreme than Sedna right we thought Sedna was weird this guy has a semi-major axis greater than a thousand au so out here it's going out to almost 3,000 quite an incredible set of objects we have now by the way I'm going to send myself on a tangent we've we've understood the physics by by which this twisting happens and it's an effect which I had actually been known since the early 1960s called the Kozai effect and had been pointed out in the asteroid belt as well but even before that it had been pointed out by a Russian guy named Leda and they late 50s because the first Russian satellites came crashing down into the earth Earth's atmosphere because the potential of the averaged kind of mean field potential of the moon would twist them and and be make them more eccentric so when we published a paper we cited code there Kozai paper but not the leader of paper and I got an email recently from a Russian guy who said come to clean and to Kaliningrad I puncher in face so on that note what the heck is planet 9 planet 9 is is an object which looks until it's caught on camera I can make up what it looks like and as it looks exactly like this got one two three lightning storms it's got an orbital period of twenty thousand years a mass about ten times that of the earth we actually have constrained this number pretty well since the original publication we really do think it's ten it's not twenty it's not five the radius we must only guess based upon radius mass relationships that exist for planets around other stars exoplanets but we think it's a it's kind of like Neptune's between two and two and four Earth radii it's got a wildly eccentric orbit point six which is quite you know in a stark contrast with but the rest of the nearly circular orbits of of our planets quite pointy inclined as well and got a visual magnitude of twenty-four so if you're an astronomer you think I heard somebody go oh so visual magnitude twenty-four is it's pretty dim okay but it's not as dim it's not so dim that it's undiscoverable in fact there's basically one telescope on earth that is perfectly suited for the search observational search for planet nine and it's this guy right here the Subaru telescope Japanese National Observatory it's an eight metre telescope and you know 24th magnitude is is well within its capability is given you know so we all have to have about twenty nights on the Subaru telescope to complete our our search area so this is Mike and myself in the Subaru in the Superdome it's huge I had you know I never really observed before and I didn't didn't appreciate the extent to which this thing is a behemoth and because you guys are my home crew I'll I'll tell you what planet nine is so this is the nice guy I'm told and this guy right here is the Orion constellation my cat's name is Orion so this is one of the constellations that I actually do know and over here this star goes through Orion's shield now depending on which which picture of Orion you look at is either holding a sword or shield or sometimes a bow but planet 9 aphelion is right here so that's where you got to look okay so this guy this way you guys can can tap into your inner hipster for when it's found say oh I knew this I knew it was real I know well way before it was popular a couple last thoughts about planet 9 what does planet 9 mean for our solar system turns out planet 9 is the least weird thing about our solar system it's it's the thing that makes our solar system they didn't better into the Galactic planetary census with its high eccentricity of 0.6 it fits better into the overall orbital distribution of planets in general than our circular orbits that scrape the bottom of this plot in the last 20 years we've discovered more than 3,000 planets that orbit other stars and and they don't tend to look like the solar system we are we are the anomaly so to speak and planet 9 is perhaps we're linked to the extrasolar world I sometimes like to say that the planet 9 is our solar system's exoplanet and final thought is that the thing that kept us up at night was that maybe we made all of this up right I mean that's that's kind of you know as a as a scientist you try not to believe yourself too much and we thought maybe we you know kind of subconsciously constructed all of our of our statistics to to tell us that indeed this is all relevant and after all statistics is just another way that human beings lie to one another so we were really worried that you know the next set of orbits that would be discovered and the Kuiper belt would you know make this cluster go away and then we'd be would be pretty embarrassed but the good news is since then objects have been discovered and they all fall exactly where a model predicts them to be this is an example of a new orbit that's been discovered by a Canadian survey the reason the picture looks so bad is that somebody in in Mountain View took a picture of somebody else's talk and then posted it on Twitter and then I screenshot screen captured the twitter so so that's the the true new new methods of celestial mechanics I'm not gonna go through this I will I will simply put up a picture this is my friend mentor and colleague and sometimes workout buddy Mike Brown with whom I have the pleasure of working and also I wanted to acknowledge people working in my group Katherine deck Chris Spalding Henry no Natalia Storage Peter Bueller and Elizabeth Bayley they were not directly involved in this work but still my daily experiences at Cal Tech would not be the same without the awesome dynamic conversations that I have with these guys and girls they're awesome so at this point I want to say thank you you

Channel: caltech

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Length: 28min 7sec (1687 seconds)

Published: Tue Jul 05 2016