welcome to the science for the public lecture series science for the public is an organization committed to bringing science information and issues to the general public visit our website for our program good evening i'm leave on step for science for the public and i welcome you to tonight's contemporary science issues and innovation program tonight we have the pleasure of talking with a real innovator in astrophysics dr scott keny dr kenyon is a senior astrophysicist at the harvard smithsonian astrophysical observatory he received his ph d in astronomy from the university of illinois champagne abana in one nine hundred eighty three he joined the smithsonian astrophysical observatory first as a post doctoral fellow and then worked his way up over the years to senior tenured position dr kenyon has made a number of significant contribution astrophysics these include the evidence that even very young stars a million years or so can a create enough material from surrounding gas and dust to form planetary systems he's especially well known for his innovative computer code called orchestra which is one of the leading codes for simulating planet formation his calculations were the first to demonstrate that the day bring the disks around the standard reference works and astrophysics dr kenyon is a fellow of the american association for the advancement of science and a fellow of the american physical society and a member of other distinguish scientific societies his awards include the copernicus medal in one nine hundred eighty seven and the hoops prize of harvard shared with two others in one thousand nine hundred ninety five we are very honored indeed to welcome dr scott kenyon welcome center it's a pleasure to be here thanks for having me and let's start with the stars or tell us about star formation if you will sure well if you if you go out on a nice dark night in the middle of winter and and you can actually see the stars you can see the rise the arayan constellation which is a hotbed  and in the middle of the sword is the great arayan nebula so the great arayan nebula is in the middle in the middle star of the sort of around him and what you see here is a bunch of red gas which is all hydrogen gas which is caused to glow by high energy photons emitted by the bright stars in the center of the nebula which is in the in the middle here in the big white light area again where you see all a bunch and you can see a bunch of stars if you look really closely and every one of those stars is only one to two million years old and so what happens here is the cloud is a big what we call molecular clouds of molecular hydrogen so to hydrogen atoms for form together as a molecule a bunch of helium atoms and trace elements which is all the stuff we're made of carbon nitrogen oxygen and silicon and so on and so this cloud is a big cloud it has enough material in it to make one hundred thousand or maybe a million stars and the little bits of the cloud become gravitationally unstable and they collapse and as the clown collapses yes it's rotating all just like you know an ice skater brings his or her arms in and speeds up the cloud also it's rotates faster and faster it collapses into the center to form a little star and around that will be a disk around the size of the solar system give or take a little a little bit here and there and not only is this the diameter of this disk right for the solar system it has another mass to make the planets in our sol every young star and throughout the milky way galaxy of stars formed every year so we have one star year in the galaxy everyone comes with the building blocks of a planetary system i see the  early early stars would they have formed these kinds of disks probably every star that forms has to form with a disk and now the first starts will not have as many heavy elements that we have it all right you know beyond helium as the stars that are forming now because right after the big bang most of the elements were hydrogen and helium a little bit of lithium and beryllium and maybe a teeny bit of carbon but not much and so they didn't have as much material to form a solid particles the way current stars do and so you know whatever planets they would make would have been very different from the planets that would be made now th this nice image that was taken by the hubble space telescope is a big image of a ryan and we can look closer so here is a close up of four star systems in iran and so what you see when you look at these these objects is you see a little dot in the center that's a newly formed a million year old star and it probably looks the way the sun did four and a half billion years ago when the sun was only one or two million years old and you see that every one of the nebula that's being ionized by these very bright stars and this desk that's around the star is blocking out the light from the background so these are called silhouette is because all you do is see them as a silhouette you just see their shadows against the background but you know these discover about the size of the solar system they have enough mass to make the solar system and you know eventually they'll a planetary system ok so it is inevitable that you will have planetary systems maybe not that's or something like that everywhere every star has the makings of a system and whether that happens or not  is something that depends a lot on chance what happens sure it is what the stars like what its roundings are like whether it's a single star or a binary star yes triple star and there are quadruple and so what kind of planetary system it eventually makes depends on all sorts of things that can happen between the very first instant the disc is formed and the next few young tens of millions of years i say show you what kind of an artist's conception of a desk so this is an artist's conception of a disk around a young star below the yellow ball in the center of the disk is the young son only a million years old and there this big disk mostly hydrogen some helium and lots of trace elements and some very small dust grains micron size grains like you can see at a sun be you know in your home and those are mostly silicate by a quart or something like that and in the inner part close to the sun  it's too hot for anything else but silicates to condense out of the gas and farther out it's very cold and so ices can condense out of the gas and so the grains in the inner part of the disc are rocky in the outer part of the disk the something that's twice as massive or three times as massive and it's you know i like to say that plan information is you know works like the dust bunnies under your bed yeah that it's an agglomeration process and things you numbers or anything is there in order for example gas giants as to pose to rocky is there is that all kind of a sequence which comes first does it matter what we think we have an idea of this  northern maine or very modern some place like that you can see the dark clouds of taurus where individual stars are forming and there are a million or two million years old and you know it's happening all the time and every one of them has a disk around it and in the in the disk you know there's you know the temperature of the disk gradually decreases outwards the soccer stars are about the temperature of the sun the sun has a temperature about six thousand degrees and so these stars are about four thousand and so in the inner part of the disk the the grains of the gas are pretty warm and so water which is in the gas can't condense out and form ice so the grains  deflect and attract one another and so why objects become kilometer to ten kilometer size they grow a little faster and so in the inner part of the disc this is a rocky process big rocks are colliding as you go farther out in the disk it gets cooler because your father away from the sun you don't get as much radiation although water can start to condense out onto the grains and make ices and so now we have ice balls growing so in the inner part we have rocky balls in the outer part we have ice balls and we think that you know eventually the ice flows get bigger and bigger and bigger and they will eventually get large enough that they're gravity can keep hydrogen on their surface so on the earth you know if you have a hydrogen balloon or a helium balloon right you know you let it go and it's caught on and that's because the earth isn't massive enough to keep the helium in the hydrogen in your balloon you know on the table say so because gravity attracts everything but just the hydrogen the helium there's not enough gravity to keep the hydrogen in the helium bound to the earth but if the earth were five or ten times more massive than when you and we would probably be a little smaller if the earth were say five or ten times more massive when we had a helium filled balloon it wouldn't  off and if the earth were ten to twenty times more massive the hydrogen balloons wouldn't fly up either they would be bound and so that's what we think happens to differentiate the earth from say jupiter jupiter which is a nice gas plants like the rocky right within these disk it's very easy to make objects that are about the mass of pluto to mars ok that takes about one hundred thousand years ok you know and that where the earth orbits  takes you know ten thousand to one hundred thousand years around the orbit of jupiter and saturn because they're farther away from the sun it takes a little longer maybe one hundred thousand to a few hundred thousand years then it gets tricky because we're not really sure how an object goes from the mass of mars to several times the mass of the earth yeah in the inner part of the solar system we have all these mars mass objects and they come eventually they'll collide and merge into a bigger earth and we think we understand that beyond the orbit of earth and mars where we have the gas giants it's a little tricky and we're still learning about how that process works but we know that it has to be don completed in a few million years because when we look at young stars you know when we look at a ryan it's a million or two million years old and we see disks around stars there's another region and that you can see at night in the winter sky called percy eye which is called the double cluster in perseus which is two star clusters with hundreds of thousands of stars and they are about fifteen or twenty million years old they have no discs so there are no stars don't get to have disks by the time they're twenty million years period and is ten million a year period ten to twenty million year period that the disks go away and we have a lot of clusters of stars regions where we can get their date ages pretty well not we don't know that it's  to the nearest year or something like that but at the nearest you know half a million years or something we know these are a million years old and these are ten and these are three and we can see that the disks gradually go away so we have a time frame based on the observations that we have of star forming regions that the gaseous planets have to be made in a few million years so somehow jupiter has to get its ten earth mass core in say half a million years just to pick a man very very fast it is very fast and then it creates this hydrogen and helium io in a few million years and it has to do it very quickly because if it doesn't do it very quickly it doesn't have any hydrogen or helium to a create anymore because the disk is gone and so you can imagine that that can create why diversity happens in the planetary system what are the initial conditions has and that so happens you know it's like a person growing up you know you you know you have a decision do you go to the baseball game tonight or do you listen to your favorite const concert group with your friends and so those different choices change the kind of person you are and you know that happens to planetary systems or people but different things happen to them that change whether they're you know you end up with an earth mass planet or on mars mass planet or a jupiter right with one thing on a planetary system you know we have an idea everybody is in their right place but they move there's a possibility that they move is that correct are a lot of what we call chaos so when you start out with this nice disk of gas and dust a given particle has a pretty well defined or a bit yeah and it has a strong pretty circular orbit so it has no eccentricity to it so it's always pretty much at the same distance from the star at the beginning at the beginning now as these things grow and they get bigger and bigger and bigger they have their own gravity and so once you have say several pluto mass planets or a bunch of mars mass planets they start and jostling one another around i'm like going into a crowded subway system you know everybody wants to get on the car and so as people jostle to get to the planets you know because they have gravity are you know they're not they're not elbowing each other away but they're gravity itself goes over a large area and it affects their neighbors and so then they they see their orbits start to be more eccentric and then they can the orbits sometimes can cross and there's a period in the growth of planetary systems where the orbits are actually chaotic where if you asked well what is the actual orbit of this mars sized rock going around the sun you wouldn't be able to tell because you know every year or every two years it has a different orbit because it's being jostled by all these other planets that are trying to form but eventually you know let's say in the around the orbit of the earth you have maybe twenty or so or thirty or so lunar mass or more massive objects that are colliding over time to form the earth as they collide and jostle one another round of venture there is sort of a king of the hill yeah and it gathers up all the others over time and it becomes the earth and it clears out its orbit and it as its carrying out its orbit its orbit becomes more circular and so the orbits go from being circular in the beginning to chaotic in the middle to nearly circular at the end i see i see and during this time when the orbits are becoming organized of the planets the planets can move radially in around a process that's become known as migration and y migration can be very fast and the planet can migrate actually into the into the star or very close to the star sometimes it can migrate out sometimes it doesn't migrate very much at all because a gravity of the of  planet outside its orbit may keep it from migrating too far or the planet inside might push it away and so gravity is a very funny force because we think of gravity as attracting yeah object yeah but gravity also you know even though it's always attracting ends up repulsing something and so you know the earth keeps its orbit clear because it pushes other things out of the orbit and venus those areas right but maybe not all of them from what they've discovered what what is the story on that while the habitable zone just to make sure we're all discovered yes a bank j f is is a region we've decided being human induced to life the life we understand and so we want an area or a volume around a star where you're not too close to the sun or the stars so it's not too hot and it's not so far away from the star that it's too cold and so what we call the habitable zone is the region where we think that if you put an earth mass planets with oceans and some kind of atmosphere the temperature would be conducive to the life that we understand now it could be that the real habitable zones in the universe and com everything because we don't understand how about what you are yet but from what we understand as life we have this habitable zone and it extends more or less from the orbit of venus to the orbit of mars ok give or take right and you know if you if the sun were hotter then we would move that zone farther away and if the sun were colder we would move it closer in and so stars have a range of temperatures from much cooler than the sun to much hotter sun so there are a range of these habitable zones from very very close to cold stars to very far away from hot stars ok and now there's no guarantee that a planet will actually form within up just inside the habitable zone and another one will end up just outside it and in the star star systems that where we've identified planets most the stars are inside a much the planets around the stars are inside this habitable zone so we now know of about two thousand planets give or take it's amazing how fast that it is amazing how many planets there are now and you know when just two decades ago essentially none but most of them are inside what we would call the habitable zone i say so they're too close to their central stars to be what we would think of as siddur conducive to life right now there are almost know the closest planet to the sun but if you moved it to the earth's orbit you know it would be the right temperature for life but it has no atmosphere and it has no water and it's not going to get in there and there's no way for it to get anymore and so that would be an inert planet from our way of thinking and so you're not guaranteed that you have all these ingredients that we think of as necessary for life that you have a planet the mass of the earth you have water you have an atmosphere you have all this stuff that you need yeah and you know you could have a planet that has all those characteristics but could be too far away or too close the the business of how astrophysicists evaluate gases around what why is that so significant why do those looking for what kind of gases are on the planet whe we look at these gaseous disks around young stars we see the gases that we you know in love in the universe we see carbon monoxide we see carbon dioxide we see water so we know that in this molecular  we want to know what its composition is and what you know how and that tells us how the planet was made so if a planet has lots of methane and no a a it tells us one thing and if it has a lot of ammonia and no methane it tells us something else because those two molecules condense out of the gas at different temperatures and as i remember only condenses out at a colder temperature than methane ice and so something we would think that something bad has more ammonia should be formed in a colder region and something that has more methane and if you only see water ice but no methane ice or no among eyes then maybe it was formed farther inland so we look for these signals of where in the disk this about you know how jupiter formed and you know it has other you know other elements in it and we try to piece together the history by looking for not only among the methane but you know every element because every element tells you a little bit about where and how the system formed what condensation temperature you've got there and so that's indispensable information that you can get right now because you know every system every planetary system or every young star system with a disk that we look at is a snapshot and so when we look at the disks in ryan we see a bunch of disks as they are now and they're all a couple million years old but we have no idea what those disks looked like you know three hundred years ago and three hundred years from now and but we try to find another star forming region that's a little older than ryan and another one that's a little younger than right and so we get all these snapshots and our goal is is to make a movie we would like to make the star formation plan affirmation movie and a star with stars are ten thousand years old and we look at the sun that's four hundred four and a half billion years old and we look at stars that are ten billion years old and we get snapshots of all different levels of planets and debris disks which are the debris left over from planet formation and we just try to string this all together in a way that makes sense within that disk like within our gifts there is little to real from super basic elements life gold and silver and uranium are probably pretty common ok i thought those were but they're rare but there are i mean they're they're rare in the sense that they're not a big constituent of the solid elements of the solar system that we've used to understand the formation of the solar system our various radioactive elements now uranium is a radioactive element which has a very long half life but there are other and so that's why we still have a lot of uranium today is because it's half life is is long compared to the age of the earth not longer than the age of the earth but a long time here to it so that there's still a lot of it around but there are other radioactive elements that have very short have lines you know ranging from days to millions of years to hundreds of millions of years and the ones that are just a few million years can give us a really good clue about how the solar system formed so there's an element called aluminum twenty six which is radioactive and it has a half life of i mean around a million years and we see the decay supernovae which spew out all these radioactive elements and very involved red giant stars which view out another set you know if there was one close enough to the solar system it will drop finally mr pluto right but i mean you did a wonderful i guess it was in the harvard gets at or something was a very nice interview with you there about pluto and this was before this was just at the time of the fly little bit different way than the public not a big different way because i'm not a geologist and i don't study the surface evolution of planets at all and but it is fascinating that there can be such little all very tiny planet and it's very tall mountain and you know compared to the size of the planet you know you would have to climb two to two and a half times mt everest you have to you know took  hundred or six hundred kilometers across so you know the chasms are really deep compared to the size of the planet and it's just amazing so that's the big thing so that's that's so that's really fascinating  in terms of my work yeah it's not as interesting because it's not what i do know day to day i don't wearily worry about how the geology of pluto should be different from the geology of carillon right but i'm fascinated tenth of the mass of pluto in the moon is something like an eighty of them mass of the earth and it also orbits very closely so the orbital period of karen around pluto is six days so if you're but unlike the earth pluto's hemisphere is also law so the same hemisphere is a pluto and charon are always facing each other and that's unusual that's it's not unusual in our solar system to have such such title walking because because they're both because they're both there so such similar masses and it's thought that they came into being this way by a big collision pluto form somewhere in the solar system charon from somewhere else and they collided and they became a binary and while they became a binary in this collision karen kicked up a little bit of pluto surface and pluto kicked up a little kilometers across so they're you know a million times give or take less massive than pluto and charon on and they are bits pretty closely and there are four little ones and you know since i study planet formation i'm sort of fascinated with well how often with this kind of collision happen what with the outcome b and so my colleague and i ben bromley did some calculations about how this might work and we predicted that there would be some additional moons outside the orbits of the current moon so the outermost moon now is called hydra and all of pluto's moons have to be named after some come thing associated with the underworld hydra is the outermost moon and it orbits i think with a period of around a month or earthbound month off thirty or forty days and b we thought that there might be some smaller moods outside the orbit of hydra so we're hoping that new horizons t well i know they took pictures of the whole system and we're hoping that eventually they will find some other moons which will asteroid or something that's called service so they had to have another name called kerberos and hydra is the outermost one so you can see that they're not round balls but neither are they you know funny put it back into our theory of how the moons form to try to get something that has reasonable shapes from the point of view you know the observation right well just one point on that is that to be to earth's life the collisions were so frequent that the earth was a big molten ball and you know if the collisions were not quite as frequent you know if you know because we think the earth formed over several tens of millions of years but if the earth formed over several hundreds of millions of years say it would not be molten because the collisions wouldn't be fast enough to keep the heat of the collision because every time something i remaining time we're running ahead of time i've wanted to talk about your work well so what we what we try to do and i'll try to give an idea of why we do what we do is i mentioned that we have this movie that we make and so we observationally we have a lot of images or snapshots of the history of planetary systems and we need some way to organize those and we could just organize them based on the ages  of stars and so we do organize it that way but there are a lot of things that happened that might make one system seem younger than another system and i can give you one example there's a there are ten billion year old star that have lots and lots of debris around them and so they have these big debris disks and you could actually see the solar systems debris disk if you go to to a nice dark place like northern vermont or northern new hampshire maine and you go out just after the sun is set you'll see a band of light coming up from where the sun set going up like a cone and that's called  and that's a bunch of millimeters sized particles in the disk where all the trust your planets are and when we observe those dust particles around another star we call that a debris disk now our solar system is about one hundred times to fate to be detected by our current instrumentation but there's a star that's twice as old as the sun that has a desk of debris that's ten thousand times than the sun and so there's something it looks young compared to the sun which is sort of from our point of view sort of dead in the sense of the doesn't have this debris the solar system is formed and so it's not very interesting from the point of view of evolution any more and so we need some organizing principles so tell why is this ten billion year old star different from the sun and we since we can't do experiments we do calculations and so we make simulations on the computer and this is a characteristic of astronomy that dates back one hundred years now because you know astronomers one hundred years ago were trying to understand the structure of the sun so they made they didn't make computer models but they made theoretical mones and then they did lots of mathematical calculations on paper pieces of paper to figure out what the structure of the sun would be and how long it could there and things like that and so we follow in this tradition of trying to construct a theoretical model of a numerical model for how planets form and how they evolve and so in doing that we can put a bunch of physics into a calculation and you know we solve a bunch of equations to see how this initial disk that i described earlier this disk of gas hydrogen and helium and just greens how will it evolve and by and then we take snapshots of this dist two so because we can't look at the evolution every second we take a snapshot of it every hundred years or every thousand years or something like that and we try to match our snapshots to the snapshot that observers observational astronomers get when they take images with space telescope or when pluto flies by two horizons fly by pluto and so we constructed this code to understand this long term evolution so that we can put the observations in context and then make predictions of what ok for this system if you look at it in more detail you should see this and so as i described for pluto we predicted there should be more movement and we have a set of reasons why there should be more moons and based on these calculations and so the calculations are it's a bunch trajectories around the the star and so when we have enough of these what we call embodies that interact repetition and we follow how they interact and how they move one another around and things like that and so we can make predictions of what things should look like and this is now an indispensable tool specially your orchestra i think it's like this that the number one system for this that because it predicts very well  codes are really important for trying to understand how things came to be and our solar system and other solar systems and we make predictions some of the predictions turn out to be true some of them novelists and so you know based on the new data that whatever it is that the problem and we try to fix it and we then we do a new set of calculations and we asked ok can we match the observation now and sometimes you can't and sometimes you can't are you twiddle with it and you keep changing the physics because there are a lot of things we don't know and so you get a match and then you say ok now that we have a match to this we predict a new set of prediction i go out and look for the start of an art yeah in a way to construct these codes because  you know george whether role was a scientist who started using these kinds of codes for planet formation and you know decades before i started and you know he said you have to be careful not to put the whole kitchen the sure that you have to understand what's essential and what's not that's akin to you say it's an art right because you you you say oh i could put this in but i'd like the calculation to be done enough and so you know our computers aren't fast enough to do the calculation of your dreams because you can't put everything in that you would like to put in and get the calculation finished in your lifetime and so you have to pick and choose what kind of physics you put in and to do that you have to decide well what's important what am i trying to understand and ok maybe i maybe i won't worry about trying to understand this because i think it involves too much you know intricate things that i don't understand to put into this code so there's an art to it there's a lot of science into it that you have to decide exactly you know how to solve things and that's you know you have  some choices and some of that is is intuition and an art rather than you know well it has to be done this yet and you see these codes every day yeah if you do a google search that's one of these codes it's a different so you know traffic patterns you know where i traffic control you all of these things use very sophisticated code and you know you want high quality practitioners to be doing these things  to the flow of this field at this time yes it was wonderful to talk with you i hope we'll have another chance we run completely out of time i do thank you very much for joining us tonight that was my pleasure