A Short History of Planet Formation

so tonight we have a really a very special lecture which I think you're really going to enjoy for those of you who don't know Carnegie Sowell Carnegie observatories where the astronomers work and those of us who put on this series are of course here based in Pasadena but we're one of only six departments as part of the Carnegie Institution for science and we've had some previous speakers from one of the departments called DTM which has a few other astronomers but tonight we have our very first speaker from the department of geophysical laboratory which is a really interesting department based in Washington DC and they do all sorts of high-temperature high-pressure experiments tonight's speaker Anat Johar will tell you all about that she's very excited I saw her talk about a year ago in DC when I was there and that when I saw her talk I said we have to get her for our lecture series and so she was the first person we reached out to this year when we put the series together and she's gonna tell you all about her very exciting work with troops has very good implications for astronomy as you'll see this is not a nuts first time here in Southern California she actually spent a good amount of time here she got her PhD from UCLA so this is a return home for her in some ways and in 2008 so she's she's the youngest staff member at this in our department called GL back east so help me welcome up phones please put your phones on silent if you haven't done that already excellent so please help me welcome our speaker tonight the not Johar thank you thank you so much it is a real honor to be here tonight speaking to all of you and in such a lovely lovely venue so what I'd like to tell you about tonight is a little bit about planet formation and this is really an exciting time to be studying or even thinking about planet formation because recent discovery systems that Kepler has found over the past six or seven years so the colors oops sorry the colors show you the closest planet to the star is red and then yellow and then green and blue so you can see the ones that have more colors have more planets and you can see that there are different sizes of planets and the most important part that I want you to get from this animation is how many planets there are so 20 years ago we thought we are really special we had these eight or nine planets in our solar system and today every star that you look at in the sky has at least one planet we think orbiting it or maybe many many more and so planet formation you know we we started thinking about it in terms of our own solar system but really there's so much more to be learned and so with Kepler we now have a really good sense of how many exoplanets there are at least that we found so far and how diverse the different planetary systems are and so a lot of what we know about planet formation we know through astronomical observations so these have been termed the pillars of creation this is a Hubble Space Telescope photograph of the Eagle Nebula and what it shows you is the birth region of stars okay so we take the astronomical observations and then for those of us like myself who are not astronomers we try to bring them to the lab and try to understand what they're actually showing us and so if we think about planet formation and we look at an artist's rendition of what that might look like what we start with is a cloud of gas and dust and that cloud of gas and dust is diffuse and it's spherical and it's slowly rotating and as it rotates it starts to collapse and when it starts to collapse most of the material goes to the center and that's the protostar and the rest of the material starts to flatten out into a disc surrounding that protostar and gas and dust is just rotating around and a lot of the gas is going inwards towards the star so the star at the end actually makes up at least in our solar system more than 99% of the mass of the solar system so all this material is going around and around and most of it is going to go into the star and so as I said a lot of what we know we know from astronomy so this is a photograph taken by Alma the telescope and what you see or what we think we see is exactly what I was just showing you these concentric rings showing where planets are starting to form and where the protostar is starting to form in the middle and so over time all the dust that hasn't gone into the star a lot of the gas gets expelled by this massive star in the middle and all of the dust starts to coalesce and it bumps into each other and the dust grains get bigger and bigger and bigger as they bump into each other and over time you start getting less and less stuff surrounding the star and it ends up in a stable configuration of planets now how the dust coalesce is and then turns into planets is actually very difficult to understand we've been able to understand how the dust can get to about a meter size and then there's a problem of how does it get from a meter to a kilometer size but for the point of this talk it's important just to note that this process here where you have a lot of bigger objects actually was very very chaotic okay it wasn't a very simple situation where planets are starting to circle around and get bigger and bigger without bumping into each other turns out they bumped into each other a lot and the most famous for our purpose of a giant impact like this where two planets bumped into each other is how we formed our Moon so we think our moon form from when a mars-sized body impacted the earth and when I'm about to show you is a simulation done by one of our postdocs back east and DC so what you see here is the proto-earth being hit by a mars-sized body and the colors show you the extent of shock heating okay so how hot it was really getting and what you see is that this body came and it merged into the earth for the most part and all this other stuff that's on the outside is what ended up forming our moon okay this is the leading hypothesis for how our moon formed and so it was very chaotic it's thought that earth and Venus actually had a lot of these giant impacts throughout history so I explained to you how the solar system formed right but what I really study is how the planets formed themselves and so we started with dust and then we got bigger and bigger and bigger and when a planet gets bigger it starts to melt on the inside and it starts to melt for several reasons one is it formed so early in solar system history that it caught some of the radiogenic isotopes that decay and that decay heats up the internal portion of the planet also those impacts like the one I just showed you heat up a planet the kinetic energy turns into heat and it starts to melt the planet and so what happens is a process called differentiation and all that means is that the planet separates into layers okay so we have in this case you see a core in the middle a mantle and a crust it's not that simple there are lots of other ways that planets can differentiate sometimes they fully differentiate sometimes they only melt a little bit sometimes they don't melt at all it's pretty complicated but for the for the purpose of this talk what I'm really going to focus on is when you have a core with a mantle so when you got so hot but the whole planet was molten and the iron got so it was all melted and the iron is so dense that it sinks to the center of the planet how do we know that we have iron sink to the center of a planet right so everything I just told you sounds great but how do we actually know this well one way is that nature is very kind to us and sometimes we get samples from space that just land on the surface of the planet okay so in 2013 this is an example of the meteorite that fell in Russia caused a lot of mayhem but for a scientist who studies meteorites this is incredibly exciting because you see the meteorite fall right when you see it fall it's fresh you can pick it up and you can study it and you know that it just came to earth it hasn't been contaminated by people or by animals right so this was very exciting and we have places like this meteor crater in Arizona right where we see a huge crater in the earth that was formed by a meteorite that fell to earth so what's the way that we know that the planets are differentiated but they have these layers is by looking at these meteorites so some meteorites look like this they just look like rocks and there are many that we will never find because they just look like rocks on the surface of the planet and we'll never think that they're meteorites and what's amazing about these meteorites is that they never melted so they formed at the same time as our solar system as our planets but they never melted so they have the same composition same starting composition as the starting composition of our solar system and if you remember back to a few minutes ago I mentioned that the Sun in our solar system makes up 99% of the mass so if it makes up 99% of the mass of our solar system it must have the bulk composition of our solar system so if you look at a plot of the composition of the Sun first is the composition of these unmelted meteorites this is a one-to-one line you see that for the most part they agree really really well so we have these meteorites that have the composition the starting blocks if you will of our solar system there are some elements that don't agree lithium is it stable and stars and nitrogen carbon and oxygen are very volatile and so they don't hang around meteorites very much but for the most part that's really good correlation so we have these chondrites these unmelted meteorites that tell us what the starting materials were for our planets and then we have a chondrites which form from the crust of planets or of an asteroid and we have meteorites that are made out of pure iron nickel okay mostly iron a little bit of nickel and these meteorites are the reason we know that there's iron and nickel and the core of planets because huge chunks of iron fall to the earth so that crater in in Arizona the meteor crater was made by a huge chunk of iron metal falling from the sky so when we think about the interior of our earth right we know we have iron there's been a lot of many books many movies made about the core of the earth so what exactly is the core of the earth well the most interesting thing about the core is that we can never sample it okay so it's this amazing place on the earth that we know is there because we have these meteorites and I'll explain to you other reasons why we know later but we can never get a sample of it so as a scientist this is both exciting and very frustrating because I can never actually see it myself and so the largest the deepest mine on earth is in South Africa it's a gold mine it's about four kilometers deep the Kola super-deep borehole was something too the union drilled in the 1970s and 80s and it got to be twelve kilometers deep we have these amazing again nature is very kind to us we have these amazing inclusions that get brought up within diamonds that tell us about the mineralogy of what's going on in the in the mantle of the earth that we can never sample and that's great for up to several hundred kilometers depths but the core of the earth is down here and this is several hundred kilometers depth right so there's no way we're ever going to be able to get down there so how do we know that it's there in the first place we have earthquakes so earthquakes are this amazing thing that can cause terrible tragedy but they can also give us a lot of scientific information and so when an earthquake goes off it sends waves into the interior of the earth that then bounce off of layers just the way an ultrasound works right it bounces off of layers and when it bounces back up you start to see a pretty pretty picture of what's going on in the interior of the planet this one happens to be about eight years old now this one is like four and a half billion years old right so the discovery of the Earth's core in 1906 Richard Dickson Oldham discovered that we had a core in the earth by looking at seismology by by looking at the waves that were bouncing off the core and 30 years later anga Lehmann who was a Swedish geophysicist and seismologist discovered that we had two cores we have an outer core and an inner core there have been many pictures of what the interior of the planet looks like over the years and from 1990 ish and on we've found that the planet is very complicated there's a lot going on in the mantle but we're now we're very sure that we have a solid inner core and a liquid outer core and we know it's liquid because certain waves that are released by earthquakes that don't go through liquid and so they just stop they cause a shear and because there's they can't go through liquid and they just stop we know that the core must be liquid and then they'll start again in the inner core so we have four planets for terrestrial planets in our solar system so everything I just told you is great for Earth right we have earthquakes we have seismology but what about on other planets where we don't have seismometers setup and we can't really tell what's going on in the interior so one thing we have is meteorites from other planets so I just really quickly want to show you how we know that we have meteorites from other planets so let's take Mars for example we have a whole suite of meteorites from Mars how do we notice we know this because we know the composition of the gases that make up the atmosphere of Mars and we also have meteorites where when they escaped the Martian atmosphere they trapped little bubbles of the gases as they left the Mars the Martian atmosphere and so by measuring the gases trapped in these meteorites we know that they have the exact same composition as the Martian atmosphere a gas that we've been able to measure through Landers and orbiters around Mars so we have meteorites from other planets so that's very helpful we can learn a little bit about what's going on there we have Rovers but around here you probably know pretty well and we have orbiters so this is the messenger mission that orbited around mercury but what can we learn about planets from orbiters for example well it turns out that figure-skating can teach us a little bit about planetary science so when a figure skater spins right she's spinning but she wants to start going a little faster and so she brings in her hands and her legs and as she brings them in she spins faster and faster and faster this is called a moment of inertia and this is how we know what goes on inside of Planets because the more mass you bring inside closer to your axis the faster you spin so if a planet has more a core than mantle more dense core it will spin faster than a planet that doesn't and so by measuring the moment of inertia of planets we can learn more about what it looks like on the inside so instead of looking at the planets like this I look at the planets like this okay so I look inside the planets I want to know what's going on inside what the layers look like how big they are and how they ended up this way so each planetary body has its own unique pressure so pressure as a function of size temperature and compositional space what it's made out of the four planets in our in our inner solar system don't have the same composition on the surface they all look slightly different and so as John mentioned I conduct high pressure and high temperature experiments and the reason I do that in order to understand about planets is that I can choose a pressure temperature and Composition for each of my experiments and then see how that relates to the planets that I see and so these are the this is the equipment that I use in the lab so I'll take you through this this is called a piston-cylinder apparatus ok so pressure equals force over area the more pressure you put on something or excuse me the more force you put on something the higher the pressure so this piston cylinder and this multi anvil put a lot of force on little samples in order to get to very high pressure so this is showing you what a capsule looks like that we put our samples in before we put it into this piston cylinder it's a hydraulic press it just uses oil pressure to control to control the force this is a multi anvil for the multi anvil it can go to a bit higher pressure than the piston cylinder so the samples get a little bit smaller and this last one over here is called a diamond anvil cell this one's the most interesting because instead of adding more force in order to increase the pressure we just decrease the area okay so we're kind of being tricky we're trying to go the other way around and the area is so small that it's just the top of the culet of the diamond so we take two diamonds and we've cut off the culet so that they're they're flat and then we put a sample in between them and then we put a little bit of force and we get to very very high pressure and because diamonds are transparent we can look right through them and look at our sample so the pressures that we get at in the lab so the pressure Mount Everest right about one atmosphere okay the deepest ocean about a thousand atmospheres the center of the earth is about 3.6 million atmospheres that diamond anvil cell can get beyond the pressure in the center of the earth and you can even make its way these days to trying to get at more giant planet like pressures okay the piston cylinder and the multi anvil can't get as high but the samples are much bigger so they're easier to work with I have to give a plug for the laboratory where I work because it's a really amazing place and one of our most famous scientists was a man named Norman Bowen and this is a picture of him in about 1950 and he's the one he wrote a book called the evolution of igneous rocks he's the one who figured out that at different pressures and temperature different minerals will crystallize and you'll end up with different rocks and then these men here are the first ones to ever reach in a laboratory a pressure of a million atmospheres and this is Dave mal he still works at the lab with me and so we are the geophysical lab is they were the pioneers for this diamond anvil cell research and forgetting to very high pressures in the lab so very quickly this is a colleague of mine his name is yang GUI Fei and I wanted to give you a sense of what it actually looks like to do an experiment because this is always something that's very hard to visualize I showed you the equipment but what is it actually how does it actually work and so what he's doing is he's taking a bunch of oxide so we take normal rock compositions and we mix them together in oxide form and we add it to a bunch of metal so metal and rock right we're trying to form a little planet and we grind it together so that it's homogeneous for a really long time and then we put it in an oven to get rid of all the ethanol and any water that might be in there and then we put that that oxide mix that composition into a tiny little capsule that we hold with tweezers and then that goes into a zirconia octahedra which then go into these eight tungsten carbide cubes okay and this the wires you see our thermocouple so that we know the temperature of the experiment and we take that cube and we put it into the multi anvil apparatus we hook up the thermocouple so that we can make sure we know the temperature and then we crank up the pressure and temperature and we leave it up there at the conditions that we want for as long as we want okay so you can see this experiment was done at 1800 Celsius at about like 10 Giga Pascal's which is about a thousand atmospheres or so and then we cut the power off really fast to quench very quickly what's going on in that experiment we want to know what was going on during the experiment so we cut off the power very very quickly so that everything freezes in place and then we take it out and we look at it and we formed a little planet right so we have we have a mantle we have a core it's very cute my kids really love it and then sometimes we get you know a bunch of little cores and then we polish it and then we analyze what we see within that experiment so what we see in the lab is on the order of centimeters right but what we're trying to discuss and we're trying to simulate is something much much bigger everything I just told you is stuff that is research that's been going on at the lab for decades okay so doing these experiments and measuring the chemical composition of the experiments has been going on for a very long time but in my research and something that I've brought to the lab is that I add an extra layer to this research and that is I study isotopes so what is an isotope okay so if we look at the chemical I mean excuse me the element iron okay iron has an atomic number of 26 so what does that mean it means it has 26 protons okay but really there are three different forms of iron all of them have 26 protons but they have different numbers of neutrons and this changes their masks slightly because neutrons have mass so we have the same number of protons different number of neutrons it's all iron but because of that tiny little difference in mass it actually causes the different isotopes to behave slightly differently and that slight difference I will argue will tell me a lot more about how a planet formed than just looking at the chemical composition so I'm not just looking at the chemical composition of the mantle and the core I'm actually measuring the isotopes in that mantle and in that core and looking at the comparison of the two I do that with this instrument which is called a mass spectrometer and so what you do is you put your sample in one side of it it goes through an electrostatic analyzer in a magnet and here it just collects the different masses okay so you you measure how much iron 54 how much iron 56 how much iron 57 and then you just look at why they're different from one another okay so here we have our four terrestrial planets interiors I told you that they had iron in them but actually there's more than just iron ok there's iron there's a little bit of a nickel and there's other stuff so why do we think that there's other stuff well if you look at the density of pure iron at the conditions of that the core is at there's actually a slight difference between iron and the core and so there's something else in the core and it's light because it's causing less density okay so what is that light element in the core and is it different between the four terrestrial planets so I'm gonna take you through two or three very short examples of how we use isotopes to tell us what's in these cores okay so the first is we're just looking at silicon isotopes so it's just like iron it has three stable isotopes and if you look at the siliconized hopes of the earth versus meteorites and these are those conducts remember chondrites are supposed to be the exact same starting composition as the earth so why would their isotopes on earth versus those of contracts be different nobody had any idea so we did experiments in the lab and we found that when you separate a core from a mantle you suck out some of the isotopes into your core and if you look at that and you can plot it as a function of temperature and so you know what temperature the earth formed at approximately you can say exactly what the silicon isotope ratio would be that would be different between the metal and the silicate and when you do that it lines up exactly with the meteorites and the earth and so by doing these experiments we've been able to determine that they're silicon in the core of the earth along with the iron and the nickel and we can say about how much as well the same thing can be done for mercury except on mercury we don't have any meteorites for mercury mercury is too close to the Sun any meteorite that gets flung off of mercury will not come back out to the earth it'll probably go into the Sun instead so we don't think we have any meteorites from mercury but we can do the same sort of thing so this is the messenger mission that orbited mercury and based on their on their data they were able to determine that there's a solid iron core for mercury a molten core with iron sulfur and silicon and then this FES layer now you'll notice that mercury is mostly core why is mercury mostly core versus the earth which is core plus this huge mantle well if you think back to those giant impacts that I showed you for the earth for example it's thought that there was a giant impact that haen't mercury so hard that it's mantle got stripped off of it and just flew into the Sun and so the only thing that's basically left is this core of a planet but if we don't have meteorites for Mercury at least we don't think we do every now and then a scientist will tell you that they found a meteorite for Mercury but it's very hard to tell whether or not they really there really is one and so we thought okay well if this is true and there's this much silicon in the core of Mercury then we can tell you what a Mercurian meteorite would look like in isotope space so now the next time someone says they think they have a meteorite from Mercury we can tell them to measure the silicon isotopes in that meteorite and then we can know whether or not it really is from Mercury so there are people actually going through museums trying to do this what about Mars so Mars is super interesting because we've done a lot of research on Mars we know a lot about Mars between the Rovers that have been there and the orbiters and a lot of work has focused on the interior of Mars there's actually a NASA mission that's going that was supposed to launch this year but we'll probably launch in two years called insight that's going to put a seismometer on Mars so we're gonna know a lot more about the interior of Mars so Mars is thought to have a lot of sulfur in its core okay so we did experiments where we looked at the iron isotopes that would be in the mantle of Mars as a function of the amount of sulfur and what we found is that while the Martian meteorites have the same iron isotopes as chondrites according to our experiments they should be way out here and so this idea that Mars has a ton of sulfur in its core we actually think is wrong we actually think that there's much less based on these experiments so what about pressure right so the earth is really really big and it has a lot high pressure compared to mercury for example or Mars so what happens if we do our little isotope study but we do it in the diamond we'll sell if we bring it to really really high pressure now for many many years it's been thought that pressure has no effect on isotopes so when I was in graduate school I would hear this all the time from professors that that pressure has no effect on isotopes it's been shown since the 1950s and it kind of becomes Dogma right like people just say it over and over and over again and so I'm a little stubborn and so I decided that I wanted to see this for myself okay so in the last couple of years I've spent a lot of time trying to look for an isotope effect at high pressure and what I just found a couple weeks ago is that pressure actually does have a very large effect on isotopes and we can now use these isotopes to tell us not only about what's inside the earth because it's at high pressure but even more interestingly one day maybe not in my lifetime but when we can measure spectra from exoplanets right if we could ever measure isotopes in those spectra we'd be able to say what's in the interior of those exoplanets because so many of the exoplanets are so big so we started out with four terrestrial planets we have interiors that look very different our focus for the future is to understand how what's going on in the interiors of these planets affects the surface right because the interiors are going to be a certain composition based on the size of the planet and its history what's inside is going to affect what's outside right so if you bring elements in to the core for example or to the mantle they're not going to be on the surface anymore and so the surface will then be different therefore the atmosphere will also be different and the atmosphere is today astronomically detectable so how does the interior affect the surface affect the atmosphere affect life maybe this is where we're trying to go in the future right this is complicated and requires a bunch of different types of scientists coming together and putting our heads together trying to go from the inside out in order to understand more about these exoplanets that I showed you in the beginning of the talk so the next time that somebody shows you an animation of Kepler for example right so these again are the Kepler exoplanets that were found but this time more recently somebody colored them relative to their temperature not just their size and so here's our solar system here so you can see the difference and what you see is this amazing diversity all these different temperatures all these sizes all these different orbits so the next time you see something like this I hope that you not only think about what's going on on the outside but also how what's going on on the inside can affect what's happening on the outside and with that I want to thank some interns I've had over the years and some postdocs whose research I just showed you and of course the Carnegie Institution and NSF for funding and I thank you for your time okay so yes I have to repeat the question so the first question had to do with moonquakes and whether or not there's a seismometer on the moon as far as I remember a seismometer was placed on the moon but it was placed on the moon incorrectly and so it's not actually touching the surface as well as it should and so a lot so a lot of the measurements have been reanalyzed recently and it's what actually it's why we know that the moon has a core is because a lot of the old data have recently been reanalyzed and and they have found that there's a moon on the core on the moon so yes and hopefully there will be one on mars soon that will work very well the second question had to do with Planet 9 Planet X so everything I told you about planet formation was figured out before we knew about all these other exoplanets and this Planet X them might or might not be in our solar system and so you're right you know a lot of it can change and a lot of it will have to change because a lot of those planetary systems that I showed you have planets that are in the wrong places it doesn't make sense how could something so big be next to a star and have smaller planets you know further out like a lot of it doesn't really make a lot of sense and so what I'm hoping you take away from this is that this is what we thought into now but over the last six years with Kepler everything is going to need to be rethought and so our hope in the lab is that the astronomers will inform us what they find we will try to mimic it in the lab and then we can kind of come up with a better and more encompassing theory yes so that's a great question so he asked about the gassy Giants and he said a lot of what I said was about the interior terrestrial planets and that's absolutely right so there are two theories for how the gas giants formed one is the same theory I showed you just now core accretion right and the other is called disc instability and one of our colleagues at DTM has done a lot of work on that and so it's unclear exactly how they formed but you're right what we're trying to do the reason we're trying to get to higher and higher pressure in the lab is because we're trying to understand more about the pressure inside the gas giants it's thought that the gas giants also have a metallic core but maybe a metallic core not made of iron hydrogen for example becomes metallic at a certain pressure okay so so it's very possible that the insides of these planets could have metallic cores could have hydrogen cores could have rocky portions we're not sure but the higher pressure we can get in the lab the higher the pressure we hang at the lab the closer we can get to understanding the interiors of the gas giants and the exoplanets that are so big I'm sorry that's pressure act I didn't understand no the pressure at the very center of the planet is three and a half million atmospheres know it as you get inside it gets more and more and more pressure it's it's a function of depth if there's a lot of force if there's a lot of pressure in the center of the planet that's why another reason we have an inner core is because the pressure is so high that the iron just turns solid again it's no longer molten that's a great question so we hypothesize that as you're squeezing things get more compact right and so the atom gets more and more and more compact and what has to happen is that the bonds between the atoms you need to get stiffer and stiffer it's difference differ and so you're squeezing these things and so their volume is going down more importantly the bonds are getting stiffer and as the bonds get stiffer the isotopes change I assume that they get it just if you think about the shape of the of the orbits and the atoms they just squeeze they just there's less space I think between the nucleus and where the electrons go you know I was inspired by Carl Sagan I I went to Cornell and so I for my undergraduate and so I was very inspired by him and being in the same area where he used to teach what would happen if you if you change the isotope ratio in the core you mean what can we learn by that change or would we notice a difference there would be no physical difference that we would notice other than it would tell us about how it formed so we would never notice so nature gives a natural abundance of isotopes there's just a natural abundance that exists and how those change we would never notice unless we measured them but it can tell us about the process that caused them to change so there's a problem there's a name for this problem that just escaped me but there's a problem that as you get when you have very small dust grains they stick together through like electrostatic forces right they start to stick together and then as you get bigger things start to they're not big enough to have a gravitational pull right so they just start to bounce off each other and they don't really stick and so there's this problem in the planet formation theory where you can get to a certain size and you can if you skip you know a kilometer so then you can make it big again from gravitational poles but a gravitational attraction but in between it's fair heart and people really haven't been able to figure out as far as I know how to get through that divide they blow apart they don't really stick together as well but a lot of those simulations like the one I showed you for the giant impact a lot of people do simulations and they do lab experiments also trying to piece it together yeah yeah so what we're trying to do is it's actually very interesting so technologically what is the next thing that we can do in order to get to higher pressure right so we have these diamonds and I told you that pressure equals force over area so what we're doing now is we're making our own diamonds so we have a CVD chemical vapor deposition laboratory at the geophysical lab and we make our own diamonds and what we're trying to do is where we're creating the same shape right and then we drill a little hole within the diamond and put the sample in there so the samples are getting even smaller right and it's even stronger because it's within the diamond and so there are ways like that that we're trying to get at getting to higher pressure changing the design of the diamond cell one way or another I don't think there's a limit I think I think technology you know is amazing yeah yeah so there's shear waves and compressional waves oh I'm sorry she wanted to know why certain waves don't go through liquid whereas others do so there's two types there's there's shear waves and compressional waves and the shear waves don't so you know when you you guys live in LA so you have earthquakes right and there's there's different kinds of shaking okay and the compressional waves move in a certain way where they can go through anything because they move it best to describe it without a chalkboard so the shear waves basically can't move through liquid they they they can't they can't they there's no shear I yeah it just doesn't it the liquid doesn't shear and so and so they they can't go through the waves I can draw it for you later yeah so I'm being recorded so I need to be slightly careful but the day before I left to come to LA a colleague showed me a diamond I told you they're diamonds bring inclusions from the lower portion of the earth oh the question is sorry whether or not we could really ever find a piece get a piece of the core and the inclusion in the diamond was metallic it was a piece of metal iron metal and so the question is where did that metal come from could this diamond have come from so deep in the earth that it's somehow grabbed a piece of the core right or maybe not even a piece of the core maybe a remnant of when the core formed or something right so that's one option is these diamonds the more the cool thing about these diamonds is that we get them from places like De Beers because they're really ugly because they have tons of inclusions in them so people don't want to buy them right so they gave them to the scientists to do the research and so we have tons and tons of diamonds that we can look at so that's one option and then there was a professor maybe at Caltech I'm not sure who had an idea that he wanted to take a big chunk of iron and kind of put it into the earth and somehow watch it as it went through the earth but that would take a really really really long time so we can't physically ever get down there but nothing's to say that we haven't figured out a way that maybe nature can bring it to us we just need to find the right tracer are there any techniques of finding of looking at the spaces between very small particles yes so there's a synchrotron technique so using synchrotron radiation we can measure the volume and how the volume changes as a function of pressure so that we can do in terms of actually knowing the space and I don't know but I know for sure well the next rate of so x-ray diffraction is an option for knowing the crystal structure and and synchrotron radiation will tell you can tell you the volume but I'm not sure about inside of that volume how things change yeah can you give you can isotopes help you learn about the rate of accretion so there's two different types of isotopes there's stable isotopes like the one I just told you about which have no time information there's radiogenic isotopes which are decay at a certain rate and so that's how we know how old the earth is right that's how we know how old meteorites are is by measuring the radioactive decay and so there are ways people have used to they use dating techniques for the using these radiogenic isotopes in order to map out you know when the solar system first formed when the first solids in the solar system formed so those are called calcium aluminum inclusions and they're thought to be the first solids that formed in our solar system so we know how old those are and then we know how old the parent bodies of the chondrites are and we know how old the earth is so using those sorts of dating techniques you can kind of get a timeline for when we had tiny little specks to when we had more planetary sized to when the moon formed that sort of timeline can absolutely be obtained oh that was yeah that was hypothetical it still acts like iron but but lots of elements do change their properties so like I said hydrogen becomes metallic right it's no longer a gas there are lots of elements like that that that do change their properties and you can watch it through a microscope as you're compressing but iron it goes through phase changes so yes okay so all these elements will go through phase changes as you compress them and so they'll know or be stable and if you do x-ray diffraction and you look at their crystal structure it will shift right at a certain point at a certain pressure because they're no longer stable in that configuration so they kind of twist a little bit so to make a little bit to fit in their new space and so that does happen and the properties of that phase change are different so it has a different thermal conductivity it has it does have different properties that's correct no boy does the core spin in a different rate than the rest of the earth I assume yes it must yes the question is how could there be rock rock inclusions in an iron matrix so are you talking about the the palace sites the ones that have the green chunks so those are actually my current focus of my research because they're so fascinating so one of the meteorites I showed you was this really beautiful one that was metallic and it had these green chunks I didn't go into any detail about it because it we're still trying to understand how they form that way but the hypothesis over the last couple of decades is that those meteorites formed at the core-mantle boundary of an asteroid so where the core meets the rock now that might be true we don't really think that's true anymore some people now think that they were formed through impact so a lot of what I told you tonight is is newer research that the early solar system was very very chaotic right that that wasn't really what people thought a decade or two ago and so a lot of impacts impacts are now being used as the reason for what we see and so one of the new hypotheses for PAL sites is that a meteor a big asteroid hit another asteroid melted the metal because the metal has a lower melting temperature than the rock and then the metal kind of went around the rock kind of filled in you know little fragments and then froze in place it's iron nickel metal and really beautiful green olivine crystals olivine is a magnesium silicate and it's the main component of the Earth's mantle and probably other Mantle's yeah yeah the density change what is the density change when you compress samples it's I don't want to make up a number I think it's on the order of a few percent I think so yes that's the answer to your question yes that's right a slinky that's nothing good yes yes and you do this and you do this that's brilliant yes did you hear that yeah yeah yeah so the question is about the Kuiper belt and the Oort cloud and I am NOT the expert on that so I actually just met the person who discovered the Kuiper belt at UCLA on Thursday he's a professor at UCLA so Pluto and all these dwarf planets right are part of the Kuiper belt and I I'm not really sure there's there's their models for how the solar system forms that are newish that involve the migration of planets the giant planets and the idea is that the the giant planets kind of came in and disturbed what was going on and then kind of came out and I don't know maybe you know no I I don't know much about how they formed but it I think it has to do with the migration of the giant planets are you still dealing with an incompressible fluid with a molten core at such high pressure what do you mean I think I don't think so I think it would still be a it would stay whatever the compression is at that pressure it would stay at if that makes sense now you remember the the liquid core is convecting vigorously that's why we have a magnetic field right and so and so I think I think it would still be an incompressible liquid I have no idea is there a limit to the compressibility the compressive strength of diamond so we do break diamonds regularly this idea that they don't break is not true but they usually break when we make a mistake so they usually break when when the two flat sides are not perfectly flat because then you're kind of like bending one right into the other right but when they're perfectly flat you know to the eye of a human being we can get them to pretty high pressure but that that is the biggest problem when we get to high enough pressure is that the diamonds break and that's that's been the reason why we haven't gotten to higher and higher pressure earlier is that at a certain point the diamond just breaks and so a lot of people are trying to come up with materials that might be harder but we can't not yet at least yes yes so for my research what's interesting about a magnetic field is that for example Venus doesn't have a magnetic field but earth does the Venus is very similar to the earth in many ways right Mars had a magnetic field for a short amount of time but no longer does mercury has a magnetic field magnetic field on earth we think is is there because we have the liquid and the outer core right so we have these conducting fluids fluid with a with a big chunk of metal on the inside so because of that and because Venus doesn't have a magnetic field we think maybe Venus doesn't have a solid core or doesn't have a liquid core right mercury has both and so it has a magnetic field but there are astronomers who study magnetic fields on X so an exoplanet yeah in order to understand more about magnetic fields but for me it's more interesting in my research for where what it means about the core because with or without the magnetic field that's telling you something about the state of the core can you create the Geo Dynamo in the lab so there's a professor at UCLA I know a lot about UC likes I went to school there there's a professor at UCLA who has a huge tank of liquid metal that can that rotates and they're trying to understand how magnetic fields are created it's very cool it's called the spin lab so I know we have more questions you feel free to come up after

Channel: FORA.tv

Views: 15,622

Rating: 4.7658539 out of 5

Keywords: Planet Formation, Anat Shahar, Carnegie Institution for Science, space, exoplanets, Jupiter, Saturn, Mercury, Earth, The Big Bang, universe, NASA

Id: VAKSzsJcpQk

Length: 64min 41sec (3881 seconds)

Published: Wed Apr 20 2016