Exoplanets and Beyond - Sara Seager - 5/12/2018

good afternoon and welcome to the fourth and final session of today's symposium honoring the scientific legacy of Richard Fineman my name is Nick Hutzler I'm an assistant professor of physics here at Caltech and I will be chairing this session that focuses on new and exciting ways to observe the universe around us our first speaker is Sara Seager professor of planetary science physics and aerospace engineering at MIT professor Seager is a member of the National Academy of Sciences and a MacArthur Fellow and her main research goal is to find and identify another earth including searching for signs of life by way of bio signature gases in planetary atmospheres she will tell us about this exciting search in her talk titled exoplanets and beyond please join me in welcoming professor Seager [Applause] thanks everyone I'm starting with this picture from Mauna Kea in Hawaii just showing you a star studded sky because we think that all each every star has planets or a planetary system and all stars just to remind ourselves our Suns and if our Sun have planets it makes sure that other it makes sense that other stars who also and they do in fact after wandering about this humans thinking about other stars and other planets for thousands of years it turns out that the very nearest star to us aside from our Sun Proxima Centauri appears to have about an earth-mass planet around it so there are lots of stars and lots of planets out there and just to convey how many known planets here's an animation zooming away from Earth you might not be able to see the white stars but this is a real map of the sky the colored ones are stars with known planets now I did not know Fineman but of course like every undergraduate student in the world who could I had a copy of the red book it was like a paperback the red books lectures on physics with the white border and the dark pages that you know have this weird texture to them if I could see Fineman today I would want to share with him that there are truly thousands of stars with planets out there and that underline all the techniques that astronomers used to find planets are the very basic equations found in Volume one of those lectures and so in exoplanets you know we're not using physics to understand crazy new things like at the time helium that's cooled into a liquid and superfluid but we're using them to explore other planets and to understand what they're made of and the chance of finding life around them now I've stopped this animation at about a thousand light years and our Milky Way galaxy is a hundred thousand light years in diameter and we heard earlier from Michael Turner that we think our universe has hundreds of billions of galaxies our own Milky Way has hundreds of billions of stars and so if you just do the math and count like how many stars are out there and thinking that almost all stars have planets you know surely there has to be planets out there that are like earth with signs of with life on them and in fact although the universe is so vast it's only the very nearest neighboring stars we have access to to study in detail and I'll come back to the head so the first thing we do in exoplanets is just take all the planets we know and plot them on this diagram it's called that we just say it's the in this case I'll tell you what this is it's showing you planet radius it's on a log scale so Earth would be here at one earth size this is ten earth size Jupiter's about 11 times the size of Earth on the bottom you see semi-major axis also on a log scale so Earth would be here at one you've nap tun and Jupiter and all these different colored points are planets it's not all the known exoplanets it's just the ones that have like a semi-major axis or properties that I could put on this diagram but just look at how this diagram is so full of planets that actually there are planets that are a hundred times more than a hundred times closer to their star than Earth is to our Sun and some of these planets would be some of them are small rocky planets that would be so hot as heated by their star that their surfaces are hot enough to melt rock it's just like those horror stories we're hearing about Hawaii today they wouldn't have volcanoes erupting necessarily but the surfaces would be so hot that there would just be liquid lava lakes everywhere there's a whole bunch of planets in here that appear to be the most common type of planet in our galaxy two to three times the size of Earth and in fact we don't really know what those planets are there's no solar system analog they could perhaps be water worlds 50 percent or more water by mass like scaled up versions of Jupiter's icy moons or they could be giant rocks with hydrogen envelopes we're not sure now it's fair to say here that this dark part of the diagram is dark because our techniques don't reach there yet and I just have a little bit of a crazy slide you don't have to follow this slide I kind of condensed half of semesters like undergraduate physics class on this slide because I wanted my physics professor and graduate student here just to know that it's a very great subject pedagogically speaking because you can work out fundamentals from first principles for underlying every planet finding technique and I've just sort of listed some of them here if you wanted to browse them I've just sketched out some selection effects because some only techniques work for some types of planets and not others and I'll come back to one or two of these things a bit later but for now it's just fair one more thing I wanted to say was that you know you can overanalyze this but don't like for example you see one population here and another down here these are transiting exoplanets found by ground-based searches which because of the blurring effects of Earth's atmosphere and the day/night cycle can only find big planets close to the star the ones down here are found by the Kepler space telescope small planets and this is actually they haven't found big planets because these smaller planets are 10 times more common than Jupiter sized planets but our takeaway from this plot is that in exoplanets in terms of the types of planets out there anything is possible within the laws of physics and chemistry and it turns out in exoplanets as well it's an interesting field because the line between what is considered mainstream and what is considered crazy is constantly shifting and you couldn't have had this talk 20 years ago so just a smattering of planets all by the radial velocity technique if you were paying attention back then the planet and star orbit their common center of mass and astronomers measure the Doppler shift of the star and infer the presence of a planet and now there are so many techniques and so many planets the field is really so rich well let me move on to another summary diagram this one is putting planets that we can measure the mass and the Sun and the radius and so effectively we can have an average density and two different techniques have to be used one could measure size and one could measure mass and here I'm also showing you a log-log plot this is showing you planet size now I have the scientific notation notation Earth and Venus Uranus and Neptune Saturn Jupiter and this is planet mass so here by the way to any planet binding technique that we have Earth and Venus would actually appear basically the same now what I'm showing here are curves for illustration of constant composition so imagine for a moment it's purely for illustration there was a planet just made of iron and as you would add imagine adding more mass to like a giant sphere you might expect it to increase as our cube which it does initially but as more and more masses added to this type medical planets fear the interior starts compressing and that compression means that it doesn't and eventually if you added enough mass it would flatten out now each of these points are planets and I just wanted to put up a few equations because I looked around the room and I think actually like ninety percent of you could try to infer what planets are made of based on their mass in size with this sort of simplified set of equations mass of a spherical shell hydrostatic equilibrium where the pressure gradient force is balanced by gravity and all the physics is buried here in the equation of State how the pressure temperature and density are related in thermodynamic equilibrium and in this field actually there's a we have to get these equation of states which are unique for each material by experiments or density functional theory computer simulations or you know very high pressures we can assume all electrons or there's like a sea of electrons surrounding nuclei but I was just reading the news from the other day in exoplanets and people a team used the laser Ignition facility at lol and they went to like I want to say to Tara Pascal's or 1.4 tera Pascal's that's like millions of atmosphere pressure that we have here with iron and they do these like experiments with lasers and they heat it up just for like a nanosecond and measure the material just to sort of get the properties of iron and other things at high pressures so we can use it to CIN understand the range of what planets could be made of I just want to tell you that because in exoplanets we don't inspire new physics but that's one example maybe like one of the only ones where we do inspire new experimental physics and so on this pot you can see all the planets and there's some really interesting things going on here here you can see that there are planets of the same size spanning two orders of magnitude and mass these are giant planets where the very massive ones what's happening is that in their interiors there's very high pressure I like to call the atoms and their pressure ionized where electrons are popped off at high pressure and the nuclei can squeeze closer together so even though the whole planet is more massive and their outer layers you know the planet is getting bigger on the inside it's getting compressed because the nuclei can squeeze closer together and so the planets are of the same size we also have planets that are the same mass that are very different in size jupiter-sized planets some that are almost twice the size of Jupiter and we write down the equations that describe how a planet when it's formed hot and somewhat big contracts and cools as it ages as the energy the planet is formed with the gravitational potential energy from when it formed slowly escapes out the planet contracts and cools we don't know what the missing energy sources that's keeping these planets very inflated now there are several theories and there's probably people in this room who work on it everyone has their favorite theory probably you know nature is most certainly smarter than we are and it's probably a number of different reasons about why that is happening um by the way there are no planets in this part of the diagram because the planet wouldn't be gravitationally bound it would be too low density for its gravity there aren't any here I was always hoping to find a planet that would be like a hundred times earth mass like a giant massive rocky world but so far nature doesn't seem to make them it seems to make rocky planets down here that quickly as they get more massive appear to have accumulated gas envelopes to make them lower density I forgot to mention what these curves were this was pure iron these would be silicates this is water and this would be like cold hydrogen and anyway one more thing was there all these planets here we're not sure what they're made of it's somewhat ambiguous based on their mass and size and kind of where they fall in this diagram my pot is unfortunately somewhat out of date in this box here I'm showing you planets that would have higher high enough density that they would follow along these curves here of silicate or silicate and iron and they actually would have to be rocky planets based on their average density and you know sometime you could take this or fun and work through all no matter how you slice them dices there are definitely rocky worlds out there and in our whole search for life and the thought of life on other planets we want to start with rocky planets that have a solid surface as we know it and that's where we're headed so just to summarize that first part of my talk exoplanets are diverse covering nearly all masses sizes in orbit so far that we've been able to find anyway small rocky planets are common oftentimes little can be known about an individual exoplanet I mean I'm clearly giving you a very high-level rapid-fire summary but sometimes all we know is the planet size and orbit and that's it and so our goal is to learn more about planets and in this case the transit technique is very powerful you can get a mass and a size and you can also study the atmosphere and in the search for a smaller and smaller planets right in the hell I wanted to just show you why one of the reasons why transiting exoplanets are so popular now it turns out that Earth's size compared to our Suns size radius the size fish is about one part in 102 Sun size so if you square that you get the area that's in part one part in 10,000 and this little drop in brightness you're seen here if you can imagine measuring the Stars brightness as a function of time the brightness drops by a tiny amount this is the planet 2 star area ratio so for an earth transiting a Sun that's one part in 10,000 and I guess I don't know if everyone here is like a theorist or modeler but I know there's some experimentalists questions do you have to measure things to one part in 10,000 would you want to it turns out earth is 300 thousand times less massive than our Sun and in terms of reflected light it is 10 billion times fainter so you know which would you work on if you wanted to find another earth would you do transits at one part in 10,000 radio velocity for one part in 300,000 or would you do one part in 10 billion well it's always fun more fun to do the harder one of course so hopefully I have time to get back to that at the end of my talk now in fact astronomers in exoplanets we don't use the phrase like there's plenty of room at the bottom we actually have another phrase it's called the race to the bottom and by that we mean the bottom size of stars because it's not just that a planet I've drawn this fake planet on this real image of the Sun and the same sized planet on like a sketch of a star a small red dwarf star that is 10% the size of our Sun this is the smallest type of star pretty much possible any smaller and colder than fusion wouldn't happen inside the star and actually a group of astronomers went out purposely to search these very smallest stars and took like the 20 likes a brightest of these very small dim stars and actually found and by the way I just put this number here so for our own earth science one part in ten thousand for this one it's one part in hundred and the probability to transit because we think that planets their orbits and the stars rotation axis is just randomly distributed so the star and planet have to be lined up just so perfectly to see a transit and the further away the planet is from the star the lower the probability for is to show transits so if you wanted to find a transiting earth probability to transit about one and two hundred and if every star had an earth every sun-like star had an earth-sized planet and earth-like orbit you'd have to look at at least two hundred thousand stars to find one but for these Trappist plants is only one in 30 and in exoplanets there is a lot of luck I don't know nature has been bountiful for us and these astronomers who went out and just only looked at 20 stars as a pilot program they found this fantastic system called Trappist one I don't how many of you have heard of Trappist one it's it's actually not the real name of it is Trappist this is why people renamed it because it was called to mass j23 stereo six soon yeah it's a bit of a mouthful but many of these stars are already known in catalogs and they already have a catalog name now for those of you who want to peruse that gorgeous transit light curves you can for those of you I wanted to show you this cartoon showing you that the star is so small it's almost the size of Jupiter and remember what I told you about compression in the core which is why it can be the same size in a very different mass here's our Sun for comparison and these planets are blank kind of indicating that we don't really know anything about them although if you read the popular news one day hey there's definitely chance for life on them another day is no there's no chance for life they probably have no atmospheres another week the news would say hey these are water worlds they probably don't have chance for life because if you imagine a pure ocean world there may not be any where to concentrate nutrients contrary like the ingredients for life and so the debate kind of goes on we really don't know much about it now I do work most I do a lot of different types of work and sort of a fair amount of it would be on exoplanet atmosphere we're not sure if these ones have atmospheres but instead of telling you about like my computer codes and more details let me take a little you know mental break and take you on a virtual trip to a planet orbiting an M dwarf star now there are lots of M dwarf stars people are searching and there are many many known exoplanets around small M dwarf stars the stars are anywhere from ten to fifty percent the size of our Sun so first of all for some of these planets I forgot to mention that for these planets the planet has to be relatively close to the star because these small stars have very low energy output and so if you want to think of a planet in the so-called habitable zone where the planet has heated with a thin atmosphere as heated by the star is not too hot not too cold but just right for life it's relatively close to the star and actually by Kepler's law then the planet would go around the star fairly rapidly like these Trappist planets have periods of just a few days a few to ten days so if we could go to one of these planets the star the Sun might be very big in the sky but because the planets are so close to the star by tidal interaction with the star the planet has most likely evolved to its lowest energy state which is tightly locked every time the planet rotates one time it also orbits once just like our moon does with earth our Moon almost always shows it shows the same face to earth at all time but actually a little more than half because it has this Librarian so what that would mean if we could go to this planet is that the star of the Sun would be in the same place in the sky at all times so you could choose to visit where it's always daytime or where it's always night or for me I'd go to where it's always sunset so I could see a very long green flash so on this planet because of Kepler's law being so close to the star a year would be let's just say about ten days and for any kids in the audience I saw one patiently sitting in the back your birthday would be every ten days now on the other hand maybe visiting this planet wouldn't be so great because the stars have flares they like bursts of energy of high-energy particles that would be very damaging what kind of sunscreen would you bring in you might get like mutations for those of you blue to your phone that wouldn't be a good idea because the higher particles would destroy the electronics it's electronics on your phone so we're not really sure about these planets they're the easiest way for us to find planets where we can search for life but it turns out that the very energetic flares are a concern they always kind of have been we kind of sweep it under the rug because it's easier to find planets around these stars now how many of you have heard of the Carrington event yeah in the 1850s astronomers were first realizing there was some connection between star and our Sun and magnetic field and events on earth actually there was an astronomer and like an amateur M quasi amateur professional astronomer named Carrington apparently he couldn't get like a job at an observatory so he used his own money from his family's Brewing Company and one day he was studying the Sun and he saw it brighten around a sunspot and about a day and a half later our earth became electrified there was an induced current because part of the Sun was ejected a small part with its own little magnetic field and it hit earth and at the time telegraph operators you know they could take the batteries out of their Telegraph and it still worked because the air all around was charged now at the time astronomers didn't disseminate their information yet they didn't totally understand the connection between the Sun and that and Maxwell's equations weren't yet articulated so people didn't totally know what was going on but they I forgot to mention the northern lights were seen almost down to the equator it was this incredible event on earth and people do worry about it today because if we get another event like that today we have our power grid and which you know wouldn't fare so well under those conditions now about back to Trappist the Kepler space telescope were looking at a field for 80 days that included the trap F star and astronomers found that it had 44 zero flares in 80 days and they only estimated because Kepler's like white light but most of the energy in these flares comes out at much higher energy that one of those events in 40 days was equivalent to the Carrington event but the planets are so close to the star they're much more likely to intercept it so with that in mind I don't think we'd want to visit the planet at all and I'm not sure if these planets are gonna have life or if they even have atmospheres so sorry bro so to do more on exoplanets and to learn if they have atmospheres and we could correlate that with the star stars activity we want to learn more about planets I already showed you this diagram and now I'm superimposing on it stars where we have observed atmospheres this isn't like totally accurate because the plot is made just from like creating a database so I didn't go back and double-check every last one that it was right you can see the ones with atmospheres fall into certain categories there the transiting planets where the planet goes in front has a star and they're directly image planets where we can block out Starlight and see the planet directly and right now we're pretty limited to just you know certain types of planets and I wanted to just say that when I think of the search for life I divided up into transits and to direct imaging because those are the types of planets the atmosphere as we can see for transits we pretty much have to go to space above the blurring effects of Earth atmosphere and for a direct imaging it could be ground or space now let me briefly tell you about exoplanet atmospheres and you can see on the left there a cartoon showing you the atmosphere it's like a very exaggerated atmosphere of an exoplanet and here the star light can shine through the atmosphere and just like shining a flashlight through a fog some light makes it through some doesn't act I just put this equation for anyone who knows remembers anything about reading to dispenser but essentially there's light going through it gets exponentially attenuated if there are molecules absorbing but for our purposes now conceptually just think about the planet if it's transparent it's a certain size and if there's a wavelength where the atmosphere is blocking the Starlight from getting through the planet looks a tiny bit bigger that's kind of what all of transient exoplanet atmospheres is based on and so in that regard how big that atmosphere is really matters and I only picked one real data set of have I kind of cherry picked one example to show you of an atmosphere and let me walk you through this this is showing you the transit depth so how deep the transit is and this is wavelength in microns this is showing you visible wavelengths here near-infrared here and this is a little further in the near-infrared and this would be Spitzer Space Telescope the rest of this is Hubble Space Telescope now what you have to do is think that if the planet had no atmosphere if had clouds when we couldn't see an atmosphere and this would just be a straight line so I think I think you can all agree with me this is different from a straight line and you can see here the planet is looking bigger at certain wavelengths where the atmosphere is absorbing and this is one of our very best datasets in exoplanet astronomy of a atmosphere and this is giant water vapor features now this planet is just an incredibly it's called a hot Saturn it's a very low density planet Saturn is about 0.67 grams per cubic centimeter and it's average density this one's even lower we're like 0.2 it's a very puffy planet with a giant atmosphere and that makes it easy to easier relatively easier to observe now for exoplanets in our search for life we do have a plan myself and like the whole community working on this and that's the James Webb Space Telescope we want to use the james webb space telescope to study atmospheres like in this plot but for smaller and smaller planets down to earth size going in front of em dwarf stars and actually we have this mission look did you see this little telescope it's actually not that little it's bigger than it's about my height and like about this big it's called Tess it's an MIT led NASA mission transiting exoplanet survey satellite we call it the finder scope because gonna find planets and all the planets that finds that are suitable the whole community will be using the James Webb Space Telescope to follow up actually it had a spectacular launch on April 18th SpaceX Falcon 9 rocket out of Cape Canaveral and the plume was burning so brightly and the rocket just like went like it seemed like it was going on forever and Tess ISM going into a very unusual orbit it's a highly inclined highly elliptical orbit about earth where it's a final perigee will be something like 20 earth diameters away the earth radii away and it'll like have this so it can spend 13.7 days most of it away from Earth where the reflected light and heat from Earth won't be bad for observing it's a brand new orbit for observations okay so in a search for life we're not there yet but we hope to get atmospheres of small planets and on earth its oxygen our best gas that we have our atmospheres 20 percent by volume oxygen but without plants and without photosynthetic bacteria we would have no oxygen and I'm gonna take a little aside for a second and talk about something not related to physics or exoplanets because I embarked on this problem and I think it helps to show like the sort of wonderful journey of exploration that we all get to do so I worked on exoplanet I work on exoplanet atmospheres and the question is could there be any other bio signature gases other than oxygen that are really great indicators of life elsewhere and when I was doing this I had this crazy theory how many of you get emails about crazy theories I know a lot of you probably almost happen right well I had my own crazy theory not in physics though but in chemistry and for a while I thought you know what if all what if life makes all gases because it turns out in our atmosphere every gas to the part per trillion level actually is produced by life although it usually has a dominant source that is not related to life so he went through my limited knowledge list and it turned out that was so so who does the MIT professor go to with a crazy theory lied to or the next level up which is Nobel laureate so he went to Jack szostak he welcomed myself and my two biochemistry colleagues and within about 10 seconds he came up with a counterexample and crushed us so we go back to the drawing board and we would do like a big data fusion data gathering project combinatorics codes like they do in drug discovery to like seed molecules and make them bigger and bigger and we came up with a list of 14,000 molecules that are all molecules they're gonna be like exhaustively but nearly complete lists of molecules that are in gas form at room temperature and pressure as well as like a giant database from scaring the literature and scraping all the websites possible for all molecules made by life and what we found was actually even more interesting which my brilliant postdoc Janusz Kowski found was that actually it turns out that life has very specific path even though out of those 14,000 gases life produces only about a quarter of those it actually has very specific types of molecules or fragments of molecules we call motifs that life entirely avoids and I've taken this kind of detour now to explore with my team why that is and in some cases were working to explain it away with this sort of thought about there could be inroads into origin of life and toxicity and maybe even drug discovery so it's my favorite thing I wish I could have spent my whole talk talking about that because it's my main thing that I've been working on when I actually get to get on my computer and do some coding so in the search for life I mean I only have a few minutes left so you know transits are only the first part of a long story they're very limited because you have to have this fortuitous alignment and it's limited to small stars I didn't talk about that but because this atmosphere annulus superimpose on the size of the star is a problem so there are many other ways to find planets I mean to study atmospheres and each one is crazier more sophisticated than the last we have giant ground-based telescopes the 30-meter telescope which is a huge huge telescope it will be able to study planets directly imaging them dwarf planets like Proxima Centauri our very nearest star which has a planet that is not transiting and will be able to block out the Starlight and what I forgot to mention in my talk is that here at Caltech there's like you know half a dozen expert EXO planet astronomers one and pretty much per slide of what I talked about working on these problems and we have even crazier idea that I wanted to share with you briefly is called star shade and star shade is a giant specially shaped screen here you're seeing an animation of the star shade unfolding getting unfurled from its stowed position with this truss opening up in these petals snapping into place this was conceived of in the 1960s by Lyman Spitzer and he worked out all the math to show you that you have to use the star shade special shape for diffraction to block out the light from a point source star so you don't have the Airy ring pattern destroying your image and actually it was revisited every decade in some form or another until today when we actually think it's possible to build it and there's a lot of people working on this right now but here's a picture of myself and a couple of team members at the JPL laboratory it's also there's another version of star shade made by Northrop Grumman Corporation so I wanted to end my talk with like let's call it prediction or forecast and here by the way we're zooming out from that same animation - now fake image of our galaxy and I know someone's gonna ask I've wire the planet from that specific shape it's purely selection effect reasons the Kepler space telescope looked in a certain direction for four years so there's a lot of plants in that direction micro lensing involves the Bulge which is highly densified with stars you need it's a very low probability kind of events you need lots and lots of stars to search for and that's why it's there so in this field it is somewhat easy because we know small rocky planets are very common they're basically everywhere we know at the James Webb Space Telescope because it operates at near-infrared wavelengths where molecules are active will see water vapor it pretty much has to be around because water is a very common hydrogen and oxygen are very common it's locked away in minerals it just has to be in planets so we I believe that with the James Webb we will see planets um with with water vapour actually it turns out that any college student today was born when exoplanets were first discovered or later and so two people today who are in college it makes sense of course their exoplanets and so we hope to have a future 10 years from now where people say of course there are planets with water vapor indicating water oceans and so 30 years from now and that's kind of a long time but I have to be conservative hopefully we will have planets for we see signs of oxygen in addition to water and other things where we may not be sure that there is life out there but it'll be enough to kind of keep the keep the search going it's like a multi-generational project and finally just while I wrap up I did want to give something more even more speculative but in some ways like my job is really hard but in other ways it's really easy because we have these big telescopes we know how to build things in space and large telescopes on the ground but if we don't find anything in that really tiny space of just you know a few hundred light years or tens of light years the next generation will have a whole new set of they'll have to have like a paradigm shift entirely love to have self-assembly in space or printing things in space figuring out ways to scale up to search even more stars is going to be the way that they're gonna have to do it so to finish just to summarize we know thousands of exoplanets orbiting nearby stars small rocky planets are very common and the next generation telescopes will study small exoplanets and atmospheres for the search for water and bio signature gases thank you thank you for professor Seager for that very interesting talk and I'd like to open it up to questions thank you for a really really clear lecture I feel like I learned a lot which led to some questions the first one is why is the earth so unique in that first blood you showed of a method it looked like it was kind of on its own Ruth is definitely on its own because right now our techniques can't reach there yet earth is so small and low mass and it's so faint compared to our Sun it's nearly impossible to find we're just lucky that nature provided so many different planets most of the ones we found find are either big planets or they're small planets orbiting small stars okay and in the next slide on the mass versus ice it looked like all of the predictions that came from a sort of single like iron plant in Aswan were much flatter than what the reality of planets is so why is it that planets change in that you know different can occur from what it would be from a single composition or constant composition well it appears that when planets start form the sort of very hand wavy bigger picture is that they create rocks you know and gas rocks and dust rather and once they get to a certain mass they start to like accumulate or suck in based on gravity all the gases around them and start growing so people just think for some reason the planet stalls out in a smaller size it won't just keep getting more and more massive it has to somehow have volatiles either outgassing or being collected from the nebula we don't have a great answer that's the best we can give you and how do you measure the mass you made very clear how you measure the size but why didn't you the mass is measured in most cases by the Doppler method it's called the planet and star orbits the common center of mass and astronomers can measure the line-of-sight motion to literally walking speeds of centimeters per second and they have to infer the mass it would take too long to like work through it all but it's an effect of the mass making that planet wobble that we can measure mass last one how does a white as a locking happen the moon locking that you describe also happens instantly it's because the planet there's tides interacting so imagine that you have the star and the okay it's gonna be hard answer this really quickly but you have the star and the play and the planet actually along gates just a tiny bit but then the planets rotating so now that's elongated but it wants to pull back and so over time that just kind of makes it lined up so it doesn't have that extra energy problem so in one of your earlier slides with the where you're plotting mass against radius I noticed at some point with me curves it got to the point where increasing mass will actually decrease the radius was that snart effective that data could there possibly be planets where they have such a high mast if the radius starts to decrease I always show that plot to physicists because they always have a lot of questions about it now there's probably no planets of that mass actually but it would actually decrease there are things called white dwarf stars you know that when you basically keep adding mass and eventually it becomes like all neutrons and it's super dense so yeah if you could actually would be something else but there's probably no planets there we probably have to call it something else if it was in that regime okay you mentioned that oxygen and methane are signs of life in a planetary atmosphere is it preposterous to think that in 30 to 50 years looking for exotic signatures of industrial contamination or even the exhaust of rocket fuel might be a possibility of narrowing down the scope of investigation yes and people love the thought and like on our planet we have chlorofluorocarbons and sodium lamps and other things it could be possible in a very far future but you have to think about those lines are extremely narrow and there's there don't have like oxygens this giant signature it's very spectroscopically active and there's a lot of it so if we can find a way to do very very a huge huge collection area it may be possible sometime in the future from a biologist point of view and an evolutionary point of view I'm very aware of how the Earth's atmosphere has changed across the period when life originated on earth till what it is now and certainly the oxygen level is way higher now it was earlier so I'm just wondering how much your search for life permissive gases in these atmospheres are really informed by this this deep paleontology about what was going on the Earth's atmosphere a long time ago and also some of these sulfur bacteria and so on like that which obviously don't need oxygen astronomers now it's kind of like a lake that's called a toy model or a cottage industry we'll put anything in our model that we can so we do rely too heavily on oxygen we're very Terra centric it's a bad habit the answer eccentric monitor eccentric I mean modern Terrace modern air center yeah no we certainly do consider everything we can it's tricky though because all the small things like hydrogen sulfide and methane all these small gases that microbes do make they're making them by exploiting chemical potential chemical energy gradients but if there's any way to like catalyze the reaction that life that uses probably somewhere else on the planet just based on the different temperatures and pressures it would happen anyway so hydrogen sulfide comes in volcanoes and methane is coming out of mid-ocean ridges so we struggle to think of like which environment could these gases accumulate and be meaningful but yes that's a whole huge field of like growing research now to sort through false positives even in the case of oxygen and all these other gases and other times and other atmospheres so yeah and maybe I'll wrap up with a quick question we've got my favorite question yet so I hope you're gonna ask that one oh jeez do you happen to recall Jack show stacks counter example the thing is I can't recall what it was that's just weird um it was some hydrocarbon but if I do I have like one absolutely okay so I'm sure that you had all done the problem the same way I did because I was doing this combinatoric seed molecule and I took the big six biochemical elements carbon nitrogen oxygen sulfur phosphorus hydrogen so I just took each of the six and I paired them in all possible ways they have to make sure that they're like I don't have a missing electron gap like I have to make sure that it's you know neutral and then we do some other tests to make sure they actually exists like by scraping web sites or trying to figure out their volatile so that's what I did and he said first so that's totally wrong which is what one of my colleagues have said who I didn't listen to because nature doesn't do it that way nature would you the common networks and everything but hydrogen and then hydrogen gets populated at different like valence ease so for example you could have carbon that have a triple bond and just two hydrogen's Brigid hydrants a double bond and four hydrogen's or hydrogen in the sea and so nature would do it that way and so I had done it totally wrong and I had like kind of created my own like in a burst of a selection effect so I just how my colleague he was right and then go back to the drawing board on him you know one final quick question thank you what about looking for signs of civilization like different levels of light like you know light of cities because you see those planets quite well in the orbits and the transits so could you could you look for different inhomogeneities and light levels and things like that so right now it's like completely out of the question and normally I would just sort of go on and say except in the spirit of the conference and what I said before that the line between what is considered crazy and what could be mainstream is constantly shifting and so all of these ideas that you've mentioned people have believed or not written papers about it and that case it would be quite hard to do because the light from these cities would be so tiny plus now for people who like astronomy we have like full cut off lighting so eventually they may evolve to a way where they don't have like light that's just leaking to space let's thank professor Seager again for a very interesting talk [Applause] you

Channel: caltech

Views: 7,933

Keywords: Caltech, science, technology, research

Id: vtXB50jBUzM

Length: 40min 30sec (2430 seconds)

Published: Wed May 23 2018