 Hello there everybody My name is Phil Lamar and I'd like to welcome you to NASA's ask the astronomers live The show where we have live astronomers Online live here to answer your questions about the universe. We do the live part you do the ask part and You can ask your questions of our scientists in the comments section at the universe unplugged website It's also where you can find out about upcoming shows and see lots of fun astronomy videos And that's as you can see on the bottom of the screen there universe unplugged.org and When you do submit your questions make sure to include your social media handle, which hopefully is Even your name along with your question so that we know who we're answering our question to all right today we are talking to two astronomers who Study seven planets that orbit one of our nearby stars. So that's two astronomers seven planets one nearby star and The first of our two astronomers is dr. Eric Eagle from the University of Washington. Hey, Eric. Hello Eric You'll you'll start by telling us a little bit about yourself and and the work you do Well, thanks for having us on the show I'm an astrophysicist and professor of astronomy at the University of Washington I spent my career studying black holes gravitational lenses and planets and in the last decade my work is focused on Transmitting of exoplanets like the ones we'll talk about today. I build models to detect these measure their properties I've discovered some new planets with the Kepler spacecraft and also use the Spitzer Space Telescope to create a map of an exoplanet Wow, who knew that I figured all the hard work was just finding them But you apparently do all the work after they're found exactly. Yeah Fortunately, you have some help and fortunately on the show today. We have some help We have dr. Victoria Meadows also at the University of Washington. Hi, Becky. Hello Hi, tell the audience why we're so impressed with you Okay, well, I'm a professor of astronomy and I'm director of the astrobiology program at the University of Washington So we're training scientists to search for life in the universe I study terrestrial planets, so that's rocky planets like the earth and Venus within our own solar system And I'm very interested in studying the smaller Possibly rocky planets that we're going to find around other stars and I work Looking at trying to understand what the planets atmospheres in particular alike and to figure out what they're made of So what the planet is like? Now you mentioned you're looking at rocky planets because I'm presuming those are the ones that are most Likely or probable to have some form of life. So is that is that one of the yeah That's a great going in assumption I mean at the moment where we're looking for life that we could at least recognize And so where we think that you know if a planet has an ocean on its surface Then it's more likely to be able to support life and that means it needs to have a surface So it needs to be rocky. So that's why we're very interested in rocky plants. Ah Got it. I love that now and audience. How many of us knew the term astrobiology? Vicki did All right today we are going to be talking about And this amazing group of seven planets that were discovered around the nearby star trappist one now Eric Vicki, can you guys tell us a little bit about their discovery and maybe even Why someone named a star trappist one? Eric Yeah, the story goes back Well 30 years to the first discovery of planets orbiting other stars, which we call exoplanets exo because they're outside the solar system and After the first ones were found they had very different properties to the planets on our solar system We found very large gaseous planets orbiting very close to their stars It was tough going to try to find rocky planets more similar to our earth And so about a decade ago 2010 or so there was a Belgian astronomer Mikael Guion who developed a robotic telescope to monitor Very small nearby stars any reason that if you could look at the smallest stars, you could find smaller planets He carried out a survey he did that trappist and that's a acronym. I mean it's an honor of Belgian beers made by trappist monks And he located this robotic telescope high in the mountains in Chile and get a better view of the southern sky And so by 2015 they had surveyed 50 stars looking for transiting planets a Transit is when a planet passes in front of a star And this is fairly improbable because most planets are going to orbit randomly on the sky And it's only occasionally that their orbits will pass edge on meaning the planet will go in front of the star And so we had to look at a lot of stars to have the chance of detecting planets And so by 2016 they had announced they had found their first star that they'd surveyed With the planet system of three planets and so that was called trappist one because of that first discovery I See and of course the reason you need it to be a Planet that passes between where we're looking and the star is because if it's going around the star that way We just won't be able to see it correct exactly Yeah, so you have to get lucky and therefore you have to look at a lot of stars Occasionally especially since planetary systems are fairly flat You'll get a lucky case where several planets will go in front of the star And you'll be able to measure their orbital periods and see the shadows as they pass in front of the star That's how we detect them We see the star get a little bit dimmer for a percent or so for about a half an hour or a little bit more And that's how we detect these planets Well, then there see now you've told me what our main goal in Creating spacecraft should be so we can see better Exactly We can get different angles but the fact is we've been able to find some exoplanets and Particularly these ones are trappist one now Vicky. Can you tell the folks what makes these planets so special? Yeah, sure. And actually if we could have image five that would be great Yeah, so this are the really important things for the first of all there are just so many of them So if you look at this image here, you can see the trappist one system and there's actually seven planets They're all roughly earth-sized and if you look down at the solar system You can see that the only roughly earth-sized planets in our solar system are Venus and Earth But in the trappers one system, we've got seven of these guys Potentially to study so we're very excited to see what you know other planets, you know the same size as the earth might look like Also, three of them are potentially at the right distance from their parents star to Support liquid water on their surface as I said, that's what we think makes a planet more likely to be habitable able to Support life. So there's this concept of the habitable zone Which is you know that that region around a star where if you place a planet with you know, roughly earth-like atmosphere You would expect it to be able to have an ocean on its surface So in in our solar system, we have earth and Mars within that habitable zone But in the trappers one system, we've got three planets e f and g That are all within that habitable zone So that's super exciting to be able to have planets that are roughly earth-sized and at the right distance to potentially support liquid water and potentially life That's so funny it just makes me feel like You know looking at how many Planets are in the habitable zone around trappers one versus our solar system. It's sort of like Being from Iowa and going to New York for the first time. There's so many here There's a lot and it gives us a so you know much better statistical chance of finding something really interesting interesting now the We titled this episode or some title was how do you weighing an exoplanet now? How how do you weigh and why do you weigh an exoplanet? Who wants to try this? That's a great question. Yeah, so we we do this with lots of telescope time If you want to show image six we used quite a few different telescopes to study this planet system So at first with the ground-based discovery I mentioned in Chile We then followed these planets followed the star with other telescopes on earth and we started to find indications of additional planets and eventually got very confusing and so then we just Applied to the Spitzer Space Telescope, which is the upper left telescope here To observe the star for 20 days straight and that's when we sorted everything out and found wow There's seven planets orbiting the star we see shadows of every single one of these planets The closest one orbits in a day and a half out to the other one that takes about 19 days to orbit the star and So with that 20-day discovery we knew the locations of these planets We knew when they would be going in front of the star and so over the next several years We continued to use the Spitzer Space Telescope the Kepler telescope in the lower left called K2 and its successor mission as well As several ground-based telescopes the speculose Telescope is depicted at the bottom, which is a successor to the trapezoid survey and then the lower right is Hubble Which also looked at the star so we had All these and more telescopes trained on these the star for several years Waiting until each of these transits occurred and timing when that transit occurred So with those measurements over several years we were able to look at the planet's interactions And so if you roll the animation This shows a Simulation of the system as you would see it if you're looking down in it So about 90 degrees from where we actually see it where we see the planet's going front of the star The size of the star and the planets are exaggerated and here you can see Animation of just what would be the two innermost planets in the system Every time they pass each other the gravitational pull of the two planets causes them to get a little bit closer And then they separate and so that causes the planets orbits to change slightly It's like a ticking clock, but it's not ticking precisely And so every orbit when the planet goes in front of the star We measure the time at which it goes in front of that star and if the planets just Interactive with it that planet then we might see it come a little bit earlier or a little bit later And it takes some time for these interactions to grow with time It takes They kind of do this dance that happens every 500 days or so kind of like the diagram I've drawn in the chalkboard behind me They pirouette around the star and they do it in a synchronized manner at least the outer five planets do so it took about Two pirouettes about a thousand days for several years to get enough data to be able to measure these gravitational interactions between the planets and From that we were able to get very precise measurements of the planets masses relative to the star We actually measure their mass not their weight weight is determined to find on earth But mass is something something has an outer space With those measurements, we are able to then use these data to try to understand something more about the interiors of these planets I see. Oh, that's fascinating. So the weight rather the mass of the planet Determines how much gravitational pull it has and you can measure its effect on the other planets By seeing how much it affects another planet you can figure out over time What their weights are in relation? Well, what their individual weights are by looking at how they react to each other exactly? Yeah, that's okay That's why you weigh them and how you weigh them. Okay, although I do have to say I want to ask Eric You said you had the was it Spitzer for 20 days straight. Yes Did how many other astronomers were calling you angrily? It's like, you know checking out the book that everybody needs for the exams like you can't keep it the whole time Eric Fortunately, we had a big team so there are about 30 astronomers from three continents at least that we're working on this And so we had a big enough group that we couldn't get pushed around too much But there's actually a time allocation committee that gave us the time So we were fortunate enough that they were willing to grant that because at that point we didn't know there were seven planets We just had some sufficient because things from the ground didn't make sense. We couldn't really disentangle what was going on interesting and and Vicki the You know the amount of data they were they were able to get from that What is this information tell us from your perspective about what the planets might be or look like or you know? Yeah, no that that data set is amazing because the incredibly precise measurements that Means that we're actually able to start to figure out what the planets might be like in their interiors so Because Eric and the team were able to measure the masses So precisely and we had the sizes because they transit and meant we could figure out the densities of the Bodies how dense how how dense are they are they fluffy things like gas or they dense things like rock and so if we look at Image number three here What we were able to do the amazing precision on the measurements meant that we were now able to start to think about Okay, what are these things like on the inside? And so the team came up with three hypotheses for what it would be like And they're really super interesting So so one of them so the bottom line is the densities that were measured were all sort of Uniformly a bit a little bit less dense than the earth right so so they're they're probably terrestrial planets But they're a little bit fluffier And then that's why is that right so the three the three theories we have are well Maybe they look just like the earth for the most part, but their iron cores are smaller So that would make them less dense overall if they had less of an iron core like you know Half or two-thirds of the the iron core that our own planet has or they have no core at all Which would be fascinating which would be that you know They have all the ingredients to make a terrestrial planet But there was so much water in there and it reacted that the iron so you ended up with basically rust through the planet That was coupled into the silicate in the mantle. So it's all mantle no core Or and I think the most fascinating theory is that they pretty much look like the earth But they have loads more water in there in there either in their interiors or in this case And we modeled The oceans on the surface of the planet. So they could be sort of more like water worlds And that might make the less dense overall just having way more water on the surface So either as a steam atmosphere for the hotter planets. So So with those precise measurements, we can start to actually try and figure out what these things are like I see that's right. That's that's one of the Three things I remember from high school science volume time mass Equals density and so and from that Those calculations you can come up with those amazing theories. I wow Can't wait to figure out it. Which one is right? but um, Eric You know Vicki was talking about how precise the measurements were How was your team able to achieve this level of precision? Well, it's quite a bit of time. So the the first the seven planets were announced in 2017 and because Interactions between the planets are really small As they interact over time their their tugs on one another can add coherently and grow in amplitude And so you get these sort of oscillations in the times at which the planets pass in front of the star That's have a period of about 500 days and so The other thing is that we actually have limited times when we can point these telescopes at this star It's only certain times of the year where we can actually Take a telescope and point it at The trappist one star if we're using a space telescope the limitation is that you don't want to point that telescope Too close to the sun and you don't want its Solar panels to not point at the sun If we're on earth then we have to wait for darkness and that only happens in certain times of the year And so it took a bit literally about four years worth of monitoring these planets to really precisely pin down The orbits of the planets around the star and the interactions between the planets We also had to do quite a bit of analysis. So this is all um, this analysis was carried out and Creative computers over nine days. I think we had 30 computers turning away So it was quite a bit of computational effort that took about half a year and then took about half a year to get published Uh, and it was published about a month ago. So it was uh, it's quite a long and arduous process to get to this point But if we can show image number eight This is actually the final result of our data set. Um, the plot shows the radius of each planet Versus its mass and everything is in units of the earth. So the earth is a little green dot at one one It's measured in earth units as itself You can see venus and mars fall on the dash curve which shows Composition similar to that of the solar system terrestrial planets And then the the colored regions are the probability distributions at each of these planet measurements that we made With those four years of data and as vicky said, you can see these all lie a little bit above this dash curve So that's what told us that these planets are slightly less dense than our solar system planets if they if these planets Had a solar system like composition We'd expect them to fall right along that dash curve But they all are offset and it's only with these very precise measurements that we could discern that offset previous data It weren't good enough to do that Wow, so the precision is Really a matter of taking the time Exactly. Yeah That's That's fascinating because you know, obviously we live in a world now where we have computers that are able to you know do You know the kind of work that would have taken you know humans alone so much time But observation still takes just as long Yes, and in the past speed that up with gigabytes Exactly in the past people it'll be a lot more patient with their solar system because the planets and outer solar system Take decades to orbit. So fortunately with these these short period planets are at trapezoid and we can do it in a few years instead of having to wait lifetimes But although that does explain why all of the you know the Ancient you know philosophers and astronomers that we hear have had incredibly long beards They had they were waiting a long time Exactly Decided not to say Now I love the the the chart that you had comparing the trapezoid one exoplanets to our plans But but vicki, can you tell us a little more in depth how Our small town planets complete compared to those big city exoplanets Yeah, I mean sort of a summary of what I've said before They the trapezoid planets are similar size, but less dense overall. Um, so you can kind of think of them as cousins to our planets It's very likely they have you know, they're terrestrial at some to some degree But they're a different kind of terrestrial they've either got much higher volatile content or very different core mantle structure And so I think I think that's super exciting That the one thing that that is probably quite different about them that you can't really tell from just measuring them Is that the kind of star they orbit that that trapezoid one is this teeny tiny little m dwarf star? That nonetheless might have been quite fierce when it was young So m dwarf stars have a lot of activity and brightness when they're young until they finally settle down onto the main sequence Which is where stars end up and to spend most of their lives And because of that these planets have probably undergone a very different History a very different life. They had a very different sort of experience that our planets have Because our sun didn't go through that wild or early phase And so so that's also truly truly fascinating. You have these we don't know from the masses alone How that has changed things. So maybe it's giving us a hint in the different density But I think the most exciting thing will be actually Looking at these planets to figure out what their atmospheres are like and then maybe trying to see if we can Tell that these planets had a different history to our own Interesting interesting So for anybody who's just joining us or missed our intro We are talking with victoria meadows and eric eggle about the latest results about the seven planets orbiting the nearby star trappist one So Right now. Let's see if we have a few questions To ask you astronomers Ah, here we go. Um, this one is Let's let's let's start personal What got you guys interested In studying exoplanets Vicki Um, well, I I've always been interested in planets in general. So, um, I did a really interesting PhD thesis where I observed a whole bunch of different things But my favorite thing that I observed was the planet venus, which is shown here in image nine Um, and so I got to know venus pretty well I actually searched for water vapor in its lower atmosphere and I looked at oxygen air glow in its upper atmosphere And I I joked that, you know, I became an astrobiologist But I started off by studying water and oxygen on the least habitable planet in the solar system Um And again, those those things are there not because that planet is is habitable But just because of sort of the different phenomena that we were looking at, you know The greenhouse effect in the surface and also the air glow and the the motions of the upper atmosphere So that's what we're looking at. So I've always been very interested in terrestrial planets I I've never made a terrestrial planet. I didn't like And so I've always been interested in seeing again, you know, whether we can compare planets in our solar system to other planets out there So, um, yeah, so learning about exoplanets, whether they're like our own terrestrial planets And whether or not they're potentially habitable and able to support life is kind of the trajectory that I took in my career I see I see eric. How about you? I got into it, uh, sort of by chance So when I was first a graduate student The first exoplanets were found around the pulsar, which is similar to black holes, which I was also interested in But I felt with a one planetary system orbiting this really exotic neutron star pulsar Didn't really make sense to pursue that as a career. And so I sent my TFT studying black holes Which was pretty fulfilling. I ended up working on an idea that led to the event horizon telescope Which uh image of black hole, which was announced a year plus ago but in The mid 90s other exoplanets were found around more sunlight stars And the numbers started to grow and became more interesting. And so, um, I by kind of a coincidence when I was working on Gravitational lensing the study black holes I realized some of the equations applied back to exoplanet systems And so that was my entry back on early 2000s into the exoplanet field And I think most different than bicky. I didn't have any much background in planetary science I was more interested in the thrill of a chase in the novelty of discovering something new And in addition, it didn't hurt that exoplanets were somewhat more interesting than black holes because we actually live on a planet So humans feel like they can maybe relate to planets a little better than black holes Are pretty fascinating as well Yeah, wow, that is fascinating Huh, so you went from pulsars to black holes to exoplanets. Yeah, exactly Interesting. Um, all right guys, let me ask you this What do you see as the next steps in studying trappist one? and Please tell me the next steps don't Include Elon Musk Maybe I'll leap into that one first. Um, yeah, I think that uh, again getting the spectra of the atmospheres and Having that potentially tell us about the history of these planets whether they've lost atmospheres or lost oceans Being able to tell whether we see hints that they're habitable or not habitable So whether they have an ocean or not And also looking for life and you might think well, that's like a really grand goal that we can't do for like decades But no with the james web space telescope, which is scheduled to launch this year. Hopefully the end of it I think that We are going to have the capability potentially to observe the atmospheres of these trappist planets And that is pretty exciting. So we're going to use the fact that they transit in front of their star to Get observations of the atmosphere and we do that by looking for wavelengths At which the planet appears to get bigger So so in some colors of light it'll be some one size and other colors will appear to get bigger And that's because the atmosphere around it is actually absorbing the light at those wavelengths So it tells us there's something in the atmosphere that's absorbing So that could be an oxygen molecule or a water molecule or a carbon dioxide molecule And so it gives us, you know a chance to figure out what's going on in their atmospheres So if we can do that And even if we detect only a few different types of molecules We can start to learn about the history of these planets again, whether they've lost an ocean And start to get at potentially maybe even just simple Simple pairs of gases that don't seem to want to coexist with each other that might potentially indicate life So that is potentially possible in the next five years or so given, you know, whenever jw is too long just Okay. Wow. Okay. So James Webb is gonna help us Get more data on exoplanets Eric, what do you see is is the next steps other than what I think he just said Yes, well, I am very excited about James Webb Space Telescope as well And in getting the spectra that Vicki mentioned It will actually be very difficult to do that experiment And so it's going to take many observations of many transits of each planet in front of the star to try to detect that very thin atmosphere that these potentially have and And so many transits means that we'll get many transit times And so we'll actually be able to probe with much more precision The masses and orbits of these planets So we're actually going to be able to even better characterize their bulk densities and pin down even better whether they Continue to show this really common Composition they all seem to have a very small scatter about a single composition, which is fascinating Especially that it's offset from the solar system And with that data, we can actually check to see that the assumptions in our analysis are correct And so we'll be able to Pin down their properties Bolt properties more precisely and in addition at the same time be able to measure their atmospheres So the James Webb Space Telescope we've applied to use. I think we put in something like 10 proposals And we'll see if we if the time allocation committee Is favorable to us and gives us some time to study these planets That's great. That's so it'll be Some a whole bunch of new data coming in We have one more question from Michael Harris Simowich Actually, thank you Michael because this is a question I had as well. How far away is the trappist one star system from us? It is 40 and a half light years away We use parsec so I had to pause for a second The center of the galaxy is about 25,000 light years away. So we've been saying trappist one is this close star Well, it's a relative. So 40 light years is very close relative to the size of the galaxy That's one of the great advantages of studying this particular planet system is the close proximity Of the star in addition to the fact the star is so small which makes the planets easier to study relative to the small size of the star I say, okay. So we didn't travel very far to get to that big city. So basically We didn't come from Ohio. We came from I don't know Irvington That's okay 40 and a half. It's funny because you know as a sci-fi reader I've rarely heard light a light year Measured in such a small number 25,000 light years 40 and a half A half a light year Oh, here's one more question Are there any other earth-sized planets? that have masses Like in trappist one, not sure who this question is from but I guess in studies of Other galaxies. Are there other earth-sized planets that have masses? Who wants to take that? Is that is that an astrobiology question for the mass? But I can talk about other sized planets, but for masses, I'll ask Eric Yeah, so for masses Trappist one right now is the best we can do. There are some other Similar earth-sized planets that have mass measurements that are very low precision We also have larger planets for which we have mass measurements that are fairly good precision but still None really quite compare the trappist one The best comparison actually is to our own solar system And so in some ways, uh, this These measurements are kind of taking planetary science to another Solar system, which is really exciting as far as the terrestrial planets are concerned And I will say there are other earth-sized planets that we know out of there Some of them very interesting because they're also in the habitable zones of their parent stars But there are others that are interesting that are not in their habitable zones They're much closer to the star than the habitable zone. We call these exovenuses And so these are what appears to be terrestrial planets very close to their star That might have some similarity with venus in our in our solar system And so we're very interested also to get spectra of those with the James Webb space telescope Um and potentially see if they have dense carbon dioxide atmospheres or no atmosphere or dense oxygen atmospheres Or, you know, what happened to these guys? What was their history like? How did they turn out? That's well and vicky. That's interesting that they are venus-like planets because obviously that's your sweet spot Yep Yeah, so even though I'm an astrobiologist and I'm my my first love is the habitable planets I'm so very interested in how planets lose their habitability You know and that evolution, you know, what happens to those planets over time and how how do they end up? You know, because that's that's a big question for us as humans as well as you know How do how do terrestrial planets, you know, how do their atmospheres and surfaces and interiors evolve and What are we going to end up like eventually? Right That's right Yes, that's using data to look into the future Um, now here's a question from Marissa Myers Do you see similarities between trappist one and jillies 180? Um Anybody feel like they uh Have a handle on that. Yeah, I can address that so the there's an interesting thing that So the Kepler spacecraft found a lot of small planets similar in size to earth But around very distant stars and those stars were too far away to use the Doppler technique to measure the masses of those planets And so we have sizes, but no masses so we couldn't compute the densities of those planets Um, there's other stellar systems like glissie 180 that Marissa is asking about Where the planets have been detected with the Doppler technique But the planets weren't edge on so we couldn't see the transit So we don't know the size of the planets because we don't know how big a shadow they cast across the star And so the trappist one system is kind of unique in that these planets are in their stars potential habitable zone Um, if they have the right atmospheres for liquid water to host liquid water on the surface But we also have both mass and radius measurements to compute the density and so that makes it kind of unique But otherwise it is somewhat similar to the glissie 180 system Although that has longer orbital period planets and we don't have the sizes because they don't transit in front of their star uh, I say That's Yeah, I just find it so fascinating that we're using shade and you know shape to You know get this Amazingly precise science. I I always say to my kids like no human beings classify things according to shape and shade And there's a reason because you can get a whole lot of information just based on the shape and shade of something Especially over time All right. Um, wow. Thank you guys for giving us so much fascinating fascinating information. Um before we wrap up Do you guys have any um You know final thoughts Deep thoughts that you'd like to share with uh with the audience They don't have to be deep. I think I don't know that one. Um, yeah I think what I really want to get across to the audience is just how exciting this system is because of um that the small star Uh, which means that we can you know Observe the atmospheres of these planets much more easily than any other system And because of the janitor space telescope Um, we are in the next five years going to start to learn about the atmospheres of planets like our own but outside Opening around other stars and we will have our very first chance to to look for life And I will say you know extra to rest of your life I will say that you know that the chances that we'll see anything are probably low We've only got three chances with those three planets, but still to start that search is really quite amazing Absolutely Eric Well, so that I mentioned at the beginning that the trappist survey surveyed 50 stars There's now My belgian colleagues are now doing a bigger survey called speculoas another backer name Spells the name of the belgian cookie That has bigger telescopes and more of them and they're surveying 500 stars So we're really excited about this speculoas survey that it might find other trappist one like systems The other thing is that a lot of the science being done has a huge amount of data that's taken And it's too much for astronomers to look through so it's possible For the general public for you to get involved in this search you can go to the zooniverse website And there are several projects that involve Exoplanets that you can actually look through data and potentially find something like we have done Really a non-professional can go to what was the site? zooniverse It's like universe but with zoo replacing the you Got it So you can go there and have a non-professional can have access to some of this information and help Sort through it Exactly because the data amounts are so large you can use a computer just to storm Down the data to some point But you eventually have to look at it by eye because it's really only you know Person's eye that can really see something that is that a plan or not? And so it it actually is very useful for astronomers to partner with the public and the search for exoplanets Excellent and It's nice to hear you guys won't be replaced by by robots anytime soon All right Thank you both for joining us here today and Thank you out there for watching And learning about the incredible trappist one star system Now you can see this video as well as all of our other universe unplugged videos at the website universe unplugged.org Or you can just click on the link in the comments that you should be able to see so please Subscribe on youtube and you'll be the first to know when our next Asti astronomers live comes out Follow us on facebook to catch the live show and until that next one i'm philamar here with eric aigle and vicki meadows and this has been Asti astronomers live. Thanks for watching. Thanks very much and go to