Daniel and Kelly’s Extraordinary Universe - What is the future of exoplanet research?

Episode Date: March 1, 2022

Daniel and Jorge talk to planet hunter Dr. Jesse Christiansen about what we have learned and what we might learn about exoplanets! Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy, which is more effortful to use. use unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials is easier.

Complex problem solving takes effort. Listen to the psychology podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcasts. Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, every case has a story to tell. And the DNA holds the truth. He never thought he was going to get caught.

and I just looked at my computer screen. I was just like, ah, gotcha. This technology is already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, Jorge, did you follow the launch of the James Webb Telescope? Yeah, I saw that. Well, to be honest, I was in Hawaii. so I wasn't plugged into the news,

but I saw that it was all over the place and people were very excited. And were you, like, terrifying in the edge of your seat that it wasn't going to work? Well, I'm just glad it didn't explode on launch, I guess. That's always a good thing. So would you say that the NASA team

did, like, a good job of getting everybody emotionally invested in this $10 billion project? It was pretty dramatic, you know? Whenever you have a launch, you know, anything can happen. And I know they had some delays and some, you know, expectations

and people were hanging by the seat or their pants, right, to see the telescope opened up. Yeah, but you know, it worked so well and unfolded so smoothly. I was wondering if it might have made like a better story if it hadn't gone so well, if there'd been some like ups and downs. Were you hoping something would go wrong, Daniel?

Yeah, you know, you need a little bit of a dip at the end so that our heroes can like triumph in the last moment. I see so the engineers can swoop in and fix all the mistakes that the physicists made. Exactly. In the end, the engineers are always the heroes. I'll watch that movie. Hi, I'm Horham, a cartoonist, and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I'm definitely

buying a ticket for the movie called Engineers Save the Day. But they do it every day, Daniel. You don't need to buy a movie ticket. It's happening around you all the time. But we need Hollywood to, like, dramatize it to, you know, glorify it to, you know, glorify these people. I see, I see. Yeah, we need a big name movie star or maybe cartoonist to play these characters on film. So who's going to play you in the Hollywood version of your life, Jorge? I have thought about that question, Daniel. It's going to be Harry Chum.

But welcome to our podcast, Daniel and Jorge explained the universe, a production of IHeard Radio. In which the scientists and the engineers really do save the day by helping you crack the mysteries of the universe. On this podcast, we think that the entire mystery is It's like a fantastic puzzle. It's like a Christmas present waiting to be unwrapped. And we cannot wait to discover what the universe has to tell us.

So we love to talk about everything that's out there in the universe, everything that's close by, everything that's far away, and explain all of it to you. That's right, because scientists not just save the day, but they also help us understand the day. What makes a day? How can we have days and nights? Those were big questions in the history of human civilization. And we figured it out. We figured out that we are sitting on a big round rock going around a big,

bright orb that's a continual explosion of fusion energy and we didn't know that before but now we do and probably there are lots of unsung heroes in the history of those discoveries like we talk about Galileo who looked through the telescope but who built that telescope who really polished those lenses and made sure the thing actually worked yeah a lot of amazing technicians who are behind the tools that scientists make they rarely get credit right I mean they do get their name in the 3,000 author papers right or they don't sometimes they don't they just end up in the acknowledgments. At least they got paid, right?

You do pay the engineers, right? I pay my engineers, absolutely. But we have learned incredible things about the nature of the universe, and every time we open up new eyeballs, we illuminate new parts of the universe, and it always comes with surprises. It always tells us that the universe isn't quite as we expected. And while we've been looking at the night sky for thousands of years,

it's only been the last few hundred years that we've understood that there might be planets around other stars, and only the last few decades that we've been able to actually see some of those planets. Yeah, it's pretty mind-moggling, I guess, to think about the arc of human history, right, and human knowledge. Like, we started out in caves or in savannas, just, you know, trying to stay alive,

thinking that what we can see with our eyes is everything that there is about the world. But then that's sort of expanded to the whole planet and to the whole solar system and to the whole galaxy and the whole multiple galaxies and galaxy clusters and maybe even other universes. That's why I'm always telling people that physics matters because it changes the whole context of what it means to be alive. The whole scope of the universe, the stage on which your entire life takes place on, is determined

by what we know about the universe. And what's incredible is how much more we know than people knew 1,000 years ago and even 100 years ago and even 20 or 30 years ago. There are things that are now routinely known by just random people walking around on the street that professional astronomers were dying to know just 20, 30, 40, 40. years ago. Yeah, physics matters and it also anti-matters, technically, right? There's a certain symmetry about your role in human society. Fortunately, we matter more than we anti-matter. So there's a matter, anti-matter asymmetry to physics. You have more matter than antimatter, or more matter in

general. I've noticed. I've seen how much coffee and cookies you guys consume in your seminars. And donuts. It's really more about the donuts. But yeah, in the last few hundred years, we've realized, we've learned a lot about our contacts, our sort of place in the galaxy in the universe. And even in the last few decades are sort of consciousness about where we are in the universe and how rare we are has really sort of almost exploded in a way. Absolutely. And as we learn more about the universe, we get more answers and those answers just inspire more questions. Are the things that we are seeing typical or are they weird and unusual? Are there things out there still waiting to be discovered? What surprises wait just beyond our ability to see out into the universe? And so today on

the podcast, we'll be asking the question. What is the future of exoplanet research? Exoplanets, that's always a cool word. It is a really cool word. I love putting exo in front of everything. You know, we have exoplanets. We have exo moons. One day we'll drink exo coffee.

Well, I can't wait for the exo physicist. You know, get them out of here. I hope one day we have exo podcast listeners, meaning people in other solar systems subscribing to the podcast. Well, technically every listener is an exo podcast listener because they're not in the podcast. Right? Exxom means like outside of. Yeah, that's true. Yeah, they're in orbit around the podcast.

Yeah. So in the last few decades, there's been sort of an explosion in our knowledge about planets and other solar systems. That is planets that are not in our solar system that are not, you know, going around our sun. It really is incredible how much we have learned just in the last few decades. In the 90s, we had never seen another planet around another star. For all we knew, this was the only star in the universe that had planets around it. In the same way that we still don't know if there is life around. any other star. We didn't even know if there were planets around any other star until the 1990s. And slowly we saw one and then two. And now, as you say, there's been a veritable explosion of these

discoveries. Right. Well, before the 90s, I guess we imagined it or we assumed it, right? Like, we saw all these stars out there in the universe and the galaxy and we imagined, like, you know, we can't be the only star with a planet. So there must be planets around other stars. We just didn't have, like, direct evidence or proof of it. That's right. We didn't have direct evidence. But, you know, if you read back into the history, it's sort of surprising how long it took people to put those two things together to realize, hold on a second, there are planets around our star, there might be planets around other stars, that seems sort of obvious, but it wasn't until a few hundred years ago

that people put those two ideas together and wondered how many planets might be out there in other solar systems. And these days, it's sort of a bonanza of exoplanet discoveries, and that may get even more explosive as we get the new James Webb Space Telescope up and running, which just launched recently in December, right? That's right, a very exciting moment for the entire astronomy community, everybody on pins and needles as their $10 billion toy launched and then unfolded in space without a hitch. And it's always very exciting in these moments when you open up a new eyeball onto the universe because it shows you things that nobody has ever seen. No human has ever known these facts.

And we will soon get data from it and it will tell us things about the universe that no human has ever known before. So to give us some context in sort of the current status of exoplanet research, our search for other planets outside of our solar system, we thought we'd bring in a guest, a very special scientist who specializes in sort of tiling up all of these exoplanets. All right. So it's my pleasure to introduce our guest on today's podcast, Dr. Jesse Christensen. She's a project scientist of the NASA Exoplanet Archive and also a research scientist

at the NASA Exoplanet Science Institute at Caltech. She has a PhD in 2007 from the University of New South Wales in Australia. She's won a bunch of awards, including in 2018, the NASA Exceptional Engineering Achievement Medal, and also the University of Southern Queensland Research Giant. I was wondering if that was actually a typo on your CV. Is that giant or grant? It is actually giant. So you are a giant of research.

In someone's eyes, I am a giant research. Was it a giant grant as well? I wish it had come with like a giant novelty thing. It didn't. I've got a little framed thing, though, it's nice. She's also very active on Twitter as Aussie astronomer, where she recently coined a new phrase in astronomy, which is the name of people who live in the Milky Way. You called us the Milky Weegeans.

I did. I did. After some thought, after some consideration, that's what I landed on. Wait, what's the term? Milky Wigian. Milky Wigian. I was looking for other places that ended in Way, and I landed on Galway. way and people from gollway are called gollwegians and i was like there it is so milky wegeons it sounds a little sort of

like witchcrafty maybe like or am i thinking wicket wikin oh yes so so not milky wickens that would be something different that's the other planet exactly that's right that's what happens when witches spill their breakfast cereal all over themselves they're milky wikins anyway we are milky wiggins all of us and we are curious about the nature of the galaxy and the planets in it and all the planets that are around stars other places in the galaxy and so we've asked jesse to come on the podcast and answer all of our questions about exoplanets past and future thanks very much for joining us today thank you for having me i'm excited to be here wonderful so first i think we should get started just with the basics of exoplanets how is it that we can see exoplanets planets around other stars from

earth i mean if i look up in the night sky we can just barely see the stars how is it possible to see planets going around those stars you've really hit on the the verb there, so C, we don't actually see almost any of the planets that we find. What we do is we look at the stars that they orbit and observe changes of those stars that are induced by the presence of the planet. And we can do this a few different ways. The planets pull gravitationally on the stars, so the stars actually wobble in the sky. And we can see that when we measure their velocity and when we measure their precision very precisely. The stars are all kind of just wobbling around in the sky a little bit if they have planets. Another way we

we see them as if the planet orbiting the star blocks some of the light from the star. If it's lined up just right and eclipses the star, then we see that the brightness of the star changes. So you're right, it's very difficult to see planets. So what we really do is look at the stars and see the changes induced by the planets. It's pretty wild to think about that all the stars are out there, at least the ones with planets, are wiggling. You know, like if you look at the night sky, that means most of those stars are wiggling. Even our sun is wiggling. Yeah. So actually, Jupiter, which has about 1% the mass of our solar system is actually dragging our sun around the middle of our solar system. So if you were an alien

civilization looking at our sun, you would basically see that it's moving with this roughly 12-year periodicity in the middle of our solar system. And from that, you could infer that there was a giant planet on a 12-year orbit, pulling it around. And then you could guess that we had a Jupiter-like planet. Wow. Could they guess that we're here? If they had really, really, really, really precise instrumentation, more precise than the instrumentation that we have been able to develop so far, they could, in fact, in further presence of Earth, and in fact, the whole solar system, but this is a leap in technology that we have not made yet. And that makes me wonder, like, what can they know about Jupiter?

So you say that they could see that Jupiter's here. What exactly can they know? Because they can't see it directly? So can they know things like its orbital period and its mass and its volume and what it's made out of? What can we actually know about these planets? Right. So if they could only see the wobble of the star, basically the only thing they'd be able to measure

would be its orbital period, so how long it takes to grow around the star, and the component of its mass that's along the line of sight between the star and them, which is to say that if Jupiter is lined up just right so that it's orbiting between the star and the observer, then that is the maximal pull that we can see. That's the maximum wobble will be if it's lined up just right. But most of the planets aren't lined up just right. They're tilted a little bit compared to that plane. So some of the pull of the star is in a direction we can't see. It's in a direction, you know, orthogonal to our line of sight, at right angles to our line of side. So we don't see that component.

We only see the component of the wobble that's in our direction. So we get a minimum mass, we call it. So you get an orbital period and a minimum mass. So for Jupiter, for instance, they'd get some minimum mass of one Jupiter mass. And they'd be like, okay, it's a gas giant. And we know, given the way things are constructed in the galaxy, if you have something that weighs a Jupiter mass, you know that it's mostly hydrogen and helium. It's not mostly rock or mostly ice.

It's mostly hydrogen and helium. So you could infer that it was a gas giant. So you'd have its period, you'd have its mass, a minimum mass, and you'd have some guess at its bulk composition. The other thing you could know if you know what kind of star it's orbiting is its temperature, because the orbital period tells you how far away from the star it is. So Earth, with our period of 365 years,

is just the right distance to get the right amount of radiation from the sun for water to be liquid on the surface. And that's kind of the holy grail of what we're doing right now, trying to find planets that are this right temperature. So you'd be able to guess its temperature. It's rough equilibrium temperature knowing how far it was from the sun. So you can actually get a lot just from this wobble on the sky. I think that's really fascinating.

You say that you can guess what's in the planet just from knowing how big it is. Is that just from knowing like how much hydrogen and helium and lithium and uranium there is out there in the universe that you're guessing how much of a serving of each of those components a big planet might get? Yeah. So we can start with what we think a protoplanetary disk is made of. So when a star is born, it's born from, from a cloud of dust and gas. And the amount of dust in that cloud,

dust is basically like the solid materials that aren't in gashes form. So the amount of dust in that cloud basically puts a limit on how many rocky planets or rocky cores of bigger planets you can make out of this protoplanetary disk. It's like making a cake. If you only have two eggs,

you're only going to be able to make one cake. If you have six eggs, maybe you can make three cakes or one, you know, three tier cake. So you're really constrained by these ingredients in your initial disk of material that's creating your planets. But that's sort of statistical, right? It's like if somebody took everything in the grocery store and then blended it up into a tornado,

you're talking about like how much flour and how many eggs might fall into a planet. You don't actually know for an individual planet, whether it's like unusually large lump of uranium at its core or something. Is that right? Right. So for instance, if you were in an American supermarket and you blended everything up, your planets would have a lot of cereal in them. There'd be a lot of breakfast cereal compared to other countries that I've lived in. Right. There wouldn't be any veggie mite, for example.

Exactly. You wouldn't have your veggie mite-flavored planets. One thing we do know is if you have something the size of Earth, that's not really big enough if it's just a hydrogen and helium ball to hold itself together compared to all of the other forces that are going on in the formation and evolution of a planetary system. So if you have something that's the size of Earth, you're pretty sure it's mostly rock,

just given the amount of gravitational pull you need to hold something together. So you couldn't really have like a tiny gas dwarf because it would just disperse. And that's from the wobbling, right? But from the eclipse, and I think we can, can we tell other things about the planets? If the planet's eclipsing, we can get so much more information. It's really quite great. And that's the method that I use. So now I'm going to like presetilize about the transit method. So if the planet goes in front of the star and you know how big the star is and you can measure how much dimmer the star gets, then you know how big in size the planet must be to block that much light. So for instance, Jupiter in front of the sun blocks about 1% of the star is. And you can measure how much dimmer the star gets, then you know how big in size the planet must be to block that. So, the light. So if you're looking at a sun-like star and you see that something's blocking 1% of the light, you know, it's a Jupiter-sized planet. Once you have size and mass, now you can really start to say things about the density of the planet and what it might be made of

and really start to get strained, oh, it must be 50% rock and 50% a gaseous atmosphere. The other cool thing about planets that go in front of stars is that their atmospheres go in front of the stars as well. Now, picture the Earth, so that the Earth is a rock and it has this thin, gaseous atmosphere around it. Now, if you were, again, let's be this alien civilization looking at the sun. If you were lined up just right so that the earth passed in front of the sun and blocked some of the light, then the sunlight would go through the earth's atmosphere. But just a tiny little bit through the thin layer of atmosphere. Yes, it would be a tiny amount of the atmosphere. But the molecules in that atmosphere, so our atmosphere's got oxygen,

it's got nitrogen, it's got water. The molecules in the atmosphere block some certain wavelengths of light. So, for instance, if you look at the Earth's atmosphere at 1.4 micron wavelength light, which is where water absorbs, the Earth actually looks bigger because the atmosphere is opaque at 1.4 microns because of the water. So this is what we do for planets around other stars. We look at their size as a function of wavelength to work out when is their atmosphere opaque and when is it transparent. And that tells us what molecules must be in that atmosphere, blocking light at certain wavelengths and letting it through at other wavelengths. So we have this, like, spectral fingerprint of the atmosphere of the planet on literally just the brightness of the star

changing at different wavelengths. And then you start to be able to say, okay, cool, this planet's got methane, it's got carbon dioxide, it's got iron rain coming down out of the atmosphere. You can tell so much cool stuff if you can see into the atmosphere. That's like watching the star rise over the planet, right? It's like sunrise and sunset. It's incredible. Exactly. And our atmosphere, you know, does interesting things to the sun as sunrise and sunset. And it's the same kind of thing. The more atmosphere, the light is going through, the more imprint of the planet's atmosphere goes on the sunlight. And you said a couple times, like, if things are lined up just right, you know, if Jupiter passes across the line of the sun between, you know, the sun and these observing aliens, then these

methods can work. It seems like things have to be lined up kind of in a lucky way. Doesn't that really limit our ability to discover exoplanets? Yeah, so using the transit method, it really does limit us. So an Earth-like planet around a star like the sun has about a one in 200 chance of transiting from our point of view as we look at all the stars around us. What that means is that you really have to look at a lot of stars in order to catch the ones that are lined up just right. So the NASA Kepler mission that I worked on for 10 years looked at 200,000 stars to try and find the systems that were lined up just right. So that's with the transit method. There are other methods like the wobble method, you don't need to be lined up just right. There is also, going back to your very, very original question, there's a method called the direct

imaging method, which is basically exactly what it sounds. If the star is close enough to us that the separation between the star and the planet on the sky is big enough, we actually have like pretty exquisite instrumentation that you can use to block out the star light very carefully and look around the star to find any little glowing points of light, which could be planets. So we do have a handful, maybe a few dozen now, directly image planets. Now, this is a few thousand. Now, this This mostly only works for very big planets, like even bigger than Jupiter, that are quite young. Because as planets are forming and the balls of gas are contracting, they're radiating out this heat, which makes them quite bright at certain wavelengths. So we can directly image some

kinds of young, giant planets. And then it doesn't matter how they're lined up. But we do have to be looking at the system at the right time to kind of maximize that separation between the star and planet. So there's still a timing issue. It's sort of like you're trying to measure the number of cats in your neighborhood, but you know you're not very good at spotting them. And so like every time you're Every time you see a cat, you imagine, well, I saw this one cat, there must be actually 200 cats out there that I'm not seeing. You have to have this estimate of your inability to see planets so you can extrapolate from what you do see to what's actually out there. Right. And that's actually exactly what I did on the NASA Kepler mission.

I injected fake planets into the data to see how good we were at finding them. Like, you know, pretending I just put cats everywhere and I was like, okay, how many cats do we see? I know that I secretly hid 200 cats in this neighborhood. How many cats did we see? So that's exactly what I did. And that was how we were able to say that, you know, Kepler found two and a half thousand planets. From that, we were able to infer that the galaxy has billions of planets, given the numbers of stars we looked at and the number of planets we found. The most exciting discovery from the Kepler mission is that exoplanets are everywhere in our galaxy.

So just to forestall the conspiracy theorists, you injected fake data into a NASA mission, but you told people you were injecting fake data. Yes. And I had to jump through a lot of hoops to do this. And it was quite funny. I had to keep the simulated data on a separate server that was never given access to the outside world. There was no way to log into the server from the outside. And even now, years later, whenever somebody announces a new Kepler planet, I have to go and double check that the period and characteristics of this new planet aren't a match for the fake planet that I injected into that light curve. So there's a lot of safeguarding to make sure that this simulated data is never can for real planets. Wow. And how many cats have you found out there? So we think that almost every star has planets around it. The smaller the star, the more planets they have. So M dwarfs, which are the most ubiquitous star in our galaxy, 75% of the hundreds of billions of stars in our galaxy are Mdorfs. We think that M dwarfs have multiple rocky planets like Earth around them, which is wild because that means there are hundreds of billions of rocky planets in our galaxy, which is so cool. That is really very cool. Yeah, it's amazing. And you're sort of part of the James Webb

Space Telescope as well, right? So I am interested sideline to James Webb Space Telescope. So I haven't done a lot of atmosphere work myself. I do more of the demographic stuff that Daniel was talking about working out how many cats we couldn't see because of the cats we could see. So James Webb is more going to be looking at the cats very carefully and being like, okay, this is a Siamese and this is a Burmese and this is a calico. And it uses the transit method as well, right? It takes sort of like giant pictures of space. Yes. So the transit method with what I was describing the transmission spectrum. So as the starlight goes through the planet's atmosphere, we've been able to do this with Hubble and Hubble's been able to give us really exquisite results, but we're really

pushing Hubble to the very, very, very limits of what it can do. And we're still looking at pretty big planets like Neptune's size planets and above. So with James Webb, which is, you know, times bigger in radius, so nearly 10 times bigger in collecting area, we're going to be able to look at smaller planets, like Earth-sized planets, and start to look at the atmospheres of those. And that's, you know, obviously I don't have to explain why it's super interesting to look into the atmospheres of Earth-sized planets that we find. We want to know how common are things like, you know, carbon and oxygen and nitrogen and phosphorus and, you know, methane and all of these like super interesting base chemicals that we build life out of. That's the

next question. Now we know rocky planets are everywhere. are rocky planets with the ingredients for life everywhere. That will be super cool to know. That would be super cool. And I also heard that you can sometimes look at the weather in some of these exoplanets by looking at sort of the delays in the signals and the way it sort of moves around the sun. Yes, exactly. So on Earth, one of the things we can see is the phases of Venus.

So Venus, you know, because it's interior to us, sometimes we see the full face of Venus get illuminated and sometimes we only see a phase of it. We can do a similar thing with exoplanets around other stars. If we measure the brightness of the system very, very precisely, as the planet is orbiting around the star, it actually starts reflecting light back towards us as it goes behind the star. So we build what we call a phase curve. And you can see things like, you know, jets and weather and spots and stuff coming and going.

And, you know, it's very crude, but we can basically reverse engineer these phase curves into maps of the surface. And we can see variability. We can see that, you know, the surfaces of these planets, the upper atmospheres, which is really what we're looking at, the upper atmospheres of these planets are changing, which is basically weather. And then my husband makes fun of me because he says, we're all just becoming exomeatologists, not astrophysicists, because we're just measuring weather on other planets. But I still think that's pretty amazing. Yeah. I can't wait for that telecast where you're like throwing, you know, sticky magnets with symbols of suns and clouds up on the planet, extra planets.

Oh, yeah, yeah. And tomorrow on 55 Cancray E, get ready for some storms. It's going to be a bad day. There's going to be raining iron, so bring us... The iron storms will be bad tomorrow. You know, keep your umbrellas with you. Your diamond umbrellas. Exactly, your platinum umbrellas.

And so the James Webb can do this because it gathers more light because it has a larger collecting surface or also because he can see different kinds of light. So that and those two things and also a third thing. So it's bigger. It's six and a half meters as compared to Hubble, which is two, two and a half meters. It's got different wavelength. So it's more in the infrared and mid-infrared. So remember how I was talking about water, which absorbs at 1.4 microns, that's in the near

infrared. That's not a wavelength of light we can see with our eyes. That's a wavelength of light that you see with like night vision goggles. It's one of the, it's a signature of heat and warmth in the infrared. So it's a different wavelength. So that covers a whole bunch of the really interesting molecules that we care about like carbon dioxide and carbon monoxide and carbon monoxide and water. And the third thing is we've built these four just amazing instruments, which are really you know, engineered to take advantage of James Webb's location in space, its wavelengths, all of the interesting things that we're going to look at. So we're going to be able to get much higher resolution spectra. So be able to break those wavelengths of light into, into finer and

finer gradations. And then you can start to do all sorts of interesting things like look at isotopes, you know, is it heavy water or is it normal water? And what does that mean about where that planet must have formed in that protoplanetary disk? And was the water delivered later from the outer solar system? you know, all this cool stuff once you can start to get more detailed observations. Wait, did you say we can test the water in other planets? Yeah, so one of the things we could be able to do if you have high enough resolution is measure isotopes. So isotopes are basically, you know, molecules that have atoms that have different amounts of neutrons in the center, but the same amount of protons. So we have something called

heavy water, which is basically water where instead of hydrogen and oxygen, it's deuterium and oxygen. And we, on Earth, we use heavy water to basically measure where, we think the water came from on Earth. So where Earth is right now was too hot in the early solar system for liquid water. So we think that most of the water on Earth was delivered from the outer solar system by comets. So during the formation of the solar system, it was a really chaotic, violent place. You know, planetismals are forming and smashing into each other, orbits are changing and exchanging energy with each other. And you have this huge cloud of material, the Khyber Belt, and then outside of that, the Oort Cloud, which are just, you're throwing

stuff at the inner solar system constantly. So we think that the oceans on Earth largely came from comets from the outer solar system smashing into Earth and delivering like these giant balls of ice. Like comets are just big balls of ice and dirt, basically. And one of the ways we think this is true is because we've been able to measure the isotopes of like what rate of heavy water is there to normal water on Earth versus the comets that we see. So if you have precise enough spectra of exoplanet atmospheres, you can start to do the same sort of thing. Look at isotopes and start to use that to map out where you think things formed. a lot of open questions about how planets form and how they migrate to where we see them today.

Wow. Testing the water on exoplanets. You also said we could measure like how much CO2 there is. Does that mean that we can tell whether the water on those planets is like still water or sparkling water? Yes, this is the Perrier planet over here. Is it flavored water? Like the big trend right now? Almost certainly. Exactly. Well, Nestle probably owns the water rights to all these planets already. Oh, yeah. Almost certainly true. Somewhere in the legal paperwork, there's like, this water and on all planets, all their water too. So the James Webb has these amazing abilities because it's bigger, because you can see deeper

into the IR, and also because it has these new instruments. Can you say something about the technology that was developed for the James Webb Telescope, specifically? I was reading about these incredible sensors that they use to detect like individual photons. Yeah. So that's actually one of, been one of the big breakthroughs in the last few decades. So, you know, everybody nowadays has really, really fantastic CCD in their phone, right? everybody just pulls out their phone and takes great images, high-resolution images. The goal for a long time has been able to do this at other wavelengths.

So CCDs uses specific technology to turn visible light photons into electrons and then, you know, turn that into images. But at other wavelengths, that exchange doesn't happen the same way. So there's a lot of interest in developing infrared detectors and ultraviolet detectors that do as good a job, basically, as your iPhone does. And that's been one of the real advancements in the last few years, these breakthroughs is making these infrared detectors that conserve the number of photons, which means you don't lose any, you can measure absolute numbers of photons,

and that do it at a high enough efficiency that you can get really, really good measurements, even on very faint things, which is a lot of what Web will go for. I'm not going to be able to give you any more technical details than that, because I didn't build any of them. Well, that's all super fascinating, and we have a lot more questions for you about exoplanet research, but first we have to take a little break. December 29th, 1975, LaGuardia Airport.

The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being left. loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism.

Law and Order Criminal Justice System is back. In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcast, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam.

Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet.

So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the secretary. Podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like, you're not going to choose an adaptive strategy, which is more effortful to use unless you think there's a good outcome as a result of it, if it's going to be

beneficial to you. Because it's easy to say, like, go you go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier. Ignoring is easier. Denial is easier. Drinking is easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers.

I'm Gretchen Whitmer, Jody Sweeten. Monica Patton. Elaine Welter-Roth. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them. Every episode gets real about the why behind these changes.

and gives you the inspiration and maybe the push to make your next pivot. Listen to these women and more on She Pivot's now on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. All right, we're back and we're talking to Dr. Jesse Christensen, Project Scientist of the NASA Exoplanet Archive. Dr. Christensen, I think even sort of part of this whole sort of revolution in exoplanets, I mean, basically before the 1990s, we didn't really have direct evidence or even indirect evidence of planets and other stars, but this also sort of come about in the last 30 years, right? In 1995 was the first discovery of a planet using this wobble method around a star like our sun. Actually, a few years before, in 1992, we had found planets around pulsars.

So a pulsar is what happens at the very end of the life of a star. that has puffed off its outer layers and it's collapsed into a neutron star and it's spinning super super super super fast thousands of times a second and if you're lined up just right to this spinning star you actually see pulses of radiation coming out thousands of times a second so some people who weren't actually hunting for exoplanets the exoplanet hunters were off here looking over looking at normal stars so some people who were looking at pulsars found this pulsar that was the pulses were sometimes coming early and sometimes coming late and sometimes coming early and sometimes coming late and they were like, what's happening? And they realized that there must be something around

this pulsar that was gravitationally pulling on it. So sometimes the pulsar was moving towards us and sometimes it was moving away. So there was kind of like a Doppler effect. Like if you've ever had an ambulance drive past you in the street and it's like, wee, weo, weo, weo, this is what was happening to the pulsar and they realized it had planets, which was cool, but also kind of a bit of a side thing because pulsars are so strange and people were looking for planets around stars like the sun. So it's really only been in the last 30 years. years that we've found planets. And it's been such an explosion. Now, we're about to hit 5,000 planets, which is going to be a cool milestone that we're going to celebrate at the Exoplanet Archive. But yeah,

it's really the fact that technology got us to the point where we could do this search. Yeah, it's a pretty amazing technological feat. And you sort of described it as an explosion. Is that sort of what you were expecting back in the 90s? Or has this sheer amount of number of exoplanets, has that been a surprise? Yeah, it's really interesting. So when I joined the Exoplanet Hunt, which was in the mid-2000s as a grad student. There were not very many planets known yet. Like it was still in the dozens to a hundred or so, but they were being found, which is why I was excited to do this as a grad student and to search for them. And I will say, I spent four years searching for them using two different surveys, and I never found a single one, but they still gave me a PhD. So it's good. You can get a PhD in

planet hunting without ever having found a planet. That's all right. I've been a particle physicist for more than two decades, and I've never found a new particle. So I'm still looking. Well, solidarity, Daniel, solidarity. And then basically as more and more surveys came online and the telescopes got bigger and the instruments got better, what we've really seen is an exponential rise. If you plot the number of planets with time, it's exponential. And I refer to this as Mamajek's law,

because Eric Mamajek was the first person to note this exponential rise. And basically the doubling time, you know, you know, had this Morse law for computers where the doubling time is like every two years or so. the doubling time for exoplanets is about every two years or so. So 27 months about. So what we're seeing is the number of exoplanets we know is doubling every slightly more than two years. If you keep extrapolating, that means we're going to hit a million planets by like 2037, which sounds ridiculous. But if you actually look at the upcoming NASA and European Space Agency and Chinese Space Agency missions, there's a lot of real estate that we haven't searched yet that we will search in the next few decades. So I'm actually not surprised if we hit this million in the next 50s. years. Wow. And these are just a million planets we've seen, right? The number of planets out there is much, much, much bigger. Exactly. These are a million planets that we've been able to individually detect and confirm in some way. And this is the kind of thing that we can now

explore and, you know, ask fun science questions about, but take us sort of back again to the early 90s. Is this what people anticipated? Did people know, given the technology that was coming online, we would soon have all these planets? Or did people not really understand how many planes, were out there? You know, it was a really open question because we had a sample size of one, right? Like our star had planets around it and there were billions of stars in the galaxy. You know, a lot of people had postulated that there were planets and we just didn't know how many.

We didn't know whether things like the solar system were rare and happened very rarely or whether they were ubiquitous or somewhere in the middle. And from what we can tell, it seems like they're ubiquitous. Like if you have the physics and the ingredients to make stars, then you have the physics and the ingredients to make stars, then you have the physics and the ingredients to make planets. So I don't think it's a surprise that we've found that they're ubiquitous, but I think it's still an amazing achievement that we've been able to confirm this intuition. I don't think anybody expected it would be exponential in rise,

but it really became a big industry in astronomy to go hunting for exoplanets. Once we realized that the technology had finally gotten past that threshold needed to detect exoplanets, that everybody wanted to do it, and it was the new hot thing. Is that what you put in your business card? Dr. Christensen, a planet hunter or exoplanet hunter? I do usually call myself a planet hunter. It makes me feel very Lara Croftian. That's pretty cool, yeah.

Out of the thousands of exoplanets found, do you have any favorites or any particularly weird ones that we found? I do have a favorite system. So the technology has gotten to the point where we have more data than we can look at. And what that means is a lot of us have turned to citizen science projects. So citizen science projects are usually when scientists make a hundred. whole bunch of data available online and ask people to answer a pretty simple question about it, like help us classify this or mark a bad pixel or translate this word or just do some simple repetitive tasks that needs to be done millions of times. And, you know, we train computers to do it

too, but people are really, really good at seeing things that computers miss. Like, our brain's ability to do pattern matching is still unparalleled. Like, it's really important that we know the difference between a tiger and a zebra. So, you know, our brains are super good at it. So in 2017, my colleague Ian Crossfield and I set up a citizen science project called Exoplanet Explorers, where we had data from the Kepler telescope and we basically were just like, help us find planets in it. Like here are, here are the data. Look and see what you see. And we were really, really lucky enough to get picked up by BBC Stargazing Live, which is this like annual televised astronomy extravaganza, like imagine Woodstock for astronomy, where they do three nights of

primetime television and they're interviewing astronomers around the world and throwing from this telescope to that telescope. What's happening over here? We're looking at Europa. So we were lucky enough to get our project on that TV show and we had 10,000 volunteers look at planets. And within 48 hours, we had found this new system. It's called K2138. And I'm going to pause here and apologize because exoplanet names are garbage. I'm sorry. Astronomers shouldn't be allowed to name anything. But the system is called K2138. It's got six planets in it. They're all between the size of Earth and Neptune. The reason I really love this system is that five of the planets are in a resonant chain. So what that means is that their orbital periods are related to each other

with very, very simple integer ratios. And we see that in our solar system. So for instance, the Galilean moons of Jupiter, three of them are in a one to two to four ratio. So for every, you know, four times I-O goes around, the next one goes around twice. And for every two times that one goes around, the next one goes around once. So they're all locked in this resonance. And that's partly how you can get so many moons like crammed so close together because they're in this really stable formation and they're kept that way by the resonance. So this system, K2138, has these five planets that are all in a three to two resonance. So the inner one goes around three times, the next one goes around two times. For every three times that one goes around, the next time

one goes around two times and so on. The reason that is cool is because the three to two resonance, if you've ever studied music theory, is the perfect fifth interval. So the, the, first two notes of twinkle, twinkle, little star. So this, this system is basically singing twinkle, twinkle little star to us because they're all in this, this perfect fifth resonance. And it was found by citizen scientists and we got to like announce it on live on TV. It was super cool and has such a fun story. So that's, that's my favorite one that I've been able to publish. That's amazing. But I don't know about letting the internet choose the names. I don't think that usually goes well. Planet Mcplanet face, right? Yeah, unfortunately. So the IAU, the international

astronomical union has actually had several competitions, worldwide competitions to let people name some small number of exoplanets. And they've been, you know, they've been good and bad ones. I like some of the suggestions. Some of them are strange. The problem is that the IAU hasn't been able to get professional astronomers to adopt them. Like if I've published this as K2138, and I've always called it KT1.38, if you come along and call it, you know, Liberty and the next one's called fraternity and the next one's called whatever the third one is that I've forget, but one of them is the three French things. I'm not going to call it those. I'm going to call it K2-138.

Yes, egalitate. That's right. Thank you. So there are these names, but they haven't stuck, unfortunately. Well, the real problem is going to be when the aliens come from that planet and they discover that we name their planet K2-138, they're going to be pretty upset if you don't adopt their local name. Or maybe they like it. And this was exacerbated. So just recently, we announced the second exo-moon candidate.

So this is a candidate moon around an exoplanet around another star. So the star is Kepler 1708. The planet is Kepler 1708 B because it's the first planet found around the star. And the moon is Kepler 1708 B, I, like the Roman numeral little I. For the first moon around the first planet around the star, Kepler 1708. And that's just about as unromantic as you can get for what could be the second moon we've ever found around another planet around another star. And why is the first planet called B? Why isn't it called A?

Ah, good question. We borrowed this from binary star nomenclature where the primary star is always A. And then the secondary star is always B. Capital A and capital B. So when we started naming planets, we kept this convention that the primary star is A. And we started using little B and little C for the planets. You get into some really interesting corner cases here where you have like a binary star system where both of the stars have planets because then you end up with, you know, such and such,

big A little B and such and such big B little B and it's yeah it's a lot it's a lot happening it's enough to confuse the milky we jeans in all of us super cool let's get more into that but first let's take a quick break December 29th 1975 LaGuardia Airport the holiday rush parents hauling luggage kids gripping their their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake,

a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot.

He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them.

I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he's. He now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like,

It's easier to punch someone in the face. When you think about emotion regulation, like, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome as a result of it if it's going to be beneficial to you. Because it's easy to say, like, go you, go blank yourself, right? It's easy.

It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier. Ignoring is easier. Denials is easier. drinking is easier, yelling, screaming is easy.

Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps and their lives and career. years. I'm Gretchen Whitmer, Jody Sweeten, Monica Penn, Elaine Welterah. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them.

Every episode gets real about the why behind these changes and gives you the inspiration and maybe the push to make your next pivot. Listen to these women and more on She Pivots. Now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. And we are back talking to Dr. Jesse Christensen from the NASA exoplanet archive. So we've observed all of these solar systems and you said we found all of these planets and some of them are weird and fascinating and interesting. Isn't it true also that we can only see certain kinds of planets like you've talked about

how we can see Jupiter but it'd be really hard for us to see Earth? Is it possible for us? us to extrapolate to what those invisible planets are, to what those solar systems actually look like based on the few planets that we've seen? How do we make those extrapolations and how uncertain are they? Yeah, there's a lot going on in that question. And there's a lot of people who are working hard on answering that. So one thing I'll say is that we think that planets like the Earth are common, but not because we've actually found any confirmed robust detections of planets like the Earth. Unfortunately, Kepler in the end didn't quite achieve the sensitivity it needed to find Earth-like planets. We do know that planets just a little

bit closer to the Sun than the Earth is are common. And we do know that planets just a bit bigger than the Earth are common. So we do extrapolate, which is dangerous, always dangerous. But we extrapolate from that to say that Earth-sized planets at the right distance from their stars to have liquid water are common. So even that already is an extrapolation to say that Earth-like planets are common. We feel pretty good about it, but not, you know, the best. So we haven't actually found a solar system analog yet, something that has like inner rocky planets out to the distance of Earth and Mars and then outer giant planets like Jupiter, Saturn, Uranus, and Neptune.

We're just not there without precision yet. But we don't think that they're uncommon, given what we do know. And this comes back to the Invisible Katz argument. We can do complicated population analyses where we, you know, fall back on like Bayesian statistics and prior knowledge to say, okay, if this system had seven planets and they were distributed in roughly the same way as the planets of our solar system, how many of them could we have seen? And for instance, because the planets in our solar system aren't exactly lined up in the same plane, there's no alien civilization

that could see all eight planets transit. You could only ever see a subset and have to infer the larger sample. And so infer is the important word there. So again, we have to put some prior. We have to say, we think that the mutual inclination, so the spread in the orbital planes of the planets, should be less than, you know, let's say 10 degrees. Because if you start to get too spread out, then they start to interact with each other dynamically and become unstable.

But again, we're already making assumptions, which might turn out later to be wrong. So you put some prior on how spread apart the planets could be. Then you look at how many planets you've seen and say, okay, we've likely missed 70% of the planets are in these systems, which means that there are, you know, three and a half times as many. So that's kind of how we do it.

We do have to make some assumptions, and they may be wrong. But, you know, if you give astronomers two planets, they'll start to try and do statistics. So you're saying the reason we haven't seen other systems like ours, it's not because we don't see them. It's just that we, so far, we can't have seen them or can't be able to see them. Exactly.

So some of the NASA missions are sensitive to planets close to the star, so closer in than Earth. And some NASA missions are sensitive to planets further away, Like the direct imaging planets need to be very far away. And there's another technique that I haven't talked about called microlensing, which is sensitive to planets that are far away. So the wobble method that we talked about and the transit method are both biased towards detecting planets close to the star.

And then the other methods are biased to finding planets far away. What we haven't really been able to do a good job yet is marry those results together and say, okay, we have a complete census. We have a good idea what's happening in the inner regions of the solar systems and we have a good idea what's happening in the outer regions. And that's one of my big scientific goals for the next decade, because NASA is about to launch a new mission called the Nancy Grace Roman Space Telescope, which will happen in the second half of this decade. And it's going to do a big microlensing survey, so this is this other detection technique, of the galactic bulge.

And it'll find a lot of planets in the outer solar systems. And then the question is, how do we take the results from Kepler, which did a fantastic job of mapping our inner solar systems? and the results from Roman, which should do a fantastic job of mapping out of solar systems and, you know, overlap them somewhere in the middle and get a consistent answer for what does the whole solar system look like around these other stars? So that's one of my big goals is to be able to join the results from Kepler and Roman together so that we can finally talk about solar system analogs and how common they might be. It's almost like planets the size of the Earth are kind of hiding out there,

which is, I guess, a good thing, I guess, if we're trying to hide from evil aliens. Yeah, if you look at the sensitivity curves of Kepler and what's predicted for Roman, Earth is like just snug, like right in the middle just where they meet. Like it's possible that we still don't quite get there even with Roman. Earth is just really small. Unfortunately, I think we'll get there. Another thing that NASA is planning is a really big UV optical infrared mission for 20 or 30 years from now, which will have one of these direct imaging instruments on it.

And the goal of that will be to actually take a picture of a planet like the Earth. around a star like the sun, which will be an incredible achievement for humanity. Is that the sort of only way we'll be able to see other Earth-like planets through direct pictures, or do we just need a new kind of technology or just improve the technology that we have? Oh, yeah. There's very, very cool ideas for new technology that would happen like on the order of 50 to 100 years. So for instance, one way you can get good resolution is by making one telescope

really, really big or by getting two telescopes and putting them far apart. and looking at the same thing. And that's called interferometry. There's ideas for an interferometer that would be the size of our solar system, right? Like you'd have some telescopes way out in that direction and some telescopes way out in that direction and they would look at a planet around another star

and use the resolution that they gain from being, you know, many, many, many astronomical units apart, which is the distance from the Earth to the Sun, to be able to map the details. There's another really cool idea concept for a future thing, which is to use the Sun as a gravitational lens. So everything with mass bends space time, right? Like you're bending space time right now as you sit there.

So the sun is bending space time. And that's what magnifying glasses do, right? They bend light so that it comes together in a certain way to make it look like things are closer. So you could imagine putting a telescope on the other side of the sun and using the sun as a gravitational lens to magnify a background star and planets such that you could see it in more detail. Like how cool is that? That would be super awesome. Basically you're talking about building a lens the size of the sun. just gathering a huge amount of light, which allows us to see dimmer objects and to magnify them.

Is that right? You're using the sun as a giant lens because it's bending space time the way a normal, you know, glass lens, bends air and light. Right. You guys are really thinking big. Now you got James Webb up there. You're like, wow, we can do anything. Yeah.

The fact that that deployment sequence is going so well is super, super relieving. Like so many people have worked on James Webb for so many years. And there were so many moving parts. But so far, fingers crossed, all of the big things have happened and happened the right way. So go James Webb. Can you also give us something of a map of like where we have looked for these planets? I know that some of these things are capable of seeing planets close by and some of them are capable of seeing things far away.

Have we explored our entire galaxy as much as we can? Oh, yeah. So actually we really haven't. So our galaxy, our Milky Way galaxy is what we call a grand spiral. So if you could look down on it, it's got these lovely huge. huge spiral arms. And we're just like out in the burbs. So the galaxy itself is about 100,000 light years all the way across. And we're about 30,000 light years from the middle. So we're kind of, yeah, just out on the edges, basically. Basically, almost all of the planets that we found so

far are within a few thousand light years. So remember, 30,000 light years to the center of the galaxy. We've really only searched like this little bubble around us out what we call the local solar neighborhood and you know the 5,000 or so planets that we found so far are almost all very close to us now i say very close space is really really really really really really big even just a few light years away is is with our current technology basically inconceivable for us to visit we can send messages and they will still take years to get there to our closest star alpha centauri which is four light years away it would still take us four years to get a message to even the closest star. So while we have only searched our local cellar neighborhood, that is still a really big

blob of space. So now come back and picture the whole galaxy again and think about this tiny circle off to one side that we've been able to explore and now think about what else could be in galaxy. That's what keeps me hunting, right? Like that's so cool. It's such a big space. And as our instruments get better and our technology gets better and our ideas get better, we're just going to be able to explore more and more and more of it. And is there a possibility that our local solar neighborhood is like unrepresentative. We have this history in science and especially in physics of generalizing from our experience and then discovering, oops, that was a mistake. Is it possible that what we've learned about solar systems is only applicable to this little neighborhood and that

there are more planets for star somewhere else or fewer planets? Or do you think it's likely that what we've learned so far is true across the Milky Way? Oh, it is such a good question. And now I'm going to share something. So my research group just met this morning and a postdoc that I'm working showed us a plot. And this is like a brand new plot where we're trying to map out how the occurrence rate of planets, how common planets are changes with properties of the galaxy. And he showed us this plot this morning that showed that a occurrence rate of planets might decrease with your distance from the galactic plane. So remember I said we're in a big spiral. Now, almost all of the stars are in a big disk. But there are some stars that are out of that

disc. So they're out of the plane of the galaxy. And so this is literally just he showed us this plot this morning and we all just sat there like, cool, what does it mean? So it could be the fact that as you get out of the plane of the galaxy, it's harder and harder to make planets. And now the immediate question is, why is that? We know that stars out of the plane of the galaxy have fewer heavy elements. So, you know, how I said dust and gas earlier, they have less dust compared to gas. Maybe that means it's harder for them to make planets. We also know that stars out of the plane of the galaxy are older than the stars in the plane of the galaxy, which is where most of the star birth happens, then the stellar nurseries are almost all in the plane. What is age

have to do it? Why was it harder to make planets 11 billion years ago than it is now? So these are all like super interesting questions that literally we're trying to answer right now. There are good reasons to believe that, you know, planet formation might be different in different parts of the galaxy. For instance, as you get closer and closer to the center of the galaxy, the stellar density gets more and more crowded and the stellar radiation gets more and more concentrated. So it might be harder to make certain types of planets. It might be harder to keep planets once you've made them, as you know, especially as you get closer and closer to the center and things start to get really crowded. So yeah, there's a, there's a lot of questions

about how planet occurrence might change as you move around the galaxy. So, you know, imagine like the first season of a TV show where you're just looking around your local neighborhood and you're like, cool. And then the second season is like, oh, wait, this is just like one neighborhood in a huge city. So we're just starting to peek outside our neighborhood and see what could be happening. Not all Milky regions are maybe made the same way. Exactly. Exactly. So for instance, life on Earth, If you look at the equations for the chemical energy gradients that describe life on Earth, there's like heaps of carbon atoms and heaps of hydrogen atoms and heaps of oxygen atoms and heaps of oxygen atom and one phosphorus.

So like literally the rate of life on Earth is governed by how much phosphorus we have? And like, is that true elsewhere in the galaxy? And do other places in the galaxy have enough phosphorus to make life if they use the same chemical energy gradients? That's super interesting and important. You know what? I just pieced it together. So we call people from Norway, Norwegians.

That's where Milky Way and then we would be Milky Weigens. Exactly. You got it. You're there. It rolls off a ton. It only took me an hour. Sorry. It took me 18 hours.

Someone asked what we should call them and I kind of went away and was like, huh. And then I pondered for a while. And eventually I landed on Milky Weegens. It only took you an hour. It took me much longer. See, sometimes astronomers are good at choosing names. There you go. I'll take one, one victory.

So let me ask you to speculate a little bit. there's this big dark part of the galaxy we haven't seen and so many planets which are currently invisible to us that suggests that there might be surprises out there right it could just be that it looks the way we expect but you know the universe seems to always have surprises for us in store and you give us a sense for the sort of range of possibilities like what kinds of things might we discover when we turn on these new eyeballs and explore the rest of the galaxy yeah like what do you think we're going to know in 20 or 50 years well one thing I hope we know in 20 or 50 years is how many Earth-like planets are there that we can actually see with our instruments. That would be

amazing. In terms of what's the unknown unknowns, one thing that surprised us a lot is the fact that the most common kind of planet we have found is between the size of Earth and Neptune. So in our solar system, there's a big jump. We have all the little planets up to the size of Earth, and then we have all the giant planets that start at Neptune and go up. But there's a gap. So Neptune is about four times the size of Earth. And in our solar system, there's nothing. in that gap. As we have explored the galaxy around us, the most common kind of planet we have found is in that gap. It's bigger than Earth, but smaller than Neptune. And so do you call it a Super Earth or a Mini Neptune or do you have some other crazy name for it? We actually call them both of those

things and kind of depends on what science case you're trying to make. So Super Earths, we think, are up to maybe one and a half to 1.6 times the size of the Earth. And then above that, we think that they're compositionally more like Mini Neptunes. But we actually don't know. And one of the big open questions is, could they actually be just a different kind of planet, not just a big rock or a small ice ball, but like an ocean world, like something that's, you know, predominantly water? Is there some other, you know, configuration of compositions of rock and iron and ice shells and different kinds of ice and water that can build these planets?

So one of the things I hope we know in 20 to 50 years is what are super Earths and what are many Neptunes, like, you know, are they a new type of planet that we don't have an our solar system? Because at the moment, only having a bulk composition, so we know the size and we know the mass, it doesn't give us a good idea of how the mass breaks down inside that sphere, basically. So we don't know yet. And I'm hoping we will know. The things that have surprised us a lot so far, besides this discovery of this, you know, new type of planet, it has a lot to do with configurations. So for instance, finding giant planets like Jupiter right next to the star that orbit in just a few days.

So the very first kinds of planets we found were these hot Jupiters, we call them because they're Jupiter's heated up to thousands of degrees. So finding hot Jupiters was a big surprise. Finding these really compact systems of planets like K2-138 that I described, which is a series of resonant planets in this chain, that's also been really new because, you know, in our solar system there's nothing between the sun and Mercury. In K2-138, there's six planets that are closer to the star than Mercury is.

They're all really packed in type. So finding these dynamically packed systems. So as we start to explore more space, which includes younger stars, it includes more metal poor stars with less heavy elements, finding out what kinds of planets they make and how soon they make them. So for instance, the reason we look at young stars and look for planets is to try and work out how long does it take to make a planet? Because different planet formation theories predict different timescales.

So we're hoping to look at young stars and work out how quickly they make planets. And, you know, we'll probably be surprised. We'll probably find out they make them super fast. We'll be like, ah, okay. So there's lots of things I expect to be surprised by in the next 20 to 50 years. But mostly new types of planets in new types of configurations is what I expect. That's awesome. Me, one last question, Daniel?

Yeah. If you find a combination Neptune Earth, why didn't you call it a Nepturth? I like Neptini as the mini Neptune substitute. That sounds like a cocktail. And in fact, many of us astronomers have gotten together at more than one conference to drink Neptini's. And the next morning you have to wake up and drink a lot of hot Jupiters to recover, right? Exactly.

Right me, one last question, Dr. Christensen. What's it like to be a planet hunter? Like when you discover a new planet, can you describe that feeling? Sure. So there's this phrase you might have heard, the saying, you know, where the generation that was born too late to explore Earth, but too soon to explore space. And I feel in just this incredibly privileged position, I feel like I get to explore space. I get to discover new worlds around other stars.

And so, you know, the long nights at the telescope, you know, it's 3 a.m. The instrument's been misbehaving. You have this one candidate you really, really want to get a good luck at. The sky's finally clear. You get the data and you look at it and you see it's a planet. And, you know, I always just like sit back and put my hands on my face. And I'm like, yes, okay, yes, great, awesome. And then you move on to the next candidate because you only have like two hours

before the sun's going to come up. And some of them won't turn out to be real planets. But, you know, there's always this moment where you get to sit there and be like, I know something that no one else knows right now. Like, I know that this is a planet. And you just get to savour it for a second and just be like, that's really cool. And then I usually send like an all caps email to my collaborators. We've got one.

Because you might be the only person in the galaxy that knows about that planet or the universe. I'm never sure whether I'm more scared of us being alone or not being alone. Right. Like, is it a scary thought to be the only one who knows about it? Or is it a scary thought to not be the only one who knows about it? That's like you need another niptini. Yes, right. That'll help. I'll settle it. All right. Well, thanks very much for coming on and answering all of our very serious and very silly questions about exoplanet futures.

It's been a pleasure. Yeah, the pleasure is mine. Thank you so much. Thanks for listening. And remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. Your podcast from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. then everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism.

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