Planetary Radio • May 24, 2023

Exoplanet enigma: Unpacking the discovery of a "forbidden" planet

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Shubham Kanodia

Carnegie Postdoctoral Fellow

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Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

This week on Planetary Radio, Shubham Kanodia, the lead on a paper about a so-called “forbidden planet,” TOI 5202 b, joins us to talk about this strange world and why it's upending our understanding of planetary formation. Then Bruce Betts and Sarah Al-Ahmed will team up for What's Up, a look back at this week in space history, and a preview of the upcoming night sky.

The “forbidden” planet TOI-5205b
The “forbidden” planet TOI-5205b This artist’s conception shows the gas giant TOI-5205b transiting, or passing in front of its host star. This world has been called the “forbidden planet” because of its size and proximity to its small red dwarf star, which goes against our current understanding of planetary formation.Image: Katherine Cain / Carnegie Institution for Science

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The above animation shows how TESS will observe the sky. TESS will watch each observation sector for at least 27 days, before rotating to the next one, covering first the south and then the north to build a map of 85 percent of the sky. (NASA's Goddard Space Flight Center/CI Lab)

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What three moons of planets in our Solar System have average densities greater than or approximately equal to 3 grams/cm3?

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What will the OSIRIS-REx mission be renamed when it starts its new mission to the asteroid Apophis after it drops off its asteroid Bennu sample at Earth?

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Transcript

Sarah Al-Ahmed: A forbidden planet gets the spotlight, this week on Planetary Radio. I'm Sarah Al-Ahmed of the Planetary Society, with more of the human adventure across our solar system and beyond. Occasionally discoveries are made that break our expectations and lead to a greater understanding. This week, Shubham Kanodia, who's the lead researcher on a paper about a forbidden planet called TOI-5202b, joins us to talk about this strange world and why it's upending our understanding of planetary formation. Then Bruce Betts and I will team up for What's Up, and look back at this week in space history. We'll also let you know what you can look for in the upcoming night sky. But first, here are some space updates. Good news everyone, especially for fans of Jupiter. The European Space Agency's JUICE mission to explore Jupiter's icy moons, has deployed its previously stuck antenna. It was only just about a month ago that I was chatting with Olivier Witasse, project scientist for the JUICE mission. We were so excited about this mission's observations of Jupiter's moons, but then the mission hit a snag. The antenna on one of the instruments failed to deploy after its launch in April. It took some doing, but the mission engineers finally managed to deploy the antenna by using another moving part on the spacecraft to dislodge a jammed pin. Now you're thinking with portals, and there's even more good news from the Jovian system. Some Planetary Radio fans will remember back when I spoke to Scott Bolton in January. He's the principal investigator for NASA's Juno mission to Jupiter. At the time, he discussed the mission's upcoming observations of the wacky volcanic moon, Io. Well, buckle up, because the first images of Io came back and they're so cool. Juno's been studying Jupiter from orbit since 2016, and now it's finally turning its sites to the innermost of Jupiter's large moons. Over a series of flybys, the spacecraft will observe Io's volcanoes. It'll also measure how often they erupt, how bright and hot they get, their groupings and even the shapes of their lava flows. I can't wait for the next close passes so we can learn even more about this strange, eruptive, pizza looking moon. And interestingly, it turns out that Saturn's rings may be younger than we previously thought. New research using data from the Cassini spacecraft suggest that the giant planet's iconic set of rings may have only formed less than 400 million years ago. That's over 4 billion years after the planet itself formed. The rings may also be short-lived in cosmic terms. The system of dust and small rocks that's circling the planet may only last for about another few hundred million years. On the one hand, it's sad that Saturn's rings are going to disappear, but on the other, how lucky are we to live in a time when they're so bright and beautiful? You can learn more about these and other stories in the May 19th edition of our weekly newsletter, the Downlink. Read it, or subscribe to have it sent to your inbox for free every Friday at planetary.org/downlink. Now on to the Forbidden Planet. In an astounding discovery that challenges our understanding of planetary information, a group of astronomers under the leadership of Carnegie's Shubham Kanodia, have discovered a weird planetary system. It has a large gas giant orbiting a small red dwarf star, called TOI-5205. This discovery was featured in the astronomical journal. Red dwarf stars are way more common than stars like our sun, but they're generally considered unlikely hosts for gas giants, because of their formation histories. The newfound planet, called TOI-5205b was first detected by NASA's Transiting Exoplanets Survey Satellite or TESS. When that world passes in front of its star, from our perspective here on earth, it blocks about 7% of its host stars' light. That makes it one of the largest known exoplanet transits we've ever discovered. I had to know more, and thankfully Dr. Shubham Kanodia, the lead researcher on the paper and a Carnegie post-doctoral fellow, was happy to share. Hi Shubham.

Shubham Kanodia: Hello.

Sarah Al-Ahmed: Despite everything we know about space, new discoveries are being made all the time, and some of them are fundamentally challenging our understanding of the universe. You work specifically studying giant planets around M dwarf stars. How did you get interested in the subject?

Shubham Kanodia: I started with my PhD at Penn State where I started building instruments. So I've always been interested in exoplanets. And what we realized is when I got to Penn State, there's a niche that hasn't been fulfilled yet, and that's to study M dwarfs. And so, M dwarfs are basically stars that are like the sun, but they're much cooler than the sun. So the sun for reference, is something around 6,000 degrees, whereas M dwarfs are about half of that in temperature. So they're much cooler, much redder, they're much smaller than the sun, so they're extremely faint. But the interesting thing is, they found like 75% of the galaxy, so there are hundreds of billions of M dwarfs out there. But because they're so small and red, and because the earth doesn't go around an M dwarf, traditionally they have been ignored when it comes to planet studies. But what we realized is that because they're smaller and lower in mass, because they're lighter than the sun, planets going around these stars should be easier to find if we can get over the fact that these stars are much redder. So they require near infrared instruments, instead of the optical ones that we typically use to find exoplanets. So that's how I started and that's how I got into M dwarfs, by trying to build these instruments at Penn State, and just being really lucky to be a part of a great team and get involved there.

Sarah Al-Ahmed: Is it easier for us to find larger planets around these types of stars, and is that why you're focusing your efforts there?

Shubham Kanodia: It should be easier to find these planets, just if you think about because they're bigger, they'll have larger signals. If you think of it like a car's headlight and you have a fly going in front of it, that's typically what we are trying to do. That's the amount of light that's being blocked by a planet. Or think of a stadium light, maybe that's more accurate. So if you're looking at the light from a stadium, those floodlights, and you have a tiny mortar of fly go in front of it, that's what it's like to find an earth in front of a solar-type star. That's the tiny amount of light being blocked. Now, because these M dwarfs are smaller, instead of a stadium floodlight, I don't know, you can think of something that's maybe a hundred the brightness of a stadium floodlight, and it should still be fairly difficult to find an earth-like planet. But because the giant planets are larger, instead of a fly, now maybe you have, I don't know, a pigeon going in front of the light. So it's just going to block more light. And similarly should be easier to measure the mass of these objects, because they're more massive. And what we do to measure the mass, is the doppler effect. So it's basically something similar to if we have a siren from a fire brigade going around you, and as it's approaching you, it's going to sound red, the blue shifted, and as it's going away from you that the pitch is going to change. So that's the same thing we do, but with the light from the star as the star is wobbling back and forth because of the planet. So I say it should be easier to find these objects, but in reality the problem is they're extremely, extremely rare. So you need to look at a lot of stars to find one of these objects.

Sarah Al-Ahmed: That's interesting, because as you said, this type of star is far more common, and you would hope that you would be able to find way more planets there, but it is so, so challenging, even to find any planet at all. You're hoping for just the right angle between our planetary system and earth observing outward. And sometimes it can get really tricky, even if it's a giant planet, in the case of this one.

Shubham Kanodia: Yeah. There are many ways to find planets, and the one I think I just mentioned is the transit method. And that's typically done best from space where you can look at thousands and thousands of stars at the same time for maybe 20, 30 days, sometimes years at a time, and just try to find these tiny tips which could signify planets. But there are lots of other ways, for example, the Doppler technique, there's microlensing and many other really fantastic ways that people have come up with. I should mention that these stars, which are everywhere in the galaxy, in fact, I mean if we could look in the infrared and if our eyes were, I don't know, maybe five times bigger, the night sky would be full of red stars and not white stars, just because there's so many of them and they do have more planets. But most of the planets these red stars have, are really small earth-like planets. So it's great if we are trying to find earth-like planets, which in principle could have life on them. But at the moment what we are going after is trying to find giant planets because we think that those are much harder to explain and are a bigger mystery than just finding the planets.

Sarah Al-Ahmed: Is that what your research team was trying to accomplish here? Were you looking for this type of strange large planet, or did you stumble upon it in your broader research on this type of planetary system?

Shubham Kanodia: The group I'm part of, a large fraction of us focus on these giant planets around low mass stars. So we've coined the term GEMS, which is basically giant exoplanets around M dwarf stars. And I think, one thing to note here is that astronomers love their acronyms. So if you go through the astronomy literature, there's full of random jargon, which makes no sense. And it turns out these are just acronyms that some board astronomer has come up with or some proposal of paper. So GEMS is one of them. That was our attempt at calling these planets. So what we are doing over here is, we realize that now, and in particular this is the advantage of the recent space telescope that's NASA's TESS mission, so that's the Transiting Exoplanet Survey Satellite, which was launched a few years back and is pretty much looking at the entire sky every 27 days, or a patch of the sky every 27 days, but over a couple of years, it looks at the entire sky. And because it's looking at the entire sky, it's looking at millions of these M dwarfs. And this is pretty much the first time where we have a survey that's looking at so many M dwarfs, which is the only reason why we can find a reasonable number of these objects, these giant planets, which so far have been really, really difficult to find with smaller samples. So that's how we started getting into this. We realized that this opportunity with the TESS mission and the instruments we built at Penn State, to measure their masses and confirm these planets.

Sarah Al-Ahmed: I think to put this in context, it was maybe 30 years ago we were discovering the first exoplanets ever. And when I was getting my degree in astrophysics, I did my research originally in finding exoplanets. And we were literally doing it one planet, one star at a time with telescopes on earth. And then the Kepler space telescope launched in 2009, and completely changed the game. But we've had a recent explosion of exoplanetary discovery, specifically because of TESS. And it only launched I think five years ago, and it's literally created so much data that we're only just beginning to be able to come through it.

Shubham Kanodia: Yeah, absolutely. Yeah, like you mentioned the Kepler mission, I think that was one of the biggest revolutions of the past decade where it just said that just one patch of the sky can completely transform our understanding of what exoplanets look like, what their numbers are, what's the most common type of exoplanet. I mean, a slight tangent here, but after the Kepler emission, we realized that the most common type of exoplanet in the galaxy is a planet that in fact doesn't even exist in our solar system. It's the super earth mini Neptune class of planets, which are just slightly bigger than Earth, slightly smaller than Neptune, and something like that doesn't exist in the solar system. So it was a complete mystery as to how do these objects form, and why isn't one orbit the sun? But Kepler was looking at just one part of the sky up until the prime mission, and now we have TESS, which is looking at the entire sky, and it has its pros and cons, but I think for our project, the biggest advantage of TESS is that it's looking at so many M dwarfs that we can then follow up from the ground.

Sarah Al-Ahmed: So was your team just combing through a pile of data on a bunch of different planets of this type when you suddenly stumbled upon one that didn't seem normal?

Shubham Kanodia: No. The way we go about this is, we start by looking at, so there are certain planet candidates that are released by the TESS science team. So we go through some of those, but then we also in parallel have our own effort where we basically download all the TESS data, and try to find signatures of planets around M dwarf stars, so these are the red stars. And then we see the signatures which are really large. So if you have a big planet going in front of a small star, it's going to block a lot of light. So those are the dips we look for in the light from the star, these really massive, large transit depths. And then we find one of those that gets us interested, and we start curating a catalog of these which we slowly try to follow up, validate and see which ones of them are real planets. And it turns out that 50% of them, they're not planets, it's either another star, it's some other, what we call a false positive. So it's a false positive signal which we try to weed out and eliminate before whatever is left is then extensively followed up to characterize its planetary nature.

Sarah Al-Ahmed: What kind of follow up observations did you do to really make sure that this was a real planet and not just some really strange quirk?

Shubham Kanodia: Yeah, because it was so unexpected in some sense, that how is such a massive planet orbiting such a small star? And for reference, this star is something like 40% the mass or radius of the sun, so it's really small star, and the planet is slightly bigger than Jupiter. So what we started off with doing, is just getting some what we call reconnaissance radial velocity. So these are just a couple of measurements, but not necessarily at the highest precision. So we started off by getting a couple of them, which ruled out most of the astrophysical false positives. They ruled out that the object going around the star is not another star, it's not a massive sub stellar object. So it's a either low mass, what we call a brown dwarf, or indeed a planet in itself. So that confirms the fact that okay, now things are going to get exciting. So even if it's a brown dwarf or a planet, in both scenarios this would be quite a new discovery and would be a challenge to explain. And once we do that, what we try to do is, we also simultaneously try to confirm the host star. So because TESS is looking at the entire sky, it has really large pixels, just like the pixels we have on our phone, which are really tiny, the pixels on TESS are really large. So what we need to do is, we need to confirm that the transit we see or the dip we see is indeed around this star, the M dwarf, the low mass M dwarf. So we do that by trying to observe additional transits from the ground, using other facilities that we have access to, through our team, through our institutions and so on. And using a combination of the transits, the Doppler measurements and a few other things, that's how we confirm the planet nature and measure its mass and radius.

Sarah Al-Ahmed: It's pretty close to its star and fairly large. How long does it take to go around its star, and how many transits did you actually get to look at?

Shubham Kanodia: I think in the TESS data set, TESS looked at it for what is called two sectors, I believe. And then after we published the paper, there was also a third sector that had just been observed. And each of these sectors is about 27 days. So that pretty much matches the lunar cycle, which is not a coincidence, FYI. So we have two sectors of TESS data in publication. And the planet just takes about one and a half days to go around the whole star. Earth takes 365 days, but this object is so close to the whole star that it can go around the whole star complete like one year, quote, unquote, in 1.6 days. So it's a really fast orbit, but because the host star is so small, it can still do that without coming in contact with the star, and basically being blown away. So it takes about 1.6 days to go around the star, and I think there must be at least 10 to 12 transits in TESS, and then we obtain an additional four or five from the ground by using the different telescopes.

Sarah Al-Ahmed: So far we've just been calling this the exoplanet, but that's because its name is TOI-5205b. And as astronomers do, we come up with all these fun acronyms and nicknames, does your team have some nickname for this thing so you don't continuously get tongue-tied trying to say it over and over again?

Shubham Kanodia: Not really. I think by this point we've just resigned ourselves to our faith that we just have random four digit names for most of these objects. So this one is 5205, and each of the other ones we go after and confirm, is basically named after the host star. TOI stands for TESS Object of Interest, because it was discovered by TESS. I mean, it has some other names, but those are even uglier and much longer, so we just stick with the TOI.

Sarah Al-Ahmed: And people who are going to learn more about planets, even if presented with this data, you've got a giant planet really close to its star, it wouldn't be immediately obvious to them that this breaks our ideas of planetary formation. So as an expert, when did you realize that this world was so strange, and how did that impact your team?

Shubham Kanodia: As I mentioned, we started with the reconnaissance Doppler measurements, and then we got a few more. We had an estimate of its mass, so there was no ambiguity left than that this thing is indeed a planet, and in fact it's very close to Jupiter in its mass and radius. So we are talking about an object the size of Jupiter, the mass of Jupiter, that's orbiting such a small star, a 40% solar mass, in an orbit which is so close to the whole star. That was step one. Then we are like, "Okay, this thing exists, now let's try to understand how could it have formed." So what we did was, we used some planetary interior models, which basically tried to predict what would the interiors of these objects look like. And to be honest, we don't know that very well. In fact, we are just starting to scratch the surface quite literally and metaphorically when it comes to the gas chains in our solar system. And I think every time we send new probes, we understand that they're more complex and complicated than we'd ever imagined before. So our models for these exoplanets are also, I would say, are fairly simple in some sense, and I think really talented people are making great advances in that. But what we did is, we used one of these models to estimate what we call the heavy element content. So now another side about what astronomers is, we are very, very lazy. So when it comes to the universe, the universe is basically just hydrogen, helium and everything else, which is just plugged into one category, called metals. And our geologist friends, our planetary scientist friends hate us for that, when in fact this a running joke between us. But nonetheless, we use these models to estimate the metals in the planet, or the heavy elements in the planet, we use the terms interchangeably. And what we find is that if we run those models and do that, it turns out that the planet has a lot of heavy elements. It's really metal rich, compared to say, Jupiter. And that's puzzling, even just if this was orbiting any other star. But then when we think about the mass of the star and where these planets form, these planets form in these things called, protoplanetary disks. That's basically going back to how stars form, stars collapse. When you have a cloud of gas, it starts to collapse, and then in the middle, if it's a denser region, it gets hotter and hotter. If it gets hot and dense enough, you can start to fuse hydrogen to helium, and you basically have this balanced ball of gas where you have gravity and radiation, trying to fight each other. But then the rest of the material in the gas, in this molecular cloud which has gases, which has ices, carbon, oxygen and all kinds of fun things, they start to collapse into this thing called a disk, a protoplanetary disk. And these basically, as the name suggests, it's a disk, it's almost a two-dimensional, like a Frisbee, with some bits to it. And over the past few years we've been able to measure the masses of some of these discs. So using another telescope, and by we, I mean the general astronomy community, using the new telescope called ALMA in Chile, at the Atacama Desert. They're able to use this microwave telescope to actually measure the masses of protoplanetary disks. Not the same ones, but young protoplanetary disks, which should be similar. And I say should be similar, to the disk in which planets like these formed. And that's just because we cannot turn back time about three or four billion years ago to probably when these planets formed, so we have to do the next best thing, is that try to find similar disks. And what we see is that these disks, which we think are similar to the ones that in these planets formed, are much lower in mass than the planet itself. So typically, we think that these discs have to be 10 to a 100 times more massive than the planet, because planet formation as a whole, at least from what we think about solar-type stars, like the sun, is fairly inefficient. But what we are finding now is that either planet formation around these M dwarfs, especially when it comes to the giant planets, and that was one of the revelations of this paper, that it has to begin really early when the disc is much more massive. And when the disc is much more massive, if you think of a 2D Frisbee, it's more massive, but that's also because a lot of the material hasn't fallen into the host star. So it's more massive, it's more active, there's also more cloud of material and gases going around the star, which makes it much harder to study the disks. So the younger, earlier mass of disks are not as well understood. Typically, we rely on these protoplanetary disks instead. And I think what we are starting to believe now is that planet formation must begin a lot earlier, at least when these giant planets are concerned. Or the other option is, it still begins at when we thought it does, but it begins in disks that are really, really massive, and those types of discs must in some sense be anomalously massive, of which not a lot exist in our current studies. So those are the two interesting things that we realize as we studied this object.

Sarah Al-Ahmed: That is really interesting. And it sparks a question for me, if this planet has a high metallicity, what's going on with the star? Have we taken spectra of the star to see if that entire system is just basically higher in metals?

Shubham Kanodia: For the star itself, and I guess when it comes to M dwarfs, they're notoriously difficult to measure the metallicity for the host star. So we don't have a very strong metallicity constraint. I think what we have from the spectra is a very coarse estimate, which suggests that it's not likely super metal rich north, super metal poor, it's probably quite close to the metallicity of the sun, so we just call it solar metallicity. When it comes to the metallicity of the planet, we have again a very coarse estimate from these planetary interior models, which make a lot of assumptions. And we think it's on the metal rich side. I wouldn't call it super metal rich, but we think it's slightly more metal rich than Jupiter, with the caveat that there's a lot of uncertainty in this. So to answer the question, or how do we improve our metallicity estimate of the planet, I think that's where the next set of observations comes in, which we are very excited about and that's the James Webb Space Telescope. The James Webb Space Telescope, and I'm sure you've introduced this in another podcast, but it was launched I think, a couple years back, and it's basically going to revolutionize our understanding of planetary atmospheres, and is a branch of that leading from atmospheres to interiors and planet formation as a whole. So what we are hoping to do, and in fact lately just last week, in fact almost to the hour, is when we heard back the results from the cycle two JWST observations, and we found out that our observations had in fact been accepted. Over the next 12 months, we'll be studying this and six other stars, six other stars hosting giant planets around M dwarfs, and try to understand what the atmosphere looks like, and is it different? Is the atmosphere metal rich, is it metal poor? And what does that mean for the interiors of these planets? So that's going to be the next step. To actually answer the question, is this system anomalous in itself, or is it quite a standard system and our understanding is basically flawed?

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Shubham Kanodia after the short break.

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Sarah Al-Ahmed: I want to send a congratulations to you and your team for getting that James Webb Space Telescope time, because I know just hundreds of teams applied for that. And when I asked you to come on the show, it was prior to this announcement that you were actually going to be getting the telescope time, and I was wondering, so I'm glad you can confirm that. That's awesome.

Shubham Kanodia: Yeah.

Sarah Al-Ahmed: Is it easier for JWST to study this particular planetary system, because this planet is so close to its star and so large that it blocks out about 7% of the star's light when it passes in front of it. Does that allow us to analyze the atmosphere a little more easily?

Shubham Kanodia: It should make things easier, because now you have a short orbital period, or a short ear on the planet, which means that the transit or the amount of time it's blocking the host star is also fairly short, which makes it easier to schedule observations. It also makes it cheaper to do observations, because it just takes shorter. And then I think, I guess what I should mentioned earlier is the fact that it's such a big planet around such a small star, so it's blocking so much light. In fact, it's one of the deepest transits of all known planets, and that should make it easier to observe a JWST, and give us a much larger signal.

Sarah Al-Ahmed: That's so cool. I'm really excited to see what that does for our understanding of this planet. It would be really fascinating to find out that this world is not actually forbidden. That's what people are calling it in articles, the forbidden planet, but maybe planetary discs just start collapsing into planets earlier, and maybe larger planets form around these M dwarfs more often than we think.

Shubham Kanodia: Right. And I think that's the next part of our in parallel that we're trying to do, is just continue going through the TESS data, and that's the survey we are currently conducting. By systematically going through the TESS data, try to understand how frequently do these objects really occur. And there have been a few preliminary studies which indicate that they're fairly rare, and I guess that's not a surprise, but what we're trying to do is by looking at about a million M dwarfs, try to get a precise estimate on what the occurrence of these objects is. And then in parallel, we have some other follow up programs. For example, I mentioned the GWSD survey that just got accepted, and we are trying to understand the atmospheres from the ground. We are trying to understand the orbits of these planets. We are trying to see if we can understand the disks in which these planets form better, so we have a lot of parallel efforts. I think we've managed to get a few people excited to start looking into these systems.

Sarah Al-Ahmed: What would it tell us about exoplanets as a broader population and just planetary formation in general, if in fact planets started forming earlier on in the timeline?

Shubham Kanodia: The one advantage of these planets are, because they're so massive, orbiting stars that are so small, it's easier for them to break our current understanding. These aren't the most massive planets. They are massive Jupiters around solar-type stars as well. They're massive Jupiters around solar-type stars that orbit in similar periods really close to the host star. So in that sense this is not an anomaly, but I think the combination of factors, massive planet, low mass star, short orbital period, basically means that it's very easy for this to defy our current understanding. And I think that's the USP of this object, that because it breaks our understanding, that means that there's something new that's required. Either we need to stretch our theories, we need to improve our measurements, or basically it's going to be a combination of the two that we need better measurements and better models, and combine the two to see what is lacking in our current understanding. So I think, that's the key step going forward.

Sarah Al-Ahmed: Planetary formation is just such a cool subject, and we're only just beginning to study it, so there's a lot we don't understand.

Shubham Kanodia: Yeah. People have been studying this for decades, and I think some really, really smart and talented people, but it's a fairly complex problem.

Sarah Al-Ahmed: Yeah. And now we finally have instruments like TESS and JWST to help us answer these fundamental questions. So when planets form in these protoplanetary discs, they're very influenced by the star that they're forming around. Large stars necessarily put out way more light, and that light radiating into that proto-planetary disc can actually blow stuff away and change the way that planets form. So maybe it's easier to form these larger planets in closer to these smaller stars just because they don't have as much radiation pressure, as one example.

Shubham Kanodia: I think irrespective of your favorite theory of planet formation, so when it comes to giant planet formation, there are two possibilities. One is the core accretion model where you basically start off by building again, quote, unquote, metal core in the protoplanetary disc, and then once it reaches a certain mass, you just start eating up a lot of the gas in the disc very, very quickly. You can do that in a few thousand years, the gases secretion. The other model is gravitational instability, which is where you have a really massive disc, and before it reaches the class two or the protoplanetary disc phase, when it's still a proto star, because the disc is so massive, it becomes unstable and it starts to form these spiral arms, like we see for example in the Milky Way. The Milky Way has spiral alarms, so those spiral arms can sometimes collapse to form giant planets. So these two models in principle could form these planets if we provide them the right conditions. Now, gravitational instability cannot form planets that are very close to the host star, because it requires a disc to be fairly cold. So that would mean that the planet formed quite far away, and then somehow migrated all the way inwards and then stopped right there, and didn't just go further into the star and just get eaten up. Core accretion in principle can form planets that are so close to the star, but the problem has always been that there isn't enough material available to form these planets so close to the star. So there's the in situ formation model, which suggests that these gas chains could form basically where we find them right now. I think that just about explain some of the Jupiters we see around solar-type stars, because they have slightly more massive disks, but when it comes to this object, we are struggling to explain the formation of this planet from the disk as a whole. So what I mean by that is, if we take the entire protoplanetary disc, collapse it into one ball of heavy elements, it's still an inception by a factor of five or 10 to form this object. So it must be a really, really massive disc by maybe 10 to 50 fold. And even so, you cannot form this object where it's found right now, it has to have formed further out where there's a lot more material available, and then migrated inwards. The point you mentioned about the radiation from the star does play a role, but I think for the purpose of this planet, it's almost unambiguous. At least I don't see how it could have formed where it's found right now. It could have formed slightly closer in, because it's easier to cool down a disc around this type of star, than a more massive star. So in that sense, it could have been true that it's slightly closer in, but I think by slightly closer in, I mean instead of one and a half day, maybe 10, 15 year orbit.

Sarah Al-Ahmed: It's really interesting, because even in our solar system we think that, say Jupiter as an example, formed closer in to the sun, and then migrated outwards. And how these planets move from place to place and why, and how that has to do with their formation and how it impacts other planets in the system, is absolutely fascinating.

Shubham Kanodia: There's still lots of hypotheses as to how our solar system formed, and I think that's all they are, hypotheses. And we come up with a new one and it explains some of our observations, but then we come up with new observations which break the hypotheses, and I don't think we can really say we have a uniform theory that's universally accepted in terms of how the solar system formed, because we've just started to understand Jupiter's atmosphere slightly better, say the Juno mission, or its interior slightly better. And we see that it couldn't have formed where it's found right now. So it probably formed in a different location and then moved in, and then probably moved back out, and then did all kinds of weird dances with the other planets affecting them. So it's quite a mystery as to how these objects form even in the solar system, let alone outside. In some sense it's easier to study the solar system, because we are right here. So there's a lot more data, a lot more photons. On the other hand, exoplanets offer us a lot more statistics, because we can find thousands of them, where the solar system is just one system which somehow evolved and formed in a certain manner. The exoplanetary system and sciences allow us to probe a lot of different kinds of formation evolution scenarios.

Sarah Al-Ahmed: Are there other things going on in the solar system that could be affecting its position within the planetary disc with proximity to the star?

Shubham Kanodia: We start off by naming the object, the first object we find, b, or rather the first planet we find, b. And in this case it's a small b, because it's a planet, but we haven't seen any signatures or evidence of additional objects in the system. So there aren't any other transiting objects in our radial velocity document data. We don't see any other signatures of a massive companion. That being said, we have really just scratched the surface when it comes to probing the system. We don't have a long baseline to find objects that are much further away. So if there was something that's going around the same star with a period of, I don't know, say two years, we would not have found it in our radial velocity data. So there could certainly be something up there, even something that's fairly massive, but we just don't have the sensitivity to see it.

Sarah Al-Ahmed: That would make it even more complicated, because we're already struggling to figure out-

Shubham Kanodia: Absolutely.

Sarah Al-Ahmed: ... how this planet is that massive. If the disc was even more massive than that and there's another planet out there, that would just pose a whole host of other questions. What do you hope that we're going to learn about planetary formation just broadly, by continuing to study this planet and also the other ones that you're going to be studying with JWST?

Shubham Kanodia: The advantage of these objects is that they break our current understanding, they stretch our current understanding. They're pointing out the problem areas, and those problem areas don't just matter for planets around M dwarfs, or giant planets are not M dwarfs, but those are universal to our planet formation understanding. When it comes to M dwarfs in particular, I think it's extremely imperative to understand how objects form around them, because the high sensitivity that GWST has, are the best hope of finding bias signatures or signs of life or a habitable atmosphere, is going to be for planets around M dwarfs, and particularly the trap response system. So that's probably the foster child for JWSD atmospheric observations of small planets, because small planets, earth-like planets around solar-type stars, have much smaller transit depths, they're going to be harder to characterize. So most of the current small planet observations which you will see, will be for M dwarfs. So understanding planet formation around M dwarfs, is not just important from understanding planet formation in general, because they form 75% of the galaxy, but from a more practical point of view, to understand our observations for JWST and better inform them, we need to understand these objects.

Sarah Al-Ahmed: Yeah, I want to say, three months ago I had the opportunity to talk to Jacob [inaudible 00:37:01] Geiger, who's a member of one of the teams that's going to be looking at the TRAPPIST planets with JWST. And I cannot express how excited I am about this. I know that we're already beginning to look at these worlds, but that many earth-like planets around a star with the potential for being habitable is just absolutely stunning, and I hope at least one of them turns out some really cool results, they're not just all lifeless rocks.

Shubham Kanodia: That's the hope. I think lots of people have their fingers and toes and everything else crossed, hoping that one of them has an atmosphere that we can detect.

Sarah Al-Ahmed: Did you celebrate when you found out that you were going to be able to use JWST to actually follow up on your research?

Shubham Kanodia: Yeah, I think that was definitely a big surprise. And while we put our best foot forward, it was also a fairly ambitious proposal in terms of what we expected. It was a fairly large proposal. I think this was the largest proposal to get accepted in exoplanets this cycle. And we are trying to observe atmospheres for planets that have never been looked at before with either JWST or Hubble HST. So this was a fairly new region of parameter space that has not been looked at. And instead of starting with one, we said we'll look at seven of them, and basically try to understand them as a population, and then compared them with existing surveys and data. That was our goal. So it was definitely a surprise. I think we somehow managed to get it, and we are still surprised how, but we somehow managed to get the time, and now it's just a matter of getting the data and making the most of the data and seeing what we find there.

Sarah Al-Ahmed: It's a tricky thing, because there are so many topics that we want to know more about, and there's only so much JWST time before it literally stops working. So the entire astronomy community is just racing to get time on this telescope. I think even given that context, it makes sense that your team was granted that time, because there are just these giant gaps in our understanding of how planets form, and it will be really useful to study this. So makes sense to me.

Shubham Kanodia: I'm glad we could convince you.

Sarah Al-Ahmed: Well, thanks for sharing this with us, and I'm really intrigued to learn what this is going to tell us. It'll be a little while before you get all your results back from JWST, but if you find something really cool, I'd be very interested to talk to you again in the future, because this is only just the beginning of researching this population of planets, and as much as people want to call it forbidden, I think almost nothing is forbidden in space. Things are weird, and the more we learn, the more we stumble over things that we particularly don't understand. That's where the true revelations in science come from.

Shubham Kanodia: I mean, the first exoplanet was found in a location that we didn't expect, so that was in some sense forbidden. And then fast-forward 25 years, is number 5,000 of them and thousands of people studying them. So yeah, who knows what the next few years hold?

Sarah Al-Ahmed: I'm so excited for all the kids out there that are just getting excited about space. We're going to have access to all of this data. It's absolutely startling.

Shubham Kanodia: I think it's a very exciting time going forward.

Sarah Al-Ahmed: Yeah. For exoplanet discovery, for returning to the moon, for exploring other worlds with quadcopters, finally learning more about Venus, it feels like right now is just an absolute renaissance in astronomy. I'm also really excited too about the potential for sending a mission to Uranus, and hopefully someday Neptune. But as you said, most of the planets we're finding are these mini Neptune-type planets, and we don't even understand what's going on with the icy giants in our own solar system yet.

Shubham Kanodia: Right, just because they're so far away and it takes so long to reach them. I mean, most of our understanding of our solar system is informed by missions like Pioneer and Voyager, which if you believe was launched in the '70s and even before that. So there's a few decades, in fact many decades that have elapsed since then. And I think lots of people are hoping that we could convince the funding agencies to have the next flagship missions be to the icy giants.

Sarah Al-Ahmed: It's time, it's absolutely time. I'm happy that Voyager is still chugging along, and they only just recently managed to extend the lifetime on Voyager 2 by swapping around where all the battery power is going within that poor probe out there in the dark, far from earth and interstellar space, but Voyager can't be our only understanding of those planets forever. We got to go back.

Shubham Kanodia: Almost 50 years now since Voyager 2 launched. People are working on a lot of new, both ground-based and space-based missions. I mean, I think the next revolution will be from the so-called ELTs, the Extremely Large Telescopes, these really, really massive 30, 40, 25 meter telescopes that are currently being planned and constructed in different parts of the world, which will give us just so many photons from these stars that we can start with things that would happen unimaginable, even 10 years back. And then from the space, people are starting to work on the successor for JWST, like the Habitable Worlds Observatory, the HWO, which will basically be able to do the same things as JWST, but for solar-type stars, and actually hopefully find an earth analog. I mean, that will be a few decades out, but in the interim you have missions like the Roman Space Telescope named after Nancy Grace Roman, find here at NASA, which I think will also be a game changer. It's scheduled to find maybe thousands of exoplanets planets by itself.

Sarah Al-Ahmed: It's so exciting. Well, thanks for joining me Shubham, and I wish you and your team luck, because studying that many exoplanets with JWST, that's ambitious, but I believe you can pull it off.

Shubham Kanodia: Thank you. Thank you.

Sarah Al-Ahmed: I love it when people discover things in space that we didn't expect. The more you look into it, the more you realize just how wacky, diverse, and beautiful this universe really is. Now let's check in with Bruce Betts. He's on a hype train right now, because he's going on vacation to see his son's graduation. We had to record a week early, so I won't be able to share all the wonderful messages that people sent me this week, but that's okay. What's up Bruce?

Bruce Betts: What's up, is what's up.

Sarah Al-Ahmed: Truth. But what is up? I mean, what is in the night sky, man?

Bruce Betts: Oh, oh, oh, literally? We got Venus looking super bright over in the west. Love it, love it, love it. Check it out in the first couple hours after sunset, brightest dry-like object up there. Got Mars hanging out, getting closer to it. It's dimmer and reddish. When we go to the predawn, we've got Jupiter looking bright and getting easier and easier to see, but still low in the horizon, and Mercury, and it's hanging out in the predawn for a few weeks. It will be at its highest point on May 29th, so you can check that out. And Jupiter still above it, much brighter, and Saturn looking yellowish above that. So planets, planets, evening, morning, doesn't matter, you got planets to check out.

Sarah Al-Ahmed: I should be embarrassed to admit this, but I think Mercury is a planet that I've never looked at through a telescope.

Bruce Betts: It's a nasty little bugger, it's always staying low. It's just bopping around. It's all quick, like that Roman god thing that it's named after. The interesting thing about Mercury through a telescope, as I'm sure you know, is that if you have a big enough telescope to resolve it some, you see it go through phases just like Venus, but even faster. You don't see much of anything else, nor did anyone else for eons, until we started spending spacecraft. Although radar was a party, that was the first time we figured out that it was a three to two orbital residence, rather than one-to-one. Pretty exciting. That's just a bonus dip into random space fact territory. All right, we go into this weekend's space history. 2008, Phoenix landed on Mars, in the polar regions of Mars. Did some digging around, found some water, had a good time. We were involved with a microphone on that that never got turned on. It's a long sad story, but we have microphones on Mars getting sounds now. We don't, but NASA does, and it's very cool. Whew, that was a lot of tangents this show. Sorry about that. No, I'm not. All right, onto woof, woof, woof, random space fact.

Sarah Al-Ahmed: Was that you or your actual dog? I would believe that you would teach your dog to say, "Random space fact."

Bruce Betts: I would, I've tried. But speaking of dogs, funny I'd mention that, the Pluto moon, Kerberos or Cerus spelled with a K, because Cerus was already taken for an asteroid, but the three-headed dog from mythology, so they took the Greek spelling with a K. Here's the real point. Features on Kerberos are supposed to be named all about dogs from literature, mythology, and history. That's the good news. Bad news is to my knowledge, they haven't been able to resolve any features on Kerberos, but if they have, someone let me know. And so, we look forward to the day when we have the resolution. And in the meantime, start coming up with your lists from literature, mythology, and history. Okay.

Sarah Al-Ahmed: I'm going to have to think about this one. A whole world covered in cute dog jokes.

Bruce Betts: It's a small world. It's only five kilometers by 12ish kilometers in size.

Sarah Al-Ahmed: Still counts as one world.

Bruce Betts: All right, let's move on. Before I go off on any more tangents, let's find a new set of tangents for me in the trivia contest. So I asked you, what will the OSIRIS-REx mission being renamed when it starts its new mission to the asteroid Apophis, after it drops off its asteroid Bennu sample at Earth. I would ask you how we've done, but we have no idea because...

Sarah Al-Ahmed: Well, because we are recording this early, because Bruce is going on vacation.

Bruce Betts: Oh yeah, blame it on me.

Sarah Al-Ahmed: Totally your fault. But it does mean that I guess people might get a little extra leeway on me for sending the answer in on this one.

Bruce Betts: All right, well, you're the judge, jury and giver of gifts on this one. Do a great job, and you can go ahead and insert your brilliant words of wisdom right now.

Sarah Al-Ahmed: All right, well, the dice have spoken, and our winner this week is Laura Dodd from Eureka, California. The answer, and I love this one is, OSIRIS-APEX, which is short for Osiris Apophis Explorer. I love going from OSIRIS-REx to OSIRIS-APEX. Well, Laura, you're going to be receiving a Redsky Core rule book from Solar Studios, and clearly the dice rolls are already in your favor, because you won this week. So I'm sure it's all going to go well. Happy gaming.

Bruce Betts: Wow, that was great. Good job, Sarah, and congratulations everyone, way to go. And it turned out the answer, which I had no idea, it turns out to be OSIRIS-APEX, but then you told them that, short for Osiris Apophis Explorer, but then you told them that, but in case you didn't, I just told them that. Meanwhile, let us move on to our next trivia contest which is, what moons of planets in our solar system, so moons of planets, have average densities greater than or approximately equal to three grams per cubic centimeter, or 3,000 kilograms per cubic meter, if you prefer your pure MKS system. And there are, hey, I'll just say there are three of them. Tell me what they are. Go to planetary.org/radiocontest. So these are ones that have densities that are approaching more, that are rockier and not as icy and not as fluffy.

Sarah Al-Ahmed: Yeah. For people who remember back to high school chemistry class, one gram per cubic centimeter would be water, so definitely a more heavy moon. You have until May 31st at 8:00 AM Pacific time to get us your answer. And I've been collecting all these cool exoplanet posters that all the space events I've been going to for the last year or so. So I'm going to go into my collection and select three random exoplanet space posters, and send them to the winner this week.

Bruce Betts: Very cool. Random exoplanet space posters.

Sarah Al-Ahmed: But really though, I mean I love collecting all of those NASA artwork posters for each of the different planets. Every time they come out with a new set, I either try to get one in person or print them out to add to my collection, so I'm always happy to add to someone else's space poster collection.

Bruce Betts: Hi, everybody. Go out there, look at the night sky and think about graduating from college. And Kevin, ooh, that's a rather personal reference. Thank you and goodnight. Congratulations. Go Kevin, go.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week with the winners of our STEP grant, or science and technology empowered by the public, grant program. I'm going to be away on vacation as I adventure with my family and friends to this year's Electric Daisy Carnival in Las Vegas, Nevada. I'm so excited. But our friend, Mat Kaplan, the show's creator and the former host of Planetary Radio, is going to be back to share the grant winner's amazing project proposals. Planetary Radio is produced by the Planetary Society in Pasadena, California, and is made possible by our planet loving members. You can join us at planetary.org/join. Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor, Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. And until next week, ad astra.