Hello, and welcome to SETI Live. I'm your host, Beth Johnson, communication specialist here at the SETI Institute. Thank you to our viewers from around the world for joining us today. And please let us know in the comments where you are watching from. Also, welcome to listeners to the podcast version of SETI Live, which is available on most podcast platforms. Today, I have the pleasure of being joined by Renyu Hu from NASA JPL.
We are going to talk about a super earth called 55 Cancri e, which is about 41 light years away from Earth. And it's a pretty interesting world and it has an atmosphere and JWST has gotten to examine it. So welcome, Dr. Hu. That is kind of awesome. Renyu, how are you doing? Thank you for having me. It's a great pleasure to be here. Yeah, we're really, really glad to have you here. So let's kind of kick this off. So you have a rocky world with an atmosphere. Are we talking about an Earth 2.0?
Is this place habitable? Ah, yeah. Unfortunately, we're not talking about an Earth 2.0 because 55 Cancri e is much larger than Earth. For one thing, it's about two times the size, the radius of Earth, and about eight times as massive as our planet. But also, it's much hotter. It revolves around more or less a sun-like star, but it completes its orbits in only about 18 hours. It takes a year for Earth to do that. So it's much closer to its star, and therefore, it's so much hotter.
So this world is going around pretty quickly. It's close in. It's kind of super hot. How was it discovered? Yeah, so there's a, you know, we've been knowing about exoplanets in the past 40 years. So it's a young field. But 55 Cancri is one of the early discovery of exoplanets, actually. So it is initially discovered by looking at the wobbles of the star, 55 Cancri. So it's basically the 55th brightest star in the constellation Cancer.
So it's a fairly bright star, it's nearby, and it has been the target of looking for the small motion of the star caused by potential planets around it once this technique has been invented and applied to stars. So the initial discovery comes about the year 2000. And a few years after that, people are refining the characteristics of the planet. So apparently, the star has several planets. Some are giant planets, and 55 Cancri is the small one.
So scientists have been observing the wobbles of the stars through the Doppler shift that this wobble caused to the stellar spectrum. and they can back out the existence of this planet. So that's how the how we initially know about, you know, there has to be a small planet in that in around that planet, around that star. Sorry. So and around the year of 2010, We know the orbital period of the planet reasonably well. We have some ideas about how massive the planet is.
But at the time, using both Spitzer Space Telescope and a small space telescope called MOST, M-O-S-T, from Canada, People were able to catch what we call transit of the planet. That's another exciting aspect of this. So this monitoring found out that the planet actually, from our perspective, the planet pass in front of the star you know, every orbits.
So this actually gives us the way to, you know, to measure how large the planet quite directly, because, you know, when the planet pass in front of the star, it blocks part of the stellar light. So you cause a dimming in the light. So that's what we call transit as the phenomenon. So through this, then we know that the planet is transiting and we know, you know, pretty well that the radius and the mass of the planet. So that's really interesting.
So so the planet was originally discovered using the radial velocity method. Correct. So how how it affects. So you have your star, you have your star, which is going to be a little green screened. And then you have your planet, which is kind of going here. But it they tug on each other a little bit. And then, as you said, it bends the light, the atmosphere changes. Okay, so you've found a planet.
Everybody thinks it has an atmosphere, but no one is really certain what that atmosphere is or how thick it is or where it might come from. You have a very hot world. I'm guessing, and I'm not guessing. This is in the press release, people. I don't guess. But the planet is tidally locked. So we're saying that it's so close in that the same side of the planet is always facing its star, correct? That's what's most likely to be.
And I just want to say that the initial discovery, while we know the existence of the planet, we know that the planet, you know, we measure the mass of the planet by radio velocities, and we know that the planet is transiting. So the question at the time, you know, then there's this immediate question whether the planet has an atmosphere. It's just because that the precise measurement of the mass and the radius, which is actually quite an achievement by themselves, right?
This is a planet around another star. That points to a density of the planet that most of the planet should be rocky or it should be like Earth has a rocky surface. mantle or core. So it's more or less like a rocky planet within the error bar of those measurements. So then the question becomes, now that we have a massive rocky world, very hot, whether this rocky world would have an atmosphere. There are some initial indication that it has one.
For instance, just by looking at the mass in the radius, it is actually slightly larger than it would be if it's just truly 100% rocky and without any gas. And by slightly larger, I mean it's quite a small difference here. And you can explain this by, for example, having a particularly small core. And it's not definitive evidence that it has an atmosphere, but it's an indication that an atmosphere could help explain the Mach-Sander radius.
And also, you know, around 10 years ago, a group of scientists, including myself, have been using the Spitzer Space Telescope. And at the time, we don't have JWST. So we have Spitzer in space and that can take precise measurements of this transit phenomenon. in the thermal infrared. So that's exactly what we did. And we actually look at what we call the secondary eclipse. So the planet pass behind the star. So there's another geometry.
It's not just the planet pass in front of the star, but the planet at every orbit also goes behind the star once. So when that happens, the light from the planet would be blocked momentarily by the star itself. So that allowed us to measure the light from the planet directly. So we did that using Spitzer. So we got the secondary eclipse and using that we measure how bright the planet is in the mid-infrared wavelengths, which is sort of translating to how hot the planet is.
So that gives us some ideas of the temperature on the planet, which is at the time also consistent with the existence of an atmosphere. So those are some early indications of, you know, we might have an atmosphere on this rocky world. All right, and I want to talk to you some more about this atmosphere and what it means, but I want to welcome in people from where they're watching. We're already kind of getting a pretty global audience here.
So I want to welcome in people so far from New Zealand, Georgia, I'm guessing the state, not the country, Mauritius, New Jersey, Scotland, and Brazil. So welcome in, everybody. Thank you for letting us know where you are at, and thank you for joining us. So Renu, There's an early hypothesis that this planet has an atmosphere. You've now gotten to look at the atmosphere using JWST, of course, which means a bigger, newer infrared telescope.
What is the evidence that JWST provided that either proved or refuted this hypothesis that 55 canker E has an atmosphere on it? Right. Yeah. So, you know, when I... When we asked to think about observation plans for JWST, the 55 Cancri, it was actually the first come to mind. Because at the time, there was, of course, the atmosphere hypothesis. But there is another hypothesis that the planet could just not have an atmosphere or have a, because it's so hot, over 2,000 degree Celsius hot.
So it can have a vaporized rock atmosphere, very alien to us, but not volatile rich atmosphere. So both of these scenarios could explain the existing data at the time. So that's why we, want to use JWST to find that out. As you said, the JWST is larger, it has a six-meter telescope, but it also has a nice set of instruments that provides us the ability to measure the light from the planet all the way into thermal infrared at a wide wavelength coverage.
And that turned out to be essential for us to first confirm whether the planet has an atmosphere, and second, obtain some initial information about what the atmosphere may be made of. And so when you say volatiles, I just want to make sure that the audience understands kind of what you're talking about. What is the difference between sort of like a vaporized rock and volatiles? So what are we saying when we make that designation?
Yeah, so I guess what I mean by that is the volatiles that is sort of familiar to us. There will be things that will be in the gas phase at room temperature. So it will be the element, it will be the gases made of carbon, oxygen, nitrogen, sulfur, for instance, water, CO2, methane, et cetera. So we do think that the planet shoe form in the rocky planet shoe form with these ingredients.
But, you know, given the fact that the 55 can create that particular planet is just so close to this whole star and it's constantly irradiated by its star. So it could lose the initial carbon oxygen, you know, nitrogen in domen. And it's actually quite exciting scientifically to find out whether it has lost all these quote unquote volatiles, or it retains some of it and become an atmosphere. And what did you find out using JWST? So what do we have for this atmosphere? What's it got? What is it?
Yeah, so we took two measurements. So one is using what is a NIRCAM. It's the name of the instrument that operates between four and five micron. And the other is MIRI, the mid-infrared instrument that operates between 5 and 12 microns. So together, we get a spectrum of the planet. So basically, we measure the life of the planet from 4 to about 12 microns. So that's unprecedented wide wavelength coverage. So what do we learn from it? So first of all, we measure the life from the planet.
And then, therefore, we can back out how hot the planet is. So the JWST measurements has high fidelity confirmation of The planet's temperature has to be lower than what it would be if it doesn't not have an atmosphere. So this is quite a long statement. Just let me unpack it a little bit. So without the atmosphere, we expect the surface of the planet to be around 2,500 Kelvin. So it's about 2,200 Celsius. And you have to... Excuse me for not giving the Fahrenheit number. Don't worry about it.
Go with the scientific explanation. So what we measure instead, the temperature on the surface of the planet is only 1,800 Kelvin. So that's quite a difference from what it would be if it does not have an atmosphere. So why the atmosphere would make it appear to be colder? So the atmosphere is actually very good at transporting heat from the side that the planet is facing the star to the side of the planet that is not facing the star.
So if you have an atmosphere, the heat from the star will get transported more efficiently. So the side that is facing the star will just appear to be colder. So that was predicted by all the models. And that's what we see exactly. And so that by itself is a very strong indication that there has to be an atmosphere on the planet. And additionally, because we have the wavelength coverage and we split the light into chunks in this wavelength, so therefore we've got a spectrum of the planet.
that spectrum seems to contain some modulations. It's not a straight line. It has some up and downs. And this spectral modulation is most consistent with the absorption of gas in the atmosphere and the absorption of carbon monoxide or carbon dioxide in the atmosphere. So that's another independent evidence that suggests that this is a volatile rich atmosphere. I want to talk to you some more about what this means for our solar system. Because from what I'm hearing, this is not a habitable world.
This is not some place that we would expect to find life. So, you know, of course, here at SETI, we love all of the science, but we're kind of focused on life. So I'm going to ask you a little bit more about that as we go. I'm going to welcome in a few more locations here. We now have New York. We have Ohio, Ontario, Canada, and Australia. So we added another bit of the world going on here. All right. Renu, the atmosphere is volatile, but the planet is super hot.
One of the things that you guys talk about in the press release and the paper is that it's probably covered in magma oceans. And of course, this leads me to ask you, how does this particular finding, what does it mean for understanding our own solar system? How do we relate this back to the beginnings of our planet itself? Right. So as you said, you know, the planet itself in 55 Cancrii itself is not habitable because it's way too hot and there won't be conditions for liquid water, for example.
But the fact that we found an atmosphere and this atmosphere, you know, volatile rich, probably rich in carbon monoxide and carbon dioxide and probably have other gases. And because of the high temperature, this atmosphere will be in contact with a molten lava surface. The scientific term for that is magma ocean. And then the atmosphere, you know, the gas actually dissolve into the magma ocean. So it's actually a nice balance, the system between the atmosphere and that magma ocean.
The fact that we have you know, witness a system like this is actually very exciting for understanding the evolution of rocky planet in general that includes the rocky planet in the solar system. And the reason for that is the scientists think that both Earth, Venus, and to a large extent, Mars, have experienced this magma ocean phase when they're young. When this planet was just formed, the planet would have some strong internal heat that actually melt the surface.
So at the initial phase of these rocky planets, there's a brief period where it's to some extent similar to 55 Cancri where it has a magma ocean, it has a volatile atmosphere in exchange with this magma ocean. And what's more important is that the outcomes of these rocky planets' evolution, whether a rocky planet become Earth or Venus, for example, what's going on in that magma ocean phase, even though quite brief, has strong bearings on the outcomes.
So before, we try to understand this magma ocean phase, the interaction between the atmosphere and the planetary interior, the retention of these volatiles against all the other forces, for example, bombardment from the star, et cetera. We try to understand this mostly from a theoretical perspective in order to understand the evolution of the rocky planet in the solar system and the condition for the emergence of the habitable worlds.
But now, because we have exoplanets, we have these planets that are so hard and it's permanently in this magma ocean phase, then we can use astronomical observations to observe this planets in the magma ocean phase. So we sort of can use observations to catch this process in action so that this will be helpful for us to validate the models, to refine our models and understandings of the evolution of rocky planets in general.
That's really fascinating and exciting to be able to apply these exoplanets to our own past and have a way of sort of getting a glimpse into what the early solar system might have been like for us as well. I want to ask, we're getting a few questions from our audience in, and there's a few that I want to ask you. So I'm going to take a moment and kind of go through some of these. Jason would like a little bit more clarification on the planet.
So can we kind of go back just to sort of reiterate what this planet is? What does a super earth mean? And, and what, there's also a bit of a reference to the Goldilocks zone, which I know is a term we're all kind of done with, but how does, you know, what is this planet? What is a super earth? And, and, you know, how does that, how do we classify these worlds? Right. So for 55 Cancri e, it's, it's a larger planet than earth. It's about two times earth size and eight times earth mass.
And, its host star is more or less sun-like, but if the planet 55 Cancri e were to be in the solar system, it's a separation from the star. It's only 1 25th of the separation between the sun and Mercury. So it's actually in a very close in the packed orbit. And therefore it receives a ton of radiation from its star and it's very hot. So it is not in the Goldilocks zone, however you define that term. But it's a hot, large, rocky planet.
Okay, so to sort of sum that up, so a super Earth, it's not about it being Earth-like, it's about it being more Earth-sized. And super Earth is sort of how we qualify these planets that are about, you know, one and a quarter to two times greater than Earth, but not as big as Neptune. And there's actually a gap in between, not relevant to today's topic, but there it is. So... Another question, and this comes up a lot, so I want to bring this up.
Are you using artificial intelligence models at all to analyze this data, to detect other planets? Is it enhancing the discovery process? If you are, what's the situation using artificial intelligence, machine learning, large language models, those kinds of things? So in this particular study, we did not use advanced artificial intelligence models, for example, neural networks in the study.
On the other hand, as you can imagine that the astronomical observations, the raw data comes with a lot of impacts from cosmic rays, the instrument noise, and all of that. So we have used substantial data science techniques and a variety of statistical techniques to measure these systematics and to remove them. Okay. So it does enhance, you know, if you're, if you're using them, it does sort of, it enhances your ability to weed out some data. So that's, that's always really good.
One more from our audience. Does this exoplanet, this is Marcus, does this exoplanet experience tidal friction from its host star? Do we, do we know that yet? We don't. There are theoretical predictions about to what extent you will have tidal heating on this planet. There is a very tight constraint from past observations that what we call the orbital eccentricity of the planet has to be very small. So the planet itself is in a circular orbit.
orbit, which sort of makes sense because it's a fairly mature system. The age of the system is on the orders of billions of years. If there will be eccentricity and tidal circulation, then that should have already happened. And we're looking at the end state of the evolution here. So yeah, there are some estimates of the how much the tidal friction and other impact, the tidal impacts will still remain on the planet. Okay. Well, Renu, thank you so much.
We're getting ready to wind down here and I have my last question for you. So it sounds like to me that you have been studying this particular planet for a very long time. Now that JWST has looked at it and you have some idea on the atmosphere, what's next for you with this planet and what's next for you in general as far as research goes? Are you going to continue working on observations of 55 Cancri E?
Yes, so we're very excited about this discovery and we're very pleased that the JWST is giving us this opportunity to find out about these planets and their atmospheres. So for 55 Cancri, we do want to gather more observations and to find out, for instance, how large the atmosphere is.
So right now we don't know exactly whether it's you know one bar or like the size of our atmosphere or you know much larger like a hundred bar for example um so we believe that more observations should be able to tell uh tell us answer about that question and we also want to you know get a better handle on the composition of this atmosphere. Because this will tell us the specifics of this atmosphere magma ocean interaction, which is very important for our general understanding of rocky planets.
And we also would like to, perhaps in collaboration with colleagues in astronomy, to expand the studies into other potential rocky planets. We do want to understand, for example, you know, whether the planet has atmosphere, what planetary parameters control these things? You know, whether it's the size of the planet, does larger planet more inclined to have you know, maintain an atmosphere or the other way around.
Or, you know, we want to see whether a hotter planets or the cooler planets more likely to have this kind of atmospheres or secondary atmospheres. So we want to expand the study into a group not just 55 can create but a group of planets to answer these questions. I think that's great. I love how I feel like we're all living in some amazing times when it comes to planetary science. We've gone from we only know of these planets in our solar system to, oh, look, we found planets around other stars.
They're weird. They're strange. They're not what we were expecting. we're not finding a whole lot of solar systems like our own. What is this about? And now we're getting really kind of into that with JWST and being able to see what atmospheres are composed of. I feel like we're getting into the nitty gritty now of how do planetary systems form and evolve. And so it's really an exciting time in research. I'm saying that this is great. So congratulations on this paper.
Congratulations on hitting the point where you can say, no, it's got an atmosphere. Yes, yes. So Renyu, thank you for joining us. Very appreciative of you taking the time today to talk to us and our audience. Thank you everybody for watching today. This is the SETI Institute and we are a 501c3 nonprofit looking for the answers to, you know, How did life form in our solar system? And is there more of it out there? And making sure that we talk to all of you about that.
If you're interested in supporting, please go to SETI.org slash give now and make a small contribution to help us keep bringing these outreach programs to you. Thank you again, Dr. Renyu Hu, for joining us from JPL to talk about 55 Cancri E and its rocky world with an atmosphere. So hopefully when you have more results, you will come back and tell us about those too. I'd love to. And thank you very much for having me. And it's great to be with you all. Thank you so much.
And thank you again, everybody. We will see you next week. We have two streams, Wednesday morning and Thursday morning. So keep an eye on those schedules. And we've got some more interesting stuff. I think there's a black hole and some greenhouse gases. So join us. It's going to be pretty cool. All right. Thank you, everyone. Have a great rest of your week.