Planetary Radio • Apr 19, 2023

Under Alien Skies with Phil Plait

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Phil Plait

The Bad Astronomer, science communicator, and author

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Sarah Al-Ahmed

Planetary Radio Host and Producer for The Planetary Society

Phil Plait, the Bad Astronomer, joins Planetary Radio to discuss his new book, “Under Alien Skies: A Sightseer’s Guide to the Galaxy.” The book takes the reader on an imaginary journey to 10 spectacular locations in space and shares the strange and beautiful experience visitors would have if they could witness it for themselves. Stick around after the break for What’s Up with Bruce Betts and a chance to win a copy of “Under Alien Skies” in our space trivia contest.

Under Alien Skies book cover
Under Alien Skies book cover Under Alien Skies: A Sightseer’s Guide to the Universe by Phil Plait, the Bad Astronomer, was released on April 18, 2023. The book takes the reader on an imaginary journey to 10 spectacular locations in space and shares the strange and beautiful experience visitors would have if they could witness it for themselves.Image: W. W. Norton & Company

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Trivia Contest

This Week’s Question:

Where in the Solar System is the best place to go if you want to find sulfur dioxide frost?

This Week’s Prize:

A copy of “Under Alien Skies: A Sightseer’s Guide to the Universe” by Phil Plait.

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, April 26 at 8am Pacific Time. Be sure to include your name and mailing address.

Question from the April 5, 2023 space trivia contest:

On what planet was the city Freehold located in the lore of the Destiny video games?


In the lore of Bungie’s Destiny 2 video game, the city of Freehold was located on Mars.

Last week's question:

What was painted on the front of Yuri Gagarin's flight helmet and why?


To be revealed in next week’s show.


Sarah Al-Ahmed: Under Alien Skies. This week on Planetary Radio.

Sarah Al-Ahmed: I'm Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our Solar System and beyond. Are you a fan of The Bad Astronomer? We're about to dive into Phil Plait's brand new book, Under Alien Skies: A Sightseer's Guide to the Universe. We'll bring you some of the latest space news from around the globe, and as always, we'll check in with Bruce Betts for our what's Up segment and a chance to win a copy of Under Alien Skies in our Space trivia contest. Congratulations to the European Space Agency on the successful launch of the Juice mission. The Jupiter Icy Moons Explorer is now on its way to Jupiter. It launched at 5:15 AM Pacific Time, that's 12:14 PM UTC, on April 14th, atop an Ariane 5 rocket from the European Spaceport in Kourou, French Guiana. The mission will explore Jupiter and three of its largest icy moons, Europa, Ganymede and Callisto. The spacecraft will arrive in the Jovian System in 2031, so we're all going to have to be patient. But when it gets there, it's going to spend two and a half years orbiting Jupiter and conducting flybys of these icy moons before it settles into orbit around Ganymede and spends at least nine months there. We'll give you all the details next week. When I speak to Olivier Vitas, project scientist for the Juice mission. In other space news, SpaceX says that their Starship vehicle is ready to fly. The new spaceship, which SpaceX hopes to someday carry astronauts to Mars, now awaits the US Federal Aviation Administration's approval for its first uncrewed launch test. With the combination of the super heavy rocket first stage and the star ship's upper stage, this would be the largest and most powerful rocket ever launched. NASA has funded its latest batch of far out ideas. The Innovative Advanced Concepts Program funds futuristic projects that may have the potential to revolutionize space exploration. This year's winning projects include a quantum radar system for remote sensing, a plan to pulverize incoming asteroids, an extremely high-speed propulsion system driven by radioactivity and so much more. And you'll love this one. The latest, most detailed global map of Mars ever created is now available to the public. You may have caught Bruce Betts me talking about this map in last week's episode because it's awesome. Stitching together 110,000 individual images taken over six years by the Mars Reconnaissance Orbiter, scientists at Caltech created a 5.7-terapixel map of Mars. You heard that right, 5.7-terapixels. If you play around with this thing, you can actually zoom into a resolution of five meters per pixel. And lastly, if you haven't had a chance to check out the new picture of Uranus from the James Webb Space Telescope, it's our Wow of the Week in the April 14th edition of the Downlink, our weekly newsletter. The Downlink includes links to all of these stories and so much more. You can read it or subscribe to have it sent your inbox for free every Friday, at Our guest this week is Phil Plait, also known as The Bad Astronomer. Phil is here to discuss his new book, Under Alien Skies: A Sightseer's Guide to the Universe. It takes us on a tour of the cosmos like never before. As an astronomer and science communicator, Phil has captured the imaginations of space enthusiasts for years, and his latest work is no exception. Under Alien Skies transports the reader to 10 of the most spectacular sites the universe has to offer using the latest scientific research and Phil's own creative flair. Phil has authored a couple popular science books, namely Bad Astronomy and Death From the Skies. He's also appeared on numerous TV shows like The Universe and How the Universe Works. I'm personally a big fan of his work on crash course astronomy. Phil's last appearance on Planetary Radio was back in 2011, so it's wonderful to have him back on the show. Thanks for joining me, Phil.

Phil Plait: Thanks for having me on.

Sarah Al-Ahmed: I'm really excited to dive into your new book because I had a wonderful time reading this and I've spoken with several friends and other Planetary Society members that were also really happy to hear that you have a new book coming out.

Phil Plait: Well, that's terrific. I love hearing that, of course. But I think is there some sort of rule that if your CEO is blurbing the book, you have to read it. It's in the contract, right?

Sarah Al-Ahmed: Its in the contract. Anything Bill Nye says something good about I have to read.

Phil Plait: Yeah. I emailed Bill a few months ago asking him if he could blurb it. And I've known Bill a long time and was science writer on his show, Bill Nye Saves the World. So it seemed like kind of a no-brainer to ask him to do it. And he gave me a nice blurb. That was lovely.

Sarah Al-Ahmed: He's such a nice guy. It's wonderful working with him. But your new book is called Under Alien Skies: A Sightseer's Guide to the Universe. And right out the door, I have to ask, is this a reference to The Hitchhiker's Guide? And why did you do that?

Phil Plait: It didn't mean to be, and it wasn't really intended to be because of course The Hitchhiker's Guide is a useless tome that'll basically just get you killed. If I recall correctly from reading all the books back when I was in high school and college. And this one also won't help you stay alive, I think if you actually visit these places because if you go anywhere but Earth, you're going to be dead within seconds. However, if you do visit these places and you want to kind of know what you're in for, if you want to have the experience of visiting the moon or Saturn or something like that, that's what I was trying to do. And the trend these days is to always have a subtitle with a book. You can't just have a book titled this, it has to be this, colon, that. And I was trying to think of something to put in there and I thought, well, it is, it's a sightseer's guide to the universe. It's what it is. Instead of just writing a sort of straightforward science book saying, "Here's how black holes work," it was more like, "You are in a spaceship, you are passing by a black hole. What do you see? What do you experience? What happens when you do this?" And that's when I realized this really is more like a guidebook than it is a descriptive astronomy book.

Sarah Al-Ahmed: And I really like that mechanic because as you said, there's many books you can pick up. It'll just tell you what a black hole is like. But getting those little story blurbs in between really kind of made it feel fun and interactive, a little bit halfway between an actual novel and a science book. Why did you choose to write it that way?

Phil Plait: In my last book, Death From the Skies, apparently also, I'm under contract to have the word skies in all of my books, and that's my own fault. It's the way the titles worked out. But in Death from the Skies, I wrote about all the different ways that the universe can try to kill us. So asteroid impacts, solar storms, roving black holes, whatever. And I thought it would be fun to write a short vignette in the beginning of each chapter, sort of describing how these events would unfold. That's sort of a mechanical idea, I realized would work really well for this book too. And I talked to my publisher about it. Do I really want to have a format that's similar to the last book I just wrote? And she said, "Well, you wrote that book 15 years ago." I tried to write a book once a decade or so. In this case, because the point of this book is not simply to describe things, but to actually experience them and say, "You are here," starting each chapter with a sort of science fiction vignette, which is how that works, where you are standing on Mars and this is what's happening around you. I really wanted to immerse the reader in this environment. And as someone who's always wanted to write science fiction but has never really, I've just been too lazy, I've never been motivated enough to actually sit down, write stories and send them to a publisher and get rejected. I felt like it would be more fun just to write really short vignettes that are just a few paragraphs long, just enough to give you a taste of this sort of thing. And I love reading that sort of stuff. And if you write the sort of stuff that you love to read, I figure that's going to connect with the reader as well. So that's why I did that.

Sarah Al-Ahmed: I think too, it makes it a fair bit more accessible to people. It can be a little daunting to try to dive straight into a book that's solid science. But this gives you a good way to put yourself in the shoes of someone on that world and then figure out how we learned the things about this that you could write these chapters. So I found that to be a really kind of useful and fun mechanic. I know you talked about this a little bit in the preface about how you basically wanted to explore these places, but we're unable to, we don't have these spaceships. So all you really have is that spaceship of the imagination. Is that why you ended up writing this book? Is this just kind of an homage to your childhood love of wanting to stand on these worlds?

Phil Plait: Sure. Ever since I was a little kid watching, gosh, Lost in Space and Star Trek and Space 1999, in the movies and all of that, I loved science fiction. And when I was a kid and I wasn't that discerning, just the fact that they were in rockets going to other planets and there were weird aliens and stuff, that's all I cared about. And then as I got older, I was more concerned with things like plot and character and development of themes. But the idea of going to these other planets, that was something I really, really, really loved. And that was part of the motivation for this. And the other part was a little more practical, as an astronomer myself and professional and amateur astronomer, I did this for a living, but also, I have a telescope. I take it out when I can and I've done that my whole life. When I was younger, I used to take my telescope out, especially on Halloween. And let me tell you, if you're an amateur astronomer and you want people to look through your telescope, Halloween night is the best time to do it because you have a lot of people coming to your door, typically. I would do this, I would set up my telescope in my driveway, point it at something easy like Jupiter or Saturn. Saturn was always a favorite. And say, if you want a piece of candy, you got to look through the eyepiece and that way you can really get people interested in this kind of stuff. And when I did that, especially with Saturn, a lot of the times the reaction I would get was they would kind of look up at the sky and then look down and then look down the telescope tube, "Are you holding a picture up?" Because it looks so beautiful and perfect and just like Saturn, right? And they would ask me a lot of the times, "Is this what it would look like if you were there?" That was such a common question. The answer to that depends on the object. And with Saturn, the answer is yeah, pretty much what you see through a telescope. Although, when you're there, you see better. But when it comes to a nebula, gas cloud, the answer is no. The the physics are a little different than you might expect and what you see is not what you get through a telescope or taking photos that you see online or something like that. And I wanted to, in this book sort of answer that question. That was actually the motivation. If you said, "Why do you write this?" It's because I wanted to answer this question for people, what did these things look like if you were there? But like I've been saying, it's not just what it would look like, it's what it would be like if you were there. And that's something I love. I love to think about this sort of thing, let my imagination run wild, but also to let it be informed by the best science I could find. And that's why I wrote this book.

Sarah Al-Ahmed: And you did a fantastic job of it because as I was reading through, it not only gave the obvious details about these locations, but also really nitty-gritty things that I've been asked maybe once in a lifetime. As an example, in the first chapter on the moon, you talk about the location of the earth on the sky and how it would hang generally in the same area because of the way that the moon rotates and all those things. But later on in the chapter, you go into the details about where you could stand on the moon, where the earth was just close enough to the horizon that you might see at horizon set because of that vibration. And those are the questions that people think about, but are really hard to get answers for on the internet unless you deep, deep dive. So I really appreciated that those kinds of details were in there.

Phil Plait: Well, thank you. It is funny you mentioned that specific thing because I've always been told when I was younger, they say, "Well, the moon spins at the same rate it goes around the earth. And so we always see the same face." And if you were standing on the moon, the earth would look like it was always in the same spot of the sky, no matter when you look. It's always in a certain direction. And that's not true because the moon's orbit is elliptical and it's tilted a little bit with respect to the earth's equator. And so sometimes when it's at the nearest part of its orbit, perigee, when it's closest to earth, the orbit and the spin don't line up exactly right. And we can see a little bit past what we normally can see on one side of the moon, and that's true east, west, north, and south. And so we actually see, it's a little bit more than 50% of the moon surface. And what that means is if you're standing on the moon, the earth is moving around in the sky. And I thought, well, how much? Probably not that much. And so I started researching this, looking it up, and it's like, I can't find the answer. I don't know what this is. And it was ridiculously hard to try to find what is the motion of the earth in the moon's sky. I wound up using planetarium software, Stellarium, which is online, it's wonderful. If you don't know Stellarium, it's a great piece of software. It's free. There's a web version and an app and you can use it to put yourself on the moon or just to see what the sky looks like. There's a ton of stuff like that. And the earth made this enormous ellipse on the sky, so many, many degrees across. And I thought, really? That can't be right. And then I sat down and did the math. I didn't want to do the math because the math is hard, it turns out. But then I started drawing diagrams and everything to myself and I thought, oh my gosh, this really is a much larger movement than I expected. And then it occurred to me, well, if you're on the, quote, unquote, edge of the moon, the part of the moon where it's right on the limb of the moon as we see from earth, then yeah, you're going to see the earth rise and set over the course of a month. It seemed obvious to me when that thought came up. And it's like, but why doesn't anybody ever talk about this? So I wrote about it.

Sarah Al-Ahmed: Yeah, that's the reason I brought it up actually, because I've got a full degree in astrophysics and had no real understanding of this until later, someone walked up to me and was like, "No, that's wrong." And I had to actually sit down and think about it. So I'm really glad that people are going to be able to read about it because that's one of those moments where it seems so obvious in retrospect, but really not easy to find answers to that. And this book is so full of all of these little gems.

Phil Plait: Thank you. And I was terrified to write half of them because I thought, if I get this wrong, I am never going to hear the end of it. And for a lot of the chapters, it was qualitative work. It wasn't that hard to say, what color is the sky of Saturn if you were inside the atmosphere? And things like that, that wasn't so bad. But a lot of it was quantitative. I had to work out a lot of numbers and I took a lot of notes and then put them aside, and then a week later started again from scratch without looking at them and then compared them. Because I was terrified I was going to get something wrong. And in fact, for one chapter about a planet around a binary star, I was thinking, well, if you're on Tatooine, you're standing there next to Luke Skywalker and you're watching the twin suns setting. If they're eclipsing binaries, if these two stars are about the same size and they orbit each other relatively rapidly, one is going to block the other one. And when that happens, half of your light goes away, half of your heat source goes away in the sky. How much does the temperature drop? And I started doing the math and I got a number that didn't make any sense. And it was really bugging me. And then I realized, oh, I'm starting from the wrong equation. I'm starting from this complicated equation that tells you the temperature of a planet given how hot the star is, how big the star is, how far away the star is, how big the planet is. There's all these different things that go into it. And I realized that's not the right equation. I had to step back and derive that equation from scratch. And it's like, oh God, I'm in grad school again, having to figure this stuff out. And then I got an answer that made a lot more sense to me. And it was interesting to have to not just look at the math, but think about what that math is telling me. When you do that, it leads you to thinking about, I don't want to say trivia, but factoids, these details like the earth rises and sets on the moon if you're in the right spot, or here's how quickly the temperature will drop on a planet, or how many stars, if you're in a planet orbiting a star in a globular cluster, how many stars will be bright enough to cast a shadow? Or how long can a planet orbit a star when there's so many other stars close by and their gravity is affecting the orbit of that planet? I read a lot of papers and it kills me that if I were to print these papers out, I'd have a stack a meter high on my desk. And yet, for a lot of that, it's a line in the book. It's like, there's one thing I'll say in the book and it's like, yeah, I had to read four papers to get that line right. So there's a lot of that stuff hidden in the book, and I learned a lot writing this.

Sarah Al-Ahmed: How long did it take you to write this book?

Phil Plait: About a week.

Sarah Al-Ahmed: About a week?

Phil Plait: No. When I wrote Death from the Skies, I did not have a full-time job. I actually quit my full-time job to write the book, and it took about, I think 10 months. This one took two and a half years, all in all, from sitting down and saying, okay, I'm going to start writing this thing to finishing, it was about two years. A little bit more maybe.

Sarah Al-Ahmed: It's interesting because I was trying to think about that timeline because there are some events that are talked about in the book that are actually fairly recent, and this was the thing that really sparked it for me. In the chapter about asteroids, you actually take the time to talk about the DART mission. That was just, it feels like cosmically yesterday. So did you have to add things into this book after you were already done writing it, or how did that happen?

Phil Plait: Yeah. Another terrifying thing about writing an astronomy book besides worrying about all the math and making sure you get everything right. And I'm not guaranteeing I got everything right, let me say that too. There are bound to be errors in the book. That always happens, and sometimes you smack your head after it publishes. But one of the things you have to worry about is the world catching up with you. You're writing this book in this year and it doesn't come out for a year and a half. And so what's going to happen in that year and a half? And with astronomy, everything is going to happen. Somebody's going to discover this, which is going to throw everything you've got into the trashcan. I don't remember exactly what I was thinking with the DART mission. It's kind of like as I'm writing this, I'm thinking, well, I have to talk about asteroid impacts a little bit. We're talking about landing on a small rubble pile, asteroid like Bennu or Ryugu, these two asteroids that have been visited by Hayabusa2 and OSIRIS-REx, these two space missions that are returning samples from the asteroid to Earth, and it's mostly about there being rubble piles and how they're shaped and what it would be like to stand on them and all that. But we have to talk about impacts a little bit. And the DART mission was coming up and at one point, I think it had launched before I sent the final manuscript in. But I told them, if something happens here, if we learn something interesting, I'm going to want to change it. And they were like, it's okay up to a certain date you can do that. And so I think I just put in, in square brackets, insert DART results here. It's kind of like that. So you always have to worry about that. And when I did Crash Course Astronomy, which is a 46 part short video series that I did with Hank Green, the New Horizons mission was months away from Pluto. And so I had an episode about Kuiper belt objects and trans-Neptunian objects, these objects out past Neptune. And I basically just said I could talk about Pluto, but everything I'm going to say is wrong. The one thing we know about Pluto is that everything we know is going to be wrong after New Horizons passes, so I'm just going to not do it. And I said that on camera. So you have to be aware of that stuff and just say things are going to change.

Sarah Al-Ahmed: I remember that in Crash Course Astronomy, actually. I love that course. It's something I point people to quite frequently.

Phil Plait: Thank you.

Sarah Al-Ahmed: That's part of what's so fun about space science as a general premise. We're learning so much, so quickly these days that necessarily things like that happen. You didn't even have pictures of Pluto at that moment that weren't fuzzy blobs, and then suddenly, it's a whole world. Is that part of why the layout of the chapters, you stop by Saturn and you give this beautiful description of the rings and the moons and what that would be like, and then you skip straight to Pluto. And I was wondering if that was because you were just particularly fascinated with Pluto or if it's because we don't have as much information about Uranus and Neptune.

Phil Plait: Uranus and Neptune are just boring. Who cares about them? I sure hope my friend Heidi Hammel listens to this podcast. She's an astronomer friend of mine for a long time, and she spent her career studying those planets.

Sarah Al-Ahmed: She's on our board of directors. I'll point her to it.

Phil Plait: Oh, is she? I didn't know that. Oh, perfect. That's perfect. She's great. Yeah, Uranus and Neptune are really interesting and I've observed them many number of times through my own telescope. I didn't write about Jupiter. I couldn't write about everything and the book was already running really long. I mean, oddly enough, from the way I'm answering your questions, I tend to go on a bit. I wanted to write about Mercury and Venus, I wanted to write about other things, but you have to pick and choose. It turns out the universe is quite large and diverse and there's a lot of neat stuff to see in it. I wasn't going to write about Pluto originally. What really got me to write about it, not just the New Horizons mission, which was so amazing and which showed us so many cool things, it was more that was the last outpost of the Solar System. Whether you think Pluto's a planet or not, and I'm happy to argue because I'm a gadfly when it comes to that kind of stuff. I like irritating both sides. People who think it's not a planet, people who think it is. No matter what you think of it, if you discount Eris, which is also a large round body out there, and probably one or two more that we may not have discovered yet. It's sort of the last sentinel of the Solar System. It's the last big object maybe before interstellar space. And the idea of visiting that, talking, describing about what it would be like to stand there and look up and see its moon, Charon, up in the sky and looking back toward Earth, which is such a human thing to do. You travel all this distance and go, "Where'd I come from? Let me look back there." Talk about that. But the idea of turning away from the sun on Pluto and looking into the black and thinking, that's it, the Solar System is literally behind me and in front of me is the galaxy. And when I thought of that, it's like that one scene, that one line I kind of have to write at this chapter now because I really want to end on that statement, and that's what I did.

Sarah Al-Ahmed: And it kind of fills you with this moment of existential dread. I'd never really considered it before, but that moment where you're not really sure where earth is in the sky, I'm probably going to be thinking about that for a while. But just standing on Pluto and not knowing where the earth is as you're looking out is absolutely terrifying.

Phil Plait: You know it's near the sun. You're four and a half billion kilometers out from the sun and the earth is only 150 million, so the earth is always going to be close to the sun in the sky. But it doesn't get that far away from the sun like mercury is in our sky. Except when you're on Pluto, the earth stays really close to the sun and it would be hard to see it for a large fraction of Earth's orbit, for a large fraction of the year. It's too close to the sun to even see. It was thoughts like that really made me want to write this book. It's like what is surprising about being on these places?

Sarah Al-Ahmed: I think my favorite one is where the person falls into the rubble pile asteroid.

Phil Plait: And that was another one where I was like, "Is that really correct?" And I double and triple and quadruple checked it. Yeah, when you think of an asteroid as being a rubble pile, it's hard not to think of it like a pile of rubble on earth where somebody's constructing a house and they get their bobcat or their bucket loader or whatever, and they scoop up all this crap out of the ground. And it's loaded with chunks of quartz and all these different kinds of rocks that we have on earth. And those rocks are hard. A chunk of quartz, you break it with a hammer, it's hard to do that. On a rubble pile asteroid, it's not quite like that. These rocks are actually incredibly fragile. And it was OSIRIS-REx that dropped down onto Bennu. Do I have that right?

Sarah Al-Ahmed: Yes.

Phil Plait: Ryugu was Hayabusa2 and they shot bullets at the asteroid to get samples. And OSIRIS-REx went down to the surface of Bennu and had kind of a scoop. Not really, but that was what it was kind of doing, collecting samples from the surface. And the thing buried itself half a meter into the asteroid. When the sample arm basically touched the surface and there was notification we have touched the surface, and even though it was moving very slowly, it basically kept going. And if they hadn't had, not retrorockets, but basically it was cold nitrogen gas pointing in the right direction to sort of slow it down and then move it away from the asteroid, if those things happened to have have turned on, it would've buried itself under the surface of this asteroid. The rocks would've just crumbled underneath it. And I realized, yeah, if you're an astronaut trying to land on the surface of a rubble pile, you better be careful because you're going right in. There's a joke on the internet that I was led to believe that quicksand would be more of a daily danger in my life from watching TV shows when I was a kid. Because everybody goes to an island and they're, "Oh, quicksand." But in fact, these rubble pile asteroids are kind of like that. And so I like the idea of you put your spaceship 100 meters away from the asteroid and you kind of jump down to the surface. You'd better be careful because you're going to sink right into it.

Sarah Al-Ahmed: I think that's why I loved it so much because just watching that, I think they called it a touch and go maneuver, the tag where OSIRIS-REx just tried to touch the surface. Watching the video of all these little flecks just flying away and then the spacecraft coming back with way too much samples. Little parts were just falling out of its little chomper mouth as it was backing away.

Phil Plait: Yeah, that's what happened with those OSIRIS-REx. It was designed to get, I think they wanted to get 200 grams of material and it got 500 or up to a kilogram. And they were actually worried they wouldn't be able to close the container because there was so much asteroid jammed into the container. But yeah, the video of that, when that video came back, that was staggering to see these things up close and realize... We had images of Eros, Itikawa, which is a comet, and you can see that there's a lot of rubble on the surface, but there's also smooth areas. But then to go to these two and see that they're all rubble, that actually... There are no flat places on these things where they could... They were worried about getting a sample out of this thing because there just wasn't a place that wasn't covered in boulders, or even small rocks that could damage the spacecraft. It's unearthly. It's literally unearthly. I don't know how my chapter on that would've turned out, how I would've written it without those videos, without the missions to Bennu and Ryugu. You can picture it in your head kind of, but then to see an image, here's what it looks like, it really changed how I saw these things and made it a whole lot easier to write those chapters.

Sarah Al-Ahmed: Yeah, I think of it now as kind of like a forbidden ball pit just floating in space.

Phil Plait: Exactly. It's jumping into a box full of styrofoam peanuts, or I think I mentioned a ball pit in the book too. It's like, yeah, there's a surface, but not a good one.

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

Casey Dreier: Hi, it's Casey Dreier. I'm the Chief of Space Policy here at The Planetary Society. And I just want to take a moment to thank you for being part of the world's largest and most influential nonprofit space organization. Together, we are on a remarkable journey to make a better future for humankind through space science and exploration. Your support in the United States enables our team, my team, to work to make sure every US representative and senator in our Congress understands why space exploration is a critical part of US national policy, from workforce technology, to science to even international relations. Each year we urge Congress to maintain robust funding for NASA's ongoing missions, guaranteeing that they stay on course and achieve their scientific goals. Now look, there are 81 new faces in Congress and several returning members that are joining space related committees. For the first time. All of these could influence NASA's future endeavors. And already, they have begun to discuss next year's NASA budget. The time to act is right now. So in addition to writing Congress yourself, which you can do if you live in the United States, there's something you can do to bolster our advocacy work. And anyone can do this, anywhere in the world, and that's to make a donation. Thanks to the generosity of a fellow Planetary Society member, your gift today will be matched up to $75,000. This ensures our advocacy efforts will continue to thrive. Now, to make your contribution, you can visit On behalf of everyone at The Planetary Society, thank you for your support and helping us champion the future exploration of space.

Sarah Al-Ahmed: These are all places that we've been and be able to send missions and check out up close, which is why we can get such a clear depiction of what these places are like. But from there, you jump out into places far beyond anywhere we've ever been out into other star systems, binary star systems, nebulae, black holes. I know that we are right on the cusp of learning all these strange things with particularly instruments like the James Webb Space telescope. So I'm thinking about the chapter that you wrote that very heavily features the TRAPPIST-1 system. We're about to get all sorts of new information about that, that might completely change that chapter. What would you do in that instance? Do you think you might update the book, new updated version, or just let it stand?

Phil Plait: It depends on the publisher. If we sell out the first printing run, knock on wood, if I can update it, that would be interesting, wouldn't it? Or I can just ignore anything that's wrong and everything that I wound up predicting correctly, I can just say, "See, let's look at how brilliant I am." So TRAPPIST-1 is what they call an ultra-cool M dwarf. It's a red dwarf star, but it's really, really, really low mass, really, really cool, I mean by temperature. And feeble. It only shines with a fraction of a percent of the brightness of the sun, the luminosity of the sun. It's about the same size as Jupiter. It's really just barely a star. And surprisingly, it has a system of planets. It has seven known planets. All seven of them are very roughly earth size. Some are smaller, some are bigger. But we think that all seven of them are rocky terrestrial like planets. And they all orbit the star extremely close in. And I don't think it's the first M dwarf that was found to have planets, but it was sort of the first one where it was an extremely small star. A lot of planets, the first planets discovered, and four of them were discovered at the same time and then three more later, they're all rocky small worlds. And three of them are orbiting close enough to be in the habitable zone of that star. So if this is just a rocky ball with a decent atmosphere, liquid water could be on the surface, it wouldn't have to freeze or boil away. That right away, that's all pretty amazing stuff. This was only discovered recently. The star was only discovered in the 1990s, the planets around it after that. And so this was all brand new. But we have observed it enough that I could actually say, if you're on planet E, let's call it Planet E the one that's habitable, what do the other ones look like in your sky? And when I was a kid watching Star Trek, they'd have these matte paintings in the background of something, it'd be on an alien world, and there'd be this gigantic moon or another planet, huge in the sky, way bigger than our moon, in our sky. And I think that's so cool. And then when I learned more about astronomy, and I thought, that's unlikely. Having a planet that big is going to have all sorts of gravitational problems on your planet. But now we're finding out, no, that's actually not that bad from these TRAPPIST-1 planets. The other planets are physically big enough to see and maybe roughly the size of our moon in the sky or even bigger. So again, that's catnip. There's no way to avoid writing about that. If you're a science fiction fan and an astronomer, you really want to be able to put these two things together. And after I wrote that chapter, and it was less than a month ago, JWST results showed that the innermost planet apparently doesn't have an atmosphere. As the planet passes in front of the star and behind the star, the light from the system changes a little bit, and they can analyze that light and say, "Well, how much light do you expect to see?" And there's just nothing that indicates that this planet has an atmosphere. If it had an atmosphere, there would be changes in the amount of light and the character of the light from the system. And there wasn't anything like that. So they're like, "Well, that's just a barren rocky ball," as hot as Mercury or such, maybe not that hot. I don't know the exact numbers. But in my book I say, "Yeah, it's too hot." And I even say, "Listen, this is a system we've just discovered. We're learning more about this all the time." I was reading papers that had just been published as I'm writing this chapter. And so I even say, "Let's just say this is how things are. Let's imagine this and be there." And at some point, you have to draw a line in the sand and just say, "Okay, this is how we're going to do it."

Sarah Al-Ahmed: It's absolutely wild how much has changed so quickly. Over the course of your career, you've gone from Hubble Space Telescope to now we know that there's over 5,000 exo-planets and we're analyzing their atmospheres, and it's just been a few decades. It's absolutely bonkers. I can't even imagine what we're going to learn in the next decade.

Phil Plait: Yeah, it's something that I've read about my whole life, these astronomers who said, "I studied quasars and when I was in grad school, we didn't know anything about these things. And now we study them all the time." And that happens to every astronomer over their careers, especially because of the acceleration of our understandings of things. I was in grad school just starting my PhD research when the first planets were found orbiting a pulsar. And I had just gotten my PhD when the first hot Jupiters were found around Solar type stars. And now we have over 5,000 exoplanets. The first planets were discovered because their gravity was affecting their stars, and we were seeing a doppler shift in the star light. There was a lot of controversy. Are these really planets? Are these star spots? Are these stars in the background changing their brightness and affecting what you think you're seeing? And there was a lot of arguing about that for a long time. And then the first transiting exoplanet was seen, they predicted it. They said, judging from the way the star's behaving, we predict that this planet will transit at this time. And then they observed it, and there it was pretty much right on time. And I remember reading that and going, "Well, we're done." The arguments evaporated overnight. It was a revolution. And when I say overnight, I mean everybody looked at that paper and went, "Okay, these are planets." And so to see that happen and then to start realizing I have access to a 14-inch telescope at the university I was working at the time, and it's like, we could observe these things. You can actually detect these planets. They've been there this whole time. So yeah, it's amazing to see that kind of stuff happen over a career, let alone over a week of that sort of change. But we can still imagine, given what we know about exoplanets, because that's a whole thing now, a whole field of astronomy, and we can extrapolate what it would be like.

Sarah Al-Ahmed: I think the chapter on globular clusters was actually my favorite specifically because it's so difficult to find information about that. And I'd always wondered what would it be like to be on the surface of one of those worlds when the sky is full of stars? The density of stars in that space is so high. And you answered so many of my questions about it. Could I read by star light? How many shadows could I see? It was beautiful.

Phil Plait: Oh, well, thank you. That was actually the first chapter I wrote. This book is based on an article I wrote in 2003 for Astronomy Magazine. Again, it was just sort of this idea. It's like people are always asking me this, what do these things look like if you were there? The internet was around, but not like it is now. And it was hard to look up a lot of this stuff. And in fact, when I looked up a paper on a globular cluster and had a list of the stars in it, you have this many red giants and this many blue stragglers, just these different kinds of stars that are in it. And I was disappointed because it looked to me like you wouldn't see that many bright stars in a globular cluster. Most of the stars in there are actually quite faint. These objects are so old that any star is more massive than the sun even. And some of them, for even the sun. You're talking about an object that's 12 billion years old. The sun doesn't have a 12 billion year lifespan. After 12 billion years, the sun's going to turn into a red giant and go away. So any stars, even as massive as the sun, are gone in a globular cluster. And so it kind of made sense to me that, really, most of the stars are going to be really faint. We now have way better observations since 20 years ago. And a lot of these stars will be intensely luminous, brilliant stars in your sky, a lot of them will shadows. And that part's a little bit tougher because if you have two light sources, your shadows get less distinct. If you have one light source, you have this really dark, deep shadow. But if you have two, the second light source fills in the shadow a little bit. There's not as much contrast. So I wrote about globular clusters for the article, and then when I had to pitch the book, I had to write a chapter, and that's the chapter I decided to write. I probably should have done Saturn. It might have been an easier sell because it's not quite as weird as a globular cluster, but they did buy the book, so that worked out pretty well.

Sarah Al-Ahmed: Am I remembering correctly that you said in the book that Saturn would be the place that you would like to visit out of these locations?

Phil Plait: Yeah, I think so. Just to see it up close. Saturn was the first thing I ever saw through a telescope when I was a little kid. And I've told the story a million times, but my parents bought a cheapo department store telescope. If you're of a certain age, you may remember Tasco telescopes. They were garbage, but they were good enough, wobbly and all that, but they're good enough to set up and look at the moon and Saturn. And I looked through the eye piece and it was like, yeah, this is what I want to do for the rest of my life. And it was pretty amazing. And when Saturn's up, that's always the first thing I want to look at through my telescope. We've sent space probes there over my lifetime, the Voyagers and one of the Pioneers went by Saturn, and those pictures were really cool, but they were still kind of blurry and weird. And then Cassini. Man, Cassini just changed everything. Just knowing that the rings are way more complex than we thought, really weird structures in the rings that I actually struggled describing because it's like, how do I describe this without... If I have a picture up in front of you and I say, "Well, here's going on," and you go, "Oh, okay." But if I'm just using words, it's a lot harder. Although there are pictures in the book, of course, to show this kind of stuff in diagrams. But just to be able to see that stuff, to see gravity as the artist. The moon orbit's the earth. Okay, we can see that, but you're not seeing sort of gravity directly. The earth orbit's the sun, but you're not seeing what the gravity's doing. You go to Saturn, you are seeing what the gravity's doing. There are gaps in the rings caused by the gravity of the moons. There are tiny chunks of moonlets embedded in the rings that are drawing ring particles to themselves and creating these weird shapes like propellers. To be able to see that, especially Daphnis, which is a tiny moon in the Keeler Gap, a 40 kilometer wide gap in Saturn's rings. And as it moves around in that gap, it's drawing the ring particles from either side of the gap toward it, and it creates these ripples in the rings that move up and down. You can see that in the Cassini images, it's pretty clear, to actually think about what it would be like to be in that and to see the sort of candy ribbon of ring particles moving around you. How could you not want to see that? The moon and Mars, yeah, fine, fine. I want to go to Saturn's rings. I want to stand or be in a spaceship in one of those gaps and see the rings being sculpted by the gravity of a moon so small that you could walk around it in a couple of hours. That to me, would be the culmination of a lifetime.

Sarah Al-Ahmed: If you had the opportunity to go and see these rings knowing that you wouldn't be able to come back to Earth, would you do it?

Phil Plait: Sure. I mean, what's here? Have you looked around lately? I get that question a lot from people. It's like, "Would you go into space if you could?" And the answer is it for me is no, no. If I read in a car, I get sick. If I get on a kid's backyard swing set, if I swing for too long, I get sick. And for a TV show, once I got into a fighter jet and flew around at 4Gs, and that was a lot of fun. But the quick change between just sort of flying and then suddenly snapping 90 degrees and going into one of these turns, yeah, I don't ever, ever want to have a day like that again. I really just wanted to die. And so yeah, unless it's like the Enterprise where they have artificial gravity and everything's all set, that would be fine. Strapping myself into a rocket and going to these places, nope, nope, nope, nope. Cassini works just fine for me.

Sarah Al-Ahmed: Just get five Cassinis around every planet, we'll be fine.

Phil Plait: Yeah. It's just double NASA's budget for criminy sake. And of course, if only there were some sort of space advocacy group that promoted these sorts of ideas, like The Planetary Society.

Sarah Al-Ahmed: If only. But we'd be happy to have one mission at each world. And that's the point that we're at right now. It would be wonderful if we had a mission around Uranus right now, or mission around Neptune or another mission around Saturn. Now, Saturn is kind of lonely out there.

Phil Plait: Now we know what questions to ask, what machines, what instruments to build to go to Saturn. And Venus, it's Venus that's killing me right now. There have been four landers that took pictures from the surface for an hour before they melted. And we've had these orbiters and the technology from the '90s, the Magellan orbiter was, that was amazing, but it was just enough, it was such a tease, just enough to say, "We don't really understand what any of this stuff is." And so I'd love to see, with the advances in technology, to see a dedicated orbiter mapping the surface, even dropping a probe and sampling the atmosphere. Venus is so weird and it's so much like Earth, and then took a wrong turn sometime a billion or two years ago, and I'd like to know why. It's gorgeous. So we'll get really cool images and everything, but the science we could get from it and what we would learn in turn about the Earth, I think is more than enough justification for VERITAS or some other mission to get there and really take a deep look at this planet.

Sarah Al-Ahmed: Well, thankfully there are a lot of missions that are proposed or being built to go there right now, but as you said, VERITAS, super important. We want to save that mission. It's kind of on hold right now, so I'll just take a moment. If anybody wants to help us save this mission, we've already gotten over 1,000 people to write into their representatives to save VERITAS. So if you want to help out with that, you can go to our action center at, and you can find our form letter there that you can send to your representatives if you live in the United States.

Phil Plait: I think my representative thinks the earth is flat, I think so. I'm not 100% sure how he would feel about a mission of Venus. But anybody listening to this podcast, I would hope most of you are already members of The Planetary Society. But if you're not, and I was not asked to say this. Sarah has nothing to do with this. But this is a fantastic organization, and if you're listening to this because I tweeted about it or something, please sign up, join up, and help them advocate for more planetary exploration because my book is part fiction and a lot based on science. But it would be really cool to be able to write a sequel based on new science from new missions. So help out The Planetary Society, and let's find out more about these other worlds.

Sarah Al-Ahmed: Thanks for saying that, Phil. I really appreciate it. Because we are, we're trying to explore these things. Reading this book, just impressed upon me just how beautiful what we're learning is and how much it needs to be shared. Because there's so much of this that we know as people that are steeped in astronomy, but there are just people walking around out there in the world that have no idea how beautiful the rings of Saturn are, or the fact that black holes are a thing that you can just orbit and not immediately die. There's so much that I wish I could share with everyone, which is why being a science communicator is so fun. You never know when you're going to change someone's life or change their perspective on the universe.

Phil Plait: That's true. It's hard to describe the feeling when you get an email from somebody saying, I had no idea about this, and whatever this is. When I'd written the book and I was talking the publisher and they have a promotional person and my editor, we were chatting about what do we want to say about this book to promote it? What do we want to do? And she said, "What are sort of the facts you want people to walk away with and what are the sort of basic things?" My walkaway was more of an overview of saying, "I want people to understand that these places exist." All of the planets and places I talk about in the first half of the book, we've explored them with spacecraft. Planets around binary stars exist, we've found them. Planets in TRAPPIST-1, those exist. So I was taking more of a big picture thing. But then she said, "The moon doesn't have air." And I realized, yeah, she really wanted somebody who really doesn't know necessarily anything about space. If you say to them, "The moon doesn't have air, and that means the sky is black even when the sun is up," you and I are astronomy nerds, and most of the people listening to this are going to be astronomy nerds and of course they know that. But the vast majority of people out there may not really understand that, or they may have heard it, but it hasn't really sunk in or they've not put all the pieces together. And so that's the kind of thing I think we need to do too, is to just show them this is what it's like. These are really basic things that we know, and from there, we can say a lot and there's a lot more we want to know because you can never know enough. That's sort of the motto of science, you can never know enough.

Sarah Al-Ahmed: Well said. Well, thanks for taking me on a journey through this book and for writing it.

Phil Plait: Terrific. Thank you so much for saying that. I really appreciate it, and thanks for having me on the show. This has been a lot of fun.

Sarah Al-Ahmed: Thanks for joining me, Phil. I really appreciate it. There were so many years I spent as an aspiring science communicator, watching Phil's content and trying to learn how to up my game. It's really fun to get a chance to finally speak with him, and I had a wonderful time reading his book. If you'd like to get your hands on a copy too, here's your chance. Bruce Betts, the Chief Scientist of The Planetary Society is here for what's up and an opportunity to win a copy of Under Alien Skies, in our Space Trivia Contest. Hey, Bruce.

Bruce Betts: Hey, Sarah. How you doing?

Sarah Al-Ahmed: Doing really well. How about you?

Bruce Betts: Hunky-dory. Spiffy keen,

Sarah Al-Ahmed: Spiffy-keen. All right, so what's up in the sky this week, Bruce?

Bruce Betts: Well, if you're the part of the world where you can see it, there's a hybrid solar eclipse that has totality in kind of the central part of the eclipse. Then on the edges, it's a little farther away due to the curve of the earth, so you get an annular eclipse. All of that follows a thin line over the northwestern corner of Australia and up to east to more and western New Guinea islands, Eastern Indonesia. But you'll get a partial eclipse visible throughout most of Indonesia and Australia. And so you can see for more or check things out. That is April 20th. On April 22nd, everyone without a cloudy sky can see the crescent moon hanging out near Venus, making a beautiful pairing over there in the west in the early evening, and you can start staring at the Lyrids meteor shower that peaks on the night, on the 22nd and 23rd. It's kind of a medium middle of the road, average kind of meteor shower, so it's got about 20 meteors per hour at its peak seen from a dark site. You'll see fewer that get washed out from obviously a light polluted site. But the good news is there won't be much moonlight. Crescent moon will set early in that evening, and so those evenings will not conflict much with your meteor watching. Oh, one more. We'll just throw in April 25th too. The moon is near Mars, which is getting dimmer up higher in the sky than Venus, although Mars is starting to drop too.

Sarah Al-Ahmed: Yeah. Going back to that hybrid eclipse, I know we've talked before about total solar eclipses, but have you ever seen an annular solar eclipse?

Bruce Betts: Yes, I have.

Sarah Al-Ahmed: I haven't done that yet.

Bruce Betts: I just got lucky. I lived near one in the '90s. Somewhere on film that I don't know where it is. I have great pictures of it. It was just sitting over the Pacific Ocean as seen from Southern California, very pretty with the annular eclipse. Now it's still as I point out to people, and that difference between 99% of the sun covered and 100% is a really big deal. Total solar eclipse is way cooler, but annular, also very cool.

Sarah Al-Ahmed: Very cool.

Bruce Betts: Anyway, let us move on, shall we? To this week in space history, 1970, Apollo 16 landed humans on the moon and 20 years later, 1990, the Hubble Space Telescope was deployed. Still working. I'm sure it's had like five repair missions, but still really cool.

Sarah Al-Ahmed: If only JWST would last that long. Hubble might still be working long after JWST goes cold.

Bruce Betts: That's the perfect time to go onto-

Random space fact.

Sarah Al-Ahmed: This time with extra enthusiasms.

Bruce Betts: ESA, congratulations on that Juice spacecraft getting launched. That's great. And it's headed off to Jupiter several years from now and it has solar panels to power it, and they're the biggest solar panels out there on spacecraft to date, planetary spacecraft. And that's because of course, the light at Jupiter's is not that big. So you're probably wondering how big are those solar panels? What can we relate that to? Well, how about a badminton court? The total area of the Solar panels on Juice is about the same as badminton. Or if you're into more newer sports that are getting popular, it's about the same as a pickleball court.

Sarah Al-Ahmed: Pickleball.

Bruce Betts: It's a thing. You use wooden battles and you do it on a quarter of a tennis court size thing, and then I think you hit pickles back and forth. That's at least how I like to envision it, but I think my son said it's different than that. But for those pickleball players out there, the time you're there or hanging out playing badminton on an official court, you think, wow, that's a lot of solar panel. All right, we move on to a question that more than I, although I know some about, I asked everyone in the lore of the Destiny video games on what planet was the city Freehold? How did we do?

Sarah Al-Ahmed: We did really well on this one. People really love this question, probably because it's a really fun game. The answer is that Freehold is located on Mars, or rather it was before the fall of the Golden Age of humanity and Mars getting taken over by a bunch of extraterrestrials and the darkness game. Total bummer.

Bruce Betts: Yeah, well, that's why I said was the City of Freehold.

Sarah Al-Ahmed: Spoilers, but our winner this week is Matthew Scully from Alexandria, Virginia. And Matthew, you'll be winning a Goodnight thermal Oppy Mug. I wonder if I have any extra Destiny swag around here I can put in there. But we got a lot of comments from people that were really excited about this. Richard Harrison, from Akron, Ohio wrote us to say that he's a longtime fan of Destiny and can finally confidently answer the space trivia question. It just only took him four years to finally enter one. So thanks for sending us your answer, Richard. And I also liked this one from Nate Bacca in Indianapolis, Indiana who said, "I was very excited about this question. I'm a huge Destiny lore nerd and a big fan of Planetary Radio." And he's been a member of The Planetary Society for 10 years.

Bruce Betts: Excellent, thank you.

Sarah Al-Ahmed: Yeah, relate to that. I'm also a huge Destiny law nerd, and since so many people wrote in to say that they love Destiny 2, I thought I would take a moment just to say rest in peace to the voice actor who played Commander Zavala in Destiny 2, Lance Reddick, who passed away in March. But I loved how people reacted in the game. I was playing Destiny on the night that Lance passed away, and people gathered around his character in the video game and paid tribute to him for hours on end, and it went all through the weekend. So it was a really nice gamer moment.

Bruce Betts: Wow.

Sarah Al-Ahmed: Yeah. So what's our question for this week, Bruce?

Bruce Betts: Moving to a totally different topic. Where in the Solar System is the best place to go if you want to find sulfur dioxide, frost? And in case there's any question since that's kind of vague, best is judged by me in case there's a question. I don't think there will be. Best place to go if you want to find sulfur dioxide frost. Go to

Sarah Al-Ahmed: And remember, it's according to Bruce.

Bruce Betts: Yes.

Sarah Al-Ahmed: You have until April 26th at 8:00 AM Pacific time to get us your answer. And whoever gets this one is going to win an actual copy of Phil Plait's new book, Under Alien Skies. So if you really like the interview that we just did, we will send you a copy of this book.

Bruce Betts: All everybody, go out there, look on the night sky and think about cattle.

Sarah Al-Ahmed: Cattle.

Bruce Betts: Moo. Thank you and goodnight.

Sarah Al-Ahmed: We've reached the end of this week's episode of Planetary Radio, but we'll be back next week to celebrate the launch of ESA's Juice Mission with Project scientist Olivier Vitas. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by our members who crave the exploration of other worlds. You can join us as we continue to nerd out over our strange and beautiful place in the cosmos at Planetary/org/join. Mark Hilverda and Rae Paoletta are our associate producers. Andrew Lucas is our audio editor, Josh Doyle composed our theme wishes arranged and performed by Pieter Schlosser. And until next week, ad astra.