Planetary Radio: Space Exploration, Astronomy and Science - It's Hot! Plutonium 238 is Back

Episode Date: October 28, 2013

Casey Dreier tells the winding tale of Plutonium 238, the radioactive isotope that is vital for exploration of the solar system. The US came dangerously close to exhausting its supply. Even with production restarted, there are major challenges facing explorers. Learn more about your ad choices. Visit megaphone.fm/adchoicesSee omnystudio.com/listener for privacy information.See omnystudio.com/listener for privacy information.

Music Halloween fun with Plutonium, this week on Planetary Radio. Music Welcome to the travel show that takes you to the final frontier. I'm Matt Kaplan of the Planetary Society. Plutonium, or one variety of it that can't be used for atom bombs, is making a comeback. Casey Dreyer will tell us why that's a very good thing for planetary science. Bill Nye gives us his take on gravity, the movie, not the force of nature.

And Bruce Betts joins me for a spooky edition of What's Up. We begin with senior editor Emily Lakdawalla. Emily, it would seem to be an appropriate time to talk about the space race, if there is one, but not the space race that all of us used to know and love between the U.S. and the U.S.S.R. No, it's this time that there seems to be something of a space race heating up in Asia, although officials in various Asian countries deny the fact that it's a race. But I think there's certainly a race for status going on. Start us with this piece that you wrote on the 28th, the day that we're speaking about it,

about the progress China's making toward its lunar soft lander. That's right. China's planning to launch a very large soft lander that carries a opportunity-sized rover on its back. That launch is going to take place in December. Just today or yesterday, they shipped the rocket to the launch site. It should arrive in a couple of days, and they'll start stacking that and get it ready to accept the spacecraft. And they've also announced that they're making progress in the selection of the name of the rover, which they're doing through a public contest. And there's a list on the blog of 10 possible names that they're choosing from for the rover, including one that was a white rabbit that was a companion to the goddess Chang'e

when she went to the moon in the first place. So I think that seems like a very likely possibility, but there are nine other good choices, and anybody, including you listening to this, can vote for the name. And I like that choice. I think I would go for Jade Rabbit, and the imitation is the sincerest form of flattery. So thank you for honoring the Planetary Society, China. Let's go on to India. They also have a mission that is leaving even sooner. That's right. Their Mars orbiter mission is launching very soon, early in November,

to head to the red planet and be their first mission beyond Earth orbit, which was very exciting for the Indians. Of course, China had a Mars orbiter called Yinghuo-1 that launched toward Mars with the Russian Phobos Grunt spacecraft. But that spacecraft is now on the bottom of the ocean having failed to leave Earth orbit. So if India succeeds with this, it will be the first Asian country to get a spacecraft into orbit around Mars. So I wish them all the best of luck in their race to get there and actually do some good science with the spacecraft on Mars' atmosphere. Absolutely. I want to join you in wishing the best of luck to both of these nations as they become even bigger players in the world of planetary exploration.

Emily, thanks so much. Thank you, Matt. She is the senior editor for the Planetary Society and our planetary evangelist. You can also see her in the pages of Sky and Telescope magazine, where she is a contributing editor. Up next is the science guy, Bill Nye. Bill, I'm hoping that you can provide your thoughts about the movie, which finally this week dropped to number two. It had been the number one film in the United States for three weeks. Gravity.

Well, if you're asking for my thoughts, Matt, that's never really an issue. Yeah, it was good. I watched it. I watched it in giant 3D. I had dinner with my colleague on the board of directors of the Planetary Society and dear friend Neil Tyson. And the Space News article about human spaceflight started with a reference to Neil's references to what he considered the scientific inaccuracies in the movie Gravity. Yeah, he apparently kind of ranted about it in Twitter. Our point in the science community is that you could make it right.

I mean, it could be just as scary and terrifying and weird without having these extraordinary leaps of scientific inaccuracies. You can't fly from one space station to another in the fire extinguisher. I mean it's just – it's too far. The differences in speeds are just too high. And the other thing that I think struck a lot of people about it, you'd expect the character's hair to behave differently in zero gravity. And as an actor, I have been in zero gravity several times. And it's not that hard to make your hair fly around.

On the other hand, it's inspired a lot of people. Oh, yeah, yeah. I'm with you. I mean, as I say, I enjoyed it. It's charming. And the threat of a spaceship, a satellite collision leading to a cascade of collisions is very real. I don't want to give too much away in the movie, but this sort of thing leads to trouble.

Don't you also think that it made space look just gorgeous? Oh, yeah, yeah. Kowalski's closing comments about how beautiful it are are good. I mean, space, I think everybody who goes there comes back a little bit changed. They see the fragility of the Earth, the thinness of the atmosphere, and how there are no political boundaries. So what are you people fighting about? This is all worthy. But what we want to do, Matt, we want to go farther and deeper into space with people. We would like to no longer timidly go where 600 people have

already flown. To paraphrase another bit of science fiction. Yes, an important bit, I might add. Yes, absolutely. So I encourage everybody to see that movie, know and appreciate that there are some things that are probably unreasonable. But the idea that space is dramatic and does bring out the best in us is quite worthy. The passion, beauty and joy, the PB&J of space exploration is in that movie. And so it's worthy. It's good. Thank you, Bill. Thank you, Matt. He's the CEO of the Planetary Society, Bill Nye, the science guy.

And in just a few moments, another of my colleagues at the Society, Casey Dreyer, about the reemergence of plutonium-238, essential for much of space exploration. My colleague Casey Dreyer sometimes seems to spend as much time in Washington, D.C. and elsewhere on the road as he does in our office. That's appropriate because Casey is the Planetary Society's advocacy and outreach coordinator. The truth is he's much more than that. For example, he has just written a great article about plutonium-238 for the Planetary Report magazine. In it, he describes the fascinating science, history,

and necessity of this isotope in solar system exploration. Casey, welcome to Planetary Radio. It's not like we don't see each other all the time around the office, but it's good to have you in front of the microphone. Yeah, it's nice to be on the other side for once. So you have this great piece that I just described in the Planetary Report, TPR as we call it around here. What is this stuff, PU-238? PU-238 is a shorthand for plutonium-238, which means it's an isotope of the element plutonium. So an isotope means it has some extra neutrons than your kind of standard part of the periodic table.

It's an element that's incredibly important for space exploration, and primarily, actually, the interest is in space exploration. It was actually the first artificial isotope ever discovered of plutonium. It was the first isotope of plutonium discovered back in the 30s. And it has a nice little property. Just sitting by itself, it kind of heats itself up and dissolves. It has a half-life. It turns into uranium-234, and that process gives off little alpha particles, which are basically little helium nuclei, as they are released from this radioactive decay, they bang into their surroundings and they heat it up. And this heat can be turned into

electricity. And that electricity can be very useful, say, if you're going into deep space. And it's just using thermocouples, which I remember we made thermocouples in my middle school science class. And you just heat them up and you get electrons running through it. It's exactly the case, yeah. And you have this great photo of this glowing pellet of this stuff. This stuff is really hot. Yeah, it's over 1,000 degrees. I should have said, how hot is it?

Yeah, it's about 1,300 degrees Celsius, which is quite hot. But it's kind of this really nice, it's very 1300 degrees Celsius, which is quite hot. But it's kind of this really nice, it's very stable at that temperature. The radiation that it gives off, you know, most people think about radiation and plutonium, and they're thinking about nuclear weapons. And this is actually cannot be used for nuclear weapons. This is only used for basically peaceful purposes as an energy source. It's not fissable to that level of energy. It just gives off at this nice steady pace.

And plutonium-238, that heat, all you need is what you said in these thermocouples. It just needs any kind of heat source. Plutonium-238 happens to be very stable, and it has what's called a half-life of about 88 years. That means in 88 years, it'll decay halfway from its original amount. You know, you can last for decades in these deep space missions. This also explains why we can't just go out and mine this stuff. Yes, exactly. It'll disappear within the course of a few hundreds of years. And that's, it has to be created and it has to be created constantly. What happened? We used to make this stuff and then we stopped. Yeah, so plutonium has been really popular within NASA

and a lot of countries, Russia's primarily space missions, because it's this handy source of electricity. NASA has used, I think, a total of about 27 missions over its history, sending, for civilian purposes, sending plutonium as the power source into space. And during the Cold War, we just produced tons of this stuff. If you look at the Voyager spacecraft, for example, or even Pioneer, you see these little fin-like elements sticking out of one side of it.

They stick out maybe five feet or so from the center of the spacecraft. These little finned things are called radioisotope thermoelectric generators. I know it just runs off the tongue. And that's what contains the plutonium. That's the thermocouple that creates the electricity. Back in the day, in the 70s and 60s, they had tons of plutonium-238 because they were making tons of plutonium-239, which is the plutonium used in nuclear bombs. That goes boom. Yeah. To put it succinctly, yes. And so they would just kind of piggyback onto these processes. The Department of Energy, which is the only federal agency in the United States that is allowed to make radio isotopes.

And they make it for other parts of government. The U.S. government has a monopoly on making these things because they're dangerous and they can be used for bombs. And it's expensive. It takes a lot of work to make these. And they can be used for bombs. And it's expensive. It takes a lot of work to make these. So back in the day, you would make plutonium-238 primarily in this place called the Savannah River National Laboratory,

which is a big Department of Energy laboratory in South Carolina. In 1988, towards the end of the Cold War, this reactor had been around for over 30 years. It was built in the 50s. And you had a series of generally, I wouldn't call them catastrophic, but very dangerous safety lapses that caused the reactor to have to be shut down. As it was shut down, they found more problems. They found cracks in the cooling pipes

and things you don't want to find in a nuclear reactor. While they were fixing that, the Cold War ended in the early 1990s. So they never bothered to open it up again because they didn't need the kind of plutonium to make weapons that they used to. And when that closed, that was the only place producing plutonium-238 for NASA. So with the end of the Cold War, we kind of inadvertently closed off our ability to produce new plutonium-238 for space missions. Why didn't we just buy it from somebody else?

I mean, you said the Russians like to use this stuff. Yeah, and that's actually what we did. Starting in the 90s, the Department of Energy started to purchase plutonium from Russia. Russia is the only other country that we know of that has been able to make plutonium-238 because it's a tricky process. You have to be able to produce other types of radioactive materials, and that's a big investment for a country to do. So for many years we bought plutonium from Russia.

Actually, a big chunk of the plutonium that powers the Curiosity rover is Russian plutonium. This is that big rump on the end of Curiosity. I didn't know that there was Russian plutonium in there. We simply didn't have enough to do it on our own? Yes, and this actually comes to the big core of this article. Once we stopped making plutonium in there. We simply didn't have enough to do it on our own? Yes, and this actually comes to the big core of this article. Once we stopped making plutonium, we stopped making plutonium. That stuff started to, you know, we only had a finite supply,

and we don't exactly know how much we had, but it wasn't that much. It was good for a couple decades of NASA missions, but as we mentioned earlier, this stuff decays away over time. There's a built-in clock, a countdown clock on this stuff. It's decreasing, and every time you send a mission out into space that uses plutonium, you take a little more away from that supply, and eventually you're going to hit zero. And when you do that, all parts of the solar system that require plutonium to power a spacecraft will be closed off to NASA until we make more, which is not an easy thing. So we go years, and people knowing this is the case, but it's only very recently that things have started to turn around.

That's true. It was probably the early 2000s where people really started to see the crisis point. Jim Green, who's the director of planetary science at NASA, this is the division of NASA that funds and manages all of these solar system spacecraft. When he came in about 2006, he initiated this program to convince basically the White House and other people within NASA to say, we need to start making plutonium again. They were looking at a crisis level in about 10 years where they would run out of plutonium. And it takes years to make this stuff. You can't just switch plutonium. And it takes years to make this

stuff. You can't just switch on a factory. It takes many years to make this. And then only then you're making it at a certain rate. And you have to build up a supply again. So you had the situation where we're potentially looking at the end of outer planet solar system exploration. You're looking at the end of sending any spacecraft to where there's shadow. And this is such an interesting point that I didn't realize that Jim Green told you, that to go to places like the dark side of Mercury, you need plutonium. Yeah, it's not just outer planets. That's the thing. You know, great example, Curiosity rover, as you said, has this rump on the end of it

with plutonium. Why is that? Because it's dusty on Mars. It's what killed Spirit, because dust landed on its solar panels. So you send something with plutonium if you want it to last more than 90 days. And you can work at night, too. Yeah, and you can work at night, and it does all of these nice things for you. You can go in next to very high cliffs that you couldn't go to that have shadows.

And as you said, dark side of Mercury, dark side of the Moon. Lunar nights are two weeks long. You have all of these places that you can't use solar panels. It's not just the outer planets. And so without plutonium, you kind of just give up on the majority of the solar system. That's Casey Dreyer. He'll be back to tell us more about the return of plutonium-238 in a minute. This is Planetary Radio. Greetings, Planetary Radio fans. Bill Nye here. Thanks for listening each week. Did you know the show reaches nearly 100,000 space and science enthusiasts? You and your organization can become part of Planetary Radio by becoming an underwriter. Your generosity will be acknowledged on the air

each week, as well as on the Planetary Society website. To learn more, visit planetary.org slash underwriting. That's planetary.org slash underwriting. Thanks again for making us your place in space. Hi, this is Emily Lakdawalla of the Planetary Society. We've spent the last year creating an informative, exciting, and beautiful new website. Your place in space is now open for business. You'll find a whole new look with lots of images, great stories, my popular blog, and new blogs from my colleagues and expert guests. And as the world becomes more social,

we are too, giving you the opportunity to join in through Facebook, Google+, Twitter, and much more. It's all at planetary.org. I hope you'll check it out. Welcome back to Planetary Radio. I'm Matt Kaplan. My guest this week is my colleague, the Planetary Society's Advocacy and Outreach Coordinator, Casey Dreyer. We're talking about Casey's just-published article in The Planetary Report about Plutonium-238, the radioactive isotope in short supply that is needed for many of the most exciting and revealing planetary science missions. many of the most exciting and revealing planetary science missions. One of the leaders of the campaign to restore production of PU-238 is Jim Green, Planetary Science Division Director for NASA. Is it fair to call Jim Green sort of the hero of this story?

I think he's one of many heroes, actually. That's kind of what I mention in this story. This wasn't one person that could solve this problem. And it took a lot of coordination. That's kind of the incredible thing. It took the coordination between NASA, people within NASA, took the coordination of the Department of Energy, people within the Department of Energy, people within the White House, people within the Office of Management and Budget, people in Congress and various committees in Congress all working together to create what essentially is a poisonous isotope of a somewhat dangerous radioactive isotope for the sole purpose of exploring space.

I think that's actually kind of a beautiful expression of our modern age, that this is something that's happened. So there's no one person, but there are key people. I think Jim Green is a key person in this. So who's paying for this, and what is it costing? That's an interesting story, and I do go into this further in the article. But effectively right now, NASA is paying for the entire production of plutonium-238. This is new. It used to be that the Department of Energy, per its charter essentially,

provided isotopes to other departments in the government, primarily the Department of Defense. When NASA asked to start making plutonium again, the DOE offered to pay for it. And the part of Congress that's responsible for the Department of Energy said no. And it went back and forth like this for a few years until NASA basically gave in and agreed to pay for the entire amount, which is about, right now, $15 million a year. It's actually not very much, but this is $15 million a year coming out of NASA's Planetary Science Division, which, as many of your listeners know, has been facing some really tough financial problems in the last few years. So it's money they have to kind of scramble up. They

consider it a fundamental requirement for the program. So they can't not pay for this. And so they kind of got stuck with the bill, unfortunately. And again, it's $15 million. This is out of the Department of Energy's total budget of around $30 billion. So it's kind of a chump change, but it went back and forth. It was kind of amazing, the back and forth that happened. And this was made a very high priority by the scientific community as well, right? Oh, yeah, absolutely. I mean, any scientist who wants to explore, basically, as we said, anywhere in the solar system that may be in shadow occasionally has a vested interest in this. Any person who likes missions like Voyager and Curiosity and Galileo and Cassini,

these all use plutonium to power them. You want to go out and explore Neptune? You need plutonium. You want to go out and explore Pluto some more? You need plutonium. You want to do an interstellar precursor mission? You want to try doing another Voyager and going out beyond the solar system? You absolutely need plutonium. And anybody who wants to do something kind of more than just what we've been doing, we need this. Yeah, I want to put check marks by all of those.

I got to talk to Jim Green briefly about this about a year ago, and he was clearly very proud of this accomplishment and should be. But he also talked about the other part of the research that's being done to use plutonium as a fuel source. We only have a minute or so left, but could you say something about the development of this new type of generator that doesn't use thermocouples? Yeah, so NASA kind of has this two-pronged approach. So it's trying to create new plutonium-238 to just have, and then also it's trying to use a new radioisotope thermoelectric generator

that doesn't use, or that is more efficient, I should say, than our old ones. This is called the ASRG. It's called the Advanced Sterling Radioisotope Generator. Also just rolls off the tongue. And unlike the thermocouple, it uses a moving part. It uses basically a little piston that generates an electric field. It's far more efficient. It's about four times more efficient than current radioisotope thermoelectric generators. And it can really save the amount of plutonium. We just need a lot less to produce the same amount of electricity. However, when you put something in space, particularly for these missions that go into deep space,

you need something that lasts probably 15, 20 years. Developing hardware that has that kind of reliability is difficult and time-consuming. So right now they've been working on ASRGs for about 10 years. They're not ready to go yet. They're promising 2016, but they just recently canceled a test mission, basically, where they just run it in a little lab in the Glenn Research Facility in Ohio, at NASA's facility in Ohio. And they canceled that because they don't have the money. This is one of the consequences of the budget cuts to the planetary program. The proposed Europa mission has decided that ASRGs were just not ready for primetime,

and they couldn't risk it on a big mission like that. So they're back to either using plutonium-hungry MM-RTGs, basically, the regular RTGs that we talked about, or sticking on giant solar panels like Juno. So it's a work in progress, but it's a key element to the solution. And if they don't get those, the new processes that they're developing for plutonium can't produce enough to feed these regular RTGs. You can do maybe one mission per decade with that level of production. They can't make more than about one kilogram per year.

That's like a couple of pounds. Yeah, yeah, it's just a couple of pounds a year. And they could maybe do more with more money, but it's unlikely we're going to see more money. It is good to hear that this stuff is back in the pipeline. It is, and for all the little bit of doom and gloom about this, this is actually, I do want to emphasize, this is a success story. And as you said, Jim Green is justifiably proud of this. They moved a lot of pieces together.

And even though NASA's paying the bill, fundamentally, the U.S. is moving towards making plutonium again. This is in progress now. And it's a bright spot, an otherwise kind of dreary picture for planetary science in the United States. Casey Dreyer is the Advocacy and Outreach Coordinator for the Planetary Society. The truth is he does many, many other things around here. One of the other things he does, listen, take 30 seconds, tell people about what you're doing right now with Cosmos. Not the new one that we're all looking forward to, but the one made by our founder, Carl Sagan. Yeah, so it's kind of an anticipation of the new one that starts in early spring.

We're not exactly sure next year. To kind of prep for it, I'm running a rewatch of the original series. Every week on Sunday nights, I'm getting together with my friends and watching an episode of Cosmos in order, and I'm encouraging people, our members and people around the world, to watch it with their friends and family too. I'm calling it Cosmos with Cosmos, as in cosmopolitans. You don't have to have a Cosmo, but you can have a beer or a drink or popcorn or whatever with your friends

and to talk about it because there's nothing else thought-provoking episodes of science and our history and our place in space. And as part of that, every Monday for the next 13 weeks, I'm going to be posting an essay about each episode of Cosmos as we go through it and having this really interesting online discussion. We've been having some really cool comments from people who worked on the series, new people who are coming in and enjoying it and watching it for the first time. And it's a really fun thing to do. So check out. It's on planetary.org.

Every Monday there will be a new post, Cosmos with Cosmos. So there it is at planetary.org. Casey, I look forward to talking to you again. Happy to on planetary.org. Every Monday, there'll be a new post, Cosmos with Cosmos. So there it is at planetary.org. Casey, look forward to talking to you again. Happy to be here, Matt. The piece we've spent most of our time talking about, it's the article that Casey has put in the current issue, the brand new issue, the Planetary Report that does go to members. It's the September equinox or equinox issue. We'll also be online, but again, they're for members only, right? Yep, absolutely. This is a benefit of membership to read this.

There's a lot of original reporting that we did for our members. So sorry, non-members, you'll have to sign up. And non-members who are hearing this on the podcast version of the show, you can probably do that pretty easily as well at planetary.org. Thanks again, Casey. Time for What's Up, once again on Planetary Radio. Every week, he drops in to tell us about the night sky and much more. That's Bruce Betts, the Director of Projects for the Planetary Radio. Every week he drops in to tell us about the night sky and much more. That's Bruce Betts, the director of projects for the Planetary Society. Welcome back.

Thanks, Matt. Hi. Hi. You wouldn't think that the trivia question that we have today would generate some pretty entertaining answers, but it did, as you'll hear. Oh, cool. I look forward to it. In the meantime, let's talk about the night sky. We've got Venus just still for another few weeks looking super, super bright, low in the western sky shortly after sunset. Middle of the night, Jupiter rising in the east, also looking quite bright, hanging out not that far from Orion and a bunch of other bright stars. Not that far from Orion and a bunch of other bright stars. And then Mars coming up in the 2 a.m., 3 a.m. type realm, looking reddish, dimmer. It'll keep getting brighter over the coming months. We move on to this week in space history. First, a dark or a bright note, depending on how you look at it.

1957, Sputnik 2 and the heroic Laika, whether Laika liked it or not. And first animal in space. Forty years ago, happy, happy, happy, Mariner 10 launched. First use of a gravity assist to fly by one planet to get to another. Did a flyby of Venus and then was our first look and only look at Mercury with a spacecraft for a few decades. Until Messenger got there not that long ago. How cool. I mean, I knew that it went to Mercury,

but I did not know it was the first use of a slingshot effect. It was slingshotting from Venus to Mercury. Very cool. Because it's hard to get to Mercury, strangely. I remember that, talking about MESSENGER and all the gyrations it had to go through to get there. Just like going to the outer solar system, there's a different kind of energy change you need to do. It's still a really big energy change going to the inner solar system.

I think it'd be just like falling off a solar system. It would be if we weren't already going tens and tens and tens of thousands of kilometers per hour. Yeah. You have to bleed off a bunch of that. All right. We move on to... One more space fact. Okay.

I broke you that time. Sometimes I just speechless it's rare there i'm surprised no one's busted in here to find out to finally see the ghost that we're told haunts this building happy halloween happy halloween celebrate it so a lot of don't mind me it's okay a lot of talk sorry didn't expect you to get you laughing so much it's a lot of talk about uh dwarfs in the in the universe we we got white dwarfs and uh and then red dwarfs and and now dwarf planets but also dwarf galaxies kind of like some of these other definitions it's it a little fuzzy, but basically it's a small galaxy composed of only up to several billion stars.

Ha! Puny! Dwarfish. That's small, but compared to the Milky Way, for example, a healthy, vibrant, big, strapping kind of galaxy at 200 to 400 billion stars compared to just a few billion. That's us. 200 to 400 billion. That's us. We're not one of those little Smurf galaxies. Those tend to be heavily blue-shifted.

What was the name of Scott Carpenter's Mercury spacecraft? And what did we find out, Matt? We got the most complete answers from our winner this week, LJ. That's retired Lieutenant Leonard Johnson out of Park Ridge, Illinois. Not far, as it turns out, from where Scott Carpenter's Mercury capsule now lives, where it resides, and where people can go and see it. Back to that in a moment. The seven Mercury astronauts, they all had names with seven in them, and Scott Carpenter chose Aurora 7. Indeed he did.

Aurora 7. The first of them, Alan Shepard, Freedom 7. John Glenn, the first in orbit, Friendship 7. And Scott followed John Glenn, the first in orbit, Friendship 7, and Scott followed John Glenn. Kurt Burt and Mark Harry, they both filled us in about the location of Aurora 7. It's in Chicago, Illinois. That'd be fun to go see. I'd love to see it there at the Museum of Science and Industry.

I hope you're going to enjoy this one as much as I do. Scott Coulter, he said, This Scott's spacecraft is not to be confused with Scott Tracy's Thunderbird 1, as the Tracy's sons were named for five of the Mercury 7 astronauts. Did you know that? I did know that. What did they used to shout when they took off? Thunderbirds are go. I love that show. Then how did you not know this? That's a good question. I'd completely forgotten.

Leave it to Torsten Zimmer to finish it up today with something pretty funny. You noted last week that Scott Carpenter's capsule, Aurora 7, came down pretty far off course, like 400 kilometers. Torsten says it was shortly after that that NASA stopped using Apple Maps. Little known fact. Thank you. Thank you, Torsten. Thank you, everybody, for entering, and we're going to give you another chance right now. All right. I blame this on Matt. On Matt, if you don't like it, we're going to do a little, it's up to you to come up with a little bit of a play on words, a little bit of thought required maybe not much if you say you matt if you were forming a as people have want to do forming

a singing group that was going to perform without instrumental accompaniment and you wanted a star a very bright star literally a star to be in the group what star would you ask a star to be in the group, what star would you ask? A star to be in my group that sings without instrumental accompaniment. Yeah, what one makes the most sense? I think I've got it. Go to planetary.org slash radio contest and give us your answer. But get it to us by Monday, November 4

at 2 p.m. Pacific time. All right, everybody go out there, look up the night sky, and think about what song you would sing right now without musical accompaniment. Thank you, and good night. Fly me to the moon and let me play among the stars. He's Bruce Betts, the director of projects for the Planetary Society. He joins us every week here for What's Up. Planetary Radio is produced by the Planetary Society in Pasadena, California,

and is made possible by the glowing members of the Planetary Society. Clear skies.