The Prospects of Heavy Metal
Asteroids, ho! Pioneering space miners dream of Psyche, the largest metal asteroid in the solar system.
(sound of desert wind)
[0:01] Narrator: Sometimes it seems like our future is doomed. Climate change, killer viruses, nuclear holocaust… there are too many ways our species could flicker and die out like a sputtering candle in the dark. Dystopian movies about the future, like 2015’s “Mad Max, Fury Road,” reflect this bleak outlook.
(movie trailer clip: “Mad Max Fury Road”)
“In this wasteland, I am the one who runs from both the living and the dead. A man reduced to a single instinct: survive.”
[0:38] Narrator: Up until now, much of this season’s podcast has been about asteroids that present yet another threat to our survival. If a massive rock from space hit us, the world as we know it could end in an instant, consumed by fire and fury, the very air we breathe transformed into a toxic cocktail. Slightly smaller ones that don’t threaten the whole planet still could take out a city or lay waste to wide areas.
But some don’t see asteroids as a threat. They see them as an opportunity. In fact, these idealists think asteroids could be a solution to many of our problems.
Asteroids contain an untold wealth of natural resources. There are millions of asteroids, and they hold vast amounts of carbon, potassium, uranium, titanium, platinum… just to name a few elements with commercial uses. There is far more water in the asteroids than in all of Earth’s oceans. Why fight over the meagre scraps available on our tiny planet, when space contains an abundance of everything we’d ever need to sustain our civilization, essentially forever?
The astronomical value contained within asteroids may be fully realized if we become an interplanetary species. Entire space cities could be built from asteroids, allowing us to leave the cradle of our planet and cast ourselves into the great cosmic frontier.
Asteroid mining could even help protect our home planet. If we see a large asteroid headed for Earth, rather than kick it off course, we could mine it out of existence. In this view, near-Earth asteroids are like the solar system sending us express care packages, so we don’t have to travel all the way to the asteroid belt to get them.
Near-Earth asteroids also could be exploited as Nature’s shuttle buses. Rather than rely on cramped and fragile spaceships that need tons of fuel, why not instead hop on the next asteroid that taxis by? Asteroids could be our skipping stones to the stars.
As one of the lead scientists on NASA’s upcoming DART mission to the asteroid Didymos, Andy Rivkin of the Applied Physics Lab is invested in the potential of asteroids.
Andy Rivkin: Asteroid mining is something I find really interesting. My science research focuses on hydrated minerals on asteroids, and that seems to be what people think they want to mine. Like clay minerals, actually even something like kitty litter has 10 percent water by weight even like before it's used… after it's used, who knows. Talc, baby powder has 10 percent water by weight. So it's not water in the form of droplets, but water that's bound into the minerals, so the idea is that you can extract them from the minerals, and then take the water and use it for propulsion. At least one of the companies has been developing thrusters that literally use water for the thing they spray out.
[3:34] Narrator: In the last episode, we heard how NASA’s OSIRIS-REx mission is helping us learn more about the asteroid Bennu, including how much water it has. Bennu is on the list of “potentially hazardous asteroids” that could hit our planet someday.
Andy Rivkin: Asteroid mining has a lot in common with planetary defense and also with science, the same kinds of questions: is the interior of a body represented by the exterior, can you tell a book by its cover basically for asteroids. How do you handle material on the surface, if you mess with it here, is something going to happen over there, because you've destabilized the surface?
Whether or not there's asteroid mining in the next ten years or 20 years or 50 years, I don't know. It is definitely like science fiction-sounding from when I was a kid. Ideally, we get into a situation where we have a healthy asteroid economy, and we can all help get data for each other.
[4:59] Narrator: Welcome to On a Mission, a podcast of NASA’s Jet Propulsion Laboratory. I’m Leslie Mullen, and this is season two, episode six: The Prospects of Heavy Metal.
(movie clip: “Avatar”)
“Their damn village happens to be resting on the richest unobtanium deposit within 200 clicks in any direction. I mean, look at all that cheddar.” (evil laugh)
[5:25] Narrator: In the 2009 movie “Avatar,” the planet Pandora was targeted by those eager to plunder its deposits of unobtanium – to the great dismay of the native population.
Unlike planets, asteroids are bare rocks exposed to the harsh vacuum of space. So they’re unlikely to host any life that would object to mining activities.
Although this sort of thing sounds like science fiction, several companies have already been established to develop asteroid mining technology. And since 2016, the tiny European country Luxembourg has been setting itself up as a space resources hub, after establishing an initiative to provide funding and other support to asteroid mining companies.
Like the California Gold Rush of the nineteenth century, these space pioneers hope to strike it rich.
(movie clip: “The Treasure of the Sierra Madre”)
“We’ve struck it, Curtis. Look. From the looks of things, we’ve struck it rich! Look over here, I think we’ve got, what do you call it?”
“A Mother Lode!”
“Hey Howard, Howard, look! Look at this rock, it’s full of gold!”
“I wouldn’t pay you dinner for a carload.”
“It ain’t gold?”
“Pyrite, Fool’s gold.”
[6:43] Narrator: Mining asteroids isn’t a fool’s dream, but the pay-off is pure speculation. There are web sites that estimate the billions or even trillions of dollars that different asteroids are worth, but most asteroids haven’t yet been studied in sufficient detail. The value of an asteroid depends on other factors, too. Here’s Andy Rivkin again.
Andy Rivkin: There have been a few papers where people have tried to look at the economics of it. You know, if you found a pure platinum asteroid and brought it to Earth, then all of a sudden the price of platinum goes down to zero, right? So I think a lot of people are imagining that the most valuable material is something that's useful in space, and gets used in space.
[7:22] Narrator: Keeping asteroid resources in space avoids the problem of flooding the market back here on Earth. It also means you don’t have to worry about how to bring so much material back to our planet in a safe and cost-effective way.
NASA missions to asteroids aren’t going there to stake a claim, but to learn more about them – which includes creating maps of their elements. Space-age prospectors keep a close watch on these missions, and of particular interest is one that will launch in three years, to the metal asteroid Psyche.
News reports earlier this year claimed Psyche had enough gold to make every person on Earth a billionaire. Later reports debunked this as misinformation, spread to create a scare in the gold market and drum up interest in the digital currency Bitcoin.
Psyche is still largely a mystery, and claims about its gold content are wildly premature. But we’ll learn more about the asteroid when NASA’s spacecraft arrives there in 2026. Lindy Elkins-Tanton of Arizona State University is the lead scientist for the mission.
Lindy Elkins-Tanton: Psyche is both the name of a metal asteroid in the outer asteroid belt, and it's the name of the mission that we are sending to go visit that asteroid. There is only one large metal object in our solar system, and it is this asteroid, Psyche. And humankind has never visited a metal body before. And we've only ever visited bodies made of rock, like the Moon, or Mars, and bodies made of ice or gas, but never one of metal. And so this will be the very first time that humankind will ever go into space to visit a metal world; a new kind of exploration.
[9:01] Narrator: Earth and other rocky planets contain most of their metal in their core. The planets in our solar system formed when dust and rocks swirling around the young Sun smashed together. The heat of these impacts kept the young planets molten as they grew larger, and gravity caused the denser elements - like iron and nickel – to sink down and form a core, and lighter elements like silica to float and form a crust.
Lindy Elkins-Tanton: Our leading hypothesis for what the asteroid, Psyche is, is that it's the stripped-off metal core of a little planet, a planetesimal, so they're called, that formed just in the first couple of million years of the solar system.
If the solar system, instead of being 4.568 billion years old, that's the date to the very first solids that formed around our baby Sun, instead of that, if it was 24 hours long, then these little planetesimals would have formed in the first 10 seconds. So they're little messengers from the very beginning of the solar system. And the leftover shrapnel of them, the parts that were not incorporated into our growing planets, that didn't become a part of the Earth, are there in the asteroid belt. And so they give us a little window into the past.
But if indeed Psyche is the metal core that had all the rocky exterior stripped off of one of these planetesimals, it lets us look not just into the past, but also into the interior, because we will never see the Earth's core, or Mars' core, or the core of the Moon, which has a little core. This is the only core that humankind will ever be able to visit.
But here's the great thing: as unlikely as it is to go through the process of stripping all the rock off a planetesimal and then hiding that core in the asteroid belt for the age of the solar system for us to find, that's the most likely idea we have for what it is. So all of our other hypothesis of what it could be instead are even less likely. And the only thing I can say for sure is that it's going to surprise us when we get there, and probably all of our best intentions and abilities to try to guess what it is ahead of time will be wrong.
[10:58] Narrator: At over 200 kilometers in diameter, Psyche is more than 20 times taller than Mount Everest. It’s the tenth-largest asteroid in the asteroid belt, and the biggest metallic one. Our view of Psyche has been somewhat limited, though, and we have a lot of questions about it, including just how much metal it actually has.
Lindy Elkins-Tanton: That's a key point: how do we really know what it's made of? Our best data comes from radar bounced off of Psyche and received back at Arecibo radar dish in Puerto Rico, which itself seems like a technology miracle to me: that we can send radar all the way to the outer asteroid belt and get the return, but that radar tells us that it's very, very reflective, more reflective than rock, and that it has, along with some optical observations, it has some special thermal properties that say that it has to have connected metal through the whole thing. That's the only way we have to really explain that.
We hope that it's all metal. That would be great. We don't know. It's certainly metal-rich. And so then, what can we make of that kind of data? One, is that it could be the core of a planetesimal. That's our number one. Maybe it is a droplet from a much bigger collision between two much larger bodies, say Mars-sized bodies, early in the solar system that actually threw off a droplet of their metal cores. That's possible. But then we wonder what bodies would those be, and is there any other evidence of them?
Then, another idea is maybe Psyche is material from the very inner solar system, right next to our hot, young star, that might have driven off the oxygen and left a mainly metal body that never melted and was never part of a planet. That would be amazing. Theoretically, that kind of material has been hypothesized to exist, but we don't have any samples of it, so that puts it lower down on our likelihood list.
[12:50] Narrator: When asteroids break up and send meteorites raining down on Earth, sometimes those pieces are rich in iron. A famous example is in the Hayden Planetarium at the American Museum of Natural History in New York City. Known as the Willamette Meteorite, it is the largest meteorite ever found in North America, and the sixth-largest in the world. It’s ten feet tall, 6 feet wide, and weighs over 31,000 pounds.
The Willamette Meteorite is about 91 percent iron, 8 percent nickel, and also contains traces of cobalt and phosphorus. It’s classified as a type III iron meteorite. Different meteorites are put into different family groups, depending on their composition. This can help scientists try to figure out where in the solar system the meteorite originally came from.
Lindy Elkins-Tanton: We have a nice collection of iron meteorites on Earth. They are thought to come from quite a number of parent bodies; to be shrapnel, basically, of broken up planetesimals. But – this is always exciting -- there's one family of meteorites here on Earth called the IV-As; very poetic in the way that we name meteorites. The IV-As. They seem to come from a large body that froze from the outside to the inside, and the only body that matches that in the current-day asteroid belt is Psyche. So that's very tempting to think that maybe the IV-As come from Psyche, but I don't think we'll ever be able to prove for sure whether they do or not with our mission. We're not going to be able to measure those tiny, tiny trace metals to know what family we could match Psyche with.
[14:27] Narrator: Asteroid miners will have to wait for a highly detailed map of all of Psyche’s resources. The Psyche spacecraft instruments won’t be able to measure all of the metals, but the mission scientists think they’ll be able to answer other important questions.
Lindy Elkins-Tanton: Our number one goal is to be able to say, "Psyche is the core of a planetesimal" or "it is not the core of a planetesimal". But then we'll measure a number of other different characteristics with our instruments. One of the things that we're going after is, how oxidized is Psyche? Is there a lot of oxygen mixed in? The amount of oxygen can give us an idea of where in the solar system it started. So that might help us to understand something about, was it thrown inward from further out? Was it thrown outward from further in? Did it more or less start where it is? So we do hope to, as a secondary goal, learn something about the structure and origin of the asteroid belt.
Like any mission group that's worked on something for a decade and is still years away from launch, we have so many hopes about what we might be able to explain.
[15:36] Narrator: How a relatively small metal asteroid could help reveal the evolution of the entire asteroid belt takes a page from an interesting period in history.
Lindy Elkins-Tanton: Back in the late 1800s, there were these two scientists, Titius and Bode, and they created something that's often just called Bode's Law, where they thought they had a mathematical statement that explained why the planets are where they are around our Sun. Except it didn't work for Neptune maybe, but it predicted there should have been a planet between Mars and Jupiter.
And it actually set off one of my very favorite things of all of planetary science, which was a search for the missing planet. It was organized by a German astronomer named Franz Xavier von Zach, and he got all of these astronomers all over Europe to try to find the missing planet from Bode's Law. They had a proper name, but they called themselves Die Himmels Polizei, The Celestial Police. The Celestial Police were there to set right an order to the heavens, the way police would on Earth. They set off to try to find this missing planet. So first they found Ceres. Then, they kept finding more asteroids.
And in 1852, on March 17th, and that is, in my mind, at least no longer St. Patrick's Day, it is now Psyche Discovery Day, an astronomer named Annibale de Gasparis in Naples found Psyche. What happened was, they kept on finding asteroids, until finally, they realized there was no planet there, there were just asteroids.
Now as we can look more and more closely at the asteroids we see how different all of their compositions are. It's hard to imagine that they could possibly have come from a single planet. Many of them are material that never melted. Then, we have material like Psyche that definitely melted. So reasoning would say these were never a single planet.
So we go from the intuitive, "There should be a planet there." "Oh, okay, maybe it was a planet that was ripped into pieces." No, even that doesn't work. It's a different story. This is a beautiful example of what feels intuitively correct to us as humans, and then what we can actually show to be right or wrong when we look at it in more detail. It’s almost like a little lesson in scientific thinking.
[17:44] Narrator: Lindy’s research into how the solar system evolved led to her current role as the lead scientist on the Psyche mission.
Lindy Elkins-Tanton: I was writing papers about the theory of how our planets formed from their very first steps, and then, to try to make predictive models of how that might change or how it might have made the planets we have today. And I got an email back in 2011 from two scientists here at Jet Propulsion Laboratory, Bruce Bills and Daniel Weinkert, saying, "Lindy, we read your paper. We think it's really interesting and we wonder if we could think about creating a mission proposal to test your hypothesis."
So we went through this seemingly magical process of thinking about where we could possibly go in the solar system that would test the ideas that we had, and bringing together the scientists to work on it, and then bit by bit adding the engineers and the project managers and the schedulers and the budgeters and the graphic designers and the marketers and all the amazing people that go into making a mission bit by bit. And then, going through the multiple, multiple step process of proposing to NASA.
[18:51] Narrator: In the huge effort to get a mission selected by NASA to fly to outer space, teams come together in interesting ways.
Lindy Elkins-Tanton: Dr. Jim Bell, who's the Deputy PI for Psyche Mission, and also a planetary scientist of vast repute. He's been on the camera team for every Mars rover, for example. I knew him as an extremely serious, highly-revered scientific figure. And what I didn't understand is that he has this wicked sense of humor and this huge enthusiasm for life.
So after one of our early, early team meetings when we're all jazzed about what we're doing, he goes, "Psyche, it's heavy metal. We've got to get piercings, we've got to get mohawks. It's heavy metal!"
(music: “Asteroid” by Kyuss)
And then we started joking about tattoos. Then, because we were all enthused, it was the end of the day, we did a pinky swear that if we were selected for flight, we would get tattoos.
You know, this was back when there was, like, 1 percent chance we would ever be selected. There were so many reasons we were never ever going to be selected. So it was a pretty safe pinky swear, actually. And then, we were selected. So now six of us have tattoos.
(music: “Asteroid” by Kyuss)
And, of course, many, many people would never get a tattoo for whatever reason: personal reasons, religious reasons; no pressure, it does not indicate a greater dedication to the team.
We have a tattoo of an artist's rendition of Psyche in the present day. One person had a classical sculpture of the goddess Psyche. Psyche was given a symbol by the discoverer back in 1852, back when all solar system objects were given symbols, until we discovered there were so many we could not possibly do that. So Psyche has a beautiful symbol; some people have done that.
[20:40] Narrator: The symbol for Psyche is a semicircle topped by a star. The semi-circle represents a butterfly's wing, a symbol of the soul, since “psyche” is the Greek word for “soul.”
Lindy Elkins-Tanton: So we were at our first or second big team meeting. At Psyche we don't have science meetings and engineering meetings, we have team meetings where everybody's invited, so there's 150 people in the room, all different ... And Jim's up there talking and he comes to his last slide, and it's a picture of a priest at a confessional, and it says, "Confessions", and we're like, "What is he talking about?" Then, he starts taking off his jacket and we're like, "Oh my God, what's happening?" Then, he rolls up his sleeve and he got a tattoo, and it was fresh, this was his first unveiling, all around his upper arm with the symbols of every solar system body that he'd been on a mission to visit, and it included the symbol for Psyche. So he brought the house down. It was so dramatic.
[21:28] Narrator: Lindy’s mission tattoo is located on her hand, near the base of her thumb.
Lindy Elkins-Tanton: This is my own hand-drawing of what one of those planetesimals in the first 1.5 million years of our solar system might have looked like if you cut it in half. Someone told me it looks like an avocado. So there's a metal core, and then there's a liquid, rocky ocean around it with the little currents and the eddies in what's called a magma ocean stage of this planetesimal.
I have it tattooed on my hand because it's about having agency and doing things with your hands.
[22:02] Narrator: For Lindy, this sense of agency – of taking action -- is an essential part of her vision for the future.
Lindy Elkins-Tanton: If we can create a society of people who are problem solvers and who have a sense of agency to start solving problems, then I think that would take care of all of the biggest problems we have on Earth. And in a very real sense, I think exploring space is a part of that process, because it's in our genetics as humans to explore. It gives us a chance to be our best selves. It gives us a vision of a community that is spreading out, becoming interplanetary, giving us the chance to recreate how we think people should be, to be our better selves.
If we can do things like have a team of 500 people put together this robotic probe, Psyche, that goes out for three and a half years into our solar system and explores this unknown kind of world and sends us back the information, if we can do that, then surely we can fix some of these other problems here on Earth.
And so that's how it all comes together for me. I think all of us love the inspiration of doing these crazy activities. Think about what a step of human evolution it is that we can use systems engineering and put together teams that build instruments and missions and spacecraft that are so complicated that no single person understands how they all work, and they work flawlessly for decades and decades. If that's not an indication that humankind can continue to evolve to become better, I don't know what is.
[23:43] Narrator: Lindy’s path to working on a mission to outer space was not straight-forward. Space science wasn’t in her sights when she was growing up in Ithaca, New York.
Lindy Elkins-Tanton: This was a town my parents had moved to because they wanted to live in a small town with a hyper-intellectual vibe, thanks to the universities there, but also about 10 minutes from really wild areas. So I'm very widely interested in the natural world. I thought I wanted to be a veterinarian until I learned that dogs and horses hate veterinarians; not all of them I'm sure. But I wanted to just be with the horses and the dogs, and then I realized that wasn't right. I also, I love art. I thought I wanted to do music for a while.
I have always had an interest in science, but I've always had an interest in so many things. And I didn't go straight through in science. I spent eight years working in business, and then I came back when I was 31 to do my PhD. So I have this unusual, wobbly, wiggly path; never undirected, but just not toward a single possible goal.
The question: "Was there that moment when you knew that you wanted to do this?" I used to feel a bit like an imposter and a failure, because the answer is, "No." So many people would tell you, "Oh, when I was 10 and I saw Saturn's rings through a telescope for the first time, then I knew I had to be an astronomer and it was my life's goal to create a mission." And I feel like those are the people who end up in places like where I've ended up; these people with a singular drive. So I would like to just put a plug in there for the rest of us who have just worked forward in the best direction we could at all times, but not necessarily with one unvarying goal in mind.
[25:20] Narrator: Lindy earned a Masters degree in geology from MIT when she was only 21. But despite this achievement, she wasn’t as self-assured as she is today.
Lindy Elkins-Tanton: I had so little confidence in my ability to talk about science convincingly that I refused to go to a conference where my Master's material was being presented on a poster. It terrified me.
You know, where did that insecurity stem from? When I went into MIT as a freshman, there were only 20 percent women in the undergraduate, and there was a pervasive attitude amongst the undergraduate men and women that the women were there on suffrage and that we all had lower test scores. It turned out that was not true, but that was the way everyone felt. So maybe that's a part of it. I think that the reasons that I was insecure to go to that conference and stand in front of my poster went way deeper and had all sorts of different roots for me.
I think like many people I can tell the story of my childhood as kind of a nirvana of frolicking in the fields and the forests with our dogs and stuff. Or I could tell it as kind of a nightmare of other aspects, and they're both true, and I think that's true for a lot of people. They were largely family issues, of relatively common kinds. It's shocking to me how destructive some of those common issues of society and family can be. And so they left me with different kinds of scars that I had to deal with.
I also had scoliosis, so I wore one of those metal back braces that comes up to your chin. I wore that for 10 years. And I know that that formed a bit of my feeling about interacting with others and also physical confidence. But I would also say that, on the other hand, it was not that big of a deal. I rode horses and competed in jumping, despite my doctor's wishes that I would not. I have wonderful friends from that time; I wasn’t lonely. So it's complicated, isn't it? It's complicated.
[27:15] Narrator: Psyche may be the Greek word for “soul,” but in modern psychology, the psyche is the measure of the human mind, the scientific understanding of human nature.
Lindy Elkins-Tanton: Sometimes you just need to take a little time in your life and do your therapy and figure out your demons, and then you step forward with a clearer slate and less fear and more confidence, and that was true for me. I can't even locate that person in myself anymore, that complete terror of standing up and speaking in front of my poster.
Sometimes it just takes work, and I'm really glad that I did that work, because I can no longer even connect to the fear that I used to have. It just is gone.
[27:54] Narrator: In the Greek myth about Psyche, she must undergo a series of seemingly impossible trials in a quest to be reunited with her lost love. One interpretation of Psyche’s story is that it represents the triumph over life’s misfortunes in the pursuit of happiness.
Lindy’s perseverance also has paid off, and she finds it incredible that now she’s leading a NASA mission to the metal asteroid Psyche.
Lindy Elkins-Tanton: Oh, I feel so lucky. There are so few of us who get to do this, and so few women who get to do this. I think I'm the second woman to win a competed deep space mission.
[28:29] Narrator: Beyond the science and engineering, the Psyche mission collaborates with several artistic programs at Arizona State University. Lindy also leads an interplanetary initiative through the university to study what kinds of problems could crop up in future human space colonies.
Lindy Elkins-Tanton: What we're trying to do is help bring together all disciplines to help create humankind's positive space future. One example is, we want to understand something about what the social and legal norms will be for settlements side by side on the Moon or on Mars. This is a completely unsolved problem. And we don't even know what people's predilections would be.
And so we've had social scientists, and psychologists, and professional graphics designers and game designers work together under the direction of a professor of theater to create a game, a multiplayer game, that collects legitimate social science data on behavior while it's being played around this problem.
We're really talking about the sense of community and also the sense of sovereignty. When you have a Chinese Mars base right next to an Elon Musk Mars base, what will their common behaviors be, for example. Then we're also trying to solve really specific tech problems that lie in the way of moving into our space future as well.
[29:43] Narration: As Hollywood tends to do, this possible future is often depicted in a negative light – just see how poorly space colonists fare in the Alien movie franchise.
(movie clip: “Alien”)
“Final report of the commercial starship Nostromo. Third Officer reporting. The other members of the crew – Kane, Lambert, Parker, Brett, Ash, and Captain Dallas – are dead. Cargo and ship destroyed. I should reach the frontier in about six weeks. With a little luck, the network will pick me up. This is Ripley, last survivor of the Nostromo, signing off.”
[30:33] Narration: But scientists like to focus on the brighter side. The more optimistic view is that the human expansion into outer space is not to be feared, but embraced.
By moving beyond our small world, past the edge of understanding, and mining the mysteries of the universe in a quest to gather more knowledge, we increase the chances our species will live on. And in the process, we may even answer enduring questions about our place in the cosmos: Who are we? Why are we here? And are we alone?
Lindy Elkins-Tanton: One of the things we're trying really, really hard to learn right now is what makes a planet habitable for the kind of life that we recognize. And it turns out that when we go and we look at these little asteroids, these little pieces of the planet-forming process, each one is so different and each one surprises us completely, and puts another piece of the puzzle together about how we built planets like Earth and Venus. And that begins to teach us, "Why are Earth and Venus different? Why can we live on the Earth and not on Venus?” And when we go looking for another place where something might live, how would we be able to tell whether it was a promising place to look or not?
One of the big, driving questions that we constantly have is, "Are we alone in the universe? Are we the only life?" Oh my goodness, the existential implications of this, in every direction. It comes right down to the most fundamental philosophical and religious and sociological questions we have: finding out whether or not there's other life in the solar system, in the universe.
[32:13] Narrator: Psyche may be the largest metallic asteroid we’ve found, but there are even bigger asteroids out there. Next time, our outer space journey continues with a mission to the largest objects in the asteroid belt.
Excerpt from Episode 7: Planet Asteroid
Marc Rayman: We weren't out just exploring chunks of rock. Dawn explored two of the last uncharted worlds in the inner solar system. What could be cooler than that?
[32:37] Narrator: If you like this podcast, please subscribe, rate us on your favorite podcast platform, and share us on social media. We’re “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory.