Picture of two persons in white lab coats and face masks under golden umbrella.

Episode 4: Lucy in the sky with asteroids

Astronomers are examining pint-size pieces of the solar system—like asteroids and comets—more closely than ever before.

A solar array for NASA’s Lucy spacecraft unfurls as it is tested at a Lockheed Martin facility in Colorado. Set to launch in October, Lucy will need two of these arrays to generate power during its 12-year mission to explore Jupiter’s Trojan asteroids. These ancient swarms, which orbit the sun alongside the giant planet, may hold clues to the solar system’s original layout.

How did the planets form? How did life happen? Where did Earth’s water come from? To answer questions like these, scientists used to go big—looking at planets, dwarf planets, and moons—but now small is the new big. Technology is zooming in on the pint-size stuff—asteroids, comets, meteors, and other chunks of space rock—that couldn’t be studied before, and Lucy, a spacecraft designed to visit eight asteroids near Jupiter, is poised to learn how the secrets inside these small bodies are reshaping ideas about the big old solar system.


ADRIANA OCAMPO (NASA PROGRAM EXECUTIVE): What sparked my interest in space was just dreaming about the stars.

AMY BRIGGS (HOST): This is Adriana Ocampo. She’s a NASA scientist, and back when she was a kid in Argentina, she’d grab her dog and head to the roof of her house. 

OCAMPO: You know, we would go—every evening that we had a clear sky—to the rooftop and look at the stars. And I used to ask myself, What were those points of lights? What were they composed of? Were they people like us out there?

BRIGGS: That dream brought her to NASA. And once she became a scientist, Adriana had her own brush with one of those little points of light. Not a star, but an asteroid. In the 1980s, a research team was pushing a theory that was extremely controversial at the time. They thought an impact from outer space wiped out the dinosaurs.

OCAMPO: And the challenge was—when 1980 they came out with their publication, they didn’t have the location of the impact crater. 

BRIGGS: The scientists had found evidence in Earth’s rock layer that they interpreted as a massive impact, but they couldn’t find a massive crater to go with it. Their theory needed a smoking gun. Back then, Adriana happened to be studying impact craters. 

OCAMPO: You know, so every circle seemed like a potential impact crater, and it was just embedded in my brain.

BRIGGS: So with impacts on her mind, Adriana saw another scientist present satellite imagery at a conference. It was totally unrelated to the dinosaur thing. The images showed Mexico’s Yucatán Peninsula. And Adriana noticed this huge semicircle, about a hundred miles across, embedded in the landscape. 

OCAMPO: And it turns out that afterwards, I went to talk to him and said, “Well, what do you think that is?” And they didn’t have any idea what it was. And I said, “Well, have you ever thought of what—that it could be an impact crater?” He said, “Well, what do you mean?”

BRIGGS: Adriana traveled to Mexico to check it out for herself. And she realized that the crazy theory about an asteroid killing the dinosaurs? Not so crazy now, because she found the smoking gun.

OCAMPO: That confirmed that indeed that had been an impact crater under, you know, a thousand meters or a kilometer of soil. It was hidden. So you could be standing in top of the impact crater and not know it.

BRIGGS: The crater is called Chicxulub. And today, thanks to research by Adriana and many other scientists, it’s widely accepted that this object from space did kill the dinosaurs and more than half of all species on Earth at the time. Now Adriana is leading a different kind of research, but it still centers around space rocks. And this one also started with a dream. She’s the program executive of a NASA mission called Lucy. Its team is about to launch a mission to a group of asteroids called the Trojans. 

OCAMPO: You know, I call it the team of dreamers because they made a dream to go explore the Trojan asteroids—an area that never had been explored before—and they are making it a reality.

BRIGGS: Asteroids and comets are leftovers from the birth of the solar system: a cosmic rubble pile that humans used to write off as barren and uninteresting. They were more interested in big things, like planets. But not anymore. Astronomers have huge questions about how we got here. Like, why does Earth have water and life? And how did the solar system even form in the first place? 

OCAMPO: The formation of the solar system is something that has occupied the minds of many scientists for many, many decades, if not centuries. You know, how did we came to be, how did the solar system form and even the location of where the planets are today.

BRIGGS: More than ever, scientists think those big answers could come from some of the smallest objects in the solar system.

I’m Amy Briggs, executive editor of National Geographic History magazine. And this is Overheard: a show where we eavesdrop on the wild conversations we have here at Nat Geo and follow them to the edges of our big, weird, beautiful world.

This week: If you thought stars and planets were the only important things in the sky, think again. We’ll go behind the scenes of a NASA mission that’s exploring pint-size worlds and learn how asteroids could help us piece together how the solar system took shape. Plus, even though Hollywood gets asteroids wrong—I’m looking at you, Bruce Willis—we’ll explain how it helped kick off this real-life research and how we’re learning to protect ourselves from the next killer impact. 

More after the break.

So, before we dive into the world of small space stuff, I need to come clean and confess. It’s something you’d never know just from hearing my voice, but it can affect my objectivity. So here goes: I’m short. Like five-three-on-my-tiptoes short. And being vertically challenged has always made me root for the little guy. So I kind of have it out for people who overlook the importance of small things. Like, remember when Pluto got downgraded from planet to dwarf planet? I took that a little personally. So when it comes to astronomy, my allegiance is with the little guy.

MICHAEL GRESHKO (NATIONAL GEOGRAPHIC SCIENCE WRITER): As our understanding of the solar system has improved over time, it’s become increasingly clear how important the small objects are in refining our understanding of what’s going on. 

BRIGGS: This is Michael Greshko. He’s one of Nat Geo’s science writers, and he’s written a cover story about the interest that scientists have for asteroids and comets. But it wasn’t always that way. In the early 1900s, some astronomers dismissed asteroids as “vermin of the sky.” They blocked our views of stars or distant galaxies, so these space rocks were more annoying than interesting. 

GRESHKO: I think far from being just the leftovers—just the stuff we can ignore, the astronomical stamps to collect—small bodies are critical to our understanding of those big questions.

BRIGGS: So to understand why they matter, you have to start at the beginning. No, like, the very beginning. If you travel back in time far enough, you arrive in a solar system with no planets in it. 

GRESHKO: More than four and a half billion years ago, the sun—what is now the sun—forms in kind of a stellar nursery. It’s in this sort of big cloud of gas and dust. 

BRIGGS: The newborn solar system was shaped like a disk—a big Frisbee made of star stuff. Over time, the Frisbee coalesced into the planets and other bodies. But exactly how that happened is still up for debate. One thing we do know: It wasn’t smooth. Far from it. 

GRESHKO: Another piece of this is that this is not an orderly process. This is—it’s chaotic. It’s violent. Things are slamming into each other. Collisions are happening all the time.

BRIGGS: Some of the planets’ orbits changed drastically. For example, the giant planets appear to have formed much closer to the sun than they are today. But something made them move farther out, and scientists want to know more about how that happened. Also, some of these collisions hit close to home. According to what’s known as the giant impact theory, another planet-size object clobbered Earth. Our planet survived—obviously—but not in one piece. A huge chunk flew away from Earth, and that became our moon.

GRESHKO: But ultimately, we get the planets we have today and all of this other flotsam and jetsam that didn’t form into planets but was born at the same time of the same stuff. And we call those objects today comets and asteroids and trans-Neptunian objects and all these different populations that all exist on the same spectrum of leftover.

BRIGGS: Over time, we realized those leftovers have a lot to tell us. And in the past 20 years or so, research into small objects has exploded. That’s partly because of technology. Better telescopes and high-res digital cameras made it possible to zoom in on tiny objects like never before. But Michael says there was also a critical window when asteroids grabbed our attention. 

GRESHKO: In 1998 there was a period—there was just a few days in March of 1998 where there was some concern of an asteroid impact that would affect us in the 2020s.

BRIGGS: Yeah, so imagine waking up to headlines that the world might end in 30 years. Not so great. Thankfully, scientists quickly announced that it was a false alarm. But that scare couldn’t have come at a more fitting time. Just a few months later, not one but two major movies hit theaters, both featuring killer impacts from outer space. 

In Armageddon, Bruce Willis leads a ragtag crew to nuke an oncoming asteroid—which, by the way, is something that only works in the movies. And in Deep Impact, President Morgan Freeman gives a rousing speech after—spoiler alert—a comet wipes out the eastern United States. The specter of an impact loomed so large that Congress immediately told NASA to study the threat of killer asteroids. 

GRESHKO: And by July 1998, NASA had formalized an office to look for specifically near-Earth objects. But it turns out that when you focus on finding near-Earth asteroids and you spend a lot of time with a lot of telescopes pointed to the night sky to try to find near-Earth asteroids, you end up finding a lot of other stuff too.

BRIGGS: So picture a solar system diagram—the kind you may have studied in grade school. That diagram would have eight planets—or nine, if you count Pluto, which I do. Throw in a few more dwarf planets, plus a couple hundred moons. And then factor in asteroids, comets, and other small objects. The solar system gets much more crowded.

GRESHKO: So as of 2021, astronomers have cataloged slightly more than a million objects in the solar system. There’s almost certainly many, many, many, many more—billions, if not trillions, of objects in the solar system. It’s just a question of whether we’ve gotten good enough to see them.

BRIGGS: And now we’re not just seeing these little leftovers. We’re visiting them. Michael got a window into how NASA is actually studying asteroids.  

GRESHKO: So OSIRIS-REx is a NASA mission that late last year touched down on the surface of an asteroid called Bennu.

BRIGGS: OSIRIS-REx actually isn’t the first spacecraft to land on an asteroid. The Japanese space agency did it in 2005 and then again a few years ago. But this is NASA’s first time touching down. Michael was at mission control last year for that moment, when Osiris-REx made contact with Bennu. He says even though it was a tense moment, the mission’s leader was strangely at peace. 

GRESHKO: He’d been working on versions of this mission for 16, 17 years at that point for a window of time on the surface of this asteroid no more than, you know, 10, 20 seconds, more than 200 million miles from Earth.

BRIGGS: OSIRIS-REx touched down and scooped up some of Bennu’s rocks and dirt—or regolith, to use the technical term. The spacecraft is set to return home in two years, and just by getting close to Bennu, it made some groundbreaking discoveries, like the fact that the asteroid has small amounts of water stored in its rocks. Now, since the cargo is so rare, researchers want to make sure they don’t let any data go to waste. Michael says OSIRIS-REx will adapt some techniques pioneered by the Japanese missions. 

GRESHKO: They were very careful about the way that they opened the canister, et cetera, to get some of the stuff that had even come off of the—kind of the grains and pebbles that they collected as gas, which is, I think, the first time anybody’s ever gotten that measurement. 

BRIGGS: Since it will take OSIRIS-REx a couple of years to return home and then it’s gonna take time to analyze the sample, it could be a while before we learn anything more about that asteroid.

But this fall, a new explorer takes flight: Lucy. 

CATHY OLKIN (PLANETARY SCIENTIST): So we’re going to send the Lucy spacecraft to visit the Trojan asteroids, which are the remnants—or you could think of them as the fossils—of planetary formation. 

BRIGGS: This is Cathy Olkin. She’s the deputy principal investigator of the Lucy mission—one of the top scientists. And she’s no stranger to ambitious missions. Before Lucy, she worked on New Horizons, which gave us our first close-up view of Pluto. But for almost 20 years, Cathy’s had her eyes on one group of asteroids. They’re called the Trojan asteroids.

(To Olkin) So when did a mission start coalescing in your mind, and how long did it take to get it off the ground? 

OLKIN: Yeah, so one thing—you have to be very persistent in spaceflight and space exploration.

BRIGGS: Humans have sent a few spacecraft to asteroids and comets, but nobody has ever explored the Trojans. So in 2009, Cathy was part of a team that first proposed a mission to the Trojans. NASA said, No thanks. In 2010, she tried again. Still, no dice. 

OLKIN: But every time we learned more, and we modified and improved our proposals until we submitted a proposal in 2014 that was this Lucy mission.

BRIGGS: Cathy proposed flying past not one or two objects but seven different asteroids—more than any other mission by far. And this time, NASA said yes. So, first things first. Lucy is a spacecraft, not a person. The mission takes its name from Lucy the fossil—the early human ancestor discovered in Africa in the 1970s.

OLKIN: And this fossil revolutionized our understanding of human origin. And our intention with the Lucy mission is to revolutionize our understanding of solar system evolution.

BRIGGS: Now, you trivia buffs out there may remember that the original fossil was named Lucy because scientists were listening to the Beatles song “Lucy in the Sky With Diamonds” as they celebrated the discovery. Well, Lucy the spacecraft has a Beatles tie-in too. 

OLKIN: The Lucy mission will be in the sky with diamonds. We have a diamond, a cultured diamond that’s part of our optical system on one of our instruments. So we’ll be taking diamonds into the sky with us.

BRIGGS: So are the Beatles played in the lab for inspiration … or?

OLKIN: Yeah. Recently we’ve been saying “Peace and love” and “groovy” to each other quite a lot, really getting in the spirit of it.

BRIGGS: So, you say you want a revolution in understanding the solar system. Here’s what Lucy is going to find out. Jupiter has two asteroid entourages: one that orbits in front of it and one behind. They’re not moons. They’re just locked in the planet’s orbit because of Jupiter’s gravity. These are the Trojans. We’ve cataloged about 10,000 of them, but the total number could be in the hundreds of thousands. Lucy is going to fly by seven Trojans, plus another asteroid in the main asteroid belt.

Even though the biggest Trojan is 160 miles wide, from Earth they just look like tiny pinpricks of light. Cathy says studying the solar system is kind of like studying the ancient pyramids. From the outside, you can only learn so much. 

OLKIN: But if you looked at the rubble in a site where the parts that didn’t get used in the pyramid are, you could maybe learn more about the composition or what else is inside that pyramid. So in this case, the Trojan asteroids are kind of like the rubble pile that wasn’t used to make the pyramid. So we can have clues to what was used to make up those giant planets. 

BRIGGS: So, what kind of information could the asteroids have? Here’s one mystery. Scientists think heavy elements like calcium and iron came from a star exploding in a supernova. But somehow they ended up here on Earth and even in our own bodies. It’s not clear how they got here. But according to Adriana Ocampo, the program executive we heard from earlier, Jupiter played an important part. 

OCAMPO: And Jupiter was that big blender that brought all those molecules to the inner solar system during its formation. So we think then that was how eventually our planet acquired a lot of these key elements during its formation.

 BRIGGS: Since the Trojans are in Jupiter’s neighborhood, they could help us unpack how exactly that big blender worked. Last year, Michael Greshko was lucky enough to visit Lucy in person. So we’ll tag along for his face-to-face look at an asteroid explorer.

More after the break.

Lucy’s journey to the Trojan asteroids started in a Lockheed Martin facility in Colorado. The mission is partly run by NASA and Lockheed Martin, as well as the Southwest Research Institute, Arizona State University, and Johns Hopkins University. When Michael Greshko visited, the team was assembling Lucy in a clean room. It’s like a big, sterilized hangar to prevent outside contamination, like the kind of thing you’d see in a sci-fi movie. So before he could see the spacecraft… 

UNIDENTIFIED: There’s your hood. Go ahead and put that on first.

BRIGGS: Michael had to suit up. 

GRESHKO: So I’m wearing like a white—it’s like a slippery synthetic fiber suit with boots and gloves where the cuffs are taped up. 

UNIDENTIFIED: And then the goal is to get into this thing without dragging on the floor too much. 

GRESHKO: I’m wearing a hood, a face mask. 

BRIGGS: So you’re full-on beekeeper. 

GRESHKO: Oh, I’m full-on. Yeah.

[To unidentified person] All right. Well, hey, look at that. These are like very svelte pajamas. 

BRIGGS: Inside the clean room, Michael wasn’t even allowed to use his own notebook, in case tiny paper fibers came loose. They gave him a special, approved notebook instead. Michael met up with Cathy Olkin, and she gave him a tour.

OLKIN: We have this instrument pointing platform, which is so cool to be right next to it. [Laughs.] And the terminal tracking cameras will...

BRIGGS: Michael says, up close, Lucy looks like a big bug. There’s a rectangular body, roughly the size of a small car. It’s tricked out with specialized cameras, as well as instruments to measure temperature and communicate back to Earth. And sticking out from the sides, like wings, are solar panels more than 20 feet wide.     

GRESHKO: As we see this spacecraft being assembled and tested component by component, you know, it was it was hard to believe then and it’s hard to believe now that, like, I was in the room with something that’s going to space and is going to be observing objects that have never been seen up close before—ever.

BRIGGS: When you’re the first explorer charting new territory, you have to start at square one. One thing Cathy Olkin wants to know is, What color are these asteroids?

OLKIN: When we look at the Trojan asteroids, we see some are less red and others are more red. 

BRIGGS: So why is it important to know what color the Trojans are? I mean, it seems like such a basic question, like, are there blue, are there red? 

OLKIN: It is a basic question. And actually that tells you a lot about our knowledge of these Trojan asteroids. As seen from Earth, they’re just a point in the sky.

BRIGGS: The color differences here are really subtle. To our eyes, the Trojans probably look gray. But Lucy can detect color wavelengths our eyes can’t see. Those little differences give hints about what the asteroids are made of. So understanding the color of the Trojans’ surface is an important clue to figuring out where they formed. Lucy is also keeping an eye out for water ice and carbon dioxide ice. If we find those on an asteroid, maybe we’ll start to figure out how they ended up on Earth. 

OLKIN: So that’s one of the reasons it’s important to understand what the Trojan asteroids are made of. It’s a hint as to where they came from.  

BRIGGS: Mm-hmm. Do you have any educated guesses right now what that composition could be? Like, we thinkin’ the same kind of rocks as Earth or…? 

OLKIN: You know, we don’t know. And that’s part of the excitement of going to the Trojan asteroids. 

BRIGGS: But even though Lucy heads to the launchpad in October, it’s going to take some time to get those results. Lucy will travel at an average speed of about 40,000 miles per hour, which is pretty fast. But it has almost four billion miles to cover. 

OLKIN: It’s far away and everything is moving, and sometimes the best way to get there energetically is not by a straight line. In fact, it never is by a straight line. 

BRIGGS: So Lucy’s flight path looks like a pretzel. It loops around Earth a couple of times so that our gravity flings it toward Jupiter. If all goes well, in 2027—almost two decades after she first proposed the mission—Cathy will see the Trojans up close for the first time.

OLKIN: I’m just so glad we have a spacecraft and it’s, you know, all ready for launch. So it’s exciting. It’s been a long time coming.  

BRIGGS: So, by studying small bodies, scientists are looking for answers about our beginnings: the beginning of our solar system, maybe even the beginning of life itself. But those leftover space rocks, clanging around the solar system? They could also bring the end. Earth is pocked with scars from asteroid and comet impacts, just like the crater Adriana Ocampo discovered. 

OCAMPO: And we know that eventually in the lifetime of our planet, it will happen again. So if we are a smart species, we are going to get ready and be preparing.

BRIGGS: Now, killer space rocks shouldn’t keep you up at night. NASA says as far as we can tell, no big asteroid will cross our path in the next hundred years. But what if we did need to deflect one, like in the movies? Could we pull it off? Well, we’re about to find out.

OCAMPO: Later this year after Lucy launches the DART mission, which is a mission to deter the trajectory of an asteroid in case it could be on an impact trajectory with the Earth.

BRIGGS: So NASA picked a tiny, harmless asteroid, and Michael Greshko says the plan is to send a spacecraft hurtling toward it, like a cue ball. 

GRESHKO: Which is sort of a tech demo for one technique in which you send a spacecraft, a small spacecraft, really, really fast and collide with an asteroid in such a way—just give it a slight nudge. 

BRIGGS: That nudge would alter the asteroid’s orbit just a tad. 

GRESHKO: If you do that early enough, you know, maybe a hundred years ahead of time, by the time that that predicted impact were to happen, its orbit is harmless.  

BRIGGS: This mission is only a test. But if it works, it could show that for the first time ever, life on Earth is not defenseless against an oncoming asteroid. Adriana Ocampo says that shows why we need missions to uncharted parts of the solar system. 

OCAMPO: We’re living in the golden era, I think, extraordinary of space exploration and especially for small bodies, and now we’re putting the puzzle together. 

BRIGGS: Today’s research could pave the way for even bigger things. Maybe we’ll eventually colonize the solar system and learn how to mine asteroids. It’s not gonna happen anytime soon. But it’ll never happen if we don’t take baby steps now. 

OCAMPO: That’s why we need to go to space exploration. It’s really part preservation of our species as well. Not only we want to learn more about our neighborhood, our planetary neighborhood, our solar system. We want to go and learn how to live on other planetary surfaces like Mars and the moon.

BRIGGS: Those are big dreams. And to make those big dreams come true, we have to pay attention to the small stuff. 

We only had time to scratch the surface of asteroids, comets, and other small space stuff.  For more, paying subscribers can check out Michael Greshko’s Nat Geo cover story, about how the little guys are remapping the solar system. 

The link is in our show notes. You can also find a closer look at the OSIRIS-REx mission. You might be wondering, how did an unmanned spacecraft pick up a sample from an asteroid 200 million miles away from Earth? Turns out the answer is something like a Roomba attached to the end of a pogo stick. I swear I’m not making it up. Read the article.

We also have a story about how astronomers are studying interstellar objects, the first space rocks known to visit us from a totally different star system. And learn why some scientists think we might be living in an age with more meteor impacts than normal.

So that’s all in the show notes, right there in your podcast app. And if you like Overheard, please take a minute to rate and review us. It’s a big help. 


Overheard at National Geographic is produced by Jacob Pinter, Ilana Strauss, Brian Gutierrez, Laura Sim, and Marcy Thompson. 

Our senior editor is Eli Chen. 

Our senior producer is Carla Wills. 

Our Executive Producer of Audio is Davar Ardalan. 

Our fact-checkers are Robin Palmer and Julie Beer. 

Our copy editor is Amy Kolczak. 

This episode was sound-designed and engineered by Hansdale Hsu.

This podcast is a production of National Geographic Partners. 

Whitney Johnson is the director of visuals and immersive experiences. 

Susan Goldberg is National Geographic’s editorial director.

And I’m your host, Amy Briggs. Thanks for listening, and see you all next time.


Want more?
How do you recover a sample from an asteroid? Send a spacecraft equipped with something akin to a Roomba at the end of a 10-foot pogo stick. Bennu’s orbit brings it close to Earth. Now we have a precise calculation of the odds that—gulp—it will collide with us.

Coming soon from NASA: a demonstration to test whether we could avert an oncoming asteroid

Also explore:

In the early 1800s, astronomers wanted to find a missing planet. Instead, as our video series Nat Geo Explores shows us, they discovered the asteroid belt.  

For the first time, scientists are studying interstellar interlopers—asteroids and comets visiting us from another star system. 

The solar system has always been a violent place. But Earth’s recent history suggests a rising tide of celestial impacts, according to one study.

And for paid subscribers:
Michael Greshko’s National Geographic cover story explains how the study of small objects is rewriting what astronomers know about the solar system. 

If you like what you hear and want to support more content like this, please consider a National Geographic subscription. Go to natgeo.com/explore to subscribe today.