November 5, 2019


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Transcript

Perry Como’s “Catch a Falling Star”
Catch a falling star and put it in your pocket,
Never let it fade away.
Catch a falling star and put it in your pocket…

Instrumental version of “Catch a Falling Star”

[0:14] Narrator: There once was a mission to outer space that caught a falling star by its tail.

The mission was called Stardust. As it came close to comet Wild-2, this NASA spacecraft captured some of the icy, dusty particles that fly off the comet and make up its spectacular tail. Stardust brought this precious comet cargo back to Earth in 2006.

Perry Como’s “Catch a Falling Star”
Catch a falling star and put it in your pocket
Never let it fade away…

Stardust used aerogel to capture the comet particles. This silicon sponge-like material is 99.8 percent empty space. Because of its hazy blue look, aerogel is often called “frozen smoke.” Aerogel was able to trap the fast-moving yet delicate comet particles without destroying them. The particles that bore their way through the aerogel look like miniature comets, suspended in time.

Scientists are still studying those Stardust samples to gain insight into the nature of comets. There’s even a web site, Stardust@home, where anyone can volunteer to search through the microscopic images of Stardust’s aerogel collector, and help identify the particles.

The fragility of the comet particles is one reason to send a spacecraft all the way out there to get samples. Even if the comet fell to Earth – and we think many comets have hit us in the past – the fiery descent through our atmosphere would burn up its ices and other vulnerable elements.

The same goes for asteroids. Only the most rugged bits make it through. When asteroids hit the ground they’re called meteorites, and we’ve collected thousands of them. They come to us of their own accord, all the time. But comparing the meteorites we’ve collected to what we’ve observed in space, we know they only represent a small fraction of the asteroids out there. 

Stardust wasn’t the only “sample return” mission to objects that look like falling stars when we see them streak through the night sky.  The Japanese Space Agency, JAXA, sent their Hayabusa spacecraft to the asteroid Itokawa, and brought some of it back to Earth in 2010. JAXA followed up with the Hayabusa 2 mission, now at the asteroid Ryugu, and plans to return samples of that asteroid back to Earth next year.

The asteroids visited by the Hayabusa missions have orbits that could cause them to hit Earth someday. They’re on JPL’s Sentry list of potentially hazardous asteroids. Ryugu is a kilometer in size – large enough to affect the whole world if it hit. Itokawa is about a third of the size of Ryugu, 330 meters, but still big enough to be a continental catastrophe.

It’s a striking contrast: on the one hand, these asteroids are so big and strong they’d deal a powerful blow if they ever punched through our atmosphere. And yet, to study them well, we need to gather their stardust and gingerly place it in a package marked “handle with care”.

Perry Como’s “Catch a Falling Star”
…Just a pocketful of starlight.
Catch a falling star and put it in your pocket
Never let it fade away
Catch a falling star and put it in your pocket
Save it for a rainy day….

(intro music)

[4:07] Narrator: Welcome to “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory. I’m Leslie Mullen, and this is Season 2, Episode 5: Catch a Falling Star.

(music)

If you look at a map of all the asteroids in our solar system, it’s overwhelming and a bit frightening. The asteroids look like hornets in a mad swarm around the Sun. But that asteroid map is deceptive, because it’s not to scale. Space is actually mostly empty. The asteroids in our solar system aren’t packed closely together like in the Star Wars movie, “The Empire Strikes Back.”

Movie clip: “The Empire Strikes Back”

“What are you doing? You’re not actually going to go into an asteroid field?”
“They’d be crazy to follow us, wouldn’t they?”
“You don’t have to do this to impress me.”
“Sir, the odds of successfully navigating an asteroid field is approximately 3,720 to one!”
“Never tell me the odds.”

[5:01] Narrator: We tend to disregard the odds of asteroid threats to Earth, as well. Astronomers will say, “This asteroid has a one-in-a-million chance of hitting us.” Even though those odds are extraordinarily low, that often gets interpreted as, “Oh no, an asteroid is going to hit us!”

Movie clip: “The Empire Strikes Back,” Chewbacca’s and C3PO’s reactions to asteroids

[5:26] Narrator: When an asteroid passes us by, we can’t just breathe a sigh of relief. They often come back.

(music)

They’re orbiting the Sun, just like we are, but at different speeds and on different paths. So when astronomers determine an asteroid’s odds of hitting us, they have to not only consider this loop around the Sun, but all of its future loops as well. 

JPL scientist Steve Chesley keeps tabs on where asteroids are going.

Steve Chesley: For tracking asteroids, our data source are these telescopes that are constantly plowing the skies, looking for objects, and whenever they find something they send it in and we update the orbit. So we don't update the orbits necessarily when we want to. We do that when we get more data.

Sometimes objects are so interesting that we’d say, "Hey, we need to know where this is." Maybe because it's threatening the Earth or maybe because a space mission wants to go there. So then they will point the telescope where it's supposed to be. Now, if those predictions for where it's supposed to be are very approximate, they might have to do a lot of work to recover the asteroid.

The fun thing in asteroids is you can do that in the past. You can kind of do time travel because everybody's saving their images. And even film from the 1950s has all been digitized, and so if you have an asteroid you want to know where it was sometime in the past, you can go to those files, and update the orbit that way.

[6:53] Narrator: It’s not a simple connect-the-dots exercise, though, because asteroids don’t follow straight lines through the solar system. Sunlight that warms the surface of asteroids can steer them in unexpected directions. This is known as the Yarkovsky effect.  

NASA web series clip: “Robot Astronomy Talk Show”

Robot host IR-2 (Ed Wasser): “The Yar-who-see-what’s-ee?
Cameron Diaz “Oh, the Yarkovsky effect is very cool.”

[7:13] Narrator: On a NASA web series, the “Robot Astronomy Talk Show,” the actress Cameron Diaz schooled the robot host about the Yarkovsky effect. 

NASA web series clip: “Robot Astronomy Talk Show”

Robot host IR-2 (Ed Wasser): “So you’re saying that when an asteroid absorbs sunlight on one side, that side emits infrared energy that pushes it out of its normal orbit.”
Cameron Diaz: “Exactly. The more sunlight it’s able to absorb, the more infrared energy it emits, and the farther it gets pushed.”

[7:38] Narrator: Asteroids all experience this effect to different degrees, and Steve says figuring out how it changes an asteroid’s orbit around the Sun can be difficult.

Steve Chesley: When an asteroid is first discovered, we really don't know even which way the asteroid is being pushed. It could be pushed ahead or behind in its orbit. That can be a very complicating effect on the Earth hazard prediction for many asteroids.

Now we have on the order of 100 near-Earth asteroids for which we can see and estimate the amount of the Yarkovsky effect, but there's still 20,000 more near-Earth asteroids for which we have no insight of what the Yarkovsky effect is doing to that body.

(music)

[8:22] Narrator: Radar measurements can help narrow down how an asteroid is deviating from its expected path, but such measurements can only be made when an asteroid is relatively close to us. Radar also can provide better details on an asteroid’s size and shape, which is good to know if you’re trying to figure how sunlight is heating their surfaces.

And asteroids come in a medley of forms: some look like dog bones or walnut shells, others are an irregular jagged mishmash. One Halloween, an asteroid with features like a human skull flew past us, a wicked cosmic joke. Some asteroids are enormous, and some are very small. They come in different colors and flavors: metallic, stony, icy.

Why are the asteroids all so different? Why are they even out there in the first place?

To answer such questions, NASA has sent missions to investigate them. The Galileo mission to Jupiter was the first to flyby an asteroid, back in 1991. The first mission to orbit and land on an asteroid happened seven years later, with the NEAR-Shoemaker spacecraft’s visit to asteroid Eros. At nearly 17 kilometers in length, Eros is the second-largest near-Earth object, six kilometers bigger than the asteroid that led to the dinosaur extinction. Luckily for us, Eros is not heading our way.

The asteroid Bennu is another story. Bennu’s orbit around the Sun brings it close to Earth every six years, and there’s a small chance it could hit us in the year 2196. Bennu is 500 meters in diameter, taller than the Empire State Building. If it hit us, the impact would unleash 80,000 times the energy of an atomic bomb.

This threat is enough to have motivated a recent study about the best way to steer Bennu off course. HAMMER, an acronym for “Hypervelocity Mitigation Mission,” would be a battering ram of a spacecraft. We’d have to throw a lot of HAMMERS at Bennu to move it, between a dozen to 80, depending on the amount of time we have before it hit.

But Bennu might not respond the way we think it will. We need to learn more about it. With that in mind, NASA’s OSIRIS-REx mission is currently orbiting Bennu and sending us images of its rough craggy surface.

Astronomers think Bennu is a shattered fragment, a remnant from a collision between two larger asteroids. That impact chipped Bennu off and tossed it out of the asteroid belt, the region of space between Mars and Jupiter that contains millions of asteroids. Bennu still bears the marks of being a crash survivor; it’s a rubble-pile of rocks, loosely bound together by gravity.

The lead scientist of the OSIRIS-REx mission, Dante Lauretta of the University of Arizona, says they hadn’t realized just how loosely bound some of those rocks are.

Dante Lauretta: So, yeah, the asteroid is regularly tossing material off into space. This certainly was unexpected and caught us by surprise. 

(music)

A lot of them are falling right back down and landing on the asteroid’s surface. Some of them are actually getting trapped in orbits around the asteroid, which is really exciting because it allows us to track them over many days, and even weeks, and then start to learn something about the detailed gravity field of the asteroid. And then some of them are at high enough velocities, above what we would call the escape velocity of the asteroid, and they're leaving Bennu and going into interplanetary space.

There is no concern for spacecraft safety, it's a small enough amount of material and, overall, moving relatively slowly.  So even if one of these were to hit the spacecraft, it wouldn't cause any damage that would impact our ability to achieve the mission.

[12:03] Narrator: The dance of rock particles around Bennu is just one more challenge for the spacecraft.

Dante Lauretta: We're navigating in a micro-gravity environment, and that has a lot of unexpected and small forces that act on the spacecraft. So in addition to the gravity of the asteroid, we're also getting pushed around by the solar wind, material out-gassing from the spacecraft, heat radiating off of the asteroid. All of those have a substantial impact on the trajectory of the spacecraft. So we're constantly taking images and updating the position and figuring out where we're going to be in the future, and that drives a very intense operational timeline for the team. Basically, within 24 hours of making a science observation, we have to do a navigation solution, determine the position and velocity of the spacecraft relative to the asteroid, and then get that up on the spacecraft so that it can accommodate the differences in where we're actually going to be, versus where we thought we would be when we first made the design.

[13:00] Narrator: The difficulty of even navigating a spacecraft around an asteroid suggests that moving one could be a tough task. But OSIRIS-REx is not there to move Bennu; its goal is to gather a sample from it.

Even though rock particles are drifting off Bennu, the OSIRIS-REx mission wasn’t designed to capture them like the Stardust mission did for comet Wild-2. Instead, a device at the end of a long arm, extending from the underside of the spacecraft, will collect material from the asteroid’s surface. After the device touches down for five seconds, springs will bounce the spacecraft back up, kind of like a pogo stick. In those five seconds, the device will gather asteroid dirt in a unique way.

Dante Lauretta: Touch-And-Go Sample Acquisition Mechanism, or TAGSAM, which is the device that we place on the surface, is basically a vacuum cleaner working in reverse. So, with a vacuum cleaner you create an area of low pressure and it pulls the air and the dirt through a filter. With TAGSAM we actually bring our own air, because the asteroid is an airless body, and we blow it down into the regolith, or the soil, on the asteroid, creating a region of high pressure underneath the filter, and then it grabs the gravel and rocky material and pushes it up into an air filter.

(vacuum pulling up rocks FX)

The TAGSAM is designed to pick up a minimum of 150 grams of material, and its capacity is over two kilograms. 150 grams is like a Grande Starbucks coffee cup.      

[14:29] Narrator: The samples OSIRIS-REx will bring to Earth will reveal more about Bennu, and they could help us better understand the history of our solar system.

 (music)

Asteroids are left-overs from all the material that swirled around our young Sun and came together to form the planets.

Dante Lauretta: So we're really interested in the earliest stages of solar system formation, and there's no geologic record of that period on the Earth or on the Moon or on Mars, so if you want to understand how planets formed, then you need to go back to the small bodies - the asteroids and comets - which have been largely unaltered since the earliest stages of the formation of the solar system.

We think when the solar system was young and material was just starting to form, there was a disk of material, of gas and dust, that was spinning around the protosun, we call that the protoplanetary disc or the solar nebula. And there was a temperature gradient: when you were close to the Sun things were very hot, and you formed what we would say are refractory minerals, like calcium and aluminum. Then, as you move away, things got colder and different minerals became stable. You had the silicates that make up the majority of rocky material, and the metals. Then you had things that would incorporate sodium and potassium and then you got out to ices, like water. Then, as you got farther out, even to more extreme ices like methane, ammonia, carbon monoxide, which freeze out at very low temperatures.

[15:52] Narrator: Bill Bottke, Director of the Department of Space Studies at the Southwest Research Institute in Boulder Colorado, says we’re still trying to get a handle on how asteroids have moved around since our solar system formed.

Bill Bottke: So the asteroid belt, I think, is fairly ancient, but it may not have looked exactly the way it does now, four and a half billion years ago. It may have been more massive, we may have had more material there. The asteroid belt has been changing a lot. There's even sort of extreme models to say at one point, the asteroid belt was completely empty. And then during planet formation processes, material from the same zone where you're making the Earth and Venus and the rest threw material into the asteroid belt from the inside. And then you're also taking all these small bodies forming in the giant planet zone, you're putting them into the asteroid belt. So the asteroid belt is sort of a clearinghouse for things all the way across the solar system. All that activity would have happened very early.

The objects are very, very old. But also, dynamically, we have models trying to say how would you get these objects on to these orbits in this fashion? Our models can only work if they happen at very early times in solar system history.

But there's this other issue as well, which is why the asteroid belt is filled with material that looks... for those that know what an ordinary chondrite is, this is a very standard type of meteorite falling on the ground. It tends to be fairly stony, it has very little water. And then there's another kind of material we have in the asteroid belt, called carbonaceous chondrites, this material is more primitive, more water rich. Seems like it formed at colder temperatures and such. And we have a mixture of those two in the asteroid belt, but the mixture isn't uniform.  And the question is, why do we have that mixing? And how do you get such diversity of compositions within a really small span of the asteroid belt, because the asteroid belt’s not that big. If you took all the mass in the asteroid belt, and you put it into one single object, that object’s only about five percent the mass of the Moon, so there's not much stuff there. And it's also spread out over a huge distance.

[17:42] Narrator: The locations of asteroids today may be largely due to Jupiter, the biggest planet in the solar system.

Bill Bottke: So Jupiter, we think, started maybe not so different from the Earth. It begins to grow. We think it's forming when there was a solar nebula around. And if objects get large enough, they can start to grab the gas. And then as they grab the gas, they get larger and still larger, and they can go almost into a runaway process, where they're getting lots and lots of gas.

So if they then get big enough from that process, then they can start to gravitationally interact with the disc of material around them. And so what happens is that they're pulling on the gas disk. The gas disk is interacting with the planet, and that can actually cause them to migrate inward, in some cases. In other cases can cause them to migrate outwards. It all depends on the real specifics of what's going on with this gravitational interaction.

[18:29] Narrator: Scientists figured out that planets can switch places like this because when we look at exoplanet systems -- planets orbiting other stars – sometimes we see Jupiter-like planets closer to their Sun than the tiny scorched planet Mercury is to our Sun.

Bill Bottke: For really large, Jupiter-size planets that are living right next to the star, we don't think they could have formed there. And so that's a big clue that somehow in these systems, maybe their versions of Jupiter started farther out and then migrated inward.

[18:57] Narrator: Perhaps that accounts for the asteroid belt between Jupiter and Mars. As Jupiter moved toward the Sun, its gravity swept the asteroids ahead of it, like a giant broom. But Jupiter may have scattered more asteroids than it gathered.

Bill Bottke: When Jupiter reaches its full size, it actually creates a lot of excitation in the solar system. And if Jupiter migrates and other worlds migrate, you can do all sorts of interesting things to the asteroid belt. So the asteroid belt may have lost a lot of mass, not by collisions, but by dynamics. Imagine making an asteroid belt, and then exciting a lot of material out of it. So you're just left behind with survivors that are some small fraction. That may be what our asteroid belt is today.

[19:32] Narrator: NASA plans to launch another mission, called LUCY, to visit asteroids that share an orbit with Jupiter. Known as Trojans, these asteroids might be able to tell us more about whether Jupiter migrated.

If Jupiter bellied up closer to the Sun, and other planets shifted inward or outward, that would have been a period of massive upheaval. Asteroids would have been tossed about, smashing into each other and hitting the planets too. Our Moon still bears the scars of intense asteroid pummeling. During the Apollo missions, the lunar astronauts explored craters made by these asteroid impacts.

NASA Apollo 15 mission; Geology Station 2 on Mt. Hadley Delta
Jim Irwin: It looks fairly recent, doesn't it, Dave?
Dave Scott: Yeah, it sure does! It sure does, and I can see underneath the upslope side; whereas, on the downslope side, it's piled up. Boy, that is really something. Hey, let's get some good pictures of that before we disturb it too much.
Joe Allen: And it probably is fresh; probably...
Dave Scott: Okay.
Joe Allen: ...not older than three and a half billion years.
Dave Scott: Can you imagine that, Joe? Here sits this rock, and it's been here since before creatures roamed the sea on our little Earth.

(music)

Bill Bottke: When the Apollo astronauts went to the Moon, they brought back samples from a number of different places on the lunar near side. And then they took the samples back and dated them, and they seemed to see a lot of ages that were showing up around 3.9 billion years ago or so. And so some people suggested, well, that might mean that there was a big impact spike at 3.9. Okay. And they suggested a lot of the biggest craters we see on the near side of the Moon were from that time. Now, that was in the early Apollo days, since then we've gotten a lot better information on the Moon, from our various satellites and things. We've gotten much more sophisticated in the labs and the work. And there's been a lot of revisions of how to put the different objects we have in context. And now a lot of people think that a lot of the 3.9 ages we’re getting are simply from one of the biggest impact basins that's on the near side, and that's called Imbrium.

So Imbrium may have thrown its material all across the near side of the Moon. And so we see these 3.9 ages, we may just be getting the Imbrium age again and again and again.

Now, with that said, there's also this puzzle, right? So this is where you can sort of go back and forth on this. There's about 40 craters on the Moon larger than 300 kilometers or so. But two of the three largest out of that 40, probably with ages not so different than 3.9. And there's some interesting evidence that's coming from the GRAIL mission, that suggest that other basins also may have ages similar to Imbrium. And it's not just the Moon, we have other constraints, that while interpretation is always the issue, they suggest that maybe something big was happening between about four and 3.6 billion years ago.

And then this model came along, called the Nice model, which suggested that the giant planets formed in a certain configuration. And then many hundreds of millions of years after they went through this big instability, which caused them to migrate, and really changed the whole configuration of the solar system. The question is, when did it happen? So for many years, we argued that since there was all these indications of an increase in impacts around 3.9, maybe the Nice model happened at 3.9. That kind of made sense.

But now we're starting to look at the idea that this planet reconfiguration happened very early in solar system history. And if it did, then that would take away its ability to make the late impacts that we see.

So the biggest problem with the Nice model having a long delay is that systems that want to go unstable, go unstable, right?  It's kind of like, you know, when you have an avalanche, it's hard to have the snow piled to sit there and sit and sit and sit before it goes, it wants to go.

 (avalanche sound FX)

[23:10] Narrator: The solar system formed 4.6 billion years ago, and scientists think if the planets migrated, it had to have happened early in that formation process. A heavy bombardment of asteroids 3.9 billion years ago still seems early to us, but it’s more than 500 million years after that possible period of planet migration.

Asteroids are like clues to the scene of a crime long after it happened.

(“Law & Order” TV show stinger)

Anyone who watches crime shows knows the first 48 hours are vital for collecting clues. For those who study the solar system, the clues are billions of years old, and they don’t always line up.

Bill Bottke: Imagine you're Sherlock Holmes and you go into a room and there's a dead body on the floor.

(“Sherlock” BBC TV show theme song)   

You see blood splattered on the wall and you see bone fragments. And as a detective, he'll look at the blood splatter and the bone pieces and the rest, trying to say, "Okay, how was this murder committed?" So essentially asteroids and comets are the blood splatter and the bone chips and everything else we need to understand planet formation. The planets themselves are useful, but they've been subject to a large number of events which are sort of random in nature. So it's hard to necessarily say what happened. Small bodies, because of their nature, their diversity, their orbits and the rest, provide really powerful constraints for our planet formation model.

So right now we're visiting the asteroid, Bennu. Bennu has turned out to be this amazingly fascinating world. And I've also been enjoying watching the mission Hayabusa2 from the Japanese space agency. They're going to this asteroid, that's a little bit Bennu-ish called Ryugu. And both are going to bring back samples. The story they tell is going to be a story of planet formation. But it's also going to be a story of what's happened in the asteroid belt over the last few billion years.

[24:53] Narrator: For OSIRIS-REx lead scientist Dante Lauretta, the rock samples taken from asteroid Bennu are akin to getting DNA samples from a crime scene.

Dante Lauretta: I compare it to a forensic investigation. When you look at meteorites, you haven't had control of the chain of evidence. You don't know who's handled them, if they've been contaminated just by landing on the surface of the Earth. We have gone through an enormous amount of effort to keep the samples clean and to document any contamination that might be introduced to them so that we will know the material that we find inside the samples definitely came from the asteroid.

We're really interested in the role carbon-rich asteroids like Bennu may have played in seeding the surface of the early Earth with the materials for the origin of life.  We're interested in amino acids, nucleic acids, sugars, lipids that might form cell walls, anything that we think was critical to building the first bio-molecules on Earth.

[25:54] Narrator: The hunt for molecules vital to life within Bennu was a major inspiration for the name of the mission. The “O” in “OSIRIS-REx” stands for “Origins.”  In case you’re curious, the other letters in “OSIRIS” stand for “Spectral Interpretation, Resource Identification, and Security.”  “Rex” is Latin for “king,” but for the mission, it stands for “Regolith Explorer.”

As acronyms go, OSIRIS-REx is a bit tortured, but Dante chose it partly because of the mission’s parallels to the Egyptian god Osiris. Among his many gifts, Osiris was thought to have brought vegetation, fertility and life to Egypt. Asteroid Bennu’s potential to hit Earth someday reflects Osiris’s darker side, as the God of the Dead.

Dante has a penchant for strategic puzzles and creative associations. When he’s not leading space missions to solve the mysteries of the solar system, he’s designing board games.

Dante Lauretta: I make games that are science based. We use those as tools to engage kids in getting interested in science and higher education. I teach a class here at U of A called, “Gameful learning and community outreach.” So we recruit students and train them to be mentors. Then, every week they go in to the Boys and Girls Club clubhouses and they bring in science-themed games, not just our games. There's actually a broad movement of researchers and scientists who are building games that have strong science content built into the gameplay. The kids like playing board games, they like meeting college students. The whole concept is to bring University of Arizona undergraduates into the clubhouses to give them role models and people they can relate to, ask questions to, and learn about college. And then through the science-themed games they learn something about science as well.

(music)

I actually went to the Boys and Girls Club as a kid, it was one of the places that I hung out. My mom was a single parent, and she needed a place for me to go where I can be taken care of after school, mostly in the summertime. I grew up in rural Arizona, a little area called New River. I was the first person in my family to go to college. I really didn't even know what it meant, to go to college. It really wasn't obvious to me what options were out there. I mean, my family worked in restaurants or jobs like that. So I kind of figured that's what I was going to do. But then I did a lot of work like that and it's hard and you know, it's not very glamorous.

Fortunately, I was able to get to the University of Arizona as an undergraduate student because I did well in high school and they had Regent scholarships. And that really changed everything for me. To be able to go to college for free and figure out that there was professional opportunities to be scientists, and eventually I discovered planetary science, and that's where my career path was really set.

[28:46] Narrator: As a child, Dante always had an interest in science, and he especially loved science fiction novels.

Dante Lauretta: I was a really big fan of some of the nineteenth century science fiction. They were in the school library as classic books. Things like Charles Dickens or Emily Bronte, I didn't really care for any of that stuff, and then I found “The Time Machine” by H.G. Wells.

Excerpt from “The Time Machine,” by H.G. Wells:

“I am afraid I cannot convey the peculiar sensations of time travelling. They are excessively unpleasant. There is a feeling exactly like that one has upon a switchback—of a helpless headlong motion! I felt the same horrible anticipation, too, of an imminent smash. As I put on pace, night followed day like the flapping of a black wing. The dim suggestion of the laboratory seemed presently to fall away from me, and I saw the sun hopping swiftly across the sky, leaping it every minute, and every minute marking a day.”

Dante Lauretta: And I was like, "Okay, this is the kind of book that I like to read." So you know, “Twenty Thousand Leagues Under the Sea” and “Journey to the Center of the Earth,” and the whole idea of scientific expeditions I thought was just really fascinating, and I want to be part of one of those someday.

[30:03] Narrator: Now as lead scientist on the OSIRIS-REx mission to the ancient asteroid Bennu, he’s on a science expedition with his own time machine.

Dante Lauretta: That's right, we are going back in time to the dawn of the solar system.

(music)

[30:17] Narrator: The samples OSIRIS-REx will gather could take us back to when our planet first got its vast oceans.

Dante Lauretta: There's a big question in planetary science about where did Earth's water come from. We're obviously a unique planet in having abundant liquid water at the surface, and from our theories of planetary formation, Earth shouldn't have formed with that large amount of water. It had to be brought in from something like an asteroid or a comet. And we think these water-rich asteroids are the most likely sources, and so we will be trying to understand if the water in Bennu has the same isotopic composition as the water in our oceans.

[30:53] Narrator: Asteroids like Bennu don’t have lakes of liquid water on them; rather, the water molecules are bound up in minerals like clay. That water is of interest not only to answer questions about our planet’s past. For those who want to mine asteroids for precious resources, asteroid water is at the top of their list.

(Excerpt from Episode 6: The Prospects of Heavy Metal)

Andy Rivkin: The idea is that you can take the water and use it for propulsion. It is definitely like science fiction from when I was a kid.

[31:20] Narrator: More on that, next time.

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.

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