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Season Two, Episode 7: Planet Asteroid

Season 1Episode 7Nov 19, 2019

What’s in a name? Whether you call it a planet or an asteroid, missions that explore small worlds are always exciting.

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(music: “We are the Planets” by StoryBots)
We are the planets of the solar system
Different sizes for every one
The music never ends
We are such good friends
And we all orbit the sun


[0:10] Narrator: How many planets are in our solar system? Growing up, most of us were told there are nine. The four rocky planets close to the Sun – Mercury, Venus, Earth, and Mars – plus the more distant giant planets Jupiter, Saturn, Uranus, and Neptune. And then finally, the tiniest and most distant planet, Pluto.

People now debate whether Pluto is a planet, or if it instead should be classified as just one of the many objects that make up the Kuiper Belt, which rings the solar system beyond Neptune.

But we’ve had this debate before, more than two hundred years ago, long before Pluto was discovered. Here’s Marc Rayman, Chief Engineer for Operations and Science at JPL.

Marc Rayman: The planets from Mercury to Saturn of course were known even to ancient astronomers. But when Herschel discovered Uranus in 1781 with a telescope, that was the first time a planet had been discovered in anybody’s memory. And then in 1801, Giuseppe Piazzi discovered what turned out to be another planet. He named it Ceres for the Roman goddess of agriculture and grain. And in fact, if you had cereal this morning, then you have an etymological connection with the good goddess. And this planet resided in the solar system between the orbits of Mars and Jupiter.

Astronomers quickly recognized that Ceres was smaller than the other planets, but that’s okay. It was a planet. In 1807, Heinrich Wilhelm Olbers discovered another new body in that part of the solar system, Vesta. And by then, Olbers and somebody else as well had discovered two other bodies, so there were now four objects known to orbit the Sun between Mars and Jupiter. And for the better part of the next two generations, these objects were known as planets. And in fact, children would learn in school the names of the planets, and it included Vesta and Ceres.

[2:06] Narrator: Odds are, you were never taught about the planets Ceres and Vesta. That’s because as astronomers discovered more and more objects orbiting between Mars and Jupiter, they realized Ceres and Vesta were part of a much larger population that we now call the asteroid belt.

Marc Rayman: And so we now recognize that Vesta and Ceres are two, albeit the two largest, but nevertheless two of the literally millions of objects orbiting the Sun between Mars and Jupiter.

You know, you don’t discover all of them at once. You discover the first and then eventually another and another, and the more you discover, the more you learn about the cosmos. And so as our knowledge changes, maybe our vocabulary should change to keep up with it. In 2006, the International Astronomical Union created a new category of solar system bodies called “dwarf planets.”

Well whatever you think of that decision, at the time that category was created, Pluto was the second known object to fit in that category, Ceres having been discovered 129 years before Pluto, also satisfies all of the attributes of a dwarf planet. Vesta comes close, but doesn’t quite. But still, Vesta and Ceres are big places, and in fact they’re the two largest objects between Mars and Jupiter. Pluto is among the largest of the myriad objects orbiting the Sun outside the orbit of Neptune.

[3:33] Narrator: We knew a lot about Pluto after gazing at it for many years with telescopes, but when NASA’s New Horizon’s spacecraft flew by Pluto in 2015, it revealed many surprises. Whether you call Pluto a planet, a dwarf planet, or a Kuiper Belt object, it’s a complex world with tall mountains and a glacier bigger than Texas that’s shaped like a heart.

Marc Rayman: I think one of the things that we all learn is whenever we explore some distant destination, it always turns out to be more interesting than we could ever have imagined. No matter how creative we think we are in understanding the cosmos, we always find surprises. The universe isn’t the way we want it to be, or the way we think it’s going to be, it is the way it is. Our job is to learn what that is. And that’s what I think is so exciting.


[4:54] Narrator: Welcome to “On a Mission,” a podcast of NASA’s Jet Propulsion Laboratory. I’m Leslie Mullen, and this is Season 2, Episode 7: Planet Asteroid.

(music: “Stars and Planets” by Liz Phair)
Stars rise and
Stars fall
But the ones that shine the brightest aren’t stars at all
There are the planets just like us
And from big to small
We all shine, shine, shine
We all shine

[5:23] Narrator: Planets generally are big round objects that circle the Sun. A planet also has “cleared its neighborhood” of smaller objects in its orbit, like a broom sweeping away dirt. But not everyone agrees with this definition. What to call an astronomical object can become a point of heated debate.

In the children’s story “The Little Prince,” the title character’s home planet is an asteroid.

(“The Little Prince” by Antoine de Saint-Exupéry, reading by Kenneth Branagh)
“The planet he came from was hardly bigger than a house! That couldn’t surprise me much. I knew very well that except for the huge planets—like Earth, Jupiter, Mars, Venus–which have been given names, there are hundreds of others, that are sometimes so small that it’s very difficult to see them through a telescope. When an astronomer discovers one of them, he gives it a number instead of a name. For instance, he would call it, “Asteroid 325.”

I have serious reasons to believe that the planet the little prince came from is the asteroid B-612. This asteroid has only once been sighted only once by a telescope. In 1909, by a Turkish astronomer. Who had then made a formal demonstration of his discovery at an International Astronomical Congress. But no one had believed him, on account of the way he was dressed. Grown-ups are like that.”

[6:45] Narrator: In 2007, NASA sent a spacecraft called “Dawn” to explore Ceres and Vesta. Whether you call them giant asteroids or dwarf planets, Ceres and Vesta are as complex and interesting as any other place we’ve explored. Marc was the project manager on the Dawn mission.

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?


There are millions of objects in orbit between Mars and Jupiter, in orbit around the Sun in the main asteroid belt, and yet Vesta and Ceres are the two largest and together they constitute around 40 percent of the mass of the main asteroid belt.

Vesta… even though it doesn’t qualify officially as a dwarf planet, it really is more like a mini planet than it is like a big chunk of rock. It’s 350 miles in diameter at the equator. It’s got a huge crater, deep in the southern hemisphere that’s more than 300 miles in diameter. And at the center of that crater is a mountain two and a half times the height of Mount Everest. Our planet doesn’t have anything like this. Think of this, one in every 16 meteorites seen to fall to Earth came from the impact that excavated that giant crater on Vesta, probably more than a billion years ago. I think most people know we have meteorites from Mars and from the Moon. But Mars, the Moon and Vesta are the only solar system bodies to which we have linked specific meteorites. And we have far more from Vesta than we do from the Moon or Mars, and yet Vesta’s much farther away even than Mars is. I think that’s really remarkable.

And Ceres: a dwarf planet with a substantial inventory of water, most of it frozen, but perhaps even some still underground in liquid form. Sometimes that water makes its way to the surface, and in the cold vacuum of space that ice sublimates — that is, transforms directly from being a solid to a gas. So the water molecules will dissipate, but they would leave behind the salts that were dissolved in them. And now when we look at many of Dawn’s pictures of Ceres, we see these mesmerizingly bright features that we now understand to be those dissolved salts left behind when the water sublimated.

We discovered cryovolcanoes — cryo, cold — volcanoes on Ceres. And instead of erupting the kind of lava that we are familiar with from Earth, what comes out of the volcanoes on Ceres is a mixture of rock, salt, ice and water, so that’s a kind of mud. We found the tallest mountain on Ceres, more than 13,000 feet high, is a cryovolcano, and planetary geologists have now, with Dawn’s data, identified a couple of dozen ancient cryovolcanoes.

. [10:02] Narrator: Before they could make these discoveries, the Dawn spacecraft had to first go into orbit around Vesta, and then do that again for Ceres.

Marc Rayman: The detailed exploration required orbiting them, not just flying by. For most solar system bodies that we’ve investigated, first we send a spacecraft to fly by. And Vesta and Ceres, in terms of solar system exploration, are very unusual in being the only massive objects which we didn’t first fly by, but immediately started by orbiting, which presented some challenges for the Dawn Mission.

To go to a distant solar system body, get into orbit, then maneuver in orbit, then break out of orbit, escape from that object’s gravitational clutches, travel elsewhere in the solar system, and then get into orbit around another body, and maneuver in orbit there, is far beyond the capability of conventional chemical propulsion. You just simply can’t do it.

The ion propulsion allowed us to, for the only time so far ever, to orbit two distant extraterrestrial destinations. The way I think of it is, Dawn is an interplanetary spaceship doing a mission that would have been truly impossible with any other existing technology.

[11:20] Narrator: “Ion propulsion” sounds like something right out of Star Trek.

(clip from TV show: “Star Trek” season 3, episode 6: “Spock’s Brain”)
“What do you read, Mr. Spock?”
“Configuration unidentified. Ion propulsion, high velocity. Though of a unique technology…”

Marc Rayman: The ion propulsion system is 10 times the efficiency of conventional chemical propulsion. This would be like having your car get 300 miles per gallon. With the same amount of propellant, you can undertake a much, much more ambitious mission.

And so, let me remind you how a conventional propulsion system works. You take a gas and you heat it up, or you put it under pressure, and you push it out of a rocket nozzle. And the action of the gas going out of the nozzle causes a reaction that pushes the spacecraft in the other direction. Well, ion propulsion works on the same principle, but instead of heating the gas up or putting it under pressure, we give the gas a little electrical charge. So we use the gas Xenon, and when we give these atoms an electric charge, they’re called ions — hence ion propulsion. And when they have an electric charge, they can feel the effect of a voltage.

So we have two metal grids only about 10 times the thickness of your hair, so they’re very, very close together, and we put a large voltage, more than 1,000 volts between them, and that accelerates these charged atoms, these ions, and we can then use that to shoot the ions out of the spacecraft at speeds up to 90,000 miles per hour. And because the ions go out with such high velocity, they have such a large action, they cause a large reaction.

It’s no different from when you open up the end of a balloon, the gas rushing out pushes the balloon in the other direction. And the faster we shoot out these ions, the faster the spacecraft will go in the other direction.

(clip from TV show: “Star Trek” season 3, episode 6: “Spock’s Brain”)
“Isn’t she a beauty.”
“Interesting design.”
“I’ve never seen anything like her. And ion propulsion at that! They could teach us a thing or two.”

Marc Rayman: Part of what’s so exciting about a mission like Dawn is we got to pilot this advanced spaceship on an 11-year mission to boldly go where no… Well, you know.

(music: “Star Trek” theme)
“To boldly go where no one has gone before!”

[13:37] Narrator: Every space mission has challenges that test the mettle of the captain and crew. The Dawn mission was no exception.

Marc Rayman: Most interplanetary spacecraft use devices called “reaction wheels” to control their orientation in the zero gravity of space. A reaction wheel is sort of like a gyroscope, it’s a disk that’s electrically spun. And by changing the speed that the wheel rotates, you can cause the spacecraft to rotate around the wheel, or to stabilize.

And the spacecraft needs three of these reaction wheels, because there are three dimensions like pitch, roll, and yaw, or X, Y, and Z. And so Dawn carried four of these reaction wheels, because we were sending it on a nearly decade-long mission, and if one failed, we wanted to have one in reserve. These were essential to the operation of the spacecraft, but one of them failed in 2010, about a year before the spacecraft got to Vesta.

It still had three, so that was okay. But if another one had failed, then we would not have been able to control the spacecraft. So the spacecraft got to Vesta in July of 2011, had a fantastically successful mission there. And as it was departing in August of 2012, another reaction wheel failed.


[15:01] Narrator: The loss of the second reaction wheel meant they had to figure out a new method for pointing the spacecraft.

Marc Rayman: By all rights, we really should have lost the mission, because when we designed it, there was no concept of flying the spacecraft with anything fewer than three reaction wheels.

Dawn carried a small supply of hydrazine for an obscure technical reason, and that is the reaction wheels would gradually spin faster and faster and faster. And so the way to slow them down was to fire the hydrazine through some very tiny thrusters, to rotate the spacecraft against the motion of the reaction wheels.

[15:42] Narrator: By using the tiny hydrazine rockets, they could regain control of the spacecraft. But there was another problem.

Marc Rayman: That wasn’t how we intended to operate Dawn, so it didn’t have enough hydrazine on board to operate that way. Carrying enough hydrazine to fly this many-years-long mission would have required too much hydrazine; that’s why you use reaction wheels. But it meant that we had to undertake a very ambitious campaign to conserve the hydrazine, to stretch it so it could last long enough to complete this mission.

It was another two and a half years and 900 million miles to fly the spacecraft from Vesta to Ceres, and at Ceres another reaction wheel failed. By this point, now three reaction wheels had failed.

Essentially we were flying a different spacecraft at that point, because hydrazine was the critical metric, for any plans we made, any new ideas we had. For everything we did, one of the key questions was, how much hydrazine is it going to cost? Or how can we do this differently to use less hydrazine?

[16:52] Narrator: They were able to conserve so much hydrazine that they not only completed their mission at Ceres, but they extended the Dawn mission for several more years. Once the hydrazine ran out, the engineers had to make sure the spacecraft wouldn’t crash into Ceres.

Marc Rayman: Dwarf planet Ceres has a substantial amount of water, it has organic chemicals, and internal heat. These are many of the ingredients that are important for life. And I’m not saying there’s life on Ceres, but Ceres could have chemistry that’s related to the chemistry that gave rise to life on Earth, and perhaps elsewhere.


And so we didn’t want to contaminate this pristine and important environment of interest to the study of the possibility of life elsewhere in the universe.

I like to think of the Dawn spacecraft as an inert celestial monument to human creativity and ingenuity, orbiting the dwarf planet that it unveiled. It won’t be forever, but it will certainly be for decades. And it could well even be for centuries, if not millennia. And so people, when they listen to this podcast when it comes out, and then when their children listen to it, and maybe their grandchildren and maybe future historians, if they can figure out how to play those primitive podcasts from sometime back in the 21st century, even then, Dawn likely will still be in orbit.

[18:28] Narrator: The history of space exploration has always been important to Marc.

Marc Rayman: I became interested in space when I was four years old. And, well, I need to take a step back and tell you, I was scared of witches. The kind that fly on broomsticks like in The Wizard of Oz.

(movie clip: “The Wizard of Oz”)
“I’ll get you, my pretty! And your little dog too!”

I was outside, one evening in Toledo where I grew up, and saw a streak of light go through the sky.


And ever the logical youngster, I concluded it was a witch flying on her broomstick, and I was terrified. My parents reassured me that it wasn’t a witch, it was a shooting star, something burning up in the atmosphere, what I would now call a meteor. That just fascinated me. And so the terror and all the bad feelings I had associated with it just suddenly transformed, and I was hooked. By the time I was in the fourth grade, I knew I wanted to get a PhD in physics and work for NASA.

[19:29] Narrator: He started writing letters to space scientists all around the world.

Marc Rayman: Any place that there were people who were interested in exploring the cosmos, and I wanted to learn from everybody. Because I don’t think of our missions as just NASA missions, I think of all of them as missions of humankind. I had an insatiable appetite for everything having to do with space and science, and anything I could get felt like a treasure, whether it was an object, an artifact, something to read, or just pure knowledge. I just wanted it all.

I started that when I was very young, but continued it for quite a long time. Even when I was a graduate student in physics and working on my doctorate, I still tried to find the time to send at least two letters every weekend, someplace in the world.

So while I was a graduate student in physics, working at the Joint Institute for Laboratory Astrophysics, an FBI agent called me and asked if he could come visit me in my lab. I assumed that he wanted to talk about somebody I had known who had moved into the defense field so they could get clearances for their work. So he came into my lab, and he said… Oh, first of all, I should tell you his name. Gilberto Contreras, special agent for counter intelligence. I love that name Contreras, counterintelligence.

But just as I was sitting down, he said something to the effect of, “The FBI would like to know why you’re writing to the Soviet Union and the People’s Republic of China?” And one of the questions I asked him was, “Look, I’ve been doing this since I was nine years old, what took you so long?” But, of course, a nine-year-old writing to those countries perhaps doesn’t attract their attention as much as somebody who’s getting a PhD in a high technology field, and that’s what Agent Contreras explained to me. I asked him if he had read my letters, and as he put it, “At the FBI we don’t believe gentleman read gentleman’s mail.”

And he also made me aware that I could be a target for recruitment by the KGB. He told me that the KGB might be interested in several things about me, including, do I gamble? Do I drink? And as he put it, “Do I chase skirts?” Which to me sounded like a term right out of the 1950s.

So that was a fun experience. It might bother some people, but I mostly thought it was just neat, as did many of the other graduate students. I have a black belt in karate, and so (laughs) a number of them would whistle the James Bond theme song when I’d walk by.

(music: “James Bond” theme)

[22:22] Narrator: When Marc came to JPL, one of his projects was the outer space version of James Bond’s high-tech gadget lab.

Marc Rayman: Deep Space 1 was the first of a series of missions that were designed to test advanced, risky technologies on space missions. So a problem that space projects get into is, if you’re in charge of a multi-hundred-million-dollar space mission, you’re not rewarded for taking big risks, you’re rewarded for a successful mission, for getting the scientific results in the least risky way possible. And it’s very, very difficult to prove that a new gadget will work in a space mission, because space is forbidding. There’s vacuum, and radiation, and extremes of temperature, and many other aspects of the environment that are difficult for devices to tolerate, and they have to work very reliably.

So I was part of a group that formed this program called the New Millennium program that was flying some of these advanced technologies. And the way I like to think of it is, Deep Space 1 and the other missions of the New Millennium program took the risks so that future missions wouldn’t have to.


[23:46] Narrator: The difficulty of sending a mission to a comet or asteroid is something Steve Chesley knows a lot about. But instead of the engineering challenges of driving a spacecraft, Steve comes at it from the other direction. He’s part of a group at JPL that keeps track of how comets and asteroids move through the solar system.

Steve Chesley: Comets are notoriously difficult because they’re emitting gas and that, coupled with dust, drives them off course from what the gravitational forces would send them. And that outgassing is fundamentally random, so it makes the prediction problem very difficult.

Asteroids also have these non-gravitational accelerations. The asteroid heats up from the Sun, and then it rotates and re-emits that heat in a different direction from where it was absorbed, and that tends to drive these asteroids, again, off course from where they would be going if it was just gravity from all of the known objects in the solar system moving them around.

[24:43] Narrator: Two years ago, a strange object called “‘Oumuamua” was discovered taking a most extraordinary path.

Steve Chesley: For ʻOumuamua, it was pretty clear almost from the earliest detections that this was a very unusual object. We were able to observe it after it had passed by the Earth. So we saw it going away.

[25:01] Narrator: ‘Oumuamua was discovered by the Pan-STARRS search program in Hawaii. The name, “‘Oumuamua” means “scout” in Hawaiian. Paul Chodas of JPL’s Center for Near Earth Object Studies says ‘Oumuamua’s path told us of its origins.

Paul Chodas: ‘Oumuamua came from another star system.

[25:19] Narrator: This was the first time astronomers had spotted an object passing right through our solar system, rather than circling the Sun.

Paul Chodas: We had been expecting for decades to find a comet on such an orbit. Because we know that the comets in our solar system didn’t form there, in distant space. They were ejected by the planets during the formation of the solar system, in particular Jupiter, the most massive planet. And there must have been a lot of comets that were ejected completely from the solar system, floating through interstellar space. So we expected other star systems to do the same thing.

[25:56] Narrator: ‘Oumuamua didn’t seem like a typical comet, though.

Paul Chodas: It didn’t form any coma, the atmosphere, or any tail, so I guess it wasn’t icy. So that really opens up a lot of questions. How did it form, and what it’s made out of? It was bizarre. And then, we looked at the light curve of that. It had a dramatic change in brightness with time, over seven or eight hours, much more so than any asteroid we’d seen in our solar system. So that was strange. Assuming it’s equally bright on all sides, that indicated that it was very long and thin.

[26:30] Narrator: Astronomers saw the object as a point of light. Because that light is sunlight reflecting off the object’s surface, by tracking how the brightness changes over time, they can get a sense of the object’s shape and how it’s moving. The sunlight reflecting off ‘Oumuamua flashed bright and then dim in a way that suggested it was shaped like a cigar, tumbling over and over again.

Paul Chodas: So another surprise, because none of the objects in our solar system are shaped like that. So a bizarre shape, bizarre trajectory. And after another month or so, the trajectory started deviating. So it was actually being pushed. It was accelerating, but in fact as it moves away from the Sun, it’s decelerating because the Sun’s gravity is holding it back. But it was decelerating at a slower rate than it should be, which means something was pushing it. We call that a non-gravitational acceleration, and comets experience that all the time. It was, I think, due to outgassing, because it’s a normal amount of acceleration for a comet. But there was no evidence of outgassing. So it’s a real conundrum, this object.

[27:42] Narrator: Objects traveling in from the outer solar system are faster than objects that normally live closer to the Sun. But Paul says at 87 kilometers per second, ‘Oumuamua broke all the speed records.

Paul Chodas: It’s very fast. Faster than anything we’ve seen, basically. We might get a comet passing by the Earth at 60 kilometers per second. But this one is going faster than those.

[28:05] Narrator: But it’s really not an alien spaceship… right?

Paul Chodas: The interstellar object was behaving bizarrely, and so we’re getting into the question of: is that an alien object like in “Rendezvous with Rama?” You know, some alien spacecraft passing through the solar system. Okay… I just think that the odds of that are very minuscule compared to the odds of it being a natural object.


[28:27] Narrator: Just this year, astronomers spotted another interstellar object, named 2I/Borisov. The “2-I” refers to it being the second interstellar object ever found. “Borosov” is the name of the amateur astronomer in Crimea who discovered it. 2I/Borisov will be visible until the end of 2019, but astronomers have already seen that it looks and behaves just like comets in our solar system, and it has a similar chemistry.

2I/Borosov may be only the second interstellar object we’ve ever seen, but it clearly is a comet. Steve says that sometimes, it’s hard to define exactly what a far-distant object is.

Steve Chesley: Asteroids are just defined by the fact that they look like stars. They don’t have any fuzziness or tail or any kind of indication of emissions that we see in comets. And comets, by contrast, just don’t look like stars. There’s something about them that gives an indication that material is coming off: tails or coma or other kinds of strange shapes.

Well, for ʻOumuamua, it should have been a comet. A lot of people looked very hard for a coma on ʻOumuamua and didn’t find it, so then suddenly the Minor Planet Center that looks after these things had to sort of backpedal and change the designation from a comet to an asteroid-style designation, which is unusual. And then much later, we found that there were these outgassing effects, which is expected for a comet. So ʻOumuamua is in this gray area.

A lot of things in the outer solar system that we don’t call comets because they’re too far away to have this outgassing, they’re too cold, if you brought it in close to the Sun, it would definitely be a comet. There’s also all these objects in the main asteroid belt that are designated as comets because for a number of reasons, they have shown that they’re active. They’re spinning so fast that they shed material: they shed gravel, dust, rocks. Those are called comets, but they clearly have nothing to do with what we think of as comets because there’s no ice involved. Also, asteroids in the main belt, they’ve just gotten smacked by something very small, say a meter-sized boulder, raises a huge cloud of dust. It gets called a comet. In fact, we have asteroids that are probably dormant or defunct comets and they just look like stars, and that’s why they’re called asteroids.

The difference between comets and asteroids is sometimes useful, and other times very confusing and not very useful. It worked really well for hundreds of years, and suddenly in the last decade or so, the utility of the comet-asteroid distinction is becoming weaker and weaker.

[31:03] Narrator: Steve is familiar with astronomical grey areas. He was at the International Astronomical Union meeting in Prague in 2006, where they voted on whether Pluto is a planet.

Steve Chesley: I’m happy to say that I voted to demote Pluto from its status as a planet because it really wasn’t that unique given that it’s a part of a population of similar objects.


The Kuiper Belt is this population of small- to medium-sized bodies upwards of even 1000 kilometers, but Pluto and Eris is the other one, that’s quite large. They’re part of a population, hundreds of thousands, in fact, of objects out beyond Neptune that are orbiting the Sun. Pluto was just the first one discovered by decades, and for the longest time there was no understanding that there was a population of objects out there, even though early on folks like Kuiper had predicted that there had to be a population of objects out there.

If you go back to what happened in the 1800s when Ceres was found in the main asteroid belt, and then they found Juno and Pallas and Vesta and a bunch of other objects orbiting, and they came to realize at the time that this wasn’t really just a planet, this was a whole population of bodies. Ceres was demoted from planet to minor planet. And I think it’s interesting how history repeats itself. The same story more or less happened in the outer solar system with the Kuiper Belt where Pluto was discovered. There was this long gap before the second object out there was discovered, I think it was 1992? And so there was a long time where it was the only one and it was presumed to be very special. Now we know that Pluto, while it’s very special, it’s not that unique, it’s part of a population.

Science has to adapt to the observations that we have. When I was a kid, there were nine planets, and you could see them on your placemat, the map of the solar system. We know now that that’s not a really very accurate depiction. We have the four terrestrial planets, the four gas giant planets out beyond that. You have this debris belt between Mars and Jupiter, and another debris belt outside of Neptune.

Now, there’s lots of very special, very interesting objects out there, and the New Horizons mission gave us these fantastic pictures of Pluto and its satellites and they went on to MU69 and gave us a really incredible view of that Kuiper Belt object. There’s such a richness of avenues to investigate. So it’s not denigrating those bodies, but it’s putting the solar system in its proper context.

[33:37] Narrator: Next time, On a Mission

Excerpt from Episode 8: Diamonds in the IceRalph Harvey: We really are recovering bits and pieces of other worlds, but at an absolute fraction of the cost of going there. What it really costs us is the travel to Antarctica and a little bit of skin off our noses and far too many pounds of butter. But the return is phenomenal.

[33:59] 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.

[run time: 34:13]