Debating Pluto's Planethood with Alan Stern

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Redeem your 50% off@rosettastone.com startalk today. Coming up on Startalk, we're reopening old wounds regarding the status of Pluto. I've got with me in my office Alan Stern, mister Pluto himself, and we spend the whole time talking about that little bugger in the outer solar system.

Neil deGrasse Tyson

Welcome to Startalk, your place in the universe where science and pop culture collide. Startalk begins right now. This is startalk. Neil degrasse Tyson here, your personal astrophysicist. Today we're going to do cosmic queries.

And we got chuck for this, right? Oh, definitely. But this is a very special cosmic query it is. Oh, this hits deep. Yes, it does.

Chuck Nice

This is the Montecue and capellettes. This is the west side story of dwarf planets.

Neil deGrasse Tyson

We got with me, my friend and colleague, Alan Stern. Alan, welcome back, Neil. Thank you. Give me some love here. Oh, man.

Allen, welcome back to the crib here. We're here at my office at the American Museum of Natural History. And you're one of the world's. I'm gonna say. I'm not gonna say one of.

I'm gonna say the world's expert on Pluto. Can I say that? Wow. You just did. Yes, the man.

But let's hold Pluto just for a minute. I just wanna catch up. I haven't seen him in years. I gotta say this Pluto thing, though, sometimes I feel like I'm typecast, like an actor on Gilligan's island. Oh, that's the only thing people talk about, is Pluto.

No, no, actually, I don't want to. We'll get to Pluto because this is a cosmic quarries. And so people can't. They can't shake Pluto. You know that people can't shake Pluto.

Alan Stern

That's everybody's favorite planet. Everybody's favorite. So. But let's catch up. What have you been doing?

Neil deGrasse Tyson

So you're still a vice president at the Southwest Research Institute in San Antonio, part of the space division. Very busy research institute. A lot of different scientific. Lot of science, a lot of engineering. The institute was formed back in the 1940s for public good.

Oh, my gosh. And does a lot of federal research, state and local stuff, but also research consortiums for industry. Everything from oil and gas, it being Texas. Automobiles. Yeah, but electric vehicles, automated vehicles.

Alan Stern

Just thousands of engineers and scientists. Cool, cool. So you've been there for. Since you left NASA? That's right.

Neil deGrasse Tyson

Okay, so you may remember I was at the launch of New Horizons mission back in 2006. And if I remember correctly, that mission to Pluto was the most powerful rocket with the lightest payload ever, just in combination so that it could accelerate and get the hell out there before you died. Mission accomplished. That's the number one rule in any science project. When I was a little kid, I was washing cars and.

Alan Stern

And babysitting and doing everything I could think of to buy bigger and bigger model rockets. You have no idea the kind you. Would launch in your backyard. Yeah. Estes model rockets.

Neil deGrasse Tyson

Yeah, right. Oh, wow. Yeah, yeah, yeah. Right. And the biggest one was the Saturn V with like 4d engines or something, right?

Alan Stern

The D engines. The D engines were bigger. That the one where you stomped on a balloon and it shot it off with water. Yeah, I couldn't get any further. That's starter kit.

Neil deGrasse Tyson

That's starter kit. Yes, exactly. That's lame. But then we got the new Horizons 100, you know, 80 1ft tall rocket, 70 foot payload bay, most powerful variant. I got to order every upgrade.

Alan Stern

I'll take the lightweight nose cone with, like, all five solid rocket motors, everything to make it go as fast as possible. And then we built this little spacecraft the size of a desk, very compact. So this thing was built to launch school bus sized spy satellites and big communication satellites and things like that. And we more or less took an Atlas V, amped it up with every upgrade you could think of, and then launched it basically empty. And of course, you got the highest possible burnout speed.

So, you know, Apollo astronauts, three days to the moon. We're now talking about new horizons no longer about your kid model rocket. Right? Yeah, he transitioned very quickly. That was.

We're in the big boy rock. Yeah, that was a blurry transition. I was like, man, you were a. Really advanced kid, but think about this. Apollo would launch 25,000 miles an hour, three days to the moon.

Chuck Nice

Nice. You know? Tom Hanks. Right? Exactly right.

Alan Stern

New horizons, 9 hours. Right. And didn't you get to the asteroid belt in three days or something? Well, not that quick, but we got to the asteroid belt in record time, faster than any spacecraft. Just three months.

Neil deGrasse Tyson

Right, right. And Jupiter in a year. Okay. But this also meant by the time you got to Pluto, you were booking. Yeah.

Right. So how do you slow down to even take a picture of Pluto? I mean, in the old days, we got used to flybys, right. And later on you went into orbit. But this was like the resurrection of the flyby.

Chuck Nice

Right? Right. Where you got to get ready for all your days in just a few seconds. And one shot. One shot.

Alan Stern

Once you're gone, you're not making anything. Right. Get it? Right. So wait a minute.

Chuck Nice

Can we read just one blurry picture with a sound effect that goes, meow, meow. You hope the pictures are not.

Neil deGrasse Tyson

So anyway, it was a fond memory being there. And so it took how long to get to Pluto? It took nine and a half years. Nine and a half years, because it's a long way. And so you just, at the, in the Bahamas, day end, the of.

Over those nine years, what happened? That's all I was doing. Yeah. So when you do that busy. I mean, you had a lot to do.

Chuck Nice

When you do that. When is the optimum time? When is Pluto closest to us so that you can intercept it. Right. Well, we actually.

Alan Stern

The optimum time in order to get there fast is when it's in a certain orbital position, but it's not closest. It's near closest. But what really matters is in the plane of the solar system. Okay. And we got there right at that exact time.

Neil deGrasse Tyson

In fact, what he left out there is that Pluto's way, the out of the plane of the solar system. Oh. That was implicit, unstated. So at the point where it crosses the plane of the solar system, you don't want to launch something from here and have to leave the plane of the solar system. That's where all your momentum is fuel.

Alan Stern

And that slows you down if you have a spin, fuel climbing out of the plane. Okay, right. Cause you're already in the plane with Earth. Right. And you got.

Neil deGrasse Tyson

Yeah. All this adds to your favor. Okay, continue. Sorry for that interruption. Where were we?

It was nine years. Nine years out. Right, yeah. So nine years. But you know, like the voyagers which went all the way out to Neptune.

Chuck Nice

Yeah. They had 500 people on that project, scientists, engineers, flight controllers by the time we did. Yeah, yeah. The whole way. Exactly, yeah.

Alan Stern

And by the time. And we did it with 50 people. Wow. And so the 50 of us were doing the work. You're doing everything.

Neil deGrasse Tyson

Yeah, doing everything. And so we were pretty busy. So then with our friend of Startalk, David Grinspoon, he's been on Doctor Funky Spoon. Doctor Funky spoon. Yeah, yeah.

He's. You banded together with him to write chasing new horizons. Yeah. And with it, with his long subtitle. Yeah.

What was that subtitle? Inside the epic mission to explore the 9th planet. Did he say 9th planet? 9Th planet. Get back to that boy.

Alan Stern

Here we go. Blood drawn. Already shot across the bow. Blood drawn. Here it is.

Neil deGrasse Tyson

Blood drawn. No, so, I mean, that book was needed because Pluto was a big mystery for so many people for so long. Well, yeah. And this mission was so much in the public eye that really needed to be documented. Of course.

Alan Stern

David's an amazing writer. Yeah, we all love David. We all love David. So also since then you've been in space, I hear. Yeah.

Neil deGrasse Tyson

You went above the Karman line. Wow. We did that on virgin Galactic. On virgin Galactic. Neil's Pluto news upset you that much?

Chuck Nice

You're like, I'll show you. I'll go investigate it myself. Let me get into it. Prove it myself. Let me.

Neil deGrasse Tyson

I'm going to space. Dammit. How long was it? Like four minutes of weightlessness? About.

How long is that? Four minutes between engine cutoff and reentry yeah, but a hell of a ride and a tremendous experience to see the planet. So what science were you doing on it? Yeah, I wasn't. You weren't just joyriding?

Alan Stern

Right, right. As much as I wanted to look out the window, I was sent. I'm going to be doing a NASA mission, which is going to be determining how well the virgin galactic spacecraft can be used to do astronomy on these missions, like unmanned sounding rockets. And on this first mission, I did some physiological experiments using myself as the guinea pig and also some practice for the astronomy mission. Kind of get the timing of everything down.

Neil deGrasse Tyson

Okay, so you weren't purely a tourist, right? Right. That's noble, but still sucks. I'd rather just look out the window the whole time. Right.

Chuck Nice

Yeah, just be there for the ride. You know what I mean? And you would love it. You should do it. Yeah, I don't.

Neil deGrasse Tyson

I don't know. Beautiful view. Yeah, why not? Why wouldn't you? Any industry that considers an exploding rocket on the launch pad a success.

Chuck Nice

I'm not. No, no, they don't call it success. They call it an experiment rich in data.

Neil deGrasse Tyson

That's even worse. That's what the rocket people call. So what else you've been up to? Been doing a lot of research as a scientist, right? Cause your expertise is obviously not just Pluto.

You're solar system objects of all kinds. Uh, of, uh, asteroids, comets. Yeah. Working on, uh, things all across the solar system, even the moon. Um, I'm on Europa Clipper that's going to be launching this year to study Europa and the ocean of Europa, the plumes and the potential for biology.

The liquid. The liquid under surface. Yeah, yeah. I'm on the Lucy mission, which is an asteroid mission just got launched in 2021. Lucy an acronym.

Alan Stern

No, Lucy's a pretty name. It was named after Australopithecus. Lucy. Oh, that Lucy. Which was named after the Beatles.

Neil deGrasse Tyson

Lucy and the sky with diamonds. Yes. Yeah. And it's all about. Everything goes back to the Beatles, the Australopithecus.

Alan Stern

It's about the origin of our solar system, just like the origin of human hominins. I see what you did there. The Lucy mission. Very cool. Yeah, yeah.

Neil deGrasse Tyson

All right. What do you, what data are you gathering to tell you about the origin of this little solar system? Well, all these missions contribute to that, right? It's. It's a big, kind of like CSI, right?

Alan Stern

With hints and clues everywhere, and you have to build a whole CSI. The solar system. All of a sudden, Alan takes off his glasses. Yeah.

There we go. There we go. So mysteries unsolved, you know, the Lucy mission is a good example. The asteroids it's going after co orbit with Jupiter. Neil won't like this, but they orbit in Jupiter's orbit and there are tens of thousands of them that Jupiter has not cleared.

Nonetheless, planet Jupiter. So these are the Trojans, rockets of trojans, leading and trailing. Lucy is the first mission to go explore them. It's thought that these trojan asteroids, just. To be clear, so these are places in the Jupiter sun system where forces of gravity and centrifugal forces balance.

Neil deGrasse Tyson

So like lagrangian points, okay, right. We did a whole thing on lagrangian points. That's a whole explainer. So Jupiter has a forward and trailing lagrangian point and stuff finds itself there trapped in it. Yeah, it's like it doesn't know where to go.

Cause there's nothing pushing it anywhere. Exactly. And there they go around the solar. System like the wizard of poppy fields. You just wander in and you just stay.

Alan Stern

It's a little like that. And the objects that are there are thought to be sourced from the same region as a lot of the Kuiper belt objects. Okay, so we're going there so we can compare them to the Kuiper belt objects. That new horizons is explored. Nice, nice.

And we see if it's really right. Part of the story is just remind. Me, the leading ones were trojans. Didn't they have a different name for the trailers? So why do you trailing ones?

Chuck Nice

So Trojans, I mean. Cause I'm thinking Trojan horse when I hear Trojan. Or is it. So it's gotta be some origin for why they call it Trojan. And I'm not a historian, but didn't.

Neil deGrasse Tyson

They call the other ones a different name? There's just a leading and a trailing cloud. Right, but they're called the Lagrange points. Four and five. Four and five l four l five.

But I think only one of these packs are called trojans. And I think the other packs, no. They'Re both called trojans. They are promising. I think they have individual names.

I got people more obscure. Well, they hide something. That's what we know. They're what? They're Trojans.

Chuck Nice

They're hiding something. We should not trust them is what I'm saying.

Neil deGrasse Tyson

So I'm glad we're finally learning more about these objects. Cause they're just sitting out there waiting. Yeah. And they've been begging for exploration and never begging. Never.

Alan Stern

And now the Lucy mission's gonna go see almost a dozen of them. Some of them have satellites, and we'll visit some of those. Okay. And that mission got launched in 2021. We just did a first practice asteroid flyby in the main build.

We're gonna do another practice asteroid flyby in 2025. How many people get to say that it's practice with a whole asteroid? That's amazing, I gotta tell you. Cause we gotta get it right on those flybys. Starting in the late twenties, we'll do a whole series.

Late 2020s, late 2020s, we'll do a whole series of flybys, of trojans. Then we'll dive back in our orbit, down close to the sun, and come back out and go to the other Trojan cloud, where we'll complete that exploration. If there's an extended mission, we'll do even more. And this will all end in the 2030s. So it's a long term program of exploration.

Neil deGrasse Tyson

So, just to be clear, once you've established this orbit around the sun going out to Jupiter, it's minimal fuel, right? Because you've already earned this orbit, and so now you're just sort of redirecting it a little bit. Right? So the rocket does the initial boost, and then we do Earth gravity flybys. We've already done one.

Alan Stern

We have two more to do to make the whole mission come. And the principal investigator, Hal Leveson, is part of the team that dreamed up the whole geometry and orbital mechanics of how you get so many flybys into just one mission. Right? Right. This is the genius of what they got to do.

Neil deGrasse Tyson

Like with the Cassini mission to Saturn, right? It's orbiting Saturn, but it's visiting of moons every time, and all these loop orb. Oh, let's check out this other one. Do a little adjustment. I mean, it's brilliant that we can exploit the gravitational fields of other stuff, and it's almost diabolical.

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Alan Stern

I'm Ali Khan Hemraj and I support startalk on Patreon. This is startalk with Neil degrasse Tyson.

Neil deGrasse Tyson

So Alan. Neil. Ow. Neil. That's a pattern.

Don't get me started. Okay? Get me started. Neil, we alerted our fan base that you were gonna be on and most of them knew your expertise, but others were fresh in the room for that. And we collected questions.

Yes, we did. And these are Patreon members? Yes, they are. Excellent. These are the people who keep us afloat.

Alan Stern

Let's see, what questions? Yeah, what do you have? All right, here we go. I haven't seen them. I don't know anything about them.

Chuck Nice

Let's go with Sean Raven fire. Now, I wonder if that's a real name. Raven fire. Raven fire. Sounds like a video game character.

I am Sean Raven fire. I am here to collect the crystals. The crystals.

All right. Not even the money, right? It's gotta be something. Your money is meaningless. Give me the crystals.

Okay. Sean says, hey, I'm still a little fuzzy on the difference between minor planet, dwarf planet and planetoid. Can you please explore the difference? I'm fuzzy, too, actually. Yeah, yeah, everybody's fuzzy.

Alan Stern

Because the terms are not, you know, some of them, like planetoid, no one uses. You hear it very occasionally. No scientist I know uses the term planetoid. I don't even hear. What do they call Theia?

Neil deGrasse Tyson

Wasn't that a planetoid? So thea that made the moon, the term is planetary embryo. That's the term that's really used. This sounds like a pc thing. You gotta add syllables and add another word.

Alan Stern

But that is the term that's used. Planetary embryo. That collided with Earth. Earth to make moon, make the earth. I did not know that'd be a planetary spermatozoa.

Chuck Nice

I'm sorry, you're talking about nephrons. But, you know, the embryos are basically the building planets, lot more of them originally than there are now because many of them combined through collisions to make bigger and bigger objects. Theia ended up spalling material into orbit around the earth, and it collided. That created the moon. But most of theia ended up in the earth.

Right. And this was a big thing. It was the size of Mars. Right. Big hit.

Alan Stern

Right. Okay, so I was just trying to get my vocabulary straight here. So you would call that a planetary embryo, not a planetoid, because no one uses that. It's really an archaic. Is that the same as protoplanet?

Chuck Nice

The planetary embryo and protoplanet, those are interchangeable. Oh, we're good. So protoplanet. Good. All right.

Neil deGrasse Tyson

So now, for the longest while, my whole life growing up, we're about the same age. I knew of this thing called the minor planet, circular. Right. Which tracked asteroids, basically. So I always thought of asteroids collectively as minor planets.

Is that term still a thing now that we've added vocabulary to the system? Sometimes it's used, and it's mostly used for the small, kind of potato shaped, lumpy things in the solar system, not the bigger things. The term dwarf planet. I'm actually very proud of this. I coined the term in 1991 in a research article in the journal Icarus, and it was meant to be Icarus.

Features planet based solar system based science. This is the distinct from first Astrophysics. Journal, research journal of Solar System Science. And Carl Sagan was one of the original editors of it back in the sixties, seventies, when planetary science was being born as a field. And in 1991, I published an article that was about prediction, mathematical prediction, that there would be a large number of pluto like objects discovered.

Alan Stern

And I termed them dwarf planets in analogy to dwarf stars and dwarf galaxies. And so forth. And they're meant to be because that. Word is already in use. That makes sense.

Are much smaller planets, the ones that are the size of continents.

And that term has been used very widely. And we see dwarf planets all across the Kuiper belt, which is part of the revolution of the Kuiper belt that we didn't know about till the nineties, is that dwarf planets are more populous than the four terrestrial planets and the four giant planets combined. And there's one dwarf planet orbiting in the asteroid belt called ceres. Ceres, the largest of the asterisks, which is a mini planet itself. Okay, so, right, okay, right.

Asteroids, kind of a zip code. So, you know, it's like a Kuiper belt object is kind of meaningless. It's just an object in the Kuiper belt. It's like a zip code, technically. New horizons, the spacecraft is a Kuiper belt object for the time being.

It's an object in the Kuiper belt. Okay, right. So that's just a zip code. Right. But how do you get up to the term specifically?

Chuck Nice

I'm not trying to push back here. Cause I'm out of my league between you two, but I wanna know, how do you go from being floating rock to planet? Cause there's gotta be a difference between. Yeah. One of them is how do you make the jump from, you know, let's start.

Neil deGrasse Tyson

Let's back up. How do you go from potato to dwarf planet? Okay. Yeah, yeah, yeah. So the thing about potato sized objects.

Alan Stern

So these are things that are the size of counties or mountains. And they're, you know, most of the asteroids that you can look up in a book or that we've flown spacecraft by, they're lumpy and they have irregular shapes. And that's because that's the shape that, as they were assembled, they just came to rest in when the assembly was finished. And that shape is controlled by the material strength of the object. The thing is, as objects get bigger and bigger, more and more massive, eventually they get massive enough that their self gravity causes them to form into a sphere.

And then we call them planets. Once they're big enough to be a sphere, like Pluto, they're planets. The smallest of them are called the dwarf planets. And then there are larger planets that are earth or Jupiter size, eventually. And those are all spheres.

There's a continuum. They're all spherical objects. So sphere is definitely a determining characteristic. It's the hallmark. It's one of them.

It's the hallmark. It's one of them. If you're on Star Trek and they show up somewhere and turn on the viewfinder. Everything is round, you see around rocky something or thing with an atmosphere that's round. You go other.

There are a planet this week. All right, let me ask you this. Both, but did we get through? Dwarf planet, a planetoid planet. What?

Chuck Nice

Minor planet.

Alan Stern

Minor planets are these little rocky guys. They used to be called 18 hundreds, 19 hundreds term. Minor planet. Right. And that's kind of a legacy term.

Chuck Nice

All right, so before we move on to the next question, one last question. Asteroid itself is very legacy because who was it? Not Herschel? Was it.

Alan Stern

Somebody around 1800? Some dude, yeah. He's got his telescope and he sees this dot of light. Like stars are just dots of light. They're so far away.

Neil deGrasse Tyson

They're just dots of light. In your telescope. They see a dot of light, except it's moving, right. And it's like. So it looks like a star, but it's not a star.

So asteroid, star light. Star light. Right. So that's like the biggest misnomer there ever was. Right?

Right. Yes, visually. But if you would care what the thing is. And we still call them asteroids. Star like from the greek.

Chuck Nice

Excellent. Just legacy. That's legacy. All right, so one last thing, and then we're gonna move on. Cause I'm taking up way too much of the patreon's time.

Does composition have anything to do with it? So, let's just say that it's round, but it's a bunch. It's an aggregate of just larger objects, but they're not really. They're not condensed, they're not really solid, just kind of a congregation. We haven't seen anything like what you're describing.

Alan Stern

Oh. And if you look across the planets of the solar system, whether they're made of ice or rock or they're gas giants or whatever, they're all contiguous bodies, not agglomerations like you're describing. Right, right. They're one big spherical thing, because the gravity crushes everything into that spherical shape. Okay.

Right. They might have a core and a mantle and a big atmosphere above it, for example. Or they might have a core and a mantle and an ocean layer like Europa, and then a layer, an outer layer, for example. Right. But they're all the same.

They're essentially spherical objects, and their shape is driven by the force of their own mass that creates self gravity. Okay, you know another way to say this is if you had three objects that were each themselves massive enough to be their own sphere, right. And you bring them together, right? They're making a sphere.

Chuck Nice

There you go. I got you. That's how. That's how it rolls. That's how it rolls.

That's how it rolls. We're making a sphere no matter what. But the same thing applies when stars collide and they can merge into a still bigger star, into a larger sphere. Right. Right.

Alan Stern

And it's the same physics all the. Way through no matter where you are in the universe. That's the good thing about physics. There you go. That's true.

Neil deGrasse Tyson

All right, give me some more. All right. And make this quicker this time. All right, here we go. This is.

Chuck Nice

This is Andrew Coffey who says good day, Doctor Tyson. Lord Nice. Sir Allen, I know very little about Pluto, so I'm super excited to hear you talk. I'm hoping you can enlighten me. I'm wondering if celestial bodies like Pluto are only able to form and exist at the extreme distance from the sun.

Or could they be orbiting closer, perhaps near a smaller or cooler star? And if so, do we hope finding an exoplanet that is similar, simply too small or too far away from the star to be seen from the distances involved in our observations? Thank you. That's two parts. One, you know, is the distance from the sun.

Alan Stern

The main part is, you know, could you have them close to the sun? Right. In fact, everything we know about the origin of the solar system indicates that Pluto formed at something like half its present distance from the sun. That the solar system is more compact originally. And Pluto and most of the other dwarf planets of the Kuiper belt were transported outward with all the small bodies of the Kuiper belt.

But Ceres is another example. Now, Ceres is in the asteroid belt. It's a dwarf planet. Some people think it formed there. Others can argue that it may have come from the Kuiper belt itself.

So we don't know. But we know that dwarf planets can exist much closer to the sun. So just for clarification's sake, because there are people who may not know the proximity of. When you're talking about asteroid belt, Kuiper belt, the sun, Pluto, and so how's it go? Where does it go?

So the sun's in the middle of the solar system, right. It's the big Kahuna. Right. That controls all the other orbits. Right.

And then we have the four rocky planets, Mercury, Venus, Earth and Mars, right? And then there's an asteroid belt just beyond the orbit of Mars, okay? It stretches for something like 100 million mile outward. Jesus. Okay, it's big.

Chuck Nice

I did not know that? And then you got this gas giant. That's amazing. Who knew that? Then you have Jupiter, Saturn, Uranus, Neptune.

Right. By now, you are. Neptune's orbit is 30 times as far away from the sun as the earth is. Right? Right.

Alan Stern

And probably 15 ish times as far away as the asteroid belt. Right. Okay. Okay. And then beyond Neptune's orbit is this second belt, or disk like region, called the Kuiper belt, discovered in the 1990s but predicted back in the 1940s and fifties.

And that's where Pluto orbits and a bunch of other dwarf planets and a bunch of much smaller Kuiper belt objects that are more like asteroids but much more icy than the asteroids. Wow. Okay. And if I understand correctly, the Kuiper belt was a negative prediction. What does that mean?

I didn't learn that in school. Yeah, I think it was a negative prediction. I think Gerard Kuiper published a paper saying that there should be a reservoir of objects. I don't know if he called them comets at the time, who have objects just beyond the red blooded planets. And since we don't see any there, then he was making some inference about the early solar system.

Neil deGrasse Tyson

So he was using the absence of evidence as an evidence for something else. And then we find stuff there and we name it after him. Yeah, I think it was actually a little different. My recollection of the. The literature from back then is that there were really two scientists.

Alan Stern

One was named Kenneth Edgeworth and the other was Gerard Kuiper. They were both making predictions that beyond the orbit of Neptune, that there was something like an asteroid belt that Pluto orbited in and that it might contain other planets in it, but it was really beyond the technology of the mid 20th century. The telescopes couldn't do it. And detectors. Yeah.

And, you know, you had, like, Clyde Tombaugh squinting at photographic plates. They didn't have the data. Now, I talked about the discoverer of Pluto. So they didn't have. They had big enough telescopes, but they didn't have sensitive enough cameras, and they didn't have computers to do the painstaking data.

Now.

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Chuck Nice

This is AJ Staveley who says hello. Doctor Tyson Lord. Nice Doctor Allen, so much respect. I am AJ from Atlanta, Georgia. My question is, what unanswered questions has new horizons answered?

Or you have discovered about the Kuiper belt that researchers like yourself didn't already know or you were surprised about? Also, if is Pluto's dance with Sharon, why it appears to be so geologically active? Thank you so much. So a two part question, but both very cool. All of that.

Alan Stern

We found a lot of discoveries, okay? And you don't have enough time on this show. If I came back two or three. Let'S go top three, then. A good example is that Pluto itself, we wondered for a long time if its surface would be flat or rugged.

Basically because we knew the surface is made of nitrogen ice, and nitrogen ice is structurally weak. It would make a surface that was almost entirely flat. It's so weak that even Pluto's gravity would just flatten it out. Yeah, exactly. Smooth it out.

Got it. But if the nitrogen is just defrosting on top of a water ice crust, you could have mountain ranges and canyons and craters and all the rugged topography that we actually saw. So we answered that question the first day with the first pictures that came back from new horizons of Plano. And then when we went further out into the Kuiper belt and made the first flyby of a small Kuiper belt object, we found out how they were born, how they were formed. This was not an accidental encounter.

Neil deGrasse Tyson

You're targeting. Yeah. You're targeting other Kuiper belt objects with that trajectory. And this was a goal of the mission. And a billion miles beyond Pluto, we flew by this Kuiper belt object, Arrokoth.

Alan Stern

No one had ever been to a Kuiper belt object. And from it shaped off. Yeah. It means sky in the Powhatan indian language. Okay, yeah, I knew that.

Chuck Nice

Who doesn't know? Wait, wait, wait, wait. You went to Pluto and then went another billion miles? Yeah. And now we're almost twice as far as Pluto now and still exploring.

Neil deGrasse Tyson

Okay. But when we got to Arrokoth, from its geology and geophysics, we could determine that one of the major two theories of how planets get their start, how planetesimals, the seeds of planets, form, was wrong and the other theory was right. And we found that, essentially, that these little planetesimals, the seeds of planets, form very gently and through a very slow local accretion process in which they can. Rather than collide rapidly rather than collisions. And there were decades in which computer models were warring.

Alan Stern

And in one fell swoop, new horizons. Settle that with the data on Arakov. It showed. You pick one out of a bag and look at it up close, and you could tell one theory's right, one theory's wrong. Beautiful.

Neil deGrasse Tyson

So it means they just kind of gather. Everybody comes together, little pockets. And the little pockets end up with little material, boulders and hills and mountains that collide with one another very gently and just stick due to self gravity and build up a lumpy thing. Not big enough to be a round thing, just a lumpy thing. Right.

And tell us about the Pluto Charon dance. Oh, yeah. That was the other question. So the question was whether Pluto's intense geologic activity could be due to that. And it turns out, not due to that dance, to the gravity neutral gravity of Pluto and its big moon that are in a very special state called tidal equilibrium.

Alan Stern

Turns out that because of that equilibrium, all those forces that might heat Pluto or make that geology go are long gone. And tidal equilibrium, you mean double tidal lock? Yeah, that's right. There we go. We know what that is.

But that can't be the cause of Pluto's geology. It's got to do something else. Okay, all right. Interesting. Very good.

All right, that might have to do with the ocean that we think is inside of Pluto, just like Europa. So the ocean is not rigid, so it can shake things up. Right. Well, it's also as it freezes, releasing heat. How?

Latent heat you know about. Yeah, yeah, yeah, yeah. And that can power the job. Physics 101. So wait a minute.

Neil deGrasse Tyson

What? Okay, I failed physics 101. Freezing gives off heat. It does it. It releases heat.

Chuck Nice

Mm hmm. All right. Okay. All right. I'm gonna tell you right now.

I've been on this earth for a little while now. That's the first time I ever heard somebody say freezing gives off heat. So I'm just gonna call bullshit. No, no, you get dry. No, no, I got one for you.

I'm joking. No, I'm joking. I got one for you. No, I'm serious. No, no, I got one for you.

Alan Stern

I got one. Go ahead. Ready? Are you ready? Are you seated?

Neil deGrasse Tyson

Okay, I'm seated. Let's look at the other side. So you have water on the stove. Right? And you're heating it.

Right. And you. As you heat it, the temperature rises, correct? Correct. Okay.

Then it hits what temperature? Boiling point 212. 212. You keep heating it. Yes, you do.

Where does the heat go? Wait a minute. It does not raise the temperature. Correct. It turns into steam.

So the heat simply goes and changes. It from liquid to the molecular change is itself. That itself. Okay. Okay.

So now you go the other direction. So now you go the other direction. Yes. Now you're gonna. You're gonna suck energy out of the water.

The temperature drops. Right. And then there's a point where you're still sucking energy. The temperature doesn't drop. Oh, man.

And all it does is change. Change the molecular state. Right. Damn. That's.

Alan Stern

Where was he when you took that? Physics might have done better. That might have done a lot better. You might have had. I had Neil.

Neil deGrasse Tyson

Yeah. So we call it latent heat. There's terms for it in physics. Latent heat. It's really physics one along.

Chuck Nice

How y'all doing? I'm latent heat. Hey.

Okay. All right. You've personified Leighton healers. I will never get this out of my head. I know, right?

You can't do. Oh, God. Also, Sharon, just. In the traditions of the field, Pluto is roman, God of the underworld, and moons have traditionally been, not in all cases, but in many cases, traditionally named for greek characters in the life of the greek counterpart to that roman God and that way, both, there's an homage to both cultures. So Pluto's counterpart in Greek is what, what's his face?

The underworld. Hades. Hades. Yeah, Hades. Okay.

Neil deGrasse Tyson

It's also the place, but it's also the guy, okay? And the ferryboat driver known to river sticks to take you across the river Styx is named Sharon. Sharon, yes. There you go. That's where that came from.

Chuck Nice

Sharon. Okay, here we go. Greetings, Doctor Trison and Doctor Allen. I'm Jasmine from the wine country here in northern California. I'm very curious, what's the big deal about Pluto?

Does it even really matter if it's a planet or not? Why all the fuss over this icy rock at the edge of our solar system? Look at that. Oh. Can I venture a guess that it's been with us so deep in our culture that it's hard to shake any adjustments to those?

Alan Stern

Well, that's a guess, but as a scientist, the real reason is that Pluto is the archetype. It's the heralding body of this whole new type of planet. The dwarf planets that we've discovered in the outer solar system. They're active, they have moons, they have atmospheres in some cases, and far from being a rock, it's a big spherical thing. Right, right.

And that's why we call it a planet. We don't know what else to call it. There you go. All right. Planet modified by the word dwarf, right?

Like giant, giant planet for Jupiter. A gas. I don't have a problem. I mean, that's in fact, where we agreed. Okay.

Neil deGrasse Tyson

And one of the correspondence I got back when I was pilloried by third graders. Cause here people know. I don't have to give the backstory here. Dear Doctor Tyson, why are you so mean?

Alan Stern

Well, what's really sad is not that he's mean, it's just that he's wrong.

Oh, snap. What happened? Geek fight.

Neil deGrasse Tyson

No, no, it's like. So you failed your freshman physics. He did great at all. That he did all the way up through PhD, but he's failed his planet test. No.

So we have the word paper, right? Right. And we have construction paper, corrugated paper, toilet paper, a card stock paper. Card. Right.

So this paper is a. Is a very broad category. And then we modify that with whatever is the next word and we know exactly what anybody's talking about. Okay, so I don't have any problem with that. Just let.

So it was. I've always felt there's been a shortage of vocabulary to. So, in other words, let me hear. I'm sure we agree here. Jupiter and Earth should not be called the same object in orbit around a star.

Alan Stern

I disagree. Yeah, they're round, but one is huge in gases, and Earth is smaller than storms on Jupiter's weather system. So wouldn't it be cool if we just had a different vocabulary so that when I use the word, you know exactly what I was talking about right? Now, if I just say I discovered a planet orbiting a star, is it gaseous? Is it rocky?

Neil deGrasse Tyson

Is it large? Is it small? Is it. And I have to ask 20 questions just to understand what anybody's talking about. That's the cool part of science.

Alan Stern

And as. No, that's a weakness of science. As a planetary scientist. Planet is part of the term of what our field is all about, right? And so we know what planets are.

They are the things, the central objects of our field, and they are the large things that orbit stars, and they range from the smallest large. They know they're large when they become round, and gravity dominates. And from the dwarf planets all the way up to the giant planets, that's a continuum of objects we all call planets, and planetary scientists agree on that. And in the planetary science research literature, there's no debate. I don't have a problem.

Neil deGrasse Tyson

I just. I'm a big fan of words. I have six dictionaries on my shelf over there from different eras, and I watch words come and go. I'm just saying, if you have to modify the word planet in order to know what someone is talking about, that's a clarion call for another word, a word yet to be invented that captures both of those simultaneously, and so it's a shortcoming of the lexicon. That's all I'm saying.

That's all I'm saying. Look at me, all blank. You see how these looking mouths. You see her? I'm telling you.

Chuck Nice

Did you see that face? I'm telling you, by that. Yeah. For example, we have different kinds of human beings. Short ones, tall ones, skinny ones, big ones, right?

Alan Stern

We have north Americans and Europeans and South Americans. And that doesn't mean we need a new term for human beings. It just means adjectives, help. In the english language, there are all kinds of ways to add descriptors to planets, to stars, to galaxies. We do that all through science.

Right? And we got to get over these small number fears, right? I mean, if we going to have only eight planets kneel. I'm afraid the periodic table's got to stop at beryllium. You know the periodic table has 100 umpteen elements in it, right?

We're not afraid of a large number of those. No. Just like we're not afraid of having 50 states. Right? Or countless numbers of stars and asteroids and everything else.

Chuck Nice

We only have 49 states. Texas is not a state.

Just ask anybody from there. I've been to restaurants called Texas is a planet.

Alan Stern

So we get used to big numbers of planets now that we see them around stars and lots of them in our own solar system. Doesn't star Trek have a much more nuanced system and nomenclature for planets? Yeah. Cause they classify planets. Star Trek is fiction.

We're talking about facts. No, no, but let's imitate fiction. Okay, I was on your side until that statement right there. How dare you, sir?

Neil deGrasse Tyson

Send them away. What? Factor one? No. So I'm just saying there's a term, a succinct term that references.

Is it an oxygen nitrogen planet? Is it gravity? There are ways of folding that into the term so that someone says, I. Mind Star Trek having lots of kinds of planets. See, I guess I'm all in.

Alan Stern

We got ocean worlds, right? I'm all in. We got volcano worlds and we got biologically active worlds. Sterile worlds. It's all good.

Neil deGrasse Tyson

All in. Adjectives rock, don't they? On it. Alan, great to have you back on. Thanks so much, Neil.

Ok, it's a pleasure. All right, great. Thanks. We're done here. Oh, my gosh.

But we're really not done. No, we have solved nothing. We must do it again because nothing has been resolved. So this has been startalk, the Pluto cosmic queries edition, if I may call it that. We're going to have to get Alan back because we just barely scratched the surface here.

Anyhow, thank you, Alan, longtime friend and colleague. Thanks so much, Chuck. Always good to have you. Pleasure. All right, Neil degrasse Tyson here, your personal astrophysicist, as always.

Chuck Nice

Keep looking up.

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Debating Pluto's Planethood with Alan Stern

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Episode Chapters

1: Introduction to the Debate

2: Historical Context and Emotional Impact

3: Scientific Insights from New Horizons

4: Defining Planethood

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