Debating Pluto’s Planethood with Alan Stern

Coming up on StarTalk, we’re reopening old wounds regarding the status of Pluto.

I’ve got with me in my office Alan Stern, Mr.

Pluto himself.

And we spend the whole time talking about that little bugger in the outer solar system.

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.

This, this.

This is the Montague and Capulets.

This is the West Side Story of Dwarf Planets.

We got with me my friend and colleague, Alan Stern.

Alan, welcome back to…

Neil, thank you.

Give me, give me, give me some love here.

Alan, 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 not going to say one of, I’m going to say the world’s expert on Pluto.

Can I say that?

Wow.

You just did.

But let’s hold Pluto just for a minute.

I just want to catch up.

I haven’t seen him in years.

I got to say this Pluto thing, though.

Sometimes I feel like I’m typecast like an actor on Gilligan’s Island.

Oh.

The only thing people talk about is Pluto.

No, no.

We’ll get to Pluto because we…

This is a Cosmic Queries, and so people can’t shake Pluto.

You know that.

People can’t shake Pluto.

It’s everybody’s favorite planet.

It’s everybody’s favorite.

But let’s catch up.

What have you been doing?

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…

A lot of science, a lot of engineering.

The institute was formed back in the 1940s for the 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.

To automobiles.

Yeah, but electric vehicles, automated vehicles, just thousands of engineers and scientists.

So you’ve been there since you left NASA.

That’s right.

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 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.

Estes, yeah.

Right?

Oh, wow.

Yeah.

Right?

And the biggest one was the Saturn V with like four D-engines or something.

Right.

The D-engines.

The D-engines was the biggest.

I only got the one where you stomped on a balloon and it shot it off with water.

Yeah.

Yeah, I couldn’t get me further.

That’s a starter kit.

But then we got the New Horizons, 181-foot tall rocket, 70-foot payload bay, most powerful variant.

I got to order every upgrade.

I’ll take the light-weed, nose comb.

I would 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 size spy satellites and big communications satellites and things like that.

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 Apollo astronauts, three days to the moon.

We’re now talking about New Horizons, no longer about your kid model rockets.

Yeah, that key transition very quickly there.

We’re in the big boy rockets.

Yeah, that was a blurry transition.

I was like, man, you were a really advanced kid.

But think about this, Apollo, we launched 25,000 miles an hour, three days to the moon.

You know, Tom Hanks, right?

Right.

New Horizons, nine 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.

In any spacecraft.

Just three months.

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 and 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.

Right.

Right.

Where you got to get ready for all your data in just a few seconds.

And one shot.

Once you’re gone, you’re not making a new turn.

You can’t come back.

Right.

So, wait a minute, can we just…

One blurry picture with a sound effect that goes, Nyaaawww.

You hope the picture is not blurry.

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.

Wow.

Because it’s a long way.

And so, you just in the Bahamas over those nine years?

That’s all I was doing.

Yeah.

So, when you do that…

I mean, you had a lot to do.

When you do that, when is the optimum time…

When is Pluto closest to us so that you can intersect it?

Right.

Well, we actually…

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.

Oh, okay.

But what really matters is in the plane of the solar system.

Okay.

And we got there right at that exact time.

In fact, we set a time…

What he left out there is that Pluto’s way the f*** out of the plane of the solar system.

That was implicit and 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.

And that slows you down if you have to spend fuel climbing out of the plane.

Right.

Because you’re already in the plane with Earth.

Right.

And you got…

Yeah, all this adds to your favor.

Okay, continue.

I’m sorry for that interruption.

Where were we?

We took a little detour, but no, it was nine years.

Nine years out.

Yeah, so nine years.

But you know, like the Voyagers, which went all the way out to Neptune, they had 500 people on that project.

Scientists, engineers, flight controllers.

By the time we did…

Yeah, the whole way.

Exactly.

And by the time…

And we did it with 50 people.

And so the 50 of us were doing the work of all this.

You’re doing everything.

Yeah.

And so we were pretty busy.

So then with our friend of StarTalk, David Grinspoon.

He’s been on…

Dr.

Funky Spoon.

Dr.

Funky Spoon.

Yeah.

He’s…

You banded together with him to write Chasing New Horizons.

Yeah.

And with this long subtitle.

Yeah.

What was that subtitle?

Inside the epic mission to explore the ninth planet.

Did he say ninth planet?

Ninth planet.

We’ll get back to that.

Blood drawn.

Dude, it’s happening already.

Shot across the bow.

Uh-oh, here it is.

Blood drawn.

So that’s, 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, you know, so much in the public eye that really needed to be documented.

Yeah.

Of course, 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.

You went above the Karman line.

Wow.

We did that on Virgin Galactic.

On Virgin Galactic.

Did the Pluto news upset you that much?

You’re like, I’ll show you.

I’ll go investigate it myself.

I’m proving myself.

I’m going to space, dammit.

How long, was it like four minutes of weightlessness?

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.

So you weren’t just dry riding?

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.

So you weren’t purely a tourist.

Right.

Right.

In fact, it’s noble, but still sucks.

I’d rather just look out the window the whole time.

Yeah.

Just be there for the ride.

And you would love it.

You should do it.

Yeah.

I don’t know.

Beautiful view.

Why not?

Any industry that considers an exploding rocket on the launch pad a success, I’m not…

No, no.

They don’t call it success.

They call it an experiment rich in data.

That’s even worse.

That’s what the rocket people call it.

So what else have you been up to?

Been doing a lot of research as a scientist.

Because your expertise is obviously not just Pluto.

Solar system objects of all kinds, asteroids, comets.

Yeah.

Working on things all across the solar system, even the moon.

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 under surface.

Yeah.

I’m on the Lucy mission, which is an asteroid mission.

It just got launched in 2021.

Lucy an acronym?

No, Lucy is a pretty name.

It was named after Australiopithecus Lucy.

Oh, that Lucy.

Which is named after the Beatles.

Lucy in the sky with diamonds.

Yeah.

Everything goes back to the Beatles.

The Australiopithecus, it’s about the origin of our solar system.

Just like the origin of ship Hominem and Hominem.

I see what you did there.

The Lucy mission.

All right.

What data are you gathering to tell you about the origin of this little solar system?

Well, all these missions contribute to that.

It’s a big, kind of like CSI, with hints and clues everywhere, and you have to build a whole story up.

CSI, the solar system.

All of a sudden, Alan takes off his glasses and you go, yeah!

Mysteries unsolved.

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 has these pockets of the Trojans that are leading and trailing.

Lucy is the first mission to go explore them.

It’s thought that these Trojan asteroids…

So these are places in the Jupiter-Sun system where forces of gravity and centrifugal forces balance.

So like Lagrangian points.

We did a whole thing on Lagrangian points.

So Jupiter has a forward and trailing Lagrangian points and stuff finds itself there.

It gets trapped in it?

Yeah, it doesn’t know where to go because there’s nothing pushing it anywhere.

And there they go around the solar system.

Like the Wizard of Poppy fields.

You just wander in and you just stay.

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.

So we’re going there so we can compare them to the Kuiper belt objects that New Horizons has explored.

And we see if it’s really right.

If that’s part of the story.

Just remind me, the leading ones were Trojans.

Did they have a different name for the trailing ones?

So why do you call them Trojans?

I mean, because I’m thinking Trojan horse when I hear Trojan.

So there’s got to be some origin for why they call them Trojans.

And I’m not a historian of Trojans.

But didn’t they call the other ones a different name?

They’re just a leading and a trailing cloud.

Right.

But they’re called the Lagrange points four and five.

Four and five.

L4, L5.

But I think only one of these packs are called Trojans.

And I think the other pack…

No, they’re both called Trojans.

I think they have individual names, but they’re more obscure.

Well, they hide something.

That’s what we know.

They what?

They’re Trojans.

They’re hiding something.

We should not trust them is what I’m saying.

So I’m glad we’re finally learning more about these objects because they’re just sitting out there waiting to be…

Yeah, and they’ve been begging for exploration and never…

Begging.

Never.

And now the Lucy mission is going to go see almost a dozen of them.

Some of them have satellites and we’ll visit some of those.

And that mission got launched in 2021.

We just did a first practice asteroid flyby in the main belt.

We’re going to do another practice asteroid flyby in 2025.

How many people get to say that?

Let’s practice with an whole asteroid.

That’s amazing, I got to tell you.

Because we got to get it right on those flybys.

And then starting in the late 20s, we’ll do a whole series of…

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.

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.

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.

We have two more to do to make the whole mission come.

And the principal investigator, Hal Levison, is a 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.

This is the genius of what they got to do.

Like with the Cassini mission to Saturn.

Right.

It’s orbiting Saturn, but it’s visiting of moons every time.

All these loop orbits.

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.

Thanks I am Olicon Hemraj, and I support StarTalk on Patreon.

This is StarTalk with Neil deGrasse Tyson.

Thanks watching.

So, Alan.

Don’t get me started.

Okay, get me started.

We alerted our fan base that you were going to 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.

Oh, excellent.

These are the people who keep us afloat.

Let’s see what questions we have.

Yeah, what do you have?

All right, here we go.

I haven’t seen them.

I don’t know anything about them.

Let’s go with Sean Ravenfire.

I wonder if that’s a real name.

Ravenfire sounds like a video game character.

I am Sean Ravenfire.

I am here to collect the crystals.

Not even the money, right?

It’s got to be something.

Your money is meaningless.

Sean says, Hey, I’m still a little fuzzy on the difference between Minor Planet, Dwarf Planet and Planetoid.

Can you please explore the differences?

I’m fuzzy too, actually.

Everybody’s fuzzy because the terms are not…

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?

Wasn’t that a Planetoid?

Theia 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.

But that is the term that’s used.

Planetary Embryo that collided with Earth to make the Earth…

I did not know that.

Planetary Spermatozoa?

I’m sorry, you’re talking about nevermind.

The embryos are basically the building planets.

There were a 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, it created the moon, but most of Theia ended up in the Earth.

And this was a big thing, it was the size of Mars.

Big hit, 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, the planetary embryo?

Embryo and protoplanet, those are interchangeable.

Oh, we’re good, so protoplanet.

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, 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 solar system-based science.

This is the first research journal of solar system science.

And Carl Sagan was one of the original editors of it back in the 60s, 70s 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.

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.

So 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 until the 90s, 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.

The largest of the asteroids, which is a mini planet itself.

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.

Right?

So that’s just a zip code.

Right?

So now how do you get up to the term specific?

I’m not trying to push back here because I’m out of my league between you two.

But I want to know how do you go from being floating rock to planet?

Because there’s got to be a difference between…

There’s a big difference.

You know, one of them is…

How do you make the jump from, you know…

Let’s start.

Let’s back up.

How do you go from potato to dwarf planet?

Yeah.

Yeah.

So the thing about potato-sized objects…

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.

And eventually, 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.

If you’re on Star Trek and they show up somewhere and turn on the viewfinder, and you see a round rocky something or thing with an atmosphere that’s round, you go, oh, they’re a planet this week.

All right, let me ask you this, both.

Did we get through a dwarf planet, a planetoid planet?

Minor planet.

See, you said there’s no minor.

Minor planets are these little rocky guys.

They used to be called, said, 1800s, 1900s term, minor planet.

And that’s kind of a legacy term.

All right, so before we move on to the next question, one last question for both of you.

In fact, asteroid itself is very legacy.

Because, who was it?

Not Herschel, was it?

Somebody around 1800.

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, they’re just dots of light in your telescope.

They see a dot of light except it’s moving.

And it’s like, so it looks like a star, but it’s not a star.

So, asteroid, star-like.

So, that’s like the biggest misnomer there ever was.

Yes, visually, but if you care what the thing is, and we still call them asteroids, star-like from the Greek.

Just legacy.

All right, so one last thing, and then we’re going to move on because 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, they’re just kind of a congregation.

We haven’t seen anything like what you’re describing.

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.

They’re one big spherical thing, because the gravity crushes everything into that spherical shape.

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 an outer ice, for example.

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.

You know, nobody’s saying this.

If you had three objects that were each themselves massive enough to be their own sphere, and you bring them together, they’re making a sphere.

There you go.

I got you.

That’s how the universe…

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?

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.

All right, give me some more.

And make this quicker this time.

This is Andrew Coffey, who says, Good day, Dr.

Tyson, Lord Nice, Sir Alan.

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, is the distance from the sun…

The main part is, could you have them close to the sun?

In fact, everything we know about the origin of the solar system indicates that Pluto formed…

It’s something like half its present distance from the sun, that the solar system was more compact originally.

And Pluto and most of the other dwarf planets of the Kuiper belt were transported outward with all those other 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.

So how does it go?

Where does it go?

So the sun is in the middle of the solar system.

Right.

It’s the big kahuna, right?

It controls all the other orbits.

And then we have the four rocky planets, Mercury, Venus, Earth and Mars.

And then there’s an asteroid belt just beyond the orbit of Mars.

It stretches for something like 100 million miles outward.

Okay, it’s big.

And then you got the four gas giants.

That’s amazing.

Then you have Jupiter, Saturn, Uranus, Neptune.

By now, Neptune’s orbit is 30 times as far away from the sun as the Earth’s.

And probably 15-ish times as far away as the asteroid belt.

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 50s.

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.

And if I understand correctly, the Kuiper belt was a negative prediction.

What does that mean?

I didn’t learn that in school.

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 we call them comets at the time, but reservoir of 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.

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 literature from back then is that there were really two scientists.

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 analysis tools.

Clyde Tombaugh was a discoverer of Pluto.

So they didn’t have big enough telescopes, but they didn’t have sensitive enough cameras.

They didn’t have computers to do the painstaking data analysis.

This is AJ Stavely, who says, Hello, Dr.

Tyson, Lord Nice, Dr.

Alan, 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, 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.

I’m trying to get through all of that.

So we found a lot of discoveries and you don’t have enough time on this show if I came back two or three more times.

All right, let’s go top three then.

A good example is 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, you got it.

But if the nitrogen is just a frosting 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 Pluto.

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.

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, Eracoth.

No one had ever been to a Kuiper Belt object.

And from its shape, it means sky in the Pohatian Indian language.

Okay, yeah, I knew that.

Who doesn’t know that?

Wait, 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.

But when we got to Eracoth 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 colliding at high speed.

Rather than collisions, interesting.

And there were decades in which computer models were warring and in one fell swoop, New Horizons settled that with the data on Eracoth.

And 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.

So it means they just kind of gather.

Everybody comes together.

Just come together.

They start off in 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.

Right.

Just a lumpy thing.

Right.

And tell us about the Pluto-Sharon 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?

To that dance.

To the gravity.

To the mutual gravity of Pluto and its big moon that are in a very special state called tidal equilibrium.

Turns out that because of that equilibrium, all those forces that might heat Pluto or make that geology go are long gone.

Tidal equilibrium, you mean double tidal lock.

Yeah, that’s right.

Oh, here we go, we know what that is.

But that can’t be the cause of Pluto’s geology.

It’s got to do with something else.

Okay, interesting.

Very good.

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 that.

And that can power the geophysics.

With Physics 101.

So wait a minute.

What?

Okay, I failed Physics 101.

Freezing gives off heat?

It does.

It releases heat.

Mm-hmm, all right.

All right.

I’m going to 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 going to call bullshit.

No, no, I got one for you.

No, I’m joking.

I got one for you.

No, I’m serious.

No, no, I got one for you.

Go ahead, go ahead.

Are you seated?

Okay, let’s look at the other side.

So you have water on the stove.

And you’re heating it.

Right.

And as you heat it, the temperature rises.

Correct.

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.

It does not raise the temperature.

Correct.

It turns into steam.

So the heat simply goes and changes it from liquid things up.

So the molecular change is-

Itself.

That itself, okay.

Okay, so now you go the other direction.

Yeah, so now you go the other direction.

Now 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 both does this change state.

Change the molecular state.

Right.

But damn, that’s…

Where was he when you took that physics?

You might have done better.

I might have done a lot better.

You might have.

Had I had Neil.

Yeah, so we call it latent heat.

There’s terms for it in physics.

Latent heat.

It’s really physics 101.

Hi, how y’all doing?

I’m latent heat.

You personified latent heat.

Yes, yes, yes.

I will never get this out of my head.

I know, right, you can’t do.

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.

Okay.

And that way both, there’s an homage to both cultures.

Yeah, you get both cultures.

So, Pluto’s counterpart in Greek is what?

What’s his face to the underworld?

Hades.

It’s also the place, but it’s also the guess.

Okay, and the ferry boat driver to take you across the River Styx is named Sharon.

Sharon.

Yes.

That’s where that came from.

Sharon!

Okay, here we go.

Greetings, Dr.

Tyson and Dr.

Alan.

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?

Whoa, look at that.

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?

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?

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.

Like giant.

Giant planet for Jupiter.

I don’t have a problem.

I mean, that’s, in fact, where we agreed, okay?

And one of the correspondence I got back when I was pilloried by third graders.

Because here, people know I don’t have to give the back story here.

Well, what’s really sad is not that he’s mean.

It’s just that he’s wrong.

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.

So we have the word paper, right?

And we have construction paper, corrugated paper, toilet paper, a card, stock paper, right?

So this paper 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.

So I don’t have any problem with that.

So I’ve always felt there’s been a shortage of vocabulary.

So in other words, I’m sure we agree here.

Jupiter and Earth should not be called the same object in orbit around a star.

I disagree.

No, yeah, they round it, 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?

Is it large?

Is it small?

And I have to ask 20 questions just to understand what anybody’s talking about.

But that’s the cool part of science.

No, that’s a weakness of science.

As a planetary scientist, planet is part of the term of what our field is all about.

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 are 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 is no debate.

I don’t have a problem.

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.

Look at me.

Do you see how he’s looking at me?

Do you see that face?

I’m telling you.

By that, for example, we have different kinds of human beings, short ones, tall ones, skinny ones, big ones.

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.

And there are all kinds of ways to add descriptors to planets, to stars, to galaxies.

We do that all through science.

And we got to get over these small number fears.

I mean, if we’re going to have only eight planets, Neil, I’m afraid the periodic table’s got to stop at beryllium.

You know, the periodic table has a hundred and umpteen elements in it.

Right?

We’re not afraid of a large number of those.

Just like we’re not afraid of having 50 states, right?

Or countless numbers of stars and asteroids and everything else.

We only have 49 states.

Texas is not a state.

It’s its own country.

Just ask anybody from there.

I’ve been to restaurants called Texas is the Planet.

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, because they classify all planets.

Star Trek is fiction.

We’re talking about facts.

No, no, but let’s imitate fiction.

Alan, I was on your side until that statement right there.

How dare you, sir?

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…

You don’t mind Star Trek having lots of kinds of planets, you see?

It’s just fine.

I’m all in.

We got ocean worlds, right?

I’m all in.

We got volcano worlds, and we got biologically active worlds, and sterile worlds.

I’m all in.

It’s all good.

Adjectives rock, don’t they?

On it.

Alan, great to have you back on.

Thanks so much, Neil.

It’s a pleasure.

It’s great.

Thanks.

We’re done here.

Oh my gosh, but we’re really not done, are we?

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.

Thank you, Alan.

Longtime friend and colleague.

Thanks so much.

Chuck, always good to have you.

All right.

Neil deGrasse Tyson here.

You’re a personal astrophysicist, as always.