♪ ♪ ZACHARY QUINTO: From the comfort of our home world, bathed in the warm light of our life-giving star... (rocket engine roaring) ♪ ♪ MAN: The 8-4-4 century interface... QUINTO: ...we've set out to explore every one of the planets.

♪ ♪ (wind blowing) (metallic clank) We've pushed further into the dark of space.

♪ ♪ But after decades of exploration, just two probes have explored the most inhospitable and distant reaches of the solar system's strangest realm.

♪ ♪ DERRICK PITTS: This is a region of the solar system that we really had very little information about.

♪ ♪ QUINTO: Their instruments waking up to find astonishing vistas... (lightning crackles) unlike anything encountered before.

LEIGH FLETCHER: It's at that moment you realize you're looking at something that's very different.

QUINTO: Places where all the rules are broken.

FRAN BAGENAL: This was a really strange system.

So why is Uranus so tipped on its side?

QUINTO: Where everything we thought we knew is being rewritten.

♪ ♪ (liquid rushing) NOAH HAMMOND: Geysers like this one even exist on Triton, where it's 30 times farther from the sun.

♪ ♪ QUINTO: Incredibly, we have pushed the frontier all the way to the solar system's most distant outpost... ♪ ♪ Pluto.

♪ ♪ ALAN STERN: A small planet should be simpler, and they should run out of energy in their internal engines and stop evolving, like the moon did, billions of years ago.

♪ ♪ (chuckling): Pluto didn't read any of those textbooks.

QUINTO: "The Planets: Ice Worlds"-- right now, on "NOVA."

♪ ♪ ("The Void" by Muse playing) ♪ They'll say no one can see us ♪ ♪ That we're estranged and all alone ♪ ♪ They believe nothing can reach us ♪ ♪ And pull us out of the boundless gloom ♪ ♪ They're wrong ♪ ♪ They're wrong ♪ ♪ They're wrong ♪ ("The Void" ends) ♪ ♪ QUINTO: Far, far away... beyond Mars... ♪ ♪ past the storms of Jupiter... and the rings of Saturn... ♪ ♪ where the distance from the sun is measured not in millions but billions of miles... ♪ ♪ lies a region unlike anywhere else in the solar system.

♪ ♪ Out here, the planets are utterly bizarre... even unnerving.

Uranus is an oddity even in a solar system of oddities.

♪ ♪ QUINTO: Temperatures approach absolute zero, (thunder rumbling) at which everything grinds to a halt.

Yet, somehow, the worlds here are still teeming with activity.

♪ ♪ Neptune was a great excitement, all sorts of strange things going on.

♪ ♪ (water erupts) QUINTO: A place where cold doesn't always mean frozen.

FLETCHER: It's at that moment you realize you're looking at something that's very different.

♪ ♪ (thunder rumbling) QUINTO: And even deeper into the darkness, past where the planets end... a vast expanse scattered with mysterious bodies awaits.

Our jaws just dropped to the floor.

PITTS: If ever there were an object that turned out to be far more surprising than we ever would have imagined, that's Pluto.

QUINTO: There is no part of the solar system more puzzling.

This is the realm of the ice worlds.

♪ ♪ MAN: 60 seconds, all continuing to go well.

QUINTO: Travelling to the most distant planets, Uranus and Neptune, is so hard, we've only managed it once.

(engines ignite) ♪ ♪ MAN: We have ignition, and we have liftoff.

QUINTO: This first mission to the farthest part of the solar system is only possible thanks to some help from the worlds closer to the sun.

MAN: 25 seconds into the launch, all continuing to go well.

♪ ♪ QUINTO: ...making the most of a rare planetary alignment.

♪ ♪ People realized that there was an opportunity coming up in the 1970s that only comes up every couple of hundred years, where the planets in their orbits kind of line up in just the right way so that you can slingshot from one to the next.

♪ ♪ MAN: The guidance data coming back shows that we're right on the money.

The key idea here is that you could use the gravity of each planet to accelerate the spacecraft, speed it up, and shorten the trip time.

(indistinct voices on radio) QUINTO: If it works, this series of planetary boosts will help Voyager cross nearly 900 million additional miles of space before reaching the first of the ice worlds.

♪ ♪ This is a region of the solar system that we really had very little information about.

We had excellent cameras and sensors and so on.

And we used that to go out into the solar system and see things for the first time we had never seen before.

♪ ♪ QUINTO: Almost nine years into its mission, Voyager begins its approach to an entirely unexplored planet and reveals a world weirder than we had ever imagined... ♪ ♪ A vast ball of gas, 14 times the mass of Earth and four times its diameter.

Sensors detect an atmosphere of 83% hydrogen and 15% helium.

But it's the 2.3% methane, that by absorbing red light and reflecting blue, lends Uranus its color.

♪ ♪ GRINSPOON: Just this giant, pretty much featureless, blue-green ball that seemed unreal.

♪ ♪ FLETCHER: They could see none of the activity that you're familiar with on Jupiter.

And it's at that moment you realize you're looking at something that's very different.

♪ ♪ Poor Uranus, it's got rather boring clouds, truth be told.

So there wasn't a lot to see with the cameras.

♪ ♪ QUINTO: Uranus spins on its axis once every 17 hours, which should generate dramatic storms.

So why is it so featureless?

Voyager detects a clue.

(wind blowing) Temperatures here are the coldest of any planet in the solar system.

There's simply not enough heat to drive the storms seen on Jupiter and Saturn.

Uranus is an entirely new class of planet: an ice giant.

♪ ♪ And more surprises are to come.

♪ ♪ Uranus has rings.

♪ ♪ BAGENAL: We knew long ago from telescopic observations the rings were there at Uranus, we didn't know their configuration or their shape.

♪ ♪ QUINTO: Voyager begins to explore the ring system and spots something curious in the shadows... ♪ ♪ two moons-- Cordelia on the inner edge of the brightest ring and Ophelia on the outer edge, help to organize the system.

♪ ♪ FLETCHER: Particles within the rings can be moved inwards or outwards as these tiny objects called shepherd moons, whose gravitational force can shape and sculpt the rings themselves ♪ ♪ QUINTO: But it's the orientation of the orbits of these moons and the rings themselves that singles out Uranus as the strangest of worlds.

♪ ♪ FLETCHER: Uranus looks bizarre.

The rings, rather than looking like that when you look through a telescope, they're actually orbiting up and over the top of the planet.

The whole thing is tipped, like a spinning top.

QUINTO: A bizarre orientation that hints at an unusual past.

♪ ♪ ♪ ♪ Since the beginning, everything in the solar system has been circling in the same direction.

♪ ♪ It begins with the vast cloud of material that orbits the young sun.

♪ ♪ Over time the material draws together... (rocks crashing) forming each of the planets.

♪ ♪ Today they all orbit the sun and spin on their axes in the same counterclockwise direction as that primordial cloud... ♪ ♪ except for Venus and Uranus, which spin in the opposite direction.

But Uranus is even stranger, because the entire planet is on its side.

BAGENAL: This was a really strange system.

So why is Uranus so tipped on its side?

If a roughly Earth-sized object smashed into Uranus late in its formation history, then that would've had the proper amount of momentum to basically knock it on its side.

♪ ♪ (explosion echoes) ♪ ♪ QUINTO: Not only did the collision tip the planet over, but it may also help to explain another of Uranus's mysteries: why the planet is so cold.

That impact presumably relinquished all of that internal energy that the planet had when it first formed and has left it as a relatively dead and sluggish world.

♪ ♪ QUINTO: We learn so much during this brief encounter.

But Uranus still holds many mysteries.

♪ ♪ And Voyager's strangest discoveries are yet to come.

♪ ♪ After Uranus, it must cover another billion miles of empty space before it will see another world.

(waves lapping) GRINSPOON: We can say the numbers, but can we really wrap our heads around something that large?

In order to help ourselves do this, we can make scale models.

QUINTO: At the center of the solar system is our sun, a ball of fire 850,000 miles in diameter.

♪ ♪ But if we scale the whole system down by a factor of 600 million, the sun becomes the size of this light.

♪ ♪ And walking out, you pass all the rocky inner words within the first 500 years.

♪ ♪ But to get to the outer solar system is far harder.

♪ ♪ On our scale, we have to cross the harbor to reach the next planet, nearly a mile away.

GRINSPOON: And we've reached the orbit of Jupiter, the largest of the planets and the first of the gas giants.

♪ ♪ (car door closes) QUINTO: Even farther, at almost twice the distance from the sun as Jupiter, we reach Saturn.

♪ ♪ GRINSPOON: Now as we approach Saturn, the light is getting noticeably dimmer, and yet from Earth, we still see it, because it's a big, bright, planet, and it's surrounded by those bright, reflected rings that act as a mirror, sending so much light back towards us.

♪ ♪ QUINTO: Beyond here the planets are separated by hundreds of millions of miles of dark, empty space.

♪ ♪ Now, we are three miles from our model sun.

♪ ♪ GRINSPOON: We're reaching the orbit of Uranus, twice again as far from the sun as Saturn.

Out here at Uranus, there's only about .2% of the light that we get at Earth from the sun.

♪ ♪ QUINTO: Heading out into the dark, 1.7 billion miles from the sun and we begin to fully understand the distances Voyager faces on its journey to the farthest reaches of the solar system.

♪ ♪ GRINSPOON: Now finally we've reached the realm of Neptune, the outermost of the giant planets.

Back there on that little island, where Earth and the other planets are basking in the warmth and the glow of the nearby sun, it feels as though we've come quite a long way.

♪ ♪ QUINTO: In 1989, after 12 long years, Voyager finally crosses the great expanse of space between Earth and its most distant planned objective.

(laughing, chattering) (scientists marveling, applauding) ♪ ♪ QUINTO: Neptune, an ice giant... 17 times the mass of Earth.

♪ ♪ A billion miles farther from the sun than Uranus, Neptune is almost chemically identical.

♪ ♪ Yet, bizarrely, it couldn't be more different.

GRINSPOON: Neptune in a way was almost a relief, because it wasn't featureless, you know?

(laughing): It was like, "Oh, good, a planet with, with clouds and features again."

(thunder rumbling) BAGENAL: Neptune was a great excitement.

It's got swirling clouds, really strong winds... (wind whipping, thunder rumbling) At 1,500 miles an hour, incredibly fast, the fastest winds that we've got in the solar system.

(thunder rumbling) ♪ ♪ FLETCHER: One of the things that Voyager discovered was an immense, dark vortex within the atmosphere... ♪ ♪ a huge, swirling dark spot.

♪ ♪ We say it's a giant storm, it just... those words don't fully contain... we're talking about a storm the size of the planet Earth or larger.

QUINTO: And the surprises keep coming.

Even though it's much farther out, Voyager discovers Neptune is warmer than Uranus.

It emits two and a half times the amount of heat it receives from the sun.

♪ ♪ And the source of the heat is another oddity of this strange planet.

PITTS: In fact, when we look at this dynamic activity in these extraordinarily cold regions, we really are at a loss to understand just what's going on here.

♪ ♪ QUINTO: One theory is that the buildup of pressure beneath the thick layers of cloud... (thunder rumbling) turns the carbon in the methane into a rain made of diamonds.

They then melt as they fall into the interior of the planet, producing the extra heat.

(thunder rumbling) As the heat makes its way out into the frozen cold of space, it churns the entire atmosphere, whipping up winds around the globe.

FLETCHER: There are no mountain ranges, no valleys, no continental boundaries to get in the way of the perfect fluid-dynamical flows.

(thunder rumbling) What that means is that when you start a weather pattern going, when you start a vortex spinning or you start a plume rising, there's very little to get in the way of it.

So those winds that develop and go around, they just keep going around and around.

There is nothing to slow them down, no friction with the surface.

♪ ♪ QUINTO: And the extreme cold here makes the atmosphere less viscous... allowing the gases to move faster... ♪ ♪ creating supersonic winds that outpace anything seen on Jupiter or Saturn.

♪ ♪ Voyager 2 has almost completed its grand tour.

♪ ♪ But the spacecraft's visit to Neptune includes an encounter with another puzzling world.

Roughly the size of our own moon, but scarred by deep cracks and pits, Triton is covered by a sheen of icy nitrogen.

♪ ♪ We expected it to be a frozen, silent world.

But one incredible image that Voyager sends back contains something entirely unexpected.

♪ ♪ (liquid rushing) Here, nearly three billion miles from the sun, huge geysers erupt nearly five miles into space.

♪ ♪ (geyser erupting) HAMMOND: Geysers like this one even exist on Triton, where it's 30 times farther from the sun, and it is so cold, yet you still how... have this intense geologic activity going on.

♪ ♪ QUINTO: At -391 Fahrenheit, Voyager found Triton to be one of the coldest places in the solar system.

♪ ♪ So what could be causing these eruptions to burst from the frozen depts?

♪ ♪ HAMMOND: The surface of Triton is covered in a thin layer of nitrogen ice, and it is so cold on Triton, that nitrogen, which is a gas on Earth, is frozen solid to the surface.

But right where the sun is striking, it starts to vaporize a little bit in the subsurface QUINTO: As weak sunlight passes through the nitrogen-ice surface, it heats up a layer of darker particles several feet below.

And in some spots that heat is just enough to vaporize the frozen nitrogen.

A lot of gas builds up, and then it bursts through and creates a geyser that goes 8,000 meters into the sky.

But although the faint light of the sun is just strong enough to power Triton's geysers, it is likely too weak to explain the cracks and pits elsewhere on the surface... ♪ ♪ ...rugged features that cover half the moon.

♪ ♪ (geyser erupts) What caused them is thought to be linked to Triton's odd path around Neptune.

HAMMOND: Its orbit is really unusual.

It orbits in the opposite direction that the planet spins.

Now, most moons orbit in the same direction that the planet spins, because we think most moons form at the same time as the planet in a disc of material around the planet.

And since Triton is going the opposite way, we think it must have formed in a different way.

♪ ♪ QUINTO: One theory is that billions of years ago, Triton wasn't a moon at all.

♪ ♪ It formed way beyond Neptune... ♪ ♪ ...a huge, wandering object that eventually ends up close enough to Neptune to be drawn in by its gravity... ♪ ♪ and trapped in its unusual orbit.

♪ ♪ HAMMOND: So when Triton first goes into orbit around Neptune, it's not going to be a perfectly circular orbit.

We expect it to be highly eccentric, where it's getting closer to and further from Neptune.

And when that happens, Triton is going to get stretched and squeezed by the immense changes in gravity as it moves in and out.

And that stretching and squeezing is going to put an intense amount of heat into Triton.

♪ ♪ QUINTO: The ancient molten interior then explodes up through the faults in the moon's crust.

♪ ♪ Over time, Triton's orbit becomes more and more circular.

♪ ♪ No longer stretched and squeezed, the moon cools, leaving the rugged surface we see today.

♪ ♪ As it leaves Triton and Neptune behind, Voyager's mission is over.

It will never encounter another planet.

But as it heads out of our solar system to the ocean of stars beyond, it carries with it an interstellar message in a bottle, should it ever encounter something-- or someone-- else.

♪ ♪ MAN: These unique disks contain photographs of everyday life as well as voices, the music of Beethoven and Chuck Berry, a baby crying, and a heartbeat.

(heart beating) QUINTO: On its lonely journey into darkness, Voyager passes through an unknown region of space... that in just a few years will be described for the first time.

♪ ♪ STERN: The discovery of the Kuiper Belt in the 1990s is probably the single most important discovery of the space age.

It completely changed everything.

It was as if we had a map of the Earth without the Pacific Ocean on it, because we didn't know it was there.

QUINTO: The Kuiper Belt is the most remote part of the solar system.

Here trillions of frozen lumps of water, ammonia, and methane circle the distant sun.

Like, the Kuiper Belt is what we call the third zone of the solar system.

This is what we think is the most primitive region, a zone of icy objects beyond Neptune's orbit.

♪ ♪ QUINTO: Incredibly, by the early 2000s our telescopes become powerful enough to just make out these unbelievably distant objects.

♪ ♪ We found Sedna and Eris and Makemake and Haumea and Ixion and more.

And we now know of more than 2,000, uh, you know, Kuiper Belt objects.

♪ ♪ QUINTO: This is the solar system's new frontier.

♪ ♪ And in 2006, a new probe is primed to leave Earth on a mission to explore it.

MAN: Five, four, three, two, one.

(rocket engines firing) We have ignition and liftoff of NASA's New Horizons spacecraft... (crowd cheering) on a decade-long voyage to visit the planet Pluto and then beyond.

GRINSPOON: It just shoots up so fast, it's the fastest launch ever from Earth.

♪ ♪ STERN: As soon as we were launched we had to test all the backup systems and plan the most sophisticated flyby of Jupiter that had ever taken place.

♪ ♪ QUINTO: Even with the extra kick from Jupiter's gravity, it will still take ten long years to reach the Kuiper Belt.

GRINSPOON: In order to ensure that it was going to last for the decade, they built in a lot of redundancy.

There were sort of two of everything-- computers and the guidance systems.

♪ ♪ And they figured out how to hibernate-- the first spacecraft that, that hibernated.

STERN: But it had really never been done before, to put the spacecraft largely to sleep, let the spacecraft just silently coast, then we could extend the life of the electronics No spacecraft mission had ever really used hibernation as a day-to-day way to cross the solar system.

GRINSPOON: That was scary because, you know, you turn it off, and you hope that it comes back on again.

♪ ♪ QUINTO: New Horizon's first target is the Kuiper Belt's most famous resident... ♪ ♪ HAL WEAVER: The discovery of Pluto was back in 1930, and Clyde Tombaugh, a Kansas farm boy, was using the telescope at the Lowell Observatory in Arizona.

CATHY OLKIN: Every clear night Clyde would go out and, and take images of the sky on photographic plates.

And when it was cloudy or during the day, he would compare those plates.

♪ ♪ WEAVER: When you're looking out at the sky, how do you tell something is a star versus a planet?

Well, planets actually move relative to the stars and that's because they're much closer to us than the stars.

So what Clyde Tombaugh noticed that there was this little speck moving across the stars.

♪ ♪ And then Clyde Tombaugh discovered Pluto.

♪ ♪ QUINTO: It is crowned the ninth planet, a title Pluto enjoys for 76 years.

♪ ♪ But while New Horizons continues its decade-long voyage, a debate rages back on Earth... one that will challenge Pluto's very status as a planet.

GRINSPOON: According to the International Astronomical Union, a planet has to be orbiting the sun.

It needs to be large enough and massive enough that its gravity can pull itself into a spherical shape... GRINSPOON: And it has to have cleared its zone, meaning that it is sort of the gravitational bully of its, of its own realm.

♪ ♪ QUINTO: The problem is Pluto's region of the Kuiper Belt is packed with hundreds of icy objects.

♪ ♪ Pluto doesn't meet the criteria for being a planet, because it hasn't cleared its orbit.

By that definition, Pluto clearly belongs to a, a different, um, sort of grouping.

♪ ♪ QUINTO: Pluto is now classified as a dwarf planet, along with the other larger worlds of the Kuiper Belt.

♪ ♪ But the debate still continues.

♪ ♪ I think planetary scientists really never stopped calling Pluto a planet.

Pluto is what it is; it doesn't make any difference whether we call it a planet, a full-fledged planet versus a dwarf planet.

Defining them and labelling is really a side thing, it is a periphery to the important thing, which is exploration.

♪ ♪ (chattering) WOMAN: We are searching for frequencies, stand by.

♪ ♪ Standby for telemetry.

♪ ♪ QUINTO: After nine years of flight, NASA attempts to reawaken New Horizons from hibernation.

STERN: The first words he said were, "Alan, we have lost contact with the spacecraft."

♪ ♪ And all of a sudden, I get a message that the spacecraft is shut down.

I couldn't believe it.

It was, it was heart stopping.

And here we had just days until the flyby was to begin to put Humpty Dumpty back together again.

♪ ♪ QUINTO: Nine years of faultless space travel would all be a waste if New Horizons couldn't be brought back online.

♪ ♪ It wasn't easy, but they pulled it off with precisely three-and-a-half hours to spare.

WOMAN: We are in lock with telemetry with the spacecraft.

(scientists cheering, applauding) Yes!

Give me a hug!

(applause continues) ♪ ♪ (scientists applauding) QUINTO: New Horizons gives us our first close-up glimpses of the most distant world ever visited.

A world that, until now, had only appeared as a fuzzy blob.

We thought the surface would be geologically dead, because Pluto is so small.

When New Horizons came by and took all of these pictures it literally broke everything we thought about it.

♪ ♪ GRINSPOON: Pluto was a shock and a revelation in so many ways.

It's turned out to be one of the most fascinating objects in our entire solar system.

♪ ♪ WEAVER: Giant water-ice mountains as high as the Rocky Mountains in the United States.

♪ ♪ Bladed terrain.

♪ ♪ We're seeing ancient parts of Pluto but also ridiculously young parts of Pluto.

♪ ♪ HAMMOND: We even think we see dunes, which get blown around by the very thin atmosphere A small planet should be simpler, and they should run out of energy in their internal engines and stop evolving, like the moon did billions of years ago.

(chuckling): Pluto didn't read any of those textbooks.

♪ ♪ QUINTO: One of the most fascinating features beamed back by New Horizons is the region named after the planet's discoverer: Tombaugh Regio.

We got our, our first full-frame view of Pluto and saw this, this region that looks like a heart, this heart-shaped region.

♪ ♪ QUINTO: The western lobe of the heart is called Sputnik Planitia... a giant plain of frozen nitrogen, methane, and carbon monoxide... ♪ ♪ that stretches for over 330,000 square miles.

♪ ♪ And at its edge lies a range of mountains made of frozen water ice.

They rise nearly four miles into the dark skies above the plain.

♪ ♪ As odd as that is, there is something even weirder about the region.

It's the size of the states of Texas and Oklahoma combined, and we can't find any craters on its surface.

There are almost no impact craters on this, which means something is happening on the surface.

QUINTO: Pluto's heart is young, fresh ice.

So what's creating it?

It's smooth, but it wasn't completely smooth, it had this beautiful pattern of sort of cells or polygons.

♪ ♪ QUINTO: Detailed imagery beamed back by New Horizons reveals a puzzling network of hexagon and pentagon shapes... ♪ ♪ that crisscross the frozen nitrogen surface.

♪ ♪ BAGENAL: It looks like there's material that's convecting underneath, like soup on the stove.

You have these things turning over, making these shapes on the top.

♪ ♪ So we scratched our heads and wondered what could be making this strange behavior.

♪ ♪ QUINTO: Our working theory is that somewhere deep in Pluto's interior are radioactive elements that generate heat as they decay, warming up a liquid layer beneath the planet's crust.

♪ ♪ We think underneath the exotic ices on Pluto's surface, and underneath the water-ice crust, which could easily be a 100 kilometers thick, that there's actually a layer of liquid water that surrounds a rock core.

♪ ♪ QUINTO: This sunless ocean of water that has existed for billions of years beneath the surface of Pluto is being gently warmed by heat from the interior.

♪ ♪ That little bit of heat that's leaking out, we think is enough to drive the convection and these exotic patterns that we see on Sputnik Planitia.

And that's because nitrogen is, it's very soft, it doesn't take much heat to make it move.

♪ ♪ QUINTO: As the nitrogen slowly bubbles up, the area is constantly being resurfaced, scouring away any impact craters.

OLKIN: It's warmer underneath, and so then the glacial ices are upwelling in the middle, and then spread out and then downwell on the side, and that's what make those... makes those polygonal patterns that we see on the surface.

We had no idea to expect that.

QUINTO: But why all this activity here and nowhere else?

Perhaps Pluto's heart is the site of a huge impact... ♪ ♪ that long ago punched a large hole in the surface almost down to the vast ocean beneath, a great hole that slowly filled with soft nitrogen ice, and now gently churns just above a warmer ocean.

♪ ♪ (bubbling) So there's a lot more going on on Pluto than we had ever imagined.

You don't have to be a giant planet, or a terrestrial planet, to be an amazing place in the solar system.

STERN: It just completely changed our view of how small planets operate and how they can be as, as complex as big ones.

♪ ♪ QUINTO: New Horizons' closest encounter with Pluto lasts just hours.

Its fleeting visit reveals the tiny speck that Clyde Tombaugh saw moving across the sky to be a dynamic, vibrant world.

But Tombaugh died nine years before New Horizons left Earth, so he never saw Pluto up close.

STERN: He had asked if a mission ever did get launched that some of his ashes could be sent on the journey.

And to think that Clyde's ashes, you know, flew by Pluto, and, you know, he was finally visiting the place that he discovered, that was pretty cool.

♪ ♪ QUINTO: And Pluto holds a final surprise.

As New Horizons turns its camera back for one last look... ♪ ♪ it captures an image of Pluto's atmosphere glowing in the dark.

There's the blue ring of its atmosphere looking hauntingly familiar, like the Earth's atmosphere.

Not only can we see a number of layers in the atmosphere, but we can also see mountains on the surface of the planet sticking up into that atmosphere.

♪ ♪ QUINTO: A thin, blue sky over a hidden ocean of water, three billion miles from Earth.

♪ ♪ That image just epitomized everything we had done.

♪ ♪ STERN: That's my favorite picture from the entire flyby.

And I took to saying that the solar system had saved the best for last.

QUINTO: But New Horizons isn't done.

It expands its exploration of the Kuiper Belt by continuing on, towards a new target.

PITTS: This was an opportunity for the New Horizons spacecraft to now look at a different object out in the Kuiper Belt, something that might be much more typical of what could be found out in this region.

♪ ♪ QUINTO: On January 1, 2019, it beamed back pictures of the most distant object ever visited.

♪ ♪ WEAVER: This object may be the most primitive object ever encountered by a spacecraft.

♪ ♪ QUINTO: Two icy rocks frozen in the moment of collision.

WEAVER: By looking at this today, we think we're looking back in time to the origin of the solar system.

♪ ♪ (rocks thudding) QUINTO: A window into the processes that created the solar system that we call home.

♪ ♪ New Horizons gives us a glimpse of our origins before it follows Voyager on an eternal journey out into the stars.

♪ ♪ Just six decades ago, we left Earth for the first time.

♪ ♪ Since then we've gone on to explore the whole expanse of the solar system.

♪ ♪ With each flight, curiosity has driven us further.

♪ ♪ RIVERA-VALENTÍN: For us to continue doing something that is very natural and intrinsic to all of us, and that is answering the big questions and exploring the unknown.

QUINTO: And as our technology has evolved, each encounter has taken us closer.

♪ ♪ McKINNON: I think exploring the planets is just a, it's a great adventure that we can all participate in.

♪ ♪ QUINTO: We've landed robotic explorers... (air rushing, metal clanking) on Mars... ♪ ♪ Venus... (wind whistling) (rocket disengaging) and even a distant moon of Saturn.

♪ ♪ GRINSPOON: I feel as though we're absolutely just at the beginning of planetary exploration.

♪ ♪ QUINTO: These first steps have only scratched the surface... ♪ ♪ but they reveal a solar system of limitless wonder... and beauty.

PITTS: There's still more for us to discover.

There's still more surprises out there.

There is a lot of exploration left for us.

♪ ♪ QUINTO: As we continue to push farther and stay longer in our quest to piece together one of the greatest stories ever told: ♪ ♪ the story... of the planets.

♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪