Space's Deepest Secrets

Pluto, a tiny dwarf planet

in the far reaches of our solar system,

has set the world of astronomy alight.

We were expecting it to be dead, frozen, just sitting there,

and what we saw was completely the opposite.

Pluto is bursting with drama...

Soaring mountains, flowing glaciers,

and churning, icy plains.

You have to understand how profound this is.

No had no expectation that Pluto would be alive.

More than that, we don't know how it's possible.

Today, investigators race to unravel

this strange planet's dark secrets.

Do alien volcanoes cover its surface?

Is its mysterious heart-shaped plain evidence

of a giant impact?

And is Pluto’s biggest moon, Charon, a cosmic thief?

The new horizons' observations of Pluto

are like a giant detective story...

The clues are all there,

and now we need to unravel its mysteries.

We dive deep inside this icy world

to reveal Pluto’s mysterious hidden history.

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Investigators across the globe are trying to solve

one of the biggest mysteries in astronomy...

Why a tiny world at the edge of our solar system

appears to seethe with geological life.

From earth, Pluto is barely visible...

Three, two, one...

so NASA launches the new horizons space probe

on a 3.1 billion mile voyage to examine it up close

for the very first time.

And as we sent new horizons on its approach to Pluto,

that little faint dot became this stunning, profound,

remarkable world with a complexity

that we could've never imagined.

New horizons team member Cathy Olkin

follows every step of this space probe's journey

here at mission control.

This was the best image that we had of Pluto

before the spacecraft got there in 2015,

and you can see there's really no detail.

It's blurry.

You can't see any surface features.

It's just a blob.

After nine years of travel,

new horizons takes the first ever

high-resolution images of Pluto’s surface.

What it reveals stuns the world.

When I first saw this image,

I was delighted and I was amazed.

This detail on Pluto far exceeded anything that

I thought we'd see.

Before new horizons, Pluto was a complete mystery.

Since new horizons, Pluto is an even bigger mystery.

There's so much going on on Pluto’s surface

that one image alone,

it's a lifetime's worth of work to understand it.

3.7 billion miles from the sun,

scientists expect Pluto to be a cold, dead,

heavily cratered world.

What they find is astonishing.

Nitrogen freezes out the atmosphere,

coating the land in a thick frost.

Mountain ranges tower above.

And clues hint that the presence of a liquid ocean below.

But Pluto’s most striking feature is a vast,

smooth heart on its surface where massive nitrogen glaciers

slowly flow into a deep, icy basin.

Mountain ranges...

Smooth plains...

Flowing glaciers...

All suggest that Pluto is geologically active.

But how is that possible so far from the sun?

We had never seen Pluto up close,

so we had a certain set of expectations.

It's out there at the edge of the solar system,

it's not receiving much light from the sun,

so we expected it to be a dead, icy world

probably covered by craters.

Well, it turned out to be anything but.

What could be causing Pluto’s active geology?

Investigators start with Pluto’s most striking feature...

Its giant, heart-shaped, nitrogen ice glacier.

They name the western lobe Sputnik Planitia,

but sputnik Planitia is a mystery.

It's far smoother than scientists expect.

Our solar system is filled with speeding asteroids and comets.

These smash into planets and leave their scars behind.

Sputnik Planitia should be covered in these scars,

but it's smooth, as if some mysterious force

is healing the surface, but what?

At NASA Ames research center in California,

Dr. Orkan Umurhan believes the weird material

that makes up the plain is key.

So, on the earth, nitrogen exists in gaseous form

and makes up 70% of the atmosphere,

and that's because it's really warm on the earth,

but on Pluto, because it's so cold,

all that nitrogen exists in the form of ice.

Nitrogen ice flows on to the lowland plain

from vast glaciers that surround sputnik Planitia,

but then the ice does something very unusual...

It forms a strange pattern.

Could these shapes be a clue

to what's wiping out the craters?

All that ice makes its way into sputnik Planitia,

and when you do a close-up

and you zoom in on sputnik Planitia,

you see honeycomb patterns all over that place.

Surprisingly, Orkan thinks this pattern

is something we've all seen before in everyday life.

A few days after the close encounter with Pluto,

we had hauled on out to a Japanese restaurant,

and they brought out the miso soup,

and I looked in the miso soup, and I was like, "oh my god,

it's the same patterns that we see on sputnik Planitia."

Orkan replicates this effect in the lab

by heating miso soup.

The churning patterns that appear on bowls of hot liquid

are called convection cells.

Convection occurs when hot liquid rises

from the bottom of a deep container

and cool liquid sinks down from the surface.

This rising and falling creates

and a patchwork of honeycomb cells on the surface,

just like the patterns on sputnik Planitia.

So, what we're seeing is the patterns

that that's forming in the fluid

and they're remarkably similar to the patterns that you see

on Pluto’s sputnik Planitia.

Orkan thinks the nitrogen ice

in sputnik Planitia acts like a slow-motion liquid.

The faint heat of the planet's interior drives pockets

of warm ice upwards, creating the weird pattern

and wiping out any craters on the surface.

So you can imagine, you get this giant convection-cell pattern

where it's like a conveyor belt

going around in a circle like this.

Miso soup helps to solve the mystery

of the honeycomb pattern,

but it also reveals something extraordinary

about sputnik Planitia.

Convection needs a very deep body of fluid to be effective.

What scientists first thought was a plain

must really be a basin of ice as deep as the Atlantic ocean.

But how could such a vast basin form?

The leading theory suggests that four billion years ago,

a space rock more than 60 miles across drifts into Pluto’s path.

It smashes into the crust,

blasting out a colossal scar 620 miles wide

and 5 1/2 miles deep.

Nitrogen from the atmosphere

condenses on the lowest-lying parts of the crater

and settles as frost, filling in the depression.

Over billions of years, the nitrogen ice churns away

to create the honeycomb pattern we see today.

A giant impact solves the mystery

of Pluto’s honeycomb heart.

But not all of sputnik Planitia seems to play by the same rules.

The lower edges of this vast plain

are just as smooth as the insides,

but there's no sign of convection cells here.

Do the fringes of sputnik Planitia

have a very different self-healing superpower?

And could Pluto’s mysterious mountains actually be volcanoes

made from solid ice?

Pluto's iconic heart, sputnik Planitia,

is a giant basin filled with nitrogen ice.

It should be covered in asteroid craters,

like the rest of the planet,

but something is smoothing it out.

Honeycomb convection cells account for most

of the smoothing, but not all.

At the Southern edges of sputnik Planitia,

the ice is still smooth,

but there's no sign of any convection.

What we suppose is that the basin in this area

is too shallow for convection to take place.

On Pluto, temperatures drop to a frigid

minus-400 degrees Fahrenheit.

Orkan suspects this makes the nitrogen ice

behave in a very unusual way.

He thinks that the ice could be self-healing.

To test his ideas, Orkan runs a computer simulation

of sputnik Planitia to see how nitrogen ice flows

at Pluto’s freezing temperatures.

We start the process, and you can see that the nitrogen ice,

under its own weight, smoothes itself out.

Orkan's simulation reveals that at Pluto’s

temperatures, the nitrogen ice in sputnik Planitia can flow.

It has the consistency of molten candle wax.

This means when an asteroid hits it,

something astonishing happens.

An asteroid pierces Pluto’s atmosphere

and strikes the left lobe of its heart.

It blasts out an enormous crater.

The thick, partially frozen nitrogen

that coats the damaged surface begins to flow.