Pluto, for so long a mystery,
has finally been revealed.
And these astounding images have rocked science.
Everywhere we looked, it looked different.
And that shook us to the core.
Icy volcanoes, fast-flowing glaciers,
and mountain ranges as big as the Rockies.
We thought Pluto would be dead and boring.
We couldn't have been more wrong.
In 2015, Pluto showed us its heart.
But does its greatest secret lie below?
Could tiny Pluto harbor alien life forms
3 billion miles from the sun?
Have you ever dreamed about traveling out of this world?
My name is Mike Massimino,
and I turned that fantasy into a reality
when I space-walked to repair the Hubble space telescope.
Great job, Mike.
Now as we expand our knowledge of our solar system
from Mercury to the cosmic unknowns,
I want to take you on a personal journey to...
Captions by vitac... www.Vitac.Com
captions paid for by discovery communications
welcome to "the planets." I'm Mike Massimino.
Nothing excites me more than learning about
the latest discoveries in space.
With new technology, we are able to see
further in our solar system than ever before.
Pluto... The distant dwarf planet,
remained a complete mystery for many years.
But now photographs from NASA's New Horizons spacecraft
have completely opened our eyes.
Robotic probes armed with scientific instruments
have been compiling a family photo album
of our solar system for over 40 years.
And these close-up portraits have taught us
almost everything we know
about our closest cosmic relatives.
The lesson of planetary science
is you have to go there
to really resolve things in detail
and to make the big discoveries.
But until recently,
one portrait had escaped our robotic eyes,
the dwarf planet Pluto.
Pluto used to be our most distant planet
until astronomers discovered lots of other icy objects
orbiting alongside Pluto.
And in 2006, poor Pluto got demoted.
Pluto is tiny and so far away,
around 3 billion miles,
that our finest telescope can pick out
only a faint blob.
The very best images we've made of Pluto were
with the Hubble space telescope.
And the Hubble space telescope could only get, yeah,
about 20 pixels across Pluto.
We knew that there were areas that were bright and dark.
But we didn't know what they were.
And it wasn't a very clear view at all.
This fuzzy image was pretty much
all we had to work out what Pluto was like.
We knew that it had nitrogen ice on it.
We knew it had a moon. And we knew these other things.
Um, but still you have to go there
because it is so far away,
3 billion miles or more.
We just had to go there to understand it.
Summer, 2015,
NASA's New Horizons probe flies past Pluto,
recording the first-ever close-up images
of this most mysterious of worlds.
Many scientists were expecting to find a flat,
dead world similar to our moon.
But, instead, the pictures
reveal a world of dizzying diversity.
High mountain ranges, winding glaciers,
and vast crater-free plains
that all hint at recent geological activity.
Pluto, it seemed, was alive.
We suddenly got up this image that showed jagged mountains
and totally bizarre hills and smooth plains
and no craters at all on that particular image
showing that this really was a geologically youthful region.
Some of the features revealed by New Horizons
defied simple explanation.
One of the most baffling was a pair of vast mounds
on the surface of Pluto,
each topped by a deep depression.
These mounds look just like young volcanoes.
But how could that be possible on a planetary surface
made mostly from ice?
There's nothing that can drive volcanoes on Pluto,
as far as we know... So what are these things?
The mysterious mounds on Pluto are huge,
over 100 miles wide
and around 3 miles high.
To make sense of these perplexing formations,
scientists turned to similar looking features here on Earth.
Planetary geologists like Jani Radebaugh
call them shield volcanoes.
This volcano we're heading for is called Skjaldbreidur
and it means "broad shield" in Icelandic.
So in some ways it's sort of the... the, uh,
the eponymous shield volcano
that we're about to land on.
Shield volcanoes are formed by long,
drawn-out eruptions of runny lava.
And they're said to resemble the shape
of a warrior's shield lying on the ground.
This one erupted just 9,000 years ago.
Can see a giant crater right here,
summit crater, that's typical of shield volcanoes.
And it's actually pretty deep right here,
deeper than I expected.
This is quite a young volcano.
And so you can still really clearly see that crater.
And, actually, we see the summit crater
on Pluto's shields very clearly,
and that really kinda makes us
really think they could be a shield volcano
just because of the broad shape
and a summit crater just like this.
It's not unusual
to find shield volcanoes on other planets.
Mars, like Earth, is mostly made from rock.
And it's home to the monumental volcano,
Olympus Mons,
built up from vast eruptions of hot,
runny lava millions of years ago.
But lava is melted rock and that's a problem
because Pluto should be too small
and too far from the sun to have anything melted.
If its broad features really are volcanic,
they must be made something very different to lava.
Jani Radebaugh believes the light color
of Pluto's mysterious mounds offer a crucial clue.
The kind of eruptions that make this shape of volcano
are, you know, hundreds or thousands of...
Of individual eruptions over time.
They... they erupt out of...
Of the fissure and flow out across the surface.
And then they just pile up on top of each other
and continue to flow out
building up a broad shield over time.
The same thing has happened on Pluto,
it's just the lava that's erupted from
Pluto doesn't look anything like this.
It doesn't... It's not dark in color.
It's not made of basalt.
Instead, it's made of water ice.
Unlike Earth, Pluto has a surface of frozen nitrogen
on top of a bedrock
and mantle of solid water ice.
Some of this water ice
must be melting to form
explosive flows of liquid slush
that spew out onto Pluto's surface,
just like hot rocky lava does on Earth.
The warm slush freezes rapidly on the surface,
building up to form broad icy shields,
just like the rocky shields we find on Earth and Mars.
If the water under the surface
can be melted by something, some energy,
it can burst through the surface
and flow just like lava does here on Earth.
So instead of volcanoes, like you have here,
you get cryovolcanoes, cold volcanoes,
on these more distant objects.
We have a myopic view of the universe thinking
everything has to be the way it is here.
Here on Earth, volcanoes are hot.
But on Pluto, volcanoes run cold, not hot.
But perhaps the most exciting thing
about Pluto's volcanoes
is that they're virtually free from impact craters,
meaning the warm slush that formed the ice volcanoes
must have flowed out of them really recently.
These features are very, very young.
Pluto is active today.
There hasn't been enough time
for the bombardments of comets impacting
Pluto to build up and build up a record Cr...
Uh, a record of craters on the surface.
Pluto is active today.
That's the headline.
The potential for active volcanoes
on Pluto stunned scientists.
But they pale in comparison
when close-up images
of Pluto's smooth heart are revealed
because this Texas-sized
basin of ice appears to be boiling.
NASA's New Horizons space probe spent nine years
traveling to Pluto.
But it was worth the trip.
The space craft beamed back images
proving that Pluto is young and thriving.
And it showed us, for the first time,
that icy cold Pluto has a heart.
Our solar system bears the scars of a violent past.
Impact craters litter the surface of rocky planets
and moons like our own.
Yet, on Earth, these battle scars
are wiped away by lava, water and wind.
If you look at the moon now and you look at it
in 1,000 years, not gonna be very different.
However, if you look at the Earth now
and wait an hour, right, we have weather,
we have volcanoes,
there are lakes that come and go.
The sea levels rise and fall over thousands
and millions of years.
So, uh, with, uh, all of this geologic activity,
we say that the Earth is a living world.
Scientists expected Pluto to be heavily cratered,
a geologically dead world similar to our moon.
But when New Horizons flew past in 2015,
it revealed a vast, heart-shaped icy plain,
which appears much younger than the rest of the planet.
And the western part of this plain,
Sputnik planum, was completely crater-free.
The broad, pale surface offers a window
into Pluto's unexpected activity because it looks just
like the icy glaciers do, here on Earth.
There's not a crater to be seen anywhere across that surface.
And that immediately tells us it's young.
Some of the estimates are maybe as young as 10 million years,
you know, only since that stuff
has been moved around and changed.
That's... that's today in geologic terms.
Something is regularly smoothing out
the surface of Sputnik planum,
but what?
Scientists can rule out cryovolcanoes.
They make mountains, not plains.
So what else could it be?
The first clue comes from pale snaking lines
that appear to feed into the northern rim of the plain.
These sinuous features look just like
the rivers of ice
that flow from mountainous glaciers here on Earth.
What we're looking at here is,
uh, is a massive glacier pouring out across the valley
and emptying into a glacial lake.
One of the first things we noticed when we saw the...
The close-up images from New Horizons
is not only a vast field of kind of a flat glacier
but also tiny little feeder networks into the glacier,
like valley glaciers just like this one
emptying into the larger continental glacier.
Ices must be forming in Pluto's highlands
and flowing into Sputnik planum,
just like outlet glaciers
flow from high mountains here on Earth.
But on Pluto it's too cold for water ice to flow.
So the outlets feeding Sputnik planum must be filled
with a very different kind of ice.
So the glaciers have to be made of things like nitrogen.
Now, nitrogen is what makes up most of our atmosphere.
It's a gas here.
But at those temperatures it freezes and becomes an ice,
a glacier of nitrogen.
On Pluto, nitrogen ice has the texture of toothpaste.
And it flows down mountains made of water ice.
Those glaciers are flowing.
And, what's more, there are no craters on them.
So they're active, they're young.
They're flowing right now today.
We now think Sputnik planum
is a vast basin filled with frozen nitrogen
and fed by mountainous glaciers to the north.
This steady flow of fresh nitrogen explains
why the edges of the basin are so smooth.
But what about the regions
that sit beyond the reach of the glacial flow?
Something else must be wiping out craters
in the middle of the basin.
Jani Radebaugh believes a weird pattern
on the surface of Sputnik planum suggests
an astonishing possibility...
Pluto's surface could be boiling.
Welcome to Sputnik planum.
I mean, really this is what it would look like
if we were standing on the surface of Pluto.
You see a vast, flat glacier behind us,
really white extending off to the distance,
and behind us a ring of mountains.
When we look at the surface of Sputnik planum,
we noticed that there...
There are regularly spaced cells.
And they're a little bit rounded in the middle,
they taper off at the edges.
And they really have the appearance of something that...
That formed by convection.
So if you think about a pot of oatmeal,
um, as it's... As it's boiling away,
it's bringing material up to the surface
and then it's kind of pulling it back down
again at the sides, convecting over and over again.
The nitrogen ice of Sputnik planum
could be boiling like a pot of oatmeal,
but so slowly
the roiling surface appears frozen at any time.
A similar, but much faster,
process makes patchwork patterns
in Earth's most active lava lakes.
Hot globs of lava rise up,
forming rounded cells on the surface
and cool lava sinks down,
slipping between the gaps formed
by the hottest bubbles of molten rock.
As we look at the surface of Sputnik planum,
what we're seeing is basically a lava lake in slow motion.
There's material rising up and then moving over
and descending again as it gets cool.
And, um, basically, if we could see that,
if we could speed it up over a few thousand years,
we would see individual cells
all across the surface roiling and churning
and boiling, moving, convecting nitrogen.
You really have to step back and realize
just how amazing and weird this is.
The temperature is hovering near 400 degrees below zero.
And things are bubbling up and moving around.
There's geology happening.
What you have to remember is
that it doesn't take a lot of energy
to make something as cold as nitrogen ice flow.
But it does take some energy.
And while Pluto wears its magnificent heart on its sleeve,
a second, warmer heart must be deep below the surface.
But out here in the frozen expanse
of near outer space,
the question still remains,
where's the heat coming from?
The New Horizons space probe revealed that Pluto,
a dwarf planet smaller than our own moon,
is somehow active when basic science says it shouldn't be.
Pluto is so far away from the sun, how does it heat up?
Scientists believe a secret ocean
deep within Pluto may hold the answer.
In 2015, the New Horizons probe
stuns mission scientists when it reveals
Pluto as a dynamic, living world.
Its glaciers, mountain ranges,
and likely volcanoes are all evidence
of an active geology driven by heat.
But scientists are mystified
where that warmth is coming from.
Pluto is too small to have retained the heat
from its violent formation over 4 billion years ago.
And it sits so far from the sun
that sunlight hardly makes an impact on Pluto.
Well, it's about 20 minutes before dawn right now.
And the light that we see is exactly the same
as the illumination
we'd see on the surface of Pluto at midday,
when there is the maximum amount of sunlight on the surface.
And because Pluto receives so little sunlight,
its surface is bone-chillingly cold,
as low as minus 400 degrees Fahrenheit.
If the heat that drives Pluto's dynamic geology
isn't coming from sunlight,
it must be coming from below.
But from where?
The best guess is that
Pluto has a deep subterranean ocean of liquid water
and somehow this ocean is driving heat up to the surface.
There's pretty good circumstantial evidence
that Pluto has a massive water ocean in its interior.
And over time as the planet cools,
the water must be freezing.
And as water freezes, it releases, uh,
a form of energy called latent heat.
And that release of energy from the freezing ocean
could very well be
what's powering a lot of Pluto's geology.
Could freezing water really make a planet hotter?
It sounds crazy.
But Jani Radebaugh can demonstrate
this weird quirk of physics
using an ice bath
to represent Pluto's frozen upper crust
and a cup of hot water
to represent Pluto's hidden liquid ocean.
At first, the ice bath causes
the temperature of water to drop.
But as soon as the water freezes,
the temperature inside of the glass
does something amazing:
It rises. 'Kay.
It's at 30, so it's definitely ready to freeze.
So I just wanna give it a little bit of a helping hand
and see if we can start it to freeze.
Here we go. Just a little stir.
Oh.
Oh, there it goes.
Uh, now it's completely frozen and the temperature
is dramatically climbing,
like, just seconds after it froze.
It has climbed... Climbed 8 degrees.
Look at this.
It might seem kind of counterintuitive,
but freezing water
actually gives off energy to its surroundings.
All of that kinetic energy, the motion of the water
molecules in the liquid state,
um, has to be given up
for those water molecules
to enter a solid crystalline structure.
That released energy is called the latent heat of fusion.
It actually can warm the surroundings as water
is freezing into ice.
This is how scientists believe latent heat in an underground
ocean could be driving volcanism on Pluto.
The upper most layers of the internal ocean freeze
where liquid water meets the hard frozen ice above.
This act of freezing releases latent heat,
which then travels up through Pluto's crust,
driving active geology on the surface.
I mean, this seems like just a little bit of heat
that's forming from... From this freezing process.
But if there's a... A whole layer of ocean
that's freezing up against the ice crust,
that's a tremendous amount of heat,
maybe it could bring up cryovolcanoes driven
simply by the heat from freezing in parts
of the liquid water ocean, just amazing.
Incredibly, just a few degrees
of heat leaking from Pluto's ocean
may be all it takes to drive the dynamic surface of Pluto,
to raise mountain ranges,
to fire up watery volcanoes
and to set nitrogen glaciers
racing down icy slopes.
We think you need a huge amount of energy
to drive volcanoes
and geysers and plate tectonics and all that.
But that's not really the case.
It's just that rock takes
a lot of energy to melt and do all that.
Ice doesn't take nearly that much energy.
So on Pluto, if something was able to heat it up
even a little bit and get that...
That... that water ice to melt,
that can drive the same sort of surface geology
that we have here on Earth.
And if our galaxy is filled with frozen worlds
like Pluto, the universe
just got a whole lot more interesting.
And so it could be that most of the worlds in the...
In the galaxy are... Are cold worlds.
And it might be that most of the volcanism in the galaxy
is actually the running cold volcanism
that we see on Pluto.
New horizons has shown us
that Pluto most likely has both heat
and liquid water.
And that simple fact
raises an astonishing possibility:
Could tiny Pluto,
sitting 3 billion miles from the sun,
provide a secret haven for life?
In 2002 and 2009 I helped repair the Hubble space telescope.
One of the greatest scientific instruments ever built.
But even the Hubble could only show us
dark, fuzzy pictures of Pluto.
Once the space probe New Horizons
sent back it's first color photos,
scientists couldn't believe what they saw.
Pluto might have the very ingredients needed for life.
In all the vastness of space,
we only know of one planet that's home to life:
Our planet, the Earth.
On Earth, we have all the ingredients
we needed for life to arise,
clearly, we're here.
But those three things are basically a source of energy,
liquid water, and organic molecules...
Carbon-based molecules.
We used to think Earth was the only world
with all three ingredients.
But when robotic probes visited Jupiter and Saturn,
they found multiple active moons with
underground oceans warmed by hot volcanic vents.
And these worlds also appeared to be spiked
with the basic chemical ingredients for life.
So if Jupiter's moon, Europa,
and Saturn's moon, Enceladus,
are considered potential havens for life,
why not the subterranean oceans of Pluto too?
Well, we think there's liquid water possibly on Pluto.
And there's clearly a source of energy.
Could it have that third ingredient?
And, if so, is it that bizarre to wonder
if life could arise on Pluto?
The third ingredient is organic chemistry,
the carbon-based molecules
that build the machinery of life.
Surprisingly, astronomers believe these complex chemicals
can form spontaneously in the cold of space.
All you need are simple carbon-based gases
and a source of energy, usually light.
The most active natural laboratory
we know of for this kind of organic chemistry
is the atmosphere of Saturn's giant moon, titan.
When you look at titan, it has a very thick atmosphere,
thicker than Earth's.
And it's surrounded by this haze.
And that haze is basically made of organic molecules
that are created from the more basic compounds
that have been zapped by ultraviolet light
and built up to...
To make these more complex organic compounds.
Titan's atmosphere is thick with simple gases:
Methane, carbon monoxide, and ammonia.
And when sunlight strikes titan's cloud tops,
these gases join together
to form complex organic molecules,
which hang in the atmosphere,
forming dense layers of haze.
Scientists call these naturally occurring organic molecules
"tholins."
It's a generic term, it's a blanket term
for any sort of complex,
reddish colored organic molecule
that is formed from the splitting apart
and reassembling of simpler,
uh, starting, uh, molecules.
These organic molecules, these tholins,
you can think of them as, like, the Lego
building blocks for life.
On Earth, tholin-like chemicals
make up the working machinery of cells,
the DNA and proteins that make life tick.
If, like titan, Pluto has an atmosphere rich in carbon,
could it too be producing tholins... and therefore,
perhaps a shot at life?
When New Horizons passed Pluto in 2015,
the spaceship turned to take an image of the dwarf planet
backlit against the sun.
Scientists hoped to capture
the unmistakable haze of active organic chemistry.
The results were far more spectacular
than I would've expected.
Absolutely we saw that atmosphere,
a beautiful blue ring of nitrogen gas
surrounding Pluto,
just like what we see on the Earth.
These beautiful blue-haze layers are...
Are chemical factories
manufacturing tholins,
complex organic molecules,
from the simpler building blocks in the atmosphere of Pluto,
the carbon monoxide, the methane, the nitrogen,
all these things that are in the atmosphere of
Pluto are being broken apart by sunlight and reassembled
in these hazes into these just wonderful,
delicious organic molecules.
On titan, newly produced tholins rain down
from the atmosphere onto the surface of the moon,
producing a thick orange-brown carpet of organic gunk.
Scientists hope to see something similar happening on Pluto.
But they had to wait for New Horizons
to send back its first full-color images
of the dwarf planet.
When they finally came in
and I saw these rich red, orange,
brown features on the surface,
my first thought was, "oh, my gosh.
Organic chemistry."
There are areas where things look
almost kind of reddish-brown, even sort of pinkish.
And when you see a color like that,
you immediately think organics.
And, in fact, that's exactly what this is:
Pink organic snow.
Life as we know it
couldn't exist on the surface of Pluto.
It's too cold.
But if tholins are getting cycled down
into the guts of the planet,
they could be transported to areas
where ice melts into liquid water.
And it's possible the chemical evolution
of these simple organic molecules
could continue there,
driven by Pluto's meager heat.
And perhaps, just perhaps,
the machinery for simple life could assemble
in the subsurface oceans of Pluto,
just like it probably did in the deep
oceans of Earth 4 billion years ago.
I'm intrigued by the possibilities
that the sphere of life
around our sun may extend f...
Much further away from the sun
than we ever dreamed possible.
So, you know, could there be life on Pluto or...
Or under the surface of Pluto?
I couldn't say no to that at the moment.
Um, it's an intriguing possibility.
Could there be life on Pluto?
I don't think so.
Uh, that's my own personal opinion.
You know what, you can take flour
and butter and eggs and chocolate chips
and shake 'em all up and throw 'em in an oven.
You may not get a cookie.
What you're probably gonna get is a glob.
You're gonna get a mess.
While scientists debate
the stunning possibility of life
3 billion miles from the sun,
New Horizons turns its attention
to Pluto's tiny moons.
Mission scientists knew
that Pluto most likely had five companion worlds.
But nobody could have predicted
just how plain weird
these moons would turn out to be.
We already had a couple of clues into Pluto's make up,
thanks to the Hubble space telescope.
Hubble's images revealed five moons orbiting Pluto.
But there was no telling what secrets
New Horizons would uncover.
Are there more moons we don't know about?
When New Horizons arrived at Pluto,
scientists held their breath,
eager to see what Pluto's moons would be like.
And we knew nothing about them.
So everything, literally,
that we found out about these moons
was going to be for the first time.
And it was going to be a surprise.
What incredible worlds
Pluto's five moons turned out to be.
Oversized Charon is revealed
alongside Styx, Nix,
Kerberos, and Hydra,
four tiny, icy moons,
each less than 25 miles across.
And they're unlike any moons astronomers had seen before.
These objects are spinning crazy fast compared
to what we expected.
Um, not only that but
instead of having their poles aligned
with Pluto's pole like this,
they're actually spinning on their sides.
So they're sort of going around like this,
totally crazy behavior
that we had no expectation of.
To understand these crazy orbits,
scientists find clues
in the early history of the Earth.
In the early days of
the formation of the Kuiper belt,
these icy bodies were colliding with each other quite often.
And just like here at the Earth, uh,
where a large Mars-sized protoplanet
actually collided with the Earth to form our Earth/moon system,
that's probably what happened at Pluto as well.
Pluto most likely took a giant hit in its youth
and its moons are the leftovers from this mammoth collision.
Giant Charon settled into a close spinning orbit
with Pluto, and, farther out,
the four tiny moons orbit around both bodies
like tumbling shards of icy shrapnel.
The first images of oversized Charon
show a gray, dead world pockmarked
with the scars of its violent past.
The biggest scar is huge.
It appears to almost split the moon in two.
Charon is, uh, a mess.
The first thing I thought of
when I looked at that picture
that we got in high resolution is, like,
"this is Frankenstein's moon."
This looks like a moon
that somebody basically took a hammer and chisel
to and broke it completely apart
and then just mashed it back together.
But what has the power to split a Texas-sized moon
like Charon apart
in the frozen wastelands of the outer solar system?
Scientists are left with only one option:
Water.
Four billion years ago,
Charon had an internal liquid ocean just like Pluto today.
But because Charon is smaller,
it cooled more quickly.
The entire ocean turned to ice
and poor Charon burst at the seams.
If you take a soda can and put it in the freezer,
when the water in that soda freezes, it expands.
But the metal of the can won't.
And so what happens is it gets under more
and more stress, more and more pressure,
until it ruptures and it splits open
and that stuff oozes out.
This... the... The... the system of...
Of canyons and faults across, uh,
the equator of Charon really sorta represent that...
That last gasp of geologic activity as it...
It sorta, you know, spilled its guts out
as the interior ice froze, um, and...
And, you know, on its way to becoming a dead world.
So, it was Charon's last gasp, if you will.
Charon's red-stained polar cap
also catches the eye of mission scientist.
They name it Mordor.
And this barren red-stained terrain presents the team
with perhaps their greatest challenge.
Of all the surprising things on Charon
and, uh, it's a long list,
probably the most surprising thing is Mordor.
I love that.
This is the north polar region of Charon.
And for some reason it is red.
It's covered in some sort of red substance.
We think this is probably a tholin.
It's a complex organic molecule.
Mordor appears covered with tholins, but how?
The frozen world doesn't have the ingredients
or the atmosphere
to make complex organic molecules.
The tholins must be coming to Charon premade,
but from where?
The only logical answer
is from Pluto, over 10,000 miles away.
How would it get from being made on
Pluto to getting to Charon... And, really, nobody's sure.
But the thinking is that somehow this stuff
is getting into the atmosphere of
Pluto and being transferred that way through space
to basically be deposited on the north pole of Charon.
How that works is something,
uh, I don't think anybody understands.
Uh, and that's... That's cool
because there are a lot of mysteries left
and a lot of studying to be done, uh,
even with all of the... The data we have.
There are still many questions to answer.
But we now have a handle on how Pluto works.
And it's allowed scientists
to imagine the future of this frozen world.
Incredibly, Pluto may be about to rise from a deep, cold sleep.
The images beamed back from the 2015 New Horizons mission
blew away everything we had originally thought about
the dwarf planet Pluto.
Armed with the latest images and information,
scientists now have a new theory about Pluto.
They think Pluto will spring to life,
once it enters something called super summer.
2015, a tiny robotic probe shoots past
Pluto and fires its photographic shutters.
The pin-sharp images stun the world.
Glaciers, smooth young plains,
and even the hint of active cryovolcanoes.
But one set of images
at first appeared impossible.
As we looked down on this brand-new world
to us, we saw things that,
at first, were very hard to explain.
There seemed to be these depressions and channels
that looked like lakes or even little rivers.
These flow features are made from nitrogen.
And although they're now frozen,
they appear to have been liquid
in the recent geological past.
But how?
Pluto is too cold
and its atmosphere too thin
to support liquids on the surface.
In the entire universe,
it is so difficult to get liquid.
Everything seems to wanna be a solid or a gas.
You have to have just the right circumstances
for that liquid phase of matter.
So even for something like nitrogen,
you not only have to just turn up the temperature
and get nitrogen warmer,
there also has to be some atmospheric pressure,
a thicker atmosphere is needed
to maintain liquid nitrogen on the surface.
Scientists deduce that in the last million years,
Pluto must have warmed,
evaporating glaciers
and filling the atmosphere with nitrogen.
But what could've caused such an extreme climate shift?
Scientists first look to Pluto's elongated orbit around the sun.
Once every 248 Earth years,
Pluto's elliptical orbit brings it close to the sun.
But this brief warming
isn't sufficient to thicken Pluto's atmosphere.
When it comes in close to the sun,
it goes faster and faster.
And as it moves away from the sun,
it goes much slower.
So on Pluto, summer doesn't last anywhere
near as long as winter.
But from time to time,
one half of Pluto gets a super summer
thanks to the dwarf planet's unstable tilt.
We know from the way Pluto's north
and south pole wobble over time
that that top that represents the spinning sphere
of Pluto is not nearly as stable as the Earth.
Um, our planet is tipped over at about 23 1/2 degrees
and sits that way for, you know, for...
For millennia at a time.
Pluto, on the other hand, is much less stable.
And its poles wander over time.
Once every million years or so,
Pluto tips completely on its side,
exposing the northern hemisphere
to constant sunlight
during its close pass of the sun.
And the warmth from this orbital shift transforms
the surface of the planet.
Picture Pluto as it warms,
the atmosphere thickens and fills with clouds,
a warm wind sweeps across the plains
and Pluto's glaciers begin to melt.
Like an animal emerging from hibernation,
Pluto comes to life.
It's almost as if
it's undergoing these periodic changes
where it's warmer and colder and warmer
and colder in the past
and maybe again in the future.
Will Pluto have liquid on its surface, even...
Even if only temporarily?
What would that mean? What would that even look like?
800,000 years from now,
Pluto will awake once again.
It will tilt over completely to face the sun
and its mountains will fill
with the sound of running nitrogen.
You begin to actually see flowing rivers of nitrogen.
You could stand on the shore of a nitrogen lake.
There'd be pink snow
with organic molecules coming down on you.
What a truly magical world.
The legacy of New Horizons
goes far beyond just Pluto.
It changes the way we view frozen worlds
across our galaxy
and the possibilities these far-off worlds offer.
It tells us that there's this huge stage
for the play of life out there in the galaxy,
um, a huge variety of worlds.
You image a world, it probably exists out there someplace.
That's kind of the lesson that Pluto has for us.
It... it tells us that... That things can be
a lot more interesting out there
than you can possibly imagine.
Pluto has really inspired me.
It's shown me just how wrong we can be.
We thought we understood what Pluto would be
and it was entirely different.
And as a scientist, you gotta think,
how much more out there do we have to discover?
If nothing else, Pluto taught us that.