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NARRATOR:
Our solar system is filled
with mysterious worlds...

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...wandering between
and beyond the planets.

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(collision pounds)

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MALENA RICE:
The objects that lie
between the planets

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are actually the key
to understanding

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how our solar system formed.

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NARRATOR:
Imposters, and oddballs,

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rewriting our understanding
of our place in space.

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JESSICA SUNSHINE:
It is two pieces
that are stuck together.

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It was really quite remarkable.

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(explodes)

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QUEENIE HOI SHAN CHAN:
It is possible that after
30 million years,

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Mars might have a ring
of its own.

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♪ ♪

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NARRATOR:
Studying these wandering worlds

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allows scientists to explore
regions of the solar system

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we have no chance of visiting.

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WANDA DÍAZ MERCED:
I cannot go to
the asteroid belt,

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so when a meteorite
lands on Earth,

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we will have a chunk of history
right in our hands.

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ASHLEY KING:
The Winchcombe meteorite

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was like a little treasure box
for planetary scientists.

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(geyser bursts)

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NARRATOR:
And the misfits
of our solar system

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are full of surprises.

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VERONICA BRAY DURFEY:
There are many, many worlds
out there

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that we are yet to discover

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and that we haven't
even imagined yet.

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SCOTT SHEPPARD:
It's like a box of chocolates.

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You never know what you're
gonna get in our images.

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This model of the solar system,

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it's missing all
of the most interesting bits.

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NARRATOR:
What secrets do
these wandering worlds

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reveal about our solar system?

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And what else
is lurking out there

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in the dark?

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(bursting)

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"Solar System:
Wandering Worlds,"

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right now on "NOVA."

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♪ ♪

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♪ ♪

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NARRATOR:
There's something out there
in the darkness.

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We don't know for sure
where it came from

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or how long it's been there.

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But we know it's not alone.

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It was discovered in 2018.

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A world with no official name.

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So distant,
it has been called simply

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FarFarOut.

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SHEPPARD:
FarFarOut,

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as its name implies, is very
far away.

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So, it's just a, a very faint
point of light

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that, uh, we discovered

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with one of the largest
telescopes in the world.

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JANE LUU:
Its notoriety
comes from the fact

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that it's
the most distant object

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that we have found
in the solar system.

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SHEPPARD:
And the big question is,
what do we call the next one?

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Do we just add another "far"
or not?

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LUU:
"ExtremelyFarOut,"
and then "StupendouslyFarOut,"

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and it just keeps going.
(laughs)

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♪ ♪

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NARRATOR:
12 billion miles from the sun,

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FarFarOut is not alone.

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Out here, there could be
countless other worlds

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yet to be discovered,

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wandering in the dark.

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Even closer to home,
we are only just beginning

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to explore the vast spaces
between the planets.

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Home to a myriad of worlds,

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many too small or too dark
to see.

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NANCY CHABOT:
When we think about
our solar system,

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we think about the sun,
it's in the center,

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everything else is
kind of going around it,

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and we've got the big planets,
Jupiter and Saturn,

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and the most important planet,
Earth.

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But there are so many more
secrets and mysteries

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than just these planets
that are shown in the model.

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So, to me,
the most exciting thing

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about studying the solar system
is not the planets themselves,

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but it's all the bits
in between the planets.

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NARRATOR:
These worlds could provide clues
to our own planet's story.

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RICE:
In a lot of ways,
studying the solar system

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is a way of trying
to understand ourselves.

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How did we come to be
in the first place,

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and what does it mean
that we're on this rock

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that is sailing through space?

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NARRATOR:
With distances so vast,
there's still much to discover.

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KING:
There's so much stuff

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that we just don't know
about our solar system,

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and what we do know is,
it is constantly surprising us.

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So we need to go out there,
look at these wandering worlds.

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NARRATOR:
And many questions
remain unanswered.

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LYNNAE QUICK:
Are these lost
and wandering worlds

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worthy of exploration
in their own right?

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CHABOT:
How far do these
dark regions extend

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beyond, to the edge
of our solar system?

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Are there more planets
in the dark region

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waiting to be discovered?

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♪ ♪

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(dog barking in distance)

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NARRATOR: It was the sound
that most people noticed.

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(explosion echoing in distance)

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A sonic boom in the night.

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But this was no fighter jet.

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Traveling at around
30,000 miles per hour,

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it tore through the atmosphere.

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♪ ♪

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Broke up.

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And rained down
across the fields.

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A visitor from a distant realm.

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One of the biggest chunks

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landed on a driveway
in front of a house.

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KING:
When I first saw it,
it was kind of a splat.

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I mean, it's so soft, it kind of
just made a powder

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and it threw fragments
all over the driveway.

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SARA RUSSELL:
The Winchcombe meteorite fall

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was the first U.K. meteorite
fall recovered for 30 years,

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so we've been waiting
such a long time.

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KING:
I couldn't believe that we had
a new meteorite in the U.K.

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Yeah, it was incredibly
exciting.

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And all meteorites are
scientifically priceless.

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RUSSELL:
I feel amazed and privileged

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to be able to hold something

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that may tell us about the
secrets

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of the origins of our solar
system,

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and how we got to be here.

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NARRATOR:
It's estimated as many as 50
meteorites hit Earth every day.

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Many burn up in our atmosphere,

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creating shooting stars
and meteor showers.

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But some of the largest ones
do make it to Earth.

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In 2018,
the Hamburg meteor fireball

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streaked across
the American Midwest sky.

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WOMAN:
What was that?

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Did you see a light flash
out there?

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It's particularly pristine,
because it landed

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on a frozen lake, so that
keeps it in cold storage.

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It was like the meteor selected
where to land,

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because it wanted to be studied.

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NARRATOR:
A few years later,

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a meteorite the weight
of a grand piano

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exploded in the skies
near McAllen, Texas.

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(explosion pounds in distance)

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MERCED:
Ah!

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It's like a,
like an explosion of dynamite.

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(explosion echoes)

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That big explosion,
that was a sonic boom.

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♪ ♪

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NARRATOR:
The cows weren't
the only witnesses

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that night in Winchcombe.

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Doorbell and CCTV cameras
never sleep.

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And networks of dedicated
meteor cameras

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captured it
from different angles.

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That meant it was possible
to calculate its trajectory.

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(cows mooing)

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Back over the skies of England,

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out of Earth's atmosphere,

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past the orbit of Mars,

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into the dark.

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This is where
the meteorite's journey began,

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a mysterious realm
of countless rocky worlds,

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00:10:00,538 --> 00:10:06,238
rubble left over from the
formation of the solar system:

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asteroids.

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There could be at least
a million out here.

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But they're so dark,
reflecting little light,

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they're incredibly difficult
to detect.

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00:10:24,805 --> 00:10:29,138
But asteroids don't always
stay in the asteroid belt.

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(collision pounds)

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When two collide,

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they blast fragments
in all directions,

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sending some out of
the asteroid belt forever.

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Sometimes wreaking havoc
on planets they encounter.

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♪ ♪

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Including our own.

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And asteroids
that leave the belt

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can transform planets nearby.

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♪ ♪

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A planet covered in scars
from the asteroid belt is Mars.

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Around 80 fresh impact sites
are found on Mars every year.

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♪ ♪

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And some amazing meteorites

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have even been snapped
by NASA's rovers.

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But there's
another dark rock here,

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imaged by
the Perseverance rover,

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00:12:03,038 --> 00:12:07,771
not on Mars's surface,
but orbiting overhead...

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00:12:07,771 --> 00:12:12,138
♪ ♪

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...captured during an eclipse,

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as it passed
in front of the sun.

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This is Mars's moon Phobos.

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00:12:28,071 --> 00:12:31,571
Today, the orbiting probe
Mars Express

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regularly flies
between Mars and Phobos.

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00:12:35,271 --> 00:12:39,271
♪ ♪

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00:12:39,271 --> 00:12:43,538
Its high-resolution camera

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00:12:43,538 --> 00:12:49,205
captured incredibly detailed
images of Phobos,

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00:12:49,205 --> 00:12:53,371
showing a surface covered
in strange grooves.

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00:12:55,838 --> 00:13:01,438
Phobos looks like someone has
ridden a giant bike all over it.

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00:13:09,005 --> 00:13:13,705
Astrophysicist Sean Raymond
is investigating

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00:13:13,705 --> 00:13:17,605
how objects like Phobos
could have formed.

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00:13:23,071 --> 00:13:24,671
Phobos is a strange-looking
moon.

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00:13:24,671 --> 00:13:28,371
Like this beach, it's covered in
grooves.

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00:13:28,371 --> 00:13:29,671
You might say it's

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00:13:29,671 --> 00:13:31,638
the grooviest moon
in the solar system.

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00:13:33,738 --> 00:13:37,071
NARRATOR:
The magnificent grooves
here in Spain

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00:13:37,071 --> 00:13:39,571
are formed
by geological processes

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00:13:39,571 --> 00:13:43,738
and erosion
from relentless, crashing waves.

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00:13:43,738 --> 00:13:47,205
RAYMOND:
It's so cool--
the grooves are amazing here.

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00:13:47,205 --> 00:13:50,371
NARRATOR:
But Phobos isn't anything
like Earth,

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00:13:50,371 --> 00:13:53,705
so what's going on?

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00:13:53,705 --> 00:13:56,205
RAYMOND:
Phobos certainly looks
like an asteroid.

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00:13:56,205 --> 00:13:59,405
It's covered in craters,
and it's dark in color.

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00:13:59,405 --> 00:14:01,671
So you might think
it's just an asteroid that got

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00:14:01,671 --> 00:14:06,171
too close to Mars
and then was captured in orbit.

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00:14:06,171 --> 00:14:11,338
NARRATOR:
It turns out
it's not that simple.

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00:14:11,338 --> 00:14:15,005
Phobos orbits Mars
in an almost perfect circle,

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00:14:15,005 --> 00:14:17,938
right along Mars's equator,

216
00:14:17,938 --> 00:14:19,605
and this makes us question
whether Phobos

217
00:14:19,605 --> 00:14:22,805
is really the asteroid
it appears to be,

218
00:14:22,805 --> 00:14:25,905
because captured asteroids
usually orbit planets

219
00:14:25,905 --> 00:14:28,238
on very elliptical orbits

220
00:14:28,238 --> 00:14:30,738
that sometimes take them
very far from their planet

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00:14:30,738 --> 00:14:33,071
and sometimes being much closer.

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00:14:33,071 --> 00:14:36,371
NARRATOR:
So, if it's not an asteroid,

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00:14:36,371 --> 00:14:40,038
where did this funny
little moon come from?

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00:14:43,171 --> 00:14:45,171
CHABOT:
So, in planetary science,

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00:14:45,171 --> 00:14:47,505
the joke is that you just add
an impact event,

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00:14:47,505 --> 00:14:50,205
and an impact event can explain
everything.

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00:14:50,205 --> 00:14:52,538
That might actually be true in
this case, though.

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00:14:52,538 --> 00:14:54,771
 
It's this one-off event,
and it might have been

229
00:14:54,771 --> 00:14:56,805
that an object hit Mars,

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00:14:56,805 --> 00:14:59,805
and Phobos is the result
of that impact collision

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00:14:59,805 --> 00:15:03,138
between those objects,
and that's what we're seeing.

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00:15:03,138 --> 00:15:07,005
♪ ♪

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00:15:07,005 --> 00:15:13,405
NARRATOR:
Phobos may not be
a captured asteroid at all,

234
00:15:13,405 --> 00:15:16,338
but formed from debris
thrown into orbit

235
00:15:16,338 --> 00:15:21,171
after a massive asteroid impact.

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00:15:21,171 --> 00:15:24,205
However,
this still doesn't explain

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00:15:24,205 --> 00:15:28,771
why it's covered in grooves.

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00:15:31,905 --> 00:15:37,238
Phobos is about 3,700 miles
from Mars's surface,

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00:15:37,238 --> 00:15:42,771
and every hundred years,
moves closer by about six feet.

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00:15:42,771 --> 00:15:48,505
And as it does, the tidal forces
caused by Mars's gravity

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00:15:48,505 --> 00:15:52,005
become stronger.

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00:15:52,005 --> 00:15:55,005
RAYMOND:
So, just like the moon
pulls on the Earth,

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00:15:55,005 --> 00:15:58,538
dragging the oceans
and causing the tide,

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00:15:58,538 --> 00:16:03,071
Mars pulls on Phobos,
causing tides, as well.

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00:16:03,071 --> 00:16:05,271
So, as you can see
behind me right now,

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00:16:05,271 --> 00:16:08,138
the tide is coming in
as the moon is pulling on

247
00:16:08,138 --> 00:16:09,805
the water on the Earth.

248
00:16:09,805 --> 00:16:12,771
The same process
happens on Phobos, due to Mars,

249
00:16:12,771 --> 00:16:15,571
except on Phobos, it's sand
and rock that's moving,

250
00:16:15,571 --> 00:16:17,938
instead of water.

251
00:16:19,771 --> 00:16:24,238
NARRATOR:
Those tidal forces
are pulling Phobos apart.

252
00:16:24,238 --> 00:16:30,105
And with every orbit,
the grooves widen and deepen.

253
00:16:35,071 --> 00:16:39,571
Eventually,
Phobos will drift so close,

254
00:16:39,571 --> 00:16:44,171
Mars's gravity will destroy it.

255
00:16:44,171 --> 00:16:46,871
As Phobos breaks apart...

256
00:16:49,405 --> 00:16:53,771
...most of the debris will fall
to the surface of Mars.

257
00:16:57,438 --> 00:17:01,105
♪ ♪

258
00:17:01,105 --> 00:17:05,938
But the rest will remain
in close orbit,

259
00:17:05,938 --> 00:17:12,738
spreading out to encircle
the entire planet,

260
00:17:12,738 --> 00:17:16,771
giving Mars a wispy ring.

261
00:17:20,271 --> 00:17:22,438
CHAN:
It would be quite impressive.

262
00:17:22,438 --> 00:17:25,071
I love ring planets,
I love Saturn,

263
00:17:25,071 --> 00:17:28,938
and it's not bad to have another
ring planet in our solar system.

264
00:17:31,438 --> 00:17:35,438
NARRATOR:
It seems Mars will one day
be transformed

265
00:17:35,438 --> 00:17:38,471
by the asteroid belt.

266
00:17:43,605 --> 00:17:47,638
But the asteroid belt itself
is still an enigma.

267
00:17:50,105 --> 00:17:52,438
We've flown several spacecraft

268
00:17:52,438 --> 00:17:56,638
through this
mysterious region,

269
00:17:56,638 --> 00:17:58,871
but only one
has orbited the rocks

270
00:17:58,871 --> 00:18:02,271
in the asteroid belt itself:

271
00:18:02,271 --> 00:18:07,605
NASA's Dawn probe.

272
00:18:07,605 --> 00:18:11,671
Most of these ancient remnants
are misshapen boulders.

273
00:18:13,105 --> 00:18:16,138
But one stands out.

274
00:18:21,238 --> 00:18:23,905
Ceres is much bigger
than the others

275
00:18:23,905 --> 00:18:29,105
and almost perfectly spherical.

276
00:18:29,105 --> 00:18:30,605
QUICK:
I joined the Dawn mission

277
00:18:30,605 --> 00:18:32,705
right after it reached Ceres,

278
00:18:32,705 --> 00:18:34,038
and it was so exciting.

279
00:18:34,038 --> 00:18:38,205
Dawn collected thousands
of images of Ceres.

280
00:18:38,205 --> 00:18:40,271
They showed us areas
of the surface

281
00:18:40,271 --> 00:18:42,305
that we'd never seen before.

282
00:18:42,305 --> 00:18:43,538
We thought that it's kind of

283
00:18:43,538 --> 00:18:45,005
a dead planetary body.

284
00:18:45,005 --> 00:18:47,405
Looking at those images,

285
00:18:47,405 --> 00:18:49,638
we could not, basically,
believe our eyes,

286
00:18:49,638 --> 00:18:52,105
and it was, like, "Uh,
what's going on over there?"

287
00:18:52,105 --> 00:18:55,805
♪ ♪

288
00:18:55,805 --> 00:18:59,471
NARRATOR:
At first, it appears dark
and heavily cratered,

289
00:18:59,471 --> 00:19:02,871
like its fellow asteroids.

290
00:19:02,871 --> 00:19:05,071
But Ceres is different.

291
00:19:06,938 --> 00:19:12,171
Its surface is peppered
with white crystals.

292
00:19:12,171 --> 00:19:15,705
But what are they?

293
00:19:15,705 --> 00:19:19,871
Clues come from another planet
in our solar system,

294
00:19:19,871 --> 00:19:24,571
where white crystals
are also found on the surface.

295
00:19:26,638 --> 00:19:29,671
Earth.

296
00:19:36,171 --> 00:19:40,671
HAKEEM OLUSEYI:
This mountain is made up
almost entirely of sea salt,

297
00:19:40,671 --> 00:19:42,838
the exact same stuff
that you put on your food

298
00:19:42,838 --> 00:19:44,038
at the dinner table.

299
00:19:45,638 --> 00:19:47,971
NARRATOR:
40 million years ago,

300
00:19:47,971 --> 00:19:52,771
this whole area
was under an ancient sea.

301
00:19:56,605 --> 00:19:59,638
Over time, it dried out,

302
00:19:59,638 --> 00:20:04,905
leaving behind a layer of salt
a mile thick.

303
00:20:06,405 --> 00:20:08,571
Holy moly!

304
00:20:08,571 --> 00:20:10,605
Whoa!

305
00:20:12,571 --> 00:20:15,438
♪ ♪

306
00:20:18,238 --> 00:20:19,905
It's definitely salty.

307
00:20:19,905 --> 00:20:21,771
And the thing about
salt deposits like this

308
00:20:21,771 --> 00:20:24,738
is that they're only formed
in the presence of water.

309
00:20:24,738 --> 00:20:28,405
So, that raises
an intriguing possibility.

310
00:20:28,405 --> 00:20:32,738
Could the white spots on Ceres
also be salts

311
00:20:32,738 --> 00:20:36,705
that were deposited by water?

312
00:20:36,705 --> 00:20:39,471
NARRATOR:
Finding water on Ceres today

313
00:20:39,471 --> 00:20:41,638
would be
an astonishing discovery.

314
00:20:41,638 --> 00:20:45,038
♪ ♪

315
00:20:45,038 --> 00:20:49,071
Dawn made tight orbits
of Ceres.

316
00:20:50,705 --> 00:20:54,405
And by bouncing light
off the crystal deposits,

317
00:20:54,405 --> 00:21:00,338
it determined
what they were made of:

318
00:21:00,338 --> 00:21:04,438
sodium carbonate,
a common type of salt.

319
00:21:06,671 --> 00:21:10,171
A tantalizing sign that Ceres,

320
00:21:10,171 --> 00:21:12,971
which is 13 times smaller
than Earth,

321
00:21:12,971 --> 00:21:17,238
had an ocean in the past.

322
00:21:17,238 --> 00:21:21,838
Flying just over 20 miles
from the surface,

323
00:21:21,838 --> 00:21:27,471
Dawn finds something else
in the white spots:

324
00:21:27,471 --> 00:21:30,338
hydrohalite crystals,

325
00:21:30,338 --> 00:21:36,171
another salt found on Earth
in the presence of water.

326
00:21:36,171 --> 00:21:39,838
Could Ceres still be
a water world today?

327
00:21:42,805 --> 00:21:45,405
So, "hydro" is water
and "halite" is salt--

328
00:21:45,405 --> 00:21:46,405
table salt.

329
00:21:46,405 --> 00:21:48,905
So, if you imagine a table salt

330
00:21:48,905 --> 00:21:51,738
that's got water molecules
in the structure,

331
00:21:51,738 --> 00:21:54,305
that's what hydrohalite is.

332
00:21:54,305 --> 00:21:56,571
It was very surprising
that there were hydrohalites

333
00:21:56,571 --> 00:21:58,571
on the surface of Ceres.

334
00:21:58,571 --> 00:22:00,905
CHAN:
Hydrohalite would be
very unstable

335
00:22:00,905 --> 00:22:03,238
at the surface of Ceres.

336
00:22:03,238 --> 00:22:05,238
At that pressure,

337
00:22:05,238 --> 00:22:08,405
the water molecule
would have been vaporized.

338
00:22:08,405 --> 00:22:12,505
That implies that water
was recently emplaced on Ceres,

339
00:22:12,505 --> 00:22:16,138
bound to salt crystals within
the past few hundred years.

340
00:22:16,138 --> 00:22:17,871
This replenishment
of hydrohalite

341
00:22:17,871 --> 00:22:20,171
at Ceres' surface
leads us to wonder

342
00:22:20,171 --> 00:22:21,971
if Ceres might be an ocean world

343
00:22:21,971 --> 00:22:24,738
that's masquerading
as an asteroid.

344
00:22:24,738 --> 00:22:28,405
♪ ♪

345
00:22:28,405 --> 00:22:32,138
NARRATOR:
Scientists suspect
that pools of salty water exist

346
00:22:32,138 --> 00:22:36,671
about 25 miles underground,

347
00:22:36,671 --> 00:22:39,005
raising another question:

348
00:22:39,005 --> 00:22:43,171
how did these salts
end up on the surface?

349
00:22:43,171 --> 00:22:47,505
A clue lies in Ceres' location,

350
00:22:47,505 --> 00:22:50,538
right in the heart
of the asteroid belt,

351
00:22:50,538 --> 00:22:52,605
where collisions are common...

352
00:22:52,605 --> 00:22:54,938
(collision pounds)

353
00:22:54,938 --> 00:22:58,871
...and incoming asteroids
can form cracks in the surface

354
00:22:58,871 --> 00:23:02,605
reaching the pools below.

355
00:23:02,605 --> 00:23:04,938
Exposed to the vacuum of space,

356
00:23:04,938 --> 00:23:10,338
the water vaporizes,

357
00:23:10,338 --> 00:23:14,938
leaving its cargo of salt behind

358
00:23:14,938 --> 00:23:18,838
and peppering Ceres
with white spots.

359
00:23:21,005 --> 00:23:23,005
QUICK:
There's still one big twist

360
00:23:23,005 --> 00:23:24,838
to the story of Ceres' past.

361
00:23:24,838 --> 00:23:28,571
The Dawn spacecraft found
ammonia salts on the surface.

362
00:23:30,238 --> 00:23:33,905
NARRATOR:
Ammonia salts could be traces
of ammonia ices

363
00:23:33,905 --> 00:23:37,271
that once covered
Ceres' surface.

364
00:23:37,271 --> 00:23:39,771
Frozen ammonia is common
in colder parts

365
00:23:39,771 --> 00:23:44,105
of the solar system,
but not here.

366
00:23:44,105 --> 00:23:49,971
CHAN:
Ammonia doesn't really exist
as ice at where Ceres is now.

367
00:23:49,971 --> 00:23:52,971
It has to be formed
at a distance

368
00:23:52,971 --> 00:23:55,438
further away from the sun,

369
00:23:55,438 --> 00:23:57,905
where the distance
is cold enough

370
00:23:57,905 --> 00:24:00,805
for ammonia to exist as ice.

371
00:24:00,805 --> 00:24:02,971
This suggests
that Ceres didn't form

372
00:24:02,971 --> 00:24:05,138
where it stands currently
in our solar system.

373
00:24:06,471 --> 00:24:11,038
NARRATOR:
Instead, scientists think
it formed much farther out,

374
00:24:11,038 --> 00:24:13,738
and as it wandered
towards the sun,

375
00:24:13,738 --> 00:24:16,338
the ammonia ices melted,

376
00:24:16,338 --> 00:24:21,938
leaving behind the ammonia salts
we see today.

377
00:24:21,938 --> 00:24:26,138
An imposter
lurking in the asteroid belt,

378
00:24:26,138 --> 00:24:30,971
exposed by its salty secrets.

379
00:24:30,971 --> 00:24:33,671
Ceres has
a journey of relocation

380
00:24:33,671 --> 00:24:36,905
just written
all across the surface.

381
00:24:39,905 --> 00:24:44,771
NARRATOR:
But just how did Ceres end up
where it is today?

382
00:24:44,771 --> 00:24:47,105
OLUSEYI:
The best explanation
is that it wandered.

383
00:24:47,105 --> 00:24:48,705
Well, actually, it was pulled.

384
00:24:48,705 --> 00:24:49,938
So let's say this is Ceres.

385
00:24:49,938 --> 00:24:50,971
Okay?

386
00:24:50,971 --> 00:24:53,505
We think that Ceres
formed beyond

387
00:24:53,505 --> 00:24:55,105
what is known
as the ice line

388
00:24:55,105 --> 00:24:56,871
for ammonium ices.

389
00:24:56,871 --> 00:24:58,671
NARRATOR:
Beyond this ice line,

390
00:24:58,671 --> 00:25:00,771
ammonia freezes,

391
00:25:00,771 --> 00:25:04,505
and this is where Ceres
likely started forming,

392
00:25:04,505 --> 00:25:07,605
alongside Neptune
and Uranus.

393
00:25:07,605 --> 00:25:09,871
OLUSEYI: And here we have
Saturn and Jupiter.

394
00:25:09,871 --> 00:25:11,671
Now, normally, these planets

395
00:25:11,671 --> 00:25:12,871
aren't lined up
like this.

396
00:25:12,871 --> 00:25:14,705
They're moving
around the solar system.

397
00:25:14,705 --> 00:25:17,838
And what happens is,
as Ceres

398
00:25:17,838 --> 00:25:19,838
orbited the solar system,

399
00:25:19,838 --> 00:25:22,638
Jupiter tugged on it
with its gravity,

400
00:25:22,638 --> 00:25:25,405
and Ceres ended up
right there,

401
00:25:25,405 --> 00:25:28,138
in the asteroid belt,
where we find it today.

402
00:25:30,438 --> 00:25:32,771
NARRATOR:
In the heart
of the asteroid belt,

403
00:25:32,771 --> 00:25:36,071
Ceres, once a much icier world,

404
00:25:36,071 --> 00:25:40,105
has migrated
far from where it formed,

405
00:25:40,105 --> 00:25:44,771
evidence that our solar system
is ever changing.

406
00:25:44,771 --> 00:25:46,738
♪ ♪

407
00:25:46,738 --> 00:25:50,638
Ceres isn't
the only displaced world.

408
00:25:50,638 --> 00:25:54,105
Farther from the sun,
there is another icy world

409
00:25:54,105 --> 00:25:57,705
that doesn't seem to belong
where it's found today.

410
00:25:59,138 --> 00:26:03,638
Beyond Jupiter,

411
00:26:03,638 --> 00:26:06,838
the space between the planets
gets wider

412
00:26:06,838 --> 00:26:09,205
and wider.

413
00:26:10,338 --> 00:26:13,438
And temperatures plummet.

414
00:26:15,938 --> 00:26:20,205
♪ ♪

415
00:26:20,205 --> 00:26:25,705
And a billion miles past Uranus,

416
00:26:25,705 --> 00:26:29,638
we finally reach the farthest
planet from the sun.

417
00:26:32,438 --> 00:26:35,471
Neptune.

418
00:26:35,471 --> 00:26:41,471
♪ ♪

419
00:26:41,471 --> 00:26:45,705
Wrapped in a dense blue blanket,

420
00:26:45,705 --> 00:26:51,571
Neptune has
no detectable surface,

421
00:26:51,571 --> 00:26:55,605
with clouds
of methane and ammonia.

422
00:26:57,905 --> 00:27:02,605
But there are rocky worlds
nearby.

423
00:27:02,605 --> 00:27:06,838
Neptune has at least 16 moons.

424
00:27:06,838 --> 00:27:11,338
And one is very unusual.

425
00:27:16,471 --> 00:27:21,305
Triton is the largest
of Neptune's moons.

426
00:27:21,305 --> 00:27:24,071
Its surface is coated with ice.

427
00:27:28,105 --> 00:27:30,838
And, unlike the other moons,

428
00:27:30,838 --> 00:27:33,605
Triton is an active world.

429
00:27:33,605 --> 00:27:37,738
(geyser bursts)

430
00:27:37,738 --> 00:27:40,638
Geyser-like plumes
of gas and dust

431
00:27:40,638 --> 00:27:44,571
stretch five miles high
into Triton's atmosphere...

432
00:27:46,405 --> 00:27:48,438
...which flattens them abruptly

433
00:27:48,438 --> 00:27:51,038
by 90 degrees,

434
00:27:51,038 --> 00:27:55,505
creating a vista so strange,

435
00:27:55,505 --> 00:27:58,671
it's hard to believe it's real.

436
00:28:03,071 --> 00:28:08,905
How did a moon
2.8 billion miles from the sun

437
00:28:08,905 --> 00:28:11,938
become so active?

438
00:28:17,205 --> 00:28:20,205
A clue lies
with how the planets and moons

439
00:28:20,205 --> 00:28:23,871
move around each other
in the solar system.

440
00:28:28,138 --> 00:28:30,005
CARLY HOWETT:
Every day, the sun rises
in the east

441
00:28:30,005 --> 00:28:32,138
and sets in the west.

442
00:28:32,138 --> 00:28:34,338
And the moon follows
the same course.

443
00:28:34,338 --> 00:28:36,005
And there's a reason for that.

444
00:28:37,371 --> 00:28:39,238
NARRATOR:
To understand why,

445
00:28:39,238 --> 00:28:42,971
we need to go all the way back.

446
00:28:45,071 --> 00:28:49,238
To the birth
of the solar system.

447
00:28:49,238 --> 00:28:51,205
DURFEY:
In the beginning of our
solar system,

448
00:28:51,205 --> 00:28:52,638
the sun was surrounded

449
00:28:52,638 --> 00:28:55,071
by a disc of dust and gas.

450
00:28:55,071 --> 00:28:58,438
And it was within
this spinning disc

451
00:28:58,438 --> 00:29:01,305
that the planets formed.

452
00:29:01,305 --> 00:29:02,738
PAREKH:
So that's the reason

453
00:29:02,738 --> 00:29:04,371
the planets and the moon
continued

454
00:29:04,371 --> 00:29:06,238
orbiting also
in the same direction

455
00:29:06,238 --> 00:29:09,205
around the sun.

456
00:29:09,205 --> 00:29:11,671
NARRATOR:
Moons that form
around their planets

457
00:29:11,671 --> 00:29:14,871
tend to follow this pattern,

458
00:29:14,871 --> 00:29:17,038
orbiting and spinning
in the direction

459
00:29:17,038 --> 00:29:20,905
of the planet's rotation.

460
00:29:20,905 --> 00:29:25,238
But while the inner moons orbit
Neptune in the same direction,

461
00:29:25,238 --> 00:29:28,538
Triton goes the other way,

462
00:29:28,538 --> 00:29:33,705
suggesting it didn't form
alongside Neptune,

463
00:29:33,705 --> 00:29:38,505
but came from elsewhere.

464
00:29:42,671 --> 00:29:44,205
HOWETT:
What a planet's made from

465
00:29:44,205 --> 00:29:47,038
can tell you where it formed
in our solar system.

466
00:29:47,038 --> 00:29:49,305
And that's because,
in our early solar system,

467
00:29:49,305 --> 00:29:51,805
the ingredients that
a planet could be built from

468
00:29:51,805 --> 00:29:54,205
varied as the distance
from the sun.

469
00:29:54,205 --> 00:29:57,138
So if we take Earth,
for example,

470
00:29:57,138 --> 00:29:58,805
it's got a lot of rocks and
metals, too:

471
00:29:58,805 --> 00:30:00,838
aluminium and iron.

472
00:30:00,838 --> 00:30:02,238
And Mars is pretty
similar.

473
00:30:02,238 --> 00:30:05,071
Iron, metals, and other rocks.

474
00:30:05,071 --> 00:30:08,038
So these can be paired together.

475
00:30:08,038 --> 00:30:10,071
If we do the same thing

476
00:30:10,071 --> 00:30:13,771
for the ice giants,
Neptune and Uranus,

477
00:30:13,771 --> 00:30:15,805
with big atmospheres
made of hydrogen,

478
00:30:15,805 --> 00:30:17,571
helium, and a bit of methane,

479
00:30:17,571 --> 00:30:19,238
they're huge, too.

480
00:30:19,238 --> 00:30:21,738
So we can pair those together.

481
00:30:21,738 --> 00:30:23,938
So how does Triton fit in?

482
00:30:23,938 --> 00:30:25,805
Well, its surface
is mainly nitrogen ice,

483
00:30:25,805 --> 00:30:27,205
and it's much smaller.

484
00:30:27,205 --> 00:30:30,171
It doesn't fit with either
of these two groupings.

485
00:30:30,171 --> 00:30:32,305
To understand
where it could fit,

486
00:30:32,305 --> 00:30:33,971
we have to look at Pluto.

487
00:30:33,971 --> 00:30:37,638
Pluto has a, a nitrogen
ice surface with methane,

488
00:30:37,638 --> 00:30:40,038
carbon monoxide, and water ice.

489
00:30:40,038 --> 00:30:43,005
And it's about the same size
as Triton, too.

490
00:30:43,005 --> 00:30:44,771
These are a good pairing.

491
00:30:44,771 --> 00:30:47,871
NARRATOR:
With such similar ingredients,

492
00:30:47,871 --> 00:30:51,705
Triton and Pluto could've
formed in the same place,

493
00:30:51,705 --> 00:30:55,105
but they aren't
anywhere near each other today.

494
00:30:55,105 --> 00:30:58,438
HOWETT:
Triton's located
one billion miles from Pluto.

495
00:30:58,438 --> 00:30:59,971
So how did that happen?

496
00:31:01,571 --> 00:31:05,905
NARRATOR:
Neptune might be the farthest
planet from the sun,

497
00:31:05,905 --> 00:31:09,905
but it's not the edge
of our solar system.

498
00:31:09,905 --> 00:31:13,838
Not even close.

499
00:31:13,838 --> 00:31:17,238
Almost a billion miles
farther out

500
00:31:17,238 --> 00:31:19,705
lies Pluto.

501
00:31:19,705 --> 00:31:22,705
And it's not alone.

502
00:31:22,705 --> 00:31:28,105
There are hundreds of thousands
of other worlds out here.

503
00:31:28,105 --> 00:31:32,538
This is the Kuiper Belt,

504
00:31:32,538 --> 00:31:37,438
a vast, doughnut-shaped ring
of icy bodies

505
00:31:37,438 --> 00:31:39,471
billions of miles wide.

506
00:31:41,571 --> 00:31:43,305
So dark and distant,

507
00:31:43,305 --> 00:31:49,238
it remained undiscovered
until 1992.

508
00:31:49,238 --> 00:31:51,471
LUU: We had been searching for,
uh, the Kuiper Belt

509
00:31:51,471 --> 00:31:54,505
for, uh, for five years
before we finally found it.

510
00:31:54,505 --> 00:31:57,971
So when we spotted
the first Kuiper Belt object,

511
00:31:57,971 --> 00:32:00,338
1992 QB1,

512
00:32:00,338 --> 00:32:02,305
there was jumping up
and down, and there was...

513
00:32:02,305 --> 00:32:04,971
I think we gave each other
a high five.
(laughs)

514
00:32:04,971 --> 00:32:06,838
The discovery of the Kuiper Belt

515
00:32:06,838 --> 00:32:09,138
helped us to better understand
our solar system

516
00:32:09,138 --> 00:32:11,905
as it is now,
and also its history.

517
00:32:11,905 --> 00:32:15,338
LUU:
The Kuiper Belt is
really the frontier

518
00:32:15,338 --> 00:32:18,205
if you want to understand
the solar system.

519
00:32:18,205 --> 00:32:20,371
But it is very difficult
to study it,

520
00:32:20,371 --> 00:32:24,238
because it is so far away.

521
00:32:24,238 --> 00:32:26,838
NARRATOR:
Despite the challenges,

522
00:32:26,838 --> 00:32:29,305
more than 4,000
Kuiper Belt objects

523
00:32:29,305 --> 00:32:32,305
have been discovered to date.

524
00:32:35,238 --> 00:32:37,305
And scientists estimate

525
00:32:37,305 --> 00:32:40,371
there may be 200 dwarf planets.

526
00:32:43,538 --> 00:32:47,338
Some have rings and moons.

527
00:32:47,338 --> 00:32:52,671
Some are bizarre and misshapen.

528
00:32:52,671 --> 00:32:55,205
But they
all share one thing in common.

529
00:32:57,938 --> 00:33:01,571
They're made of icy materials,
similar to Triton.

530
00:33:04,471 --> 00:33:08,738
This is where Triton belongs.

531
00:33:08,738 --> 00:33:12,005
So how did it end up
around a billion miles away,

532
00:33:12,005 --> 00:33:16,338
in orbit around Neptune?

533
00:33:16,338 --> 00:33:20,371
♪ ♪

534
00:33:24,871 --> 00:33:27,171
HOWETT:
So, to understand Triton,

535
00:33:27,171 --> 00:33:29,205
you have to understand
the Kuiper Belt.

536
00:33:29,205 --> 00:33:30,805
If this is our sun,

537
00:33:30,805 --> 00:33:33,505
the one population
of Kuiper Belt objects

538
00:33:33,505 --> 00:33:36,838
orbit it in a nice circle.

539
00:33:36,838 --> 00:33:39,605
Another population
of Kuiper Belt objects

540
00:33:39,605 --> 00:33:42,938
have a highly elliptical orbit.

541
00:33:42,938 --> 00:33:45,505
So the question is,
why are these so different?

542
00:33:45,505 --> 00:33:48,938
What caused them to be
in this weird orbit?

543
00:33:48,938 --> 00:33:50,938
Well, the answer is,
some of these objects

544
00:33:50,938 --> 00:33:53,871
are in resonance with
another planet, Neptune.

545
00:33:53,871 --> 00:33:57,138
Resonance is when two objects
have paths

546
00:33:57,138 --> 00:33:59,238
that meet up occasionally.

547
00:33:59,238 --> 00:34:01,305
And we see this
throughout the solar system.

548
00:34:01,305 --> 00:34:03,305
If you look, for example,
at Pluto,

549
00:34:03,305 --> 00:34:04,605
it'll go around

550
00:34:04,605 --> 00:34:07,538
on this elliptical orbit
twice

551
00:34:07,538 --> 00:34:11,438
in the same time Neptune has
gone around three times.

552
00:34:11,438 --> 00:34:14,205
And this resonance is an
important clue

553
00:34:14,205 --> 00:34:16,705
in understanding
how disruptive

554
00:34:16,705 --> 00:34:19,105
Neptune is to Kuiper
Belt objects.

555
00:34:23,371 --> 00:34:25,605
♪ ♪

556
00:34:25,605 --> 00:34:27,971
NARRATOR:
Scientists think Neptune formed

557
00:34:27,971 --> 00:34:31,571
much closer to the sun,

558
00:34:31,571 --> 00:34:33,971
then slowly drifted out.

559
00:34:37,538 --> 00:34:40,371
Its huge gravity
disrupted the orbits

560
00:34:40,371 --> 00:34:43,371
of the Kuiper Belt worlds
it encountered,

561
00:34:43,371 --> 00:34:45,805
kicking them into
the elliptical orbits

562
00:34:45,805 --> 00:34:49,138
we see today.

563
00:34:49,138 --> 00:34:52,571
DURFEY:
The early solar system
was complete chaos,

564
00:34:52,571 --> 00:34:56,438
filled with small bodies
growing larger

565
00:34:56,438 --> 00:34:58,238
and smashing into each other,

566
00:34:58,238 --> 00:35:01,105
sometimes destroying.

567
00:35:01,105 --> 00:35:03,271
Complete chaos.

568
00:35:04,338 --> 00:35:06,338
NARRATOR:
During all the commotion,

569
00:35:06,338 --> 00:35:11,005
Triton became trapped
by Neptune's gravity,

570
00:35:11,005 --> 00:35:15,305
slipping into its
backward orbit.

571
00:35:15,305 --> 00:35:20,605
And being this close
to a giant has consequences.

572
00:35:22,205 --> 00:35:25,805
Just as our moon raises tides
on Earth,

573
00:35:25,805 --> 00:35:30,405
Neptune raises tides on Triton,

574
00:35:30,405 --> 00:35:33,871
stretching and squashing it
like a stress ball,

575
00:35:33,871 --> 00:35:38,738
heating it up.

576
00:35:38,738 --> 00:35:41,438
HOWETT:
Triton being captured
by Neptune

577
00:35:41,438 --> 00:35:44,005
fundamentally changed
how it works.

578
00:35:44,005 --> 00:35:46,938
On Earth, we experience energy
every day.

579
00:35:46,938 --> 00:35:48,905
You might be able to hear it
in the roar

580
00:35:48,905 --> 00:35:51,671
that comes from the tide
coming in underneath us.

581
00:35:51,671 --> 00:35:53,905
(waves pounding)

582
00:35:53,905 --> 00:35:55,905
Tidal energy can force water
up through cracks

583
00:35:55,905 --> 00:35:57,405
in the Earth, like the one
in front of us,

584
00:35:57,405 --> 00:36:02,605
creating plumes
erupting up to the sky.

585
00:36:02,605 --> 00:36:07,738
NARRATOR:
On Triton, the plumes are
even more spectacular.

586
00:36:07,738 --> 00:36:11,471
HOWETT:
The plumes on Triton
would be magnificent to behold.

587
00:36:11,471 --> 00:36:15,905
Erupting from the surface,
cracks like this,

588
00:36:15,905 --> 00:36:20,005
but going five miles
into the sky.

589
00:36:20,005 --> 00:36:21,905
I mean, it'd just be
absolutely phenomenal.

590
00:36:21,905 --> 00:36:24,105
(geyser bursts)

591
00:36:24,105 --> 00:36:27,571
NARRATOR:
What creates Triton's plumes
is a mystery.

592
00:36:27,571 --> 00:36:33,005
But one theory lies
in its unusual orbit.

593
00:36:33,005 --> 00:36:36,405
HOWETT:
It's highly tilted,
and Triton orbits backwards.

594
00:36:36,405 --> 00:36:38,505
Meaning as it goes
around Neptune,

595
00:36:38,505 --> 00:36:40,671
its pull and push
that it receives

596
00:36:40,671 --> 00:36:42,571
from Neptune and its moons
changes.

597
00:36:42,571 --> 00:36:44,671
This creates a kind of friction,

598
00:36:44,671 --> 00:36:46,238
similar to the one
that you get

599
00:36:46,238 --> 00:36:48,471
when you rub your hands together
on a cold day.

600
00:36:48,471 --> 00:36:51,105
Your hands warm up,
and so might Triton.

601
00:36:51,105 --> 00:36:54,271
We call that kind of energy
tidal heating.

602
00:36:56,905 --> 00:37:00,438
NARRATOR:
As Neptune's gravity
stretches and squashes

603
00:37:00,438 --> 00:37:02,471
its giant moon...

604
00:37:02,471 --> 00:37:05,371
(plume roaring)

605
00:37:05,371 --> 00:37:07,471
...the tidal heating produced

606
00:37:07,471 --> 00:37:11,338
melts Triton's frozen
interior...

607
00:37:11,338 --> 00:37:14,438
♪ ♪

608
00:37:14,438 --> 00:37:19,471
...powering its spectacular
plumes.

609
00:37:19,471 --> 00:37:21,238
DURFEY:
Triton is a great example

610
00:37:21,238 --> 00:37:24,605
of how interconnected
our solar system is.

611
00:37:24,605 --> 00:37:26,738
And it also serves as a good
example

612
00:37:26,738 --> 00:37:30,205
of how a large, giant planet

613
00:37:30,205 --> 00:37:32,171
straying into a belt of objects

614
00:37:32,171 --> 00:37:35,271
can really mess up your system.

615
00:37:43,271 --> 00:37:48,238
NARRATOR:
Triton was plucked
from the Kuiper Belt,

616
00:37:48,238 --> 00:37:53,571
a distant realm
filled with mysterious worlds

617
00:37:53,571 --> 00:37:56,038
so far away

618
00:37:56,038 --> 00:38:00,471
we can't make them out
in much detail.

619
00:38:00,471 --> 00:38:03,238
But we have sent one spacecraft.

620
00:38:09,071 --> 00:38:13,371
It took over nine years
for New Horizons to get here

621
00:38:13,371 --> 00:38:16,905
and home in
on its primary target.

622
00:38:23,205 --> 00:38:25,271
♪ ♪

623
00:38:25,271 --> 00:38:29,905
The tiny spacecraft captured
the first close-up images

624
00:38:29,905 --> 00:38:34,838
of this Kuiper Belt world,

625
00:38:34,838 --> 00:38:37,605
revealing unexpectedly complex

626
00:38:37,605 --> 00:38:41,571
and dynamic surface features:

627
00:38:41,571 --> 00:38:45,838
mountains as high as the Alps,
made from water,

628
00:38:45,838 --> 00:38:51,171
frozen as hard as granite.

629
00:38:51,171 --> 00:38:54,938
But there's something else odd
out here.

630
00:38:54,938 --> 00:38:58,105
Another world close by.

631
00:39:06,938 --> 00:39:11,905
How did Charon and Pluto
end up almost touching?

632
00:39:16,471 --> 00:39:18,538
Charon orbits about 12,000 miles

633
00:39:18,538 --> 00:39:19,938
from the surface of Pluto,

634
00:39:19,938 --> 00:39:21,905
which sounds like a really large
number,

635
00:39:21,905 --> 00:39:23,505
but is actually really close

636
00:39:23,505 --> 00:39:25,771
for the scale
of the Kuiper Belt.

637
00:39:25,771 --> 00:39:28,471
It's very common
in our solar system

638
00:39:28,471 --> 00:39:33,438
for moons that are close enough
to their parent body

639
00:39:33,438 --> 00:39:35,671
to become tidally locked.

640
00:39:35,671 --> 00:39:38,171
And that is where one orbit

641
00:39:38,171 --> 00:39:41,305
will also be one spin,

642
00:39:41,305 --> 00:39:43,805
so that the same face
of that moon

643
00:39:43,805 --> 00:39:46,871
is presented to the planet
at all times.

644
00:39:51,371 --> 00:39:54,138
NARRATOR:
All large moons
in the solar system,

645
00:39:54,138 --> 00:39:57,605
including our own,
are tidally locked,

646
00:39:57,605 --> 00:40:02,671
only showing one face
to their parent planet.

647
00:40:02,671 --> 00:40:05,505
But in the case of Pluto
and Charon,

648
00:40:05,505 --> 00:40:10,271
it isn't just Charon that is
tidally locked to Pluto.

649
00:40:10,271 --> 00:40:14,305
Pluto is also tidally locked
to Charon.

650
00:40:14,305 --> 00:40:19,205
Both worlds constantly
face each other at all times.

651
00:40:21,571 --> 00:40:24,071
RICE:
And what that means is,
if you're on the side of Pluto

652
00:40:24,071 --> 00:40:26,171
where you're able to see Charon,

653
00:40:26,171 --> 00:40:29,538
then it'll look like it's just
hanging there all the time.

654
00:40:29,538 --> 00:40:31,438
It's not going to rise,
it's not going to set.

655
00:40:31,438 --> 00:40:35,238
It's just going to
constantly be in your sky.

656
00:40:35,238 --> 00:40:41,305
♪ ♪

657
00:40:41,305 --> 00:40:47,471
NARRATOR:
This isn't just a dwarf planet
and its moon,

658
00:40:47,471 --> 00:40:50,671
but a binary pair.

659
00:40:50,671 --> 00:40:55,238
♪ ♪

660
00:40:55,238 --> 00:41:00,471
New Horizons is still studying
Kuiper Belt worlds today.

661
00:41:04,105 --> 00:41:07,738
During the most distant
fly-by in history,

662
00:41:07,738 --> 00:41:13,505
it encountered Arrokoth,

663
00:41:13,505 --> 00:41:16,438
a bizarre snowman-shaped
object.

664
00:41:23,471 --> 00:41:25,605
SUNSHINE:
It is two pieces
that are stuck together,

665
00:41:25,605 --> 00:41:29,771
and those two pieces must have
come together very gently.

666
00:41:29,771 --> 00:41:32,405
To actually see it
was really quite remarkable.

667
00:41:32,405 --> 00:41:35,605
Any time you see a new world,
it's remarkable.

668
00:41:39,005 --> 00:41:42,405
NARRATOR:
Why do the worlds out here
in the Kuiper Belt

669
00:41:42,405 --> 00:41:46,538
form these partnerships?

670
00:41:46,538 --> 00:41:48,605
LUU:
Things become slower and slower

671
00:41:48,605 --> 00:41:50,505
as you go further away
from the sun.

672
00:41:50,505 --> 00:41:53,638
In the Kuiper Belt,
things might collide

673
00:41:53,638 --> 00:41:56,871
at the speed of a few
hundred feet per second.

674
00:41:56,871 --> 00:42:00,738
They occur at such
low-impact velocity

675
00:42:00,738 --> 00:42:03,205
that a lot of the collisions
are constructive

676
00:42:03,205 --> 00:42:08,205
rather than destructive.

677
00:42:08,205 --> 00:42:14,005
NARRATOR:
At some point in their history,
Pluto and Charon collided.

678
00:42:20,205 --> 00:42:24,638
But their slow movements

679
00:42:24,638 --> 00:42:27,905
meant this was less of an impact

680
00:42:27,905 --> 00:42:31,338
and more of an embrace.

681
00:42:36,371 --> 00:42:41,205
The Kuiper Belt is so vast
and far from the sun

682
00:42:41,205 --> 00:42:44,705
that many mysteries
still remain.

683
00:42:47,605 --> 00:42:49,805
I am often pretty amazed
that we're actually able

684
00:42:49,805 --> 00:42:52,538
to study things
like the Big Bang

685
00:42:52,538 --> 00:42:54,805
and the early universe
and distant galaxies,

686
00:42:54,805 --> 00:42:57,538
and yet we still actually
don't know everything

687
00:42:57,538 --> 00:42:59,105
that there is to know
about our own solar system

688
00:42:59,105 --> 00:43:00,605
and our own backyard.

689
00:43:00,605 --> 00:43:04,171
I'm very confident that
there are many, many worlds

690
00:43:04,171 --> 00:43:06,638
out there that we are yet
to discover,

691
00:43:06,638 --> 00:43:10,238
and that we haven't even
imagined yet.

692
00:43:10,238 --> 00:43:15,805
♪ ♪

693
00:43:22,205 --> 00:43:26,238
NARRATOR:
We can see distant stars
in the night sky

694
00:43:26,238 --> 00:43:30,071
because they burn so bright.

695
00:43:30,071 --> 00:43:32,371
Telescopes can detect planets

696
00:43:32,371 --> 00:43:36,805
as they pass in front
of their parent stars.

697
00:43:36,805 --> 00:43:39,738
Seeing worlds
in our own solar system

698
00:43:39,738 --> 00:43:42,438
is much harder,

699
00:43:42,438 --> 00:43:45,438
but not impossible.

700
00:43:45,438 --> 00:43:49,538
♪ ♪

701
00:43:49,538 --> 00:43:51,671
In 2018,

702
00:43:51,671 --> 00:43:54,771
a faint point of light
was detected

703
00:43:54,771 --> 00:43:59,571
about 12 billion miles
from the sun.

704
00:43:59,571 --> 00:44:03,105
It's thought to be
a dwarf planet

705
00:44:03,105 --> 00:44:06,138
nicknamed FarFarOut.

706
00:44:11,505 --> 00:44:16,238
This is the most distant object
yet seen in our solar system

707
00:44:16,238 --> 00:44:20,771
by some of our most
powerful telescopes.

708
00:44:20,771 --> 00:44:25,605
But it's not the limit
of what could be out there.

709
00:44:25,605 --> 00:44:31,205
♪ ♪

710
00:44:31,205 --> 00:44:34,805
OLUSEYI:
How far do you expect
the solar system to extend?

711
00:44:34,805 --> 00:44:36,538
You may imagine that it ends

712
00:44:36,538 --> 00:44:38,705
at the last major planet,
Neptune.

713
00:44:38,705 --> 00:44:40,838
However, that's not
exactly the case,

714
00:44:40,838 --> 00:44:42,205
and let me show you why.

715
00:44:42,205 --> 00:44:44,638
Here I'm gonna make a model
of the solar system.

716
00:44:44,638 --> 00:44:47,505
This rock is my sun,

717
00:44:47,505 --> 00:44:49,238
and I'm gonna place it
right there,

718
00:44:49,238 --> 00:44:51,605
and an inch away,
I'm gonna place the Earth.

719
00:44:51,605 --> 00:44:53,871
And so this will be my scale,
one inch equals

720
00:44:53,871 --> 00:44:56,805
the average distance
between the Earth and the sun.

721
00:44:56,805 --> 00:44:59,071
So now, if I go a second inch,

722
00:44:59,071 --> 00:45:02,571
I arrive at the asteroid belt.

723
00:45:02,571 --> 00:45:06,805
And to get to the most distant
major planet, Neptune,

724
00:45:06,805 --> 00:45:09,138
that's gonna be about 30 inches.

725
00:45:09,138 --> 00:45:11,305
Now, we have to keep
going and going,

726
00:45:11,305 --> 00:45:12,838
because out here is

727
00:45:12,838 --> 00:45:15,371
the most distantly
observed object ever

728
00:45:15,371 --> 00:45:17,138
in the history
of our solar system,

729
00:45:17,138 --> 00:45:18,938
11 feet away from the sun,

730
00:45:18,938 --> 00:45:20,838
132 inches,

731
00:45:20,838 --> 00:45:22,305
12 billion miles,

732
00:45:22,305 --> 00:45:25,638
is FarFarOut.

733
00:45:25,638 --> 00:45:29,505
NARRATOR:
But the solar system
doesn't end here.

734
00:45:29,505 --> 00:45:32,538
OLUSEYI:
I have to walk
another 50 paces...

735
00:45:41,438 --> 00:45:45,938
...another 186 billion miles,

736
00:45:45,938 --> 00:45:48,071
and now we've reached
our destination,

737
00:45:48,071 --> 00:45:50,905
a vast region known
as the Oort Cloud.

738
00:45:50,905 --> 00:45:54,005
♪ ♪

739
00:45:54,005 --> 00:45:56,571
NARRATOR:
Clinging on at the very edge

740
00:45:56,571 --> 00:46:00,005
of the sun's
gravitational influence,

741
00:46:00,005 --> 00:46:03,871
the Oort Cloud is
our solar system's largest

742
00:46:03,871 --> 00:46:06,905
and most mysterious realm.

743
00:46:12,071 --> 00:46:14,705
It's so deep into the darkness,

744
00:46:14,705 --> 00:46:17,905
it's almost impossible
to imagine,

745
00:46:17,905 --> 00:46:20,538
let alone see,

746
00:46:20,538 --> 00:46:23,605
filled with billions
upon billions

747
00:46:23,605 --> 00:46:27,405
of strange worlds.

748
00:46:27,405 --> 00:46:30,138
Most are thought to be
icy objects

749
00:46:30,138 --> 00:46:33,138
the size of mountains.

750
00:46:33,138 --> 00:46:38,138
But it's likely
some are made of rock.

751
00:46:38,138 --> 00:46:43,171
And if we were able to go there,
we'd discover they are pristine.

752
00:46:43,171 --> 00:46:46,505
♪ ♪

753
00:46:46,505 --> 00:46:51,371
Barely changed since the dawn
of the solar system.

754
00:46:51,371 --> 00:46:55,438
It's thought some could be older
than the sun.

755
00:46:57,438 --> 00:46:59,738
The Oort Cloud's existence
is hypothetical,

756
00:46:59,738 --> 00:47:01,938
but science doesn't deal
in fairy tales,

757
00:47:01,938 --> 00:47:06,105
so how do we know it's actually
there if we've never seen it?

758
00:47:06,105 --> 00:47:10,538
♪ ♪

759
00:47:10,538 --> 00:47:14,238
NARRATOR:
For as long as we've been
looking into the night sky,

760
00:47:14,238 --> 00:47:18,838
we've seen signs
that the Oort Cloud is real.

761
00:47:18,838 --> 00:47:21,871
And this is one of them.

762
00:47:27,538 --> 00:47:29,671
For hundreds of years,

763
00:47:29,671 --> 00:47:33,705
it's been locked in a deep,
frozen slumber.

764
00:47:36,138 --> 00:47:38,805
♪ ♪

765
00:47:38,805 --> 00:47:41,338
But now it stirs.

766
00:47:41,338 --> 00:47:45,205
♪ ♪

767
00:47:45,205 --> 00:47:48,805
As it nears the sun,

768
00:47:48,805 --> 00:47:51,538
warm rays bathe its surface...

769
00:47:56,571 --> 00:47:59,605
...and it begins to thaw.

770
00:47:59,605 --> 00:48:04,971
(hissing)

771
00:48:16,905 --> 00:48:19,871
♪ ♪

772
00:48:19,871 --> 00:48:25,471
So much debris is torn
from the surface,

773
00:48:25,471 --> 00:48:29,071
it stretches out,
forming a tail...

774
00:48:30,805 --> 00:48:34,838
...around 14 million miles long.

775
00:48:36,538 --> 00:48:40,571
This is the comet Nishimura.

776
00:48:45,305 --> 00:48:50,038
It's visible from Earth
for just a few weeks,

777
00:48:50,038 --> 00:48:55,038
before eventually heading back
into the darkness,

778
00:48:55,038 --> 00:48:59,705
just the latest in a long line
of icy visitors.

779
00:49:05,071 --> 00:49:07,105
Hale-Bopp.

780
00:49:10,105 --> 00:49:13,471
Neowise.

781
00:49:13,471 --> 00:49:19,471
They lit up our skies for weeks,
or even months, on end.

782
00:49:19,471 --> 00:49:21,305
Humans have been
captivated by comets

783
00:49:21,305 --> 00:49:23,171
because, frankly,
they're spectacular.

784
00:49:23,171 --> 00:49:25,838
CHABOT:
And the fact that they do wander

785
00:49:25,838 --> 00:49:28,405
around the solar system
from time to time

786
00:49:28,405 --> 00:49:31,705
really is a unique scientific
opportunity.

787
00:49:35,338 --> 00:49:37,671
NARRATOR:
When scientists followed
the trajectories

788
00:49:37,671 --> 00:49:39,705
of these comets back,

789
00:49:39,705 --> 00:49:43,838
they discovered they came
from the same region,

790
00:49:43,838 --> 00:49:49,338
more than 200 billion miles
from the sun.

791
00:49:49,338 --> 00:49:50,671
SUNSHINE:
If you calculate

792
00:49:50,671 --> 00:49:53,538
where the orbit
took you back to,

793
00:49:53,538 --> 00:49:55,038
it was way out,

794
00:49:55,038 --> 00:50:00,271
unbelievably far out,
what we now call the Oort Cloud.

795
00:50:00,271 --> 00:50:04,371
NARRATOR:
It's thought the gravity
of other objects in the galaxy

796
00:50:04,371 --> 00:50:09,671
can occasionally knock
these icy objects inwards.

797
00:50:09,671 --> 00:50:11,238
SUNSHINE:
But the really interesting thing

798
00:50:11,238 --> 00:50:14,471
was that they were coming
from all directions in space,

799
00:50:14,471 --> 00:50:16,738
and there had to be a cloud.

800
00:50:16,738 --> 00:50:20,205
♪ ♪

801
00:50:20,205 --> 00:50:23,405
NARRATOR:
Although we can't see
this far out,

802
00:50:23,405 --> 00:50:26,405
comets with orbits
starting in the Oort Cloud

803
00:50:26,405 --> 00:50:30,971
streak across our skies.

804
00:50:30,971 --> 00:50:33,171
RICE:
The Oort Cloud is
kind of incredible.

805
00:50:33,171 --> 00:50:34,705
No one's actually been there,

806
00:50:34,705 --> 00:50:37,205
no one's actually observed
anything within the Oort Cloud.

807
00:50:37,205 --> 00:50:40,005
They've only seen the wanderers
that have escaped

808
00:50:40,005 --> 00:50:42,105
from the Oort Cloud
for a brief moment,

809
00:50:42,105 --> 00:50:43,438
which I think is what makes it

810
00:50:43,438 --> 00:50:46,771
so spectacular
and so exciting to me.

811
00:50:46,771 --> 00:50:50,705
CHABOT:
If I could visit
one of those dark regions,

812
00:50:50,705 --> 00:50:52,905
I would have to choose
the Oort Cloud.

813
00:50:52,905 --> 00:50:54,805
We don't know that region
at all,

814
00:50:54,805 --> 00:50:57,705
we haven't ever explored it,
so for me,

815
00:50:57,705 --> 00:51:00,205
that would be
the most exciting place to go.

816
00:51:00,205 --> 00:51:03,105
♪ ♪

817
00:51:03,105 --> 00:51:04,771
NARRATOR:
We think of the solar system

818
00:51:04,771 --> 00:51:10,338
as the sun and all the planets.

819
00:51:10,338 --> 00:51:12,938
But that's just
what's close to Earth.

820
00:51:16,138 --> 00:51:19,038
As wandering worlds give us
rare glimpses

821
00:51:19,038 --> 00:51:21,838
into what is beyond

822
00:51:21,838 --> 00:51:25,338
and technology improves,

823
00:51:25,338 --> 00:51:30,771
we're discovering
more and more.

824
00:51:30,771 --> 00:51:32,805
RUSSELL:
We're really only
scratching the surface,

825
00:51:32,805 --> 00:51:35,805
so there are millions
of these tiny bodies out there,

826
00:51:35,805 --> 00:51:39,871
and we still have so many
secrets to unlock from them.

827
00:51:39,871 --> 00:51:43,838
MERCED:
There is so much information
in darkness.

828
00:51:43,838 --> 00:51:45,838
If we pay more attention

829
00:51:45,838 --> 00:51:49,571
and we trust what we perceive

830
00:51:49,571 --> 00:51:53,438
with all our senses,

831
00:51:53,438 --> 00:51:56,738
we will gain
much more information

832
00:51:56,738 --> 00:52:00,838
from those dark regions
of not only our solar system,

833
00:52:00,838 --> 00:52:02,971
but of the universe.

834
00:52:02,971 --> 00:52:05,038
This model of the solar system,

835
00:52:05,038 --> 00:52:08,971
it's missing all of the most
interesting bits.

836
00:52:08,971 --> 00:52:13,005
♪ ♪

837
00:52:35,105 --> 00:52:37,971
♪ ♪

838
00:52:38,905 --> 00:52:46,438
♪ ♪

839
00:52:50,271 --> 00:52:57,805
♪ ♪

840
00:53:01,705 --> 00:53:09,238
♪ ♪

841
00:53:10,871 --> 00:53:18,405
♪ ♪

842
00:53:20,038 --> 00:53:27,571
♪ ♪