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Our solar system
is home to giants.
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Gas giants Jupiter and Saturn
seem to dominate,
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but two ice giants determine
the fate of the rest...
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Neptune and Uranus...
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Distant planets
unconnected to us,
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or so we thought.
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We now know the fate
of the ice giants
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is entwined with our own.
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They've gone from being
these cold, dull worlds
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to actually having in them
the very secret
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of why you and I exist at all.
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Their story is of
epic migration,
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brutal destruction...
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Uranus got jabbed
and then knocked on its side.
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...Of worlds more
alive than anyone imagined.
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They hold the key to the history
of the solar system
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and perhaps to life on Earth.
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Uranus and Neptune...
Mysterious giants
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lurking in the cold outer
reaches of the solar system...
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The farthest planets
from the Sun.
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Uranus and Neptune are
sort of the sentinels
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of the outer solar system.
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They're out past
Jupiter and Saturn,
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well over, like, 2 billion,
3 billion miles from the Sun.
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Their size and location
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are a puzzle
to planetary astronomers.
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Uranus and Neptune are somewhat
of a mystery because,
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in a way, they shouldn't exist,
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or at least they shouldn't
exist where they are.
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Scientists can't understand
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how these giant planets grew
so big so far from the Sun.
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The mystery starts
4 1/2 billion years ago...
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...with the birth
of the solar system.
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In the beginning,
the Sun ignites from a disk
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of gas and dust.
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The rocky cores of the first
planets start to grow.
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They collide with the debris in
the disk as they orbit the Sun.
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But the inner planets
have a size limit.
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To grow into a giant planet,
you need gas.
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Heat from the infant sun blasts
these lighter gas molecules
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beyond a point astronomers
call the frost line.
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Out here, it's cool enough
for gas molecules like hydrogen
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and helium to stabilize.
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Jupiter and Saturn
take shape first...
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Sweeping in the abundant gas
and quickly becoming gas giants.
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But Neptune and Uranus
are different.
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Jupiter and Saturn are about
90% hydrogen and helium,
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whereas Neptune and Uranus
are more like 20%.
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So what does this
difference in gas tell us
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about their formation?
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We suspect that Uranus and
Neptune came a little bit later
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when there was not
as much gas to be swept up.
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Uranus and Neptune
have less time to suck up
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as much hydrogen and helium
before these gases disappear.
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But they're also
forming farther out,
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where it's cold enough for
other, heavier gases to freeze.
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These are swept up by
the growing outer planets.
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Out where Uranus and Neptune
are, tons of ice,
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tons of frozen gases
as we might think of them...
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Methane, ammonia, water,
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and so that's what makes up
their composition predominantly.
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They may be smaller
than Jupiter and Saturn,
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but these heavy ices
mean they grow dense.
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They become ice giants.
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But there's a problem.
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They're too big.
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The disk of gas and ice
around a newborn star
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does not last forever,
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and material in the far reaches
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of the solar system
is spread thin.
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As you move further out
in the solar system,
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the time scale for two bodies
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to find each other and collide
and accrete slows down
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because the periods around
the Sun are much longer,
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and it just takes
a very, very long time.
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Neptune and Uranus
orbit the Sun incredibly slowly,
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too slowly to collide
with enough icy material
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to grow into the giants
we see today.
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So when we look at Neptune
at this very distant orbit,
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we don't have enough time
in the solar system
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to build a planet like Neptune.
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We just don't think
we could build Neptune
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where we find it today.
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So what happened?
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It turns out,
where we see them now
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is probably not where
they started out.
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One thing we've learned
about solar systems
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is that things are
in a delicate balance,
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and planets migrate.
They move around.
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They don't form in one place
and stay there forever.
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So what has enough power
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to move a giant planet
like Neptune?
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An even bigger one... Jupiter.
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One way for planets to move
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is by gravitationally
interacting with each other,
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so they feel
each other's gravity.
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They can tug. They can pull, and
that effect can lead to planets
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slowly migrating around
in their planetary systems.
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The closer two planets
are, the greater the effect,
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and in the early days
of the solar system,
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the giant planets
are much closer together.
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On top of that,
they may have orbited
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in a different order
than we see today...
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Jupiter, Saturn,
Neptune, and Uranus.
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So what causes Neptune
and Uranus to swap positions?
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The answer lies
with Jupiter and Saturn.
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The two biggest giants lock
into a gravitational dance.
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There's always this
interplay between them.
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Think of Capoeira dancers,
balancing and moving together
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in a careful, orchestrated way.
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Over millions of
years, a rhythm slowly builds.
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These giants push
and pull each other
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into more elliptical orbits.
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But the gravitational dance
reaches a climax.
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The stretched orbits
become unstable.
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The giants move off course.
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As Saturn and Jupiter
twist out from the Sun,
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they fling Neptune
out beyond Uranus.
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As Neptune moves out
through the solar system,
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it pushes debris ahead of it.
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These are the leftover icy
fragments from planet formation.
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Neptune
snowplows these bodies out.
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They because the Kuiper belt,
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the band of thousands of
small bodies of ice and rock
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just beyond Neptune's orbit.
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You can think of the structure
of that Kuiper belt as, like,
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blood splatter on the wall
at a murder scene.
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It's the record of this
really violent of Neptune
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migrating outward
across the solar system.
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But Neptune's movement
doesn't just fling
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these small icy bodies
out into the Kuiper belt.
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It also sends some of them
crashing in towards the Sun.
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Some bombard the early Earth.
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It's the most violent time
on our planet
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since the birth of
the solar system itself,
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500 million years after
the Sun flared into life.
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It's called
the late heavy bombardment.
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During the late heavy
bombardment,
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you had rocks literally falling
down from the sky constantly.
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This would've been
a terrible time for life.
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And yet,
this cascade of icy bodies
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also brings something
essential for life.
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One characteristic of the outer
solar system bodies
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is that we often find organics.
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Organics provide the basis
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for all living organisms
we find today.
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They're carbon-based molecules
that form on the surface
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of dust grains
in the early solar system.
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The rocky inner planets sweep up
these organics as they grow...
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But the scorched surfaces
of the young planets
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are too inhospitable
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for many of these
delicate molecules to survive.
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Yet organics remain intact
on the small, icy bodies
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of the outer solar system
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that Neptune tosses
towards the early Earth.
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Neptune was the solar system's
cosmic delivery service.
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As far away as Uranus
and Neptune are,
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the existence of ice giants
in the outer solar system
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may have been critical for
the existence of Earth today.
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And the ice giants may have done
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more than give life on Earth
a kickstart.
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They may have prevented
our planet
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from being completely destroyed.
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The ice giants...
Uranus and Neptune,
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distant giant worlds
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that may have delivered
the elements of life to Earth.
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Without them, our planet itself
might not exist at all.
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These ice giants are
fascinating worlds,
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but they may be even
more important than that.
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They might be the reason
we're here.
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Around 4 billion years ago,
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the young Earth is under threat
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from our solar system's bully,
Jupiter.
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Positioned between
the rocky inner planets
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and the giant outer ones,
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Jupiter dominates
the solar system.
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When you have a behemoth like
Jupiter in your solar system,
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what it does determines in part
what everything else does.
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As Jupiter and Saturn lock
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into their gravitational dance,
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they migrate out,
away from the Sun.
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Jupiter's immense gravity
should pull Earth
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and Venus along with it.
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Earth and Venus' orbits
should stretch
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and overlap with each other.
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It's a collision
waiting to happen...
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...except... It didn't.
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So by the fact that we're
talking about this here on Earth
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suggests that Earth and Venus
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didn't have an impact
early in the solar system
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when Jupiter and Saturn
were migrating.
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Something appears
to have protected us.
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Scientists think
something yanked Jupiter
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into a different orbit
before it had a chance to pull
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Earth and Venus
on a collision course.
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But what could cause
such a large jump
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in Jupiter's migration?
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This is where the ice giants
enter the story.
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Getting Jupiter to make
a big jump in its migration
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is not easy,
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and so the best way that
the models have been able
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to actually recreate this jump
is to have Jupiter
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actually eject something
the size of Neptune
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out of the solar system
entirely.
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Jupiter has a lot of gravity,
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and if you get too close to it,
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you're going to be accelerated
as you fall in towards Jupiter,
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and it's possible that
you can eject a planet
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completely out of
the solar system this way.
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It's basically slingshotting it.
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But a planet the size of Neptune
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is heavy, even for Jupiter,
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and slingshotting it out
of the solar system
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gives Jupiter a kickback.
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Jupiter is knocked into a new
orbit, and Earth is saved.
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But which ice giant
sacrificed itself for us?
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Neptune is still
in the solar system,
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and so is Uranus.
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If you use computer models
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to basically predict
the behavior of the planets,
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what you find is that
if you start with Jupiter,
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Saturn, Uranus and Neptune,
you can't save the Earth
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without ejecting
either Uranus or Neptune,
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but they're there,
so we know that's not right.
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However, if you add
a third ice giant,
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a fifth giant planet out there,
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then that actually
makes everything work.
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You can save the Earth,
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have the planets in
their present configuration,
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and that ice giant gets ejected
from the solar system.
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Imagine our solar system
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starting with three ice giants.
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One swings too close to Jupiter.
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Our solar system's bully
throws its victim clean
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out of the playground.
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Jupiter is pushed
into a new orbit
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by the ice giant's gravity.
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Earth is saved from Jupiter's
deadly gravitational pull,
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and the solar system
becomes the safe
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and orderly place we see today.
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So we have a funny story here.
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This ice giant that may have
existed billions of years ago
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00:14:10,170 --> 00:14:12,570
yanked Jupiter back into
the outer solar system,
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00:14:12,570 --> 00:14:14,630
preventing it
from destroying the Earth,
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00:14:14,640 --> 00:14:17,100
but in the meantime,
it sacrificed itself for us,
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00:14:17,110 --> 00:14:18,970
getting ejected from
the solar system.
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We have to thank it
for our existence,
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but it's not there anymore.
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00:14:24,050 --> 00:14:25,850
We humans are really lucky.
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00:14:25,850 --> 00:14:28,980
Had the dinosaurs not gone
extinct, we wouldn't be here.
251
00:14:28,980 --> 00:14:31,920
Had this planet not been ejected
out of our solar system,
252
00:14:31,920 --> 00:14:33,850
we wouldn't be here.
253
00:14:33,860 --> 00:14:38,260
So where is
this missing ice giant now?
254
00:14:38,260 --> 00:14:39,990
The answer is pretty amazing.
255
00:14:40,000 --> 00:14:42,330
It could be clear across
the other side
256
00:14:42,330 --> 00:14:43,660
of the milky way galaxy.
257
00:14:43,670 --> 00:14:45,730
The Sun moves around
the milky way galaxy
258
00:14:45,730 --> 00:14:48,070
at about half a million miles
an hour,
259
00:14:48,070 --> 00:14:49,470
and in the history of the Earth,
260
00:14:49,470 --> 00:14:50,940
we've been around
about 20 times.
261
00:14:50,940 --> 00:14:54,670
We could've lost that planet
anywhere across the milky way.
262
00:14:57,010 --> 00:15:00,280
But is this third ice giant
263
00:15:00,280 --> 00:15:04,150
really lost or just hiding?
264
00:15:07,220 --> 00:15:11,630
January 2016...
Astronomers at Caltech
265
00:15:11,630 --> 00:15:15,030
make an astonishing
announcement.
266
00:15:15,030 --> 00:15:17,100
They claim to have
found evidence
267
00:15:17,100 --> 00:15:21,900
of a mysterious ninth planet
disrupting icy bodies
268
00:15:21,900 --> 00:15:25,570
far out in the Kuiper belt.
269
00:15:25,570 --> 00:15:29,840
Simulations suggest that if this
so-called planet nine exists,
270
00:15:29,850 --> 00:15:33,380
it is similar in size
to Neptune and Uranus.
271
00:15:33,380 --> 00:15:36,180
Could this be Earth's savior?
272
00:15:36,190 --> 00:15:39,320
Could the solar system's
primordial missing
273
00:15:39,320 --> 00:15:43,060
sacrificial ice giant
be planet nine?
274
00:15:45,460 --> 00:15:46,660
Yes, it could.
275
00:15:46,660 --> 00:15:49,000
Perhaps this third ice giant
276
00:15:49,000 --> 00:15:52,530
wasn't ejected from
the solar system after all.
277
00:15:52,530 --> 00:15:54,670
One type of ejection is
where you just take something
278
00:15:54,670 --> 00:15:56,470
and you throw it out
of the solar system,
279
00:15:56,470 --> 00:15:57,810
but another more gentle kind
280
00:15:57,810 --> 00:16:00,670
is when you don't quite
make it all the way out,
281
00:16:00,680 --> 00:16:04,340
and instead you go on
a very, very long period orbit
282
00:16:04,350 --> 00:16:07,410
around the young solar system.
283
00:16:07,420 --> 00:16:10,280
Planet nine is thought
to be so far out,
284
00:16:10,290 --> 00:16:15,220
it takes up to 20,000 years
for it to travel around the Sun.
285
00:16:15,220 --> 00:16:18,090
Perhaps it's been observing
the dramatic,
286
00:16:18,090 --> 00:16:19,830
dynamical evolution
of the solar system
287
00:16:19,830 --> 00:16:26,230
unfold from its frigid
20,000-year orbit.
288
00:16:26,230 --> 00:16:29,840
Whether planet nine
is a long-lost sibling or not,
289
00:16:29,840 --> 00:16:33,910
ice giants played a huge role
in taming Jupiter.
290
00:16:33,910 --> 00:16:39,510
They made our solar system
the haven it is today.
291
00:16:39,520 --> 00:16:43,650
But they are not
peaceful places.
292
00:16:43,650 --> 00:16:45,850
Somehow, out in the deep freeze,
293
00:16:45,860 --> 00:16:49,120
Neptune is tormented
by wild weather,
294
00:16:49,130 --> 00:16:55,660
mysterious superstorms
and maybe even diamond rain.
295
00:17:08,010 --> 00:17:11,550
Uranus and Neptune...
296
00:17:11,550 --> 00:17:14,310
Their location at the edge
of our solar system
297
00:17:14,320 --> 00:17:17,080
makes them very difficult
to study.
298
00:17:17,090 --> 00:17:19,090
The ice giants Uranus
and Neptune
299
00:17:19,090 --> 00:17:20,750
are very mysterious to us.
300
00:17:20,760 --> 00:17:23,490
They're very far away,
so they're hard to observe
301
00:17:23,490 --> 00:17:27,490
with telescopes
here at the Earth.
302
00:17:27,500 --> 00:17:28,900
As a result,
303
00:17:28,900 --> 00:17:33,030
these planets
have long been overlooked.
304
00:17:33,040 --> 00:17:37,240
The only time we've glimpsed
these distant giants up close
305
00:17:37,240 --> 00:17:41,170
was when voyager 2
flew past them in the 1980s.
306
00:17:43,310 --> 00:17:46,980
The results amazed Heidi Hammel,
part of the voyager 2
307
00:17:46,980 --> 00:17:50,120
imaging team at the time
of the Neptune flyby.
308
00:17:52,460 --> 00:17:55,920
One of the most wondrous
and frustrating things
309
00:17:55,920 --> 00:18:00,730
about planetary flybys
is that you learn so much
310
00:18:00,730 --> 00:18:06,270
that you open a whole
Pandora's box of questions.
311
00:18:06,270 --> 00:18:10,800
One observation
instantly intrigued scientists.
312
00:18:12,510 --> 00:18:16,940
Neptune has the fastest winds
in the solar system.
313
00:18:18,480 --> 00:18:20,880
Here on Earth, our winds
are actually driven
314
00:18:20,880 --> 00:18:24,350
by different temperatures
from sunshine.
315
00:18:24,350 --> 00:18:26,290
Neptune is so far away
from the Sun
316
00:18:26,290 --> 00:18:29,960
that it receives almost
no energy from our star.
317
00:18:29,960 --> 00:18:32,630
Neptune is 3 billion miles
from the Sun.
318
00:18:32,630 --> 00:18:37,960
It's really cold there, so why
does it have such fast winds?
319
00:18:37,970 --> 00:18:40,970
The less energy
a planet receives from the Sun,
320
00:18:40,970 --> 00:18:44,040
the quieter we expect
its weather to be...
321
00:18:46,110 --> 00:18:50,510
But Neptune isn't
tranquil at all.
322
00:18:50,510 --> 00:18:55,050
It's covered in
massive violent storms.
323
00:18:55,050 --> 00:18:57,720
There are storms
that are rivaling
324
00:18:57,720 --> 00:19:00,650
the size of the inner planets.
325
00:19:00,660 --> 00:19:02,520
That's a pretty big storm.
326
00:19:02,530 --> 00:19:05,260
One of the largest
ever recorded on Neptune
327
00:19:05,260 --> 00:19:09,860
is known as the 1989
great dark spot,
328
00:19:09,870 --> 00:19:12,200
a single vast tempest,
329
00:19:12,200 --> 00:19:15,270
large enough to swallow
the Earth whole,
330
00:19:15,270 --> 00:19:19,270
riding on a jet stream
with a mind-blowing wind speed
331
00:19:19,270 --> 00:19:21,810
of 1,500 miles per hour.
332
00:19:21,810 --> 00:19:23,810
Hands down,
Neptune holds the record
333
00:19:23,810 --> 00:19:27,210
for the fastest wind speeds
in the solar system.
334
00:19:27,220 --> 00:19:30,020
The fastest tornado winds
on Earth
335
00:19:30,020 --> 00:19:32,090
are only a few
hundred miles an hour,
336
00:19:32,090 --> 00:19:34,550
and that does
devastating destruction,
337
00:19:34,560 --> 00:19:38,090
so it's hard to imagine
what winds on Neptune would do.
338
00:19:38,090 --> 00:19:41,360
A probe entering
Neptune's upper atmosphere
339
00:19:41,360 --> 00:19:44,970
would record freezing
temperatures,
340
00:19:44,970 --> 00:19:47,900
minus-370 degrees Fahrenheit...
341
00:19:47,900 --> 00:19:51,710
Too cold
to generate the wind we see.
342
00:19:51,710 --> 00:19:54,970
600 miles down,
though, the probe is smashed
343
00:19:54,980 --> 00:19:58,980
by Neptune's relentless
jet stream winds.
344
00:20:04,050 --> 00:20:09,460
And the deeper you go,
the warmer it becomes.
345
00:20:09,460 --> 00:20:11,730
Neptune has almost three times
346
00:20:11,730 --> 00:20:14,330
as much heat coming
from its interior
347
00:20:14,330 --> 00:20:17,060
than you would expect
from a ball of gas
348
00:20:17,070 --> 00:20:20,330
out at Neptune's distance.
349
00:20:20,340 --> 00:20:23,470
The strange thing about
these high-speed Neptune winds
350
00:20:23,470 --> 00:20:26,870
is that they're not powered
by heat energy from the Sun.
351
00:20:26,880 --> 00:20:29,280
In fact, they're powered
by heat energy
352
00:20:29,280 --> 00:20:32,010
from Neptune's own interior.
353
00:20:34,020 --> 00:20:38,420
So where does this
internal heat come from?
354
00:20:38,420 --> 00:20:42,220
When planets form, it's a very
violent, very energetic event,
355
00:20:42,220 --> 00:20:44,620
and the planets are
actually extremely hot,
356
00:20:44,630 --> 00:20:48,430
and it takes billions of years
for that heat to leak away,
357
00:20:48,430 --> 00:20:49,900
so Neptune, it turns out,
358
00:20:49,900 --> 00:20:52,630
probably still has a
tremendous amount of that heat
359
00:20:52,630 --> 00:20:55,840
that is trapped inside of it,
and as that bubbles up,
360
00:20:55,840 --> 00:20:57,700
that's what's actually
heating the atmosphere
361
00:20:57,710 --> 00:21:00,040
and driving this
tremendous weather.
362
00:21:01,580 --> 00:21:05,910
So how does Neptune
retain so much heat?
363
00:21:05,910 --> 00:21:10,380
The secret lies deep
below the atmosphere.
364
00:21:10,390 --> 00:21:12,320
As you go down
and down and down,
365
00:21:12,320 --> 00:21:14,320
you'll just find the pressure
gets more and more intense
366
00:21:14,320 --> 00:21:17,390
until you are eventually
essentially crushed.
367
00:21:17,390 --> 00:21:20,060
That atmosphere will get
thicker and thicker like a fog
368
00:21:20,060 --> 00:21:23,060
until suddenly you would realize
that instead of an atmosphere,
369
00:21:23,070 --> 00:21:26,270
you are in an ocean.
370
00:21:26,270 --> 00:21:30,940
Neptune has
a super-dense fluid mantle
371
00:21:30,940 --> 00:21:35,810
made up of methane,
ammonia, and water.
372
00:21:35,810 --> 00:21:39,950
Really, an ice giant
is not a solid ball of ice,
373
00:21:39,950 --> 00:21:45,620
but rather a moving ocean
of swirling liquid material.
374
00:21:45,620 --> 00:21:48,760
This swirling liquid
traps the heat,
375
00:21:48,760 --> 00:21:52,630
acting like a blanket,
insulating the core.
376
00:21:52,630 --> 00:21:57,100
This is the secret
to Neptune's wild weather,
377
00:21:57,100 --> 00:21:59,030
and the intense interior heat
378
00:21:59,030 --> 00:22:02,640
and pressure
in Neptune's methane-rich mantle
379
00:22:02,640 --> 00:22:07,240
may create another
extraordinary effect.
380
00:22:07,240 --> 00:22:09,110
The pressure is so intense
381
00:22:09,110 --> 00:22:10,640
that the methane breaks up,
382
00:22:10,650 --> 00:22:12,850
and methane is made
of carbon and hydrogen,
383
00:22:12,850 --> 00:22:16,050
so if you take carbon
and you compress it a lot,
384
00:22:16,050 --> 00:22:18,390
you could get diamond formation,
385
00:22:18,390 --> 00:22:20,920
and so it is entirely possible
386
00:22:20,920 --> 00:22:24,320
that literal diamonds
are raining down
387
00:22:24,330 --> 00:22:29,330
in this ocean
of the mantle fluid on Neptune.
388
00:22:31,800 --> 00:22:35,000
From superstorms to
diamond rain,
389
00:22:35,000 --> 00:22:40,070
Neptune is strange,
dynamic beyond expectation,
390
00:22:40,080 --> 00:22:43,080
but Uranus is the real mystery,
391
00:22:43,080 --> 00:22:47,150
the victim of a cosmic
one-two punch with seasons
392
00:22:47,150 --> 00:22:50,420
unlike anything else
in the solar system.
393
00:23:05,230 --> 00:23:09,370
January 1986...
394
00:23:09,370 --> 00:23:14,710
Voyager 2 approaches Uranus
at over 40,000 miles per hour.
395
00:23:14,710 --> 00:23:19,580
Astronomers have been waiting
for this moment for 8 years,
396
00:23:19,580 --> 00:23:22,120
but on voyager's arrival,
397
00:23:22,120 --> 00:23:26,920
all that's revealed is
a bland, pale, blue ball.
398
00:23:26,920 --> 00:23:28,590
That was a little bit
disappointing
399
00:23:28,590 --> 00:23:30,320
from my perspective
400
00:23:30,330 --> 00:23:34,530
as a scientist studying
the atmosphere of the planet.
401
00:23:34,530 --> 00:23:39,530
20 years later,
everything changes.
402
00:23:39,530 --> 00:23:45,670
Telescopes reveal huge storms
raging across the planet.
403
00:23:45,670 --> 00:23:47,870
Why the enormous difference?
404
00:23:47,880 --> 00:23:53,610
The answer lies in the planet's
extreme axial tilt.
405
00:23:53,620 --> 00:23:56,950
If Neptune and Uranus
are siblings,
406
00:23:56,950 --> 00:24:00,090
Uranus is definitely
the wonky sibling.
407
00:24:00,090 --> 00:24:01,890
All the planets are tilted with
respect to the solar system.
408
00:24:01,890 --> 00:24:03,560
The Earth is 23 degrees.
409
00:24:03,560 --> 00:24:05,490
Jupiter is just
a handful of degrees,
410
00:24:05,490 --> 00:24:07,890
but Uranus is
actually on its side.
411
00:24:07,900 --> 00:24:11,100
It's tipped 98 degrees.
412
00:24:11,100 --> 00:24:14,970
Uranus' tilt is almost
four times more extreme
413
00:24:14,970 --> 00:24:17,640
than any other planet
in the system.
414
00:24:17,640 --> 00:24:21,040
It's lying so its poles
are horizontal,
415
00:24:21,040 --> 00:24:24,580
and its rings and moons
are vertical relative
416
00:24:24,580 --> 00:24:28,380
to the plane
of the solar system.
417
00:24:28,380 --> 00:24:30,980
Earth's tilt gives it seasons.
418
00:24:30,990 --> 00:24:36,660
Uranus' extreme tilt
gives it extreme seasons.
419
00:24:36,660 --> 00:24:40,130
Twice a year, its poles are
pointed directly towards
420
00:24:40,130 --> 00:24:43,530
or away from the Sun,
421
00:24:43,530 --> 00:24:47,800
so each pole has a very
intense period of midnight sun
422
00:24:47,800 --> 00:24:51,810
and a dark, cold polar night.
423
00:24:51,810 --> 00:24:55,340
It takes Uranus 84 years
to orbit the Sun,
424
00:24:55,340 --> 00:24:58,880
so those seasons last
for a very long time.
425
00:25:01,220 --> 00:25:03,080
You get, like,
20 years of sunlight
426
00:25:03,080 --> 00:25:05,820
in the northern hemisphere
as its going around the Sun
427
00:25:05,820 --> 00:25:08,750
and 20 years of darkness
in the Southern hemisphere.
428
00:25:13,830 --> 00:25:15,960
Uranus is kind of like
"game of thrones."
429
00:25:15,960 --> 00:25:18,300
You're waiting ages
for winter to come,
430
00:25:18,300 --> 00:25:20,770
and then winter lasts 20 years.
431
00:25:22,970 --> 00:25:25,970
A winter's night
or a summer's day
432
00:25:25,970 --> 00:25:27,570
that lasts for decades.
433
00:25:27,580 --> 00:25:30,710
But what happens in the interim
when the orbit of the planet
434
00:25:30,710 --> 00:25:33,510
means the Sunlight
hits its spinning equator
435
00:25:33,520 --> 00:25:36,180
rather than one of its poles?
436
00:25:36,180 --> 00:25:40,920
When it's off to the side,
the whole planet's lit up.
437
00:25:40,920 --> 00:25:46,260
As it spins, every piece of the
planet is exposed to sunlight.
438
00:25:46,260 --> 00:25:49,130
Sunlight hits the
equator of the spinning planet,
439
00:25:49,130 --> 00:25:53,130
pumping energy into the surface,
warming the atmosphere
440
00:25:53,130 --> 00:25:56,740
and driving air currents
around the planet.
441
00:25:56,740 --> 00:26:02,270
The result...
Spring and Autumn storms.
442
00:26:02,280 --> 00:26:06,810
That extreme change in how
much sunlight is distributed
443
00:26:06,820 --> 00:26:09,220
across that planet's atmosphere
444
00:26:09,220 --> 00:26:12,290
probably has an important role
445
00:26:12,290 --> 00:26:15,490
in driving this remarkable
seasonal change
446
00:26:15,490 --> 00:26:19,690
we see in Uranus' atmosphere.
447
00:26:19,700 --> 00:26:22,760
Unlike its ice giant
sibling, Neptune,
448
00:26:22,760 --> 00:26:28,030
Uranus has seasonal storms
rather than constant ones,
449
00:26:28,040 --> 00:26:31,170
so why does Uranus
roll around the Sun
450
00:26:31,170 --> 00:26:34,910
while other planets
spin like tops?
451
00:26:34,910 --> 00:26:40,180
It goes against everything we
know about planetary formation.
452
00:26:40,180 --> 00:26:42,380
In some ways, forming new
planets in the solar system
453
00:26:42,380 --> 00:26:45,390
was a lot like
making cotton candy.
454
00:26:45,390 --> 00:26:49,120
There was a direction that
everything was coming together.
455
00:26:49,120 --> 00:26:50,920
If you put a stick down in it,
456
00:26:50,930 --> 00:26:52,590
the material would
accumulate around it
457
00:26:52,590 --> 00:26:55,260
in a certain direction,
so that's why all the planets
458
00:26:55,260 --> 00:26:57,930
have roughly the same
orbital axes.
459
00:27:00,800 --> 00:27:04,540
If Uranus started out
with a vertical orbital axis,
460
00:27:04,540 --> 00:27:07,740
how did it end up
flipped on its side?
461
00:27:12,810 --> 00:27:15,080
We know there were a lot
of collisions between planets
462
00:27:15,080 --> 00:27:18,820
or planet-sized objects
in the early solar system.
463
00:27:25,230 --> 00:27:28,700
It's natural to assume
that Uranus probably got hit
464
00:27:28,700 --> 00:27:31,300
as a grazing impact
from another giant object,
465
00:27:31,300 --> 00:27:33,770
which tipped it
over on its side.
466
00:27:35,840 --> 00:27:38,640
But there's a problem
with this assumption.
467
00:27:38,640 --> 00:27:41,310
If you hit Uranus with a single
impact to knock it over
468
00:27:41,310 --> 00:27:42,780
to 98 degrees,
469
00:27:42,780 --> 00:27:45,310
then actually what you expect
is that the rings left over
470
00:27:45,310 --> 00:27:47,980
would be orbiting in
the wrong direction
471
00:27:47,980 --> 00:27:50,450
relative
to the spin of the planet.
472
00:27:54,260 --> 00:27:56,320
What event could be
powerful enough
473
00:27:56,320 --> 00:27:57,720
to flip a planet,
474
00:27:57,730 --> 00:28:02,130
but gentle enough to bring
everything in orbit around it
475
00:28:02,130 --> 00:28:05,060
along for the ride?
476
00:28:05,070 --> 00:28:07,270
A single big collision
477
00:28:07,270 --> 00:28:09,200
is probably not what happened
to Uranus
478
00:28:09,200 --> 00:28:11,540
because that would've
been too disruptive.
479
00:28:13,210 --> 00:28:14,610
It's kind of like boxing.
480
00:28:14,610 --> 00:28:18,410
Instead of one big knockout
blow, it was the old one-two.
481
00:28:20,750 --> 00:28:22,820
One theory suggests that
482
00:28:22,820 --> 00:28:26,290
the newly formed Uranus is hit
by a protoplanet
483
00:28:26,290 --> 00:28:27,550
the size of Earth.
484
00:28:29,620 --> 00:28:33,360
The blow is only glancing.
485
00:28:33,360 --> 00:28:37,560
Uranus is knocked partway
towards its current tilt.
486
00:28:37,570 --> 00:28:40,100
Its ring system
survives the impact
487
00:28:40,100 --> 00:28:42,500
and stays in orbit
around the equator.
488
00:28:45,040 --> 00:28:49,380
As the second object hits,
Uranus is tipped all the way,
489
00:28:49,380 --> 00:28:52,250
and the rings follow.
490
00:28:52,250 --> 00:28:56,120
Uranus got jabbed
and then knocked on its side.
491
00:28:58,920 --> 00:29:01,650
Uranus may orbit
the Sun sideways,
492
00:29:01,660 --> 00:29:06,990
but Neptune's moon, Triton,
has an even stranger trajectory.
493
00:29:06,990 --> 00:29:10,400
It travels around Neptune
in reverse.
494
00:29:10,400 --> 00:29:14,670
But weirder than that,
it seems to be erupting,
495
00:29:14,670 --> 00:29:17,270
and it could even harbor life.
496
00:29:32,690 --> 00:29:37,220
Wherever we see planets,
we expect to see moons.
497
00:29:37,230 --> 00:29:42,430
It seems the larger the planet,
the more moons orbit around it.
498
00:29:46,570 --> 00:29:51,070
Jupiter has 69. Saturn, 61.
499
00:29:53,440 --> 00:29:56,240
Next come the ice giants.
500
00:29:56,240 --> 00:30:00,650
Astronomers have so far detected
27 moons around Uranus
501
00:30:00,650 --> 00:30:02,580
and 13 around Neptune.
502
00:30:04,520 --> 00:30:09,060
But one stands out completely...
503
00:30:09,060 --> 00:30:12,190
Neptune's moon, Triton.
504
00:30:14,060 --> 00:30:15,460
Triton is a bit of an oddball
505
00:30:15,460 --> 00:30:18,000
because instead of orbiting
Neptune in the same direction
506
00:30:18,000 --> 00:30:19,330
that Neptune spins,
507
00:30:19,330 --> 00:30:21,330
it orbits
in the opposite direction,
508
00:30:21,340 --> 00:30:24,940
what we call a retrograde orbit.
509
00:30:24,940 --> 00:30:27,540
A giant planet and its moons
510
00:30:27,540 --> 00:30:30,280
form out of the same swirling
disk of gas,
511
00:30:30,280 --> 00:30:33,680
dust, and rocky material.
512
00:30:33,680 --> 00:30:36,550
The lighter gas falls
into the center more easily,
513
00:30:36,550 --> 00:30:38,220
forming the planet,
514
00:30:38,220 --> 00:30:40,750
while some of
the heavier rocky material
515
00:30:40,760 --> 00:30:44,490
is left over in the disk,
forming the moons.
516
00:30:46,430 --> 00:30:48,960
Typically, the moon travels
in the same direction
517
00:30:48,960 --> 00:30:50,630
that the planet is orbiting,
518
00:30:50,630 --> 00:30:52,830
but in the case
of Triton and Neptune,
519
00:30:52,830 --> 00:30:56,900
that's the complete
opposite case.
520
00:30:56,910 --> 00:30:58,500
We know it couldn't have formed
521
00:30:58,510 --> 00:30:59,710
in that orbit around Neptune.
522
00:30:59,710 --> 00:31:01,840
It had to come were
somewhere else,
523
00:31:01,840 --> 00:31:04,240
and a wonderful clue
to where it came from
524
00:31:04,250 --> 00:31:07,310
is the nearby neighbor, Pluto.
525
00:31:07,320 --> 00:31:11,380
Pluto is a dwarf planet in
the nearby Kuiper belt.
526
00:31:11,390 --> 00:31:14,590
It's only 200 miles
smaller than Triton,
527
00:31:14,590 --> 00:31:18,990
but it's not just size that
makes these two bodies similar.
528
00:31:18,990 --> 00:31:21,130
It's their composition.
529
00:31:21,130 --> 00:31:24,800
Triton is actually
most similar to Pluto.
530
00:31:24,800 --> 00:31:28,070
It has a similar amount
of rock in its interior.
531
00:31:28,070 --> 00:31:29,800
It has a similar
surface composition
532
00:31:29,800 --> 00:31:32,070
with a lot of nitrogen
and methane.
533
00:31:32,070 --> 00:31:34,410
It really looks like
a Pluto-like world,
534
00:31:34,410 --> 00:31:36,410
but it just happens
to be orbiting a planet
535
00:31:36,410 --> 00:31:40,350
instead of orbiting the Sun.
536
00:31:40,350 --> 00:31:42,620
If Triton is like Pluto,
537
00:31:42,620 --> 00:31:47,620
maybe it also started life
in the Kuiper belt.
538
00:31:47,620 --> 00:31:51,020
Could it have been captured
by Neptune's gravity,
539
00:31:51,030 --> 00:31:54,230
pulled into
the gas giant's orbit?
540
00:31:55,830 --> 00:31:59,430
It's not easy to capture a moon
into orbit around a planet.
541
00:31:59,430 --> 00:32:02,500
It's not natural for a body
to come close to another world
542
00:32:02,500 --> 00:32:04,100
and just spiral in.
543
00:32:04,110 --> 00:32:07,870
You've somehow got to put on
the brakes when it's close in.
544
00:32:09,710 --> 00:32:12,180
For Neptune to capture Triton,
545
00:32:12,180 --> 00:32:17,650
Triton had to be slowed down,
but how?
546
00:32:17,650 --> 00:32:21,190
Again, Kuiper belt objects
hold a clue.
547
00:32:21,190 --> 00:32:24,260
Many of the largest
are binary pairs,
548
00:32:24,260 --> 00:32:26,390
two worlds orbiting each other,
549
00:32:26,390 --> 00:32:29,660
like Pluto
and its large moon Charon.
550
00:32:29,660 --> 00:32:34,530
Perhaps Triton was
one of a pair as well.
551
00:32:34,540 --> 00:32:37,800
If Triton was in orbit
with a partner,
552
00:32:37,810 --> 00:32:41,340
each of the pair would
travel at different speeds.
553
00:32:41,340 --> 00:32:44,940
This speed difference is key.
554
00:32:44,950 --> 00:32:47,550
Triton's velocity is just
a little bit slower.
555
00:32:47,550 --> 00:32:50,820
As it's orbiting its companion,
it's slow enough
556
00:32:50,820 --> 00:32:53,020
that it could actually
get captured by Neptune,
557
00:32:53,020 --> 00:32:56,690
while that other one would speed
off across the solar system.
558
00:33:00,760 --> 00:33:03,500
Triton's original dance partner
559
00:33:03,500 --> 00:33:04,900
is flung out and away.
560
00:33:04,900 --> 00:33:11,100
Triton has a new, much
bigger companion, Neptune.
561
00:33:11,110 --> 00:33:17,180
But these unlikely partners
are dancing out of sync.
562
00:33:17,180 --> 00:33:21,380
Capture explains
the backwards orbit,
563
00:33:21,380 --> 00:33:25,720
but there's an even
stranger mystery to solve.
564
00:33:25,720 --> 00:33:27,190
On a moon like Triton,
565
00:33:27,190 --> 00:33:30,190
we'd expect to see
heavily cratered terrain,
566
00:33:30,190 --> 00:33:34,190
the hallmark of
geologically dead worlds.
567
00:33:34,200 --> 00:33:41,130
Instead, voyager 2 reveals a
world that's startlingly alive.
568
00:33:41,140 --> 00:33:42,870
I think one of the most
amazing discoveries
569
00:33:42,870 --> 00:33:46,410
of the entire voyager mission is
that when we flew past Triton,
570
00:33:46,410 --> 00:33:48,670
we saw these jets
of liquid nitrogen
571
00:33:48,680 --> 00:33:50,210
coming up out of the surface.
572
00:33:50,210 --> 00:33:53,410
We had no idea that this
tiny, little cold world
573
00:33:53,420 --> 00:33:56,150
out there would still be alive.
574
00:33:56,150 --> 00:33:59,950
Smooth, icy planes
cover the surface.
575
00:33:59,950 --> 00:34:02,960
Geysers of nitrogen
punch up through the crust
576
00:34:02,960 --> 00:34:07,490
and spew black dust
5 miles into the sky.
577
00:34:07,500 --> 00:34:11,760
We thought it was too far from
the Sun, too cold, too dead.
578
00:34:11,770 --> 00:34:13,900
It was just going
to be an ice ball
579
00:34:13,900 --> 00:34:18,840
like all the other moons
that had tended to be, but, no.
580
00:34:18,840 --> 00:34:21,710
It's a fresh, young surface.
581
00:34:24,850 --> 00:34:26,510
Triton's surface is
582
00:34:26,510 --> 00:34:29,250
a frosty 200 degrees
below freezing.
583
00:34:31,390 --> 00:34:36,520
Where's the heat coming from
to drive these surface features?
584
00:34:36,520 --> 00:34:42,060
The answer lies with
Neptune's capture of Triton.
585
00:34:42,060 --> 00:34:46,800
Triton's orbit is circular,
but it was once elliptical.
586
00:34:50,070 --> 00:34:53,410
As Triton moved closer in
and farther away,
587
00:34:53,410 --> 00:34:55,340
it would have been
repeatedly squashed
588
00:34:55,340 --> 00:34:58,410
and stretched
by Neptune's gravity.
589
00:34:58,410 --> 00:35:00,480
That would generate massive
amounts of friction
590
00:35:00,480 --> 00:35:01,750
inside of Triton.
591
00:35:01,750 --> 00:35:04,280
Might well have completely
melted Triton
592
00:35:04,290 --> 00:35:05,680
due to those forces,
593
00:35:05,690 --> 00:35:08,620
and as that happened,
it would have acted as a brake.
594
00:35:08,620 --> 00:35:12,490
All that friction would have
circularized Triton's orbit
595
00:35:12,490 --> 00:35:14,630
and left it in the orbit
that we see today.
596
00:35:16,830 --> 00:35:21,900
This change in orbit
is what gives Triton its heat.
597
00:35:21,900 --> 00:35:24,100
The surface of Triton
froze over,
598
00:35:24,110 --> 00:35:27,240
but the moon still retains
some of this warmth
599
00:35:27,240 --> 00:35:29,710
deep below the icy shell.
600
00:35:32,310 --> 00:35:37,120
Astronomers think there's enough
heat to melt ice into water,
601
00:35:37,120 --> 00:35:40,390
forming an underground
liquid ocean
602
00:35:40,390 --> 00:35:44,260
on a world 3 billion miles
from the Sun.
603
00:35:44,260 --> 00:35:48,860
Liquid water, heat...
There is only one question,
604
00:35:48,860 --> 00:35:52,060
and it's impossible
not to ask it.
605
00:35:52,070 --> 00:35:54,670
Could there be life?
606
00:35:54,670 --> 00:35:56,640
If there's a source
of energy on Triton,
607
00:35:56,640 --> 00:35:59,670
then perhaps there's a form
of life that figured out
608
00:35:59,670 --> 00:36:02,010
how to take advantage
of that energy source.
609
00:36:05,550 --> 00:36:07,080
An incredible thought.
610
00:36:07,080 --> 00:36:10,820
If life has carved out a niche,
this frozen ball
611
00:36:10,820 --> 00:36:14,750
could be the most distant
habitable world from the Sun.
612
00:36:17,090 --> 00:36:20,030
Neptune's moon, Triton,
might be alive,
613
00:36:20,030 --> 00:36:23,360
but Uranus' moons
are even stranger.
614
00:36:23,360 --> 00:36:27,430
They have a neat trick
to cheat death entirely.
615
00:36:40,110 --> 00:36:45,520
Uranus...
An ice giant with beautiful,
616
00:36:45,520 --> 00:36:48,790
shimmering rings and 27 moons...
617
00:36:51,060 --> 00:36:54,790
And their position is a mystery.
618
00:36:54,800 --> 00:36:59,000
Half exist within
a tightly packed orbit.
619
00:36:59,000 --> 00:37:01,470
It shouldn't be possible
for this many moons
620
00:37:01,470 --> 00:37:06,070
to be in such close
proximity to each other.
621
00:37:06,070 --> 00:37:08,670
The environment around Uranus
is very busy,
622
00:37:08,680 --> 00:37:10,740
and the system appears unstable,
623
00:37:10,750 --> 00:37:12,540
and the moons
should be colliding,
624
00:37:12,550 --> 00:37:15,550
but yet, we see these nice,
well-formed moons.
625
00:37:18,220 --> 00:37:21,220
And what's even more
surprising is that in 2003,
626
00:37:21,220 --> 00:37:23,090
the Hubble space
telescope revealed
627
00:37:23,090 --> 00:37:29,900
two new rings and two new moons...
Cupid and Mab.
628
00:37:29,900 --> 00:37:34,770
Question is, where did
these moons come from?
629
00:37:34,770 --> 00:37:39,840
A clue lies in Uranus' rings.
630
00:37:39,840 --> 00:37:41,910
In addition to the very packed
moon system,
631
00:37:41,910 --> 00:37:43,910
you also have rings
around Uranus,
632
00:37:43,910 --> 00:37:46,040
which is also
somewhat unexpected,
633
00:37:46,050 --> 00:37:48,250
but these two
unexpected qualities
634
00:37:48,250 --> 00:37:51,920
might actually
explain one another.
635
00:37:51,920 --> 00:37:56,120
Anytime you see a ring system,
you're seeing part of a process.
636
00:38:03,200 --> 00:38:04,800
There was probably a time
in Earth's history
637
00:38:04,800 --> 00:38:08,400
when it had a ring, you know,
when our moon was being formed.
638
00:38:08,400 --> 00:38:11,800
It seems that the new
moons are made up of material
639
00:38:11,810 --> 00:38:15,340
from a previous ring system.
640
00:38:15,340 --> 00:38:18,810
But when scientists
model Cupid's future,
641
00:38:18,810 --> 00:38:24,680
they discover it's dangerously
close to another moon, Belinda.
642
00:38:24,690 --> 00:38:27,620
In a few thousand years,
two of the moons in particular,
643
00:38:27,620 --> 00:38:30,560
Cupid and Belinda,
are likely to collide together
644
00:38:30,560 --> 00:38:33,360
as their trajectories intersect.
645
00:38:33,360 --> 00:38:38,030
And this collision
will create a domino effect.
646
00:38:38,030 --> 00:38:39,370
When there is a moon collision,
647
00:38:39,370 --> 00:38:42,700
that sets up a very delicate
gravitational balance,
648
00:38:42,700 --> 00:38:44,640
and it also creates
a lot of debris,
649
00:38:44,640 --> 00:38:48,910
so one collision sets off
a string of collisions.
650
00:38:48,910 --> 00:38:51,380
We think Cupid and Belinda
651
00:38:51,380 --> 00:38:53,580
will destroy
not only each other,
652
00:38:53,580 --> 00:38:56,580
but all of Uranus' inner moons.
653
00:38:56,580 --> 00:39:03,120
A runaway cascade of destruction
grinds Uranus' moons to pebbles.
654
00:39:03,120 --> 00:39:08,190
All of this will happen
in only a few thousand years.
655
00:39:08,200 --> 00:39:10,200
The fact that we are predicting
to have a collision
656
00:39:10,200 --> 00:39:12,600
within a few thousand years
feels kind of contrary
657
00:39:12,600 --> 00:39:15,530
because this system has been
here for billions of years,
658
00:39:15,540 --> 00:39:18,540
so it seems a little bit lucky
that we're looking just now,
659
00:39:18,540 --> 00:39:22,140
and we think there's going to be
a collision in the near future.
660
00:39:24,010 --> 00:39:26,480
What if this cycle
of destruction
661
00:39:26,480 --> 00:39:31,020
is a case of
Uranian groundhog day?
662
00:39:37,830 --> 00:39:39,890
When you look at
the Uranian system,
663
00:39:39,890 --> 00:39:42,860
I like to think of it sort of
like a violent hockey game.
664
00:39:46,700 --> 00:39:48,670
Guys are taking big hits.
665
00:39:52,110 --> 00:39:54,040
They can't continue,
so what must you do?
666
00:39:57,510 --> 00:39:59,650
You have to sub them in and out.
667
00:39:59,650 --> 00:40:02,110
When you look at this game
that's that violent,
668
00:40:02,120 --> 00:40:04,180
you know that the guys
you see on the ice
669
00:40:04,190 --> 00:40:07,250
are not the guys
that started the game.
670
00:40:07,250 --> 00:40:08,250
Whoo!
671
00:40:08,260 --> 00:40:11,260
It's a whole new set of players.
672
00:40:11,260 --> 00:40:12,520
Like hockey subs,
673
00:40:12,530 --> 00:40:17,330
Uranus keeps its moons
fresh by recycling them.
674
00:40:18,530 --> 00:40:19,870
Every time these moons collide,
675
00:40:19,870 --> 00:40:22,600
the debris forms
a ring system around Uranus,
676
00:40:22,600 --> 00:40:23,800
and then over time,
677
00:40:23,800 --> 00:40:28,210
that ring system starts
to spawn new moons.
678
00:40:28,210 --> 00:40:30,280
Over time, the rings of debris
679
00:40:30,280 --> 00:40:34,350
that surround Uranus
form into new moons,
680
00:40:34,350 --> 00:40:39,420
which in turn collide
and grind each other to dust.
681
00:40:39,420 --> 00:40:42,090
Uranus, it turns out,
is actually very Eco-conscious.
682
00:40:42,090 --> 00:40:43,360
Its moons shatter.
683
00:40:43,360 --> 00:40:45,760
They hit each other,
form all this debris,
684
00:40:45,760 --> 00:40:48,760
and then the moons reform
from that material,
685
00:40:48,760 --> 00:40:52,100
and then the whole pattern,
the whole cycle starts up again,
686
00:40:52,100 --> 00:40:56,640
and the moons hit, shatter, and
new moons form all over again.
687
00:40:56,640 --> 00:40:59,510
Ultimately, this eternal
cycle of life and death
688
00:40:59,510 --> 00:41:01,640
that we see with these moons
might be a story
689
00:41:01,640 --> 00:41:04,710
that is actually kind of true
of many things in the universe,
690
00:41:04,710 --> 00:41:06,510
when it comes to stars, planets,
691
00:41:06,510 --> 00:41:10,450
and maybe even
the universe itself.
692
00:41:10,450 --> 00:41:13,850
Uranus and Neptune,
693
00:41:13,860 --> 00:41:17,720
no longer forgotten outposts
of the solar system.
694
00:41:17,730 --> 00:41:23,860
Suddenly, these planets
are revealed to you as worlds.
695
00:41:23,870 --> 00:41:27,400
It's breathtaking.
It's... it's awe-inspiring.
696
00:41:27,400 --> 00:41:31,540
It's humbling,
and it makes you proud
697
00:41:31,540 --> 00:41:33,070
that you're part of a species
698
00:41:33,070 --> 00:41:34,940
that could actually do that,
699
00:41:34,940 --> 00:41:38,680
to get out there
and to see these places.
700
00:41:38,680 --> 00:41:40,950
Dynamic worlds with dramatic,
701
00:41:40,950 --> 00:41:45,750
often violent histories,
stolen moons,
702
00:41:45,750 --> 00:41:48,350
giants flung out into the cold,
703
00:41:48,360 --> 00:41:52,690
saving the Earth
from destruction.
704
00:41:52,690 --> 00:41:55,830
Uranus and Neptune are puzzle
pieces in the solar system.
705
00:41:55,830 --> 00:41:59,030
They are giant planets.
706
00:41:59,030 --> 00:42:02,370
They have a lot to tell us,
not just about themselves
707
00:42:02,370 --> 00:42:04,240
but about everything
in our solar system,
708
00:42:04,240 --> 00:42:07,240
including our own planet, Earth.
709
00:42:07,240 --> 00:42:09,710
Somewhere in the story
of the ice giants
710
00:42:09,710 --> 00:42:11,440
is the reason you and I
are actually here
711
00:42:11,450 --> 00:42:12,780
to talk about it at all,
712
00:42:12,780 --> 00:42:15,310
the reason the Earth was
able to form and stabilize
713
00:42:15,320 --> 00:42:17,520
and become an
environment for life.
714
00:42:17,520 --> 00:42:19,850
It would not be
an exaggeration to say
715
00:42:19,850 --> 00:42:22,050
that the ice giants
are the coolest planets
716
00:42:22,060 --> 00:42:23,990
in the solar system.