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Brian Cox: At this precise moment,
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on a planet far, far away...
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An alien sunrise ushers in a new day.
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But will alien eyes gaze upon it?
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Or will it go unseen?
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Just another moment
in a vast sterile universe.
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The hunt is on for the answer.
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B uzz a ld ri n: Magnificent desolation.
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- Beautiful vie w!
- Armstro n g: Isn't that something?
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Cox: The milky way.
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Hundreds of billions of stars...
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Spread across
700, 000 light years of space.
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Among them the sun,
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with eight planets orbiting around it,
including our home.
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Until very recently, these were
the only worlds we knew of.
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The only planets
we could hope to explore
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for signs of life beyond earth.
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When I first got into astronomy
back in the 19705,
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we knew of no planets
beyond our solar system.
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We didn't have the technology
to detect them, even if they were there.
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Our neighbourhood was the only place
we could look for life.
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And so the hunt for life began
in our own backyard.
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Over the last few decades,
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multiple missions have explored
our solar system's planets.
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And even some of their moons.
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But to date,
even as we continue to look,
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no convincing evidence of life has
been found on any of these worlds.
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Earth remains one of a kind.
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The only living world around the sun.
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But as the exploration
of the solar system continued,
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another search had begun...
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For worlds that lie
far beyond these shares.
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You know, the wonderful thing
about astronomy is
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that as we develop better
and better technology
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and accumulate more and more knowledge
about our universe,
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we turn more and more of these points
of light in the sky into worlds.
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I mean, that we've known is
a world for a long time,
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because that is the planet Mars.
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Butjust above Mars tonight is
a constellation called Pegasus.
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This is the square of Pegasus.
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And we now know that around there is
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a star called 51 pegasi,
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which has a planet orbiting around it,
a gas giant about the size ofjupiter,
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that goes round that faint point
of light every four days.
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It is wonderful to think
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that, in my lifetime,
in fact in my adult lifetime,
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in the last 25 years,
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we've gone from a universe
that could have been
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devoid of planets beyond
our solar system,
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to a universe that we know
is teeming with places
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that we can search for life.
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Over the last three decades,
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some of the most powerful telescopes
on earth ha ve joined the hunt,
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Searching for planets
unimaginabl y far a way,
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hiding in the dark.
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Planets like 57 pegasi b.
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The first world outside our solar system
to be detected around a sun-like star.
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57 pegasi b is a gas giant,
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around half the mass of Jupiter,
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but far closer to its star.
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Just imagine what that world
might be like.
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A world with skies torn
by Titanic winds,
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Where its hot interior is
bathed in rain of sapphires.
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In every sense,
57 pegasi b is an alien world.
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And we soon discovered that the galaxy
is full of planets
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unlike anything seen
in our solar system.
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Planets enveloped by fierce radiation.
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Their surfaces battered and stripped
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by the high energy strobing light
of their star.
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Worlds so cold
their atmospheres are frozen solid.
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Or great swollen planets,
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with the density of styrofoam.
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And fathomless atmospheres.
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These discoveries prove
that in one sense
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we really are not alone.
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There are other worlds out there
waiting to be explored.
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We estimate
that in the milky way galaxy,
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there are more planets than stars.
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Hundreds of billions of them.
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That's hundreds of billions
of places to look for life.
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But there's a catch.
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Because not all worlds,
by a long stretch,
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are like this one.
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The first planets we found appeared
too bizarre,
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too large,
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and often too close to their stars
for living things to survive.
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To find worlds where life could exist,
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we needed to look
for smaller, rocky planets
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in orbits further from their stars.
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Announcer: T-minus ten,
nine, eight, seven...
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Cox: We needed to look
for another earth.
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Announcer: Three, two,
engine start, one, zero,
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and lift off
of the delta ii rocket with kepler
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on a search for planets
in some way like our own.
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Cox: So the hunt moved to space
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with the launch
of NASA's I(Epler space telescope...
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Man: And we have separation.
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Cox: Searching for earth-like worlds
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in the galaxy beyond.
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I(epler crossed 94 million miles
of space,
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until it arrived in a steady orbit
around the sun,
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From where it looked out
with a fixed and clear gaze,
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to a single patch of sky
in the constellation of cygnus.
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Exposing its sensitive light meter
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To the light of 750, 000 stars,
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It began to look
for earth-like alien worlds.
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I(epler doesn't detect planets directly.
They are far too small.
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They're just specks of dust
relative to their parent star.
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They're also very faint.
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They don't emit light of their own,
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so they just glow very dimly
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in the reflective ambient light
of their stars.
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So kepler has
to detect planets indirectly.
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Imagine that a moth just flew
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across the beam of light
from the lighthouse.
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And I wouldn't see the moth.
But if I had a sensitive enough detector
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and everything was lined up properly,
I mightjust see
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the brightness of the light dim.
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And that is how kepler detects planets.
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Imagine there's an alien astronomer
in some distant solar system
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looking back at the sun,
and everything's lined up
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so they see the earth trace across
the face of our star.
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They would see
the light from the sun dim
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by one hundredth of one percent.
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It's a tiny amount, but it's enough.
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And if they saw
that dimming was regular,
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if they saw the star dim
once every year in this case,
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then they would infer
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that there's a planet orbiting
around the star.
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With its exquisitely sensitive
light meter,
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I(epler sees only
the regular dimming of pixels.
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Just a few bits of information.
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But from those bits, astronomers can
begin to build a picture
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of the worlds that dim the starlight.
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Worlds that might, in some way,
resemble our own.
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Worlds like kepler-36b.
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The planet was
one of kepler's earliest discoveries.
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Orbiting a star similar to our own,
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we 'd found a world that at first glance,
might seem familiar.
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Weighing in at around four times
the mass of our own planet,
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kepler-36b was one of the first
of a new class of planet,
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a super-earth.
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The kepler data doesn't
just allow us to say
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there's a planet around that star.
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It allows us to characterise
those planets.
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So, by looking at the precise way
that the light fades
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and then rises again,
and the timing between the dips,
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we can measure the orbit of the planets.
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And if there are multiple planets
in the system,
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we can even estimate their masses.
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So, the kepler data allows astronomers
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to paint a picture
of the worlds it discovers.
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But the more detailed our picture
of kepler-36b became,
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the less earth-like
this super-earth appeared to be.
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It orbits very close to its star,
circling once every 74 days.
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And it has company.
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A gigantic gaseous companion
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with an orbit unusually close
to its smaller sibling.
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The proximity of both its star
and sister planet,
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allows us to imagine
the bizarre conditions
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that may exist
on the surface of kepler-36b.
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The planet may be tidally-locked
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which would mean that one hemisphere
always faces the star.
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On this side, the punishing heat could
turn the ground molten,
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creating rivers of lava that would
criss-cross the surface.
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The planet could experience
violent eruptions
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as the gravitational pull
of the gas giant triggers
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intense volcanism,
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Each time it passes by.
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But kepler-36b could
also be a planet of ice.
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Because if it's tidally-locked
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the far side would face permanently
away from the star.
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And we could imagine
a freezing, cold hemisphere
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shrouded in eternal darkness.
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For now, this is all
just informed speculation.
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But we are beginning to build
a picture of these worlds.
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I mean, imagine a world
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where the sun stays at the same point
in the sky forever.
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So, one side of the planet is
in eternal night
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and the other side in eternal day.
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And even the twilight strip
between day and night,
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we think, would suffer
from extreme conditions.
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So, kepler-36bjust goes to show
there's so much more
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to having a habitable world
than just the composition of the planet.
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There's the details of its orbit,
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and also the nature of the other objects
in the solar system
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that are orbiting
around the star with it.
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Kepler-36b is just one
of thousands of planets
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that I(Epler has discovered.
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We now know beyond doubt
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that our galaxy is home
to a diverse collection of alien worlds.
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Each one of the over 4, 000 planets
that we've discovered to date,
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is different from all the others.
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They really are an alien
and exotic bunch,
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and there's certainly no planet
that's identical to the planets
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that we know of in our solar system.
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And I think that reveals a deep truth
about the universe.
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Because although the laws of nature
that form the planets are simple
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and the same everywhere,
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and the fundamental ingredients
out of which the planets are made,
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are simple and the same everywhere,
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the nature of a planet also depends
on the history of its formation,
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and the environment
around its parent star,
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out of which the planet formed.
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And those are all radically different.
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So, each planet has
a different story to tell.
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I suppose in that sense,
planets are like human beings.
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And this wholly unexpected
but exciting disco very
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certainly complicates
the search for life.
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We needed to narrow the search
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for planets further,
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but not too far away
from their parent stars.
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Planets at just the right distance
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for their surfaces
potentially to be habitable.
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Alien worlds
with one precious ingredient
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that makes earth a living planet.
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Now, you might legitimately ask
can we transfer all the knowledge
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we have of life here on earth
to planets elsewhere in the universe?
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Well, I would answer emphatically
"yes, we can,"
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because the laws
of nature are universal.
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So, the laws of physics
and chemistry that underpin biology
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here, on this planet,
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will apply to every planet
out there in the universe,
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whether we've discovered it or not.
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The chemistry of life requires
a few basic ingredients.
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Carbon, nitrogen, oxygen, iron.
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And it also requires a ready supply
of high quality energy
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from heat within the planets
or perhaps from starlight.
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But life here on earth also requires
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one very important fundamental
extra ingredient, which is liquid water.
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Liquid water is
a deceptively complicated substance.
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It's a very powerful solvent.
But it also has structures
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which are constantly forming
and disappearing within it,
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which act as a kind of scaffolding
around which biology happens.
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Organic molecules are
orientated by that scaffolding
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so they can react together.
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Now, it is certain
that every living thing
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here on earth requires
liquid water to survive.
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And I would say it is
a very good assumption
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that every living thing anywhere
out there in the universe
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will require it, too.
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The universe is filled with water.
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Great reservoirs have been detected
throughout the galaxy,
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amongst the gas clouds of giant nebulae.
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But just because water is plentiful,
246
00:26:43,121 --> 00:26:46,401
that doesn't mean
that it necessarily ends up
247
00:26:46,481 --> 00:26:49,081
in oceans on planetary surfaces.
248
00:26:56,441 --> 00:26:59,201
Of the eight planets
in our solar system,
249
00:26:59,281 --> 00:27:04,561
only one has liquid water flowing
permanently on its surface today.
250
00:27:10,001 --> 00:27:14,641
An ocean world where,
long ago, life began.
251
00:27:34,241 --> 00:27:37,921
Around four billion years ago,
life on earth would have begun
252
00:27:38,001 --> 00:27:41,601
probably in places
not dissimilar to this,
253
00:27:41,681 --> 00:27:45,881
where there's geothermal activity,
a source of energy,
254
00:27:45,961 --> 00:27:49,921
in contact with rich concentrations
of reactive chemical elements
255
00:27:50,001 --> 00:27:54,761
and minerals, but also crucially, that.
256
00:27:54,841 --> 00:27:58,161
The magical solvent, liquid water.
257
00:27:58,241 --> 00:28:04,641
Now, many rocky planets out there
in the galaxy will probably have this,
258
00:28:04,721 --> 00:28:08,441
but far fewer, we think, will have that.
259
00:28:08,521 --> 00:28:12,161
Large bodies of liquid water
on the surface.
260
00:28:12,241 --> 00:28:14,481
So, that's why
there's a kind of a catchphrase
261
00:28:14,561 --> 00:28:16,201
in the astro-biology community,
262
00:28:16,321 --> 00:28:19,441
which is if you want to search for life,
263
00:28:20,561 --> 00:28:22,001
follow the water.
264
00:28:35,801 --> 00:28:37,961
Whilst life on earth was evolving,
265
00:28:45,121 --> 00:28:47,601
724 light years away,
266
00:28:48,641 --> 00:28:52,681
amidst a collapsing cloud
of gas, dust and ice,
267
00:28:57,681 --> 00:28:59,721
a small star was born.
268
00:29:06,521 --> 00:29:10,081
And the cloud's
swirling leftovers condensed
269
00:29:10,161 --> 00:29:12,561
to form a brand new world.
270
00:29:19,641 --> 00:29:24,201
In 2075, I(Epler found a planet
orbiting comfortably
271
00:29:24,281 --> 00:29:26,201
within its star's habitable zone.
272
00:29:41,681 --> 00:29:44,441
More than eight times
the mass of the earth,
273
00:29:44,521 --> 00:29:47,001
k2— 78b is a giant,
274
00:29:57,201 --> 00:29:59,961
With a powerful gravitational pull.
275
00:30:10,041 --> 00:30:11,841
If the planet is rocky,
276
00:30:11,921 --> 00:30:15,241
this may have allowed it to hang on
to a thick atmosphere.
277
00:30:18,321 --> 00:30:22,761
K2— 78b might have
all the makings of a water world.
278
00:30:28,921 --> 00:30:34,361
And a legendary space telescope had
kepler's new disco very in its sights.
279
00:30:40,841 --> 00:30:44,201
The most powerful space telescope
of them all
280
00:30:44,281 --> 00:30:45,401
had joined the hunt.
281
00:30:51,641 --> 00:30:56,441
Hubble examined the light
from k2— 78b's parent star,
282
00:30:56,521 --> 00:30:58,521
as the planet passed in front of it,
283
00:31:00,841 --> 00:31:05,161
and detected what may be,
a faint signature...
284
00:31:06,881 --> 00:31:08,361
Of water vapour.
285
00:31:13,601 --> 00:31:16,321
724 light years from earth,
286
00:31:17,761 --> 00:31:21,841
we may have, at last, found
the evidence of water
287
00:31:21,921 --> 00:31:23,601
on an alien world.
288
00:31:25,001 --> 00:31:27,441
This was the first observation
289
00:31:27,521 --> 00:31:29,401
of water vapour in the atmosphere
290
00:31:29,481 --> 00:31:33,801
of a planet orbiting
in the habitable zone around its star.
291
00:31:33,881 --> 00:31:36,361
Now, admittedly, measurements
of the amount of water vapour
292
00:31:36,441 --> 00:31:37,881
in the atmosphere is pretty wide.
293
00:31:37,961 --> 00:31:42,321
It's somewhere between 0.01 percent
and 50 percent.
294
00:31:42,401 --> 00:31:44,561
I mean, this is a planet
that's a long way away.
295
00:31:44,641 --> 00:31:45,921
But, for comparison,
296
00:31:46,001 --> 00:31:51,521
our planet has a few percent
water vapour in its atmosphere.
297
00:31:51,641 --> 00:31:54,241
So, that observation is important
for two reasons.
298
00:31:54,321 --> 00:31:56,481
One is, it is not zero.
299
00:31:56,561 --> 00:31:58,881
There is water vapour in the atmosphere.
300
00:31:58,961 --> 00:32:02,561
But, secondly, if the measurement
is at the lower end,
301
00:32:02,641 --> 00:32:05,441
a few percent of water vapour
in the atmosphere,
302
00:32:05,521 --> 00:32:10,361
then that is consistent
with this world being a planet
303
00:32:10,441 --> 00:32:14,201
with oceans on its surface.
304
00:32:20,161 --> 00:32:22,921
The nature of this planet is
currently the subject
305
00:32:23,001 --> 00:32:25,361
of intense scientific debate.
306
00:32:27,001 --> 00:32:30,121
The planet may be
more like a mini-Neptune,
307
00:32:31,561 --> 00:32:33,161
a gas planet.
308
00:32:36,921 --> 00:32:40,961
But, it is possible to dream
of a rocky alien world
309
00:32:41,041 --> 00:32:43,321
with skies full of clouds,
310
00:32:47,641 --> 00:32:50,241
where water droplets collect,
311
00:32:52,081 --> 00:32:53,681
and eventually fall,
312
00:32:58,721 --> 00:33:00,961
Feeding vast oceans...
313
00:33:03,521 --> 00:33:07,681
That cover the surface
of a massive planet.
314
00:33:10,641 --> 00:33:12,281
A water world,
315
00:33:21,041 --> 00:33:23,161
Where the elixir of life...
316
00:33:25,001 --> 00:33:26,801
Is in plentiful supply.
317
00:33:34,121 --> 00:33:35,841
K2 78—b is exciting
318
00:33:35,921 --> 00:33:38,361
because it's the smallest world
319
00:33:38,441 --> 00:33:41,001
with an atmosphere
that we've been able to analyse.
320
00:33:41,081 --> 00:33:43,841
And we've found
that its mass and density,
321
00:33:43,921 --> 00:33:45,961
and composition of its atmosphere,
322
00:33:46,041 --> 00:33:50,081
and it's orbit are consistent
with it being a world with water.
323
00:33:51,921 --> 00:33:56,041
And it might be a world
with oceans on its surface.
324
00:33:56,121 --> 00:33:58,201
We don't know for sure,
325
00:33:58,281 --> 00:34:02,361
but just imagine
what that small, faraway world
326
00:34:02,441 --> 00:34:06,081
around a faint red star might be like.
327
00:34:13,561 --> 00:34:16,401
I(epler went on to make
many more discoveries...
328
00:34:28,201 --> 00:34:31,401
Until, in October 2078,
329
00:34:31,481 --> 00:34:33,961
it finally ran out of fuel.
330
00:34:40,641 --> 00:34:46,721
After nine years, it had found
over 2500 alien worlds...
331
00:34:53,761 --> 00:34:59,401
Showing us just how common
potentially earth-like planets might be.
332
00:35:12,561 --> 00:35:16,281
We estimate that there may
be around 20 billion
333
00:35:16,361 --> 00:35:18,681
potentially earth-like worlds,
334
00:35:18,761 --> 00:35:22,321
that's rocky planets
in the habitable zone around a star
335
00:35:22,401 --> 00:35:27,121
that may support liquid water
on the surface, in our galaxy.
336
00:35:27,201 --> 00:35:31,401
That is 20 billion
potential homes for life.
337
00:35:42,161 --> 00:35:44,441
Now, we don't know the probability
338
00:35:44,521 --> 00:35:48,561
that given the right conditions,
life will begin on a planet.
339
00:35:48,961 --> 00:35:51,961
But we do have evidence, from our world.
340
00:35:52,041 --> 00:35:54,161
What we know is that here on earth,
341
00:35:54,241 --> 00:35:56,961
life began pretty much
as soon as it could
342
00:35:57,041 --> 00:35:59,361
after the earth had formed
and cooled down,
343
00:35:59,441 --> 00:36:01,921
and the oceans formed on its surface.
344
00:36:02,001 --> 00:36:04,281
So that might suggest
that whilst there isn't
345
00:36:04,361 --> 00:36:06,681
a sense of inevitability
about the origin of life
346
00:36:06,761 --> 00:36:08,361
given the right conditions,
347
00:36:08,441 --> 00:36:12,001
it might, at least,
be reasonably probable.
348
00:36:12,081 --> 00:36:15,041
So, I think that there is
at least a chance
349
00:36:15,121 --> 00:36:19,321
that life may have begun
on some, perhaps many,
350
00:36:19,401 --> 00:36:23,121
of those 20 billion earth-like worlds
out there in our galaxy.
351
00:36:25,401 --> 00:36:29,401
But, I think there are
two questions about life.
352
00:36:29,481 --> 00:36:33,081
One question is about the origin,
and the existence of microbes,
353
00:36:33,161 --> 00:36:35,441
but often, when we speak about aliens,
354
00:36:35,521 --> 00:36:40,481
what we really mean is not microbes,
but complex creatures.
355
00:36:40,561 --> 00:36:44,321
Indeed, things that we can
speak to, civilisations.
356
00:36:44,401 --> 00:36:47,641
What is the probability there will be
other civilisations out there
357
00:36:47,721 --> 00:36:49,001
in the milky way?
358
00:36:49,361 --> 00:36:52,801
Well, again, the answer is,
we don't know.
359
00:36:52,881 --> 00:36:55,681
But there are observations we can make.
360
00:36:55,761 --> 00:36:58,641
Patterns we can see in the milky way
361
00:36:58,721 --> 00:37:01,921
that might allow us
to make an educated guess.
362
00:37:40,241 --> 00:37:42,201
We don't know precisely
363
00:37:42,281 --> 00:37:46,401
how we highly-intelligent
complex creatures came to be here.
364
00:37:56,561 --> 00:37:58,921
But, we do know, for certain,
365
00:37:59,001 --> 00:38:01,441
that life on earth didn't
begin this way.
366
00:38:04,961 --> 00:38:08,081
We are the product of a story
that has been playing out
367
00:38:08,161 --> 00:38:11,481
for over a quarter
of the age of the universe.
368
00:38:14,721 --> 00:38:16,281
From microbes...
369
00:38:17,401 --> 00:38:23,001
To a global technological civilisation,
reaching out for others.
370
00:38:24,921 --> 00:38:28,841
For now, at least,
we remain surrounded by silence.
371
00:38:28,921 --> 00:38:32,561
The messages we've sent out
into the cosmos remain unanswered,
372
00:38:32,641 --> 00:38:35,441
and the telescopes we use
to scan the skies
373
00:38:35,521 --> 00:38:38,481
for alien signals remain quiet.
374
00:38:38,561 --> 00:38:40,081
Now, that's not to say, of course,
375
00:38:40,161 --> 00:38:42,681
that there aren't
other civilisations out there.
376
00:38:42,761 --> 00:38:46,721
We may have been looking
for the wrong thing, in the wrong place.
377
00:38:46,841 --> 00:38:51,561
But I think the answer to the question
of the great silence can be found here,
378
00:38:51,641 --> 00:38:52,721
on earth.
379
00:38:52,801 --> 00:38:56,961
Because, here, it took
four billion years of stability
380
00:38:57,041 --> 00:38:58,601
for a civilisation to emerge.
381
00:38:58,681 --> 00:39:01,321
That is a vast amount of time.
382
00:39:01,401 --> 00:39:04,521
And when we look to the other worlds
out there in the milky way,
383
00:39:04,601 --> 00:39:08,561
it's those two things,
stability and time,
384
00:39:08,641 --> 00:39:12,161
that appear to be
very rare commodities indeed.
385
00:39:21,841 --> 00:39:27,081
In 2073, the European space agency
launched the gaia space telescope.
386
00:39:30,321 --> 00:39:35,561
Its mission, to survey the stars
of our galaxy, the milky way.
387
00:39:37,841 --> 00:39:40,641
Billions of stars have been mapped.
388
00:39:44,921 --> 00:39:49,881
Each star, a potential host
for alien worlds.
389
00:39:54,161 --> 00:39:57,961
And patterns are
already beginning to emerge.
390
00:40:11,961 --> 00:40:14,841
Not all stars exist alone.
391
00:40:20,241 --> 00:40:22,521
Some have company.
392
00:40:30,841 --> 00:40:32,761
And bizarre as they seem,
393
00:40:32,841 --> 00:40:35,401
gaia has discovered around a million
394
00:40:35,481 --> 00:40:38,961
of these binary
or multiple star systems.
395
00:40:43,561 --> 00:40:46,121
We've known for a long time
that binary star systems,
396
00:40:46,201 --> 00:40:49,281
and indeed, multiple star systems exist,
397
00:40:49,361 --> 00:40:52,881
but we didn't know
precisely how common they are.
398
00:40:55,041 --> 00:40:58,121
But now, we have
a huge amount of high-precision data,
399
00:40:58,201 --> 00:41:00,761
including the gaia data, which tells us
400
00:41:00,841 --> 00:41:05,081
that around 50 percent
of all sun-like stars are
401
00:41:05,161 --> 00:41:06,681
in multiple star systems.
402
00:41:06,761 --> 00:41:10,761
And for more massive stars,
that number is 80 percent.
403
00:41:15,641 --> 00:41:20,161
So, how does the prevalence
of multiple star systems in the galaxy
404
00:41:20,241 --> 00:41:23,801
shift the adds in the hunt
for another earth?
405
00:41:25,881 --> 00:41:30,961
Could earth-like planets exist
in multiple star systems?
406
00:41:31,041 --> 00:41:34,521
And if so, what might their fate be?
407
00:41:40,441 --> 00:41:43,881
In 2020, we may have found a clue.
408
00:41:44,921 --> 00:41:50,281
A planet the size of Mars, floating
freely through the galaxy.
409
00:41:52,001 --> 00:41:54,441
A so-called rogue world.
410
00:41:56,361 --> 00:41:59,961
But planets can't form alone
in interstellar space.
411
00:42:00,841 --> 00:42:02,681
So, where did it come from?
412
00:42:19,361 --> 00:42:20,921
Dawn...
413
00:42:28,201 --> 00:42:30,881
Ushered in not by one star...
414
00:42:35,561 --> 00:42:36,761
But two.
415
00:42:46,321 --> 00:42:50,281
Perhaps the rogue world grew up
in a close binary system.
416
00:43:04,361 --> 00:43:07,801
Subject to the gravitational pull
of two stars...
417
00:43:15,601 --> 00:43:18,001
Its orbit may have been unstable...
418
00:43:26,481 --> 00:43:30,681
As its parent stars fought
to control its destiny.
419
00:43:44,481 --> 00:43:46,921
But, even in single star systems,
420
00:43:47,001 --> 00:43:50,241
the weak gravitational interactions
between the planets
421
00:43:50,321 --> 00:43:51,961
can change their orbits.
422
00:43:52,041 --> 00:43:55,681
Now, in a double star system,
the planets are not only subjected
423
00:43:55,761 --> 00:43:57,961
to the gravitational pulls
of each other,
424
00:43:58,041 --> 00:44:00,841
they're subjected
to the stronger gravitational pull
425
00:44:00,921 --> 00:44:02,561
of another star.
426
00:44:02,641 --> 00:44:06,001
So, even if a planet gets
into a stable orbit,
427
00:44:06,081 --> 00:44:10,441
it's very likely that it won't
stay in that orbit for long.
428
00:44:10,521 --> 00:44:11,841
So, in double star systems,
429
00:44:11,921 --> 00:44:16,441
the line between order
and chaos is very thin indeed.
430
00:44:21,921 --> 00:44:25,041
Even subtle changes
in a planet's orbit can lead
431
00:44:25,121 --> 00:44:27,561
to dramatic changes in climate.
432
00:44:28,601 --> 00:44:33,681
And that's why the surface conditions
on planets in double star systems may
433
00:44:33,761 --> 00:44:37,921
be unlikely to remain
stable enough for long enough
434
00:44:38,001 --> 00:44:40,521
for intelligent life to evolve.
435
00:44:48,681 --> 00:44:51,641
And the changes
in the orbits of planets can
436
00:44:51,721 --> 00:44:55,481
sometimes be anything but subtle.
437
00:45:14,641 --> 00:45:16,761
A close encounter...
438
00:45:18,841 --> 00:45:22,921
May have given the rogue world
a final gravitational kick...
439
00:45:43,841 --> 00:45:45,601
Flinging it outwards...
440
00:45:49,481 --> 00:45:53,601
And releasing it
from the grip of its parent stars,
441
00:45:59,281 --> 00:46:01,201
Setting it loose...
442
00:46:06,601 --> 00:46:09,081
On a journey through the galaxy.
443
00:46:24,081 --> 00:46:26,641
Far from the warmth of its stars,
444
00:46:28,241 --> 00:46:32,321
any liquid water the rogue world
might once have had...
445
00:46:36,841 --> 00:46:38,521
Would have frozen solid.
446
00:46:44,001 --> 00:46:47,041
Any atmosphere that once protected it...
447
00:46:55,001 --> 00:46:58,321
Would have frozen out onto the surface.
448
00:47:02,361 --> 00:47:04,761
The rogue would have become a world...
449
00:47:07,401 --> 00:47:12,241
With conditions
that no living thing could endure.
450
00:47:15,161 --> 00:47:19,441
An entire planet alone and adrift,
451
00:47:26,281 --> 00:47:31,081
Only to be detected by us,
millions of years later.
452
00:47:32,921 --> 00:47:36,561
A small earth-like rogue planet...
453
00:47:38,361 --> 00:47:40,761
Roaming the darkness of space
454
00:47:41,561 --> 00:47:43,041
for eternity.
455
00:47:53,841 --> 00:47:57,921
This lonely, wandering planet is
not a unique world.
456
00:47:58,001 --> 00:48:00,321
Although rogue planets are
very difficult to detect,
457
00:48:00,401 --> 00:48:05,361
it's estimated that there may be
over 100 billion of them in our galaxy.
458
00:48:05,441 --> 00:48:08,601
Rogue planets might be
the most common type of planet
459
00:48:08,681 --> 00:48:09,681
in the milky way.
460
00:48:11,081 --> 00:48:13,081
And although we think
most of them were torn away
461
00:48:13,161 --> 00:48:15,881
from their star soon after formation,
462
00:48:16,481 --> 00:48:21,241
this does suggest that star systems are
not always stable places,
463
00:48:21,321 --> 00:48:25,121
where complex life could evolve
over billions of years.
464
00:48:37,681 --> 00:48:41,401
Our hunt for another living planet has
only just begun.
465
00:48:45,401 --> 00:48:47,881
Yet, we've already learnt so much.
466
00:48:54,921 --> 00:48:57,921
We found our first rocky worlds.
467
00:49:00,041 --> 00:49:03,881
Some in the habitable zone
around their stars.
468
00:49:12,241 --> 00:49:17,441
Some, potentially,
with liquid water on the surface.
469
00:49:18,761 --> 00:49:23,881
Candidate worlds for future missions
to search for evidence of life.
470
00:49:29,081 --> 00:49:33,281
But we've also found hordes
of bizarre, tortured worlds,
471
00:49:35,761 --> 00:49:38,001
orbiting around violent stars,
472
00:49:46,601 --> 00:49:49,601
And a multitude of rogue planets...
473
00:49:51,561 --> 00:49:56,201
Where complex life,
as we understand it, seems impossible.
474
00:50:04,641 --> 00:50:08,921
Perhaps it's these worlds
that hint at the reason why,
475
00:50:10,561 --> 00:50:14,441
for now, one planet stands apart...
476
00:50:20,161 --> 00:50:21,441
Alone.
477
00:50:34,161 --> 00:50:37,561
Our planet seems to have
largely escaped the violence,
478
00:50:37,641 --> 00:50:40,001
the chaos, and the constant change
479
00:50:40,081 --> 00:50:42,721
that seems to characterise
a galaxy like the milky way.
480
00:50:43,321 --> 00:50:46,161
Yes, there's been
the odd mass extinction,
481
00:50:46,241 --> 00:50:49,361
but there's been
an unbroken chain of life here on earth,
482
00:50:49,441 --> 00:50:52,441
stretching back four billion years.
483
00:50:52,521 --> 00:50:54,041
And if that's what you need
484
00:50:54,121 --> 00:50:57,001
to go from the origin of life
to a civilisation,
485
00:50:57,081 --> 00:51:01,441
then, although there may be billions
of worlds out there where life began,
486
00:51:01,521 --> 00:51:04,881
there may be very few civilisations.
487
00:51:04,961 --> 00:51:09,481
But that's just an opinion.
It's an educated guess.
488
00:51:09,561 --> 00:51:12,241
And, given the profound nature
of the question,
489
00:51:12,321 --> 00:51:15,241
no matter how educated the guess,
490
00:51:15,321 --> 00:51:18,801
I think it would be ridiculous
for us to stop looking
491
00:51:18,881 --> 00:51:22,361
both inside our galaxy and beyond.
492
00:51:25,721 --> 00:51:29,081
For, we may ha ve just received
the first glimpse...
493
00:51:30,441 --> 00:51:33,601
Of a world beyond the milky way...
494
00:51:41,761 --> 00:51:44,761
Around 30 million light years away,
495
00:51:44,881 --> 00:51:48,961
nestled in the spiral arms
of the whirlpool galaxy.
496
00:51:53,561 --> 00:51:56,121
A world the size of saturn.
497
00:52:04,601 --> 00:52:08,041
A find that marks
an expansion of our horizons.
498
00:52:13,201 --> 00:52:17,441
The beginning of the hunt
for extra -galactic planets.
499
00:52:21,121 --> 00:52:24,481
The potential disco very
of a planet orbiting around a star,
500
00:52:24,561 --> 00:52:28,601
in another galaxy is something
that I never thought I 'd see.
501
00:52:28,681 --> 00:52:31,561
And it opens up
the intriguing possibility
502
00:52:31,641 --> 00:52:34,161
that we might be able to explore
not only the question,
503
00:52:34,241 --> 00:52:39,041
"are we alone in our galaxy?"
But, "are we alone in the universe?"
504
00:52:42,241 --> 00:52:46,961
And the answer to that question
may lie far in the future.
505
00:52:47,041 --> 00:52:49,521
We might never answer that question.
506
00:52:49,601 --> 00:52:53,841
But I said, the question
”are we alone?” is profound,
507
00:52:53,921 --> 00:52:55,721
because answering it would teach us
508
00:52:55,801 --> 00:52:58,641
much more
about what it means to be human.
509
00:53:02,761 --> 00:53:06,121
Well, I think we become
a little bit more human
510
00:53:06,201 --> 00:53:08,921
with every world that we explore,
511
00:53:09,001 --> 00:53:12,801
because that ability
to lay the foundations,
512
00:53:12,881 --> 00:53:17,841
to explore questions to which we may
never receive answers in our lifetime,
513
00:53:17,921 --> 00:53:21,801
questions for our children
or our grandchildren to answer,
514
00:53:21,881 --> 00:53:25,361
is a fundamental part
of what it means to be human.
515
00:53:25,441 --> 00:53:30,081
It's a fundamental part
of what makes us so special,
516
00:53:30,161 --> 00:53:32,561
here on this little world,
517
00:53:32,641 --> 00:53:37,761
looking up at the stars,
whether we're alone or not.
518
00:53:53,961 --> 00:53:58,441
Man: Five. Four. Three. Two.
519
00:53:58,521 --> 00:54:00,521
Engines start. One. Zero.
520
00:54:00,601 --> 00:54:04,001
And lift off
of the delta ii rocket with I(Epler,
521
00:54:04,081 --> 00:54:05,761
on a search for planets,
522
00:54:05,841 --> 00:54:09,401
in some way, like our own.
523
00:54:09,481 --> 00:54:12,361
We had worked together, thousands
of people worked together,
524
00:54:12,441 --> 00:54:14,881
and it's all coming together.
525
00:54:15,961 --> 00:54:17,521
Man over radio: And we have separation.
526
00:54:19,201 --> 00:54:22,121
Sara seager: It was so emotional to see
the project they had worked on
527
00:54:22,201 --> 00:54:25,401
for so many years or decades
finally go to space,
528
00:54:25,481 --> 00:54:29,441
and all that hope and promise,
all bundled up in the machinery.
529
00:54:37,081 --> 00:54:39,441
Cox: I(Epler was an immediate success,
530
00:54:39,521 --> 00:54:44,281
discovering over 2, 000 new planets
in its first four years of operation.
531
00:54:50,161 --> 00:54:52,361
But in the summer of 2072,
532
00:54:52,441 --> 00:54:55,841
the team faced a challenge
that threatened the entire mission.
533
00:55:00,001 --> 00:55:02,561
One of the things that
the kepler mission needs to operate
534
00:55:02,641 --> 00:55:04,961
are reaction wheels
that spin and hold it on target.
535
00:55:07,601 --> 00:55:11,201
So, it always points
at the same stars, and doesn'tjiggle.
536
00:55:11,281 --> 00:55:13,201
Well, we had four wheels that did that.
537
00:55:15,401 --> 00:55:18,361
Gibor basri: And we knew that we only
had a couple of spare gyroscopes,
538
00:55:18,441 --> 00:55:22,201
and we knew that spacecraft tend
to have gyros fail.
539
00:55:27,081 --> 00:55:28,921
William borucki:
And after a while, it failed.
540
00:55:29,001 --> 00:55:31,521
Three months later,
the second one failed.
541
00:55:31,601 --> 00:55:32,801
And, since we needed three,
542
00:55:32,881 --> 00:55:36,161
we could no longer look
at the kepler field of view.
543
00:55:38,801 --> 00:55:41,881
I had hope that they'll figure out
a way to work with two gyros,
544
00:55:41,961 --> 00:55:43,241
and, indeed, they did.
545
00:55:47,561 --> 00:55:50,921
Bo ru cki: So, the very clever people,
the engineers and scientists said,
546
00:55:51,001 --> 00:55:55,681
”what we can use, is we'll use
the sunshine for the third wheel.
547
00:55:55,761 --> 00:55:58,001
"We'll make this thing
reflect sunlight off it,
548
00:55:58,081 --> 00:56:01,001
"we'll use the other two wheels,
and now, we can point in the sky."
549
00:56:03,881 --> 00:56:08,601
Cox: The faint pressure of sunlight
helped stabilise the telescope.
550
00:56:09,081 --> 00:56:11,081
Basri: That was, kind of,
good news, actually,
551
00:56:11,161 --> 00:56:15,081
because it meant kepler was gonna
have to go off the kepler field now,
552
00:56:15,161 --> 00:56:18,521
and we could get all kinds
of other stars and observe them,
553
00:56:18,601 --> 00:56:21,721
and so, it actually was a boon
for stellar astronomy.
554
00:56:24,361 --> 00:56:27,201
Cox: After another four years
of disco veries,
555
00:56:27,281 --> 00:56:32,121
in total, it had found
over 2, 600 planets,
556
00:56:32,201 --> 00:56:37,081
making it, by far, our most successful
planet-hunter to date.
557
00:56:40,041 --> 00:56:44,041
Borucki: It was sad when they sent
the command to shut everything down.
558
00:56:44,121 --> 00:56:45,761
You know, it's asleep now.
559
00:56:45,841 --> 00:56:49,721
It's in orbit around the sun.
It will continue that orbit.
560
00:56:49,801 --> 00:56:52,881
But, since it launched from earth,
it will come back to earth.
561
00:56:52,961 --> 00:56:56,721
It will come and visit us again
in about 40 years,
562
00:56:56,801 --> 00:56:58,961
and my hope is people will say,
563
00:56:59,041 --> 00:57:02,601
"this is a historic telescope.
It told us about all these planets",
564
00:57:02,681 --> 00:57:05,081
and they will go up
and pick up this telescope
565
00:57:05,161 --> 00:57:06,281
and bring it back to earth,
566
00:57:06,361 --> 00:57:10,441
and put in the air and space museum
for us all to admire.
45214
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