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♪♪
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At this precise moment,
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on a planet far, far away...
4
00:00:18,869 --> 00:00:22,350
an alien sunrise ushers in
a new day.
5
00:00:28,084 --> 00:00:32,427
♪♪
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But will alien eyes
gaze upon it?
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For me, the most exciting
question in the universe
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is whether or not there are
inhabited planets
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other than the Earth.
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♪♪
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What are the chances that
out there in the Milky Way,
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there is other complex, advanced
life like our own?
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♪♪
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Today, our telescopes
are combing the skies,
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discovering bizarre worlds...
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Even in places
they shouldn't be.
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We didn't even know that that
kind of planet existed.
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So it completely shocked
our theories of planets
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and how they form.
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♪♪
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Will we ever find a world
that resembles our home?
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Earth-like planets
that orbit their stars
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at the same distance
we orbit the sun
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are very difficult to detect.
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Looking for life is not easy,
and we're going to get
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constant setbacks.
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♪♪
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Are we finally on the verge of
answering the ultimate question:
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are we alone?
30
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I think we'll actually find the
answer while I'm still alive.
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At least I hope so.
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♪♪
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The search is on.
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"Alien Worlds."
35
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Right now, on "NOVA."
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♪♪
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♪ See me when I float
like a dove ♪
38
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♪ The skies above are lined
with trees ♪
39
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♪ I'm on my knees,
begging please ♪
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♪ Come and take me away ♪
41
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♪♪
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The Milky Way,
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our galaxy.
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As many as 400 billion stars.
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♪♪
46
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Spread across 100,000
light-years.
47
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Among these stars, the sun,
48
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with eight planets orbiting
around it...
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Including our home.
50
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Humans have been looking up
at the stars for millennia.
51
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I think we're just so curious
about it,
52
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yet we don't really know
what's out there.
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♪♪
54
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Not only what, but who?
55
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We've gotten to the point
in astrophysics where I think
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the big question on everyone's
mind really is: are we alone?
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♪♪
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Is all life like us
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and will we recognize it
when we see it?
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♪♪
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00:04:03,743 --> 00:04:09,940
Today, we stand on the brink
of answering these questions.
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What is different today is that
we have a chance
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to actually address some of
these issues quantitatively,
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scientifically.
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Not just sheer speculation
and philosophically.
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If and when we do find life,
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it's going to completely change
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the way we view ourselves,
our planet, our universe.
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♪♪
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00:04:40,027 --> 00:04:44,435
Over the last 50 years,
humanity's robotic space probes
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have found their way to every
planet in our solar system.
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♪♪
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And even some of their moons.
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♪♪
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But so far,
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no convincing evidence of life
has been discovered.
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♪♪
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As far as we know,
Earth remains one of a kind.
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♪♪
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The only world where chemistry
gave rise to biology.
81
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But even as the exploration
of the solar system continues,
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another quest has begun to
discover other planets out there
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orbiting distant stars:
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exoplanets.
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It's really only in the last
few decades that we've had
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the ability to search for
exoplanets.
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♪♪
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And from the start,
scientists dream of finding one
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00:06:08,082 --> 00:06:11,465
that might host life
like our own.
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00:06:11,506 --> 00:06:13,339
It's completely reasonable
to expect that alien life
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will be quite different from
the life we find on Earth.
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But Earth is the only place
in the galaxy that we know
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for sure hosts life.
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So we start there...
Looking for an Earth twin.
95
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And then the question becomes:
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how common are Earths
across the galaxy?
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♪♪
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Over the last three decades,
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00:06:36,975 --> 00:06:39,823
scientists have deployed
some of the most
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00:06:39,855 --> 00:06:43,085
powerful telescopes on Earth.
101
00:06:43,119 --> 00:06:48,749
And used a clever technique to
detect the presence of planets
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that are too dim to see next
to the bright stars they orbit.
103
00:06:58,093 --> 00:06:59,446
Many teams started to look
for planets
104
00:06:59,469 --> 00:07:01,259
using the same technique.
105
00:07:01,293 --> 00:07:03,814
This is the Doppler technique,
or the wobble technique.
106
00:07:03,853 --> 00:07:07,683
The way the wobble method works
107
00:07:07,725 --> 00:07:08,853
is that you can imagine
that you've got
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00:07:08,876 --> 00:07:10,917
two dance partners, okay?
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One is the star
and one is the planet,
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00:07:14,507 --> 00:07:16,712
but you don't see the planet
111
00:07:16,748 --> 00:07:18,439
because it doesn't put out
much light.
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00:07:18,476 --> 00:07:22,088
And so if we look very carefully
at the star, we can see that
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00:07:22,123 --> 00:07:24,131
the star appears to be moving
away from us
114
00:07:24,171 --> 00:07:27,554
and towards us,
back and forth over time.
115
00:07:27,594 --> 00:07:30,944
And we can deduce just from a
basic understanding of gravity
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00:07:30,986 --> 00:07:32,961
that there must be something
else there
117
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and even measure its mass.
118
00:07:37,897 --> 00:07:40,615
But what astronomers discover
119
00:07:40,649 --> 00:07:46,498
is something completely
unexpected.
120
00:07:46,536 --> 00:07:48,241
The first-ever exoplanet
that was discovered
121
00:07:48,264 --> 00:07:49,639
around a sun-like star
122
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was 51 Pegasi b in 1995.
123
00:07:53,032 --> 00:07:57,539
♪♪
124
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51 Pegasi b is a gas giant.
125
00:08:07,462 --> 00:08:13,758
Around half the mass of Jupiter,
but so close to its star
126
00:08:13,798 --> 00:08:16,766
that part of its atmosphere
may have been ripped away.
127
00:08:20,421 --> 00:08:23,553
These planets are baked
by their stars' radiation.
128
00:08:23,589 --> 00:08:25,859
The temperatures are in
the thousands.
129
00:08:25,892 --> 00:08:29,570
♪♪
130
00:08:29,604 --> 00:08:31,501
Many astronomers didn't believe
it because the planet
131
00:08:31,524 --> 00:08:34,459
was in the wrong place.
132
00:08:34,500 --> 00:08:35,995
It was enormous,
133
00:08:36,036 --> 00:08:37,979
it was massive,
and yet it was parked
134
00:08:38,019 --> 00:08:41,086
right next to its star.
135
00:08:41,123 --> 00:08:42,412
And a planet has no business
being there.
136
00:08:42,435 --> 00:08:44,410
There's not enough material
137
00:08:44,451 --> 00:08:46,972
around a forming star to make
a planet that close to the star.
138
00:08:47,010 --> 00:08:54,332
♪♪
139
00:08:54,370 --> 00:08:57,218
Its skies whipped into
titanic winds...
140
00:09:02,017 --> 00:09:07,931
and a hot interior, pelted by
raindrops of molten iron.
141
00:09:07,969 --> 00:09:13,665
♪♪
142
00:09:13,696 --> 00:09:15,125
The discovery of 51 Peg
143
00:09:15,168 --> 00:09:17,340
meant that we had to tear up
the rulebook.
144
00:09:17,375 --> 00:09:20,474
♪♪
145
00:09:20,511 --> 00:09:23,195
We were hoping to discover
a planet,
146
00:09:23,231 --> 00:09:25,207
something like what we see
in the solar system,
147
00:09:25,247 --> 00:09:28,957
but instead found a planet
that had absolutely no analogue
148
00:09:28,991 --> 00:09:30,966
in the solar system, and no one
could have predicted
149
00:09:31,007 --> 00:09:32,830
that such planets
were even possible.
150
00:09:32,862 --> 00:09:38,132
♪♪
151
00:09:38,174 --> 00:09:41,720
And other discoveries
were stranger still.
152
00:09:41,949 --> 00:09:46,106
Planets blasted by
fierce radiation.
153
00:09:46,141 --> 00:09:49,207
♪♪
154
00:09:52,029 --> 00:09:55,706
Their surfaces battered
and stripped
155
00:09:55,740 --> 00:09:59,897
by the high-energy
strobing light of their star.
156
00:09:59,931 --> 00:10:07,034
♪♪
157
00:10:07,067 --> 00:10:11,857
Rocky worlds large enough
to hold on to some atmosphere,
158
00:10:11,898 --> 00:10:15,314
but so cold that the entire
surface has frozen over.
159
00:10:19,833 --> 00:10:23,795
♪♪
160
00:10:23,833 --> 00:10:26,681
And great puffy planets
161
00:10:26,713 --> 00:10:31,154
with an average density
like Styrofoam.
162
00:10:31,192 --> 00:10:36,146
♪♪
163
00:10:39,864 --> 00:10:43,694
And with diamond-crushing
pressures at their centers.
164
00:10:49,590 --> 00:10:54,413
These discoveries electrified
the world's astronomers.
165
00:10:54,454 --> 00:10:59,211
At long last, confirmation that
there are other solar systems
166
00:10:59,253 --> 00:11:04,556
out there, inhospitable
though they might be.
167
00:11:04,597 --> 00:11:07,019
These worlds are truly
amazing places,
168
00:11:07,060 --> 00:11:10,443
and we've learnt so much about
the physics and the chemistry
169
00:11:10,485 --> 00:11:13,868
of a world like this,
but they are not places
170
00:11:14,100 --> 00:11:17,362
to look for life.
171
00:11:17,396 --> 00:11:21,488
Because these are worlds
too bizarre, too large,
172
00:11:21,523 --> 00:11:24,077
and often too close
to their stars
173
00:11:24,115 --> 00:11:28,174
for living things to survive.
174
00:11:28,211 --> 00:11:30,961
Like any major scientific
revolution,
175
00:11:30,995 --> 00:11:33,963
looking for life is going to be
filled with setbacks
176
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and many false positives.
177
00:11:37,554 --> 00:11:38,536
But we have to keep on.
178
00:11:38,578 --> 00:11:41,448
♪♪
179
00:11:41,489 --> 00:11:45,102
It's a lot easier to find
something that's big
180
00:11:45,137 --> 00:11:46,458
and far away rather than
something that's small
181
00:11:46,481 --> 00:11:48,205
and far away.
182
00:11:48,240 --> 00:11:51,088
So the fact that we've found
more large planets
183
00:11:51,120 --> 00:11:53,903
is not an indication of what's
actually out there.
184
00:11:53,936 --> 00:11:55,661
It's just a matter of what's
easier to find.
185
00:11:55,696 --> 00:11:59,723
♪♪
186
00:11:59,759 --> 00:12:06,088
Finding planets like Earth would
take an extraordinary mission.
187
00:12:06,127 --> 00:12:08,088
We really needed a space mission
dedicated to finding
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00:12:08,111 --> 00:12:10,446
Earth-sized planets
in our galaxy,
189
00:12:10,478 --> 00:12:12,933
and ideally, enough of them
to give us real insights.
190
00:12:12,974 --> 00:12:14,950
♪♪
191
00:12:14,990 --> 00:12:16,136
The solution?
192
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A telescope
almost 20 years in the making.
193
00:12:20,429 --> 00:12:22,797
I was working for NASA Ames.
194
00:12:22,829 --> 00:12:25,547
I realized that if we were going
to find Earth-size planets,
195
00:12:25,581 --> 00:12:28,996
we had to build a photometer
that was good enough to see
196
00:12:29,037 --> 00:12:30,444
these small, Earth-size planets
197
00:12:30,476 --> 00:12:33,826
and find out about them.
198
00:12:33,868 --> 00:12:38,309
Some 17 years after I started,
NASA headquarters said, "Yes.
199
00:12:38,347 --> 00:12:41,893
We will build that mission."
200
00:12:41,932 --> 00:12:45,347
I was very privileged to be
at the Kepler launch,
201
00:12:45,387 --> 00:12:48,900
and we were all incredibly
nervous a few days before,
202
00:12:49,130 --> 00:12:50,675
because the previous mission
that had launched
203
00:12:50,698 --> 00:12:53,601
on the same rocket had failed.
204
00:12:53,642 --> 00:12:55,432
Their satellite went...
205
00:12:55,466 --> 00:12:57,223
Went down in Antarctica.
206
00:12:57,257 --> 00:12:59,233
And we were, like, "Uh-oh, no."
207
00:12:59,273 --> 00:13:01,379
So we were very nervous.
208
00:13:01,609 --> 00:13:05,800
T minus ten, nine, eight,
209
00:13:05,832 --> 00:13:08,102
seven, six, five,
210
00:13:08,328 --> 00:13:13,118
four, three, two...
211
00:13:13,160 --> 00:13:16,509
Engine start, one, zero,
and lift-off
212
00:13:16,551 --> 00:13:20,327
of the Delta 2 rocket with
Kepler on a search for planets
213
00:13:20,359 --> 00:13:22,018
in some way like our own.
214
00:13:26,919 --> 00:13:32,036
♪♪
215
00:13:32,070 --> 00:13:33,295
And we have separation!
216
00:13:33,318 --> 00:13:37,213
It was a spectacular
night launch.
217
00:13:37,253 --> 00:13:39,523
Kepler was launched without
a single flaw.
218
00:13:39,557 --> 00:13:44,893
NASA's Kepler Space Telescope
takes the search
219
00:13:44,932 --> 00:13:48,316
above Earth's atmosphere
into space.
220
00:13:51,045 --> 00:13:54,973
Kepler travels 94 million miles
away...
221
00:14:03,491 --> 00:14:07,932
until it arrives on a stable
orbit around the sun,
222
00:14:07,970 --> 00:14:14,299
where it looks out
with a fixed and clear gaze
223
00:14:14,337 --> 00:14:18,048
to a single patch of sky
in the constellations
224
00:14:18,081 --> 00:14:21,017
of Cygnus, Lyra, and Draco.
225
00:14:21,057 --> 00:14:24,767
♪♪
226
00:14:29,408 --> 00:14:31,863
What was special finally
was, the lid opens up
227
00:14:31,904 --> 00:14:34,272
and we see the nighttime sky.
228
00:14:34,304 --> 00:14:37,370
What we see is, the sky is
covered with star.
229
00:14:37,600 --> 00:14:38,568
Every detector is working.
230
00:14:38,591 --> 00:14:45,018
♪♪
231
00:14:45,054 --> 00:14:49,812
Exposing 42 incredibly sensitive
light sensors
232
00:14:49,854 --> 00:14:56,084
to the light of 150,000 stars...
233
00:14:56,125 --> 00:14:59,290
♪♪
234
00:14:59,325 --> 00:15:01,214
Kepler begins its search
235
00:15:01,245 --> 00:15:04,181
for Earth-like worlds.
236
00:15:23,163 --> 00:15:25,028
The problem with finding
exoplanets is,
237
00:15:25,051 --> 00:15:26,874
they just don't shine at all
238
00:15:26,907 --> 00:15:31,064
and they're around
really bright stars.
239
00:15:31,098 --> 00:15:32,986
That makes them virtually
impossible to image.
240
00:15:33,018 --> 00:15:37,525
So, astronomers came up
with a different method,
241
00:15:37,561 --> 00:15:41,905
and that's called
the transit method.
242
00:15:41,945 --> 00:15:44,400
Kepler uses the transit method
for discovering planets
243
00:15:44,441 --> 00:15:45,489
around other stars.
244
00:15:45,528 --> 00:15:47,700
And it's really simple.
245
00:15:47,737 --> 00:15:51,927
A star is bright,
and if a planet is orbiting it,
246
00:15:51,960 --> 00:15:54,830
if the planet passes in front of
the face of the star,
247
00:15:54,872 --> 00:15:57,393
the planet blocks
some of that light
248
00:15:57,432 --> 00:15:59,538
and the star temporarily
appears dimmer.
249
00:15:59,575 --> 00:16:02,543
So, if we were to bring that
down to Earth,
250
00:16:02,583 --> 00:16:06,196
imagine this lighthouse is your
star, is your source of light.
251
00:16:06,231 --> 00:16:09,232
If a moth flies in front of
that light,
252
00:16:09,271 --> 00:16:12,687
even though to your naked eye
the light looks the same,
253
00:16:12,726 --> 00:16:15,061
it actually has become
a little bit dimmer
254
00:16:15,094 --> 00:16:17,069
because the light has been
blocked by the moth.
255
00:16:17,109 --> 00:16:18,965
That's the transit method.
256
00:16:18,997 --> 00:16:23,700
♪♪
257
00:16:33,236 --> 00:16:36,946
At the time the largest camera
ever launched into space...
258
00:16:39,988 --> 00:16:45,902
Kepler is able to look for
smaller, more Earth-like worlds:
259
00:16:45,939 --> 00:16:48,361
those too small to be
easily found
260
00:16:48,403 --> 00:16:52,560
using terrestrial telescopes.
261
00:16:52,594 --> 00:16:55,911
Soon, it starts to spot planets.
262
00:16:55,953 --> 00:16:57,210
The amount of dimming
263
00:16:57,234 --> 00:17:00,136
and the time between
each dimming event gave us clues
264
00:17:00,177 --> 00:17:03,048
to a planet's size and its
distance from its star.
265
00:17:03,089 --> 00:17:07,083
And with every world it finds,
266
00:17:07,120 --> 00:17:13,165
astronomers hold their breath,
267
00:17:13,200 --> 00:17:16,496
hoping for a rocky planet
that might in some way
268
00:17:16,527 --> 00:17:22,125
remind them of Earth:
269
00:17:22,159 --> 00:17:25,062
worlds like Kepler-36b.
270
00:17:25,103 --> 00:17:29,806
♪♪
271
00:17:40,302 --> 00:17:43,880
♪♪
272
00:17:43,917 --> 00:17:46,252
Orbiting a star similar
to our own.
273
00:17:46,285 --> 00:17:49,580
At first glance,
274
00:17:49,612 --> 00:17:55,810
a planet that resembles ours.
275
00:17:55,852 --> 00:17:58,700
So when we started finding these
rocky planets like Kepler-36b,
276
00:17:58,732 --> 00:18:00,423
that were getting closer
to Earth mass,
277
00:18:00,460 --> 00:18:01,687
it was just the greatest
feeling.
278
00:18:04,651 --> 00:18:09,125
Weighing in at around four times
the mass of our own planet,
279
00:18:09,162 --> 00:18:11,399
we'd found one of the first
rocky worlds
280
00:18:11,434 --> 00:18:14,915
that could have an atmosphere.
281
00:18:14,954 --> 00:18:18,151
A so-called Super-Earth.
282
00:18:26,505 --> 00:18:28,131
What's so cool about Kepler
283
00:18:28,168 --> 00:18:31,998
is that it tells us so much more
than just, the planets exist.
284
00:18:32,041 --> 00:18:34,911
We get their sizes, we get their
orbital characteristics,
285
00:18:34,952 --> 00:18:36,611
we can get their masses.
286
00:18:36,647 --> 00:18:38,175
And so what we're learning
287
00:18:38,215 --> 00:18:40,867
is not just that the planets
are there,
288
00:18:40,903 --> 00:18:43,043
but what these planets are like.
289
00:18:48,807 --> 00:18:55,517
♪♪
290
00:18:55,558 --> 00:18:59,420
But the more closely we examine
Kepler-36b,
291
00:18:59,653 --> 00:19:01,891
the clearer it becomes
292
00:19:01,925 --> 00:19:07,043
that this is not a world like
our own.
293
00:19:07,077 --> 00:19:10,209
Finding exoplanets
in the Kepler data,
294
00:19:10,244 --> 00:19:12,317
you really have to do some
detective work.
295
00:19:12,357 --> 00:19:16,351
You're trying to find a signal
that's less than one percent
296
00:19:16,388 --> 00:19:18,560
of all the other things that are
going on in that data.
297
00:19:21,475 --> 00:19:26,080
The light from the star dims
every 14 days,
298
00:19:26,115 --> 00:19:29,825
the length of a year
for the orbiting planet.
299
00:19:29,858 --> 00:19:33,721
This rocky world orbits
incredibly close.
300
00:19:33,762 --> 00:19:37,592
And it has company...
301
00:19:37,633 --> 00:19:41,344
A gigantic gassy companion
planet.
302
00:19:44,961 --> 00:19:47,274
The discovery of the Kepler-36
system is really interesting
303
00:19:47,297 --> 00:19:50,167
because the first planet found
was Kepler-36c.
304
00:19:50,208 --> 00:19:51,965
That's a gas giant planet.
305
00:19:52,000 --> 00:19:56,954
♪♪
306
00:19:56,992 --> 00:20:01,083
The two planets have
unusually close orbits,
307
00:20:01,119 --> 00:20:03,291
creating bizarre conditions
308
00:20:03,327 --> 00:20:08,794
on the surface of Kepler-36b.
309
00:20:08,831 --> 00:20:11,701
Kepler-36b,
in many ways, is Earth-like,
310
00:20:11,742 --> 00:20:15,704
but it also is very
un-Earth-like
311
00:20:15,742 --> 00:20:17,499
in pretty profound ways
312
00:20:17,533 --> 00:20:19,738
that mean it's unlikely to have
life on its surface.
313
00:20:19,773 --> 00:20:26,233
♪♪
314
00:20:26,269 --> 00:20:28,987
Thanks to its close-by star,
315
00:20:29,020 --> 00:20:33,723
the planet's rotation becomes
tidally locked.
316
00:20:33,756 --> 00:20:36,277
One face rests permanently
317
00:20:36,316 --> 00:20:38,837
under its star's bright glare.
318
00:20:38,875 --> 00:20:45,302
♪♪
319
00:20:45,339 --> 00:20:49,082
Punishing heat likely turns
the ground molten...
320
00:20:49,114 --> 00:20:54,930
♪♪
321
00:20:54,969 --> 00:20:58,134
Creating rivers of lava
that crisscross the surface.
322
00:21:00,857 --> 00:21:03,727
On top of that,
323
00:21:03,769 --> 00:21:07,315
every 97 days,
the immense gravitational pull
324
00:21:07,352 --> 00:21:10,931
from the gas giant may trigger
325
00:21:11,160 --> 00:21:16,311
intense volcanism
on the smaller planet
326
00:21:16,343 --> 00:21:21,101
each time it passes between
the giant and the star...
327
00:21:21,143 --> 00:21:24,177
♪♪
328
00:21:24,215 --> 00:21:28,820
Throwing lava high
in violent eruptions.
329
00:21:31,799 --> 00:21:36,306
♪♪
330
00:21:46,197 --> 00:21:50,900
♪♪
331
00:21:54,772 --> 00:21:59,377
But Kepler-36b is a planet
of molten rock,
332
00:21:59,412 --> 00:22:02,729
fire, and ice,
333
00:22:02,771 --> 00:22:06,928
because its far side permanently
faces away from the star...
334
00:22:10,322 --> 00:22:14,960
creating a frigid hemisphere
shrouded in eternal darkness...
335
00:22:18,834 --> 00:22:25,457
where magma freezes into a
strange, desolate landscape.
336
00:22:25,489 --> 00:22:27,017
The Kepler-36 system
337
00:22:27,057 --> 00:22:30,374
is a perfect example of how
exoplanets are completely
338
00:22:30,416 --> 00:22:32,090
different to what we know
in the solar system.
339
00:22:32,113 --> 00:22:38,278
♪♪
340
00:22:38,512 --> 00:22:43,051
Kepler-36b is just one of
the first among hundreds
341
00:22:43,087 --> 00:22:45,902
of Super-Earth-size planets
342
00:22:45,935 --> 00:22:49,481
that the Kepler telescope
discovers.
343
00:22:49,518 --> 00:22:54,025
The more scientists look,
the more they find.
344
00:22:54,062 --> 00:22:55,767
At the time that the Kepler
mission launched,
345
00:22:55,790 --> 00:23:00,013
the team was hoping they might
find a few exciting planets
346
00:23:00,046 --> 00:23:02,185
and they were very prepared
to analyze those data.
347
00:23:02,221 --> 00:23:05,092
Within the first few months, we
realized that we did not have
348
00:23:05,133 --> 00:23:08,549
enough people to handle
the deluge of planets.
349
00:23:08,589 --> 00:23:15,594
♪♪
350
00:23:15,628 --> 00:23:19,272
The mission shows beyond doubt
that our galaxy is home
351
00:23:19,308 --> 00:23:23,400
to a multitude of diverse
alien worlds.
352
00:23:23,627 --> 00:23:28,003
♪♪
353
00:23:28,043 --> 00:23:30,433
Kepler was a game-changer
for exoplanets.
354
00:23:30,474 --> 00:23:33,704
It was a game-changer for us
here on Earth,
355
00:23:33,738 --> 00:23:38,473
understanding that there are
planets in their thousands,
356
00:23:38,506 --> 00:23:43,176
in their millions, in their
billions in our galaxy alone.
357
00:23:43,209 --> 00:23:48,228
♪♪
358
00:23:48,264 --> 00:23:49,521
We suddenly had this
new problem.
359
00:23:49,544 --> 00:23:52,163
We had gone from just having
a handful of planets
360
00:23:52,200 --> 00:23:54,622
to hundreds of planets
to look through.
361
00:23:54,664 --> 00:23:56,934
So, we needed to tighten
the net, focusing on planets
362
00:23:56,968 --> 00:23:58,430
that didn't just resemble
Earth's size,
363
00:23:58,471 --> 00:23:59,716
but its habitability.
364
00:23:59,751 --> 00:24:03,647
♪♪
365
00:24:03,687 --> 00:24:06,917
Now that they have discovered
that planets are plentiful,
366
00:24:06,950 --> 00:24:11,293
astronomers must narrow
their search to home in on
367
00:24:11,335 --> 00:24:13,059
hard-to-find planets.
368
00:24:16,870 --> 00:24:21,660
Rocky worlds that hold the one
precious ingredient that makes
369
00:24:21,702 --> 00:24:24,353
Earth a living world.
370
00:24:29,573 --> 00:24:35,072
♪♪
371
00:24:38,500 --> 00:24:44,413
Everything we know about life
372
00:24:44,451 --> 00:24:49,405
we've discovered by looking
at ourselves and our world.
373
00:24:49,442 --> 00:24:54,843
♪♪
374
00:24:54,882 --> 00:24:57,022
Life on Earth is extremely
diverse.
375
00:24:57,058 --> 00:25:01,565
Millions and millions of species
of all kinds.
376
00:25:01,602 --> 00:25:06,458
And these endless
beautiful forms
377
00:25:06,497 --> 00:25:10,807
occupy just about every
available niche on the planet.
378
00:25:10,849 --> 00:25:15,356
♪♪
379
00:25:15,392 --> 00:25:17,629
We've had the opportunity
to explore a variety
380
00:25:17,856 --> 00:25:19,285
of extreme environments,
381
00:25:19,328 --> 00:25:23,103
and in pretty much all of them,
we find life.
382
00:25:23,136 --> 00:25:25,308
Earth has taught us that,
383
00:25:25,535 --> 00:25:27,805
given the right conditions,
384
00:25:27,838 --> 00:25:29,912
life is remarkably adaptable...
385
00:25:29,951 --> 00:25:34,490
And resilient.
386
00:25:34,526 --> 00:25:36,731
♪♪
387
00:25:45,725 --> 00:25:47,351
Life.
388
00:25:47,388 --> 00:25:51,066
Here on Earth, it is absolutely
everywhere.
389
00:25:51,100 --> 00:25:55,705
Once life got started,
it has held on tenaciously.
390
00:25:55,740 --> 00:25:59,123
But, where can we find life
elsewhere in the universe?
391
00:25:59,163 --> 00:26:01,303
If it's done so well here
on Earth,
392
00:26:01,339 --> 00:26:03,249
certainly this can't be
the only place.
393
00:26:03,291 --> 00:26:09,042
♪♪
394
00:26:09,083 --> 00:26:11,025
But if we're going to find life
on other worlds,
395
00:26:11,067 --> 00:26:13,521
we're going to need to know
where to look,
396
00:26:13,562 --> 00:26:15,668
because there's a lot of worlds
out there, and man,
397
00:26:15,706 --> 00:26:18,838
is the volume of space huge!
398
00:26:18,873 --> 00:26:21,656
So you can't just go looking
willy-nilly.
399
00:26:21,690 --> 00:26:23,730
You need to find a marker
400
00:26:23,769 --> 00:26:26,671
that guides you to where life
most likely can be found.
401
00:26:26,713 --> 00:26:33,074
♪♪
402
00:26:33,112 --> 00:26:34,369
For life to get started
on a planet,
403
00:26:34,392 --> 00:26:37,076
it needs a few specific things.
404
00:26:37,112 --> 00:26:40,112
You have to have energy
to power that life
405
00:26:40,151 --> 00:26:41,876
and you have to have
the right chemistry.
406
00:26:41,911 --> 00:26:44,279
But even if you have
both of those,
407
00:26:44,311 --> 00:26:47,214
there is still one more thing
that we don't know
408
00:26:47,254 --> 00:26:51,379
is necessarily going to be found
on exoplanets.
409
00:26:51,414 --> 00:26:54,098
Water,
and it has to be liquid water.
410
00:26:54,134 --> 00:26:58,771
♪♪
411
00:26:58,806 --> 00:27:03,956
Every single living thing
on Earth requires liquid water
412
00:27:03,989 --> 00:27:07,306
to exist.
413
00:27:07,349 --> 00:27:10,645
To uncover life that resembles
anything like what we have here,
414
00:27:10,677 --> 00:27:14,638
finding liquid water will
be crucial.
415
00:27:14,676 --> 00:27:16,368
There's a concept:
416
00:27:16,404 --> 00:27:17,998
follow the water.
417
00:27:18,035 --> 00:27:20,011
That where there's water,
there might be life.
418
00:27:20,051 --> 00:27:22,386
♪♪
419
00:27:36,402 --> 00:27:39,948
The universe itself
is awash with water.
420
00:27:47,121 --> 00:27:51,726
Great reservoirs have been
detected throughout the galaxy
421
00:27:51,761 --> 00:27:54,631
in vast, interstellar clouds.
422
00:28:00,752 --> 00:28:04,135
But just because water
is plentiful,
423
00:28:04,175 --> 00:28:07,209
that doesn't mean that planets
are necessarily
424
00:28:07,247 --> 00:28:09,419
the places where it ends up.
425
00:28:09,454 --> 00:28:14,888
♪♪
426
00:28:17,422 --> 00:28:18,950
So, while we've detected water
427
00:28:18,990 --> 00:28:22,252
on the moons of Jupiter
and Saturn...
428
00:28:28,397 --> 00:28:32,227
only one of the eight planets
in our solar system
429
00:28:32,268 --> 00:28:35,847
has liquid water flowing on
its surface.
430
00:28:35,884 --> 00:28:40,161
♪♪
431
00:28:40,395 --> 00:28:45,611
An ocean world where, long ago,
life began to thrive.
432
00:28:45,643 --> 00:28:50,978
♪♪
433
00:28:51,019 --> 00:28:53,223
So the challenge, then,
434
00:28:53,258 --> 00:28:56,160
was to find an Earth-mass planet
in a habitable zone.
435
00:28:56,202 --> 00:28:58,275
Meaning it's the right distance
from its host star
436
00:28:58,313 --> 00:29:00,616
to support liquid water on
its surface.
437
00:29:00,649 --> 00:29:03,170
Earth-like planets that orbit
their stars
438
00:29:03,209 --> 00:29:05,032
at the same distance we orbit
the sun,
439
00:29:05,065 --> 00:29:09,735
who are right on the limit
of what Kepler could find.
440
00:29:09,769 --> 00:29:12,453
We need to see the planet cross
in front of its star,
441
00:29:12,488 --> 00:29:15,424
and it takes us multiple orbits
to observe this.
442
00:29:15,464 --> 00:29:21,029
And so it's really, really
difficult to find these planets.
443
00:29:21,063 --> 00:29:23,879
And while Kepler
can detect planets,
444
00:29:23,911 --> 00:29:29,062
it cannot tell what
they're made of.
445
00:29:29,095 --> 00:29:34,430
To detect water, the most
powerful space telescope yet
446
00:29:34,470 --> 00:29:36,293
must join the quest.
447
00:29:36,326 --> 00:29:40,003
♪♪
448
00:29:40,037 --> 00:29:43,136
Kepler and Hubble worked well
in coordination.
449
00:29:43,173 --> 00:29:46,108
Kepler would find planets around
distant stars,
450
00:29:46,149 --> 00:29:48,190
and then Hubble would follow
them up in more detail,
451
00:29:48,228 --> 00:29:50,236
to teach us more about
the atmospheres
452
00:29:50,468 --> 00:29:52,127
of the planets found by Kepler.
453
00:29:52,164 --> 00:29:55,961
♪♪
454
00:29:56,003 --> 00:29:58,338
When a planet goes
in front of the star,
455
00:29:58,372 --> 00:30:01,090
some of the starlight shines
through the atmosphere.
456
00:30:01,123 --> 00:30:04,866
But just like shining a
flashlight through the fog,
457
00:30:04,899 --> 00:30:08,031
some light doesn't make it
through and some does.
458
00:30:08,067 --> 00:30:10,653
And by piecing together which
parts of the starlight
459
00:30:10,691 --> 00:30:12,993
make it through the planet
atmosphere and which don't,
460
00:30:13,027 --> 00:30:14,969
we can actually tell something
about the gases
461
00:30:15,010 --> 00:30:18,393
in the atmosphere of the planet
that are absorbing.
462
00:30:18,433 --> 00:30:19,851
And then we can tell something
about the makeup of the planet.
463
00:30:19,874 --> 00:30:24,151
♪♪
464
00:30:28,448 --> 00:30:32,410
In 2015, Kepler finds Hubble
a target.
465
00:30:32,448 --> 00:30:36,126
♪♪
466
00:30:36,160 --> 00:30:38,976
A world within
its star's habitable zone.
467
00:30:42,687 --> 00:30:47,673
♪♪
468
00:30:47,711 --> 00:30:50,559
More than eight times the mass
of Earth,
469
00:30:50,590 --> 00:30:55,261
K2-18b is enormous.
470
00:30:55,294 --> 00:30:58,328
♪♪
471
00:31:04,765 --> 00:31:11,388
With a powerful
gravitational pull
472
00:31:11,421 --> 00:31:16,309
that allows it to form, and hang
on to, an atmosphere.
473
00:31:16,348 --> 00:31:20,090
♪♪
474
00:31:26,779 --> 00:31:30,741
♪♪
475
00:31:30,779 --> 00:31:35,514
Hubble examines light from
K2-18b's star
476
00:31:35,546 --> 00:31:37,369
as the planet passes
in front of it.
477
00:31:37,401 --> 00:31:43,152
♪♪
478
00:31:43,193 --> 00:31:46,194
And discovers
a long-awaited signature.
479
00:31:48,920 --> 00:31:53,907
Water vapor.
480
00:31:53,944 --> 00:31:55,920
K2-18b is exciting because,
481
00:31:55,960 --> 00:31:58,197
with the Hubble observations,
482
00:31:58,232 --> 00:32:01,527
we found water vapor in its
atmosphere.
483
00:32:01,559 --> 00:32:04,560
And this is the smallest planet
to date
484
00:32:04,599 --> 00:32:07,021
which sits in the habitable zone
of its host star
485
00:32:07,063 --> 00:32:09,071
and in whose atmosphere
water has been detected.
486
00:32:09,111 --> 00:32:11,664
Earth has tiny but
environmentally significant
487
00:32:11,702 --> 00:32:13,677
amounts of water vapor in our
atmosphere,
488
00:32:13,719 --> 00:32:16,916
ranging from four percent to
less than one percent.
489
00:32:16,950 --> 00:32:19,668
So far, the data we have has
shown
490
00:32:19,701 --> 00:32:24,590
that there's anywhere between
0.01% and about 15% water vapor
491
00:32:24,629 --> 00:32:27,183
in the atmosphere of K2-18b.
492
00:32:27,220 --> 00:32:29,261
And that might seem like quite
a broad constraint,
493
00:32:29,300 --> 00:32:31,211
but we have to remember that
494
00:32:31,253 --> 00:32:33,675
this is a planet that's
many, many light-years away.
495
00:32:33,716 --> 00:32:35,261
So the fact that we can detect
this water at all
496
00:32:35,284 --> 00:32:36,779
is already really exciting.
497
00:32:36,820 --> 00:32:41,839
♪♪
498
00:32:41,875 --> 00:32:45,258
124 light-years from Earth,
499
00:32:45,299 --> 00:32:50,155
we may have found evidence
of water on another world.
500
00:32:50,195 --> 00:32:53,195
K2-18b is a huge milestone.
501
00:32:53,234 --> 00:32:55,373
It's what we call
a sub-Neptune-sized exoplanet.
502
00:32:55,410 --> 00:32:58,345
♪♪
503
00:32:58,385 --> 00:33:00,273
Now, what does that mean?
504
00:33:00,305 --> 00:33:03,786
Well, it could be, it's a planet
sort of like Jupiter,
505
00:33:03,825 --> 00:33:06,728
heavy, massive hydrogen
atmosphere, no life.
506
00:33:06,769 --> 00:33:08,330
That's like Jupiter.
507
00:33:08,369 --> 00:33:11,631
Or it could be that water
represents an ocean.
508
00:33:11,665 --> 00:33:14,120
It doesn't have
a heavy atmosphere.
509
00:33:14,160 --> 00:33:16,201
Instead, it has an ocean
and the water is evaporating.
510
00:33:16,240 --> 00:33:19,023
So it's a wonderful discovery.
511
00:33:19,055 --> 00:33:22,372
♪♪
512
00:33:26,991 --> 00:33:30,668
Within the data lies
a tantalizing possibility.
513
00:33:33,230 --> 00:33:39,526
If K2-18b's vast mass
is formed from water,
514
00:33:39,565 --> 00:33:43,428
its skies could be full
of clouds,
515
00:33:43,469 --> 00:33:48,009
where water vapor collects,
516
00:33:48,045 --> 00:33:50,828
forming droplets
517
00:33:50,861 --> 00:33:54,658
and eventually falling.
518
00:33:54,700 --> 00:34:00,549
♪♪
519
00:34:00,587 --> 00:34:04,614
A cycle, potentially feeding
vast oceans...
520
00:34:04,843 --> 00:34:08,105
♪♪
521
00:34:08,139 --> 00:34:14,053
That could stretch across
the entire planet,
522
00:34:14,090 --> 00:34:18,760
making it a water world.
523
00:34:18,794 --> 00:34:20,933
This finding is remarkable
524
00:34:21,161 --> 00:34:23,682
because, 20 years ago,
no one would have dreamt
525
00:34:23,721 --> 00:34:27,017
that we would be here today,
526
00:34:27,048 --> 00:34:29,188
talking about detecting
the atmosphere of a planet
527
00:34:29,224 --> 00:34:34,113
and trying to understand
the conditions on its surface.
528
00:34:41,351 --> 00:34:44,865
For me, K2-18b has been
a real turning point
529
00:34:44,903 --> 00:34:47,424
because it really
opens up the field
530
00:34:47,462 --> 00:34:50,333
to looking for life in these
slightly bigger planets.
531
00:34:50,375 --> 00:34:54,237
♪♪
532
00:34:54,279 --> 00:34:58,851
After the astonishing
breakthrough of K2-18b,
533
00:34:58,885 --> 00:35:02,748
Kepler goes on to make
many more discoveries.
534
00:35:02,789 --> 00:35:05,375
So, Kepler was
a really simple mission.
535
00:35:05,413 --> 00:35:07,323
It's just this minivan-sized
spacecraft
536
00:35:07,364 --> 00:35:09,634
that stared at this field
of stars.
537
00:35:09,669 --> 00:35:12,703
But that one mission discovered
so many alien worlds.
538
00:35:12,740 --> 00:35:18,011
♪♪
539
00:35:18,052 --> 00:35:21,216
Worlds that astound astronomers
540
00:35:21,252 --> 00:35:26,653
and dramatically expand our
understanding of the universe.
541
00:35:26,691 --> 00:35:28,896
As we look out into the galaxy,
542
00:35:28,931 --> 00:35:31,266
we can start
to answer the question
543
00:35:31,299 --> 00:35:34,595
of what properties do planets
and planetary systems need
544
00:35:34,626 --> 00:35:36,699
in order to support the
evolution,
545
00:35:36,738 --> 00:35:38,681
and continued existence,
of life.
546
00:35:38,914 --> 00:35:42,973
♪♪
547
00:35:43,009 --> 00:35:46,872
But nothing lasts forever.
548
00:35:46,913 --> 00:35:52,794
In October 2018,
Kepler finally runs out of fuel.
549
00:35:52,833 --> 00:35:55,321
It was sad to see
an old friend leave
550
00:35:55,360 --> 00:35:57,749
when they sent the command
to shut everything down.
551
00:35:57,791 --> 00:35:59,799
It's asleep now.
552
00:36:00,032 --> 00:36:02,216
It's in orbit around the sun,
and it will continue that orbit.
553
00:36:02,239 --> 00:36:05,240
♪♪
554
00:36:05,279 --> 00:36:07,189
To date, Kepler has given us
555
00:36:07,231 --> 00:36:09,850
over two and a half thousand
planets.
556
00:36:09,887 --> 00:36:11,775
And we're still analyzing
the Kepler data,
557
00:36:11,806 --> 00:36:14,774
so there could be many more
to come.
558
00:36:14,814 --> 00:36:17,978
♪♪
559
00:36:18,014 --> 00:36:20,731
A galactic census,
560
00:36:20,766 --> 00:36:27,160
showing us just how common
planets like K2-18b might be.
561
00:36:27,197 --> 00:36:32,980
♪♪
562
00:36:33,020 --> 00:36:35,574
We know there's about,
on average,
563
00:36:35,612 --> 00:36:38,002
two or more planets per star.
564
00:36:38,044 --> 00:36:40,860
Maybe ten percent of those are
small planets,
565
00:36:40,891 --> 00:36:42,867
ten percent of those in
the habitable zone.
566
00:36:42,907 --> 00:36:47,642
So that means there is about
20 billion planets
567
00:36:47,675 --> 00:36:48,756
about the size of the Earth
568
00:36:48,987 --> 00:36:50,449
in the habitable zone
of their star.
569
00:36:50,490 --> 00:36:53,338
We don't know about it, and we
might never know about it,
570
00:36:53,370 --> 00:36:57,048
but it is absolutely possible
that of the panoply of planets,
571
00:36:57,082 --> 00:36:59,287
of alien worlds
that Kepler has observed,
572
00:36:59,321 --> 00:37:04,788
there's actually been some
planets that host alien life.
573
00:37:04,826 --> 00:37:06,998
Maybe they have their own
forests and lakes
574
00:37:07,225 --> 00:37:10,608
filled with fish,
and skies filled with birds.
575
00:37:10,648 --> 00:37:13,682
It's so incredible to think
about the endless possibilities
576
00:37:13,720 --> 00:37:15,062
that are out there for life
to take.
577
00:37:16,920 --> 00:37:20,401
These tantalizing glimpses
of worlds
578
00:37:20,439 --> 00:37:24,018
give us a foundation
to build upon
579
00:37:24,055 --> 00:37:26,991
for the next,
even more ambitious mission.
580
00:37:27,031 --> 00:37:29,617
One, zero.
581
00:37:29,655 --> 00:37:32,372
Lift-off, the SpaceX Falcon 9
582
00:37:32,407 --> 00:37:35,473
carrying TESS,
a planet-hunting spacecraft
583
00:37:35,510 --> 00:37:38,358
that will search for new worlds
beyond our solar system.
584
00:37:38,390 --> 00:37:43,922
♪♪
585
00:37:43,957 --> 00:37:45,182
Kepler taught us about
statistics
586
00:37:45,205 --> 00:37:46,732
and how common planets are.
587
00:37:46,773 --> 00:37:50,865
But the planets found by Kepler
were often orbiting stars
588
00:37:50,901 --> 00:37:53,323
that were too distant
and too faint for further study.
589
00:37:53,364 --> 00:37:57,555
With TESS, we're looking at all
of the nearby stars.
590
00:37:57,588 --> 00:37:59,484
Vehicle has passed maximum
aerodynamic pressure.
591
00:37:59,507 --> 00:38:01,712
Because they are close
592
00:38:01,939 --> 00:38:04,177
and the stars appear bright
to us,
593
00:38:04,211 --> 00:38:07,692
we can go and learn whether they
have atmospheres,
594
00:38:07,730 --> 00:38:09,106
what the atmospheres
are made of,
595
00:38:09,139 --> 00:38:11,082
whether they have moons
and rings...
596
00:38:11,122 --> 00:38:13,676
All the stuff that is far too
difficult to study
597
00:38:13,714 --> 00:38:15,504
for the Kepler stars themselves.
598
00:38:18,289 --> 00:38:20,232
There are hundreds of people
involved
599
00:38:20,273 --> 00:38:21,768
in making the TESS mission
a success,
600
00:38:21,810 --> 00:38:23,599
and now the world
is analyzing the data.
601
00:38:23,634 --> 00:38:26,220
TESS is finding the planets
602
00:38:26,257 --> 00:38:28,014
that will make the legacy
catalogue
603
00:38:28,049 --> 00:38:30,253
that will be used
for generations to come.
604
00:38:30,289 --> 00:38:35,177
Among this vast array
of worlds, what kind of life
605
00:38:35,216 --> 00:38:38,086
are we hoping to find?
606
00:38:38,128 --> 00:38:40,398
When we say we're looking
for life,
607
00:38:40,431 --> 00:38:43,302
we usually don't say exactly
what we mean by that.
608
00:38:43,343 --> 00:38:45,798
And in fact, it turns out
defining life
609
00:38:45,839 --> 00:38:48,709
in a way that satisfies
everybody hasn't been done yet.
610
00:38:48,750 --> 00:38:51,598
♪♪
611
00:38:51,630 --> 00:38:55,013
We have to distinguish between
simple life
612
00:38:55,054 --> 00:38:58,121
and more complex,
advanced life like ourselves.
613
00:38:58,158 --> 00:38:59,798
And there's quite a difference
there, between the two.
614
00:38:59,821 --> 00:39:06,412
♪♪
615
00:39:09,772 --> 00:39:12,588
We are the product of a story
that has been playing out
616
00:39:12,620 --> 00:39:17,356
for over a quarter of the age
of the universe itself.
617
00:39:17,388 --> 00:39:20,291
♪♪
618
00:39:20,331 --> 00:39:21,859
From microbes
619
00:39:21,899 --> 00:39:23,842
to a global technological
civilization.
620
00:39:26,955 --> 00:39:30,981
With our telescopes,
we stand on the cusp
621
00:39:31,210 --> 00:39:34,211
of finding signs of at least
622
00:39:34,250 --> 00:39:36,040
simple life-forms on other
planets.
623
00:39:39,466 --> 00:39:41,921
But we have also been
calling out,
624
00:39:41,961 --> 00:39:45,224
sending out transmissions into
the galaxy,
625
00:39:45,257 --> 00:39:47,592
in the hope of connecting
626
00:39:47,625 --> 00:39:49,218
with another
intelligent species.
627
00:39:52,360 --> 00:39:55,808
For millennia,
we've looked out at the skies.
628
00:39:55,848 --> 00:39:58,085
And it's only in the last
century,
629
00:39:58,119 --> 00:40:00,357
really, the blink of an eye
for humanity,
630
00:40:00,391 --> 00:40:02,464
that we've actually been able
to send messages
631
00:40:02,504 --> 00:40:04,577
and probes beyond the Earth.
632
00:40:04,807 --> 00:40:08,190
And as of yet, we're
still waiting for a response.
633
00:40:09,831 --> 00:40:11,523
What we're hearing is
just silence.
634
00:40:15,430 --> 00:40:18,693
But with millions of potentially
habitable worlds
635
00:40:18,726 --> 00:40:22,688
in the Milky Way,
why is no one calling to us?
636
00:40:22,725 --> 00:40:25,987
♪♪
637
00:40:26,021 --> 00:40:31,259
In 2020, scientists make an
unsettling find:
638
00:40:31,301 --> 00:40:35,196
a planet, almost the size of
Earth,
639
00:40:35,236 --> 00:40:40,322
floating freely
through the galaxy, all alone.
640
00:40:40,355 --> 00:40:41,982
Did it form there by itself
641
00:40:42,019 --> 00:40:45,697
or has it been thrown out
of another planetary system?
642
00:40:45,731 --> 00:40:50,488
A planet that shows us that
the galaxy is more chaotic,
643
00:40:50,531 --> 00:40:55,233
and perhaps more hostile,
than we thought.
644
00:40:55,266 --> 00:40:56,957
As we look out through
the galaxy,
645
00:40:56,994 --> 00:40:59,002
there are many cases
646
00:40:59,042 --> 00:41:01,825
where planets would experience
much more violent histories,
647
00:41:01,858 --> 00:41:04,030
and life might not be able
to survive
648
00:41:04,065 --> 00:41:08,506
more than a billion years.
649
00:41:08,544 --> 00:41:12,407
The rogue planet may be
a refugee,
650
00:41:12,448 --> 00:41:15,962
telling us about systems
far more chaotic than our own.
651
00:41:19,103 --> 00:41:21,787
Because not all stars
exist alone.
652
00:41:24,000 --> 00:41:27,830
Some have company,
653
00:41:27,871 --> 00:41:31,254
orbiting one another in
a careful dance.
654
00:41:36,030 --> 00:41:37,511
So when we look up at the
night sky
655
00:41:37,534 --> 00:41:39,357
and we see single points
of light,
656
00:41:39,390 --> 00:41:42,205
which we assume are stars,
657
00:41:42,238 --> 00:41:45,948
often what's actually there are
two stars orbiting each other.
658
00:41:45,981 --> 00:41:50,585
But they are so close together
that they appear as one.
659
00:41:50,621 --> 00:41:55,706
We're finding that these binary
and multiple-star systems
660
00:41:55,740 --> 00:41:59,570
are actually amongst the most
common types in the universe.
661
00:41:59,612 --> 00:42:03,290
Sometimes planets orbit both of
these stars together,
662
00:42:03,323 --> 00:42:06,041
and other times, the planet
will orbit one of the two stars,
663
00:42:06,075 --> 00:42:07,123
but not the other star.
664
00:42:07,163 --> 00:42:10,098
♪♪
665
00:42:20,441 --> 00:42:21,400
Dawn.
666
00:42:26,457 --> 00:42:31,247
Ushered in by not one star,
667
00:42:31,289 --> 00:42:32,337
but two.
668
00:42:35,736 --> 00:42:38,966
Perhaps the rogue world
began its life
669
00:42:39,000 --> 00:42:43,256
in a binary system, like this.
670
00:42:43,287 --> 00:42:45,524
On a planet that's orbiting
two stars,
671
00:42:45,559 --> 00:42:47,534
there would always be
two shadows
672
00:42:47,575 --> 00:42:49,964
and you would see two sunsets.
673
00:42:50,007 --> 00:42:52,396
I like to say that science
fiction got some things right.
674
00:42:52,438 --> 00:42:56,400
What does that feel like,
the heat of two suns?
675
00:42:56,630 --> 00:42:59,729
Is that a nice heat,
or is that too much?
676
00:42:59,766 --> 00:43:01,141
There's so many questions
677
00:43:01,173 --> 00:43:04,622
around binary star systems.
678
00:43:04,661 --> 00:43:11,470
♪♪
679
00:43:11,509 --> 00:43:15,852
For a time, the planet may
enjoy a stable period
680
00:43:15,892 --> 00:43:18,282
in the habitable zone of one
of these stars.
681
00:43:23,091 --> 00:43:28,078
But the peace does not last.
682
00:43:28,307 --> 00:43:31,307
The moment there's more than
two bodies involved
683
00:43:31,347 --> 00:43:36,169
in a gravitational dance, things
get complicated really fast.
684
00:43:36,210 --> 00:43:39,245
Because each body
gravitationally affects
685
00:43:39,282 --> 00:43:41,487
every other body.
686
00:43:41,521 --> 00:43:44,718
On Earth, the most obvious
manifestation of gravity
687
00:43:44,753 --> 00:43:47,241
from a body that's not Earth
is the tides.
688
00:43:47,280 --> 00:43:49,834
The moon affects our tides.
689
00:43:49,872 --> 00:43:52,045
What can happen in these
binary systems
690
00:43:52,080 --> 00:43:55,212
is that this strong gravity
between these two stars
691
00:43:55,248 --> 00:43:58,118
can shift orbits drastically.
692
00:44:01,424 --> 00:44:04,840
This huge, combined
gravitational force...
693
00:44:08,207 --> 00:44:12,811
interferes with
the planet's orbit,
694
00:44:12,846 --> 00:44:14,702
creating chaos.
695
00:44:14,734 --> 00:44:18,957
♪♪
696
00:44:25,645 --> 00:44:27,533
There's a very thin line
697
00:44:27,565 --> 00:44:31,689
between stability
and instability.
698
00:44:31,725 --> 00:44:33,154
And when instability kicks in,
699
00:44:33,197 --> 00:44:36,165
it goes from a stable system
to a chaotic system.
700
00:44:36,204 --> 00:44:39,718
And at that point,
anything can happen.
701
00:44:39,756 --> 00:44:43,237
♪♪
702
00:44:43,275 --> 00:44:49,921
As each star and every planet
in the system pulls the rest,
703
00:44:49,963 --> 00:44:53,280
the orbits of each world
constantly shift.
704
00:44:53,322 --> 00:44:56,868
♪♪
705
00:44:56,906 --> 00:44:59,906
Further adding to the turmoil.
706
00:44:59,946 --> 00:45:04,070
♪♪
707
00:45:08,233 --> 00:45:12,161
Until a close encounter with
another world
708
00:45:12,201 --> 00:45:17,220
gives the planet a huge
gravitational kick.
709
00:45:17,256 --> 00:45:19,679
♪♪
710
00:45:30,215 --> 00:45:31,906
Flinging it outwards.
711
00:45:32,134 --> 00:45:37,503
♪♪
712
00:45:37,542 --> 00:45:41,437
And releasing it from the grip
of its parent stars.
713
00:45:41,477 --> 00:45:45,090
♪♪
714
00:45:49,765 --> 00:45:55,199
♪♪
715
00:45:58,052 --> 00:46:00,354
Setting it loose.
716
00:46:00,388 --> 00:46:03,934
A rogue planet,
wandering the galaxy.
717
00:46:03,971 --> 00:46:07,288
The planet will slowly start
to cool down
718
00:46:07,331 --> 00:46:11,968
until it is just a rock with
no source of heat,
719
00:46:12,003 --> 00:46:15,581
traveling alone through
the universe.
720
00:46:15,618 --> 00:46:20,255
♪♪
721
00:46:30,464 --> 00:46:33,661
Far from the warm embrace of
its parent stars.
722
00:46:36,736 --> 00:46:40,926
♪♪
723
00:46:43,679 --> 00:46:47,739
Any liquid water the rogue world
might have once had
724
00:46:47,967 --> 00:46:50,269
freezes solid.
725
00:46:53,918 --> 00:46:55,806
You would have the night sky
all the time
726
00:46:55,838 --> 00:46:57,846
if you were on one of these
planets,
727
00:46:57,886 --> 00:47:00,026
with no hope of a sun ever
rising.
728
00:47:00,062 --> 00:47:05,398
♪♪
729
00:47:05,437 --> 00:47:09,628
Any atmosphere that once
protected it
730
00:47:09,661 --> 00:47:12,379
freezes.
731
00:47:12,412 --> 00:47:19,286
♪♪
732
00:47:19,323 --> 00:47:20,372
Leaving the surface
733
00:47:20,604 --> 00:47:25,841
exposed to cosmic radiation,
734
00:47:25,884 --> 00:47:30,641
conditions which no living thing
could endure.
735
00:47:30,683 --> 00:47:32,375
It effectively becomes
736
00:47:32,410 --> 00:47:36,567
something of a dead planet.
737
00:47:36,602 --> 00:47:40,497
Almost a fossil of itself
flying through space.
738
00:47:40,537 --> 00:47:46,866
♪♪
739
00:47:46,905 --> 00:47:50,964
Alone and adrift.
740
00:47:58,071 --> 00:48:02,829
Only to be detected by us
millions of years later.
741
00:48:05,495 --> 00:48:07,219
The way we find rogue worlds
742
00:48:07,255 --> 00:48:10,256
is through a process called
gravitational microlensing.
743
00:48:10,294 --> 00:48:11,888
We look at a distant star,
744
00:48:11,926 --> 00:48:13,837
a star that has nothing to do
with the planets
745
00:48:13,879 --> 00:48:15,822
that we're hoping to discover,
746
00:48:15,862 --> 00:48:18,929
and between the telescope
that we're using
747
00:48:19,158 --> 00:48:21,646
and that distant star,
a rogue planet
748
00:48:21,686 --> 00:48:23,726
wanders through.
749
00:48:23,957 --> 00:48:26,925
The gravity of the planet
is really small,
750
00:48:26,965 --> 00:48:30,194
but it's enough to bend that
distant star's light
751
00:48:30,229 --> 00:48:32,913
so that we can see that it
exists and measure its mass.
752
00:48:36,084 --> 00:48:40,722
One of billions of planets
on which the spark of life
753
00:48:40,756 --> 00:48:45,775
may have begun,
only to be extinguished.
754
00:48:45,811 --> 00:48:49,194
Worlds where any civilizations
755
00:48:49,235 --> 00:48:53,807
could not have survived.
756
00:48:53,842 --> 00:48:56,625
Our planet is a wonderful place
to exist.
757
00:48:56,658 --> 00:48:58,699
We have been sheltered
through history.
758
00:48:58,738 --> 00:49:00,811
We've experienced some
large impacts,
759
00:49:00,850 --> 00:49:02,989
but we've had a relatively
benign existence.
760
00:49:03,026 --> 00:49:04,521
It could be that the reason
761
00:49:04,561 --> 00:49:06,798
we haven't found any alien
civilizations yet
762
00:49:06,833 --> 00:49:09,768
is because we live in a
particularly hospitable corner
763
00:49:09,808 --> 00:49:11,500
of our galaxy, with just the
right conditions
764
00:49:11,536 --> 00:49:13,260
for life to arise.
765
00:49:13,296 --> 00:49:17,704
Or maybe we just haven't
looked hard enough.
766
00:49:17,744 --> 00:49:23,144
Our quest for another living
planet has only just begun,
767
00:49:23,184 --> 00:49:28,487
and the only way to know if we
are alone is to keep looking.
768
00:49:28,527 --> 00:49:30,382
I still feel very amazed
769
00:49:30,415 --> 00:49:32,837
that we have so much knowledge
about these objects
770
00:49:33,070 --> 00:49:35,275
that are just so far away
from us.
771
00:49:35,310 --> 00:49:38,988
♪♪
772
00:49:39,022 --> 00:49:42,121
We have found our first
rocky worlds.
773
00:49:42,157 --> 00:49:44,045
♪♪
774
00:49:44,077 --> 00:49:47,875
Some in the habitable zone
around their stars.
775
00:49:47,917 --> 00:49:51,911
♪♪
776
00:49:51,948 --> 00:49:56,422
And even worlds with water.
777
00:49:56,460 --> 00:49:59,144
Kepler has found thousands
of new planets.
778
00:49:59,180 --> 00:50:01,188
But for every question that
it's answered,
779
00:50:01,228 --> 00:50:03,236
it's raised at least five
new ones.
780
00:50:03,275 --> 00:50:07,237
Candidate worlds
for future missions
781
00:50:07,275 --> 00:50:11,847
to search for the evidence
of life itself.
782
00:50:11,883 --> 00:50:14,949
I am actually very optimistic,
783
00:50:14,986 --> 00:50:19,623
personally, that we might find
life within the next ten years.
784
00:50:19,658 --> 00:50:25,441
♪♪
785
00:50:25,482 --> 00:50:31,199
But we have also found hordes
of bizarre, tortured worlds
786
00:50:31,241 --> 00:50:34,024
around violent stars.
787
00:50:37,384 --> 00:50:42,818
♪♪
788
00:50:42,856 --> 00:50:47,013
And rogue planets,
789
00:50:47,047 --> 00:50:52,383
where life as we understand it
seems impossible.
790
00:50:52,422 --> 00:50:56,579
What we see is a menagerie rife
with diversity
791
00:50:56,614 --> 00:50:59,910
and worlds that we could never
have imagined.
792
00:50:59,942 --> 00:51:02,031
It's like looking at those
snowflakes under the microscope
793
00:51:02,054 --> 00:51:03,680
and seeing the wondrous
structure
794
00:51:03,718 --> 00:51:05,922
that we never knew about before,
but is beautiful
795
00:51:05,957 --> 00:51:08,445
and amazing to be a part of.
796
00:51:08,484 --> 00:51:12,609
♪♪
797
00:51:12,644 --> 00:51:16,955
Perhaps it is these worlds that
will help us understand
798
00:51:16,996 --> 00:51:23,772
why, for now, one planet
continues to remain apart.
799
00:51:23,811 --> 00:51:28,285
♪♪
800
00:51:30,531 --> 00:51:32,124
You might ask,
801
00:51:32,163 --> 00:51:35,480
why do we keep searching for
these alien worlds?
802
00:51:35,522 --> 00:51:38,010
And I think the answer is
profoundly human:
803
00:51:38,050 --> 00:51:41,018
we want to know what else
is out there.
804
00:51:41,058 --> 00:51:43,131
♪♪
805
00:51:43,170 --> 00:51:45,821
I think that it's not at all
a guarantee
806
00:51:45,857 --> 00:51:48,127
that there's life elsewhere
in the galaxy.
807
00:51:48,161 --> 00:51:49,656
And what we need to do is
808
00:51:49,697 --> 00:51:51,803
to go out and make measurements
and to see,
809
00:51:51,840 --> 00:51:53,499
which universe do we live in?
810
00:51:53,537 --> 00:51:54,665
Do we live in the "Star Trek"
universe,
811
00:51:54,688 --> 00:51:57,504
where every star has lots
of planets
812
00:51:57,536 --> 00:52:00,352
with life and civilizations?
813
00:52:00,384 --> 00:52:04,028
Or are we in fact, to the best
of our ability to measure,
814
00:52:04,063 --> 00:52:05,406
truly alone?
61153
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