1
00:00:05,206 --> 00:00:06,833
Narrator:
In the universe,
2
00:00:06,841 --> 00:00:10,175
everything seems
to orbit something.
3
00:00:10,177 --> 00:00:16,048
Planets orbit stars,
and moons orbit planets.
4
00:00:16,050 --> 00:00:21,420
Some moons are volcanic,
but the volcanoes are ice.
5
00:00:21,422 --> 00:00:24,380
Others are awash
with great oceans.
6
00:00:27,628 --> 00:00:30,598
There may be more
habitable moons in our galaxy
7
00:00:30,598 --> 00:00:32,896
than there are
habitable planets.
8
00:00:32,900 --> 00:00:36,928
Narrator: Moons tell the unknown
stories of our solar system
9
00:00:36,937 --> 00:00:40,134
and show us how it all works.
10
00:00:57,892 --> 00:01:01,522
In our own solar system,
there are just eight planets.
11
00:01:03,931 --> 00:01:08,164
But orbiting six
of those planets are moons...
12
00:01:19,013 --> 00:01:22,779
...lots and lots of moons --
more than 300 of them.
13
00:01:22,783 --> 00:01:26,014
Each one is different...
14
00:01:29,123 --> 00:01:33,117
...each one a world all its own.
15
00:01:33,127 --> 00:01:36,461
Dr. McKay: Well, when we look
out on our solar system,
16
00:01:36,463 --> 00:01:37,988
we see a lot of planets.
17
00:01:37,998 --> 00:01:39,693
But even more than planets,
we see moons.
18
00:01:39,700 --> 00:01:41,395
And in many ways,
they're more interesting
19
00:01:41,402 --> 00:01:42,892
than the planets
that they go around.
20
00:01:45,439 --> 00:01:50,036
We have moons that are airless
and apparently dead, like ours.
21
00:01:50,044 --> 00:01:52,479
Then, out in
the outer solar system,
22
00:01:52,479 --> 00:01:54,277
we have moons
with oceans inside them
23
00:01:54,281 --> 00:01:57,945
and moons with atmospheres
around them.
24
00:01:57,952 --> 00:02:00,284
I'm for moons.
You can keep the planets.
25
00:02:00,287 --> 00:02:03,780
Narrator:
The biggest eruptions...
26
00:02:07,494 --> 00:02:10,054
...the coldest temperatures...
27
00:02:11,966 --> 00:02:17,427
...and the largest oceans
in the solar system --
28
00:02:17,438 --> 00:02:19,770
they're all on moons.
29
00:02:19,773 --> 00:02:21,707
There are moons
with ice volcanoes.
30
00:02:23,944 --> 00:02:28,381
There are moons with lakes of
methane and methane rainfall,
31
00:02:28,382 --> 00:02:30,851
smog clouds...
32
00:02:32,620 --> 00:02:34,748
...moons that are
so volcanically active
33
00:02:34,755 --> 00:02:38,953
that they keep remaking
their surface...
34
00:02:38,959 --> 00:02:42,156
Moons with all kinds of plumes
shooting off into space --
35
00:02:42,162 --> 00:02:46,633
really a much wider range
of environments
36
00:02:46,634 --> 00:02:49,433
than we ever
could have imagined.
37
00:02:53,741 --> 00:02:55,835
Dr. McKay:
Often, when I'm describing
38
00:02:55,843 --> 00:02:58,437
to the general public,
or even to my fellow scientists,
39
00:02:58,445 --> 00:03:00,277
these moons of Saturn
and Jupiter,
40
00:03:00,280 --> 00:03:02,874
I call them "worlds"
because they really do have
41
00:03:02,883 --> 00:03:05,181
the complexity and mystery
of a whole world.
42
00:03:06,387 --> 00:03:10,449
Narrator: Jupiter and Saturn
have over 60 moons each.
43
00:03:12,192 --> 00:03:15,093
These giant gas planets
and their moons
44
00:03:15,095 --> 00:03:18,463
are like mini solar systems,
45
00:03:18,465 --> 00:03:22,265
and each moon
has a distinct personality.
46
00:03:24,872 --> 00:03:29,002
Iapetus, a two-toned moon
in black and white.
47
00:03:36,050 --> 00:03:40,146
Titan, with a dense,
orange atmosphere.
48
00:03:47,428 --> 00:03:53,322
And icy Enceladus, blasting ice
geysers 200 miles into space.
49
00:04:02,843 --> 00:04:05,141
Each moon is unique.
50
00:04:08,282 --> 00:04:11,183
But they all have
one thing in common.
51
00:04:11,185 --> 00:04:14,246
All moons
are natural satellites,
52
00:04:14,254 --> 00:04:17,451
held in place by gravity.
53
00:04:17,458 --> 00:04:22,692
But moons do more
than just go around planets.
54
00:04:22,696 --> 00:04:25,028
They help stabilize the planets
in their orbits
55
00:04:25,032 --> 00:04:27,091
and keep the machinery
of the solar system
56
00:04:27,101 --> 00:04:28,899
running smoothly.
57
00:04:32,606 --> 00:04:34,734
Dr. Grinspoon:
The diversity of moons
58
00:04:34,742 --> 00:04:37,939
is an interesting combination
of predictable laws of science
59
00:04:37,945 --> 00:04:41,745
and then complete randomness
of just things smashing together
60
00:04:41,749 --> 00:04:44,047
and the chips kind of falling
where they did
61
00:04:44,051 --> 00:04:46,145
in a way that you could
never predict.
62
00:04:49,656 --> 00:04:53,820
Narrator: Planets and moons
begin the same way.
63
00:05:01,068 --> 00:05:03,400
Once a star turns on,
64
00:05:03,403 --> 00:05:06,031
there's a lot of dust and gas
leftover.
65
00:05:10,043 --> 00:05:14,879
Slowly, the dust particles clump
together, forming rocks.
66
00:05:19,019 --> 00:05:23,252
The rocks smash into each other
and form boulders.
67
00:05:23,257 --> 00:05:27,353
Slowly, the objects
get bigger and bigger.
68
00:05:30,597 --> 00:05:32,463
The process
is called accretion.
69
00:05:32,466 --> 00:05:35,265
Dr. Durda: One can think of it
as forming a snowball
70
00:05:35,269 --> 00:05:36,737
and rolling it down a hill.
71
00:05:36,737 --> 00:05:38,171
As it rolls down the hill,
72
00:05:38,172 --> 00:05:40,766
it collects and gathers up
yet more snow,
73
00:05:40,774 --> 00:05:43,243
which makes it roll
faster and harder.
74
00:05:43,243 --> 00:05:46,474
And so that process
of runaway accretion
75
00:05:46,480 --> 00:05:47,845
actually happens
76
00:05:47,848 --> 00:05:50,783
in the formation of the planets
77
00:05:50,784 --> 00:05:52,616
and in the formation
of moons, as well.
78
00:05:54,788 --> 00:05:56,950
Narrator:
It sounds simple enough,
79
00:05:56,957 --> 00:06:02,919
but nobody knew for sure
how it worked until 2003.
80
00:06:06,133 --> 00:06:09,000
On the International
Space Station,
81
00:06:09,002 --> 00:06:13,803
astronaut Don Pettit was
experimenting in zero gravity.
82
00:06:13,807 --> 00:06:18,711
He put grains of salt and sugar
inside a plastic baggie.
83
00:06:18,712 --> 00:06:22,808
Instead of floating apart,
they began to clump together.
84
00:06:28,589 --> 00:06:32,048
This is how both planets
and moons build up.
85
00:06:32,059 --> 00:06:35,359
But instead of taking shape
around stars,
86
00:06:35,362 --> 00:06:39,162
most big moons take shape
around planets.
87
00:06:41,668 --> 00:06:44,831
If the same process
makes them all,
88
00:06:44,838 --> 00:06:49,969
what makes all of them
so different from each other?
89
00:06:49,977 --> 00:06:54,744
Take two of Jupiter's moons,
Callisto and Ganymede...
90
00:06:58,518 --> 00:07:01,010
...two very different moons,
91
00:07:01,021 --> 00:07:04,787
each born from the same debris
when Jupiter was still young.
92
00:07:09,096 --> 00:07:11,588
Ganymede formed
close to Jupiter,
93
00:07:11,598 --> 00:07:13,862
where there was lots of debris.
94
00:07:13,867 --> 00:07:16,632
Because there was
so much material,
95
00:07:16,637 --> 00:07:19,663
it came together quickly --
in about 10,000 years --
96
00:07:19,673 --> 00:07:24,509
and it was hot.
97
00:07:24,511 --> 00:07:27,037
The heat separated the ice
from the rock.
98
00:07:27,047 --> 00:07:30,642
You can still see it in
Ganymede's distinct landscape.
99
00:07:32,319 --> 00:07:34,811
Dr. Hendrix:
The primary factor that affects
100
00:07:34,821 --> 00:07:36,915
why moons are the way
they are today
101
00:07:36,924 --> 00:07:38,153
is energy "
102
00:07:38,158 --> 00:07:40,217
how much energy
was put into them
103
00:07:40,227 --> 00:07:41,626
as heat during accretion
104
00:07:41,628 --> 00:07:45,565
and how much energy
has been lost.
105
00:07:45,565 --> 00:07:47,556
All of those factors go
into telling us
106
00:07:47,567 --> 00:07:49,126
why moons behave the way they do
107
00:07:49,136 --> 00:07:51,093
and why they look the way
they do today.
108
00:07:54,675 --> 00:07:57,770
Narrator: Callisto's surface
tells a different story.
109
00:07:57,778 --> 00:07:59,371
It formed much farther out,
110
00:07:59,379 --> 00:08:01,905
where there was less debris
and less heat.
111
00:08:01,915 --> 00:08:06,284
It took longer
and cooled faster.
112
00:08:08,088 --> 00:08:12,082
Unlike Ganymede,
Callisto's surface is uniform.
113
00:08:12,092 --> 00:08:14,652
Rock and ice never separated.
114
00:08:17,998 --> 00:08:21,491
Where a moon forms
can also mean the difference
115
00:08:21,501 --> 00:08:24,994
between survival
and destruction.
116
00:08:25,005 --> 00:08:26,439
Get too close,
117
00:08:26,440 --> 00:08:29,865
and a planet's gravity
will rip a moon to shreds.
118
00:08:34,648 --> 00:08:38,414
Scientists believe this
is what happened to many moons
119
00:08:38,418 --> 00:08:40,250
when Jupiter was young.
120
00:08:51,098 --> 00:08:54,090
Dr. Durda: And it's very likely
that Jupiter had
121
00:08:54,101 --> 00:08:56,593
an entire conveyor belt
of large moons
122
00:08:56,603 --> 00:08:58,230
that were wanting to form,
123
00:08:58,238 --> 00:09:00,206
only to be swallowed up
by the planet itself.
124
00:09:00,207 --> 00:09:03,268
The large moons we see today
125
00:09:03,276 --> 00:09:05,608
are only the last ones
that were able to stabilize
126
00:09:05,612 --> 00:09:08,013
right at the end
of that process,
127
00:09:08,015 --> 00:09:09,642
stop their death spiral,
128
00:09:09,649 --> 00:09:12,675
and survive into the position
we see today.
129
00:09:16,289 --> 00:09:19,850
Narrator: But Jupiter keeps
trying to eat them.
130
00:09:19,860 --> 00:09:23,194
The gravity of the giant planet
131
00:09:23,196 --> 00:09:26,359
reaches out and pulls hard
on the orbiting moons.
132
00:09:34,274 --> 00:09:38,006
It transforms them
from lifeless balls of rock
133
00:09:38,011 --> 00:09:41,470
into strange and dramatic
worlds.
134
00:09:57,364 --> 00:09:58,991
Narrator:
Jupiter is the largest planet
135
00:09:58,999 --> 00:10:00,296
in our solar system.
136
00:10:00,300 --> 00:10:03,600
It has 63 moons.
137
00:10:03,603 --> 00:10:08,165
The four largest are called
the Galilean moons,
138
00:10:08,175 --> 00:10:10,769
named after the astronomer
Galileo,
139
00:10:10,777 --> 00:10:13,246
who discovered them in 1610.
140
00:10:16,516 --> 00:10:18,678
They show how gravity controls
141
00:10:18,685 --> 00:10:21,711
both what moons look like
142
00:10:21,721 --> 00:10:24,213
and how they behave.
143
00:10:24,224 --> 00:10:28,422
The first
of the Galilean moons, lo,
144
00:10:28,428 --> 00:10:31,591
orbits closest to the planet,
145
00:10:31,598 --> 00:10:34,898
just 260,000 miles
above Jupiter.
146
00:10:41,975 --> 00:10:45,912
That's about the same distance
as our Moon is from Earth.
147
00:10:49,116 --> 00:10:51,073
But unlike our Moon,
148
00:10:51,084 --> 00:10:54,918
the surface of lo
has no impact craters.
149
00:10:54,921 --> 00:10:58,380
Scientists realized that meant
the surface was new.
150
00:10:58,391 --> 00:10:59,859
But how could that be?
151
00:11:03,330 --> 00:11:04,764
Every time you look at lo,
152
00:11:04,764 --> 00:11:07,199
with a spacecraft
or even with a telescope,
153
00:11:07,200 --> 00:11:08,725
it's a little bit different.
154
00:11:08,735 --> 00:11:10,260
So the geology on lo changes
155
00:11:10,270 --> 00:11:11,965
like the weather
on other planets.
156
00:11:11,972 --> 00:11:13,303
It's that active.
157
00:11:13,306 --> 00:11:18,210
Narrator: When NASA first sent
probes to fly past lo,
158
00:11:18,211 --> 00:11:20,111
they were shocked.
159
00:11:20,113 --> 00:11:22,548
They saw dozens
of active volcanoes.
160
00:11:28,755 --> 00:11:32,419
This is footage of an erupting
supervolcano on lo,
161
00:11:32,425 --> 00:11:36,828
blasting 200 miles into space.
162
00:11:36,830 --> 00:11:39,561
Everyone had
the same question --
163
00:11:39,566 --> 00:11:43,230
how could there be
active volcanoes on a moon?
164
00:11:43,236 --> 00:11:46,763
The answer was simple --
gravity.
165
00:11:46,773 --> 00:11:49,504
Jupiter's gravity is so huge
166
00:11:49,509 --> 00:11:52,376
that it reaches out
and crunches the moon.
167
00:11:55,348 --> 00:11:58,978
And it's not just Jupiter's
gravity pulling on lo.
168
00:11:58,985 --> 00:12:03,889
Other nearby moons
also pull on it as they pass by.
169
00:12:06,026 --> 00:12:07,892
So the core of the moon
170
00:12:07,894 --> 00:12:10,955
is being worked back and forth
all the time.
171
00:12:10,964 --> 00:12:13,023
It's called tidal friction
172
00:12:13,033 --> 00:12:16,264
and generates extreme heat
in lo's core.
173
00:12:16,269 --> 00:12:19,295
Dr. Durda: Almost like bending a
wire coat hanger until it breaks.
174
00:12:19,306 --> 00:12:21,468
And you feel the inside
of the coat hanger there --
175
00:12:21,474 --> 00:12:22,669
it feels rather warm.
176
00:12:22,676 --> 00:12:25,111
That tidal friction --
that internal friction --
177
00:12:25,111 --> 00:12:27,842
heats the interior of lo
until it's become,
178
00:12:27,847 --> 00:12:30,316
actually, one of the most
volcanically active worlds
179
00:12:30,317 --> 00:12:32,251
in the solar system.
180
00:12:32,252 --> 00:12:34,414
Narrator: The constant
pushing and pulling
181
00:12:34,421 --> 00:12:37,755
generates temperatures
thousands of degrees high
182
00:12:37,757 --> 00:12:39,418
inside lo.
183
00:12:39,426 --> 00:12:42,828
It blasts out
in gigantic eruptions of lava.
184
00:12:42,829 --> 00:12:45,264
Lo is the prime example
185
00:12:45,265 --> 00:12:48,963
of tidal forces
and gravitational interactions
186
00:12:48,969 --> 00:12:50,437
in the solar system.
187
00:12:50,437 --> 00:12:52,701
It is constantly being pulled
by Jupiter,
188
00:12:52,706 --> 00:12:54,663
and it's
constantly getting pulled
189
00:12:54,674 --> 00:12:56,176
by the other moons, as well.
190
00:12:56,176 --> 00:12:57,302
And so, as a result,
191
00:12:57,310 --> 00:12:59,642
there's a tremendous amount
of heat created.
192
00:13:03,817 --> 00:13:06,047
Narrator:
The floods of erupting lava
193
00:13:06,052 --> 00:13:08,646
constantly resurface lo,
194
00:13:08,655 --> 00:13:11,886
which is why there are
no visible impact craters
195
00:13:11,891 --> 00:13:14,258
on this moon.
196
00:13:17,297 --> 00:13:21,530
Gravity also heats
lo's neighbor, Europa.
197
00:13:21,534 --> 00:13:25,300
Europa's orbit is farther away
from Jupiter,
198
00:13:25,305 --> 00:13:26,568
so it's much colder.
199
00:13:26,573 --> 00:13:31,204
Instead of lava,
the surface of Europa is ice.
200
00:13:33,647 --> 00:13:36,446
The lowest recorded temperature
in Antarctica
201
00:13:36,449 --> 00:13:39,578
is minus-128 degrees.
202
00:13:39,586 --> 00:13:42,487
Europa's surface
is twice as cold.
203
00:13:44,257 --> 00:13:47,249
But underneath all the ice,
204
00:13:47,260 --> 00:13:50,025
there may be an ocean of water
205
00:13:50,030 --> 00:13:52,556
heated by
the same tidal friction
206
00:13:52,565 --> 00:13:54,795
that makes lo volcanic.
207
00:13:57,671 --> 00:13:59,799
Dr. Hendrix:
Europa has a subsurface ocean,
208
00:13:59,806 --> 00:14:02,002
almost certainly.
209
00:14:02,008 --> 00:14:07,174
And that subsurface ocean is in
contact with the rocky mantle,
210
00:14:07,180 --> 00:14:08,944
which provides heat
211
00:14:08,948 --> 00:14:11,645
and also provides,
probably,
212
00:14:11,651 --> 00:14:14,382
appropriate nutrients
to sustain life.
213
00:14:16,556 --> 00:14:19,025
Narrator:
Someday we'll send a probe
214
00:14:19,025 --> 00:14:21,790
to explore beneath the ice
on Europa.
215
00:14:25,398 --> 00:14:28,561
And maybe we'll discover
life-forms living there
216
00:14:28,568 --> 00:14:32,334
in warm European oceans.
217
00:14:36,910 --> 00:14:41,575
Out beyond lo and Europa
are nearly 60 more moons.
218
00:14:46,886 --> 00:14:49,412
They orbit much further away
from Jupiter,
219
00:14:49,422 --> 00:14:52,221
where the effects
of the giant planet's gravity
220
00:14:52,225 --> 00:14:55,092
are much weaker.
221
00:14:59,399 --> 00:15:01,493
Out here, it's too weak
222
00:15:01,501 --> 00:15:04,869
to generate tidal friction
and heat the moons.
223
00:15:06,806 --> 00:15:10,367
So these remote worlds
224
00:15:10,377 --> 00:15:13,074
are cold and barren...
225
00:15:13,079 --> 00:15:16,140
But not featureless.
226
00:15:16,149 --> 00:15:19,414
They bear the scars
of countless collisions,
227
00:15:19,419 --> 00:15:23,686
and scientists believe
it was collisions that created
228
00:15:23,690 --> 00:15:28,287
the most extraordinary
moon system of them all.
229
00:15:36,169 --> 00:15:39,002
Narrator: The planet with
the most unusual moon system
230
00:15:39,005 --> 00:15:42,066
is Saturn.
231
00:15:42,075 --> 00:15:47,479
It's spread out
over more than 200,000 miles.
232
00:15:47,480 --> 00:15:51,815
Technically, there are
more than a billion moons.
233
00:15:51,818 --> 00:15:54,844
That's right --
a billion moons.
234
00:15:54,854 --> 00:15:58,620
And all together,
they make up Saturn's rings.
235
00:16:01,628 --> 00:16:06,361
A moon can be a hunk of rock
or ice no bigger than a pebble,
236
00:16:06,366 --> 00:16:08,528
as long as it orbits a planet.
237
00:16:08,535 --> 00:16:10,560
The rings of Saturn are made
238
00:16:10,570 --> 00:16:13,369
of countless pieces
of rock and ice.
239
00:16:13,373 --> 00:16:15,865
They go from the size
of a pebble
240
00:16:15,875 --> 00:16:17,639
up to the size of a city.
241
00:16:17,644 --> 00:16:21,103
We don't refer
to all the ring particles
242
00:16:21,114 --> 00:16:24,379
that can get to be as big
as 10 or 20 meters across.
243
00:16:24,384 --> 00:16:26,944
We don't refer to them
as individual moons.
244
00:16:26,953 --> 00:16:28,819
But when we find a body
245
00:16:28,822 --> 00:16:32,053
that is maybe a kilometer
or two across,
246
00:16:32,058 --> 00:16:35,460
then you can start talking
about it as a moon or a moonlet.
247
00:16:38,465 --> 00:16:39,955
Narrator: Saturn's rings
248
00:16:39,966 --> 00:16:42,799
are one of the oldest mysteries
of astronomy.
249
00:16:42,802 --> 00:16:45,669
Where did they come from?
250
00:16:45,672 --> 00:16:49,472
To try and find out,
251
00:16:49,476 --> 00:16:51,945
NASA sent the Cassini probe
on a 12-year mission
252
00:16:51,945 --> 00:16:56,781
to study Saturn, its rings,
and its moons.
253
00:17:02,856 --> 00:17:04,950
Dr. Porco:
We took, with Cassini,
254
00:17:04,958 --> 00:17:08,019
probably the most beautiful
picture that's ever been taken,
255
00:17:08,027 --> 00:17:11,156
and I'm not the only one
who has said this.
256
00:17:11,164 --> 00:17:15,067
Cassini was in the shadow
of Saturn, cast by the Sun,
257
00:17:15,068 --> 00:17:17,127
and so you don't see the Sun.
258
00:17:17,136 --> 00:17:21,403
You see the backlit planet of
Saturn and its beautiful rings.
259
00:17:21,407 --> 00:17:24,638
You see the refracted image
of the Sun
260
00:17:24,644 --> 00:17:27,670
poking out from the side
of Saturn.
261
00:17:27,680 --> 00:17:29,944
And nestled
in all of that splendor
262
00:17:29,949 --> 00:17:32,008
is this small little dot.
263
00:17:33,953 --> 00:17:36,979
Narrator:
That tiny dot is not a moon.
264
00:17:36,990 --> 00:17:39,789
That is
the distant planet Earth,
265
00:17:39,792 --> 00:17:42,557
nearly a billion miles away.
266
00:17:45,598 --> 00:17:47,896
Most of what we know
about Saturn,
267
00:17:47,901 --> 00:17:51,303
of its rings and moons,
comes from Cassini.
268
00:17:51,304 --> 00:17:55,070
Before Cassini, we thought
there were only eight rings.
269
00:17:55,074 --> 00:17:58,977
Today we can see over 30.
270
00:17:58,978 --> 00:18:01,276
Dr. Porno".
What we have found at Saturn
271
00:18:01,281 --> 00:18:04,444
has been just literally
an embarrassment of riches.
272
00:18:04,450 --> 00:18:06,714
We're seeing something
that we had seen before,
273
00:18:06,719 --> 00:18:09,416
but now we're seeing it with
a level of detail and clarity
274
00:18:09,422 --> 00:18:10,821
that was just mind-blowing.
275
00:18:19,766 --> 00:18:21,928
Narrator:
Scientists used to think
276
00:18:21,935 --> 00:18:24,427
the rings were made
of the icy leftovers
277
00:18:24,437 --> 00:18:28,032
after Saturn was formed
about 4 billion years ago.
278
00:18:28,041 --> 00:18:29,770
But anything that old
279
00:18:29,776 --> 00:18:34,304
should be covered
with cosmic dust, and dirty.
280
00:18:36,149 --> 00:18:38,641
So why does Saturn's rings
281
00:18:38,651 --> 00:18:42,645
appear bright and clean,
almost new?
282
00:18:46,859 --> 00:18:48,418
To get the answer,
283
00:18:48,428 --> 00:18:52,456
Mission Control maneuvered
Cassini close to the rings.
284
00:18:54,834 --> 00:18:58,395
The probe saw that
all the ice pieces in the rings
285
00:18:58,404 --> 00:19:01,806
are constantly colliding
and breaking up.
286
00:19:06,479 --> 00:19:09,938
And each collision
exposes new surfaces
287
00:19:09,949 --> 00:19:12,418
that are clean and polished.
288
00:19:21,327 --> 00:19:24,957
This is what astronomers
think happened.
289
00:19:24,964 --> 00:19:26,830
When Saturn was young,
290
00:19:26,833 --> 00:19:30,770
it had no rings,
just lots of moons.
291
00:19:30,770 --> 00:19:33,398
At some point, an icy comet
292
00:19:33,406 --> 00:19:35,500
zoomed in from deep space
293
00:19:35,508 --> 00:19:38,136
and smashed
into one of those moons.
294
00:19:38,144 --> 00:19:42,047
The comet broke up
into billions of pieces.
295
00:19:45,685 --> 00:19:49,849
The impact also pushed
the moon closer to Saturn,
296
00:19:49,856 --> 00:19:53,315
where the planet's
enormous gravity broke it up.
297
00:20:00,566 --> 00:20:05,436
Now debris from the moon
and ice from the comet mixed.
298
00:20:07,674 --> 00:20:09,938
Gradually, Saturn's gravity
299
00:20:09,942 --> 00:20:14,470
pulled all those fragments
into rings around it.
300
00:20:17,283 --> 00:20:21,254
The story of moons
is the story of gravity.
301
00:20:21,254 --> 00:20:23,951
Gravity holds them in orbit.
302
00:20:23,956 --> 00:20:28,917
It heats up their insides
and shapes their surfaces.
303
00:20:28,928 --> 00:20:33,388
In the end, it controls
everything about moons,
304
00:20:33,399 --> 00:20:36,130
even their survival
and destruction.
305
00:20:38,971 --> 00:20:41,804
Gravity can even create
new moons
306
00:20:41,808 --> 00:20:48,305
by kidnapping asteroids,
comets, and even whole planets.
307
00:20:55,288 --> 00:20:57,882
Narrator: We know
that gravity makes moons.
308
00:21:00,693 --> 00:21:03,492
The standard way
is to assemble them
309
00:21:03,496 --> 00:21:06,761
from debris leftover
when planets are formed.
310
00:21:09,402 --> 00:21:12,702
But gravity makes moons
a second way, too.
311
00:21:12,705 --> 00:21:14,571
It captures them.
312
00:21:17,944 --> 00:21:21,278
Imagine a wandering comet
or asteroid.
313
00:21:21,280 --> 00:21:24,272
Somehow it gets knocked
off course.
314
00:21:24,283 --> 00:21:28,117
It wanders too close
to a planet.
315
00:21:28,121 --> 00:21:32,957
Gravity acts like
a science-fiction tractor beam
316
00:21:32,959 --> 00:21:34,222
and grabs it.
317
00:21:34,227 --> 00:21:37,356
Not quite enough gravity,
and it escapes.
318
00:21:38,965 --> 00:21:43,368
Too much gravity, and it
collides with the planet.
319
00:21:43,369 --> 00:21:47,135
Just enough,
and the comet or asteroid
320
00:21:47,140 --> 00:21:49,768
goes into orbit
around the planet
321
00:21:49,776 --> 00:21:52,006
and becomes a new moon.
322
00:21:57,483 --> 00:22:02,182
Mars has two tiny moons,
named Phobos and Deimos.
323
00:22:02,188 --> 00:22:05,920
Both are captured asteroids.
324
00:22:05,925 --> 00:22:09,486
One is pushing outward
as it circles the planet
325
00:22:09,495 --> 00:22:11,486
and will eventually break free
326
00:22:11,497 --> 00:22:14,558
and continue on its journey
through space.
327
00:22:14,567 --> 00:22:17,195
The other is circling inwards,
328
00:22:17,203 --> 00:22:20,229
a little closer to Mars
all the time.
329
00:22:20,239 --> 00:22:23,402
Eventually,
it'll smash into it.
330
00:22:31,050 --> 00:22:33,314
This is Cruithne.
331
00:22:33,319 --> 00:22:36,516
It's an asteroid, really,
just three miles across.
332
00:22:36,522 --> 00:22:41,392
But it's sometimes described
as Earth's second moon.
333
00:22:41,394 --> 00:22:44,022
Dr. Durda:
With the little object Cruithne,
334
00:22:44,030 --> 00:22:46,328
which was discovered
back in 1986,
335
00:22:46,332 --> 00:22:49,063
we start to get
into this realm of --
336
00:22:49,068 --> 00:22:51,765
of what does it mean
to be a moon.
337
00:22:51,771 --> 00:22:55,071
Narrator:
Only a few thousand years ago,
338
00:22:55,074 --> 00:22:57,600
Cruithne was
an ordinary asteroid,
339
00:22:57,610 --> 00:23:00,477
orbiting the Sun
like billions of others.
340
00:23:00,479 --> 00:23:02,379
But eventually, it wobbled
341
00:23:02,381 --> 00:23:04,748
out of its orbit
in the Asteroid Belt
342
00:23:04,750 --> 00:23:07,151
and got snagged
by Earth's gravity.
343
00:23:09,589 --> 00:23:13,457
But then Cruithne
did something unusual.
344
00:23:13,459 --> 00:23:16,053
Instead of orbiting
around the Earth,
345
00:23:16,062 --> 00:23:17,621
like a normal moon,
346
00:23:17,630 --> 00:23:20,759
Cruithne began to follow
behind it.
347
00:23:20,766 --> 00:23:24,930
And so one might call it
a sort of a moon of the Earth --
348
00:23:24,937 --> 00:23:27,269
not exactly, though,
because that object is on --
349
00:23:27,273 --> 00:23:29,401
you know, it's
on its own independent orbit
350
00:23:29,408 --> 00:23:30,910
around the Sun,
not the Earth.
351
00:23:35,047 --> 00:23:39,245
Narrator: Sometimes asteroids
capture their own moons.
352
00:23:39,252 --> 00:23:42,415
In 1993, the Galileo spacecraft
353
00:23:42,421 --> 00:23:44,890
flew past the asteroid Ida
354
00:23:44,891 --> 00:23:48,054
and found something
nobody expected --
355
00:23:48,060 --> 00:23:51,553
a tiny half-mile-wide moon.
356
00:23:53,232 --> 00:23:55,599
Dr. Durda:
The fact that we saw a satellite
357
00:23:55,601 --> 00:23:57,126
around only
the second asteroid
358
00:23:57,136 --> 00:23:59,036
ever to be encountered
with a spacecraft
359
00:23:59,038 --> 00:24:00,335
immediately tells us
360
00:24:00,339 --> 00:24:03,570
that moons around asteroids
must be incredibly common.
361
00:24:07,680 --> 00:24:10,342
Narrator: Not all
captured moons are small.
362
00:24:10,349 --> 00:24:13,979
The mother of all
captured moons is Triton.
363
00:24:13,986 --> 00:24:19,152
It orbits the planet Neptune,
and it is big --
364
00:24:19,158 --> 00:24:22,093
about 1,700 miles in diameter.
365
00:24:22,094 --> 00:24:26,361
But Triton is a moon
with an unusual story.
366
00:24:27,767 --> 00:24:30,168
Triton was
a very puzzling problem
367
00:24:30,169 --> 00:24:31,864
for planetary scientists,
368
00:24:31,871 --> 00:24:33,703
because our traditional view
369
00:24:33,706 --> 00:24:35,697
would tend to make
all the moons orbit
370
00:24:35,708 --> 00:24:38,268
in the same direction
that the planet itself spins.
371
00:24:38,277 --> 00:24:40,439
In the case of Triton
around Neptune,
372
00:24:40,446 --> 00:24:41,914
it's the other way around.
373
00:24:41,914 --> 00:24:43,507
Neptune is spinning this way.
374
00:24:43,516 --> 00:24:46,383
Triton is orbiting around
in the opposite direction.
375
00:24:46,385 --> 00:24:50,720
Narrator: This means
it didn't form like most moons,
376
00:24:50,723 --> 00:24:53,852
out of the debris leftover
from the birth of the planet,
377
00:24:53,859 --> 00:24:57,352
or it would orbit
in the same direction.
378
00:24:57,363 --> 00:24:59,889
So something wasn't right.
379
00:24:59,899 --> 00:25:04,200
Dr. Grinspoon: Triton is huge,
and its orbit is funny.
380
00:25:04,203 --> 00:25:05,193
It's anomalous.
381
00:25:05,204 --> 00:25:07,104
It does not seem
as though it formed
382
00:25:07,106 --> 00:25:10,508
as a part of the Neptune system.
383
00:25:10,509 --> 00:25:15,174
It seems much more
like a captured planet.
384
00:25:15,181 --> 00:25:18,640
Narrator:
Scientists now think Triton
385
00:25:18,651 --> 00:25:21,245
was once a dwarf planet,
like Pluto.
386
00:25:21,253 --> 00:25:24,985
And a giant planet like Neptune
certainly has enough gravity
387
00:25:24,991 --> 00:25:28,791
to capture a moon
the size of Triton.
388
00:25:28,794 --> 00:25:31,354
Dr. Hendrix: Triton
was almost certainly formed
389
00:25:31,364 --> 00:25:33,264
way out
in the outer solar system
390
00:25:33,265 --> 00:25:35,825
and then at some point
was captured by Neptune.
391
00:25:35,835 --> 00:25:38,099
Perhaps Triton, early on,
had its own moon,
392
00:25:38,104 --> 00:25:39,503
they both were captured,
393
00:25:39,505 --> 00:25:42,805
and then that moon was destroyed
during the capture process.
394
00:25:44,877 --> 00:25:47,574
Narrator:
But Triton is in danger.
395
00:25:47,580 --> 00:25:51,483
Neptune is dragging it
closer and closer.
396
00:25:53,552 --> 00:25:57,580
Eventually,
it will get too close,
397
00:25:57,590 --> 00:26:02,027
and Neptune's immense gravity
will tear it apart.
398
00:26:13,839 --> 00:26:17,298
Triton the moon will be reborn
399
00:26:17,309 --> 00:26:20,540
as a ring system
around the planet.
400
00:26:32,792 --> 00:26:35,056
But what about our Moon?
401
00:26:35,061 --> 00:26:36,893
How did it get there?
402
00:26:36,896 --> 00:26:39,263
Was it captured?
403
00:26:42,568 --> 00:26:46,368
The truth
is even more extraordinary.
404
00:26:46,372 --> 00:26:50,605
It was born in extreme violence.
405
00:26:56,082 --> 00:26:58,210
Narrator:
Our Moon, like a lot of moons,
406
00:26:58,217 --> 00:27:03,747
is rocky, barren,
and pockmarked with craters.
407
00:27:03,756 --> 00:27:09,058
But in one way, our Moon
is unique in the solar system.
408
00:27:13,165 --> 00:27:14,564
For a long time,
409
00:27:14,567 --> 00:27:16,729
astronomers thought
the Moon formed
410
00:27:16,735 --> 00:27:20,103
from debris leftover
from the birth of the Earth.
411
00:27:20,106 --> 00:27:21,972
But researchers in the 1960s
412
00:27:21,974 --> 00:27:25,171
came up with
a radically different idea.
413
00:27:25,177 --> 00:27:29,614
They suggested
it came from a giant impact.
414
00:27:43,762 --> 00:27:45,958
Dr. Hartmann:
When we first had the idea
415
00:27:45,965 --> 00:27:49,230
of forming the Moon
from a giant impact,
416
00:27:49,235 --> 00:27:52,569
that was not
a terribly popular idea.
417
00:27:52,571 --> 00:27:55,700
And I actually did have good
science friends -- colleagues --
418
00:27:55,708 --> 00:27:58,973
coming to me, saying, you know,
we really have to exhaust
419
00:27:58,978 --> 00:28:01,606
all the slow
evolutionary theories
420
00:28:01,614 --> 00:28:04,640
before we start talking
about cataclysms.
421
00:28:04,650 --> 00:28:07,950
Narrator: The evidence
Bill Hartmann needed
422
00:28:07,953 --> 00:28:09,682
was on the Moon itself.
423
00:28:12,858 --> 00:28:14,451
And the proof had to wait
424
00:28:14,460 --> 00:28:19,626
until Apollo astronauts
finally went there in 1969.
425
00:28:21,901 --> 00:28:25,428
They brought back hundreds
of pounds of Moon rocks.
426
00:28:27,239 --> 00:28:31,176
Scientists analyzed the rocks
and were amazed.
427
00:28:31,177 --> 00:28:34,841
They were identical to rocks
in the Earth's crust,
428
00:28:34,847 --> 00:28:38,909
and they'd been superheated.
429
00:28:38,918 --> 00:28:43,048
So, how did
pieces of the Earth's crust
430
00:28:43,055 --> 00:28:45,524
become superhot
and wind up on the Moon?
431
00:28:45,524 --> 00:28:48,619
Hartmann was pretty sure
he knew.
432
00:28:48,627 --> 00:28:51,494
Dr. Hartmann: This whole idea
was that the Earth forms.
433
00:28:51,497 --> 00:28:53,158
Now you hit it with something.
434
00:28:53,165 --> 00:28:56,066
You blow all this light,
rocky material off the top.
435
00:28:56,068 --> 00:28:58,799
That material goes into orbit
and makes the Moon.
436
00:28:58,804 --> 00:29:01,739
The Moon's just made
out of rocky debris.
437
00:29:05,411 --> 00:29:08,836
Narrator: Imagine our
chaotic solar system
438
00:29:08,847 --> 00:29:10,679
4.5 billion years ago.
439
00:29:17,089 --> 00:29:19,387
The young Earth is just one
440
00:29:19,391 --> 00:29:22,986
of a hundred or so new planets
orbiting the Sun.
441
00:29:28,200 --> 00:29:32,694
One of them is a Mars-sized
planet called Theia,
442
00:29:32,705 --> 00:29:35,697
and it's on a collision course
with Earth.
443
00:29:40,613 --> 00:29:42,547
They smash into each other
444
00:29:42,548 --> 00:29:45,483
at many thousands of miles
an hour.
445
00:29:57,763 --> 00:30:02,030
Theia is destroyed,
and Earth barely survives.
446
00:30:02,034 --> 00:30:06,699
The impact blasts billions
of tons of debris into space.
447
00:30:06,705 --> 00:30:11,541
The Earth's gravity pulls it
into orbit around the planet.
448
00:30:11,543 --> 00:30:14,706
Now these hunks
of leftover Earth
449
00:30:14,713 --> 00:30:18,013
clump together
and form our Moon.
450
00:30:33,432 --> 00:30:38,097
That's the theory, anyway.
But how do you test it for real?
451
00:30:40,372 --> 00:30:42,466
Here at NASA's
Vertical Gun Range,
452
00:30:42,474 --> 00:30:46,911
they're re-creating
that ancient collision in a lab.
453
00:30:49,048 --> 00:30:52,074
This 30-foot-long gun
fires a tiny projectile
454
00:30:52,084 --> 00:30:54,212
at 18,000 miles an hour.
455
00:30:57,723 --> 00:31:00,124
The projectile is Theia.
456
00:31:00,125 --> 00:31:02,719
This ball represents the Earth.
457
00:31:02,728 --> 00:31:05,925
By changing
the angle of Theia's impact,
458
00:31:05,931 --> 00:31:08,263
the team can figure out
how precise
459
00:31:08,267 --> 00:31:11,897
the ancient collision had to be
in order to make the Moon.
460
00:31:11,904 --> 00:31:13,895
In the first shot,
461
00:31:13,906 --> 00:31:18,468
Theia hits the top of the Earth
with a glancing blow.
462
00:31:18,477 --> 00:31:21,378
So, here's the Earth,
if you will, suspended in space.
463
00:31:21,380 --> 00:31:22,643
And now it's gotten hit.
464
00:31:24,350 --> 00:31:27,718
So, now we see
the planet ejecta
465
00:31:27,720 --> 00:31:30,417
is being ripped
out of the Earth
466
00:31:30,422 --> 00:31:33,084
and is forming
this giant impact basin.
467
00:31:33,092 --> 00:31:34,958
And if this
really were the Earth,
468
00:31:34,960 --> 00:31:37,986
this basin would be
thousands of kilometers --
469
00:31:37,996 --> 00:31:40,328
thousands of miles -- across.
470
00:31:40,332 --> 00:31:42,960
Narrator:
In this simulation,
471
00:31:42,968 --> 00:31:46,233
Theia only skims
off the surface of the planet,
472
00:31:46,238 --> 00:31:50,436
and very little debris
is thrown out into space --
473
00:31:50,442 --> 00:31:53,070
not nearly enough
to build our Moon.
474
00:31:53,078 --> 00:31:55,274
[indistinct conversation]
475
00:31:55,280 --> 00:31:57,647
[ Buzzer]
476
00:31:57,649 --> 00:31:59,151
[Crash]
477
00:31:59,151 --> 00:32:02,416
The second shot
is a head-on collision.
478
00:32:05,858 --> 00:32:07,257
Dr. Schultz: Ka-pow!
479
00:32:07,259 --> 00:32:11,787
That's the end of planet Earth.
It's gone.
480
00:32:11,797 --> 00:32:14,596
Some of the debris is gonna go
out of the solar system.
481
00:32:14,600 --> 00:32:16,432
Some of the debris
will reaccrete
482
00:32:16,435 --> 00:32:19,029
to form small planetesimals
within the solar system.
483
00:32:27,279 --> 00:32:29,077
Narrator:
There's no Earth left,
484
00:32:29,081 --> 00:32:30,515
so there's no gravity
485
00:32:30,516 --> 00:32:33,076
to gather the debris
and form the Moon.
486
00:32:35,154 --> 00:32:39,284
Now the gun is set
to just the right angle --
487
00:32:39,291 --> 00:32:43,524
halfway between a glancing blow
and a direct hit.
488
00:32:43,529 --> 00:32:47,830
So we'll see what happens
if the Earth barely survives.
489
00:32:54,673 --> 00:32:58,940
Oh, oh, gorgeous!
Oh, my gosh!
490
00:32:58,944 --> 00:33:00,002
Kill-pow'!
491
00:33:00,012 --> 00:33:02,640
Now we have the entire part
of the Earth
492
00:33:02,648 --> 00:33:04,138
being ripped apart,
493
00:33:04,149 --> 00:33:07,278
but the vapor plume is --
oh, my gosh.
494
00:33:07,286 --> 00:33:09,880
AW! QGGZ!
495
00:33:09,888 --> 00:33:11,822
That is gorgeous.
496
00:33:18,063 --> 00:33:23,661
But this was the beginning --
the beginning of our Moon.
497
00:33:25,471 --> 00:33:27,269
Narrator:
The experiment shows
498
00:33:27,272 --> 00:33:30,071
that Theia could have
smashed into the Earth
499
00:33:30,075 --> 00:33:32,976
and formed the Moon.
500
00:33:32,978 --> 00:33:36,539
But the collision
had to be just right.
501
00:33:36,548 --> 00:33:39,245
And lucky for us, it was.
502
00:33:45,257 --> 00:33:49,888
Today, the Moon orbits
250,000 miles from Earth.
503
00:33:51,430 --> 00:33:53,421
But when it first formed,
504
00:33:53,432 --> 00:33:56,424
the Moon orbited
just 15,000 miles
505
00:33:56,435 --> 00:33:58,369
above the Earth's surface.
506
00:34:01,039 --> 00:34:04,236
Dr. Schultz: 500 million years
after the Moon formed,
507
00:34:04,243 --> 00:34:05,677
if we looked up in the sky,
508
00:34:05,677 --> 00:34:08,703
the Moon would have comprised
a tremendous portion of the sky.
509
00:34:08,714 --> 00:34:10,182
It would have been enormous,
510
00:34:10,182 --> 00:34:12,446
because the Moon
would have been much closer.
511
00:34:14,319 --> 00:34:18,290
Narrator: Back then,
the Earth was rotating so fast,
512
00:34:18,290 --> 00:34:20,190
a day lasted just six hours.
513
00:34:23,028 --> 00:34:28,296
But the Moon was so close,
its gravity acted like a brake.
514
00:34:31,937 --> 00:34:34,406
It slowed our planet down
515
00:34:34,406 --> 00:34:38,434
until a day now lasts 24 hours.
516
00:34:40,345 --> 00:34:44,009
The Moon's gravity
also created giant tides
517
00:34:44,016 --> 00:34:46,007
that surged across the planet,
518
00:34:46,018 --> 00:34:50,148
churning up the seas,
mixing minerals and nutrients.
519
00:34:50,155 --> 00:34:52,852
This created
the primordial soup
520
00:34:52,858 --> 00:34:56,021
from which the first forms
of life arose.
521
00:34:56,028 --> 00:34:59,794
Without our Moon, life on Earth
may never have happened.
522
00:35:02,868 --> 00:35:07,863
And there may be other moons
with a link to life, as well.
523
00:35:07,873 --> 00:35:12,640
Moons may be the great biology
experiments of the universe --
524
00:35:12,644 --> 00:35:17,377
the true laboratories
of life itself.
525
00:35:23,655 --> 00:35:26,989
Narrator:
Moons are full of surprises.
526
00:35:26,992 --> 00:35:30,826
There are moons
with giant volcanoes,
527
00:35:30,829 --> 00:35:35,596
moons with vast oceans
sealed under thick ice.
528
00:35:38,437 --> 00:35:43,637
And now we know a few
are rich in organic compounds.
529
00:35:43,642 --> 00:35:47,613
In the right combination,
they might even support life.
530
00:35:47,613 --> 00:35:50,275
Dr. McKay: In our solar system,
the biological window
531
00:35:50,282 --> 00:35:53,047
through which we can understand
the rest of the universe
532
00:35:53,051 --> 00:35:55,918
may be through these moons
of the outer solar system.
533
00:35:55,921 --> 00:35:58,856
That may be where we find
our second genesis,
534
00:35:58,857 --> 00:36:00,325
and that second genesis
535
00:36:00,325 --> 00:36:03,056
is really
our first deep understanding
536
00:36:03,061 --> 00:36:05,428
of the biological nature
of the universe.
537
00:36:14,039 --> 00:36:18,272
Narrator: At first glance,
moons don't look ideal for life.
538
00:36:21,813 --> 00:36:24,976
Take Enceladus.
539
00:36:24,983 --> 00:36:29,250
It's a shiny ball of ice,
300 miles across,
540
00:36:29,254 --> 00:36:32,519
orbiting Saturn.
541
00:36:32,524 --> 00:36:34,822
It's the brightest object
in the solar system.
542
00:36:34,826 --> 00:36:37,488
It reflects 100% of the light
that hits it,
543
00:36:37,496 --> 00:36:38,793
so it's superbright,
544
00:36:38,797 --> 00:36:40,993
and that's because
it's water ice.
545
00:36:40,999 --> 00:36:43,491
Narrator:
In 2005, the Cassini probe
546
00:36:43,502 --> 00:36:48,440
spotted ice volcanoes erupting
from the surface of Enceladus.
547
00:36:48,440 --> 00:36:52,001
That meant there had to be
heat under all that ice --
548
00:36:52,010 --> 00:36:55,105
heat that created
oceans of water.
549
00:36:55,113 --> 00:36:59,710
And where there's water,
there's the possibility of life.
550
00:36:59,718 --> 00:37:03,848
So, this is Beehive Geyser
here in Yellowstone,
551
00:37:03,855 --> 00:37:06,449
and it is shooting water vapor
and water
552
00:37:06,458 --> 00:37:09,052
about 150 feet into the sky.
553
00:37:09,061 --> 00:37:11,496
And it's pretty incredible.
554
00:37:11,496 --> 00:37:14,158
So, now imagine if you're
on the surface of Enceladus.
555
00:37:14,166 --> 00:37:16,567
You would see geysers
that look a lot like this,
556
00:37:16,568 --> 00:37:21,233
and they are shooting ice grains
and water vapor into space
557
00:37:21,239 --> 00:37:23,867
thousands of times higher
than this geyser here.
558
00:37:23,875 --> 00:37:29,143
Narrator: The ice volcanoes
are powered by gravity.
559
00:37:29,147 --> 00:37:30,546
Here's how.
560
00:37:30,549 --> 00:37:33,610
Saturn's gravity works
on the core of the moon,
561
00:37:33,618 --> 00:37:34,983
heating it up.
562
00:37:34,986 --> 00:37:37,045
The underground water expands
563
00:37:37,055 --> 00:37:40,958
and forces its way up through
cracks in the surface ice
564
00:37:40,959 --> 00:37:45,260
and blasts out into space
as ice crystals.
565
00:37:45,263 --> 00:37:49,029
These are some of
the most spectacular eruptions
566
00:37:49,034 --> 00:37:50,593
in our solar system.
567
00:37:50,602 --> 00:37:54,470
They make Beehive Geyser
look like a squirt gun.
568
00:37:54,473 --> 00:37:56,965
From the ice in the volcanoes,
569
00:37:56,975 --> 00:38:01,674
scientists have detected salt
and simple organic compounds.
570
00:38:01,680 --> 00:38:04,843
That means
the water under the ice
571
00:38:04,850 --> 00:38:08,047
is not only warm
but full of nutrients.
572
00:38:08,053 --> 00:38:10,283
Sound familiar?
573
00:38:10,288 --> 00:38:13,053
Heat, water, and nutrients --
574
00:38:13,058 --> 00:38:15,493
that's how life on Earth began.
575
00:38:15,494 --> 00:38:18,293
Dr. Porco: We realize
you could have all the things
576
00:38:18,296 --> 00:38:20,663
that we associate
with oceans on the Earth
577
00:38:20,665 --> 00:38:21,962
going on inside a moon.
578
00:38:21,967 --> 00:38:24,095
It's the discovery
of a lifetime.
579
00:38:24,102 --> 00:38:27,766
Narrator: Saturn's
Enceladus has an ocean.
580
00:38:27,773 --> 00:38:29,935
So does Jupiter's Europa.
581
00:38:29,941 --> 00:38:34,742
But these aren't the only moons
where life could emerge.
582
00:38:34,746 --> 00:38:38,114
Saturn has another moon --
Titan --
583
00:38:38,116 --> 00:38:41,211
with an even greater potential
for life.
584
00:38:43,188 --> 00:38:48,092
In 2005, Cassini sent a probe,
called Huygens,
585
00:38:48,093 --> 00:38:50,050
on a one-way mission to Titan.
586
00:38:51,997 --> 00:38:54,796
For just 3 1/2 hours,
587
00:38:54,800 --> 00:38:57,098
Huygens transmitted
live pictures
588
00:38:57,102 --> 00:39:02,541
from the hostile surface,
nearly a billion miles away.
589
00:39:02,541 --> 00:39:05,875
Then the battery died.
590
00:39:05,877 --> 00:39:08,369
Dr. Porco:
It was just incredible.
591
00:39:08,380 --> 00:39:12,112
This was the first time humans
had ever touched this moon
592
00:39:12,117 --> 00:39:13,881
with something
of our own making.
593
00:39:13,885 --> 00:39:15,080
It was just an event
594
00:39:15,086 --> 00:39:17,350
that should have been
celebrated the world over.
595
00:39:17,355 --> 00:39:19,483
We should have had
ticker-tape parades
596
00:39:19,491 --> 00:39:21,585
in every major city
across the U.S. and Europe
597
00:39:21,593 --> 00:39:22,856
to celebrate this.
598
00:39:22,861 --> 00:39:26,456
It was that history-making
and that astonishing.
599
00:39:33,572 --> 00:39:36,041
Narrator:
Raindrops on Titan
600
00:39:36,041 --> 00:39:38,601
are twice as big
as raindrops on Earth.
601
00:39:40,645 --> 00:39:43,546
But the rain isn't water.
602
00:39:43,548 --> 00:39:46,347
It's methane.
603
00:39:46,351 --> 00:39:48,285
[thunder crashes]
604
00:39:50,488 --> 00:39:53,480
On Earth, methane is a gas,
605
00:39:53,491 --> 00:39:57,962
but on Titan, it's a liquid
because the moon is so cold.
606
00:40:01,600 --> 00:40:03,932
Dr. McKay:
There may be methane icebergs.
607
00:40:03,935 --> 00:40:06,427
There are certainly
methane lakes and rivers,
608
00:40:06,438 --> 00:40:08,839
and there's methane rain
and methane clouds
609
00:40:08,840 --> 00:40:10,865
and maybe bugs
swimming in methane.
610
00:40:10,876 --> 00:40:14,574
Narrator:
Bugs living in liquid methane
611
00:40:14,579 --> 00:40:16,775
may sound unbelievable.
612
00:40:16,781 --> 00:40:19,273
But scientists have discovered
613
00:40:19,284 --> 00:40:22,777
that Enceladus, Europa,
and Titan
614
00:40:22,787 --> 00:40:26,451
are all covered
with a substance called tholin.
615
00:40:26,458 --> 00:40:29,257
Tholin contains
the chemical building blocks
616
00:40:29,261 --> 00:40:31,423
for life to begin.
617
00:40:31,429 --> 00:40:36,230
So could life emerge
on any or all of these moons?
618
00:40:40,639 --> 00:40:43,404
We can't get our hands
on the tholin from the moons,
619
00:40:43,408 --> 00:40:46,434
so Chris McKay
makes it in the lab.
620
00:40:46,444 --> 00:40:51,143
He zaps a mixture of gases
found on Titan with electricity.
621
00:40:51,149 --> 00:40:56,485
What he gets
is a reddish-brown mud.
622
00:40:56,488 --> 00:40:58,445
So, this is
what we make -- tholin,
623
00:40:58,456 --> 00:41:02,017
this sort of nonbiological
organic material.
624
00:41:02,027 --> 00:41:04,121
It's produced by chemical energy
625
00:41:04,129 --> 00:41:06,757
put into simple molecules,
like methane and nitrogen,
626
00:41:06,765 --> 00:41:08,255
and here we got it.
627
00:41:08,266 --> 00:41:11,167
And that's the material
we see on Titan.
628
00:41:11,169 --> 00:41:14,730
We see evidence for something
like this on Enceladus.
629
00:41:14,739 --> 00:41:16,104
We see it on the surface
630
00:41:16,107 --> 00:41:18,701
of many of the moons
in the outer solar system.
631
00:41:18,710 --> 00:41:21,077
This is nature's recipe
632
00:41:21,079 --> 00:41:25,016
for making the stuff that life
eventually emerges from.
633
00:41:25,016 --> 00:41:29,510
Narrator: Somewhere in the outer
reaches of our solar system,
634
00:41:29,521 --> 00:41:32,013
OH some remote moon,
635
00:41:32,023 --> 00:41:35,857
life may have already emerged.
636
00:41:35,860 --> 00:41:39,922
But it probably won't be life
as we know it.
637
00:41:39,931 --> 00:41:42,127
Life 2.0 doesn't
necessarily have to have
638
00:41:42,133 --> 00:41:44,192
the same genetics
as life 1.0, right?
639
00:41:44,202 --> 00:41:47,263
In fact, the more different it
is, the more interesting it is.
640
00:41:49,808 --> 00:41:52,869
Narrator: Whether it's the same
or very different,
641
00:41:52,877 --> 00:41:56,472
the discovery of life
on the moons of our solar system
642
00:41:56,481 --> 00:41:59,678
will change the way
we look at the universe.
643
00:42:02,921 --> 00:42:06,118
Dr. Porco: I think that,
should we ever find
644
00:42:06,124 --> 00:42:07,455
that life had originated
645
00:42:07,459 --> 00:42:11,327
not once but twice
in our solar system,
646
00:42:11,329 --> 00:42:15,300
then you -- you can
easily dismiss any arguments
647
00:42:15,300 --> 00:42:19,533
that say that life
is unique to the Earth.
648
00:42:21,673 --> 00:42:23,573
Narrator:
Moons are small,
649
00:42:23,575 --> 00:42:27,273
but they're still
diverse and dynamic worlds.
650
00:42:27,278 --> 00:42:31,272
They help us understand
how the universe works.
651
00:42:31,282 --> 00:42:35,014
They're essential cogs
in the cosmic machine.
652
00:42:35,020 --> 00:42:37,250
Without any moons,
653
00:42:37,255 --> 00:42:40,919
our solar system would be
a very different place.
654
00:42:40,925 --> 00:42:45,590
Without our Moon, life may
never have evolved on Earth.
655
00:42:45,597 --> 00:42:47,065
And who knows --
656
00:42:47,065 --> 00:42:51,468
when and if we find new life
somewhere else in the universe,
657
00:42:51,469 --> 00:42:55,269
its home may not be
another planet at all.
658
00:42:55,273 --> 00:42:58,538
It might be...a moon.