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00:00:05,800 --> 00:00:09,237
Liftoff of Messenger on
NASA's mission to Mercury.
2
00:01:09,720 --> 00:01:12,872
Beyond the warm worlds
of the inner solar system...
3
00:01:17,760 --> 00:01:19,831
...beyond the gas giant Jupiter...
4
00:01:21,720 --> 00:01:24,838
...in the freezing regions
far beyond the Sun...
5
00:01:29,560 --> 00:01:30,630
...lies Saturn...
6
00:01:37,600 --> 00:01:39,592
...a planet made unique
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00:01:39,720 --> 00:01:45,398
thanks to a nearly 300,000-kilometre-wide
ring of frozen water.
8
00:01:57,800 --> 00:02:01,032
Here, trillions of pieces of ice
have been sculpted
9
00:02:01,160 --> 00:02:02,753
by gravitational forces
10
00:02:02,880 --> 00:02:07,238
into some of the solar system's
most stunning vistas.
11
00:02:30,800 --> 00:02:33,759
Here, on Earth, water takes many forms -
12
00:02:33,880 --> 00:02:36,793
oceans and clouds and rivers -
13
00:02:36,920 --> 00:02:42,075
but it's in its crystalline form - ice -
that it's at its most beautiful.
14
00:02:42,200 --> 00:02:44,635
Now, here, ice just adorns the landscape,
15
00:02:44,760 --> 00:02:47,798
but in the outer solar system,
where Saturn lives,
16
00:02:47,920 --> 00:02:53,871
ice is so abundant that, well,
it's become a building material.
17
00:02:54,000 --> 00:02:56,276
Now, there's no more beautiful sight
in the solar system
18
00:02:56,400 --> 00:02:58,631
than the ice rings of Saturn.
19
00:02:58,760 --> 00:03:02,720
It's almost as if a god has taken
snowflakes and sprinkled them
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00:03:02,840 --> 00:03:05,878
over a gravitational field
so we could see it.
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00:03:06,000 --> 00:03:08,310
But how could something so intricate
22
00:03:08,440 --> 00:03:12,070
be sculpted out of something so simple?
23
00:03:12,200 --> 00:03:18,595
Well, as is always the case in science,
the true beauty lies in the story.
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00:03:23,640 --> 00:03:28,431
Saturn is a planet that has undergone
some of the most radical transformations
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00:03:28,560 --> 00:03:29,835
in the solar system...
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00:03:38,680 --> 00:03:41,593
...a planet that has seen destruction...
27
00:03:50,280 --> 00:03:52,795
...and creation...
28
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...a planet that harbours hidden worlds...
29
00:04:05,720 --> 00:04:08,440
...where, just perhaps,
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00:04:08,560 --> 00:04:12,918
there may exist a second home for life.
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00:04:39,360 --> 00:04:43,400
Imagine a place with no surface
to stand...
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00:04:45,360 --> 00:04:47,397
...just an endless atmosphere.
33
00:05:01,880 --> 00:05:06,397
Compared to Earth, Saturn is so alien
that it's hard to imagine
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00:05:06,520 --> 00:05:09,399
how it could have grown
from the same ingredients.
35
00:05:11,320 --> 00:05:13,198
But go far enough back in time,
36
00:05:13,320 --> 00:05:16,916
and Saturn would appear to be
surprisingly familiar.
37
00:05:32,320 --> 00:05:36,280
Saturn began life
as tiny worlds of rock and ice...
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00:05:38,400 --> 00:05:41,120
...tumbling chaotically through space.
39
00:05:53,920 --> 00:05:57,152
Just like Earth, Mars, Venus and Mercury,
40
00:05:57,280 --> 00:06:01,479
they began to merge
and clump together and grow.
41
00:06:10,480 --> 00:06:12,676
But unlike the planets
of the inner solar system,
42
00:06:12,800 --> 00:06:18,956
Saturn was forming on the other side
of a boundary we call the snow line.
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00:06:23,440 --> 00:06:27,593
A place where the Sun is so distant,
and it's so cold
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00:06:27,720 --> 00:06:31,316
water exists
only in its frozen solid state.
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00:06:34,000 --> 00:06:39,394
Out here, trillions of particles of ice
behave just like rock,
46
00:06:39,520 --> 00:06:43,355
providing huge amounts
of extra planetary building material.
47
00:06:49,560 --> 00:06:50,994
Under the force of gravity,
48
00:06:51,120 --> 00:06:55,512
this abundant ice and rock collided
and combined...
49
00:06:58,440 --> 00:07:01,831
...helping the young Saturn
to grow into a giant.
50
00:07:19,440 --> 00:07:21,909
The details of how the planets formed
in the solar system
51
00:07:22,040 --> 00:07:23,554
is not fully understood.
52
00:07:23,680 --> 00:07:25,592
It's cutting-edge scientific research.
53
00:07:25,720 --> 00:07:27,757
I mean, we're talking about events
that happened
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00:07:27,880 --> 00:07:30,600
over 4.5 billion years ago.
55
00:07:30,720 --> 00:07:35,920
But it seems likely that Saturn was once
a world of rock and ice,
56
00:07:36,040 --> 00:07:39,670
perhaps 10 or even 20 times
the mass of the Earth.
57
00:07:39,800 --> 00:07:42,474
It's almost possible, in your dreams,
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00:07:42,600 --> 00:07:45,434
to imagine standing on its surface.
59
00:07:45,560 --> 00:07:49,679
But because of its immense mass
and its place in the solar system,
60
00:07:49,800 --> 00:07:53,760
Saturn didn't remain
a rocky, icy world for long.
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00:08:02,840 --> 00:08:07,995
As it grew older, Saturn became
a radically different kind of planet.
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00:08:10,600 --> 00:08:13,240
In the region in which the young world
was forming,
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00:08:13,360 --> 00:08:17,434
there was more than just ice and rock -
there were large amounts of gas.
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00:08:20,440 --> 00:08:23,319
And Saturn began to gain an atmosphere...
65
00:08:25,760 --> 00:08:29,390
...but on a scale unlike anything
we experience here on Earth.
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00:08:37,880 --> 00:08:41,191
It's not until you see
the Earth's atmosphere from space
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00:08:41,320 --> 00:08:44,757
that you appreciate
just how thin it really is.
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And it's a similar story
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00:08:57,200 --> 00:08:59,317
for the other worlds
of the inner solar system.
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00:09:19,600 --> 00:09:21,239
Despite being relatively thin,
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these atmospheres can exert
powerful forces
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00:09:24,640 --> 00:09:27,200
on the planetary surfaces beneath.
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00:09:37,360 --> 00:09:39,920
On Earth, you can see the effects
of an atmosphere
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00:09:40,040 --> 00:09:42,475
with nothing more than a sealed container.
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00:09:45,520 --> 00:09:48,831
It's easy to forget
that the atmosphere has a weight.
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00:09:48,960 --> 00:09:54,274
There's a column of air stretching up
about 100 kilometres above my head.
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00:09:54,400 --> 00:09:57,552
That's a lot of molecules,
and it exerts a pressure.
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00:09:59,760 --> 00:10:03,595
You really see it if you look at what
happens to this bottle.
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00:10:03,720 --> 00:10:06,872
We filled it with air
from the top of the mountain,
80
00:10:07,000 --> 00:10:08,719
which is about 3,000 metres.
81
00:10:08,840 --> 00:10:12,800
Now, up there, the atmosphere
is about 25% less dense
82
00:10:12,920 --> 00:10:15,674
than it is down there, at sea level.
83
00:10:15,800 --> 00:10:17,553
So, as we descend,
84
00:10:17,680 --> 00:10:21,196
the atmospheric pressure outside
is increasing,
85
00:10:21,320 --> 00:10:22,720
and the pressure in here
86
00:10:22,840 --> 00:10:25,514
is just what it was
at the top of the mountain,
87
00:10:25,640 --> 00:10:28,997
and so you see, visually,
that force in action,
88
00:10:29,120 --> 00:10:33,558
and that is squashing the bottle.
89
00:10:33,680 --> 00:10:35,558
Physics in action.
90
00:10:35,680 --> 00:10:37,239
It's brilliant, innit?
91
00:10:41,400 --> 00:10:44,791
While just a few hundred metres
of atmosphere can crush a bottle...
92
00:10:47,640 --> 00:10:49,871
...if an atmosphere gets big enough,
93
00:10:50,000 --> 00:10:52,196
it can transform an entire planet.
94
00:11:01,600 --> 00:11:04,320
Within just a few million years
of its birth...
95
00:11:05,800 --> 00:11:10,636
...Saturn had grown as large as it could
from rock and ice alone.
96
00:11:13,000 --> 00:11:16,516
And now it turned
to another building material -
97
00:11:16,640 --> 00:11:21,590
the hydrogen and helium gas left over
from the formation of the Sun.
98
00:11:28,720 --> 00:11:30,791
This gas would have been too light
99
00:11:30,920 --> 00:11:33,594
for the smaller worlds
of the inner solar system to hold on to.
100
00:11:34,760 --> 00:11:38,515
But Saturn's great mass
created gravitational forces
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00:11:38,640 --> 00:11:40,677
powerful enough to draw it in.
102
00:11:45,080 --> 00:11:49,791
Trillions upon trillions of tonnes
of hydrogen and helium gas
103
00:11:49,920 --> 00:11:52,754
began to envelop the planet.
104
00:11:57,160 --> 00:12:01,871
And as this new atmosphere grew,
it transformed the surface below.
105
00:12:08,680 --> 00:12:12,230
Enormous pressures,
created by the weight of this gas,
106
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heated rock and ice so much...
107
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...they began to glow.
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As Saturn matured,
the pressure at the surface
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rose to ten million times
the atmospheric pressure on Earth.
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00:12:27,880 --> 00:12:31,635
At those kind of pressures,
matter behaves in extremely strange ways.
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00:12:31,760 --> 00:12:35,720
The very idea of a surface
becomes meaningless,
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00:12:35,840 --> 00:12:39,231
and Saturn was transformed
from an icy, rocky world
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00:12:39,360 --> 00:12:43,752
into a completely different class
of planet - a gas giant.
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00:12:53,160 --> 00:12:59,191
Saturn was now so big it could contain
nearly 5,000 Earth-sized worlds.
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But this vast, wild proto-planet
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was totally unlike
the Saturn we see today.
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00:13:10,960 --> 00:13:14,237
To discover how that world emerged,
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00:13:14,360 --> 00:13:18,070
we had to send spacecraft
to meet it close up.
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00:13:27,000 --> 00:13:30,960
We have ignition,
and we have liftoff of the Titan-Centaur,
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00:13:31,080 --> 00:13:33,470
carrying the first
of two Voyager spacecraft
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00:13:33,600 --> 00:13:38,800
to extend man's senses farther into the
solar system than ever before.
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00:13:54,960 --> 00:13:58,317
Reports coming back indicate
those twin large solid motors
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00:13:58,440 --> 00:14:03,356
are functioning perfectly, producing
1.2 million tonnes of thrust each.
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00:14:10,920 --> 00:14:15,676
The guidance data coming back shows
that we're right on the money.
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00:14:24,680 --> 00:14:26,592
It's there!
126
00:14:30,080 --> 00:14:33,471
Voyager 2 has reached Saturn
after four years in space.
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00:14:33,600 --> 00:14:37,958
It got there just a bit early,
2.7 seconds early, to be exact,
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00:14:38,080 --> 00:14:40,834
after a flight of 1.25 billion miles.
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00:14:55,000 --> 00:15:00,029
The Voyager probes gave us
our first detailed look at Saturn,
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00:15:00,160 --> 00:15:03,517
revealing the planet
in exquisite resolution.
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00:15:08,480 --> 00:15:10,517
There's just an amazing harvest
of pictures.
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00:15:10,640 --> 00:15:14,031
You know, there's tens of thousands
of photographs of Saturn
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00:15:14,160 --> 00:15:17,915
and its rings and its moons
taken by the Voyager 2 spacecraft.
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00:15:21,000 --> 00:15:22,912
For the very first time,
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00:15:23,040 --> 00:15:27,478
we were able to study
Saturn's vast atmosphere in detail.
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00:15:29,760 --> 00:15:34,630
Saturn itself is composed
of hydrogen and helium.
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00:15:36,200 --> 00:15:39,079
And we are seeing
an exotic meteorology here.
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00:15:45,880 --> 00:15:49,794
Voyager showed beyond doubt
that Saturn's upper atmosphere
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00:15:49,920 --> 00:15:53,231
was made almost entirely
of helium and hydrogen...
140
00:15:55,920 --> 00:15:59,834
...the very same gasses so abundant
in the early solar system.
141
00:16:07,280 --> 00:16:12,400
But this once-chaotic gas was now
organised into intricate weather systems.
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00:16:16,480 --> 00:16:20,474
And one above all others
took the Voyager team by surprise.
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00:16:23,360 --> 00:16:26,319
A huge hexagonal structure
in the clouds,
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00:16:26,440 --> 00:16:31,560
so big it could fit our entire planet
within it nearly four times over.
145
00:16:34,840 --> 00:16:38,470
The atmosphere of Saturn
was revealing itself to be stranger
146
00:16:38,600 --> 00:16:41,752
and more dynamic
than we could ever have imagined.
147
00:17:02,920 --> 00:17:05,435
Atmospheres
are some of the most spectacular
148
00:17:05,560 --> 00:17:08,359
and complex planetary environments.
149
00:17:14,800 --> 00:17:18,271
Not many people see the Alps
like this. Seriously.
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00:17:18,400 --> 00:17:19,754
It's just so great!
151
00:17:21,800 --> 00:17:25,271
I was afraid that you'd just get,
you know, too sick, or something.
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00:17:25,400 --> 00:17:27,869
It's awesome! Man!
153
00:17:28,000 --> 00:17:29,480
It's fun, man.
154
00:17:31,120 --> 00:17:32,395
This is fun!
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00:17:38,560 --> 00:17:43,191
The atmosphere of every planet
takes on its own unique character.
156
00:17:45,440 --> 00:17:48,990
But what powers them
and the weather systems within
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00:17:49,120 --> 00:17:52,079
depends on where you are
in the solar system.
158
00:17:53,960 --> 00:17:57,397
Most of the weather on the Earth
is driven by the heat of the Sun.
159
00:17:57,520 --> 00:17:59,159
It heats the ground up, down there,
160
00:17:59,280 --> 00:18:03,559
and that in turn heats the air up
close to the ground, makes it expand.
161
00:18:03,680 --> 00:18:07,560
That means that the air becomes less dense
and the hot air rises.
162
00:18:07,680 --> 00:18:09,478
That means you get thermals,
163
00:18:09,600 --> 00:18:13,640
so energetic movements of air
from the ground into the upper atmosphere,
164
00:18:13,760 --> 00:18:16,719
and that's what we're
exploiting now... to glide.
165
00:18:26,640 --> 00:18:32,113
So all this beautiful weather
is driven by the Sun heating the land
166
00:18:32,240 --> 00:18:34,118
and causing air to move around.
167
00:18:36,440 --> 00:18:37,954
So we're sailing around.
168
00:18:38,080 --> 00:18:42,757
Sailing around in a turbulent,
moving ocean of air.
169
00:18:50,520 --> 00:18:53,354
But travel further out
into the solar system,
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00:18:53,480 --> 00:18:57,315
and the driving forces
within an atmosphere must change.
171
00:18:59,120 --> 00:19:03,399
Now, there's been weather on Saturn
for over 4 billion years.
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00:19:03,520 --> 00:19:05,591
But Saturn is a long way from the Sun,
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00:19:05,720 --> 00:19:09,555
and so those weather systems are not
primarily driven by the Sun's heat.
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00:19:11,160 --> 00:19:15,200
And yet, the storms on Saturn
are amongst the most violent
175
00:19:15,320 --> 00:19:17,596
found anywhere in the solar system.
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00:19:27,920 --> 00:19:32,790
With sunlight almost 100 times weaker
on Saturn than it is here on Earth...
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00:19:35,600 --> 00:19:39,196
...it means something else
is helping drive its weather...
178
00:19:41,760 --> 00:19:45,515
...and the huge complex forms that
arise in its atmosphere.
179
00:19:56,840 --> 00:20:01,153
By studying the cloud tops of Saturn
and its great storm systems...
180
00:20:02,440 --> 00:20:04,318
...we can now infer a great deal
181
00:20:04,440 --> 00:20:07,399
about the strange world
that lies beneath...
182
00:20:16,000 --> 00:20:19,516
...and the energy source
that helps power this planet.
183
00:20:32,720 --> 00:20:35,076
Below the upper atmosphere,
184
00:20:35,200 --> 00:20:37,317
great clouds of water grow.
185
00:20:41,840 --> 00:20:47,598
Lightning 10,000 times more powerful
than on Earth illuminates the sky.
186
00:21:02,880 --> 00:21:08,717
This lightning transforms methane gas
into huge clouds of soot.
187
00:21:18,480 --> 00:21:21,552
Deeper still, the pressures grow so great
188
00:21:21,680 --> 00:21:27,551
that these chunks of soot
are likely transformed into diamonds.
189
00:21:36,080 --> 00:21:40,120
But even these diamonds will succumb
to the pressures of Saturn...
190
00:21:41,240 --> 00:21:43,800
...eventually liquefying.
191
00:21:56,080 --> 00:22:00,120
It's not until 40,000 kilometres down
192
00:22:00,240 --> 00:22:04,029
that the major source of Saturn's energy
is revealed.
193
00:22:05,840 --> 00:22:08,150
Here, pressures are so intense
194
00:22:08,280 --> 00:22:11,830
gasses behave like liquid metal.
195
00:22:11,960 --> 00:22:15,271
Molten helium falls like rain
through hydrogen...
196
00:22:17,160 --> 00:22:19,959
...and releases incredible
amounts of heat.
197
00:22:26,680 --> 00:22:30,276
And we think that
this is the extraordinary heat source
198
00:22:30,400 --> 00:22:33,552
that has been helping to drive
Saturn's weather.
199
00:22:56,880 --> 00:23:00,271
Within just a few hundred million years
of its birth,
200
00:23:00,400 --> 00:23:02,676
Saturn had lived a life of drama.
201
00:23:03,760 --> 00:23:08,277
Now it remained largely unchanged
for billions of years,
202
00:23:08,400 --> 00:23:11,950
although still very different
from the planet we know today.
203
00:23:17,680 --> 00:23:21,151
But in time, it's great size would lead
204
00:23:21,280 --> 00:23:24,671
to one more iconic transformation.
205
00:23:34,960 --> 00:23:37,634
Saturn is a planet defined by its rings.
206
00:23:37,760 --> 00:23:41,595
If you get a child to draw a planet,
and quite a lot of the time
207
00:23:41,720 --> 00:23:44,030
they'll draw something
that looks like Saturn.
208
00:23:44,160 --> 00:23:48,632
Now, close up, they are almost impossibly
delicate and intricate.
209
00:23:48,760 --> 00:23:51,639
They're made up of trillions
of ice crystals,
210
00:23:51,760 --> 00:23:53,911
most of them no bigger than snowflakes,
211
00:23:54,040 --> 00:23:56,919
but some of them as large as houses.
212
00:23:57,040 --> 00:24:00,636
Now, if you look through a telescope,
they're highly reflective.
213
00:24:00,760 --> 00:24:05,471
They reflect sunlight back
just as powerfully as the planet itself.
214
00:24:05,600 --> 00:24:08,195
But that raises an interesting question
215
00:24:08,320 --> 00:24:11,313
because the solar system is full of dust.
216
00:24:11,440 --> 00:24:15,229
Any ice crystals that hang around
for any amount of time
217
00:24:15,360 --> 00:24:18,671
will get dirty,
and so they won't reflect sunlight back,
218
00:24:18,800 --> 00:24:20,473
they won't be as bright.
219
00:24:20,600 --> 00:24:26,517
So the question is, why, then,
are Saturn's rings so reflective?
220
00:24:29,600 --> 00:24:33,196
The answer came
from one of the most audacious
221
00:24:33,320 --> 00:24:37,030
and successful missions
to the outer solar system.
222
00:24:37,160 --> 00:24:40,870
Five, four, three, two,
223
00:24:41,000 --> 00:24:44,232
one... and liftoff
of the Cassini spacecraft
224
00:24:44,360 --> 00:24:46,750
on a billion-mile trip to Saturn.
225
00:24:48,760 --> 00:24:50,717
We have cleared the tower.
226
00:24:50,840 --> 00:24:53,309
T plus 20 seconds,
all systems are go.
227
00:24:53,440 --> 00:24:57,320
The Cassini probe was designed
to study Saturn and its moons
228
00:24:57,440 --> 00:25:01,195
and rings up close,
to shed new light on their origins.
229
00:25:01,320 --> 00:25:03,915
All systems continuing to be go.
230
00:25:04,040 --> 00:25:05,918
But whereas the Voyager probes
231
00:25:06,040 --> 00:25:08,509
had spent only days at Saturn
as they sped by,
232
00:25:08,640 --> 00:25:12,031
Cassini was built
to enter Saturnian orbit...
233
00:25:12,160 --> 00:25:14,959
Solid rocket boosters
have been jettisoned.
234
00:25:15,080 --> 00:25:18,039
Velocity 4,378mph.
235
00:25:18,160 --> 00:25:20,834
...and explore the system for years.
236
00:25:27,680 --> 00:25:29,876
Many times more massive than Voyager,
237
00:25:30,000 --> 00:25:34,711
Cassini had to take a different route
to enter orbit around Saturn.
238
00:25:36,840 --> 00:25:40,720
To conserve fuel,
it flew by multiple planets,
239
00:25:40,840 --> 00:25:43,912
slingshotting past them to pick up speed
240
00:25:44,040 --> 00:25:48,034
and change direction
over the course of seven years.
241
00:25:54,280 --> 00:25:56,920
As Cassini finally approached its target,
242
00:25:57,040 --> 00:26:01,512
it was travelling at almost
100,000 kilometres per hour
243
00:26:01,640 --> 00:26:05,190
and had to slow itself with exquisite
precision.
244
00:26:19,320 --> 00:26:20,674
Flight to telecom.
245
00:26:20,800 --> 00:26:22,200
Go ahead.
246
00:26:22,320 --> 00:26:24,357
The Doppler has flattened out.
247
00:26:38,760 --> 00:26:42,071
After its 3.5-billion-kilometre journey,
248
00:26:42,200 --> 00:26:46,558
Cassini was now able to see
Saturn's rings like never before.
249
00:26:58,280 --> 00:27:01,239
What's more,
during its long stay at Saturn,
250
00:27:01,360 --> 00:27:07,277
Cassini would be able to take
physical samples for the very first time.
251
00:27:25,520 --> 00:27:26,749
By measuring the way
252
00:27:26,880 --> 00:27:29,395
that the dust from the solar system
falls onto the rings,
253
00:27:29,520 --> 00:27:32,957
Cassini made a startling discovery.
254
00:27:40,040 --> 00:27:43,272
If the rings had been around Saturn
for billions of years,
255
00:27:43,400 --> 00:27:47,155
they should have been darkened
and dimmed by the dust.
256
00:27:49,080 --> 00:27:51,515
But they are pristine and bright.
257
00:27:56,240 --> 00:27:59,278
And the reason is
because they are young.
258
00:28:01,840 --> 00:28:06,995
Nearly 4.5 billion years younger
than Saturn itself.
259
00:28:16,480 --> 00:28:20,599
The mystery of the origin of the rings
is an active area of research.
260
00:28:22,120 --> 00:28:24,032
And the evidence that Cassini delivered
261
00:28:24,160 --> 00:28:28,359
hints that the solution lies
not with planet itself
262
00:28:28,480 --> 00:28:34,920
but with the worlds trapped in orbit
around it - Saturn's moons.
263
00:28:39,240 --> 00:28:42,677
Saturn has 62 large moons
and countless smaller ones.
264
00:28:42,800 --> 00:28:44,200
We're still discovering them.
265
00:28:44,320 --> 00:28:47,757
So it's like a mini solar system
in itself.
266
00:28:47,880 --> 00:28:51,635
And those moons range in size
from planetary-size objects, like Titan,
267
00:28:51,760 --> 00:28:55,117
to small, irregular-shaped lumps of rock.
268
00:28:55,240 --> 00:28:59,792
And there's so much diversity in size
and form and surface features
269
00:28:59,920 --> 00:29:02,435
that the whole system
is like a history book,
270
00:29:02,560 --> 00:29:04,119
and if we learn to read it,
271
00:29:04,240 --> 00:29:09,599
then we see that Saturn has had
a very violent and changeable past.
272
00:29:09,720 --> 00:29:11,279
Look at this. This is Mimas,
273
00:29:11,400 --> 00:29:15,076
which is often called the Death Star moon
for obvious reasons.
274
00:29:15,200 --> 00:29:18,034
It has this huge impact crater,
275
00:29:18,160 --> 00:29:21,676
which tells you that once, long ago,
276
00:29:21,800 --> 00:29:23,393
there was a very violent impact
277
00:29:23,520 --> 00:29:26,638
that almost, but not quite,
destroyed the moon.
278
00:29:28,200 --> 00:29:30,317
And this is Iapetus.
279
00:29:30,440 --> 00:29:31,920
It's a very large moon,
280
00:29:32,040 --> 00:29:33,269
almost planetary size.
281
00:29:33,400 --> 00:29:36,472
It's about 1,500 kilometres across.
282
00:29:36,600 --> 00:29:41,277
And half of it is white
and half of it is dark.
283
00:29:42,680 --> 00:29:45,479
Iapetus also has
another distinctive feature,
284
00:29:45,600 --> 00:29:47,831
which is this ridge
all the way around the equator.
285
00:29:47,960 --> 00:29:50,919
And you can see the scale of it
from this photograph.
286
00:29:51,040 --> 00:29:53,271
And this is clearly visible.
287
00:29:53,400 --> 00:29:56,598
It's one of the highest mountain ranges
in the solar system -
288
00:29:56,720 --> 00:30:00,191
20 kilometres from peak
to the ground below.
289
00:30:06,480 --> 00:30:08,711
And it's thought that this formed
290
00:30:08,840 --> 00:30:12,959
because a ring
that was once around the moon -
291
00:30:13,080 --> 00:30:16,960
just liked Saturn's rings -
collapsed onto its surface.
292
00:30:24,480 --> 00:30:27,154
As Cassini continued its journey,
293
00:30:27,280 --> 00:30:32,594
it revealed in detail multiple moons
made almost entirely of ice.
294
00:30:33,720 --> 00:30:37,475
And many of them
had taken on extraordinary forms
295
00:30:37,600 --> 00:30:40,115
in and around the rings.
296
00:31:01,920 --> 00:31:05,675
As Cassini analysed the ice moons
in ever greater detail,
297
00:31:05,800 --> 00:31:07,598
it became apparent that many of them
298
00:31:07,720 --> 00:31:13,318
were made of exactly the same material
as the rings themselves.
299
00:31:16,000 --> 00:31:21,234
The rings and moons
were profoundly linked.
300
00:31:23,680 --> 00:31:25,911
But for all the moons that Cassini saw,
301
00:31:26,040 --> 00:31:30,034
it now seemed likely
that one was missing.
302
00:31:50,040 --> 00:31:52,032
When dinosaurs roamed the Earth,
303
00:31:52,160 --> 00:31:57,474
we now suspect Saturn had a moon in orbit
that no longer exists.
304
00:32:01,360 --> 00:32:07,800
A moon perhaps 400 kilometres across
and formed almost entirely of ice.
305
00:32:11,600 --> 00:32:13,512
But this world was doomed.
306
00:32:16,480 --> 00:32:18,836
It found itself orbiting too close
307
00:32:18,960 --> 00:32:22,476
to resist the immense forces
of Saturn's gravity.
308
00:32:35,880 --> 00:32:38,952
Gravity is the sculptor
of the Saturnian system,
309
00:32:39,080 --> 00:32:42,790
but also the instigator
of change within it.
310
00:32:42,920 --> 00:32:47,358
We tend to think of gravity
as a force that pulls things together,
311
00:32:47,480 --> 00:32:50,552
but it can also act to rip things apart.
312
00:32:50,680 --> 00:32:53,149
Think about the tides here on Earth.
313
00:32:53,280 --> 00:32:57,035
They're caused by the difference
in gravitational pull of the Moon
314
00:32:57,160 --> 00:32:59,629
from one side of the Earth to the other.
315
00:32:59,760 --> 00:33:03,640
And that difference, which can be
quite subtle, is also powerful.
316
00:33:03,760 --> 00:33:07,993
It can move entire oceans -
it's called tidal gravity.
317
00:33:08,120 --> 00:33:11,750
But the Earth also has a tidal effect
on the Moon,
318
00:33:11,880 --> 00:33:17,160
and because the Earth is an entire planet,
that effect is much more powerful.
319
00:33:21,440 --> 00:33:25,434
The pull of the Earth is enough
to deform the Moon's surface.
320
00:33:26,960 --> 00:33:31,352
The effect was particularly strong
4.5 billion years ago,
321
00:33:31,480 --> 00:33:34,712
when the Moon was nearly 17 times closer.
322
00:33:36,640 --> 00:33:40,520
Back then, the pull from the Earth
caused a tide of solid rock
323
00:33:40,640 --> 00:33:42,393
to rise and fall.
324
00:33:47,440 --> 00:33:49,352
If the Moon had ever been any nearer,
325
00:33:49,480 --> 00:33:52,712
it would have crossed
what we call the Roche limit,
326
00:33:52,840 --> 00:33:56,470
a place where tidal gravitational forces
are so strong
327
00:33:56,600 --> 00:33:58,432
moons can get ripped apart.
328
00:34:08,400 --> 00:34:12,474
The Romans named the planet Saturn
after their god of time and harvest,
329
00:34:12,600 --> 00:34:16,355
and in one of the more gruesome tales
from classical mythology,
330
00:34:16,480 --> 00:34:19,791
Saturn actually ate his newborn babies
331
00:34:19,920 --> 00:34:23,072
in order to prevent them
from taking his power.
332
00:34:23,200 --> 00:34:26,079
What's sort of interesting
is that what we've learnt from Cassini
333
00:34:26,200 --> 00:34:30,672
is that, at least metaphorically speaking,
they weren't far wrong.
334
00:34:44,320 --> 00:34:46,516
Just beyond Saturn's atmosphere,
335
00:34:46,640 --> 00:34:48,518
our leading theories suggest
336
00:34:48,640 --> 00:34:53,431
an icy moon must have approached close to,
or even just inside,
337
00:34:53,560 --> 00:34:55,552
the planet's Roche limit.
338
00:34:59,440 --> 00:35:02,990
As Saturn's immense
tidal gravitational forces acted
339
00:35:03,120 --> 00:35:05,589
across the moon, it began to rupture.
340
00:35:10,160 --> 00:35:14,200
Saturn began to devour its child.
341
00:36:02,920 --> 00:36:09,554
Up to 15,000 trillion tonnes of ice
broke apart in orbit around Saturn.
342
00:36:22,320 --> 00:36:25,597
Because of the speeds
the ice fragments were travelling,
343
00:36:25,720 --> 00:36:27,871
it's likely that in just a few days
344
00:36:28,000 --> 00:36:31,118
they spread out
to encircle the great giant.
345
00:36:37,800 --> 00:36:41,555
Saturn's iconic ring had been born.
346
00:37:01,840 --> 00:37:04,639
Today, the giant ring has evolved.
347
00:37:06,520 --> 00:37:09,797
Saturn's powerful gravitational field
348
00:37:09,920 --> 00:37:13,516
has helped keep
its near-perfect circular shape,
349
00:37:13,640 --> 00:37:17,156
but collisions within
have caused it to flatten out.
350
00:37:21,880 --> 00:37:25,191
Now this debris
forms a disc wider than Jupiter,
351
00:37:25,320 --> 00:37:29,200
yet on average
just ten metres thick.
352
00:37:34,000 --> 00:37:38,836
Within, moon-sized chunks of ice
orbit the structure,
353
00:37:38,960 --> 00:37:41,680
clearing great voids...
354
00:37:43,200 --> 00:37:44,759
...turning one ring...
355
00:37:46,320 --> 00:37:48,152
...into many.
356
00:37:54,040 --> 00:37:58,193
In places, moons have pulled
particles of ice upwards
357
00:37:58,320 --> 00:38:02,599
to create strange peaks
over two kilometres high.
358
00:38:04,800 --> 00:38:06,917
And in just the right conditions,
359
00:38:07,040 --> 00:38:10,317
they cast spectacular shadows
across the rings.
360
00:38:18,720 --> 00:38:22,350
This once-tiny world of rock and ice...
361
00:38:24,160 --> 00:38:28,473
...that has undergone
so many great transformations...
362
00:38:34,440 --> 00:38:37,751
...has today become
the solar system's jewel.
363
00:38:51,600 --> 00:38:55,071
Cassini had deepened
our understanding of the origin
364
00:38:55,200 --> 00:38:56,873
and evolution of Saturn.
365
00:38:57,880 --> 00:39:00,111
But its mission was far from over.
366
00:39:01,200 --> 00:39:05,513
Because just beyond the rings,
it discovered another treasure.
367
00:39:06,560 --> 00:39:11,032
A place that may hold answers
to some of our deepest questions
368
00:39:11,160 --> 00:39:15,393
about the possibility of life
in the solar system and beyond.
369
00:39:35,720 --> 00:39:39,839
Over a billion kilometres
from the warmth of the Sun,
370
00:39:39,960 --> 00:39:42,998
just on the outer edge of Saturn's rings,
371
00:39:43,120 --> 00:39:45,760
lies the icy moon Enceladus.
372
00:39:48,840 --> 00:39:50,797
Enceladus is quite a small moon.
373
00:39:50,920 --> 00:39:53,674
It's only about the size of Iceland,
actually.
374
00:39:53,800 --> 00:39:56,440
But that does not make it dull.
375
00:39:56,560 --> 00:39:59,871
It is the most reflective object
in the solar system.
376
00:40:00,000 --> 00:40:03,755
Over 90% of the light that hits it
bounces back,
377
00:40:03,880 --> 00:40:08,875
and that's because its surface
is covered in pure ice.
378
00:40:09,000 --> 00:40:11,799
It's also criss-crossed by crevasses,
379
00:40:11,920 --> 00:40:16,233
like this one you see on this glacier,
but on a much grander scale.
380
00:40:16,360 --> 00:40:20,639
The largest, known as the tiger stripes,
are over 100 kilometres long.
381
00:40:20,760 --> 00:40:23,639
But for all its surface beauty,
382
00:40:23,760 --> 00:40:28,880
it's what's going on below the ice that
makes Enceladus so special.
383
00:40:34,600 --> 00:40:37,274
What we found
beneath Enceladus's shell of ice
384
00:40:37,400 --> 00:40:40,040
must rank as one
of the greatest discoveries
385
00:40:40,160 --> 00:40:42,880
in 21st-century space exploration.
386
00:40:44,160 --> 00:40:48,439
But it was a discovery
that had been hiding in plain sight.
387
00:40:58,680 --> 00:41:02,959
This is a photograph taken
by Voyager 1 of Enceladus in 1980.
388
00:41:03,080 --> 00:41:06,790
Now, nobody noticed anything remarkable
about it at the time,
389
00:41:06,920 --> 00:41:09,515
but this image has been enhanced,
390
00:41:09,640 --> 00:41:15,432
and now you can see this sort of misty
blob off one side of the moon.
391
00:41:15,560 --> 00:41:17,392
Now, that is fascinating.
392
00:41:17,520 --> 00:41:22,640
It means something is rising up
from inside Enceladus.
393
00:41:22,760 --> 00:41:25,798
Now, when Cassini got back there
24 years later,
394
00:41:25,920 --> 00:41:30,949
it saw the same thing,
but this time in much more detail.
395
00:41:33,960 --> 00:41:35,997
As Cassini approached Enceladus,
396
00:41:36,120 --> 00:41:38,999
the anomaly revealed itself.
397
00:41:42,040 --> 00:41:47,069
Giant plumes of water vapour and ice
were erupting from its surface.
398
00:41:49,840 --> 00:41:55,837
Over 200 kilograms of material
was being released every second.
399
00:42:00,560 --> 00:42:03,234
But this material was not lost to space.
400
00:42:03,360 --> 00:42:07,240
It seemed to be feeding
one of Saturn's outer rings,
401
00:42:07,360 --> 00:42:09,033
helping to replenish it.
402
00:42:17,000 --> 00:42:20,437
And these discoveries inspired
an audacious risk.
403
00:42:23,360 --> 00:42:26,273
Piloted from over
a billion kilometres away,
404
00:42:26,400 --> 00:42:30,314
Cassini was guided dangerously close
to the plumes.
405
00:42:46,600 --> 00:42:52,517
The craft passed within just 48 kilometres
of the surface of Enceladus...
406
00:42:55,640 --> 00:42:58,633
...and Cassini was able to
touch the plumes.
407
00:43:09,320 --> 00:43:12,677
What we discovered,
thanks to a series of these flybys,
408
00:43:12,800 --> 00:43:14,678
was breathtaking.
409
00:43:16,000 --> 00:43:21,155
The ice in the plumes was actually
frozen particles of salty water.
410
00:43:23,160 --> 00:43:27,598
We had found a sub-surface ocean
leaking into space.
411
00:43:32,200 --> 00:43:34,192
Far, far from the Sun,
412
00:43:34,320 --> 00:43:38,837
Enceladus was harbouring an ocean
of liquid water,
413
00:43:38,960 --> 00:43:42,431
and it was there because of Saturn.
414
00:43:48,960 --> 00:43:52,431
Enceladus orbits Saturn
in an elliptical orbit,
415
00:43:52,560 --> 00:43:58,033
which means the gravitational forces
across the moon are constantly changing.
416
00:44:00,880 --> 00:44:06,160
It's maintained in this orbit by the pull
of another larger moon, Dione.
417
00:44:08,400 --> 00:44:13,236
These ever-shifting gravitational forces
stretch and squeeze its heart,
418
00:44:13,360 --> 00:44:16,797
warming and melting its icy interior.
419
00:44:23,600 --> 00:44:26,957
But Cassini's data
had one more surprise in store.
420
00:44:30,520 --> 00:44:34,719
As the plumes of water ice were analysed
in ever-greater detail,
421
00:44:34,840 --> 00:44:38,072
we discovered complex organic compounds
422
00:44:38,200 --> 00:44:41,352
and silica particles
that could only have come
423
00:44:41,480 --> 00:44:44,075
from hot hydrothermal vents.
424
00:44:49,320 --> 00:44:52,233
In the frozen outer reaches
of the solar system...
425
00:44:53,640 --> 00:44:57,316
...we had found a warm, watery oasis.
426
00:45:06,120 --> 00:45:11,320
Cassini has given us a glimpse
beneath the ice of Enceladus,
427
00:45:11,440 --> 00:45:15,753
and it is fascinating, genuinely,
in a scientific sense,
428
00:45:15,880 --> 00:45:18,554
because many biologists believe
429
00:45:18,680 --> 00:45:22,037
that hydrothermal vents, like those
that are almost certainly present
430
00:45:22,160 --> 00:45:24,834
on the floor of Enceladus's ocean,
431
00:45:24,960 --> 00:45:27,520
were the cradle of life on Earth.
432
00:45:27,640 --> 00:45:29,552
See, all the ingredients are present.
433
00:45:29,680 --> 00:45:32,912
There's hot water
in touch with ice and minerals.
434
00:45:33,040 --> 00:45:35,760
That's a reactive cauldron of chemistry.
435
00:45:35,880 --> 00:45:38,190
There are reactive gasses, methane.
436
00:45:38,320 --> 00:45:42,200
Cassini found molecular hydrogen
in the plumes,
437
00:45:42,320 --> 00:45:46,872
and that was one of the food sources
of primitive organisms on Earth.
438
00:45:47,000 --> 00:45:49,834
So, there really is a possibility
439
00:45:49,960 --> 00:45:54,159
that there is life in orbits
around Saturn today.
440
00:46:02,240 --> 00:46:07,031
The prospect of life on Enceladus
is exciting,
441
00:46:07,160 --> 00:46:08,355
but if it's there,
442
00:46:08,480 --> 00:46:13,236
it's likely to be only the simplest
and most primitive of organisms.
443
00:46:16,920 --> 00:46:21,790
And given how violent and changeable
Saturn's past has been,
444
00:46:21,920 --> 00:46:26,711
this world of ice and liquid water
may only have arisen relatively recently.
445
00:46:29,840 --> 00:46:34,835
Now, we don't know how long Enceladus
has been geologically active,
446
00:46:34,960 --> 00:46:36,474
how long it's had an ocean.
447
00:46:36,600 --> 00:46:40,913
If it's only tens of millions -
or even hundreds of millions - of years,
448
00:46:41,040 --> 00:46:45,432
that may have not have been enough time
for life to get going.
449
00:46:45,560 --> 00:46:50,077
But if there is life there,
then we can glimpse its future
450
00:46:50,200 --> 00:46:54,353
because there are still
hydrothermal vent systems present
451
00:46:54,480 --> 00:46:59,396
on Earth today, and life doesn't just
survive there, it thrives.
452
00:47:17,920 --> 00:47:21,914
Often found in the deep oceans
along fault lines in the Earth's crust,
453
00:47:22,040 --> 00:47:25,477
hydrothermal vents
are some of the richest
454
00:47:25,600 --> 00:47:28,672
and most complex ecosystems
on Earth.
455
00:47:30,680 --> 00:47:33,752
Feeding off the abundant bacteria
that breed there,
456
00:47:33,880 --> 00:47:38,909
these habitats support a multitude
of strange and complex organisms.
457
00:47:51,120 --> 00:47:54,557
Whilst creatures like this
will never exist on Enceladus,
458
00:47:54,680 --> 00:47:56,558
billions of years from now,
459
00:47:56,680 --> 00:48:01,038
it is just possible
that this distant world may become home
460
00:48:01,160 --> 00:48:03,914
to its own unique forms of life.
461
00:48:14,880 --> 00:48:19,397
But for Cassini, the brave new world
under the ice of Enceladus
462
00:48:19,520 --> 00:48:21,193
was a bittersweet discovery.
463
00:48:36,240 --> 00:48:38,880
13 years after it arrived at Saturn,
464
00:48:39,000 --> 00:48:42,596
Cassini's fuel finally began to run dry.
465
00:48:44,480 --> 00:48:49,111
NASA couldn't risk letting this probe
crash-land on Enceladus
466
00:48:49,240 --> 00:48:52,438
and contaminate
a potential habitat for life.
467
00:48:52,560 --> 00:48:56,520
Systems, ACS One. We've just had
transition to high-rate mode.
468
00:48:59,600 --> 00:49:04,550
And so the decision was made
to send Cassini on one final journey.
469
00:49:07,800 --> 00:49:12,033
A journey that would take it
into the atmosphere of Saturn itself.
470
00:49:14,080 --> 00:49:16,959
A journey
from which it would never return.
471
00:49:23,000 --> 00:49:26,596
And we are in the atmosphere.
472
00:49:26,720 --> 00:49:29,519
Radio signal still holding -
30 seconds.
473
00:49:48,960 --> 00:49:53,637
We just heard the signal
from the spacecraft is gone,
474
00:49:53,760 --> 00:49:56,195
and within the next 45 seconds,
475
00:49:56,320 --> 00:49:58,073
so will be the spacecraft.
476
00:50:01,400 --> 00:50:03,312
The planet that had borne witness
477
00:50:03,440 --> 00:50:06,956
to some of the greatest dramas
in the history of the solar system
478
00:50:07,080 --> 00:50:11,552
was now consuming the craft
that had told its extraordinary story.
479
00:50:24,760 --> 00:50:29,880
Cassini and Saturn had now become
inseparable companions.
480
00:50:52,720 --> 00:50:57,511
We journeyed out to Saturn to experience
and explore this great beauty.
481
00:51:03,160 --> 00:51:08,440
But in the end, we were rewarded
with insights closer to home.
482
00:51:16,920 --> 00:51:19,754
Cassini and her team of scientists
and engineers
483
00:51:19,880 --> 00:51:23,078
should be counted
amongst our greatest of explorers.
484
00:51:23,200 --> 00:51:26,352
The mission had all the ingredients -
a vessel and her crew
485
00:51:26,480 --> 00:51:29,712
drawn by the prospect of beauty
and new knowledge
486
00:51:29,840 --> 00:51:33,277
across an un-charted ocean
to an alien world,
487
00:51:33,400 --> 00:51:36,598
and as is so often the case
in exploration,
488
00:51:36,720 --> 00:51:40,191
the real treasure was found in the
unexpected shadows,
489
00:51:40,320 --> 00:51:42,789
in this case, in the shadow of the rings,
490
00:51:42,920 --> 00:51:45,992
where we found this tiny world, Enceladus,
491
00:51:46,120 --> 00:51:51,320
that may harbour life and provide us
with re-assurance that we're not alone
492
00:51:51,440 --> 00:51:52,954
in the universe.
493
00:51:53,080 --> 00:51:56,073
See? The beauty is in the story.
494
00:51:56,200 --> 00:51:59,511
Would it matter, really,
if we found life on Enceladus?
495
00:51:59,640 --> 00:52:02,314
It would only be microbes after all.
496
00:52:02,440 --> 00:52:04,511
Yes, it would matter.
497
00:52:04,640 --> 00:52:07,030
We are at a time in our history, I think,
498
00:52:07,160 --> 00:52:10,949
where we need re-assurance,
or perhaps a reminder,
499
00:52:11,080 --> 00:52:16,951
that there is beauty and knowledge
and perhaps even life and meaning
500
00:52:17,080 --> 00:52:19,197
beyond our shores.
501
00:52:29,720 --> 00:52:33,794
We will, I'm sure,
go back to Saturn and its moons,
502
00:52:33,920 --> 00:52:36,480
explore deeper, stay longer,
503
00:52:36,600 --> 00:52:40,071
and maybe one day even visit ourselves.
504
00:52:43,680 --> 00:52:45,876
We don't know what we'll discover,
505
00:52:46,000 --> 00:52:50,199
but we can be sure that
the story has only just begun.
506
00:53:18,920 --> 00:53:22,834
Cassini has been one
of the most successful probes ever flown.
507
00:53:24,160 --> 00:53:27,631
But constructing a machine
that could survive 13 years
508
00:53:27,760 --> 00:53:32,277
in the outer solar system was a huge
challenge for everyone involved.
509
00:53:34,400 --> 00:53:36,631
T plus 20 seconds.
510
00:53:36,760 --> 00:53:38,797
Even when they were proposing Cassini,
I thought,
511
00:53:38,920 --> 00:53:40,456
"No, no, this is never going to happen!"
512
00:53:40,480 --> 00:53:43,279
It was, like, maybe too ambitious,
or something.
513
00:53:47,680 --> 00:53:51,799
It's difficult to put a number on how many
people were involved in Cassini.
514
00:53:51,920 --> 00:53:55,118
Um, tens of thousands, I would say.
515
00:53:58,040 --> 00:53:59,997
This is a very, very complex effort.
516
00:54:00,120 --> 00:54:02,351
There's over ten miles of wiring,
517
00:54:02,480 --> 00:54:05,154
and you have to check out every wire.
518
00:54:06,680 --> 00:54:12,517
So it took us two-and-a-half years
to put the thing together.
519
00:54:15,640 --> 00:54:20,078
All of us spent a lot of effort
to get to that moment,
520
00:54:20,200 --> 00:54:22,635
so there's a lot of emotion
attached to it.
521
00:54:22,760 --> 00:54:28,358
And then you see it launch,
and you know that it's on a journey
522
00:54:28,480 --> 00:54:31,234
to a very, very distant place.
523
00:54:32,320 --> 00:54:34,471
And so you feel like you're going, too.
524
00:54:43,160 --> 00:54:47,234
When Cassini first began to
send close-up pictures back to Earth...
525
00:54:49,680 --> 00:54:52,036
...it was a special moment
for the whole team.
526
00:54:57,800 --> 00:55:00,190
I was sitting in what they call
the blue room,
527
00:55:00,320 --> 00:55:03,996
being interviewed while they were beaming
for the first time,
528
00:55:04,120 --> 00:55:07,318
and then one of these pictures came on,
and I just went, "Wow, look at that!"
529
00:55:07,440 --> 00:55:11,593
That was really the
jumping-out-of-the-chair moment for me.
530
00:55:14,160 --> 00:55:15,799
And it was just the first day.
531
00:55:19,480 --> 00:55:21,336
What we were seeing
was the highest resolution
532
00:55:21,360 --> 00:55:22,510
that had ever been seen.
533
00:55:24,480 --> 00:55:28,918
I saw phenomena that I'd only seen
in kind of computer simulations before,
534
00:55:29,040 --> 00:55:31,509
and now I was seeing it for the first time
535
00:55:31,640 --> 00:55:34,030
and realising all this was real.
536
00:55:36,360 --> 00:55:39,239
And we were seeing
details in the rings
537
00:55:39,360 --> 00:55:43,240
that were shocking. Shocking.
538
00:55:44,600 --> 00:55:47,957
We just lacked the imagination
that it would require
539
00:55:48,080 --> 00:55:49,912
to predict what it would look like.
540
00:55:51,680 --> 00:55:56,960
For me, when that great backlit picture
came out,
541
00:55:57,080 --> 00:55:59,072
that's when it hit, for me.
542
00:56:00,920 --> 00:56:06,040
"Oh, my God, we've done something
really unique and wonderful."
543
00:56:09,400 --> 00:56:13,679
It was like, "This is going to be...
This is going to be huge."
544
00:56:17,280 --> 00:56:20,557
Over Cassini's 13 years at Saturn,
545
00:56:20,680 --> 00:56:23,878
it explored
the planet's incredible storms...
546
00:56:25,080 --> 00:56:27,640
...the formation of its rings...
547
00:56:29,720 --> 00:56:33,031
...and discovered the oceans of Enceladus.
548
00:56:36,160 --> 00:56:40,632
But Cassini's greatest insights
may be yet to come.
549
00:56:40,760 --> 00:56:44,117
There's such a wealth of information
in the data.
550
00:56:44,240 --> 00:56:48,120
I think we've just skimmed
the top of the data.
551
00:56:48,240 --> 00:56:52,553
I think people will continue
to make discoveries from Cassini data
552
00:56:52,680 --> 00:56:55,752
for another 30 to 40 years.
553
00:56:57,680 --> 00:57:00,718
The data Cassini collected
in its final moments
554
00:57:00,840 --> 00:57:04,959
is already changing
our understanding of the planet.
555
00:57:05,080 --> 00:57:08,232
It has revealed
the rings are disappearing.
556
00:57:08,360 --> 00:57:13,913
As much as 10,000 kilograms of material
is falling into the planet each second.
557
00:57:16,320 --> 00:57:19,916
It now seems likely that
just 100 million years from now,
558
00:57:20,040 --> 00:57:23,351
Saturn's great rings will be no more.
559
00:57:27,640 --> 00:57:31,873
Cassini has shown us
that we have been uniquely fortunate
560
00:57:32,000 --> 00:57:34,435
to behold this great beauty.