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1
00:00:05,000 --> 00:00:09,560
Lift off of Messenger on Nasa's
mission to Mercury.
2
00:00:09,560 --> 00:00:12,600
# They'll say
3
00:00:12,600 --> 00:00:16,440
# No-one can see us
4
00:00:16,440 --> 00:00:20,320
# That we're estranged
5
00:00:20,320 --> 00:00:23,680
# And all alone
6
00:00:23,680 --> 00:00:26,640
# They believe
7
00:00:26,640 --> 00:00:30,800
# Nothing can reach us
8
00:00:30,800 --> 00:00:34,120
# And pull us out of
9
00:00:34,120 --> 00:00:37,360
# The boundless gloom
10
00:00:38,600 --> 00:00:45,200
# They're wrong
11
00:00:45,200 --> 00:00:48,560
# They're wrong. #
12
00:01:10,280 --> 00:01:12,120
Far, far away...
13
00:01:17,680 --> 00:01:19,000
..beyond Mars...
14
00:01:21,640 --> 00:01:25,720
..past the storms of Jupiter,
and the rings of Saturn...
15
00:01:27,600 --> 00:01:29,720
..conditions become very different.
16
00:01:32,880 --> 00:01:37,640
Temperatures plummet,
and distances between worlds
17
00:01:37,640 --> 00:01:41,640
are measured not in millions,
but in billions of kilometres.
18
00:01:44,240 --> 00:01:47,400
Here lie the most mysterious
planets of them all.
19
00:01:52,320 --> 00:01:53,360
Uranus.
20
00:01:55,480 --> 00:01:58,640
A pale blue marble
hanging in the dark,
21
00:01:58,640 --> 00:02:00,720
frozen depths of space.
22
00:02:04,320 --> 00:02:06,280
And, further out...
23
00:02:07,560 --> 00:02:10,160
..the solar system's final
true planet...
24
00:02:13,320 --> 00:02:15,280
..Neptune.
25
00:02:17,960 --> 00:02:22,400
Beyond, we thought we'd only ever
find tiny, lifeless worlds...
26
00:02:23,960 --> 00:02:25,240
..frozen to the core.
27
00:02:29,720 --> 00:02:31,720
How wrong we were.
28
00:02:58,280 --> 00:03:01,760
We live at a time when our
civilisation has unprecedented
29
00:03:01,760 --> 00:03:05,320
reach, and we have a near-permanent
presence at Mars,
30
00:03:05,320 --> 00:03:09,560
both in orbit and on the surface,
and we've had spacecraft orbiting
31
00:03:09,560 --> 00:03:15,040
Mercury, Venus, Jupiter and Saturn
for extended periods.
32
00:03:15,040 --> 00:03:19,360
But, once we get beyond Saturn,
things become much more difficult.
33
00:03:19,360 --> 00:03:21,960
The distances are vast.
34
00:03:21,960 --> 00:03:24,160
Travel times are measured
not in one months,
35
00:03:24,160 --> 00:03:28,320
but in years, decades, even.
And that means that we've only
36
00:03:28,320 --> 00:03:31,240
visited the outer planets once.
37
00:03:32,960 --> 00:03:37,800
Each visit is a voyage
into the unknown, as we strive
38
00:03:37,800 --> 00:03:41,640
to reach the most distant planetary
systems ever visited.
39
00:03:43,920 --> 00:03:47,640
And, when we do get there, our
spacecraft are travelling so fast
40
00:03:47,640 --> 00:03:50,200
that they fly straight through,
41
00:03:50,200 --> 00:03:53,240
only spending
a few hours in the system.
42
00:03:53,240 --> 00:03:58,320
But those few hours of precious data
have allowed us to begin
43
00:03:58,320 --> 00:04:02,320
to understand the mysteries that lie
there on the outer edges
44
00:04:02,320 --> 00:04:03,760
of the solar system.
45
00:04:07,040 --> 00:04:10,200
We have ignition
and we have liftoff.
46
00:04:22,080 --> 00:04:25,160
Reports coming back indicate
those twin, large, solid motors
47
00:04:25,160 --> 00:04:27,120
are functioning perfectly.
48
00:04:32,080 --> 00:04:35,680
Our first mission into the dark
was only possible thanks to some
49
00:04:35,680 --> 00:04:38,080
help from the planets themselves.
50
00:04:44,600 --> 00:04:47,440
Each planet orbits
at a different speed.
51
00:04:50,520 --> 00:04:53,760
And, for most of the time,
they're scattered around the Sun.
52
00:04:59,680 --> 00:05:03,280
But once every 175 years...
53
00:05:05,880 --> 00:05:07,720
..something rather wonderful
happens.
54
00:05:11,480 --> 00:05:13,440
The outer planets align...
55
00:05:15,320 --> 00:05:16,680
..creating a path...
56
00:05:18,320 --> 00:05:21,760
..that leads from Earth past Jupiter
and Saturn...
57
00:05:25,720 --> 00:05:28,560
..all the way to Uranus and Neptune.
58
00:05:46,360 --> 00:05:51,240
Voyager 2 had been launched
at precisely the right moment
59
00:05:51,240 --> 00:05:54,440
to take advantage of this rare
planetary alignment.
60
00:06:04,560 --> 00:06:08,040
It arrived at Jupiter
in a little under two years.
61
00:06:11,960 --> 00:06:14,000
Two and a half times more massive
62
00:06:14,000 --> 00:06:16,440
than all the other planets
combined...
63
00:06:18,240 --> 00:06:21,480
..Jupiter gave Voyager
a gravitational kick.
64
00:06:32,680 --> 00:06:35,440
Another two years on,
and Voyager witnessed
65
00:06:35,440 --> 00:06:38,560
one of the most beautiful sights
in the solar system.
66
00:06:41,880 --> 00:06:44,280
The icy rings of
another gas giant...
67
00:06:46,880 --> 00:06:48,480
..Saturn.
68
00:07:02,320 --> 00:07:04,640
And, then, on and on...
69
00:07:08,200 --> 00:07:10,040
..further into the darkness.
70
00:07:28,360 --> 00:07:32,760
Almost nine years after leaving
Earth, Voyager approached
71
00:07:32,760 --> 00:07:35,040
an entirely new class of planet.
72
00:07:46,640 --> 00:07:50,480
Just like Jupiter and Saturn,
the planet's upper atmosphere
73
00:07:50,480 --> 00:07:54,360
is composed mostly of swirling
hydrogen and helium gas.
74
00:08:02,080 --> 00:08:06,280
And hidden beneath lies
an exotic, icy mix of methane,
75
00:08:06,280 --> 00:08:07,920
ammonia and water.
76
00:08:18,360 --> 00:08:23,200
But, unlike the other gas giants,
Uranus is almost featureless.
77
00:08:27,440 --> 00:08:30,000
For all the time that Voyager
stared at the planet,
78
00:08:30,000 --> 00:08:33,360
it saw just ten cloud formations.
79
00:08:36,440 --> 00:08:38,280
And we soon discovered why.
80
00:08:44,040 --> 00:08:48,760
Uranus, at -224 degrees Celsius,
81
00:08:48,760 --> 00:08:51,360
is the coldest planet
in the solar system.
82
00:08:52,600 --> 00:08:55,400
The first of the ice giants,
83
00:08:55,400 --> 00:08:58,920
in a permanent state of deep freeze.
84
00:09:07,680 --> 00:09:10,360
Voyager spent just
six hours with Uranus...
85
00:09:12,280 --> 00:09:16,360
..and, as its gaze widened,
it took in the entire system.
86
00:09:28,000 --> 00:09:29,600
Just like Saturn...
87
00:09:30,640 --> 00:09:33,240
..Uranus has rings.
88
00:09:53,560 --> 00:09:56,520
The rings are so dark, so faint,
that they're very difficult
89
00:09:56,520 --> 00:09:58,240
to see from Earth.
90
00:09:58,240 --> 00:10:01,400
In fact, we didn't
discover them until 1977.
91
00:10:02,520 --> 00:10:05,600
They must be made of some kind of
material that doesn't reflect
92
00:10:05,600 --> 00:10:08,760
a lot of sunlight back,
and we don't know what that is.
93
00:10:08,760 --> 00:10:11,600
It can't be water ice
like the rings of Saturn,
94
00:10:11,600 --> 00:10:13,800
because they would be much brighter.
95
00:10:13,800 --> 00:10:17,640
They're also extremely
delicate and thin,
96
00:10:17,640 --> 00:10:21,200
and, again, that's a great mystery,
cos you'd expect the particles
97
00:10:21,200 --> 00:10:25,080
to collide and the rings
to spread out over time.
98
00:10:25,080 --> 00:10:26,400
That doesn't happen.
99
00:10:36,280 --> 00:10:39,080
So, something must be holding
those rings in place,
100
00:10:39,080 --> 00:10:42,680
and the answer can be seen
in this photograph
101
00:10:42,680 --> 00:10:44,360
taken by Voyager 2.
102
00:10:44,360 --> 00:10:50,040
You can see a bright, thin ring,
which is known as the epsilon ring,
103
00:10:50,040 --> 00:10:53,280
and, above it and below it,
you can see two moons.
104
00:10:53,280 --> 00:10:57,760
The inner one is called Cordelia,
and the outer one is called Ophelia.
105
00:10:57,760 --> 00:11:01,240
Now, the thing you need to know
about orbits, a moon or a ring
106
00:11:01,240 --> 00:11:05,480
particle that's orbiting closer
to a planet is moving more slowly
107
00:11:05,480 --> 00:11:09,320
than a moon or ring particle
that's orbiting further away.
108
00:11:09,320 --> 00:11:12,600
And, so, if there's a particle
in the epsilon ring that maybe
109
00:11:12,600 --> 00:11:15,840
has a collision, loses a bit
of energy and starts to drop down,
110
00:11:15,840 --> 00:11:21,720
then Cordelia tends to accelerate
that particle back up into the ring
111
00:11:21,720 --> 00:11:24,960
again to speed it up
by its gravitational influence.
112
00:11:24,960 --> 00:11:28,720
Whereas, if it's a particle on the
outer edge of the epsilon ring,
113
00:11:28,720 --> 00:11:32,640
it gets a bit more energy
and raises up in altitude,
114
00:11:32,640 --> 00:11:34,960
then Ophelia tends to slow it down,
115
00:11:34,960 --> 00:11:37,760
and, so, it falls back
into the ring again.
116
00:11:37,760 --> 00:11:41,560
And, by that mechanism,
these moons keep the ring nice
117
00:11:41,560 --> 00:11:45,040
and neat around Uranus,
and, for that reason,
118
00:11:45,040 --> 00:11:47,880
these moons have become
known as shepherd moons.
119
00:11:58,480 --> 00:12:01,440
Now, we haven't discovered
any more shepherd moons.
120
00:12:01,440 --> 00:12:03,520
Voyager was only in
the system for a few hours.
121
00:12:06,000 --> 00:12:09,640
But we assume that they're there,
orbiting around Uranus,
122
00:12:09,640 --> 00:12:12,280
keeping the other rings
precisely in place.
123
00:12:18,000 --> 00:12:22,040
The missing moons are not the only
mysterious thing about the planet.
124
00:12:28,160 --> 00:12:31,800
Uranus orbits the Sun
in a unique way,
125
00:12:31,800 --> 00:12:36,040
a consequence of events
that happened long ago.
126
00:12:59,200 --> 00:13:02,040
Uranus was born from the vast cloud
of material
127
00:13:02,040 --> 00:13:04,080
that surrounded the young Sun.
128
00:13:06,080 --> 00:13:08,480
Over time, this material grew
together
129
00:13:08,480 --> 00:13:10,560
under the influence of gravity...
130
00:13:14,440 --> 00:13:16,240
..forming each of the planets...
131
00:13:25,360 --> 00:13:30,120
..all orbiting in the same
anticlockwise direction
132
00:13:30,120 --> 00:13:32,920
as the primordial cloud
of gas and dust.
133
00:13:38,800 --> 00:13:41,640
This rotation remains to this day.
134
00:13:45,080 --> 00:13:47,880
Almost all the planets spin
on their axis in the same
135
00:13:47,880 --> 00:13:49,800
anticlockwise direction.
136
00:13:53,640 --> 00:13:56,760
But, for reasons we don't
yet fully understand,
137
00:13:56,760 --> 00:14:01,520
Venus and Uranus spin on their axes
in the opposite direction.
138
00:14:09,000 --> 00:14:11,680
And Uranus is even more curious.
139
00:14:16,440 --> 00:14:19,640
The entire planet is on its side.
140
00:14:29,400 --> 00:14:33,680
It's not known for certain why
Uranus spins in this way.
141
00:14:33,680 --> 00:14:36,120
But it seems likely
that, at some point,
142
00:14:36,120 --> 00:14:40,520
probably in the distant past,
it was hit by another planet,
143
00:14:40,520 --> 00:14:43,320
possibly the size of
Earth or even larger,
144
00:14:43,320 --> 00:14:46,680
which knocked the planet over,
and, indeed, modern computer
145
00:14:46,680 --> 00:14:49,720
simulations suggest
that when you do that to a planet,
146
00:14:49,720 --> 00:14:53,800
all the moons follow,
and you end up with the planet
147
00:14:53,800 --> 00:14:57,280
and its system of moons,
and now its rings,
148
00:14:57,280 --> 00:15:00,880
sort of corkscrewing
around the Sun on its side.
149
00:15:47,000 --> 00:15:51,840
Voyager had taken us to the most
distant planets we had ever visited.
150
00:16:00,200 --> 00:16:07,160
And, now, an almost unthinkable
distance of 1.6 billion kilometres
151
00:16:07,160 --> 00:16:12,120
of icy cold space
lay between the spacecraft
152
00:16:12,120 --> 00:16:13,760
and its next encounter.
153
00:16:36,800 --> 00:16:40,200
The size and scale of the solar
system is impossible to imagine.
154
00:16:42,040 --> 00:16:46,880
But, when we scale everything down,
then it becomes easier to visualise.
155
00:16:46,880 --> 00:16:51,600
The Sun is 1.4 million
kilometres in diameter.
156
00:16:51,600 --> 00:16:55,880
But scale that down by a factor
of around 600 million,
157
00:16:55,880 --> 00:16:59,480
and it becomes the size
of that light.
158
00:16:59,480 --> 00:17:02,960
And the Earth, Mars and the rocky
planets
159
00:17:02,960 --> 00:17:06,240
are about that big on this scale.
160
00:17:06,240 --> 00:17:10,920
And the distances are,
I think, even more remarkable.
161
00:17:10,920 --> 00:17:13,920
So, Mercury, the closest
planet to the Sun,
162
00:17:13,920 --> 00:17:16,360
would be all the way
over there by the sea.
163
00:17:26,320 --> 00:17:29,600
So, this would be where
Mercury orbits.
164
00:17:29,600 --> 00:17:33,480
And Mercury is 96 metres away.
165
00:17:34,600 --> 00:17:38,600
It's about just under
a centimetre in diameter.
166
00:17:38,600 --> 00:17:41,840
And the next planet, Venus,
is somewhere over there.
167
00:17:46,440 --> 00:17:51,720
We'd fly past Venus about
180 metres away from the Sun.
168
00:17:55,400 --> 00:17:59,440
And then head onwards
and outwards towards the Earth.
169
00:18:06,560 --> 00:18:10,640
Here, at the Earth's orbit,
the true scale of our fragility
170
00:18:10,640 --> 00:18:12,960
and isolation becomes apparent.
171
00:18:15,680 --> 00:18:20,760
The Sun there, 250 metres away
with the twinkling stars
172
00:18:20,760 --> 00:18:24,560
of the galaxy beyond,
and here's the Earth.
173
00:18:24,560 --> 00:18:27,440
Two centimetres across.
174
00:18:27,440 --> 00:18:31,000
On that pebble, all of
human history play out.
175
00:18:40,080 --> 00:18:43,320
At around 380 metres,
we pass by Mars,
176
00:18:43,320 --> 00:18:47,400
the last of the rocky planets,
and then onwards into the darkness.
177
00:19:11,120 --> 00:19:14,040
Crossing the harbour
takes us to the fringes
178
00:19:14,040 --> 00:19:15,560
of the outer solar system.
179
00:19:18,880 --> 00:19:21,200
And, now, the distances
and the sizes
180
00:19:21,200 --> 00:19:23,240
are beginning to get really big.
181
00:19:27,320 --> 00:19:30,200
Jupiter, the largest planet
in the solar system,
182
00:19:30,200 --> 00:19:36,720
is over ten times the diameter
of our Earth, and there's the Sun,
183
00:19:36,720 --> 00:19:39,760
1.3km across the harbour.
184
00:19:59,560 --> 00:20:02,680
At almost twice the distance
from the Sun to Jupiter,
185
00:20:02,680 --> 00:20:03,920
we reach Saturn.
186
00:20:05,760 --> 00:20:08,800
2.4km on our scale.
187
00:20:10,880 --> 00:20:14,240
And we really are now entering
the twilight of the solar system.
188
00:20:14,240 --> 00:20:19,160
Light levels are like early morning
or late evening here on Earth,
189
00:20:19,160 --> 00:20:21,760
but we can still see Saturn
in the night sky,
190
00:20:21,760 --> 00:20:25,160
because the planet and its rings
are highly reflective.
191
00:20:31,800 --> 00:20:36,800
As far again as all the rocky
planets, and Jupiter and Saturn,
192
00:20:36,800 --> 00:20:38,280
we reach Uranus.
193
00:20:44,600 --> 00:20:49,320
3 billion kilometres from the Sun,
and we begin to fully appreciate
194
00:20:49,320 --> 00:20:51,280
the distances Voyager
had travelled...
195
00:20:56,800 --> 00:20:59,760
..on its journey to the farthest
reaches of the solar system.
196
00:21:15,440 --> 00:21:19,520
Journey's end, Neptune,
a ball of gas about
197
00:21:19,520 --> 00:21:22,240
7.5 centimetres across.
198
00:21:22,240 --> 00:21:26,680
7.4km away
from the Sun on this scale.
199
00:21:33,480 --> 00:21:38,320
And we are still down there
on the island in Reykjavik harbour.
200
00:21:39,440 --> 00:21:44,680
Little, microscopic ants crawling
around on the surface of a pebble.
201
00:22:09,680 --> 00:22:13,960
It had taken 12 years,
but Voyager had finally crossed
202
00:22:13,960 --> 00:22:17,560
the great expanse of space
between Earth and the most
203
00:22:17,560 --> 00:22:19,400
distant planetary system.
204
00:22:34,480 --> 00:22:35,480
Neptune.
205
00:22:39,360 --> 00:22:44,800
17 times the mass of the Earth,
and even more massive than Uranus.
206
00:23:03,120 --> 00:23:07,440
But, in contrast to its sister
planet, Neptune's atmosphere
207
00:23:07,440 --> 00:23:09,400
is bursting with activity.
208
00:23:23,480 --> 00:23:27,720
What we found was a planet
of extreme weather,
209
00:23:27,720 --> 00:23:33,040
where high altitude winds whip white
methane clouds around at speeds
210
00:23:33,040 --> 00:23:35,840
of over 2,000km/h.
211
00:23:35,840 --> 00:23:38,880
Those are the highest wind speeds
anywhere in the solar system.
212
00:23:52,640 --> 00:23:55,120
And Voyager saw a great, dark spot,
213
00:23:55,120 --> 00:23:57,720
not unlike Jupiter's
great, red spot.
214
00:24:00,000 --> 00:24:04,200
A storm system the size of Earth,
that, when we looked only four
215
00:24:04,200 --> 00:24:07,280
or five years later,
we found had vanished.
216
00:24:11,360 --> 00:24:14,760
But, over the years,
we've observed more storms raging
217
00:24:14,760 --> 00:24:16,000
over the planet.
218
00:24:22,520 --> 00:24:25,800
It's one of the great mysteries
of planetary exploration,
219
00:24:25,800 --> 00:24:30,880
why a planet so far from the Sun,
with so little energy falling
220
00:24:30,880 --> 00:24:34,480
into its atmosphere from sunlight,
can have the most extreme winds
221
00:24:34,480 --> 00:24:35,720
in the solar system.
222
00:24:37,280 --> 00:24:40,440
And Voyager made yet
another puzzling discovery.
223
00:24:44,200 --> 00:24:48,640
Although further from the Sun,
the planet is warmer than Uranus.
224
00:24:53,200 --> 00:24:55,960
The source of this extra
heat remains a mystery.
225
00:25:00,320 --> 00:25:04,320
But, for some reason, Neptune emits
over two and a half times
226
00:25:04,320 --> 00:25:06,680
the heat it receives from the Sun.
227
00:25:10,880 --> 00:25:15,520
And this internal heat helps
to explain the ferocious storms.
228
00:25:19,440 --> 00:25:22,400
As the heat makes its way
from the core of the planet
229
00:25:22,400 --> 00:25:24,040
and out into space...
230
00:25:28,520 --> 00:25:30,640
..it churns up the entire
atmosphere...
231
00:25:33,120 --> 00:25:37,040
..creating winds unlike anything
seen elsewhere in the solar system.
232
00:25:43,080 --> 00:25:46,640
The probable reason that wind
speeds can be so high
233
00:25:46,640 --> 00:25:50,360
is because there's no solid surface
on a planet like Neptune.
234
00:25:50,360 --> 00:25:54,720
It's exotic liquids further down,
and gases further up.
235
00:25:54,720 --> 00:25:57,000
But there's no rocky surface.
236
00:25:57,000 --> 00:26:01,480
There are no mountains
and continents to break up the flow
237
00:26:01,480 --> 00:26:05,520
of atmospheric gases,
and, so, the winds can just whip
238
00:26:05,520 --> 00:26:08,320
around the planet
at supersonic speeds.
239
00:26:25,640 --> 00:26:29,880
Voyager 2 had almost completed its
grand tour of the solar system.
240
00:26:46,560 --> 00:26:48,720
But before it began
its lonely journey
241
00:26:48,720 --> 00:26:50,720
out into interstellar space...
242
00:26:55,160 --> 00:26:57,440
..it had one, last world to visit.
243
00:27:07,680 --> 00:27:13,120
Triton, a vast moon covered
in a sheen of frozen nitrogen.
244
00:27:15,600 --> 00:27:19,240
We expected it to be a silent,
still world,
245
00:27:19,240 --> 00:27:22,880
but Voyager was in
for one, last surprise.
246
00:27:57,400 --> 00:28:00,480
But, when Voyager arrived,
247
00:28:00,480 --> 00:28:04,560
we saw geological activity
on that frozen world.
248
00:28:04,560 --> 00:28:10,480
We saw geysers erupting up
into space 8km high,
249
00:28:10,480 --> 00:28:15,080
and then carrying dark material
100km downwind.
250
00:28:23,360 --> 00:28:28,120
Now, the key to understanding
what process caused those eruptions
251
00:28:28,120 --> 00:28:32,200
was that we noticed that the geysers
tended to erupt on a place
252
00:28:32,200 --> 00:28:35,240
on Triton's surface
below the faint Sun,
253
00:28:35,240 --> 00:28:38,320
even though it's so many
billions of miles away.
254
00:28:38,320 --> 00:28:43,040
What's happening is the sunlight
is falling on the thin layer
255
00:28:43,040 --> 00:28:48,200
of nitrogen ice, going through,
and heating up a layer of darker
256
00:28:48,200 --> 00:28:50,640
particles a metre below the surface.
257
00:28:53,920 --> 00:28:56,560
A difference of just
four degrees Celsius
258
00:28:56,560 --> 00:28:59,960
is enough for the heat
to radiate up
259
00:28:59,960 --> 00:29:04,640
and vaporise the frozen nitrogen,
creating gas.
260
00:29:08,920 --> 00:29:11,400
That gas is under pressure,
and, ultimately,
261
00:29:11,400 --> 00:29:13,840
it punches through the nitrogen ice
262
00:29:13,840 --> 00:29:18,280
carrying those dark particles up and
making the geysers of Triton.
263
00:29:23,560 --> 00:29:26,200
In the furthest reaches
of the solar system,
264
00:29:26,200 --> 00:29:30,160
the faint light of the Sun
is still enough to power the most
265
00:29:30,160 --> 00:29:32,280
distant of geological wonders.
266
00:29:37,160 --> 00:29:41,440
But this can't explain the rest
of Triton's mysterious features.
267
00:29:51,400 --> 00:29:54,800
Terrain on this scale could only
be created
268
00:29:54,800 --> 00:29:57,320
by a much more powerful force.
269
00:30:02,160 --> 00:30:06,600
And a clue seems to be lurking
in Triton's odd orbit.
270
00:30:13,640 --> 00:30:16,440
Unlike every other large moon
in the solar system,
271
00:30:16,440 --> 00:30:21,600
Triton orbits in the opposite
direction to the spin of the planet.
272
00:30:21,600 --> 00:30:23,800
And that means it's highly unlikely
273
00:30:23,800 --> 00:30:26,560
that Triton and Neptune formed
at the same time.
274
00:30:26,560 --> 00:30:30,800
If you formed a planet and a moon
out of the same collapsing cloud
275
00:30:30,800 --> 00:30:34,760
of gas and dust, then they tend
to spin and orbit in the same
276
00:30:34,760 --> 00:30:38,040
direction as the spin
of the initial dust cloud,
277
00:30:38,040 --> 00:30:43,080
so, the most likely explanation
for that is that Triton is a visitor
278
00:30:43,080 --> 00:30:47,240
to the Neptunian system, that,
unlike Voyager, never left.
279
00:30:57,560 --> 00:31:01,240
One theory is that, billions of
years ago,
280
00:31:01,240 --> 00:31:03,680
Triton was not a moon at all.
281
00:31:08,840 --> 00:31:12,400
It grew up in a region
of space way beyond Neptune...
282
00:31:16,240 --> 00:31:18,000
..the Kuiper belt.
283
00:31:24,480 --> 00:31:28,680
Here, trillions of frozen lumps
of water, ammonia
284
00:31:28,680 --> 00:31:31,160
and methane circle the Sun.
285
00:31:35,000 --> 00:31:38,880
The frozen leftovers from
the formation of the solar system.
286
00:31:47,800 --> 00:31:51,400
Perhaps Triton ended up on the inner
edge of this region...
287
00:31:58,200 --> 00:32:00,160
..and ventured close enough
288
00:32:00,160 --> 00:32:03,000
to Neptune to be drawn
in by its gravity...
289
00:32:06,960 --> 00:32:11,440
..until, eventually, it was plucked
from the Kuiper belt,
290
00:32:11,440 --> 00:32:15,960
and forever trapped in orbit
around the distant, blue planet.
291
00:32:25,720 --> 00:32:30,040
Today, Triton orbits in a nice,
regular circle around Neptune,
292
00:32:30,040 --> 00:32:32,280
but it wouldn't have
started out that way.
293
00:32:32,280 --> 00:32:34,480
When it was first captured,
it would have glanced
294
00:32:34,480 --> 00:32:38,280
past the planet and ended
up in a wide, elliptical orbit,
295
00:32:38,280 --> 00:32:42,240
sometimes being far away from
the planet, and sometimes close.
296
00:32:42,240 --> 00:32:45,480
That means that, as Triton
orbited around Neptune,
297
00:32:45,480 --> 00:32:48,520
the gravitational pull
was constantly changing,
298
00:32:48,520 --> 00:32:52,160
and that stretches and squashes
the moon, and heats up
299
00:32:52,160 --> 00:32:53,960
the interior by friction.
300
00:32:53,960 --> 00:32:55,880
It's a process called tidal heating.
301
00:32:59,480 --> 00:33:02,920
The molten interior would
have exploded up through cracks
302
00:33:02,920 --> 00:33:04,920
and faults in Triton's crust...
303
00:33:06,600 --> 00:33:09,600
..creating the ragged surface
we see today.
304
00:33:11,680 --> 00:33:14,240
And what you're left
with is a cooling moon,
305
00:33:14,240 --> 00:33:18,760
orbiting in a circle the wrong
way around the planet,
306
00:33:18,760 --> 00:33:22,440
the dramas of its past
hidden from view.
307
00:33:22,440 --> 00:33:26,360
All that remains are the geysers,
powered by the faint light
308
00:33:26,360 --> 00:33:30,920
of the Sun, painting dark streaks
across the now-quiescent surface.
309
00:33:43,000 --> 00:33:46,000
Voyager had fulfilled its mission,
310
00:33:46,000 --> 00:33:49,600
and now headed onwards,
out of the solar system...
311
00:33:52,320 --> 00:33:55,360
..where it would never
encounter another planet.
312
00:34:06,120 --> 00:34:09,920
But, elsewhere, another world
awaited our arrival...
313
00:34:12,600 --> 00:34:14,840
..far out in the darkness.
314
00:34:18,920 --> 00:34:23,160
Mission... And lift off of Nasa's
New Horizons spacecraft
315
00:34:23,160 --> 00:34:28,080
on a decade-long voyage to visit
the planet Pluto and then beyond.
316
00:34:46,280 --> 00:34:48,200
The New Horizons spacecraft,
317
00:34:48,200 --> 00:34:51,000
on its way to the very edge
of our solar system.
318
00:35:02,640 --> 00:35:05,840
Our ambition to learn
more about a small,
319
00:35:05,840 --> 00:35:10,280
intriguing world depended
on the success of New Horizons.
320
00:35:17,880 --> 00:35:21,360
As the tiny probe,
less than three metres in length,
321
00:35:21,360 --> 00:35:23,280
was sent out into the abyss...
322
00:35:29,360 --> 00:35:33,320
..most of its electronics
and all nonessential systems
323
00:35:33,320 --> 00:35:35,400
were shut down to save power.
324
00:35:38,120 --> 00:35:44,280
It would hibernate for almost its
entire 4.8 billion kilometre trek.
325
00:35:54,440 --> 00:35:57,760
Whilst New Horizons continued
its voyage to Pluto,
326
00:35:57,760 --> 00:36:01,640
a controversy arose here on Earth
about the definition
327
00:36:01,640 --> 00:36:03,320
of Pluto itself.
328
00:36:03,320 --> 00:36:06,360
See, we always knew
that Pluto is small,
329
00:36:06,360 --> 00:36:10,840
smaller than Neptune's moon Triton,
but it was discoveries made
330
00:36:10,840 --> 00:36:14,680
in the vicinity of Pluto
by the Hubble Space Telescope
331
00:36:14,680 --> 00:36:17,960
that really challenged
its status as a planet.
332
00:36:22,240 --> 00:36:27,640
From Earth, Pluto, far away on
the inner edge of the Kuiper belt,
333
00:36:27,640 --> 00:36:30,920
is so distant that, even with
Hubble, it appears
334
00:36:30,920 --> 00:36:33,360
as nothing more than a fuzzy image.
335
00:36:36,680 --> 00:36:38,880
But Pluto was not alone.
336
00:36:41,280 --> 00:36:44,200
We began to detect
other distant objects.
337
00:36:57,200 --> 00:37:00,280
Then, Hubble discovered
that another world
338
00:37:00,280 --> 00:37:02,440
is almost the same
size as Pluto.
339
00:37:10,920 --> 00:37:15,160
The discovery of these new worlds
has forced us to reconsider
340
00:37:15,160 --> 00:37:17,480
what we mean by the word "planet".
341
00:37:21,720 --> 00:37:25,800
The International Astronomical Union
has a three-part definition
342
00:37:25,800 --> 00:37:28,520
of a planet. Firstly, it has to
orbit the Sun,
343
00:37:28,520 --> 00:37:30,400
and Pluto certainly does that.
344
00:37:30,400 --> 00:37:33,320
It goes round once every 248 years.
345
00:37:33,320 --> 00:37:38,280
Secondly, it has to be massive
enough for gravity to sculpt it
346
00:37:38,280 --> 00:37:43,080
almost into a sphere, and Pluto
indeed is almost spherical.
347
00:37:43,080 --> 00:37:47,800
But, thirdly, it has to clear
its own orbit around the Sun,
348
00:37:47,800 --> 00:37:51,160
and that's essentially
a mass constraint as well.
349
00:37:51,160 --> 00:37:55,160
It has to have enough
gravity to throw things out
350
00:37:55,160 --> 00:37:57,040
from its orbital path.
351
00:37:57,040 --> 00:37:59,480
And that's where Pluto falls down.
352
00:37:59,480 --> 00:38:02,560
Now, why that extra idea?
353
00:38:02,560 --> 00:38:06,080
Well, ultimately,
it's because if Pluto is big enough
354
00:38:06,080 --> 00:38:09,440
to be a planet, then Eris is big
enough to be a planet,
355
00:38:09,440 --> 00:38:12,240
and Makemake is big
enough to be a planet,
356
00:38:12,240 --> 00:38:16,680
and tens or even potentially
hundreds of objects out there
357
00:38:16,680 --> 00:38:18,880
are big enough to be planets.
358
00:38:18,880 --> 00:38:21,760
Now, does it really matter?
359
00:38:21,760 --> 00:38:23,680
Well, I don't think so.
360
00:38:23,680 --> 00:38:29,040
Ultimately, Pluto is a world, and,
therefore, we should explore it.
361
00:38:42,960 --> 00:38:47,200
And, in July 2015,
that's exactly what we did.
362
00:38:53,320 --> 00:38:57,880
After nine years of flight,
New Horizons awoke.
363
00:38:59,600 --> 00:39:01,480
Copy that.
364
00:39:01,480 --> 00:39:04,120
We are locked by telemetry
with the phase path.
365
00:39:04,120 --> 00:39:08,920
CHEERING AND APPLAUSE
366
00:39:37,600 --> 00:39:43,040
We had our first glimpse of the most
distant world ever visited.
367
00:40:30,400 --> 00:40:33,000
Pluto is beautiful.
368
00:40:33,000 --> 00:40:36,920
And, far from being a frigid,
featureless world,
369
00:40:36,920 --> 00:40:39,280
it turns out that it
has all the characteristics
370
00:40:39,280 --> 00:40:41,800
of a dynamic, living planet.
371
00:40:41,800 --> 00:40:46,880
And, yes, it is cold on the surface,
about -230 degrees Celsius.
372
00:40:46,880 --> 00:40:50,120
I'd be walking
over solid nitrogen.
373
00:40:50,120 --> 00:40:53,000
But the blotches
that could be made out
374
00:40:53,000 --> 00:40:57,440
in the grainy Hubble Space Telescope
images turned out to be
375
00:40:57,440 --> 00:41:01,200
a tremendous variety
of geological form and structure.
376
00:41:07,360 --> 00:41:11,200
But by far the most recognisable
feature is the region known
377
00:41:11,200 --> 00:41:12,520
as Tombaugh Regio,
378
00:41:12,520 --> 00:41:16,080
or to give it its more popular
name, Pluto's Heart.
379
00:41:22,000 --> 00:41:25,640
The western lobe of the heart
is called Sputnik Planitia.
380
00:41:31,400 --> 00:41:36,280
A giant plain of frozen nitrogen,
methane and carbon monoxide...
381
00:41:39,160 --> 00:41:42,360
..that stretches for a million
square kilometres.
382
00:41:47,200 --> 00:41:51,240
And, at its edge, lies a range
of mountains made of pure,
383
00:41:51,240 --> 00:41:54,440
frozen water ice...
384
00:41:54,440 --> 00:41:58,760
..that rise up to 6km
above the plain.
385
00:42:03,840 --> 00:42:07,520
But there's something
very strange about the region,
386
00:42:07,520 --> 00:42:11,560
something that sets it apart
from the rest of this dwarf planet.
387
00:42:16,160 --> 00:42:19,680
The surface of Pluto is covered
in craters, the scars
388
00:42:19,680 --> 00:42:22,600
of impacts that have taken place
over many billions of years,
389
00:42:22,600 --> 00:42:24,760
just like the surface of our moon.
390
00:42:24,760 --> 00:42:30,680
Except, if you look on Sputnik
Planitia, it is absolutely smooth.
391
00:42:30,680 --> 00:42:34,400
There are no craters there at all,
not a single one.
392
00:42:36,840 --> 00:42:40,000
From space, the lack
of craters is striking.
393
00:42:41,640 --> 00:42:45,080
And, the closer you look,
the stranger the mystery gets.
394
00:42:54,600 --> 00:42:58,840
Detailed imagery beamed back
by New Horizons revealed a network
395
00:42:58,840 --> 00:43:01,440
of hexagon and pentagon shapes...
396
00:43:07,040 --> 00:43:10,080
..that crisscross the frozen
nitrogen surface.
397
00:43:21,640 --> 00:43:25,920
A clue to what might be happening
can be seen in these images.
398
00:43:25,920 --> 00:43:30,000
Those kind of patterns are found
elsewhere in nature.
399
00:43:30,000 --> 00:43:32,800
Here, for example,
on the surface of the Sun.
400
00:43:34,840 --> 00:43:38,480
Or here, in a liquid that's
been heated from below.
401
00:43:40,040 --> 00:43:43,200
These patterns are
characteristic of convection.
402
00:43:43,200 --> 00:43:46,720
There's a heat source which is
causing material to rise up,
403
00:43:46,720 --> 00:43:50,920
and then it cools and falls back
again, and in those circulating
404
00:43:50,920 --> 00:43:54,320
convection currents, you tend to get
patterns like this.
405
00:43:57,360 --> 00:44:00,960
So, what could be happening below
the surface of Sputnik Planitia
406
00:44:00,960 --> 00:44:05,120
is that there is a heat source deep
down which is melting the nitrogen
407
00:44:05,120 --> 00:44:09,280
ice and causing it to rise,
cool and then fall again,
408
00:44:09,280 --> 00:44:13,440
and those convection currents
are constantly resurfacing the area.
409
00:44:18,320 --> 00:44:23,040
That a small world like Pluto is
still active was a huge surprise.
410
00:44:27,280 --> 00:44:29,760
Our best theory of how this could be
411
00:44:29,760 --> 00:44:32,520
is that somewhere deep
in its interior...
412
00:44:34,640 --> 00:44:39,000
..there are radioactive elements
that generate heat as they decay.
413
00:44:43,360 --> 00:44:47,760
This heat warms a sunless,
half-frozen ocean of water
414
00:44:47,760 --> 00:44:52,000
that has existed for billions of
years beneath the surface of Pluto.
415
00:45:03,200 --> 00:45:06,240
Now, the evidence from Sputnik
Planitia that there is still
416
00:45:06,240 --> 00:45:10,400
an internal heat source, and studies
of other geological features
417
00:45:10,400 --> 00:45:13,840
on Pluto, have led some scientists
to suggest that
418
00:45:13,840 --> 00:45:16,720
that ocean of water
might still be there.
419
00:45:21,680 --> 00:45:23,680
And the relatively warm ocean
420
00:45:23,680 --> 00:45:27,120
could explain the lack of craters
on Sputnik Planitia.
421
00:45:31,280 --> 00:45:36,680
The entire area is constantly
being repaved as the nitrogen
422
00:45:36,680 --> 00:45:38,920
surface is slowly turned over.
423
00:45:50,000 --> 00:45:53,560
But why all this activity
here and nowhere else?
424
00:45:57,640 --> 00:46:01,120
Perhaps Pluto's heart is the site
of a huge impact...
425
00:46:04,160 --> 00:46:08,200
..that, long ago, punched a large
hole in the surface,
426
00:46:08,200 --> 00:46:11,040
almost down
to the vast ocean beneath.
427
00:46:13,920 --> 00:46:17,920
A hole that's slowly filled
with soft nitrogen ice...
428
00:46:20,440 --> 00:46:24,440
..that now gently churns
just above a warmer ocean.
429
00:46:27,240 --> 00:46:28,680
Imagine that.
430
00:46:28,680 --> 00:46:32,600
An ocean billions of
miles away from the Sun,
431
00:46:32,600 --> 00:46:35,560
on the frozen frontier
of the solar system.
432
00:46:35,560 --> 00:46:38,480
On this most surprising of worlds,
433
00:46:38,480 --> 00:46:41,280
there may still be
an ocean of water.
434
00:46:51,400 --> 00:46:55,920
New Horizons' closest encounter
with Pluto lasted just hours...
435
00:47:04,480 --> 00:47:07,320
..during which only one
hemisphere was visible...
436
00:47:09,400 --> 00:47:11,760
..leaving the other side a mystery.
437
00:47:30,800 --> 00:47:34,080
Pluto held a final surprise.
438
00:47:34,080 --> 00:47:38,160
As New Horizons turned its camera
back for one, last look...
439
00:47:42,040 --> 00:47:45,480
..it captured an image
of Pluto's atmosphere,
440
00:47:45,480 --> 00:47:47,240
glowing in the dark.
441
00:47:53,600 --> 00:47:57,800
A thin, blue sky over
a hidden ocean of water...
442
00:47:59,200 --> 00:48:02,520
..4.8 billion kilometres from Earth.
443
00:48:29,720 --> 00:48:31,400
We've come a long way.
444
00:48:33,440 --> 00:48:36,480
After just half a century
of space exploration...
445
00:48:38,360 --> 00:48:41,200
..we've reached every one of
the planets in the solar system...
446
00:48:46,000 --> 00:48:47,960
..and begun to tell their story.
447
00:48:58,440 --> 00:49:01,440
What's emerging is a tale
of never-ending change...
448
00:49:03,880 --> 00:49:05,840
..of dramatic origins...
449
00:49:10,080 --> 00:49:11,600
..moments of hope...
450
00:49:17,320 --> 00:49:18,920
..and loss.
451
00:49:32,160 --> 00:49:35,520
Where just eight motes of rock,
ice and gas...
452
00:49:37,200 --> 00:49:40,040
..set against the dark backdrop
of space...
453
00:49:41,480 --> 00:49:46,680
..have conspired together to
produce life on at least one world.
454
00:49:59,960 --> 00:50:02,800
"Why do we explore?"
some people ask.
455
00:50:02,800 --> 00:50:06,720
Shouldn't we deal with the problems
here on Earth before committing time
456
00:50:06,720 --> 00:50:11,480
and energy and resources
to exploring the stars?
457
00:50:11,480 --> 00:50:15,600
Well, I think focusing
entirely on our mote of dust
458
00:50:15,600 --> 00:50:18,600
would be a profound mistake.
459
00:50:18,600 --> 00:50:21,960
It would mean that we've taken
the decision to sit huddled
460
00:50:21,960 --> 00:50:24,800
in a tiny corner
of the solar system,
461
00:50:24,800 --> 00:50:26,200
wondering what we're doing here.
462
00:50:28,640 --> 00:50:32,600
It would mean that we've taken
the decision to fight amongst
463
00:50:32,600 --> 00:50:35,880
ourselves for ever-more-precious
resources,
464
00:50:35,880 --> 00:50:39,800
confined below a thin shell
of air on a small rock,
465
00:50:39,800 --> 00:50:43,640
rather than following the
three-dimensional path marked out
466
00:50:43,640 --> 00:50:45,680
by the lights in the night.
467
00:50:54,800 --> 00:50:57,880
We live in
a solar system of wonders,
468
00:50:57,880 --> 00:51:02,160
of planets of storms and moons
of ice and landscapes and vistas
469
00:51:02,160 --> 00:51:06,000
that stir the imagination
and enrich the soul,
470
00:51:06,000 --> 00:51:09,920
a system of limitless resources,
limitless beauty
471
00:51:09,920 --> 00:51:11,800
and limitless potential.
472
00:51:14,120 --> 00:51:17,520
A system that we've only
just begun to explore...
473
00:51:20,440 --> 00:51:24,680
..in a journey that has already
rewarded us with so much.
474
00:51:50,480 --> 00:51:54,600
Pluto was the most distant world
that Nasa had ever planned to visit.
475
00:51:55,760 --> 00:51:59,840
Ten, nine, eight, seven...
476
00:51:59,840 --> 00:52:03,440
The launch of New Horizons
was incredibly dramatic.
477
00:52:05,440 --> 00:52:07,720
Mission... And liftoff.
478
00:52:07,720 --> 00:52:10,400
And it just shoots up so fast.
479
00:52:10,400 --> 00:52:12,600
It's the fastest launch
ever from Earth.
480
00:52:12,600 --> 00:52:14,560
About ten miles per second.
481
00:52:19,560 --> 00:52:23,400
In order to ensure that it was going
to last for the decade across space
482
00:52:23,400 --> 00:52:26,160
and actually work there,
they built in a lot of redundancy.
483
00:52:26,160 --> 00:52:28,600
There were sort of two of
everything, computers
484
00:52:28,600 --> 00:52:30,520
and the guidance systems,
485
00:52:30,520 --> 00:52:32,520
and they figured out
how to hibernate.
486
00:52:32,520 --> 00:52:34,920
The first spacecraft
that hibernated.
487
00:52:36,800 --> 00:52:40,000
To put the spacecraft largely
to sleep let the spacecraft
488
00:52:40,000 --> 00:52:41,880
just silently coast,
489
00:52:41,880 --> 00:52:45,440
then we could extend the life
of the electronics.
490
00:52:47,560 --> 00:52:50,200
No spacecraft mission had ever
really used hibernation
491
00:52:50,200 --> 00:52:53,400
as a day-to-day way
to cross the solar system.
492
00:52:56,240 --> 00:52:57,960
As the spacecraft slept,
493
00:52:57,960 --> 00:53:00,760
it sped away from Earth
towards its destination...
494
00:53:02,120 --> 00:53:04,280
..to a world that had lain hidden
495
00:53:04,280 --> 00:53:07,640
amongst the stars for almost
all of human history.
496
00:53:09,440 --> 00:53:14,000
The discovery of Pluto was in 1930,
when Clyde Tombaugh,
497
00:53:14,000 --> 00:53:15,680
a Kansas farm boy,
498
00:53:15,680 --> 00:53:20,440
was using the telescope at
the Lowell Observatory in Arizona.
499
00:53:20,440 --> 00:53:22,080
Every clear night,
500
00:53:22,080 --> 00:53:24,960
Clyde would go out and take images
501
00:53:24,960 --> 00:53:28,400
of the sky on photographic plates,
and when it was cloudy
502
00:53:28,400 --> 00:53:31,040
or during the day,
he would compare those plates.
503
00:53:31,040 --> 00:53:35,480
And Clyde Tombaugh noticed
that there was this little speck
504
00:53:35,480 --> 00:53:37,120
moving across the stars.
505
00:53:37,120 --> 00:53:41,160
And, then, in 1930,
Clyde Tombaugh discovered Pluto.
506
00:53:42,560 --> 00:53:45,320
But Tombaugh would never
see Pluto up close.
507
00:53:47,960 --> 00:53:52,400
He died nine years before
the launch of New Horizons,
508
00:53:52,400 --> 00:53:54,240
at the age of 90.
509
00:53:55,400 --> 00:53:59,720
He had asked if a mission ever
did get launched some of his ashes
510
00:53:59,720 --> 00:54:02,320
could be sent on the journey.
511
00:54:02,320 --> 00:54:07,400
And to think that Clyde's ashes,
you know, flew by Pluto,
512
00:54:07,400 --> 00:54:10,560
and, you know, he was finally
visiting the place
513
00:54:10,560 --> 00:54:13,040
that he discovered,
that was pretty cool.
514
00:54:14,680 --> 00:54:18,720
CHEERING AND APPLAUSE
515
00:54:20,960 --> 00:54:22,000
Wow!
516
00:54:23,240 --> 00:54:27,280
Now, I mean, Pluto was a shock
and a revelation in so many ways.
517
00:54:27,280 --> 00:54:29,480
Our jaws just dropped to the floor.
518
00:54:31,160 --> 00:54:35,160
This amazing world that we would
never have known about,
519
00:54:35,160 --> 00:54:37,200
unless we sent
a spacecraft out there.
520
00:54:40,640 --> 00:54:45,560
CHEERING AND APPLAUSE
521
00:54:49,240 --> 00:54:52,480
But New Horizons didn't stop
after its flyby of Pluto.
522
00:54:55,880 --> 00:54:58,360
It continued on
for three more years,
523
00:54:58,360 --> 00:55:00,760
ever deeper into the Kuiper belt.
524
00:55:02,440 --> 00:55:04,640
The temperatures out there
are almost absolute zero,
525
00:55:04,640 --> 00:55:07,280
so everything is so well preserved.
526
00:55:08,880 --> 00:55:11,560
The Kuiper belt completely
changed everything.
527
00:55:11,560 --> 00:55:15,440
It's an archaeological dig,
if you will, into the early history
528
00:55:15,440 --> 00:55:18,240
of our solar system,
so it's a scientific wonderland.
529
00:55:20,520 --> 00:55:22,480
On New Year's Day, 2019,
530
00:55:22,480 --> 00:55:26,400
New Horizons had reached
the centre of the region...
531
00:55:29,040 --> 00:55:33,320
..and was about to encounter the
most distant object ever visited.
532
00:55:49,400 --> 00:55:52,360
This object may be the most
primitive object
533
00:55:52,360 --> 00:55:54,680
ever encountered by a spacecraft.
534
00:55:55,680 --> 00:56:00,480
By looking at Ultima Thule today,
we think we're looking back in time
535
00:56:00,480 --> 00:56:02,520
to the origin of the solar system.
536
00:56:14,960 --> 00:56:19,760
Ultima Thule's formation was perhaps
just one of the countless collisions
537
00:56:19,760 --> 00:56:21,840
that formed the planets themselves.
538
00:56:28,560 --> 00:56:32,480
But, somehow, it escaped
and was flung far out
539
00:56:32,480 --> 00:56:34,000
into the Kuiper belt.
540
00:56:35,320 --> 00:56:38,520
The worlds out there,
which are billions of miles
541
00:56:38,520 --> 00:56:43,880
from the Sun, there are so many
mysteries kept in these objects,
542
00:56:43,880 --> 00:56:46,720
and we can really go out
and explore them, and start
543
00:56:46,720 --> 00:56:48,920
to understand these mysteries.
544
00:56:50,880 --> 00:56:54,720
Like every mission before it,
New Horizons has helped write
545
00:56:54,720 --> 00:56:56,240
the story of the planets.
546
00:57:01,520 --> 00:57:04,680
A story that we're only just
beginning to tell.
547
00:57:07,760 --> 00:57:11,040
The planets of our solar system,
they're in our back yard.
548
00:57:11,040 --> 00:57:13,520
We have the technology
to be able to go
549
00:57:13,520 --> 00:57:15,520
and stand on these surfaces.
550
00:57:17,400 --> 00:57:20,920
To be able to go out there
and be able to continue doing
551
00:57:20,920 --> 00:57:23,720
something that is very natural
and intrinsic to all of us,
552
00:57:23,720 --> 00:57:27,320
and that is answering the big
questions and exploring the unknown.
553
00:57:32,560 --> 00:57:34,920
I feel as though we're absolutely
just at the beginning
554
00:57:34,920 --> 00:57:37,400
of planetary exploration.
555
00:57:37,400 --> 00:57:40,440
There's a lot of exploration
left for us.
556
00:57:49,200 --> 00:57:51,840
Journey through our solar system
with this free poster
557
00:57:51,840 --> 00:57:53,760
produced by the Open University,
558
00:57:53,760 --> 00:57:56,880
and discover more about its
planets and moons.
559
00:57:58,320 --> 00:58:00,760
Order your free copy by calling...
560
00:58:05,200 --> 00:58:06,640
Or go to...
561
00:58:11,240 --> 00:58:13,760
And follow the links
to the Open University.
47912
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