1
00:00:17,520 --> 00:00:19,480
In 1979,

2
00:00:19,560 --> 00:00:22,640
a robotic spacecraft 
flew by the planet Jupiter.

3
00:00:32,320 --> 00:00:36,280
There it found an uncharted body 
the size of our moon.

4
00:00:42,600 --> 00:00:44,760
On that small world,

5
00:00:44,840 --> 00:00:47,760
it observed something 
almost unbelievable.

6
00:00:50,520 --> 00:00:53,800
(Music: "The Planets" 
by Gustav Holst)

7
00:01:56,280 --> 00:01:58,840
We live on an active planet.

8
00:02:02,280 --> 00:02:04,440
The rock itself is alive.

9
00:02:13,080 --> 00:02:18,120
The Earth spits out 
hot lava, creating new land.

10
00:02:23,600 --> 00:02:27,280
It is a sight 
we can only watch in awe.

11
00:02:32,000 --> 00:02:35,440
I find it absolutely overwhelming 
to look inside a volcano like this

12
00:02:35,520 --> 00:02:37,200
and see hot lava oozing out.

13
00:02:37,280 --> 00:02:40,640
We can see that the Earth is active. 
It's like the lifeblood of the planet.

14
00:02:41,680 --> 00:02:43,600
For a geologist like Jim Head,

15
00:02:43,680 --> 00:02:47,200
the Earth is an inspiration 
to look further afield.

16
00:02:51,440 --> 00:02:53,480
How does this all play out 
on the other planets?

17
00:02:53,560 --> 00:02:55,320
What does it look like there?

18
00:02:55,400 --> 00:02:57,760
Would there be 
hot lava like this? Volcanoes?

19
00:02:57,840 --> 00:03:00,440
Would we see things 
like ocean basins?

20
00:03:00,520 --> 00:03:03,320
We had absolutely no clue.

21
00:03:14,000 --> 00:03:18,000
The history of this planet 
is written in its rocks.

22
00:03:19,280 --> 00:03:21,400
Over hundreds of 
millions of years,

23
00:03:21,480 --> 00:03:23,760
mountain ranges have risen up,

24
00:03:24,600 --> 00:03:27,880
entire continents 
have drifted apart.

25
00:03:30,200 --> 00:03:33,080
Is this how 
other worlds would be?

26
00:03:34,000 --> 00:03:36,480
Earth's celestial partner, 
the Moon,

27
00:03:36,560 --> 00:03:39,080
could hardly be more different.

28
00:03:42,320 --> 00:03:44,320
Nothing has happened 
on this dusty world

29
00:03:44,400 --> 00:03:46,520
for billions of years.

30
00:03:46,600 --> 00:03:51,120
Its surface shows only the scars 
of countless impacts by asteroids.

31
00:03:59,200 --> 00:04:00,880
The story of the other planets

32
00:04:00,960 --> 00:04:04,000
must also be locked 
on their surfaces.

33
00:04:04,120 --> 00:04:08,440
But they are so far away that they are 
just dots of light in the sky.

34
00:04:12,040 --> 00:04:14,280
Astronomers gazed at those dots,

35
00:04:14,360 --> 00:04:17,080
but only on one of them 
could they make out anything

36
00:04:17,160 --> 00:04:20,000
that looked remotely 
like the landforms of the Earth.

37
00:04:20,800 --> 00:04:23,000
It was the red disc of Mars.

38
00:04:27,400 --> 00:04:28,920
Over a century ago,

39
00:04:29,000 --> 00:04:31,520
an Italian astronomer, 
Giovanni Schiaparelli,

40
00:04:31,600 --> 00:04:35,920
began to chart the dark 
and light regions of Mars.

41
00:04:36,000 --> 00:04:40,760
His maps were the best we had 
until space probes came along.

42
00:04:54,000 --> 00:04:58,280
In 1964, 
NASA launched Mariner 4.

43
00:04:58,360 --> 00:05:00,080
Its mission was to fly past Mars

44
00:05:00,160 --> 00:05:02,600
and try to send back 
close-up pictures.

45
00:05:06,960 --> 00:05:09,120
The mission was 
a technical success,

46
00:05:09,200 --> 00:05:12,560
but the fuzzy images showed 
nothing particularly interesting -

47
00:05:12,640 --> 00:05:15,520
just craters 
like those on the Moon.

48
00:05:18,800 --> 00:05:20,000
Astronomers were convinced

49
00:05:20,080 --> 00:05:22,920
that the probe had looked 
in the wrong place.

50
00:05:34,520 --> 00:05:38,440
Brad Smith had spent years 
gazing at the Red Planet.

51
00:05:38,520 --> 00:05:41,840
He thought he knew where 
the interesting terrain was.

52
00:05:43,920 --> 00:05:45,480
For the next mission,

53
00:05:45,560 --> 00:05:48,320
NASA asked him 
to guide them to it.

54
00:05:49,840 --> 00:05:52,560
I had been observing Mars 
for quite some time

55
00:05:52,640 --> 00:05:53,840
(through) ground-based telescopes,

56
00:05:53,920 --> 00:05:58,320
and we had noticed that there were certain 
regions that were very changeable.

57
00:05:58,400 --> 00:06:01,040
They changed with the seasons. 
They seemed to have colours to them.

58
00:06:01,120 --> 00:06:03,080
And we thought those would be 
particularly interesting.

59
00:06:03,160 --> 00:06:08,240
So I set up the targeting 
so that Mariner 6 and 7

60
00:06:08,320 --> 00:06:12,000
would look at these particular 
areas during the approach.

61
00:06:18,400 --> 00:06:21,480
As Mariners 6 and 7 
raced towards Mars,

62
00:06:21,560 --> 00:06:23,920
they saw what appeared 
to be mountains,

63
00:06:24,000 --> 00:06:27,600
dark plains, deep canyons.

64
00:06:34,000 --> 00:06:35,640
But when the close-ups 
came back,

65
00:06:35,720 --> 00:06:39,600
Brad and NASA 
were once again disappointed.

66
00:06:40,920 --> 00:06:45,040
Unfortunately, the surface 
was very heavily cratered.

67
00:06:45,120 --> 00:06:47,400
There were dark 
and light areas to be sure,

68
00:06:47,480 --> 00:06:51,440
but it was still a lot 
like looking at the Moon.'

69
00:07:04,000 --> 00:07:06,840
Convinced that there had to be 
more than just craters on Mars,

70
00:07:06,920 --> 00:07:08,760
NASA went back again.

71
00:07:09,160 --> 00:07:12,600
Only this time the element 
of chance had been removed.

72
00:07:15,400 --> 00:07:18,360
Mariner 9 was not 
a quick fly-by.

73
00:07:18,440 --> 00:07:20,960
It was designed to go 
into orbit around Mars,

74
00:07:21,040 --> 00:07:24,200
and photograph every 
square foot of the planet.

75
00:07:25,640 --> 00:07:28,000
But as the probe closed in,

76
00:07:28,080 --> 00:07:30,960
a large dust storm 
began to stir.

77
00:07:31,040 --> 00:07:32,520
I was watching the planet,

78
00:07:32,600 --> 00:07:34,240
hoping it wouldn't be a bad one.

79
00:07:34,320 --> 00:07:37,080
But within just 
a matter of days,

80
00:07:37,160 --> 00:07:39,320
a brilliant 
yellow cloud developed.

81
00:07:39,400 --> 00:07:41,520
And we knew it was 
a bad dust storm.

82
00:07:41,640 --> 00:07:44,040
And it spread out over the entire planet,

83
00:07:44,120 --> 00:07:46,240
covering up everything.

84
00:07:49,080 --> 00:07:51,440
Mariner sat out the storm.

85
00:07:51,520 --> 00:07:54,560
And then it saw something 
poking up through the dust.

86
00:07:54,640 --> 00:07:58,760
We saw these four dark spots.

87
00:07:58,840 --> 00:08:01,800
And we weren't quite sure 
what they were.

88
00:08:01,880 --> 00:08:06,320
And one of our team members had 
pointed out there were things

89
00:08:06,400 --> 00:08:08,320
that looked like 
the tops of volcanoes.

90
00:08:08,400 --> 00:08:12,600
And he suggested that, in fact, 
these were volcanoes that were so high

91
00:08:12,680 --> 00:08:15,240
that they were actually poking up 
through the dust.

92
00:08:23,360 --> 00:08:24,800
As the dust receded,

93
00:08:24,880 --> 00:08:27,600
the four spots 
showed themselves.

94
00:08:29,200 --> 00:08:31,640
They were volcanoes.

95
00:08:31,720 --> 00:08:33,680
Giant ones.

96
00:08:36,800 --> 00:08:39,920
The biggest of them was 
christened Olympus Mons.

97
00:08:40,000 --> 00:08:42,480
It was 15 miles high,

98
00:08:42,560 --> 00:08:45,280
three times the size of Everest.

99
00:08:54,480 --> 00:08:56,840
Mars was not just another moon.

100
00:08:56,920 --> 00:08:58,880
It was a real world.

101
00:08:59,760 --> 00:09:03,680
And geologists were eager to 
draw comparisons with the Earth.

102
00:09:09,080 --> 00:09:12,480
Jim Head went straight to 
the biggest volcanoes he knew,

103
00:09:12,560 --> 00:09:14,520
on the island of Hawaii.

104
00:09:15,600 --> 00:09:18,440
I remember when Olympus Mons 
first came out of the clouds on Mariner 9.

105
00:09:18,480 --> 00:09:21,280
It was absolutely spectacular, 
 a gigantic volcano.

106
00:09:21,360 --> 00:09:23,400
I couldn't wait 
to get back here to Hawaii

107
00:09:23,480 --> 00:09:25,720
to get some sense 
of the perspective and scale

108
00:09:25,800 --> 00:09:27,600
from something I knew about.

109
00:09:27,680 --> 00:09:29,480
And here we are on the edge of this volcano,

110
00:09:29,480 --> 00:09:32,240
this incredibly large volcano, 
one of the largest on the Earth.

111
00:09:32,320 --> 00:09:34,960
And, in fact, it's like tiny 
compared to Olympus Mons.

112
00:09:36,560 --> 00:09:39,120
To travel from the central 
crater of Olympus Mons

113
00:09:39,200 --> 00:09:42,360
to its outer edge 
is a journey of 300 miles.

114
00:09:42,920 --> 00:09:45,680
In between, there's an area 
the size of France

115
00:09:45,760 --> 00:09:48,200
covered with crumbling red lava.

116
00:09:52,160 --> 00:09:54,440
But the volcanoes weren't all.

117
00:09:54,920 --> 00:09:56,440
As the dust withdrew,

118
00:09:56,520 --> 00:09:59,600
Mariner 9's cameras took 
thousands more pictures.

119
00:10:00,000 --> 00:10:02,800
A whole new world 
was taking shape.

120
00:10:09,400 --> 00:10:12,760
NASA called in 
a new type of scientist -

121
00:10:12,840 --> 00:10:15,240
planetary geologists.

122
00:10:24,920 --> 00:10:27,160
When this thing 
began to shape up,

123
00:10:27,240 --> 00:10:30,040
and we began to see all these features, 
that was the first time

124
00:10:30,120 --> 00:10:35,160
that this whole planet Mars 
had ever really begun to take shape

125
00:10:35,240 --> 00:10:38,160
in sense of knowing 
what the physical features were the geology.

126
00:10:38,240 --> 00:10:41,360
None of that stuff 
had ever been seen before.

127
00:10:41,440 --> 00:10:43,800
It was a historical moment.

128
00:10:43,880 --> 00:10:47,120
When you finally start, 
like with an orange,

129
00:10:47,200 --> 00:10:49,960
peeling the peel off

130
00:10:50,040 --> 00:10:52,720
and exposing the planet 
for what it is.

131
00:10:52,800 --> 00:10:56,760
As Mariner's cameras tracked 
across the belly of Mars,

132
00:10:56,840 --> 00:10:58,800
a giant fissure appeared.

133
00:10:58,880 --> 00:11:02,440
Each day, we get 
a new set of images.

134
00:11:02,520 --> 00:11:04,640
And as they mosaiced, then we said

135
00:11:04,720 --> 00:11:06,600
"Look at that, 
where is it going?"

136
00:11:06,680 --> 00:11:12,160
And it stretched clear across 
roughly an eighth of the planet.

137
00:11:13,280 --> 00:11:17,720
They had discovered the biggest 
geological feature ever seen.

138
00:11:20,520 --> 00:11:24,480
Vallis Marineris 
is 4,000 miles across

139
00:11:24,560 --> 00:11:27,440
and maybe 100 miles 
at its widest

140
00:11:27,520 --> 00:11:29,800
and as much as six miles deep.

141
00:11:29,880 --> 00:11:33,200
On the scale 
of the United States,

142
00:11:33,280 --> 00:11:37,160
I think it is ..., 
over there would be San Francisco,

143
00:11:37,240 --> 00:11:39,920
and over here would be New York, 
something like that.

144
00:11:40,000 --> 00:11:42,320
So it would span 
the United States.

145
00:11:42,400 --> 00:11:44,840
And this little canyon right here

146
00:11:44,920 --> 00:11:46,880
is the size of the Grand Canyon.

147
00:11:52,000 --> 00:11:54,280
The Vallis Marineris 
probably cracked open

148
00:11:54,360 --> 00:11:56,800
when the four giant volcanoes 
to its north

149
00:11:56,880 --> 00:12:00,720
pushed up and stretched 
the very skin of the planet.

150
00:12:02,840 --> 00:12:05,040
Martian geology 
is written on a scale

151
00:12:05,120 --> 00:12:07,840
that dwarfs the Earth's.

152
00:12:07,920 --> 00:12:11,280
Giant features like Vallis Marineris 
and Olympus Mons

153
00:12:11,360 --> 00:12:15,920
had been steadily growing 
in the same place for billions of years.

154
00:12:18,320 --> 00:12:21,520
It suggested that the surface 
of the planet did not move,

155
00:12:21,600 --> 00:12:25,040
unlike the drifting continents 
of the Earth.

156
00:12:26,760 --> 00:12:30,560
Mariner 9 had gone 
in search of geological life

157
00:12:30,640 --> 00:12:33,200
and had found it.

158
00:12:35,920 --> 00:12:37,600
So it was a very active planet,

159
00:12:37,680 --> 00:12:41,560
it was a planet that had 
real geology, active geology, going on,

160
00:12:41,640 --> 00:12:44,040
even in modern geologic history.

161
00:12:47,040 --> 00:12:49,360
But was it all history?

162
00:12:49,440 --> 00:12:52,320
Was Mars a graveyard 
of geological features,

163
00:12:52,480 --> 00:12:54,760
or were the volcanoes 
still active?

164
00:12:58,600 --> 00:13:00,240
To find out,

165
00:13:00,320 --> 00:13:03,520
a probe had to land 
on the planet's surface.

166
00:13:04,400 --> 00:13:07,160
Gerry Soffen was 
the mission scientist.

167
00:13:08,480 --> 00:13:11,560
But the whole point of Viking 
was to be the first time

168
00:13:11,640 --> 00:13:13,920
you really explored 
the surface of the planet.

169
00:13:14,000 --> 00:13:17,040
The Mariners had actually orbited 
or flown by the planet,

170
00:13:17,120 --> 00:13:20,400
but the idea of actually getting 
a lander on the surface of Mars...

171
00:13:20,600 --> 00:13:23,320
It was as important 
as Columbus's voyage.

172
00:13:37,320 --> 00:13:40,560
I was absolutely terrified 
that we wouldn't land successfully

173
00:13:40,640 --> 00:13:43,200
because I had spent 
so much of my life

174
00:13:43,280 --> 00:13:46,120
aimed at this great 
moment in history.

175
00:13:46,200 --> 00:13:49,240
"15,480 feet per second."

176
00:13:49,320 --> 00:13:51,280
"3,000 feet."

177
00:13:53,240 --> 00:13:56,000
On July 20th, 1976,

178
00:13:56,080 --> 00:13:58,880
Viking dropped 
into Mars's upper atmosphere

179
00:13:58,960 --> 00:14:01,080
and began its descent.

180
00:14:06,200 --> 00:14:08,840
When the landing took place,

181
00:14:08,920 --> 00:14:12,160
it was like...it was 
two minutes ago.

182
00:14:13,120 --> 00:14:16,560
I can see every single face 
and the expectation.

183
00:14:17,280 --> 00:14:19,600
The signals from Viking 
took 18 minutes

184
00:14:19,680 --> 00:14:22,320
to travel back 
to mission control.

185
00:14:22,400 --> 00:14:24,840
There was nothing 
to do but wait.

186
00:14:26,440 --> 00:14:30,360
When the touchdown came, 
I just exploded inside.

187
00:14:30,440 --> 00:14:32,400
We have touchdown.

188
00:14:32,480 --> 00:14:34,440
Yeah!

189
00:14:38,280 --> 00:14:40,240
Looking good.

190
00:14:45,120 --> 00:14:48,440
The idea of being 
there in history,

191
00:14:48,520 --> 00:14:51,800
when the first landing on Mars 
took place, was thrilling.

192
00:14:53,720 --> 00:14:56,440
And now the real waiting began.

193
00:14:56,560 --> 00:14:59,680
What would the surface 
of Mars look like?

194
00:15:00,760 --> 00:15:03,200
Was it going to be 
like some place in the US -

195
00:15:03,280 --> 00:15:06,160
Was it going to be a desert? 
Was it going to be sandy, dusty?

196
00:15:06,240 --> 00:15:08,520
But all we knew is 
it was going to be red.

197
00:15:10,840 --> 00:15:12,880
An hour after Viking landed,

198
00:15:12,960 --> 00:15:16,560
the first black and white 
pictures began to creep back.

199
00:15:22,920 --> 00:15:27,080
Line by line, the surface 
of Mars was revealed.

200
00:16:01,720 --> 00:16:04,080
Then came colour pictures.

201
00:16:04,160 --> 00:16:06,520
The surface was littered 
with rocks,

202
00:16:06,600 --> 00:16:09,960
some of them dark and porous, 
clearly volcanic.

203
00:16:10,040 --> 00:16:13,400
They must have been 
hurled there by volcanoes.

204
00:16:13,600 --> 00:16:15,600
We knew there were 
volcanoes on Mars,

205
00:16:15,680 --> 00:16:19,200
but to actually see a piece 
of the volcano was astonishing.

206
00:16:21,680 --> 00:16:25,080
But when had the pieces 
landed there?

207
00:16:25,160 --> 00:16:27,160
Viking carried a device 
to find out

208
00:16:27,240 --> 00:16:29,360
whether Mars was still active -

209
00:16:29,440 --> 00:16:33,320
a seismometer to tell 
if the ground was shaking.

210
00:16:34,440 --> 00:16:38,480
Viking listened and waited 
but felt nothing.

211
00:16:39,560 --> 00:16:42,680
For all its spectacular 
volcanoes and canyons,

212
00:16:42,760 --> 00:16:47,360
it seemed that geological activity 
on Mars was a thing of the past.

213
00:17:12,760 --> 00:17:16,520
While the Americans were putting 
all their efforts into Mars,

214
00:17:16,600 --> 00:17:19,160
the Russians headed for Venus.

215
00:17:23,640 --> 00:17:26,600
This world is almost 
as large as the Earth,

216
00:17:26,680 --> 00:17:29,760
and geologists always thought 
it would be our twin.

217
00:17:30,880 --> 00:17:33,600
But Venus was no easy target.

218
00:17:33,680 --> 00:17:37,000
The surface was hidden 
by a thick blanket of cloud,

219
00:17:37,080 --> 00:17:39,280
and below that serene exterior,

220
00:17:39,360 --> 00:17:41,440
the conditions were hellish.

221
00:17:43,560 --> 00:17:45,200
The pressure of the atmosphere

222
00:17:45,280 --> 00:17:48,400
had already crushed 
three Soviet probes.

223
00:17:48,480 --> 00:17:50,440
The Russians had found 
to their cost

224
00:17:50,520 --> 00:17:55,120
that the surface temperature was 
nearly 500 degrees centigrade.

225
00:17:57,000 --> 00:17:59,600
In 1975, they tried again,

226
00:17:59,680 --> 00:18:02,200
and equipped their probe 
with a camera.

227
00:18:02,280 --> 00:18:04,280
They hoped it would 
cling on long enough

228
00:18:04,360 --> 00:18:07,160
to send back just one picture 
of the surface.

229
00:18:17,200 --> 00:18:21,520
Mission chiefs didn't want 
anyone to know that it might fail.

230
00:18:49,960 --> 00:18:52,000
Seconds after landing,

231
00:18:52,080 --> 00:18:55,760
signals showed Venera 9's 
systems were intact.

232
00:18:55,920 --> 00:18:59,400
On the surface, the temperature 
was hotter than an oven.

233
00:18:59,480 --> 00:19:02,960
Would the probe survive 
to send back the image?

234
00:19:40,480 --> 00:19:44,360
The camera had captured 
a blurred view of some rocks.

235
00:19:44,440 --> 00:19:48,400
It was the first-ever image 
of the surface of Venus.

236
00:19:50,440 --> 00:19:53,400
But it was only 
a tantalising glimpse.

237
00:20:05,920 --> 00:20:07,560
With their next probe,

238
00:20:07,640 --> 00:20:09,920
the Russians hoped 
for something better.

239
00:20:13,160 --> 00:20:16,600
On landing, all systems 
radioed back OK,

240
00:20:16,680 --> 00:20:19,120
but there was no image 
of the surface.

241
00:20:19,240 --> 00:20:21,200
Sasha Basilevsky was on the team

242
00:20:21,280 --> 00:20:23,800
that tried to work out 
what had gone wrong.

243
00:20:24,760 --> 00:20:27,400
We had a technical meeting 
and there was discussion,

244
00:20:27,480 --> 00:20:30,840
and the chief designer 
at that time (said),

245
00:20:30,920 --> 00:20:32,200
"You know, I have an idea

246
00:20:32,280 --> 00:20:38,800
that we have landed in 
something very sticky and viscous."

247
00:20:38,880 --> 00:20:43,120
And a young, nasty voice told,

248
00:20:43,200 --> 00:20:44,480
"Yes, sir, in the shit."

249
00:20:47,800 --> 00:20:50,240
But Venera had not sunk.

250
00:20:50,320 --> 00:20:52,080
The intense heat on the surface

251
00:20:52,160 --> 00:20:55,040
had melted the lens cap 
on to the camera.

252
00:20:57,680 --> 00:20:59,280
Three years later,

253
00:20:59,360 --> 00:21:01,920
another pair of probes 
headed for Venus.

254
00:21:03,240 --> 00:21:05,200
This time, they took 
beautiful pictures

255
00:21:05,280 --> 00:21:07,800
of a lava-filled patch 
of ground.

256
00:21:08,880 --> 00:21:12,400
But when the probe tried 
to sample Venusian rock,

257
00:21:12,480 --> 00:21:15,520
that lens cap 
came back to haunt them.

258
00:21:15,600 --> 00:21:18,680
In Venera 14 as in Venera 13,

259
00:21:18,760 --> 00:21:22,280
they had a special device 
to measure electric properties

260
00:21:22,360 --> 00:21:24,160
and mechanical properties 
of the surface.

261
00:21:24,240 --> 00:21:28,960
This arm goes and puts the device 
on the surface and measures.

262
00:21:29,040 --> 00:21:32,400
And Venera 14 did it 
in a perfect way

263
00:21:32,480 --> 00:21:36,000
but it just got the cap.

264
00:21:36,080 --> 00:21:40,080
So, we measured the mechanical properties 
and electrical properties

265
00:21:40,160 --> 00:21:43,120
of that thing 
they brought from Earth.

266
00:21:53,840 --> 00:21:56,880
On the planet's surface, 
the probes could only survive

267
00:21:56,960 --> 00:21:59,200
for an hour or two at most.

268
00:21:59,280 --> 00:22:03,240
Somehow another way had to be found 
to see through the clouds.

269
00:22:16,440 --> 00:22:20,760
In 1989, NASA launched Magellan.

270
00:22:29,240 --> 00:22:31,880
Magellan wouldn't take pictures

271
00:22:31,960 --> 00:22:33,800
but would scan 
the planet with radar

272
00:22:33,880 --> 00:22:36,400
to make up the contours 
of the surface,

273
00:22:36,480 --> 00:22:39,040
cutting through the clouds 
as if they weren't there.

274
00:22:40,640 --> 00:22:44,640
We were able to actually come around 
the globe every day many times

275
00:22:44,720 --> 00:22:47,600
and build up a picture 
of the global geology of Venus.

276
00:22:54,680 --> 00:22:58,240
Magellan began 
to send back reams and reams of data -

277
00:22:58,360 --> 00:23:02,000
and a whole new generation of 
geologists set to work on it.

278
00:23:04,400 --> 00:23:08,800
When the first image taken came back 
from Magellan, I went in about 4 in the morning

279
00:23:08,880 --> 00:23:11,560
and looked at the first strip of Magellan data,

280
00:23:11,640 --> 00:23:13,520
this first track down the planet.

281
00:23:19,520 --> 00:23:23,760
To see the planet surface being 
revealed in such incredible detail,

282
00:23:23,840 --> 00:23:29,320
and to say "I'm one of the first people who's ever 
looked at this piece of ground on Venus,"

283
00:23:29,400 --> 00:23:31,520
you felt like 
such an explorer.

284
00:23:31,960 --> 00:23:33,320
The first images showed

285
00:23:33,400 --> 00:23:35,920
that Venus had 
many similarities to Earth.

286
00:23:37,400 --> 00:23:39,480
There were 
large mountain ranges,

287
00:23:39,560 --> 00:23:42,080
some of them almost 
similar to the Himalayas.

288
00:23:42,160 --> 00:23:44,120
There were long faults 
on the planet

289
00:23:44,200 --> 00:23:47,600
that looked maybe (sort of) similar 
to faults we see on the Earth.

290
00:23:47,720 --> 00:23:50,480
There were volcanoes, lots and lots 
of volcanoes on the surface,

291
00:23:50,800 --> 00:23:53,240
very large ones,  much larger 
than some on the Earth,

292
00:23:53,320 --> 00:23:55,120
others on a similar scale.

293
00:24:01,120 --> 00:24:05,160
But then an alien 
landscape emerged.

294
00:24:05,640 --> 00:24:08,080
There were these huge 
circular features.

295
00:24:08,160 --> 00:24:11,280
By huge, I mean 
250-300 kilometres across.

296
00:24:11,360 --> 00:24:13,520
They were encircled by ridges.

297
00:24:13,600 --> 00:24:16,320
They were high, 
they were sort of mountainous.

298
00:24:16,400 --> 00:24:18,920
They tended to have volcanoes 
all over the surface.

299
00:24:19,000 --> 00:24:20,640
And we just said, 
"What are these features?"

300
00:24:20,640 --> 00:24:21,480
How could they have formed?

301
00:24:21,560 --> 00:24:23,160
We'd never seen 
anything like them.

302
00:24:29,000 --> 00:24:31,800
The 3-D images revealed 
giant blisters

303
00:24:31,880 --> 00:24:34,000
that had oozed lava 
from every crack.

304
00:24:34,120 --> 00:24:37,800
And the surface of Venus 
seemed to be cut with channels.

305
00:24:37,880 --> 00:24:41,520
They looked like long rivers 
going across the surface of the planet,

306
00:24:41,560 --> 00:24:45,200
but we know with Venus' incredibly 
high surface temperatures,

307
00:24:45,280 --> 00:24:47,360
there's no way that water 
could have formed those channels.

308
00:24:47,440 --> 00:24:49,720
So they had to have 
been formed by lava.

309
00:25:00,040 --> 00:25:03,760
There were other volcanic features 
that looked like pancakes.

310
00:25:03,840 --> 00:25:06,240
They had very steep sides and very flat tops.

311
00:25:06,320 --> 00:25:10,080
And literally looks like somebody threw a bunch of 
pancakes out onto the surface of the planet.

312
00:25:10,480 --> 00:25:14,480
There were other kinds of volcanoes 
that looked like little squashed bugs, like ticks.

313
00:25:16,440 --> 00:25:19,880
Everywhere you look, you see 
some sort of volcanic feature,

314
00:25:19,960 --> 00:25:24,000
a flow, a small volcano, a weird channel -
it's just dominated by volcanism.

315
00:25:24,080 --> 00:25:27,040
And that's just something we weren't 
 prepared for really at all.

316
00:25:31,280 --> 00:25:33,800
It's intriguing 
to look at this surface

317
00:25:33,880 --> 00:25:37,000
that you say should be 
so much like the Earth.

318
00:25:37,080 --> 00:25:38,880
It's not. 
How did it get this way?

319
00:25:38,960 --> 00:25:39,760
It's just a puzzle.

320
00:25:39,840 --> 00:25:43,520
That's what makes Venus 
so interesting.

321
00:25:55,640 --> 00:25:58,600
But when had this volcanic 
surface formed?

322
00:25:58,680 --> 00:26:02,560
Geologists tried to find out 
by counting impact craters.

323
00:26:02,640 --> 00:26:04,000
When we got 
the global picture together,

324
00:26:04,080 --> 00:26:05,240
we started counting craters

325
00:26:05,320 --> 00:26:07,600
and looking for areas that had 
a high density of craters,

326
00:26:07,680 --> 00:26:09,080
and an area that 
would have a low density

327
00:26:09,160 --> 00:26:10,680
indicating old and young ages.

328
00:26:10,760 --> 00:26:13,160
When we look at the Moon, 
look at Mars, we look at Mercury,

329
00:26:13,240 --> 00:26:15,760
you have areas where you say, 
"OK, this area has more craters, it's older.

330
00:26:15,840 --> 00:26:17,720
This area has fewer craters, 
it's younger.

331
00:26:17,840 --> 00:26:19,880
The amazing part was that 
it looked like the craters

332
00:26:19,960 --> 00:26:22,280
were almost randomly 
distributed across the surface.

333
00:26:22,360 --> 00:26:25,000
And you say, "Wait a minute. 
The whole planet can't be the same age -

334
00:26:25,080 --> 00:26:25,760
it's the size of the Earth.

335
00:26:25,840 --> 00:26:27,640
How could you have a planet 
the size of the Earth

336
00:26:27,720 --> 00:26:29,880
where the entire surface 
form at the same time?

337
00:26:29,960 --> 00:26:31,360
It just didn't make sense.

338
00:26:33,200 --> 00:26:35,560
What could have happened 
for a planet

339
00:26:35,640 --> 00:26:38,640
to create all its surface 
at one time?

340
00:26:42,920 --> 00:26:46,320
Well, it was really mystifying, 
because nobody could really be sure

341
00:26:46,400 --> 00:26:48,720
since we hadn't seen anything like this. 
What was going on?

342
00:26:48,800 --> 00:26:50,960
One of the main ideas 
that came out was the idea

343
00:26:51,040 --> 00:26:54,000
that Venus may have actually been 
catastrophically resurfaced

344
00:26:54,080 --> 00:26:55,760
a few hundred million years ago.

345
00:27:02,680 --> 00:27:05,240
The idea that Venus boiled over

346
00:27:05,320 --> 00:27:06,920
in a planet-wide flood of lava

347
00:27:07,000 --> 00:27:08,880
is still hotly debated.

348
00:27:25,280 --> 00:27:28,960
But if it did, 
and has now cooled down,

349
00:27:29,040 --> 00:27:31,280
will it ever erupt again?

350
00:27:32,520 --> 00:27:36,600
The most exciting thing would be to find 
an erupting volcano on Venus,

351
00:27:36,680 --> 00:27:40,520
to say "Here we have proof, 
Venus is still geologically active.

352
00:27:40,600 --> 00:27:42,840
"It really is the planet most like the Earth,

353
00:27:42,920 --> 00:27:44,440
and here's proof of it.

354
00:27:44,520 --> 00:27:47,680
"It's not a dead planet, 
it's still alive, it's still active."

355
00:27:47,760 --> 00:27:51,960
That's something that I would give 
a lot, awful lot, to be able to find.

356
00:27:55,280 --> 00:27:58,560
Magellan scanned the planet 
for four years,

357
00:27:58,640 --> 00:28:01,000
but found no fresh lava flows.

358
00:28:02,200 --> 00:28:05,360
Venus may well be alive,

359
00:28:05,440 --> 00:28:07,240
but there is still 
no sign of it.

360
00:28:08,320 --> 00:28:11,320
Of course if you orbit 
around Earth for a year,

361
00:28:11,400 --> 00:28:13,040
you might not see 
any volcanic activity at all.

362
00:28:13,120 --> 00:28:15,600
So it's really hard to tell 
whether it's actually going -

363
00:28:15,680 --> 00:28:18,400
it's like trying to find the smoking 
gun or the smoking volcano.

364
00:28:18,480 --> 00:28:19,840
It's not easy to find.

365
00:28:22,160 --> 00:28:24,680
Despite being laid bare 
by Magellan,

366
00:28:24,760 --> 00:28:27,800
Venus remains a planet 
shrouded in mystery.

367
00:28:31,200 --> 00:28:33,320
Was Earth the only place

368
00:28:33,400 --> 00:28:36,400
where geologists would find 
active volcanoes?

369
00:28:36,880 --> 00:28:39,000
It was beginning 
to look that way.

370
00:28:43,320 --> 00:28:45,840
The only other rocky planet 
is Mercury,

371
00:28:45,920 --> 00:28:49,720
but it's a small world, 
barely bigger than our moon.

372
00:28:50,000 --> 00:28:53,840
And its surface is just 
as cratered and dead.

373
00:28:56,080 --> 00:28:58,640
No geological activity 
of any kind

374
00:28:58,720 --> 00:29:01,200
has wiped Mercury's face clean.

375
00:29:01,680 --> 00:29:03,600
Outside, it is baking hot,

376
00:29:03,800 --> 00:29:06,480
but inside, stone cold.

377
00:29:24,520 --> 00:29:27,120
There could be 
no geology on Jupiter

378
00:29:27,200 --> 00:29:28,800
and the other giant planets -

379
00:29:28,880 --> 00:29:30,840
they have no solid surface.

380
00:29:34,040 --> 00:29:37,360
There is some 
solid rock out here.

381
00:29:37,440 --> 00:29:39,320
On its way past Jupiter,

382
00:29:39,400 --> 00:29:41,680
Voyager flew 
by the planet's moons.

383
00:29:42,160 --> 00:29:46,280
No one expected much interesting 
geology on these worlds.

384
00:29:46,920 --> 00:29:51,360
We expected small objects 
the size of the Moon or smaller

385
00:29:51,440 --> 00:29:53,600
to be pretty lifeless, geologically,

386
00:29:53,680 --> 00:29:58,280
and expected them to be holding records

387
00:29:58,360 --> 00:30:00,040
of the very early solar system,

388
00:30:00,120 --> 00:30:02,720
the impact processes,

389
00:30:02,800 --> 00:30:05,640
and fairly esoteric 
kinds of questions

390
00:30:05,720 --> 00:30:08,960
that solar system geologists 
might be interested in.

391
00:30:09,040 --> 00:30:12,440
Not something the general public 
would care a whole lot about.

392
00:30:15,320 --> 00:30:18,800
The first thing we ran 
into course was Callisto.

393
00:30:18,880 --> 00:30:24,320
That was pretty much what we had thought 
one of these moons would look like.

394
00:30:25,600 --> 00:30:28,080
Callisto is dark and icy.

395
00:30:28,120 --> 00:30:30,640
Like Mercury, 
its cratered surface

396
00:30:30,720 --> 00:30:33,400
hasn't changed 
for billions of years.

397
00:30:36,800 --> 00:30:40,520
The next moon, Ganymede, is 
the largest in the solar system,

398
00:30:40,600 --> 00:30:43,360
but it too held few surprises.

399
00:30:51,760 --> 00:30:54,920
Circling closest 
to the giant planet is Io,

400
00:30:55,000 --> 00:30:57,720
a world about the size 
of our moon.

401
00:31:06,800 --> 00:31:10,120
As we looked at it 
from a great distance,

402
00:31:10,200 --> 00:31:14,160
we saw a lot of dark spots 
on the surface

403
00:31:14,240 --> 00:31:17,120
which we thought 
maybe were impact craters.

404
00:31:17,200 --> 00:31:19,840
Voyager took a few pictures, 
sailed past Io,

405
00:31:19,920 --> 00:31:22,720
and the scientists focused 
on Jupiter itself.

406
00:31:24,000 --> 00:31:27,160
Meanwhile, one of the engineers 
busied herself

407
00:31:27,240 --> 00:31:29,400
with some routine 
spacecraft maintenance.

408
00:31:30,240 --> 00:31:35,120
I came in about 9 o'clock that 
morning to the navigation area.

409
00:31:35,200 --> 00:31:36,800
And the tape with the pictures

410
00:31:36,880 --> 00:31:40,200
the spacecraft had taken 
the day before was on my desk.

411
00:31:40,280 --> 00:31:43,400
I put them on the computer system 
and I displayed them.

412
00:31:43,600 --> 00:31:47,080
And I could see that Io or the moon of Io 
was a crescent,

413
00:31:47,160 --> 00:31:50,400
as very often our own moon is 
a crescent in the night sky.

414
00:31:50,480 --> 00:31:52,960
And I went and enhanced the brightness,

415
00:31:53,040 --> 00:31:57,120
and there appeared 
beside Io an object, a huge object

416
00:31:57,200 --> 00:32:00,320
that looked like something 
I couldn't recognise

417
00:32:00,400 --> 00:32:01,960
and could never have expected.

418
00:32:02,040 --> 00:32:04,800
And it completely captured 
my attention.

419
00:32:06,920 --> 00:32:09,320
I wanted to know so badly what that was.

420
00:32:09,400 --> 00:32:12,200
I just asked myself 
"My goodness, what is that?"

421
00:32:12,280 --> 00:32:14,680
And the answer that occurred 
to me first

422
00:32:14,760 --> 00:32:18,920
was it looked like another moon 
peeking out behind Io.

423
00:32:21,240 --> 00:32:22,800
But there was no other moon,

424
00:32:22,880 --> 00:32:25,440
and no fault in the camera.

425
00:32:26,360 --> 00:32:30,520
Linda Hyder concluded this 
object had to be part of Io.

426
00:32:30,880 --> 00:32:34,240
And in fact, that was 
very hard to accept

427
00:32:34,320 --> 00:32:39,240
because the size of this object was 
enormous with respect to the size of Io.

428
00:32:49,200 --> 00:32:51,160
And when I explored it,

429
00:32:51,240 --> 00:32:54,720
I was able to find that 
this large, strange object

430
00:32:54,800 --> 00:32:56,880
It was exactly coincident

431
00:32:56,960 --> 00:32:59,720
and fell over a heart shape 
feature on Io.

432
00:32:59,880 --> 00:33:04,640
What I had discovered a huge plume 
of a volcanic eruption

433
00:33:04,720 --> 00:33:08,400
rising 270 kilometres 
over the surface of Io

434
00:33:08,480 --> 00:33:11,080
and raining back down onto it.

435
00:33:13,200 --> 00:33:15,640
So I had discovered 
the first-ever

436
00:33:15,720 --> 00:33:20,320
volcanic eruption ever seen on 
another world besides the Earth.

437
00:33:31,680 --> 00:33:36,200
We didn't really expect to find 
active volcanic eruptions

438
00:33:36,640 --> 00:33:39,280
throwing material 
from a volcanic vent

439
00:33:39,360 --> 00:33:42,960
to an altitude 
of a couple of hundred miles,

440
00:33:43,040 --> 00:33:45,440
300 kilometres 
above the surface.

441
00:33:45,520 --> 00:33:48,960
This stuff goes up with the velocity 
of a high-powered rifle.

442
00:33:49,040 --> 00:33:52,800
Of course, it comes back on the surface 
with the same velocity.

443
00:33:52,880 --> 00:33:58,520
So, a healthy place to stand 
would not be the surface of Io.

444
00:34:00,680 --> 00:34:04,920
The entire surface of Io 
is covered with volcanoes.

445
00:34:05,440 --> 00:34:09,400
This moon is awash with 
multi-coloured lava flows.

446
00:34:14,960 --> 00:34:17,520
But why is Io an active world?

447
00:34:18,000 --> 00:34:19,800
It's only the size of our moon.

448
00:34:19,880 --> 00:34:21,960
It should be cold inside.

449
00:34:22,440 --> 00:34:25,800
Head of the Voyager camera team 
was Brad Smith.

450
00:34:25,880 --> 00:34:28,600
Till now, he had concentrated 
on Jupiter's atmosphere.

451
00:34:29,080 --> 00:34:31,840
Now Io drew his attention.

452
00:34:33,200 --> 00:34:34,800
Io is a very small body.

453
00:34:34,880 --> 00:34:39,000
It doesn't have enough 
of the radioactive materials

454
00:34:39,080 --> 00:34:41,720
that heat up the rock 
as happens on the Earth.

455
00:34:41,800 --> 00:34:45,960
So we didn't expect 
any kind of volcanism on Io.

456
00:34:49,160 --> 00:34:52,920
The explanation was to be found 
in our own moon.

457
00:35:01,320 --> 00:35:05,280
And a NASA scientist 
in California had predicted it.

458
00:35:07,800 --> 00:35:11,200
Well, as you can see, 
the power of the Moon's gravity

459
00:35:11,280 --> 00:35:12,840
can move oceans on the Earth.

460
00:35:13,200 --> 00:35:16,480
Imagine what 
the power of Jupiter -

461
00:35:16,560 --> 00:35:20,920
what just 300 times the mass 
of the Earth - can have on Io.

462
00:35:21,000 --> 00:35:23,760
Now Io, as it circles Jupiter,

463
00:35:23,840 --> 00:35:27,800
approaches Jupiter closer 
at one point than at another.

464
00:35:27,880 --> 00:35:32,520
What this does is it changes 
the gravitational force from Jupiter

465
00:35:32,600 --> 00:35:34,720
and results in a giant squeeze.

466
00:35:36,440 --> 00:35:38,800
Physicist Ray Reynolds 
had realised

467
00:35:38,880 --> 00:35:41,720
that friction from the constant 
wrenching by Jupiter

468
00:35:41,800 --> 00:35:46,120
was heating up the interior of 
Io to incredible temperatures.

469
00:35:48,160 --> 00:35:50,800
We plugged in the numbers 
into our equations,

470
00:35:50,880 --> 00:35:55,440
and, lo and behold, we come out 
with thousands of degrees

471
00:35:55,520 --> 00:35:57,400
near the surface 
of this satellite.

472
00:35:57,480 --> 00:36:02,000
Well, this immediately raised visions 
in our mind of volcanoes going off.

473
00:36:03,680 --> 00:36:06,040
But nobody was prepared 
for the ferocity

474
00:36:06,120 --> 00:36:09,200
of the sulphur-spewing volcanoes 
that Voyager found.

475
00:36:20,000 --> 00:36:24,000
Io is just enormously 
volcanically active,

476
00:36:24,080 --> 00:36:26,400
more active than the Earth

477
00:36:26,520 --> 00:36:28,720
and any other body 
in the solar system.

478
00:36:28,800 --> 00:36:30,520
There is nothing that 
even comes close to it.

479
00:36:30,600 --> 00:36:34,880
Its surface is completely 
covered with volcanic debris.

480
00:36:38,800 --> 00:36:42,320
Finally, geologists had found 
a world that was alive

481
00:36:43,200 --> 00:36:45,680
and changing before their eyes.

482
00:36:46,400 --> 00:36:48,200
Draw a map of Io,

483
00:36:48,280 --> 00:36:51,720
and it will be obsolete 
the next day.

484
00:36:55,880 --> 00:36:57,680
But Io wasn't the only surprise

485
00:36:57,760 --> 00:37:00,800
Voyager found 
among Jupiter's moons.

486
00:37:01,160 --> 00:37:04,680
Next to it was 
the bright disc of Europa.

487
00:37:09,080 --> 00:37:12,080
Europa was surprisingly smooth.

488
00:37:12,160 --> 00:37:15,200
That is there was little or no 
topography on it at all.

489
00:37:15,280 --> 00:37:18,600
Scaled down, it would be 
as smooth as a billiard ball.

490
00:37:18,680 --> 00:37:21,280
And why it should be?

491
00:37:21,360 --> 00:37:23,960
Why there was no topography, 
we could only guess.

492
00:37:25,480 --> 00:37:28,640
Close up, 
the surface was baffling.

493
00:37:28,720 --> 00:37:33,320
When we look at Europa, we see 
a startling lack of craters.

494
00:37:33,400 --> 00:37:37,080
And we also see that there are 
large linear features

495
00:37:37,160 --> 00:37:39,640
that look like cracks 
on the surface.

496
00:37:46,160 --> 00:37:48,120
Reynolds thought the cracks 
might be a result

497
00:37:48,200 --> 00:37:50,800
of the constant squeezing 
from Jupiter's gravity,

498
00:37:50,880 --> 00:37:52,000
just like at Io.

499
00:37:55,080 --> 00:37:58,280
And there was a more 
intriguing possibility.

500
00:37:58,360 --> 00:38:00,520
Europa's surface is made of ice,

501
00:38:00,600 --> 00:38:04,400
and that would be much easier 
to melt than Io's solid rock.

502
00:38:04,560 --> 00:38:08,200
Our calculations indicated 
that there was a good possibility

503
00:38:08,280 --> 00:38:12,720
that there could be an ocean 
beneath a thin ice layer.

504
00:38:16,520 --> 00:38:18,200
Voyager's images were too crude

505
00:38:18,280 --> 00:38:22,600
to prove or disprove the idea 
of a subterranean ocean.

506
00:38:22,680 --> 00:38:26,520
But 20 years later, 
another spacecraft, Galileo,

507
00:38:26,600 --> 00:38:28,960
is back for a closer look.

508
00:38:31,960 --> 00:38:32,920
Close up,

509
00:38:33,000 --> 00:38:37,120
Europa's surface looks like 
a crazy paving of ice.

510
00:38:37,200 --> 00:38:40,760
There are giant icebergs 
and a network of cracks

511
00:38:40,840 --> 00:38:43,360
where it seems that hot water 
has welled up from below

512
00:38:43,440 --> 00:38:45,480
and then frozen 
instantly in place,

513
00:38:46,080 --> 00:38:50,360
just like lava from a volcanic 
fissure on Earth.

514
00:38:53,680 --> 00:38:57,640
Instead of hot rock that's coming out, 
it's water, it's liquid water.

515
00:38:57,720 --> 00:38:59,720
But the principle is the same.

516
00:38:59,800 --> 00:39:02,600
There's a fluid 
down underneath the crust.

517
00:39:02,680 --> 00:39:04,080
And from time to time,

518
00:39:04,160 --> 00:39:06,480
this pushes up and flows 
onto the surface

519
00:39:06,560 --> 00:39:11,720
much in the same way that hot lava flows 
onto the surface of the Earth.

520
00:39:22,760 --> 00:39:26,960
No actual eruption of ice 
has yet been spotted,

521
00:39:27,040 --> 00:39:29,080
but Europa has opened up 
the possibility

522
00:39:29,160 --> 00:39:32,640
of completely new kinds 
of geological activity.

523
00:39:58,440 --> 00:40:01,600
As space probes ventured 
further out,

524
00:40:01,680 --> 00:40:04,440
they found other frozen worlds.

525
00:40:16,880 --> 00:40:19,080
Among the moons 
of Saturn and Uranus,

526
00:40:19,160 --> 00:40:22,760
there were signs of strange 
geological events.

527
00:40:27,120 --> 00:40:30,080
But they all seemed 
to have occurred aeons ago.

528
00:40:37,200 --> 00:40:41,200
Then, a decade after 
its encounter with Jupiter,

529
00:40:41,280 --> 00:40:45,040
Voyager met Triton, 
moon of Neptune.

530
00:40:48,360 --> 00:40:50,920
Triton, as we got closer and closer,

531
00:40:51,000 --> 00:40:54,800
it became evident 
that it was going to be a very tiny object.

532
00:40:54,880 --> 00:40:57,760
And it was covered 
with very, very bright material.

533
00:40:57,960 --> 00:41:00,120
That made it very cold -

534
00:41:00,200 --> 00:41:03,360
the coldest thing 
we've encountered so far

535
00:41:03,440 --> 00:41:05,440
throughout the solar system.

536
00:41:06,720 --> 00:41:08,440
Triton is so cold

537
00:41:08,520 --> 00:41:10,760
that even its thin 
atmosphere of nitrogen

538
00:41:10,840 --> 00:41:14,280
freezes into a solid 
ice cap every winter.

539
00:41:14,800 --> 00:41:18,000
To have expected geologic activity

540
00:41:18,080 --> 00:41:22,440
on such a surface 
would be insane, frankly.

541
00:41:26,080 --> 00:41:28,440
But when Voyager got close,

542
00:41:28,520 --> 00:41:32,720
it saw there were dark streaks 
all over the fresh ice cap.

543
00:41:34,720 --> 00:41:38,160
Those dark markings had to be sitting 
on top of that ice.

544
00:41:38,240 --> 00:41:41,200
They had to be laid down there 
in the recent past.

545
00:41:41,320 --> 00:41:45,680
That meant something had to be going on 
to make them an active process.

546
00:41:49,880 --> 00:41:51,760
Larry Soderblom spent two months

547
00:41:51,840 --> 00:41:54,920
looking at pictures of Triton 
before he spotted it.

548
00:41:55,040 --> 00:41:58,160
He flickered pairs of images taken 
from slightly different angles

549
00:41:58,240 --> 00:42:00,480
to give a 3-D view 
of the surface.

550
00:42:01,400 --> 00:42:02,040
All of a sudden,

551
00:42:02,120 --> 00:42:05,200
he saw something that seemed 
to stand up from the ice.

552
00:42:05,960 --> 00:42:07,320
One afternoon,

553
00:42:07,400 --> 00:42:12,920
we were stunned 
to find active geysers

554
00:42:13,000 --> 00:42:16,680
shooting up 
above the Triton ice cap.

555
00:42:17,600 --> 00:42:19,400
Geysers - fountains of material,

556
00:42:19,480 --> 00:42:24,800
rising five, ten kilometres -
miles above the surface.

557
00:42:43,080 --> 00:42:46,360
Even in this dark corner 
of the solar system,

558
00:42:46,440 --> 00:42:50,640
the faint heat of the Sun 
manages to penetrate Triton's ice cap.

559
00:42:59,920 --> 00:43:04,040
It warms liquid nitrogen 
trapped beneath the surface

560
00:43:04,120 --> 00:43:08,840
to a point where it bursts out 
and rises up into space

561
00:43:08,880 --> 00:43:13,560
before turning a right angle 
in Triton's high altitude winds.

562
00:43:15,240 --> 00:43:18,640
It's almost as if Triton was 
the last sentence

563
00:43:18,720 --> 00:43:22,720
in the message that we got 
from the Voyager mission:

564
00:43:22,800 --> 00:43:25,040
that no matter 
where you go in the universe,

565
00:43:25,120 --> 00:43:27,480
expect the unexpectable.

566
00:43:33,320 --> 00:43:36,200
It changed our whole concept 
of what volcanism is.

567
00:43:36,280 --> 00:43:39,120
Our classical concept 
because before Voyager

568
00:43:39,200 --> 00:43:40,920
(what) was volcanism was hot rock

569
00:43:41,000 --> 00:43:43,280
coming out of the interior 
of a planet.

570
00:43:43,360 --> 00:43:45,640
But Voyager showed us

571
00:43:45,720 --> 00:43:49,200
that there are other materials 
as well that produce volcanism.

572
00:43:49,280 --> 00:43:54,200
On Io, we saw molten sulphur -
sulphur dioxide.

573
00:43:54,280 --> 00:43:58,040
On Europa, water is 
an important element,

574
00:43:59,200 --> 00:44:03,840
and on Triton, liquid 
nitrogen may actually be the fluid

575
00:44:03,920 --> 00:44:05,680
that is involved in volcanism.

576
00:44:09,240 --> 00:44:11,520
After so many amazing 
discoveries

577
00:44:11,600 --> 00:44:13,560
across the solar system,

578
00:44:13,640 --> 00:44:15,200
geologists are now returning

579
00:44:15,280 --> 00:44:17,400
to the Earth's 
neighbouring planets.

580
00:44:21,800 --> 00:44:25,280
In 1997, NASA returned to Mars

581
00:44:25,360 --> 00:44:27,680
with a new orbiting spacecraft,

582
00:44:27,760 --> 00:44:31,040
that's photographing the surface 
in incredible detail.

583
00:44:36,440 --> 00:44:41,000
Mars Global Surveyor can pick out 
individual boulders on the ground

584
00:44:41,160 --> 00:44:45,200
and can see places where they 
have rolled down into gullies.

585
00:44:45,680 --> 00:44:48,960
Was it wind or small tremors?

586
00:44:51,560 --> 00:44:54,600
If there is 
any activity on Mars,

587
00:44:54,680 --> 00:44:57,120
Global Surveyor should find it.

588
00:45:03,280 --> 00:45:08,520
What we're seeing now on Mars 
is like a shot from a helicopter

589
00:45:08,600 --> 00:45:10,520
compared to a shot 
from a space shuttle.

590
00:45:10,640 --> 00:45:13,920
The whole sense of Mars

591
00:45:14,000 --> 00:45:15,400
is a little bit different

592
00:45:15,480 --> 00:45:18,640
when you get down to 
the size of detail that we can see.

593
00:45:18,720 --> 00:45:21,000
And we're just beginning 
to get into that

594
00:45:21,080 --> 00:45:23,720
and get a sense 
of what's going on on Mars.

595
00:45:24,040 --> 00:45:26,480
Soon, we will have a map of Mars

596
00:45:26,560 --> 00:45:29,520
that's as detailed 
as those of the Earth.

597
00:45:39,040 --> 00:45:41,000
Now, when I come out to Hawaii,

598
00:45:41,080 --> 00:45:43,200
my whole perspective 
has changed.

599
00:45:43,280 --> 00:45:45,720
I walk around 
on the surface here,

600
00:45:45,800 --> 00:45:48,280
and, in fact, I'm beginning to see 
things that are the same scale

601
00:45:48,360 --> 00:45:49,360
that I'm seeing on Mars.

602
00:45:49,440 --> 00:45:50,560
And it's incredibly exciting.

603
00:45:50,640 --> 00:45:53,280
It's bridged the gap. 
It's brought it together.

604
00:45:53,360 --> 00:45:55,960
So it's almost like I'm 
walking around on Mars.

605
00:45:56,560 --> 00:45:58,960
I think this is the way it's worked 
with all the planets.

606
00:45:59,040 --> 00:46:02,720
Initially, (they) were alien objects 
that you had little knowledge about.

607
00:46:02,800 --> 00:46:05,640
But particularly from the 
geology, you begin to see old friends -

608
00:46:05,720 --> 00:46:08,360
volcanoes, and lava flows, 
sand dunes and so on.

609
00:46:08,440 --> 00:46:11,640
And then, little by little, 
you know, you transport yourself there.

610
00:46:11,720 --> 00:46:13,400
You think about there. 
I wake up at night

611
00:46:13,480 --> 00:46:16,520
I have a dream about being on Mars. 
It's just amazing.

612
00:46:26,960 --> 00:46:30,760
One day soon, a probe 
may also return to Venus,

613
00:46:30,880 --> 00:46:34,760
and perhaps survive for long 
enough in its hostile atmosphere

614
00:46:34,840 --> 00:46:37,560
to observe a volcano erupting.

615
00:46:49,800 --> 00:46:50,880
We know now

616
00:46:50,960 --> 00:46:54,920
that the Earth is just one 
of a family of active worlds.

617
00:46:57,760 --> 00:46:59,800
But geologists will never grasp

618
00:46:59,880 --> 00:47:01,840
the true nature 
of another planet

619
00:47:01,960 --> 00:47:03,600
until they have 
touched the stuff

620
00:47:03,680 --> 00:47:06,040
that comes from deep within it.

621
00:47:15,200 --> 00:47:18,160
The grand finale 
is still to come.

622
00:47:28,440 --> 00:47:30,400
If all goes to plan,

623
00:47:30,480 --> 00:47:34,920
the Galileo probe will end 
its mission and the millennium

624
00:47:35,000 --> 00:47:37,080
with one of the most 
breathtaking stunts

625
00:47:37,160 --> 00:47:38,840
ever performed.

626
00:47:50,120 --> 00:47:52,160
With its fuel spent

627
00:47:52,240 --> 00:47:54,960
and suffering critical 
radiation damage,

628
00:47:55,080 --> 00:47:57,960
the dying spacecraft 
will dive headlong

629
00:47:58,040 --> 00:48:02,880
into a plume of fiery ash 
from an erupting volcano on Io,

630
00:48:03,000 --> 00:48:08,200
sampling with its last gasp 
the geologist's Holy Grail:

631
00:48:08,280 --> 00:48:11,400
the inside of another world.

632
00:48:11,400 --> 00:48:13,200
subtitles corrected and synchronised by m06166