1
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I'm really glad to be here.

2
00:00:03,015 --> 00:00:04,703
I'm glad you're here,

3
00:00:04,727 --> 00:00:06,560
because that would be a little weird.

4
00:00:07,460 --> 00:00:09,565
I'm glad we're all here.

5
00:00:10,303 --> 00:00:13,156
And by "here," I don't mean here.

6
00:00:14,831 --> 00:00:15,981
Or here.

7
00:00:16,728 --> 00:00:17,880
But here.

8
00:00:17,904 --> 00:00:19,054
I mean Earth.

9
00:00:19,627 --> 00:00:23,570
And by "we," I don't mean
those of us in this auditorium,

10
00:00:23,594 --> 00:00:25,064
but life,

11
00:00:25,088 --> 00:00:26,537
all life on Earth --

12
00:00:26,561 --> 00:00:31,943
(Laughter)

13
00:00:32,280 --> 00:00:34,271
from complex to single-celled,

14
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from mold to mushrooms

15
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to flying bears.

16
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(Laughter)

17
00:00:41,736 --> 00:00:43,245
The interesting thing is,

18
00:00:43,269 --> 00:00:46,300
Earth is the only place
we know of that has life --

19
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8.7 million species.

20
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We've looked other places,

21
00:00:49,938 --> 00:00:52,035
maybe not as hard
as we should or we could,

22
00:00:52,059 --> 00:00:53,986
but we've looked and haven't found any;

23
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Earth is the only place
we know of with life.

24
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Is Earth special?

25
00:00:59,591 --> 00:01:02,045
This is a question I've wanted
to know the answer to

26
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since I was a small child,

27
00:01:03,347 --> 00:01:05,379
and I suspect 80 percent
of this auditorium

28
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has thought the same thing
and also wanted to know the answer.

29
00:01:08,879 --> 00:01:11,046
To understand whether
there are any planets --

30
00:01:11,070 --> 00:01:13,348
out there in our solar system or beyond --

31
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that can support life,

32
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the first step is to understand
what life here requires.

33
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It turns out, of all of those
8.7 million species,

34
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life only needs three things.

35
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On one side, all life
on Earth needs energy.

36
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Complex life like us derives
our energy from the sun,

37
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but life deep underground
can get its energy

38
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from things like chemical reactions.

39
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There are a number
of different energy sources

40
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available on all planets.

41
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On the other side,

42
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all life needs food or nourishment.

43
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And this seems like a tall order,
especially if you want a succulent tomato.

44
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(Laughter)

45
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However, all life on Earth
derives its nourishment

46
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from only six chemical elements,

47
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and these elements can be found
on any planetary body

48
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in our solar system.

49
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So that leaves the thing
in the middle as the tall pole,

50
00:02:03,788 --> 00:02:05,742
the thing that's hardest to achieve.

51
00:02:05,766 --> 00:02:07,658
Not moose, but water.

52
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(Laughter)

53
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Although moose would be pretty cool.

54
00:02:13,103 --> 00:02:14,261
(Laughter)

55
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And not frozen water, and not water
in a gaseous state, but liquid water.

56
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This is what life needs
to survive, all life.

57
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And many solar system bodies
don't have liquid water,

58
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and so we don't look there.

59
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Other solar system bodies
might have abundant liquid water,

60
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even more than Earth,

61
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but it's trapped beneath an icy shell,

62
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and so it's hard to access,
it's hard to get to,

63
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it's hard to even find out
if there's any life there.

64
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So that leaves a few bodies
that we should think about.

65
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So let's make the problem
simpler for ourselves.

66
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Let's think only about liquid water
on the surface of a planet.

67
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There are only three bodies
to think about in our solar system,

68
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with regard to liquid water
on the surface of a planet,

69
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and in order of distance from the sun,
it's: Venus, Earth and Mars.

70
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You want to have an atmosphere
for water to be liquid.

71
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You have to be very careful
with that atmosphere.

72
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You can't have too much atmosphere,
too thick or too warm an atmosphere,

73
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because then you end up
too hot like Venus,

74
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and you can't have liquid water.

75
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But if you have too little atmosphere
and it's too thin and too cold,

76
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you end up like Mars, too cold.

77
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So Venus is too hot, Mars is too cold,

78
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and Earth is just right.

79
00:03:25,552 --> 00:03:29,027
You can look at these images behind me
and you can see automatically

80
00:03:29,051 --> 00:03:31,648
where life can survive
in our solar system.

81
00:03:32,296 --> 00:03:33,896
It's a Goldilocks-type problem,

82
00:03:33,920 --> 00:03:36,410
and it's so simple
that a child could understand it.

83
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However,

84
00:03:39,450 --> 00:03:42,378
I'd like to remind you of two things

85
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from the Goldilocks story
that we may not think about so often

86
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but that I think are really relevant here.

87
00:03:48,056 --> 00:03:49,206
Number one:

88
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if Mama Bear's bowl is too cold

89
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when Goldilocks walks into the room,

90
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does that mean it's always been too cold?

91
00:03:59,825 --> 00:04:03,093
Or could it have been just right
at some other time?

92
00:04:03,650 --> 00:04:07,331
When Goldilocks walks into the room
determines the answer

93
00:04:07,355 --> 00:04:08,687
that we get in the story.

94
00:04:09,114 --> 00:04:10,844
And the same is true with planets.

95
00:04:10,868 --> 00:04:12,894
They're not static things. They change.

96
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They vary. They evolve.

97
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And atmospheres do the same.

98
00:04:16,750 --> 00:04:18,452
So let me give you an example.

99
00:04:18,476 --> 00:04:20,478
Here's one of my favorite
pictures of Mars.

100
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It's not the highest resolution image,
it's not the sexiest image,

101
00:04:23,658 --> 00:04:25,161
it's not the most recent image,

102
00:04:25,185 --> 00:04:28,679
but it's an image that shows riverbeds
cut into the surface of the planet;

103
00:04:29,320 --> 00:04:31,904
riverbeds carved by flowing, liquid water;

104
00:04:33,515 --> 00:04:38,401
riverbeds that take hundreds or thousands
or tens of thousands of years to form.

105
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This can't happen on Mars today.

106
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The atmosphere of Mars today
is too thin and too cold

107
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for water to be stable as a liquid.

108
00:04:44,737 --> 00:04:49,085
This one image tells you
that the atmosphere of Mars changed,

109
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and it changed in big ways.

110
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And it changed from a state
that we would define as habitable,

111
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because the three requirements
for life were present long ago.

112
00:05:01,049 --> 00:05:03,117
Where did that atmosphere go

113
00:05:03,141 --> 00:05:05,961
that allowed water
to be liquid at the surface?

114
00:05:05,985 --> 00:05:09,332
Well, one idea is it escaped
away to space.

115
00:05:09,356 --> 00:05:12,023
Atmospheric particles
got enough energy to break free

116
00:05:12,047 --> 00:05:13,700
from the gravity of the planet,

117
00:05:13,724 --> 00:05:16,413
escaping away to space, never to return.

118
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And this happens with all bodies
with atmospheres.

119
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Comets have tails

120
00:05:20,345 --> 00:05:23,602
that are incredibly visible reminders
of atmospheric escape.

121
00:05:23,626 --> 00:05:27,035
But Venus also has an atmosphere
that escapes with time,

122
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and Mars and Earth as well.

123
00:05:28,743 --> 00:05:31,711
It's just a matter of degree
and a matter of scale.

124
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So we'd like to figure out
how much escaped over time

125
00:05:34,792 --> 00:05:36,908
so we can explain this transition.

126
00:05:36,932 --> 00:05:39,543
How do atmospheres
get their energy for escape?

127
00:05:39,567 --> 00:05:41,698
How do particles get
enough energy to escape?

128
00:05:41,722 --> 00:05:44,907
There are two ways, if we're going
to reduce things a little bit.

129
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Number one, sunlight.

130
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Light emitted from the sun can be absorbed
by atmospheric particles

131
00:05:49,542 --> 00:05:51,256
and warm the particles.

132
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Yes, I'm dancing, but they --

133
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(Laughter)

134
00:05:55,693 --> 00:05:57,605
Oh my God, not even at my wedding.

135
00:05:57,629 --> 00:05:59,121
(Laughter)

136
00:05:59,145 --> 00:06:02,148
They get enough energy
to escape and break free

137
00:06:02,172 --> 00:06:04,672
from the gravity of the planet
just by warming.

138
00:06:04,696 --> 00:06:07,858
A second way they can get energy
is from the solar wind.

139
00:06:07,882 --> 00:06:12,908
These are particles, mass, material,
spit out from the surface of the sun,

140
00:06:12,932 --> 00:06:15,336
and they go screaming
through the solar system

141
00:06:15,360 --> 00:06:17,145
at 400 kilometers per second,

142
00:06:17,169 --> 00:06:19,763
sometimes faster during solar storms,

143
00:06:19,787 --> 00:06:22,509
and they go hurtling
through interplanetary space

144
00:06:22,533 --> 00:06:24,979
towards planets and their atmospheres,

145
00:06:25,003 --> 00:06:26,628
and they may provide energy

146
00:06:26,652 --> 00:06:28,780
for atmospheric particles
to escape as well.

147
00:06:29,182 --> 00:06:31,151
This is something that I'm interested in,

148
00:06:31,175 --> 00:06:32,888
because it relates to habitability.

149
00:06:33,378 --> 00:06:36,510
I mentioned that there were two things
about the Goldilocks story

150
00:06:36,534 --> 00:06:39,518
that I wanted to bring to your attention
and remind you about,

151
00:06:39,542 --> 00:06:41,781
and the second one
is a little bit more subtle.

152
00:06:41,805 --> 00:06:44,593
If Papa Bear's bowl is too hot,

153
00:06:46,180 --> 00:06:49,414
and Mama Bear's bowl is too cold,

154
00:06:51,057 --> 00:06:54,168
shouldn't Baby Bear's bowl be even colder

155
00:06:55,081 --> 00:06:56,877
if we're following the trend?

156
00:06:58,195 --> 00:07:00,507
This thing that you've accepted
your entire life,

157
00:07:00,531 --> 00:07:03,601
when you think about it a little bit more,
may not be so simple.

158
00:07:04,513 --> 00:07:08,541
And of course, distance of a planet
from the sun determines its temperature.

159
00:07:08,565 --> 00:07:10,831
This has to play into habitability.

160
00:07:10,855 --> 00:07:13,785
But maybe there are other things
we should be thinking about.

161
00:07:13,809 --> 00:07:15,425
Maybe it's the bowls themselves

162
00:07:15,449 --> 00:07:18,505
that are also helping to determine
the outcome in the story,

163
00:07:18,529 --> 00:07:19,829
what is just right.

164
00:07:20,765 --> 00:07:23,630
I could talk to you about a lot
of different characteristics

165
00:07:23,654 --> 00:07:24,805
of these three planets

166
00:07:24,829 --> 00:07:26,398
that may influence habitability,

167
00:07:26,422 --> 00:07:29,016
but for selfish reasons related
to my own research

168
00:07:29,040 --> 00:07:32,628
and the fact that I'm standing up here
holding the clicker and you're not --

169
00:07:32,652 --> 00:07:33,658
(Laughter)

170
00:07:33,682 --> 00:07:35,791
I would like to talk
for just a minute or two

171
00:07:35,815 --> 00:07:37,112
about magnetic fields.

172
00:07:37,715 --> 00:07:40,247
Earth has one; Venus and Mars do not.

173
00:07:40,825 --> 00:07:43,948
Magnetic fields are generated
in the deep interior of a planet

174
00:07:43,972 --> 00:07:47,689
by electrically conducting
churning fluid material

175
00:07:47,713 --> 00:07:50,618
that creates this big old magnetic field
that surrounds Earth.

176
00:07:50,642 --> 00:07:53,038
If you have a compass,
you know which way north is.

177
00:07:53,062 --> 00:07:54,556
Venus and Mars don't have that.

178
00:07:54,580 --> 00:07:56,494
If you have a compass on Venus and Mars,

179
00:07:56,518 --> 00:07:57,914
congratulations, you're lost.

180
00:07:57,938 --> 00:07:59,841
(Laughter)

181
00:07:59,865 --> 00:08:01,905
Does this influence habitability?

182
00:08:03,175 --> 00:08:04,477
Well, how might it?

183
00:08:05,024 --> 00:08:07,628
Many scientists think
that a magnetic field of a planet

184
00:08:07,652 --> 00:08:10,047
serves as a shield for the atmosphere,

185
00:08:10,071 --> 00:08:13,426
deflecting solar wind particles
around the planet

186
00:08:13,450 --> 00:08:15,265
in a bit of a force field-type effect

187
00:08:15,289 --> 00:08:17,989
having to do with electric charge
of those particles.

188
00:08:18,362 --> 00:08:21,989
I like to think of it instead
as a salad bar sneeze guard for planets.

189
00:08:22,013 --> 00:08:24,292
(Laughter)

190
00:08:24,962 --> 00:08:28,343
And yes, my colleagues
who watch this later will realize

191
00:08:28,367 --> 00:08:30,911
this is the first time in the history
of our community

192
00:08:30,935 --> 00:08:33,214
that the solar wind has been
equated with mucus.

193
00:08:33,238 --> 00:08:34,888
(Laughter)

194
00:08:36,977 --> 00:08:40,453
OK, so the effect, then, is that Earth
may have been protected

195
00:08:40,477 --> 00:08:41,645
for billions of years,

196
00:08:41,669 --> 00:08:43,520
because we've had a magnetic field.

197
00:08:43,544 --> 00:08:45,723
Atmosphere hasn't been able to escape.

198
00:08:45,747 --> 00:08:47,854
Mars, on the other hand,
has been unprotected

199
00:08:47,878 --> 00:08:49,720
because of its lack of magnetic field,

200
00:08:49,744 --> 00:08:51,696
and over billions of years,

201
00:08:51,720 --> 00:08:53,900
maybe enough atmosphere
has been stripped away

202
00:08:53,924 --> 00:08:56,517
to account for a transition
from a habitable planet

203
00:08:56,541 --> 00:08:58,207
to the planet that we see today.

204
00:08:59,059 --> 00:09:02,048
Other scientists think
that magnetic fields

205
00:09:02,072 --> 00:09:04,235
may act more like the sails on a ship,

206
00:09:04,958 --> 00:09:09,995
enabling the planet to interact
with more energy from the solar wind

207
00:09:10,019 --> 00:09:13,291
than the planet would have been able
to interact with by itself.

208
00:09:13,315 --> 00:09:15,806
The sails may gather energy
from the solar wind.

209
00:09:15,830 --> 00:09:18,496
The magnetic field may gather
energy from the solar wind

210
00:09:18,520 --> 00:09:21,764
that allows even more
atmospheric escape to happen.

211
00:09:21,788 --> 00:09:24,042
It's an idea that has to be tested,

212
00:09:24,066 --> 00:09:25,951
but the effect and how it works

213
00:09:25,975 --> 00:09:27,126
seems apparent.

214
00:09:27,150 --> 00:09:28,301
That's because we know

215
00:09:28,325 --> 00:09:31,400
energy from the solar wind
is being deposited into our atmosphere

216
00:09:31,424 --> 00:09:32,575
here on Earth.

217
00:09:32,599 --> 00:09:35,004
That energy is conducted
along magnetic field lines

218
00:09:35,028 --> 00:09:36,376
down into the polar regions,

219
00:09:36,400 --> 00:09:38,536
resulting in incredibly beautiful aurora.

220
00:09:38,560 --> 00:09:41,216
If you've ever experienced them,
it's magnificent.

221
00:09:41,240 --> 00:09:43,246
We know the energy is getting in.

222
00:09:43,270 --> 00:09:46,303
We're trying to measure
how many particles are getting out

223
00:09:46,327 --> 00:09:49,365
and if the magnetic field
is influencing this in any way.

224
00:09:50,722 --> 00:09:53,102
So I've posed a problem for you here,

225
00:09:53,126 --> 00:09:54,672
but I don't have a solution yet.

226
00:09:54,696 --> 00:09:55,972
We don't have a solution.

227
00:09:56,702 --> 00:09:59,059
But we're working on it.
How are we working on it?

228
00:09:59,083 --> 00:10:01,381
Well, we've sent spacecraft
to all three planets.

229
00:10:01,405 --> 00:10:02,881
Some of them are orbiting now,

230
00:10:02,905 --> 00:10:05,977
including the MAVEN spacecraft
which is currently orbiting Mars,

231
00:10:06,001 --> 00:10:09,533
which I'm involved with
and which is led here,

232
00:10:09,557 --> 00:10:11,366
out of the University of Colorado.

233
00:10:11,390 --> 00:10:13,672
It's designed to measure
atmospheric escape.

234
00:10:14,022 --> 00:10:16,496
We have similar measurements
from Venus and Earth.

235
00:10:16,953 --> 00:10:18,618
Once we have all our measurements,

236
00:10:18,642 --> 00:10:21,517
we can combine all these together,
and we can understand

237
00:10:21,541 --> 00:10:24,958
how all three planets interact
with their space environment,

238
00:10:24,982 --> 00:10:26,144
with the surroundings.

239
00:10:26,168 --> 00:10:29,690
And we can decide whether magnetic fields
are important for habitability

240
00:10:29,714 --> 00:10:30,872
or not.

241
00:10:30,896 --> 00:10:33,161
Once we have that answer,
why should you care?

242
00:10:33,185 --> 00:10:34,485
I mean, I care deeply ...

243
00:10:36,128 --> 00:10:38,134
And financially as well, but deeply.

244
00:10:38,158 --> 00:10:40,000
(Laughter)

245
00:10:40,763 --> 00:10:42,681
First of all, an answer to this question

246
00:10:42,705 --> 00:10:44,808
will teach us more
about these three planets,

247
00:10:44,832 --> 00:10:45,992
Venus, Earth and Mars,

248
00:10:46,016 --> 00:10:48,927
not only about how they interact
with their environment today,

249
00:10:48,951 --> 00:10:50,878
but how they were billions of years ago,

250
00:10:50,902 --> 00:10:52,964
whether they were habitable
long ago or not.

251
00:10:52,988 --> 00:10:54,632
It will teach us about atmospheres

252
00:10:54,656 --> 00:10:56,651
that surround us and that are close.

253
00:10:57,127 --> 00:10:59,311
But moreover, what we learn
from these planets

254
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can be applied to atmospheres everywhere,

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including planets that we're now
observing around other stars.

256
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For example, the Kepler spacecraft,

257
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which is built and controlled
here in Boulder,

258
00:11:10,433 --> 00:11:13,718
has been observing
a postage stamp-sized region of the sky

259
00:11:13,742 --> 00:11:14,989
for a couple years now,

260
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and it's found thousands of planets --

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in one postage stamp-sized
region of the sky

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that we don't think is any different
from any other part of the sky.

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We've gone, in 20 years,

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from knowing of zero planets
outside of our solar system,

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to now having so many,

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that we don't know
which ones to investigate first.

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Any lever will help.

268
00:11:40,539 --> 00:11:44,123
In fact, based on observations
that Kepler's taken

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00:11:44,147 --> 00:11:46,276
and other similar observations,

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00:11:46,300 --> 00:11:47,469
we now believe that,

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of the 200 billion stars
in the Milky Way galaxy alone,

272
00:11:52,786 --> 00:11:57,390
on average, every star
has at least one planet.

273
00:11:58,819 --> 00:12:00,322
In addition to that,

274
00:12:00,346 --> 00:12:06,047
estimates suggest there are somewhere
between 40 billion and 100 billion

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of those planets
that we would define as habitable

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in just our galaxy.

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We have the observations of those planets,

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but we just don't know
which ones are habitable yet.

279
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It's a little bit like
being trapped on a red spot --

280
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(Laughter)

281
00:12:23,984 --> 00:12:25,216
on a stage

282
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and knowing that there are
other worlds out there

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00:12:31,042 --> 00:12:33,818
and desperately wanting to know
more about them,

284
00:12:35,174 --> 00:12:39,108
wanting to interrogate them and find out
if maybe just one or two of them

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are a little bit like you.

286
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You can't do that.
You can't go there, not yet.

287
00:12:44,827 --> 00:12:48,820
And so you have to use the tools
that you've developed around you

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for Venus, Earth and Mars,

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00:12:50,163 --> 00:12:52,976
and you have to apply them
to these other situations,

290
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and hope that you're making
reasonable inferences from the data,

291
00:12:57,720 --> 00:13:00,838
and that you're going to be able
to determine the best candidates

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00:13:00,862 --> 00:13:03,261
for habitable planets,
and those that are not.

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00:13:04,139 --> 00:13:06,854
In the end, and for now, at least,

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this is our red spot, right here.

295
00:13:10,376 --> 00:13:13,712
This is the only planet
that we know of that's habitable,

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although very soon we may
come to know of more.

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But for now, this is
the only habitable planet,

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and this is our red spot.

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I'm really glad we're here.

300
00:13:24,507 --> 00:13:25,682
Thanks.

301
00:13:25,706 --> 00:13:28,937
(Applause)