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ln the beginning,
there was darkness...
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00:00:03,670 --> 00:00:05,754
and then, bang...
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00:00:05,797 --> 00:00:08,924
giving birth to an endless
expanding existence...
4
00:00:08,967 --> 00:00:11,510
of time, space, and matter.
5
00:00:11,552 --> 00:00:14,263
Now, see further
than we've ever imagined...
6
00:00:14,305 --> 00:00:16,265
beyond the limits
of our existence...
7
00:00:16,307 --> 00:00:19,309
in a place we call
"The Universe."
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00:00:23,314 --> 00:00:25,607
Lurking in the shadows
of the solar system...
9
00:00:25,650 --> 00:00:28,568
are worlds so chemically
active and misshapen...
10
00:00:28,611 --> 00:00:31,530
that they border
on the bizarre.
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00:00:31,572 --> 00:00:32,781
That l think
the most shocking thing...
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00:00:32,824 --> 00:00:37,911
was howvery different
the solar system is.
13
00:00:37,954 --> 00:00:39,079
These are the moons...
14
00:00:39,122 --> 00:00:41,623
surrounding the planets
ofthe solar system...
15
00:00:41,666 --> 00:00:43,709
moons that were once
either unknown...
16
00:00:43,751 --> 00:00:45,419
or considered afterthoughts...
17
00:00:45,461 --> 00:00:49,047
are now on the cutting edge
of astronomical exploration.
18
00:00:49,090 --> 00:00:50,132
What was surprising...
19
00:00:50,174 --> 00:00:53,135
that they all didn't look
like our moon.
20
00:00:53,177 --> 00:00:55,804
The so-called minor members
of the solar systems...
21
00:00:55,847 --> 00:00:58,181
are not of minor interest.
22
00:00:58,224 --> 00:01:02,561
What surprises await us
on these alien moons?
23
00:01:17,910 --> 00:01:20,912
Our solar system has always
been fertile ground...
24
00:01:20,955 --> 00:01:23,332
for science fiction writers...
25
00:01:23,374 --> 00:01:27,169
but with exponential advances
in telescopic technology...
26
00:01:27,211 --> 00:01:31,006
and close encounters
by unmanned probes...
27
00:01:31,049 --> 00:01:36,219
the curtain has now been lifted
on a new ballet of moons.
28
00:01:36,262 --> 00:01:37,679
Most ofwhich are
going one way around...
29
00:01:37,722 --> 00:01:40,098
some ofwhich are going
the otherway around...
30
00:01:40,141 --> 00:01:42,309
all at different rates,
passing one another...
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00:01:42,352 --> 00:01:45,937
the inner ones
passing the outer ones.
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00:01:45,980 --> 00:01:47,522
For nearly half a century...
33
00:01:47,565 --> 00:01:52,235
it was believed the solar system
was home to only 32 moons.
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00:01:52,278 --> 00:01:54,529
They ranged in size
from Jupiter's moon...
35
00:01:54,572 --> 00:01:58,200
Ganymede, larger
than the planet Mercury...
36
00:01:58,242 --> 00:02:00,369
to small
asteroid-shaped ones...
37
00:02:00,411 --> 00:02:05,457
like the Martian moons
Phobos and Deimos.
38
00:02:05,500 --> 00:02:07,626
That number has exploded.
39
00:02:07,668 --> 00:02:10,712
ln 2007 alone,
scientists announced...
40
00:02:10,755 --> 00:02:14,424
the discovery of 20 new moons
around Jupiter...
41
00:02:14,467 --> 00:02:15,967
one around Saturn...
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00:02:16,010 --> 00:02:18,261
and three around Neptune.
43
00:02:18,304 --> 00:02:22,432
What happened is
astronomical telescopes...
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00:02:22,475 --> 00:02:26,853
had available to them
what are called CCD cameras.
45
00:02:26,896 --> 00:02:28,397
These are digital cameras...
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00:02:28,439 --> 00:02:32,109
that almost everybody
has nowadays.
47
00:02:32,151 --> 00:02:34,361
lt's difficult
to hold astronomers...
48
00:02:34,404 --> 00:02:38,907
to an exact number of moons
in the solar system.
49
00:02:38,950 --> 00:02:43,662
As cameras become more sensitive
and telescopes more powerful...
50
00:02:43,704 --> 00:02:50,168
more moons reveal themselves.
51
00:02:50,211 --> 00:02:54,005
Moons are classified
in two distinct ways.
52
00:02:54,048 --> 00:02:58,051
Those like our moon travel
in nearly circular orbits...
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00:02:58,094 --> 00:03:05,100
above their planet's equators
and are called regular moons.
54
00:03:05,143 --> 00:03:07,060
While our moon formed
from an impact...
55
00:03:07,103 --> 00:03:09,896
all other regular moons
coalesced...
56
00:03:09,939 --> 00:03:11,398
from the gaseous stew...
57
00:03:11,441 --> 00:03:13,775
surrounding
their parent planets...
58
00:03:13,818 --> 00:03:17,571
a process known as accretion.
59
00:03:17,613 --> 00:03:20,323
The classic example
of regular moons...
60
00:03:20,366 --> 00:03:23,326
would be the Galilean moons
of Jupiter...
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00:03:23,369 --> 00:03:24,453
lo, Europa...
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00:03:24,495 --> 00:03:27,164
Ganymede, and Callisto.
63
00:03:27,206 --> 00:03:29,166
The material that is going
to form Jupiter, too...
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00:03:29,500 --> 00:03:30,792
but extended a little bit...
65
00:03:30,835 --> 00:03:34,296
that material
accumulates into the moons.
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00:03:34,338 --> 00:03:36,798
Moons that follow
elongated orbits...
67
00:03:36,841 --> 00:03:39,217
highly tilted
to their planet's equators...
68
00:03:39,260 --> 00:03:41,803
are called irregular moons.
69
00:03:41,846 --> 00:03:44,139
Most of these move
in retrograde orbits...
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00:03:44,182 --> 00:03:48,727
clockwise iftheir planet
rotates counterclockwise.
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00:03:48,769 --> 00:03:51,938
Phoebe, the newly discovered
moon orbiting Saturn...
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00:03:51,981 --> 00:03:54,649
is a perfect example.
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00:03:54,692 --> 00:03:56,526
She began
her celestial life...
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00:03:56,569 --> 00:03:59,613
as an independent traveler
orbiting the sun...
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00:03:59,655 --> 00:04:05,452
before being captured
by the more massive Saturn.
76
00:04:05,495 --> 00:04:07,204
Whether regular
or irregular...
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00:04:07,246 --> 00:04:09,664
moons must fall within
the gravitational reach...
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00:04:09,707 --> 00:04:11,291
of their parent planet.
79
00:04:11,334 --> 00:04:16,213
The limit ofthese orbits
is known as the Hill sphere.
80
00:04:16,255 --> 00:04:19,716
This phenomenon is named after
George William Hill...
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00:04:19,759 --> 00:04:24,513
an American astronomer
from the mid-1800s.
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00:04:24,555 --> 00:04:27,974
So a Hill sphere is this region
around the planet...
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00:04:28,017 --> 00:04:29,851
that moves along
with the planet...
84
00:04:29,894 --> 00:04:32,479
inside ofwhich
the gravity of the planet...
85
00:04:32,522 --> 00:04:37,651
overwhelms the gravity
ofthe sun.
86
00:04:37,693 --> 00:04:39,986
The moons of Mars,
Deimos and Phobos...
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00:04:40,029 --> 00:04:43,990
operate very differently
within the Hill sphere.
88
00:04:44,033 --> 00:04:48,453
lfthe planet
is rotating faster...
89
00:04:48,496 --> 00:04:52,082
than the moon it orbits,
like Deimos...
90
00:04:52,124 --> 00:04:54,417
the tidal forces
between the two...
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00:04:54,460 --> 00:04:59,881
actually shove Deimos out
further and further.
92
00:04:59,924 --> 00:05:01,341
Phobos, on the other hand...
93
00:05:01,384 --> 00:05:06,972
is rotating faster
than Mars rotates.
94
00:05:07,014 --> 00:05:08,515
These small moons
were discovered...
95
00:05:08,558 --> 00:05:13,562
byAmerican astronomer
Asaph Hall in 1877.
96
00:05:13,604 --> 00:05:16,731
He named Phobos
after the Greek god offear...
97
00:05:16,774 --> 00:05:21,695
and Deimos
for the god of terror.
98
00:05:21,737 --> 00:05:25,365
Tom Duxburywas part
of the Mariner 9 mission...
99
00:05:25,408 --> 00:05:28,743
that first photographed
the two potato-shaped moons...
100
00:05:28,786 --> 00:05:33,081
in November of1971.
101
00:05:33,124 --> 00:05:34,749
This was late at night...
102
00:05:34,792 --> 00:05:37,210
on a cold, rainy, dark,
dreary day...
103
00:05:37,253 --> 00:05:38,253
and l looked at this...
104
00:05:38,296 --> 00:05:41,464
and l turned the picture
sideways.
105
00:05:41,507 --> 00:05:53,226
lt looked like a skull,
and it was such an eerie thing.
106
00:05:53,269 --> 00:05:55,687
Phobos is in a death spiral.
107
00:05:55,730 --> 00:06:00,150
lt orbitsjust 3,700 miles
from the Martian surface...
108
00:06:00,192 --> 00:06:01,484
closer to its host planet...
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00:06:01,527 --> 00:06:04,362
than any moon
in our solar system.
110
00:06:04,405 --> 00:06:06,448
lf our own moon
were as close to the Earth...
111
00:06:06,490 --> 00:06:11,953
as Phobos is to Mars,
it would look 20 times larger.
112
00:06:11,996 --> 00:06:14,289
lts orbital period
would be in hours...
113
00:06:14,332 --> 00:06:16,916
not days like it is now,
but hours.
114
00:06:16,959 --> 00:06:22,047
And at full moon,
it would fill the sky.
115
00:06:22,089 --> 00:06:24,466
The daily tides, you know,
would rise and fall...
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00:06:24,508 --> 00:06:26,259
tens offeet
if not hundreds offeet...
117
00:06:26,302 --> 00:06:27,427
and so the Earth's moon...
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00:06:27,470 --> 00:06:30,513
would eventually crash
into the Earth...
119
00:06:30,556 --> 00:06:36,061
in such a situation.
120
00:06:36,103 --> 00:06:38,813
Phobos' predicament
is caused by a process...
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00:06:38,856 --> 00:06:41,816
known as secular acceleration.
122
00:06:41,859 --> 00:06:45,153
As Phobos races faster
than Mars rotates...
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00:06:45,196 --> 00:06:48,907
a tidal bump is raised
on the Martian surface.
124
00:06:49,158 --> 00:06:53,078
ln the process, Mars yanks
Phobos closer to its surface...
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00:06:53,120 --> 00:06:57,624
with each orbit.
126
00:06:57,667 --> 00:06:59,668
The struggle between
Mars and Phobos...
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00:06:59,710 --> 00:07:04,631
is similar to the dynamics
of a simple game of tetherball.
128
00:07:04,674 --> 00:07:09,177
lmagine the ball as the moon,
the pole as the planet...
129
00:07:09,220 --> 00:07:11,596
and the rope between
the pole and the ball...
130
00:07:11,639 --> 00:07:17,852
as the planet's
gravitational pull.
131
00:07:17,895 --> 00:07:21,523
What we see
is that the gravity...
132
00:07:21,565 --> 00:07:24,693
would pull the moon
in such a way...
133
00:07:24,735 --> 00:07:25,944
that it speeds up.
134
00:07:25,986 --> 00:07:28,530
lt goes faster and faster,
and it works its way...
135
00:07:28,572 --> 00:07:31,700
until it eventually
hits the pole.
136
00:07:31,742 --> 00:07:34,703
That's exactlywhat's
happening to Phobos.
137
00:07:34,745 --> 00:07:38,998
Phobos is going around Mars
faster than Mars rotates.
138
00:07:39,041 --> 00:07:40,333
That tidal interaction...
139
00:07:40,376 --> 00:07:43,294
is pulling Phobos in
closer and closer...
140
00:07:43,337 --> 00:07:45,714
and speeding it up
in its orbit.
141
00:07:45,756 --> 00:07:47,215
ln about 50 million years...
142
00:07:47,258 --> 00:07:49,926
we expect Phobos
to be pulled in so closely...
143
00:07:49,969 --> 00:07:56,808
it will impact Mars and
disappear as a moon of Mars.
144
00:07:56,851 --> 00:08:00,145
On the other hand, Deimos,
the further-out moon...
145
00:08:00,187 --> 00:08:02,731
is going slower
than Mars rotates.
146
00:08:02,773 --> 00:08:06,901
And so it's unwinding the string
in the opposite way...
147
00:08:06,944 --> 00:08:08,570
and what we see is Deimos...
148
00:08:08,612 --> 00:08:12,824
is going further
and further away from Mars.
149
00:08:12,867 --> 00:08:13,992
And eventually...
150
00:08:14,034 --> 00:08:16,953
Deimos will be pulled
away from Mars...
151
00:08:16,996 --> 00:08:19,122
by the gravity of the sun.
152
00:08:19,165 --> 00:08:23,168
So, over time,
Mars will become moonless.
153
00:08:29,008 --> 00:08:32,427
Because Phobos outpaces
the rotation of Mars...
154
00:08:32,470 --> 00:08:37,724
it appears to rise in the west
and set in the east.
155
00:08:37,767 --> 00:08:40,310
lnstead of the planet
turning quickly under it...
156
00:08:40,352 --> 00:08:42,479
like our moon
and most other moons...
157
00:08:42,521 --> 00:08:45,899
and thus having it
rise in the east...
158
00:08:45,941 --> 00:08:46,941
and set in the west...
159
00:08:46,984 --> 00:08:49,778
it races ahead of the rotation
of the planet.
160
00:08:49,820 --> 00:08:52,572
And so it comes up
on the western horizon...
161
00:08:52,615 --> 00:09:00,246
and races ahead and sets
on the eastern horizon.
162
00:09:00,289 --> 00:09:02,540
lt will be another
50 millions years...
163
00:09:02,583 --> 00:09:06,586
before Phobos
completely disappears.
164
00:09:06,629 --> 00:09:09,172
Before then,
it may prove useful...
165
00:09:09,215 --> 00:09:12,550
for the eventual
colonization of Mars.
166
00:09:12,593 --> 00:09:14,969
Science fiction writer
Arthur C. Clarke...
167
00:09:15,012 --> 00:09:16,471
speculated on this idea...
168
00:09:16,514 --> 00:09:19,933
in his book
"The Sands of Mars."
169
00:09:19,975 --> 00:09:24,145
Although there is no real reason
to colonize Phobos itself...
170
00:09:24,188 --> 00:09:29,526
its close proximity to Mars
makes it a natural waystation.
171
00:09:29,568 --> 00:09:30,985
From a gravity standpoint...
172
00:09:31,028 --> 00:09:33,780
it's much easier
to go to Phobos...
173
00:09:33,823 --> 00:09:35,156
which has no gravity...
174
00:09:35,199 --> 00:09:37,575
than it is to fight
the gravity of Mars...
175
00:09:37,618 --> 00:09:41,079
to get down to this surface.
176
00:09:41,121 --> 00:09:43,331
From Galileo
to Stanley Kubrick...
177
00:09:43,374 --> 00:09:46,000
the giant planets
of the outer solar system...
178
00:09:46,043 --> 00:09:49,671
have tantalized our imagination
with their enormity.
179
00:09:49,713 --> 00:09:54,592
But in reality, exploring them
is tantamount to suicide.
180
00:09:54,635 --> 00:09:55,635
The overwhelming pressure...
181
00:09:55,678 --> 00:09:57,762
from Jupiter's
massive atmosphere...
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00:09:57,805 --> 00:10:02,350
would make it almost
impossible to function.
183
00:10:02,393 --> 00:10:04,269
But the moons
of these behemoths...
184
00:10:04,520 --> 00:10:06,354
may provide a more
promising platform...
185
00:10:06,397 --> 00:10:11,526
for exploration
and even future colonization.
186
00:10:11,569 --> 00:10:14,279
Are these prisoners
of Jupiter's gravity...
187
00:10:14,321 --> 00:10:16,489
hostile worlds
with little chance...
188
00:10:16,532 --> 00:10:19,033
of sustaining organic life?
189
00:10:19,076 --> 00:10:21,035
Or might they provide
a safe haven...
190
00:10:21,078 --> 00:10:29,252
for future generations
of planetary explorers?
191
00:10:29,295 --> 00:10:31,796
Until recently,
very little was known...
192
00:10:31,839 --> 00:10:34,883
about the moons of the gas
and ice giants.
193
00:10:34,925 --> 00:10:37,260
Most of them remained
hidden in the glare...
194
00:10:37,303 --> 00:10:40,430
of their parent planets.
195
00:10:40,472 --> 00:10:44,225
Today, modern telescopes and
unmanned space exploration...
196
00:10:44,268 --> 00:10:48,146
reveal a realm populated
by a host of moons...
197
00:10:48,188 --> 00:10:50,315
from planet-like
spherical worlds...
198
00:10:50,357 --> 00:10:56,696
to misshapen ones
barely 30 miles across.
199
00:10:56,739 --> 00:10:59,365
Jupiter, the largest planet
in the solar system...
200
00:10:59,408 --> 00:11:01,492
is a moon magnet.
201
00:11:01,535 --> 00:11:03,912
Nearly 4.5 billion years ago...
202
00:11:03,954 --> 00:11:09,417
it began as a massive gas cloud
collapsing in on itself.
203
00:11:09,460 --> 00:11:11,461
This process,
known as accretion...
204
00:11:11,503 --> 00:11:14,505
formed the beginnings
of the Jovian system.
205
00:11:14,548 --> 00:11:17,008
While nearly all the gas
and spinning material...
206
00:11:17,051 --> 00:11:19,344
went into forming
Jupiter itself...
207
00:11:19,386 --> 00:11:22,513
a very small percentage
clumped in small eddies...
208
00:11:22,556 --> 00:11:24,349
within Jupiter's orbit.
209
00:11:24,391 --> 00:11:25,642
These miniature accretions...
210
00:11:25,684 --> 00:11:27,101
solidified into Jupiter's
regular moons...
211
00:11:27,144 --> 00:11:32,941
lo, Europa, Ganymede,
and Callisto.
212
00:11:32,983 --> 00:11:35,401
As Jupiter coalesced,
its massive gravity...
213
00:11:35,444 --> 00:11:39,614
began adding to its menagerie
little remaining bits...
214
00:11:39,657 --> 00:11:43,493
from the birth
of the early solar system.
215
00:11:43,535 --> 00:11:48,706
The giant planets formed early
in a gas-rich environment...
216
00:11:48,749 --> 00:11:51,417
when there was lots
of little flotsam and jetsam...
217
00:11:51,460 --> 00:11:56,381
around the solar system still
to be captured into orbit.
218
00:11:56,423 --> 00:12:01,344
The number of Jupiter's moons
ranges from 60 to over 200...
219
00:12:01,387 --> 00:12:06,224
depending on who's counting.
220
00:12:06,266 --> 00:12:07,517
What's clear is...
221
00:12:07,559 --> 00:12:08,977
ifyou could stand
at the edge...
222
00:12:09,019 --> 00:12:11,145
of Jupiter's
gaseous atmosphere...
223
00:12:11,188 --> 00:12:12,689
and look to the heavens...
224
00:12:12,731 --> 00:12:17,193
you'd see a magnificent dance
of lunar objects.
225
00:12:17,236 --> 00:12:20,029
lt would look pretty cool
to be able to see the moons.
226
00:12:20,072 --> 00:12:22,490
Every so often,
you'd see lo come by.
227
00:12:22,533 --> 00:12:24,826
Every second time
lo comes by...
228
00:12:24,868 --> 00:12:27,954
you'd see Europa
at the same time.
229
00:12:27,997 --> 00:12:29,747
And every four times
lo comes by...
230
00:12:29,790 --> 00:12:31,791
you'd see Ganymede.
231
00:12:31,834 --> 00:12:33,543
One member
of this Jovian cast...
232
00:12:33,585 --> 00:12:36,379
is so battered
by Jupiter's great mass...
233
00:12:36,422 --> 00:12:41,801
that it is literally bursting
from the inside out.
234
00:12:41,844 --> 00:12:45,847
ln February of 2007,
the New Horizons spacecraft...
235
00:12:45,889 --> 00:12:47,890
eventually bound for Pluto...
236
00:12:47,933 --> 00:12:51,019
focused its cameras on lo.
237
00:12:51,061 --> 00:12:52,687
About the size of
Earth's moon...
238
00:12:52,730 --> 00:12:58,192
it orbits 263,000 miles
from Jupiter's surface.
239
00:12:58,235 --> 00:13:02,447
What sets lo apart
from the other Jovian moons...
240
00:13:02,489 --> 00:13:05,950
is its spectacularvolcanism.
241
00:13:05,993 --> 00:13:07,452
New Horizons' cameras...
242
00:13:07,494 --> 00:13:10,329
captured detailed photos
of glowing lava...
243
00:13:10,372 --> 00:13:13,750
scattered across lo's surface.
244
00:13:14,126 --> 00:13:18,463
A huge 200-mile-high dust plume
rose above the surface...
245
00:13:18,505 --> 00:13:22,800
of the molten moon.
246
00:13:22,843 --> 00:13:25,511
lo, like all Jupiter's
regular moons...
247
00:13:25,554 --> 00:13:28,139
is named after a lover
ofthe god Jupiter...
248
00:13:28,182 --> 00:13:30,558
from Roman mythology.
249
00:13:30,601 --> 00:13:34,228
lt was discovered by Galileo
in 1610...
250
00:13:34,271 --> 00:13:38,232
first photographed
by Pioneer l in 1974...
251
00:13:38,275 --> 00:13:41,611
and again byVoyager l
in 1979.
252
00:13:41,653 --> 00:13:44,405
lts pulsating activity
has puzzled...
253
00:13:44,448 --> 00:13:48,076
and intrigued scientists
for decades.
254
00:13:48,118 --> 00:13:52,080
Leaving lo is about
a ton per second of material...
255
00:13:52,122 --> 00:13:53,623
every second of every day.
256
00:13:53,665 --> 00:13:56,667
lt's a phenomenal machine.
257
00:13:56,710 --> 00:13:57,794
l would like to go to lo...
258
00:13:57,836 --> 00:13:59,670
even though
it would be very dangerous...
259
00:13:59,713 --> 00:14:04,425
and hot and sulfurous.
260
00:14:04,468 --> 00:14:07,762
lo is too small to have
maintained a molten core...
261
00:14:07,805 --> 00:14:09,680
since its formation.
262
00:14:09,723 --> 00:14:11,432
Another mysterious process...
263
00:14:11,475 --> 00:14:14,894
must be responsible
for its heating.
264
00:14:14,937 --> 00:14:18,022
lo's entire interior
may be molten...
265
00:14:18,065 --> 00:14:21,818
because it's squeezed so much
as it's orbiting around Jupiter.
266
00:14:21,860 --> 00:14:25,238
This process is known
as tidal heating.
267
00:14:25,280 --> 00:14:26,989
The massive gravity
of Jupiter...
268
00:14:27,032 --> 00:14:33,037
is causing friction
at the inner core of lo.
269
00:14:33,080 --> 00:14:38,709
Much like a sculptor kneads
a cold lump of clay...
270
00:14:38,752 --> 00:14:46,467
Jupiter is endlessly creating
its own masterpiece.
271
00:14:46,510 --> 00:14:49,804
lf a moon gets a little bit
of tidal heating...
272
00:14:49,847 --> 00:14:51,806
it becomes malleable.
273
00:14:51,849 --> 00:14:54,308
lt can be stretched out
like clay...
274
00:14:54,351 --> 00:14:57,645
and deformed by the gravity
of the parent planet.
275
00:14:57,688 --> 00:14:59,522
The surface of the moon
is cold.
276
00:14:59,565 --> 00:15:03,317
lt breaks like pulling
clay apart quickly. lt'll break.
277
00:15:03,360 --> 00:15:05,319
But the interior,
where it's warm...
278
00:15:05,362 --> 00:15:08,114
can literally flow
and stretch...
279
00:15:08,157 --> 00:15:14,412
and be kneaded by the gravity
ofthe parent planet.
280
00:15:14,454 --> 00:15:18,166
Most regular moons
have circular orbits.
281
00:15:18,208 --> 00:15:19,792
To produce tidal heating...
282
00:15:19,835 --> 00:15:22,336
a moon must be
in a more oblong orbit...
283
00:15:22,379 --> 00:15:24,046
where the distance
from the host planet...
284
00:15:24,089 --> 00:15:28,134
changes radically
during a single revolution.
285
00:15:28,177 --> 00:15:30,845
The only way to produce
these eccentric orbits...
286
00:15:30,888 --> 00:15:34,765
is if another moon's gravity
disrupts it.
287
00:15:34,808 --> 00:15:37,560
When a moon
is in an eccentric orbit...
288
00:15:37,603 --> 00:15:39,020
a non-round orbit...
289
00:15:39,062 --> 00:15:43,357
it gets closer and farther
from its parent planet.
290
00:15:43,400 --> 00:15:45,026
When it does,
it gets squeezed.
291
00:15:45,068 --> 00:15:49,572
lt gets pulled apart
when it's closer.
292
00:15:49,615 --> 00:15:51,782
lo is in orbital resonance...
293
00:15:51,825 --> 00:15:55,453
with its companion moons
Europa and Ganymede.
294
00:15:55,495 --> 00:15:57,580
While Jupiter and lo
struggle to find...
295
00:15:57,623 --> 00:15:59,874
a synchronistic
relationship...
296
00:15:59,917 --> 00:16:01,250
Europa and Ganymede...
297
00:16:01,293 --> 00:16:04,378
are yanking lo
in opposite directions.
298
00:16:04,421 --> 00:16:05,880
Jupiteryanks back...
299
00:16:05,923 --> 00:16:10,593
and lo gets stretched
and squeezed in the process.
300
00:16:10,636 --> 00:16:12,261
The tidal heating on lo...
301
00:16:12,304 --> 00:16:15,389
which is responsible
for its prodigious volcanoes...
302
00:16:15,432 --> 00:16:17,892
has a secondary side effect.
303
00:16:18,185 --> 00:16:20,978
lt creates the largest
stationary visible object...
304
00:16:21,021 --> 00:16:22,897
in the solar system...
305
00:16:22,940 --> 00:16:30,738
a massive gas cloud
500 times the size of Jupiter.
306
00:16:30,781 --> 00:16:33,282
ln 1990,
Professor Michael Mendillo...
307
00:16:33,325 --> 00:16:35,618
and his team
from Boston University...
308
00:16:35,661 --> 00:16:39,413
discovered a large gas cloud
spanning the huge distance...
309
00:16:39,456 --> 00:16:42,875
from one side of Jupiter
to the other.
310
00:16:42,918 --> 00:16:44,919
They were the first
to photograph...
311
00:16:44,962 --> 00:16:47,838
the entire nebula,
discover its origins...
312
00:16:47,881 --> 00:16:51,259
and the mechanism
that keeps it growing.
313
00:16:51,301 --> 00:16:52,885
Now, lo is small...
314
00:16:52,928 --> 00:16:55,137
so it doesn't have
much of an atmosphere.
315
00:16:55,180 --> 00:16:56,180
But these volcanoes...
316
00:16:56,223 --> 00:16:59,433
are continually
providing material...
317
00:16:59,476 --> 00:17:00,810
that could be an atmosphere.
318
00:17:00,852 --> 00:17:02,103
But you might ask...
319
00:17:02,145 --> 00:17:04,438
"Well, why doesn't it have
tremendous atmosphere...
320
00:17:04,481 --> 00:17:07,441
if all the volcanoes
have been going on for eons?"
321
00:17:07,484 --> 00:17:10,778
Well, it's because
the material escapes.
322
00:17:10,821 --> 00:17:13,114
The key gas is sodium.
323
00:17:13,156 --> 00:17:15,491
Even though it only
makes up five percent...
324
00:17:15,534 --> 00:17:17,994
of lo's ejected materials...
325
00:17:18,036 --> 00:17:21,747
it is easily detectable
by telescopes on Earth.
326
00:17:21,790 --> 00:17:24,292
Sodium emits an orange glow.
327
00:17:24,334 --> 00:17:28,337
ln fact, sodium is commonly used
to illuminate streetlights...
328
00:17:28,380 --> 00:17:32,800
in many cities across the world.
329
00:17:32,843 --> 00:17:35,052
The sodium and the other
gas molecules...
330
00:17:35,095 --> 00:17:37,096
are pelted by light
from the sun...
331
00:17:37,139 --> 00:17:41,434
and electrons in Jupiter's
powerful magnetic field.
332
00:17:41,476 --> 00:17:43,811
Electrons and protons
are knocked off...
333
00:17:43,854 --> 00:17:47,064
some of these particles
and ionized.
334
00:17:47,107 --> 00:17:48,649
Now in plasma form...
335
00:17:48,692 --> 00:17:50,776
these ions
are taken on a ride...
336
00:17:50,819 --> 00:17:54,322
by Jupiter"s
powerful magnetosphere.
337
00:17:54,364 --> 00:17:56,824
lts speed increases
dramatically...
338
00:17:56,867 --> 00:18:03,331
because it's been picked up
by the magnetic field.
339
00:18:03,373 --> 00:18:08,210
lt's like they're taking
a ride on a cosmic carousel.
340
00:18:08,253 --> 00:18:11,839
The magnetic field lines
are the poles here.
341
00:18:11,882 --> 00:18:13,132
And then every now and then...
342
00:18:13,175 --> 00:18:16,927
a sodium atom gets picked up
along with this electron.
343
00:18:16,970 --> 00:18:20,139
And now, l'm in the Jupiter
plasma chorus...
344
00:18:20,182 --> 00:18:21,932
with all the other
ions and electrons...
345
00:18:21,975 --> 00:18:24,226
that have been captured
previously...
346
00:18:24,269 --> 00:18:26,645
and the ions
and the electrons recombine.
347
00:18:26,688 --> 00:18:30,024
The neutral is not confined
by the magnetic field...
348
00:18:30,067 --> 00:18:32,568
and it goes off
at a much higher speed...
349
00:18:32,611 --> 00:18:35,363
and that's enough
to escape from Jupiter.
350
00:18:35,405 --> 00:18:37,865
And they form the largest
visible cloud of gas...
351
00:18:37,908 --> 00:18:42,787
that's permanently
in the solar system.
352
00:18:42,829 --> 00:18:45,164
lfwe could see the nebula
with the naked eye...
353
00:18:45,207 --> 00:18:49,835
it would be the size of12 moons
in the night sky.
354
00:18:49,878 --> 00:18:51,879
lt is so enormous
that to view it...
355
00:18:51,922 --> 00:18:56,717
Mendillo and his team created
their own specialized telescope.
356
00:18:56,760 --> 00:18:59,470
Well, as it turns out,
to get a big field ofview...
357
00:18:59,513 --> 00:19:01,389
all you need is
a small lens...
358
00:19:01,431 --> 00:19:05,726
like a pair of binoculars
gives you a big field ofview.
359
00:19:05,769 --> 00:19:10,189
Even in 1991, the telescope
may have seemed ordinary...
360
00:19:10,232 --> 00:19:12,983
but its camera
was highly sophisticated...
361
00:19:13,026 --> 00:19:17,071
and, at the time,
revolutionary...
362
00:19:17,364 --> 00:19:19,198
the digital camera.
363
00:19:19,241 --> 00:19:21,242
Once you've got a picture
that's in numbers...
364
00:19:21,284 --> 00:19:23,744
you can do all kinds
ofthings with it.
365
00:19:23,787 --> 00:19:25,079
Mendillo and his team knew...
366
00:19:25,122 --> 00:19:27,957
that sodium existed
in the nebula.
367
00:19:27,999 --> 00:19:34,338
Sodium also exists
in the Earth's atmosphere.
368
00:19:34,381 --> 00:19:36,674
They were able to compare
digital photographs...
369
00:19:36,716 --> 00:19:39,343
of both Jupiter
and Earth's atmospheres...
370
00:19:39,386 --> 00:19:43,431
and bring forth an image
of the nebula.
371
00:19:43,473 --> 00:19:44,890
Well, that was very
difficult to do...
372
00:19:44,933 --> 00:19:47,476
ifyoujust had two photographs
and pieces of paper.
373
00:19:47,519 --> 00:19:49,603
But now that we have
these digital cameras...
374
00:19:49,646 --> 00:19:55,276
we've revolutionized the way
that we can process images.
375
00:19:55,318 --> 00:19:57,361
Though lo would be
a fascinating...
376
00:19:57,404 --> 00:20:00,281
scientific and aesthetic
destination...
377
00:20:00,323 --> 00:20:03,909
its hostile environment
probably precludes that.
378
00:20:03,952 --> 00:20:06,829
Even landing an unmanned probe
would be difficult...
379
00:20:06,872 --> 00:20:11,333
among lo's convulsing fissures.
380
00:20:11,376 --> 00:20:13,294
But there's another moon
orbiting Jupiter...
381
00:20:13,336 --> 00:20:16,714
which may not only support
human exploration...
382
00:20:16,756 --> 00:20:20,718
but possibly support
its own alien life forms.
383
00:20:20,760 --> 00:20:22,511
Europa is one
of the most fascinating...
384
00:20:22,554 --> 00:20:26,056
and enigmatic objects
in our solar system...
385
00:20:26,099 --> 00:20:29,560
really unlike anyplace else
in the solar system...
386
00:20:29,603 --> 00:20:34,440
and for that matter,
unlike anything on Earth.
387
00:20:34,483 --> 00:20:36,317
The surface features
are such...
388
00:20:36,359 --> 00:20:37,776
that there are cracks
in the surface...
389
00:20:37,819 --> 00:20:40,946
there's mottled terrain, there's chaotic
terrain...
390
00:20:40,989 --> 00:20:44,909
and it looks like icebergs
in some areas.
391
00:20:44,951 --> 00:20:48,662
We know Europa
is an alien moon.
392
00:20:48,705 --> 00:20:52,249
Could it be home
to alien life forms as well?
393
00:20:54,961 --> 00:20:59,215
Europa orbits 400,000 miles
from Jupiter's surface...
394
00:20:59,257 --> 00:21:01,926
about double
the distance of lo.
395
00:21:01,968 --> 00:21:04,011
And like its convulsive
cousin...
396
00:21:04,054 --> 00:21:09,767
it too is molded
by gravitational tides.
397
00:21:09,809 --> 00:21:11,810
Jupiter has the greatest effect.
398
00:21:11,853 --> 00:21:14,146
lts mass,
like a persistent lover...
399
00:21:14,189 --> 00:21:17,650
pulls the reluctant moon
toward its surface.
400
00:21:17,692 --> 00:21:19,693
Europa resists
with its own gravity...
401
00:21:19,736 --> 00:21:22,071
and they form
a kind of symbiosis...
402
00:21:22,113 --> 00:21:26,242
hundreds of thousands of miles
above the gas giant.
403
00:21:26,284 --> 00:21:29,203
But it's notjust Jupiter
tugging at Europa.
404
00:21:29,246 --> 00:21:31,872
Little lo
and larger cousin Ganymede...
405
00:21:31,915 --> 00:21:34,875
pull at Europa
from different directions.
406
00:21:34,918 --> 00:21:36,877
lt's the same
orbital resonance...
407
00:21:36,920 --> 00:21:41,298
that has such a dramatic
effect on lo.
408
00:21:41,341 --> 00:21:44,718
However, the results
are far different on Europa.
409
00:21:44,761 --> 00:21:46,887
Europa's surface is cold...
410
00:21:46,930 --> 00:21:51,100
minus 550 degrees fahrenheit
in some places...
411
00:21:51,142 --> 00:21:52,726
yet there is heating.
412
00:21:52,769 --> 00:21:55,062
And what rises
to the surface of Europa...
413
00:21:55,105 --> 00:22:01,944
is also what makes the moon
so exciting: water.
414
00:22:01,987 --> 00:22:05,197
This water, actually
a kind of glacial ice...
415
00:22:05,240 --> 00:22:07,408
is rising
from an underground ocean...
416
00:22:07,450 --> 00:22:09,910
and oozing out
onto the surface...
417
00:22:09,953 --> 00:22:14,081
repaving it as a Zamboni
does an ice rink.
418
00:22:14,124 --> 00:22:16,500
Europa's ocean
is thought to be shallow...
419
00:22:16,543 --> 00:22:23,382
only about10 or15 miles
below the surface.
420
00:22:23,425 --> 00:22:26,427
Waterwas the cradle
of life on Earth.
421
00:22:26,469 --> 00:22:31,724
Could the same be true
on Europa or other moons?
422
00:22:32,017 --> 00:22:35,394
lcy satellite oceans could be
the most common habitat...
423
00:22:35,437 --> 00:22:37,771
that exists in the universe.
424
00:22:37,814 --> 00:22:40,190
Earths might be
relatively rare...
425
00:22:40,233 --> 00:22:44,945
but icy satellites
are probably plentiful.
426
00:22:44,988 --> 00:22:49,450
ln February of 2007,
the New Horizons spacecraft...
427
00:22:49,492 --> 00:22:50,701
on its way to Pluto...
428
00:22:50,744 --> 00:22:53,120
and the outer reaches
of the solar system...
429
00:22:53,163 --> 00:22:55,456
managed to fly
close enough to Europa...
430
00:22:55,498 --> 00:22:59,335
to send back
some startling pictures.
431
00:22:59,377 --> 00:23:03,213
Seen only as the sun is rising
or setting behind Europa...
432
00:23:03,256 --> 00:23:05,883
are enormous
geological patterns...
433
00:23:05,925 --> 00:23:09,053
that have been dubbed
crop circles.
434
00:23:09,095 --> 00:23:11,138
They are very large.
435
00:23:11,181 --> 00:23:12,222
lfyou were to, you know...
436
00:23:12,265 --> 00:23:14,642
try to drive across
one of the circles...
437
00:23:14,684 --> 00:23:17,728
you would very, you know,
gently go in and travel down...
438
00:23:17,771 --> 00:23:21,482
to a location that's
a few hundred feet lower...
439
00:23:21,524 --> 00:23:23,275
than the surface
you came up from...
440
00:23:23,318 --> 00:23:25,778
and then rise back up.
441
00:23:25,820 --> 00:23:28,030
The resemblance
of Europa's crop circles...
442
00:23:28,073 --> 00:23:31,659
to the mysterious ones that dot
the countryside here on Earth...
443
00:23:31,701 --> 00:23:34,161
ends when you consider
their size.
444
00:23:34,204 --> 00:23:39,375
Each one is 2,000 to 3,000
miles in diameter.
445
00:23:39,417 --> 00:23:42,753
They're too shallow and uniform
to be impact craters.
446
00:23:42,796 --> 00:23:46,965
Asteroids and comets come
in different sizes and shapes.
447
00:23:47,008 --> 00:23:51,136
Europa's crop circles are
remarkably similar geologically.
448
00:23:51,179 --> 00:23:52,805
Although nothing
has been proven...
449
00:23:52,847 --> 00:23:55,140
it seems
the great mass of Jupiter...
450
00:23:55,183 --> 00:23:59,228
may once again be the culprit.
451
00:23:59,270 --> 00:24:00,354
The speculation is...
452
00:24:00,397 --> 00:24:03,190
that the icy covering
surrounding Europa...
453
00:24:03,233 --> 00:24:05,901
is not tethered
to the core of the moon.
454
00:24:05,944 --> 00:24:08,862
Rather, it's floating above
the subsurface ocean...
455
00:24:08,905 --> 00:24:11,824
like a spherical iceberg.
456
00:24:11,866 --> 00:24:15,244
The polar region may be
somehow shaped by Jupiter...
457
00:24:15,286 --> 00:24:18,080
and then over hundreds
of thousands ofyears...
458
00:24:18,123 --> 00:24:21,041
slowly tugged
toward the equator.
459
00:24:21,084 --> 00:24:23,627
This forms a line
of small circle depressions...
460
00:24:23,670 --> 00:24:28,215
dropping from the polar region
toward the equator.
461
00:24:28,258 --> 00:24:29,466
lf Europa's ice crust...
462
00:24:29,509 --> 00:24:32,386
has similar structure
to icebergs on Earth...
463
00:24:32,429 --> 00:24:36,432
most of it would be
under the ocean's surface.
464
00:24:36,474 --> 00:24:40,602
This has huge implications
forfuture exploration.
465
00:24:40,645 --> 00:24:42,604
lt means there has to be
something like eight...
466
00:24:42,647 --> 00:24:46,400
or nine times that amount of ice
underneath them to allow...
467
00:24:46,443 --> 00:24:50,487
that kind of a large-scale
topography to exist.
468
00:24:50,530 --> 00:24:53,323
The iceberg theory
lays to rest the belief...
469
00:24:53,366 --> 00:24:56,827
that Europa's subsurface ocean
can be easily tapped...
470
00:24:56,870 --> 00:24:58,412
through a thin crust.
471
00:24:58,455 --> 00:25:00,622
Radar mapping
and ultraviolet data...
472
00:25:00,665 --> 00:25:02,791
will prove to be
even more important...
473
00:25:02,834 --> 00:25:04,042
before a Europa lander...
474
00:25:04,085 --> 00:25:07,421
can make its way
down to the surface.
475
00:25:07,464 --> 00:25:10,215
Future explorers will have
to search out hot spots...
476
00:25:10,258 --> 00:25:12,259
in places where
this mysterious ocean...
477
00:25:12,302 --> 00:25:14,762
has welled up
through the surface...
478
00:25:14,804 --> 00:25:20,726
and from there try to find
a way to dip into it.
479
00:25:20,769 --> 00:25:23,020
Those explorers
may choose instead...
480
00:25:23,062 --> 00:25:25,939
to set up a base of operations
on Ganymede...
481
00:25:25,982 --> 00:25:28,108
Jupiter's largest moon.
482
00:25:28,151 --> 00:25:30,527
As Phobos might serve
Martian exploration...
483
00:25:30,570 --> 00:25:31,987
as a waystation...
484
00:25:32,280 --> 00:25:36,784
Ganymede might do the same
for the Jovian system.
485
00:25:36,826 --> 00:25:38,660
Larger than
the planet Mercury...
486
00:25:38,703 --> 00:25:41,079
its gravity is closer
to that of Earth's...
487
00:25:41,122 --> 00:25:44,750
than any of Jupiter's moons.
488
00:25:44,793 --> 00:25:46,376
And though
it's in orbital residence...
489
00:25:46,419 --> 00:25:48,545
with both lo and Europa...
490
00:25:48,588 --> 00:25:51,757
it's far enough away from
Jupiter to be less affected...
491
00:25:51,800 --> 00:25:55,886
by the gas giant's
relentless tides.
492
00:25:55,929 --> 00:25:57,513
And at Ganymede,
you could, say...
493
00:25:57,555 --> 00:25:58,847
park in some nice,
big crater...
494
00:25:58,890 --> 00:26:01,809
and build your domed,
protected region...
495
00:26:01,851 --> 00:26:04,603
protected from
the charged particles...
496
00:26:04,646 --> 00:26:06,146
in the Jovian system...
497
00:26:06,189 --> 00:26:09,066
and make a pretty safe
place to study...
498
00:26:09,108 --> 00:26:12,236
notjust Ganymede itself
and its magnetic field...
499
00:26:12,278 --> 00:26:14,488
and its interior
and its geology...
500
00:26:14,531 --> 00:26:17,825
but the Jupiter system
as a whole.
501
00:26:17,867 --> 00:26:20,619
Ganymede is the only moon
in the solar system...
502
00:26:20,662 --> 00:26:22,663
with its own magnetic field.
503
00:26:22,705 --> 00:26:23,872
To have this distinction...
504
00:26:23,915 --> 00:26:25,582
Ganymede must have
sufficient mass...
505
00:26:26,125 --> 00:26:27,793
and a hot inner core.
506
00:26:28,211 --> 00:26:29,670
lts mass is obvious...
507
00:26:29,712 --> 00:26:31,213
but where the heat
is coming from...
508
00:26:31,256 --> 00:26:35,425
is a bit of a mystery.
509
00:26:35,468 --> 00:26:39,847
Ganymede is affected by both
lo and Europa's tidal forces.
510
00:26:39,889 --> 00:26:42,349
But the measurements
on its orbit indicate...
511
00:26:42,392 --> 00:26:45,519
that it's round enough to avoid
the squashing and stretching...
512
00:26:45,562 --> 00:26:48,981
that its smaller cousins
endure from Jupiter.
513
00:26:49,023 --> 00:26:50,315
The thought is...
514
00:26:50,358 --> 00:26:53,110
maybe something happened
in Ganymede's past...
515
00:26:53,152 --> 00:26:55,362
to change
its orbit slightly...
516
00:26:55,405 --> 00:26:59,283
and maybe its eccentricity
got kind of haywire...
517
00:26:59,325 --> 00:27:00,409
for a little while...
518
00:27:00,451 --> 00:27:03,161
and generated a lot of heat
within Ganymede...
519
00:27:03,204 --> 00:27:04,955
and caused the core
to be hot.
520
00:27:04,998 --> 00:27:06,081
We don't really know.
521
00:27:06,124 --> 00:27:07,708
What we do know...
522
00:27:07,750 --> 00:27:09,710
is that New Horizons'
recent flyby...
523
00:27:09,752 --> 00:27:11,128
of the Jovian system...
524
00:27:11,170 --> 00:27:14,131
gave us a tantalizing glimpse
of the wonders that await us...
525
00:27:14,173 --> 00:27:16,967
on Jupiter's alien moons.
526
00:27:17,010 --> 00:27:18,844
Scientists look forward
to the day...
527
00:27:18,887 --> 00:27:21,388
a lander touches down
on one of these moons...
528
00:27:21,431 --> 00:27:23,849
and starts to uncover
the secrets...
529
00:27:23,892 --> 00:27:28,395
of these mysterious worlds.
530
00:27:28,438 --> 00:27:31,899
Another icy moon orbits
the gas giant Saturn.
531
00:27:31,941 --> 00:27:35,068
lt's too small to hold
onto its own atmosphere...
532
00:27:35,111 --> 00:27:36,236
but that doesn't stop it...
533
00:27:36,279 --> 00:27:40,616
from sapping the atmosphere
of its parent planet.
534
00:27:40,658 --> 00:27:42,910
Enceladus,
even though quite small...
535
00:27:42,952 --> 00:27:46,788
is named after a tribe of giants
in Greek mythology.
536
00:27:46,831 --> 00:27:48,749
Like lo and Europa...
537
00:27:48,791 --> 00:27:50,417
Enceladus
has an eccentric orbit...
538
00:27:50,460 --> 00:27:53,128
around its parent planet
Saturn.
539
00:27:53,171 --> 00:27:54,588
The tidal forces of Saturn...
540
00:27:54,631 --> 00:27:57,257
squeeze and knead
this tiny moon...
541
00:27:57,300 --> 00:28:01,303
and create heat
at its core.
542
00:28:01,596 --> 00:28:02,554
But unlike lo...
543
00:28:02,597 --> 00:28:04,890
it doesn't regurgitate
molten material...
544
00:28:04,933 --> 00:28:08,185
it coalesces
into a massive gas cloud.
545
00:28:08,227 --> 00:28:09,937
Water doesn't well up
to the surface...
546
00:28:09,979 --> 00:28:12,189
as it does on icy Europa.
547
00:28:12,231 --> 00:28:16,526
No, Enceladus actually
spits plumes of icy water...
548
00:28:16,569 --> 00:28:18,737
into the atmosphere of Saturn.
549
00:28:18,780 --> 00:28:20,155
So we don't call it
a volcano.
550
00:28:20,198 --> 00:28:21,782
lt's more like a geyser.
551
00:28:21,824 --> 00:28:24,660
The watervapor
is then in orbit...
552
00:28:24,702 --> 00:28:26,328
around the little tiny moon...
553
00:28:26,371 --> 00:28:28,705
or because it's near Saturn...
554
00:28:28,748 --> 00:28:32,209
Saturn's gravity can pull it
into the planet.
555
00:28:32,251 --> 00:28:35,295
lnterested by theirwork
on the torus of lo...
556
00:28:35,338 --> 00:28:37,965
Michael Mendillo and his team
at Boston University...
557
00:28:38,007 --> 00:28:40,384
began to consider
Enceladus' effect...
558
00:28:40,426 --> 00:28:43,011
on Saturn's atmosphere.
559
00:28:43,054 --> 00:28:45,806
And it turns out that water
is a wonderful catalyst...
560
00:28:45,848 --> 00:28:50,018
to have the ions
and electrons recombine.
561
00:28:50,061 --> 00:28:53,438
Before Cassini, scientists
relied on computer models...
562
00:28:53,481 --> 00:28:58,068
to determine atmospheric
conditions surrounding Saturn.
563
00:28:58,111 --> 00:28:59,903
They indicated that Saturn
should have...
564
00:28:59,946 --> 00:29:02,447
a very robust ionosphere.
565
00:29:02,490 --> 00:29:05,409
Surprisingly,
Cassini's data indicated...
566
00:29:05,451 --> 00:29:07,577
that Saturn's ionosphere
was only10 percent...
567
00:29:07,620 --> 00:29:10,372
ofwhat computer models
had predicted.
568
00:29:10,415 --> 00:29:13,834
lt seems that the icy water
ejected from Enceladus...
569
00:29:13,876 --> 00:29:16,044
is neutralizing
the charged particles...
570
00:29:16,087 --> 00:29:19,089
in Saturn's ionosphere.
571
00:29:19,132 --> 00:29:23,677
Commence liftoff.
572
00:29:23,720 --> 00:29:26,179
Scientists had learned
quite by accident...
573
00:29:26,222 --> 00:29:31,393
the effect water can have
on Earth's atmosphere.
574
00:29:31,436 --> 00:29:36,023
ln 1973, when Nasa launched
its Skylab workshop...
575
00:29:36,065 --> 00:29:39,443
it launched its last
gigantic Saturn V rocket...
576
00:29:39,485 --> 00:29:40,944
the moon rocket.
577
00:29:40,987 --> 00:29:42,863
And it had never
had a launch...
578
00:29:42,905 --> 00:29:44,781
that allowed
the space vehicle...
579
00:29:44,824 --> 00:29:48,035
to keep its engine burning
as high as the ionosphere.
580
00:29:48,077 --> 00:29:49,619
Well, this gigantic engine...
581
00:29:49,662 --> 00:29:52,122
dumped a ton per second
ofwater vapor...
582
00:29:52,165 --> 00:29:54,374
which comes out of
a giant rocket motor...
583
00:29:54,417 --> 00:29:55,542
into the ionosphere.
584
00:29:55,585 --> 00:29:59,379
And the ionosphere nearly
vanished on that day.
585
00:29:59,422 --> 00:30:02,257
lt blew a gaping hole
in Earth's ionosphere...
586
00:30:02,300 --> 00:30:04,551
the top layer
of the atmosphere...
587
00:30:04,594 --> 00:30:07,596
a hole that took the sun's
ionizing radiation...
588
00:30:07,638 --> 00:30:11,308
24 hours to repair.
589
00:30:11,350 --> 00:30:13,310
However, on Saturn...
590
00:30:13,352 --> 00:30:14,728
where Enceladus
continuously dumps...
591
00:30:14,771 --> 00:30:18,356
six tons ofwater per minute
into its atmosphere...
592
00:30:18,399 --> 00:30:23,612
the long-term effects
have been significant.
593
00:30:23,654 --> 00:30:25,572
There's no worry that Enceladus
will strip away...
594
00:30:25,615 --> 00:30:29,076
its parent planet's
ionosphere completely...
595
00:30:29,118 --> 00:30:32,871
but this tiny moon,
only 300 miles in diameter...
596
00:30:32,914 --> 00:30:36,041
has gotten the attention
of the scientific community...
597
00:30:36,084 --> 00:30:39,711
and Saturn itself.
598
00:30:39,754 --> 00:30:42,547
While we prepare probes
to Phobos and Europa...
599
00:30:42,590 --> 00:30:45,592
and study data
from Enceladus and lo...
600
00:30:45,635 --> 00:30:47,594
an entirely new set of moons...
601
00:30:47,637 --> 00:30:50,847
has literallyjust come into the picture.
602
00:30:53,768 --> 00:30:57,270
Before the1990s,
most astronomers agreed...
603
00:30:57,313 --> 00:31:00,732
that there were only 34 moons
in the solar system.
604
00:31:00,775 --> 00:31:03,944
Most of those were regular
moons like our own...
605
00:31:03,986 --> 00:31:06,780
spherical bodies
that orbit their host planet...
606
00:31:06,823 --> 00:31:08,782
in the same direction
it rotates.
607
00:31:08,825 --> 00:31:10,617
But a handful
of these satellites...
608
00:31:10,660 --> 00:31:15,205
were what's known
as irregular moons.
609
00:31:15,248 --> 00:31:18,166
These freakish moons
follow elongated orbits.
610
00:31:18,209 --> 00:31:19,918
Their orbits are often tilted...
611
00:31:19,961 --> 00:31:21,795
and they rotate
in the opposite direction...
612
00:31:21,838 --> 00:31:24,256
of their host planets.
613
00:31:24,298 --> 00:31:28,426
They look like flying potatoes
or splinters or misshapen lumps.
614
00:31:28,469 --> 00:31:31,054
They've been hard
to find before now...
615
00:31:31,097 --> 00:31:32,430
because they're very small...
616
00:31:32,473 --> 00:31:38,353
and they're also
usually very dark.
617
00:31:38,396 --> 00:31:40,897
The advent
of digital photography...
618
00:31:40,940 --> 00:31:42,732
and the use
of light-sensitive optics...
619
00:31:42,775 --> 00:31:46,987
changed the lunar terrain
within a decade.
620
00:31:47,029 --> 00:31:48,697
Dr. Brett Gladman...
621
00:31:48,739 --> 00:31:51,158
from the University
of British Columbia...
622
00:31:51,200 --> 00:31:54,578
discovered his first
irregular moon in 1997...
623
00:31:54,620 --> 00:31:57,497
at the Palomar Observatory.
624
00:31:57,540 --> 00:32:00,292
Since then, Dr. Gladman
has brought to light...
625
00:32:00,334 --> 00:32:05,463
17 previously hidden objects
in the solar system.
626
00:32:05,506 --> 00:32:08,175
So you detect objects
in the outer solar system...
627
00:32:08,217 --> 00:32:10,135
by observing them move...
628
00:32:10,178 --> 00:32:12,429
relevant to the background
stars and galaxies...
629
00:32:12,471 --> 00:32:14,181
which are stationary.
630
00:32:14,223 --> 00:32:16,641
So ifyou take
a picture of the sky...
631
00:32:16,684 --> 00:32:17,851
and you wait an hour...
632
00:32:17,894 --> 00:32:19,769
and you take another
picture ofthe sky...
633
00:32:19,854 --> 00:32:22,898
none of the stars in the galaxy
will have moved...
634
00:32:22,940 --> 00:32:26,276
but distant objects
in the outer solar system...
635
00:32:26,319 --> 00:32:29,196
will displace
by a visible amount...
636
00:32:29,238 --> 00:32:31,114
between the two pictures.
637
00:32:31,157 --> 00:32:32,407
And so by comparing
the two pictures...
638
00:32:32,450 --> 00:32:38,330
you can see, as we have here,
a moving target.
639
00:32:38,372 --> 00:32:41,416
The object could be a comet
or an asteroid...
640
00:32:41,459 --> 00:32:44,544
or, if it orbits a planet
in a retrograde fashion...
641
00:32:44,587 --> 00:32:48,048
a new irregular moon.
642
00:32:48,090 --> 00:32:50,717
Another important distinction
between regular moons...
643
00:32:50,760 --> 00:32:53,345
and their irregular
counterparts...
644
00:32:53,387 --> 00:32:55,931
irregular moons are captured.
645
00:32:55,973 --> 00:32:57,682
That is, they formed...
646
00:32:57,725 --> 00:32:59,267
independently
of their host planet...
647
00:32:59,310 --> 00:33:01,228
and most likely
were part of the debris...
648
00:33:01,270 --> 00:33:05,690
that originally formed
our solar system.
649
00:33:05,733 --> 00:33:08,985
Phoebe, the largest irregular
moon orbiting Saturn...
650
00:33:09,028 --> 00:33:11,655
is a classic example.
651
00:33:11,697 --> 00:33:15,033
Phoebe orbits Saturn
very far out.
652
00:33:15,076 --> 00:33:17,827
lt has a very elliptical
and very inclined orbit.
653
00:33:17,870 --> 00:33:21,748
lt orbits
in a retrograde direction.
654
00:33:21,791 --> 00:33:24,000
Voyager images suggested...
655
00:33:24,043 --> 00:33:26,211
that this thing looks like
it could be an asteroid...
656
00:33:26,254 --> 00:33:29,673
and so people thought maybe
it is a captured asteroid.
657
00:33:29,715 --> 00:33:34,302
Nowwe knowfrom Cassini
it's a very waterized-rich body.
658
00:33:34,345 --> 00:33:37,097
That pretty much rules out
the asteroid belt.
659
00:33:37,139 --> 00:33:40,100
The thinking is that Phoebe
could very well have come...
660
00:33:40,142 --> 00:33:41,268
from the Kuiper Belt...
661
00:33:41,310 --> 00:33:46,231
way out in the outer reaches
ofthe solar system.
662
00:33:46,524 --> 00:33:49,484
The Kuiper Belt is thought
to be the debris left over...
663
00:33:49,527 --> 00:33:51,319
after the solar system formed.
664
00:33:51,362 --> 00:33:55,240
lt revolves around the sun
beyond the orbit of Pluto.
665
00:33:55,283 --> 00:33:57,117
However, another theory...
666
00:33:57,159 --> 00:34:02,998
suggests something
altogether different.
667
00:34:03,040 --> 00:34:05,625
lt's much more likely
that Phoebe formed...
668
00:34:05,668 --> 00:34:07,836
in an independent orbit
around the sun...
669
00:34:07,878 --> 00:34:12,048
and then was captured into orbit
around Saturn...
670
00:34:12,091 --> 00:34:13,633
whereas most of
the other objects...
671
00:34:13,676 --> 00:34:15,719
that formed
near Saturn's distance...
672
00:34:15,761 --> 00:34:17,262
were either accreted
by Saturn...
673
00:34:17,305 --> 00:34:20,849
or ejected
from the solar system.
674
00:34:20,891 --> 00:34:23,727
Phoebe would then be made
ofthe planetary debris...
675
00:34:23,769 --> 00:34:26,730
that was floating around Saturn
at the time of its birth.
676
00:34:26,772 --> 00:34:30,025
And possibly it;s made up
of different material...
677
00:34:30,067 --> 00:34:33,278
than some of the irregular
moons orbiting Jupiter.
678
00:34:33,321 --> 00:34:34,654
lf this is the case...
679
00:34:34,697 --> 00:34:38,408
astrogeologists may be able
to discern and compare...
680
00:34:38,451 --> 00:34:39,617
the different ingredients...
681
00:34:39,660 --> 00:34:43,204
that birthed
these two gas giants.
682
00:34:43,247 --> 00:34:45,874
Three main theories
currently exist...
683
00:34:45,916 --> 00:34:49,085
as to how Phoebe and its other
irregular counterparts...
684
00:34:49,128 --> 00:34:50,837
lost their independence.
685
00:34:50,880 --> 00:34:53,173
Two suggest the irregulars
were captured...
686
00:34:53,215 --> 00:34:55,550
as the solar system
was still forming...
687
00:34:55,593 --> 00:34:57,552
and the planets were
still an accreting blob...
688
00:34:57,595 --> 00:34:59,679
of gas and debris.
689
00:34:59,722 --> 00:35:02,640
The gas-drag theory
is the most straightforward.
690
00:35:02,683 --> 00:35:06,394
Thick gases were swirling
around the accreting planet...
691
00:35:06,437 --> 00:35:08,438
when a comet, asteroid...
692
00:35:08,481 --> 00:35:10,565
or a shattered
combination of both...
693
00:35:10,608 --> 00:35:14,027
passed through
the gaseous mixture.
694
00:35:14,070 --> 00:35:15,779
We know that
the giant planets...
695
00:35:15,821 --> 00:35:18,281
built their regular
satellite systems...
696
00:35:18,324 --> 00:35:22,160
in a large accretion disc
around each of the planets...
697
00:35:22,203 --> 00:35:23,995
sort of like a mini
little solar system...
698
00:35:24,038 --> 00:35:26,039
forming around each planet.
699
00:35:26,082 --> 00:35:28,708
And the gas and dust
that was in that disc...
700
00:35:28,751 --> 00:35:31,878
can also serve
in its outer regions...
701
00:35:31,921 --> 00:35:33,797
as a source offriction...
702
00:35:33,839 --> 00:35:37,258
where passing planetesimals
formed independently...
703
00:35:37,301 --> 00:35:41,346
are slowed down a little bit
and captured into orbit.
704
00:35:41,389 --> 00:35:44,516
The second theory is really
a variation on the first.
705
00:35:44,558 --> 00:35:47,560
lt's sometimes called
the pull-down theory.
706
00:35:47,603 --> 00:35:49,562
Here, instead of an object
being caught...
707
00:35:49,605 --> 00:35:52,732
by simply passing through
the accreting gases...
708
00:35:52,775 --> 00:35:54,567
it is unsuspectingly pulled...
709
00:35:54,610 --> 00:35:56,444
into the forming
planet's orbit...
710
00:35:56,487 --> 00:36:00,198
by its growing
gravitational pull.
711
00:36:00,241 --> 00:36:02,242
The gas-drag and the pull-down
theories of capture...
712
00:36:02,284 --> 00:36:04,911
work well for both
Jupiter and Saturn...
713
00:36:04,954 --> 00:36:07,122
because their mixture
of ingredients...
714
00:36:07,164 --> 00:36:14,129
was massive enough to slow down
these passing objects.
715
00:36:14,171 --> 00:36:18,591
But what about the icy giants
Neptune and Uranus?
716
00:36:18,634 --> 00:36:22,429
Because ofthe extreme cold,
they formed much more slowly...
717
00:36:22,471 --> 00:36:24,013
and it's difficult to believe...
718
00:36:24,056 --> 00:36:26,808
that their icy accretion mixture
contained enough mass...
719
00:36:26,851 --> 00:36:32,063
to snare a passing piece
of the solar system.
720
00:36:32,106 --> 00:36:36,568
Yet both icy giants have
their own irregular moons...
721
00:36:36,610 --> 00:36:41,990
hence, a third theory:
three-body interaction.
722
00:36:42,241 --> 00:36:43,283
We discover
that many of the objects...
723
00:36:43,325 --> 00:36:44,951
are actually
more than one object.
724
00:36:44,994 --> 00:36:46,703
They're usually two objects...
725
00:36:46,745 --> 00:36:50,415
often that because they're both
more or less the same size...
726
00:36:50,458 --> 00:36:53,460
as the other
in a binary relationship.
727
00:36:53,502 --> 00:36:54,961
lnstead of being a big object...
728
00:36:55,004 --> 00:36:58,548
with a small object going in
an orbit around it like this...
729
00:36:58,591 --> 00:37:01,009
it's two more or less
similar-sized objects...
730
00:37:01,051 --> 00:37:02,927
going around a common orbit.
731
00:37:02,970 --> 00:37:06,055
Between the two of them
is called the barycenter.
732
00:37:06,098 --> 00:37:07,640
A binary pair exists...
733
00:37:07,683 --> 00:37:09,809
when two objects
of the same size...
734
00:37:09,852 --> 00:37:11,769
are tight enough
to the barycenter...
735
00:37:11,812 --> 00:37:16,399
to prevent a third larger object
from splitting them apart.
736
00:37:16,442 --> 00:37:17,984
But when one
of the binary pair...
737
00:37:18,027 --> 00:37:20,528
is significantly larger
than the other...
738
00:37:20,571 --> 00:37:22,405
the more massive
third object...
739
00:37:22,448 --> 00:37:26,034
has a greater chance
of separating them.
740
00:37:26,076 --> 00:37:28,661
The smaller one will tend
to have the much bigger orbit...
741
00:37:28,704 --> 00:37:31,122
swing out further.
742
00:37:31,165 --> 00:37:32,790
This brings
the smaller object...
743
00:37:32,833 --> 00:37:35,418
close enough to the planet
to be captured...
744
00:37:35,461 --> 00:37:41,758
while its partner is slung out
into an independent orbit.
745
00:37:41,800 --> 00:37:45,803
One bizarre moon seems
to defy classification.
746
00:37:45,846 --> 00:37:49,307
Triton orbits Neptune
in a retrograde fashion...
747
00:37:49,350 --> 00:37:51,518
counter to Neptune's rotation.
748
00:37:51,560 --> 00:37:53,686
That would make it
an irregular moon...
749
00:37:53,729 --> 00:37:55,396
except that it's spherical...
750
00:37:55,439 --> 00:37:57,607
and orbits
close to the equator...
751
00:37:57,650 --> 00:38:00,527
with an almost perfectly
round circumference...
752
00:38:00,569 --> 00:38:07,283
a classical description
of a regular moon.
753
00:38:07,326 --> 00:38:10,453
lt also spews out
mysterious icy plumes...
754
00:38:10,496 --> 00:38:12,622
with some indication
that it once was...
755
00:38:12,665 --> 00:38:16,584
or possibly still is
volcanically active.
756
00:38:20,631 --> 00:38:24,217
Before Voyager 2 ventured
into the outer solar system...
757
00:38:24,260 --> 00:38:26,886
Neptune's moon Triton
was assumed to be...
758
00:38:26,929 --> 00:38:29,222
a geologically dead
ball of rock...
759
00:38:29,265 --> 00:38:32,725
about the size
of our own moon.
760
00:38:32,768 --> 00:38:35,061
When Voyager
beamed back photographs...
761
00:38:35,104 --> 00:38:37,021
revealing a world
with mountains...
762
00:38:37,064 --> 00:38:40,233
fault lines, and fissures...
763
00:38:40,276 --> 00:38:42,402
indicative
of tectonic movement...
764
00:38:42,444 --> 00:38:45,947
as well as a surprisingly
thick atmosphere...
765
00:38:45,990 --> 00:38:49,576
scientists were amazed.
766
00:38:49,618 --> 00:38:51,494
Geologic forces
usually associated...
767
00:38:51,537 --> 00:38:54,330
with much warmer
and larger planets...
768
00:38:54,373 --> 00:38:56,666
might be occurring
on a frozen moon...
769
00:38:56,709 --> 00:38:59,252
slightly smaller
than our own.
770
00:38:59,295 --> 00:39:03,131
Voyager detected
no active volcanoes in 1989.
771
00:39:03,173 --> 00:39:06,092
However, like Saturn's
moon Enceladus...
772
00:39:06,135 --> 00:39:11,222
geysers periodically erupted
from the planet's surface.
773
00:39:11,265 --> 00:39:12,932
What's really stunning
about Triton...
774
00:39:12,975 --> 00:39:14,475
is notjust that it has...
775
00:39:14,518 --> 00:39:17,186
some unique geological
processes occurring...
776
00:39:17,229 --> 00:39:18,605
but the fact
that they're happening...
777
00:39:18,647 --> 00:39:22,358
even though Triton
is an irregular moon.
778
00:39:22,401 --> 00:39:24,694
Most large moons
in the solar system...
779
00:39:24,737 --> 00:39:26,946
are regular satellites...
780
00:39:26,989 --> 00:39:29,782
with the very important
exception of Triton...
781
00:39:30,075 --> 00:39:31,492
Neptune's largest moon...
782
00:39:31,535 --> 00:39:33,870
which orbits the wrong way.
783
00:39:33,912 --> 00:39:38,249
So Triton is thought to have
been a captured object.
784
00:39:38,292 --> 00:39:41,502
A captured moon that acts
like a regular one.
785
00:39:41,545 --> 00:39:43,546
How did an object
the size of Triton...
786
00:39:43,589 --> 00:39:44,922
slow down enough...
787
00:39:44,965 --> 00:39:48,134
not to either pass through
Neptune's atmosphere...
788
00:39:48,177 --> 00:39:52,764
or collide directly
into the icy planet?
789
00:39:57,686 --> 00:39:59,020
There's no sure bet...
790
00:39:59,063 --> 00:40:02,440
but some theories
carry better odds.
791
00:40:02,483 --> 00:40:05,109
Much like gamblers
at the roulette wheel...
792
00:40:05,152 --> 00:40:07,236
Triton and Neptune
played the odds...
793
00:40:07,279 --> 00:40:10,823
and trusted to luck.
794
00:40:10,866 --> 00:40:12,992
Place your bets.
Get lucky now.
795
00:40:13,035 --> 00:40:15,328
ln roulette, there are
several ways to bet.
796
00:40:15,371 --> 00:40:17,413
Each one carries
different odds.
797
00:40:17,456 --> 00:40:19,207
And like most
games of chance...
798
00:40:19,249 --> 00:40:22,585
the longer the odds,
the greater the payoff.
799
00:40:22,628 --> 00:40:24,879
20 black, 20 black even.
800
00:40:24,922 --> 00:40:26,881
There are at least
three possible ways...
801
00:40:26,924 --> 00:40:29,550
Triton could've been
captured by Neptune.
802
00:40:34,765 --> 00:40:37,308
All three hypotheses
are physically possible...
803
00:40:37,351 --> 00:40:40,478
but the first one,
the idea of gas drag...
804
00:40:40,521 --> 00:40:41,521
is the least likely...
805
00:40:41,563 --> 00:40:43,940
simply because
the period of time...
806
00:40:43,982 --> 00:40:46,984
which Neptune had
a disc of gas and dust...
807
00:40:47,027 --> 00:40:49,862
which could've captured
a proto Triton object...
808
00:40:49,905 --> 00:40:52,031
it was a very short
period of time...
809
00:40:52,074 --> 00:40:55,118
and so the window of opportunity
was very small.
810
00:40:55,160 --> 00:40:57,245
So that's like betting
on the green zero...
811
00:40:57,287 --> 00:41:00,248
on the roulette table.
812
00:41:00,290 --> 00:41:03,501
More likely is the possibility
that the proto Triton...
813
00:41:03,544 --> 00:41:05,211
sometime in
the solar system history...
814
00:41:05,254 --> 00:41:09,215
crashed into a set
of a regular...
815
00:41:09,258 --> 00:41:10,591
middle-sized icy satellites...
816
00:41:10,634 --> 00:41:13,928
and it was the collision
which gave us Triton.
817
00:41:13,971 --> 00:41:17,014
And that's like betting
on the first third...
818
00:41:17,057 --> 00:41:18,307
of the numbers
on the roulette table...
819
00:41:18,350 --> 00:41:19,892
so you have, like,
a one-in-three chance...
820
00:41:19,935 --> 00:41:22,979
of that taking place.
821
00:41:23,021 --> 00:41:26,566
Your best bet is to bet
on the even numbers.
822
00:41:26,608 --> 00:41:27,859
There you have
a one-in-two chance...
823
00:41:27,901 --> 00:41:29,068
of things happening.
824
00:41:29,111 --> 00:41:32,697
And the best bet for the capture
of Triton right now...
825
00:41:32,740 --> 00:41:35,366
is this binary capture
hypothesis because there...
826
00:41:35,409 --> 00:41:38,411
we know there are
probably thousands of objects...
827
00:41:38,454 --> 00:41:40,788
that had existed
in the Kuiper Belt...
828
00:41:40,831 --> 00:41:42,415
that would have
the right size...
829
00:41:42,458 --> 00:41:46,294
and be partnered with
another even larger object...
830
00:41:46,336 --> 00:41:51,090
and Neptune
could capture one of them.
831
00:41:51,133 --> 00:41:53,092
No one knows for sure
which number paid...
832
00:41:53,135 --> 00:41:55,386
in the early days
of the solar system...
833
00:41:55,429 --> 00:41:57,472
when Neptune captured Triton.
834
00:41:57,514 --> 00:42:00,266
However, once Triton
began orbiting Neptune...
835
00:42:00,309 --> 00:42:01,976
in an irregularfashion...
836
00:42:02,019 --> 00:42:06,063
it started obliterating anything
that got in its way.
837
00:42:06,106 --> 00:42:10,568
Neptune doesn't have a very
regular system of satellites.
838
00:42:10,611 --> 00:42:12,111
lt's thought
that the capture of Triton...
839
00:42:12,154 --> 00:42:14,655
disrupted what would've
otherwise been...
840
00:42:14,698 --> 00:42:16,699
a nice regular system...
841
00:42:16,742 --> 00:42:20,077
like the other
large planets have.
842
00:42:20,370 --> 00:42:23,122
lt's as if Triton was angry
at losing its freedom...
843
00:42:23,165 --> 00:42:26,626
and took it out on Neptune's
other hapless moons.
844
00:42:26,668 --> 00:42:31,339
But where did
this headstrong moon come from?
845
00:42:31,381 --> 00:42:33,341
Data from Voyager 2 indicates...
846
00:42:33,383 --> 00:42:36,677
that Triton's density
nearly matches Pluto's.
847
00:42:36,720 --> 00:42:38,054
This suggests a kinship...
848
00:42:38,096 --> 00:42:42,058
that no other regular moon
can claim.
849
00:42:42,100 --> 00:42:44,018
lt's suspected
that Pluto and Triton...
850
00:42:44,061 --> 00:42:48,356
are both objects that originated
in the Kuiper Belt.
851
00:42:48,398 --> 00:42:49,398
The outer solar system...
852
00:42:49,441 --> 00:42:51,025
consisted of
these large objects...
853
00:42:51,068 --> 00:42:53,528
going every which way,
essentially.
854
00:42:53,570 --> 00:42:56,531
And some of them formed
giant planets themselves...
855
00:42:56,573 --> 00:42:58,282
and some ofthem
were tossed out further...
856
00:42:58,325 --> 00:43:02,036
where they sit today
in the Kuiper Belt.
857
00:43:02,079 --> 00:43:03,830
Collisions, accretions...
858
00:43:03,872 --> 00:43:05,456
and even captures
have diminished...
859
00:43:05,499 --> 00:43:07,750
what was once
a major thoroughfare...
860
00:43:07,793 --> 00:43:11,003
of planetary
building materials.
861
00:43:11,046 --> 00:43:12,171
Early in solar system
history...
862
00:43:12,214 --> 00:43:14,966
the Kuiper Belt had
far more larger objects...
863
00:43:15,008 --> 00:43:17,134
that may have once had
a cumulative mass...
864
00:43:17,177 --> 00:43:19,095
of 50 Earths...
865
00:43:19,137 --> 00:43:20,847
whereas the current
Kuiper Belt mass...
866
00:43:20,889 --> 00:43:23,266
is much less
than one Earth.
867
00:43:23,308 --> 00:43:25,017
What's left
of the Kuiper Belt...
868
00:43:25,060 --> 00:43:27,353
is as old
as the solar system itself.
869
00:43:27,396 --> 00:43:29,772
The material that makes up
the binary objects...
870
00:43:29,815 --> 00:43:32,900
shards of collisions,
and even some alien moons...
871
00:43:32,943 --> 00:43:36,863
hasn't changed
in overfour billion years.
872
00:43:36,905 --> 00:43:38,239
lt's amazing
how really different...
873
00:43:38,282 --> 00:43:41,200
all the moons of the outer
solar system are.
874
00:43:41,243 --> 00:43:42,618
When l first got interested
in astronomy...
875
00:43:42,661 --> 00:43:43,744
as a kid in the 1960s...
876
00:43:43,787 --> 00:43:45,288
we hadn't seen
any of these moons.
877
00:43:45,330 --> 00:43:47,164
They were little dots
in your telescope...
878
00:43:47,207 --> 00:43:48,583
and so we had no idea...
879
00:43:48,625 --> 00:43:50,376
how radically different
they could be.
880
00:43:50,419 --> 00:43:51,711
But l think the most
shocking thing...
881
00:43:51,753 --> 00:43:53,004
was how, you know,
much variety there is...
882
00:43:53,046 --> 00:43:54,338
in the solar system.
883
00:43:54,381 --> 00:43:56,382
l think that blew me
and everybody else away...
884
00:43:56,425 --> 00:43:59,969
who lived through
that period.
885
00:44:00,012 --> 00:44:01,345
As we travel back home...
886
00:44:01,388 --> 00:44:04,432
from the frigid outskirts
of our solar system...
887
00:44:04,474 --> 00:44:06,976
awed by the vastness
ofthe universe...
888
00:44:07,019 --> 00:44:09,228
and the majesty
of the planets...
889
00:44:09,271 --> 00:44:11,689
it's worth it to pause
and take notice...
890
00:44:11,732 --> 00:44:14,358
of the small worlds
in the shadows.
891
00:44:14,401 --> 00:44:18,404
Those alien moons that were once
considered afterthoughts...
892
00:44:18,447 --> 00:44:20,406
hold mysteries just waiting...
893
00:44:20,449 --> 00:44:24,452
for human curiosity
to solve.
9999
00:00:0,500 --> 00:00:2,00
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