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In the beginning,
there was darkness...
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00:00:03,420 --> 00:00:05,504
and then, bang...
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giving birth to an endless
expanding existence...
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00:00:08,717 --> 00:00:11,260
of time, space, and matter.
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00:00:11,302 --> 00:00:14,013
Now, see further
than we've ever imagined...
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00:00:14,055 --> 00:00:16,015
beyond the limits
of our existence...
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00:00:16,057 --> 00:00:19,059
in a place we call
"The Universe. "
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00:00:23,064 --> 00:00:25,357
Lurking in the shadows
of the solar system...
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00:00:25,400 --> 00:00:28,318
are worlds so chemically
active and misshapen...
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00:00:28,361 --> 00:00:31,280
that they border
on the bizarre.
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00:00:31,322 --> 00:00:32,531
That I think
the most shocking thing...
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00:00:32,574 --> 00:00:37,661
was how very different
the solar system is.
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These are the moons...
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00:00:38,872 --> 00:00:41,373
surrounding the planets
of the solar system...
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00:00:41,416 --> 00:00:43,459
moons that were once
either unknown...
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00:00:43,501 --> 00:00:45,169
or considered afterthoughts...
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00:00:45,211 --> 00:00:48,797
are now on the cutting edge
of astronomical exploration.
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00:00:48,840 --> 00:00:49,882
What was surprising...
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00:00:49,924 --> 00:00:52,885
that they all didn't look
like our moon.
20
00:00:52,927 --> 00:00:55,554
The so-called minor members
of the solar systems...
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00:00:55,597 --> 00:00:57,931
are not of minor interest.
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00:00:57,974 --> 00:01:02,311
What surprises await us
on these alien moons?
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00:01:17,660 --> 00:01:20,662
Our solar system has always
been fertile ground...
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00:01:20,705 --> 00:01:23,082
for science fiction writers...
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00:01:23,124 --> 00:01:26,919
but with exponential advances
in telescopic technology...
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00:01:26,961 --> 00:01:30,756
and close encounters
by unmanned probes...
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00:01:30,799 --> 00:01:35,969
the curtain has now been lifted
on a new ballet of moons.
28
00:01:36,012 --> 00:01:37,429
Most of which are
going one way around...
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00:01:37,472 --> 00:01:39,848
some of which are going
the other way around...
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00:01:39,891 --> 00:01:42,059
all at different rates,
passing one another...
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the inner ones
passing the outer ones.
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For nearly half a century...
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00:01:47,315 --> 00:01:51,985
it was believed the solar system
was home to only 32 moons.
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They ranged in size
from Jupiter's moon...
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00:01:54,322 --> 00:01:57,950
Ganymede, larger
than the planet Mercury...
36
00:01:57,992 --> 00:02:00,119
to small
asteroid-shaped ones...
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like the Martian moons
Phobos and Deimos.
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00:02:05,250 --> 00:02:07,376
That number has exploded.
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00:02:07,418 --> 00:02:10,462
In 2007 alone,
scientists announced...
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00:02:10,505 --> 00:02:14,174
the discovery of 20 new moons
around Jupiter...
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00:02:14,217 --> 00:02:15,717
one around Saturn...
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and three around Neptune.
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00:02:18,054 --> 00:02:22,182
What happened is
astronomical telescopes...
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00:02:22,225 --> 00:02:26,603
had available to them
what are called CCD cameras.
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00:02:26,646 --> 00:02:28,147
These are digital cameras...
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that almost everybody
has nowadays.
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00:02:31,901 --> 00:02:34,111
It's difficult
to hold astronomers...
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to an exact number of moons
in the solar system.
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00:02:38,700 --> 00:02:43,412
As cameras become more sensitive
and telescopes more powerful...
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00:02:43,454 --> 00:02:49,918
more moons reveal themselves.
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00:02:49,961 --> 00:02:53,755
Moons are classified
in two distinct ways.
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00:02:53,798 --> 00:02:57,801
Those like our moon travel
in nearly circular orbits...
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00:02:57,844 --> 00:03:04,850
above their planet's equators
and are called regular moons.
54
00:03:04,893 --> 00:03:06,810
While our moon formed
from an impact...
55
00:03:06,853 --> 00:03:09,646
all other regular moons
coalesced...
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00:03:09,689 --> 00:03:11,148
from the gaseous stew...
57
00:03:11,191 --> 00:03:13,525
surrounding
their parent planets...
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00:03:13,568 --> 00:03:17,321
a process known as accretion.
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00:03:17,363 --> 00:03:20,073
The classic example
of regular moons...
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00:03:20,116 --> 00:03:23,076
would be the Galilean moons
of Jupiter...
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00:03:23,119 --> 00:03:24,203
lo, Europa...
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00:03:24,245 --> 00:03:26,914
Ganymede, and Callisto.
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00:03:26,956 --> 00:03:28,916
The material that is going
to form Jupiter, too...
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00:03:29,250 --> 00:03:30,542
but extended a little bit...
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00:03:30,585 --> 00:03:34,046
that material
accumulates into the moons.
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00:03:34,088 --> 00:03:36,548
Moons that follow
elongated orbits...
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00:03:36,591 --> 00:03:38,967
highly tilted
to their planet's equators...
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00:03:39,010 --> 00:03:41,553
are called irregular moons.
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00:03:41,596 --> 00:03:43,889
Most of these move
in retrograde orbits...
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00:03:43,932 --> 00:03:48,477
clockwise if their planet
rotates counterclockwise.
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00:03:48,519 --> 00:03:51,688
Phoebe, the newly discovered
moon orbiting Saturn...
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is a perfect example.
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00:03:54,442 --> 00:03:56,276
She began
her celestial life...
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00:03:56,319 --> 00:03:59,363
as an independent traveler
orbiting the sun...
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00:03:59,405 --> 00:04:05,202
before being captured
by the more massive Saturn.
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00:04:05,245 --> 00:04:06,954
Whether regular
or irregular...
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00:04:06,996 --> 00:04:09,414
moons must fall within
the gravitational reach...
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00:04:09,457 --> 00:04:11,041
of their parent planet.
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00:04:11,084 --> 00:04:15,963
The limit of these orbits
is known as the Hill sphere.
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00:04:16,005 --> 00:04:19,466
This phenomenon is named after
George William Hill...
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00:04:19,509 --> 00:04:24,263
an American astronomer
from the mid-1800s.
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So a Hill sphere is this region
around the planet...
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that moves along
with the planet...
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00:04:29,644 --> 00:04:32,229
inside of which
the gravity of the planet...
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00:04:32,272 --> 00:04:37,401
overwhelms the gravity
of the sun.
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00:04:37,443 --> 00:04:39,736
The moons of Mars,
Deimos and Phobos...
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operate very differently
within the Hill sphere.
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If the planet
is rotating faster...
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00:04:48,246 --> 00:04:51,832
than the moon it orbits,
like Deimos...
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00:04:51,874 --> 00:04:54,167
the tidal forces
between the two...
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00:04:54,210 --> 00:04:59,631
actually shove Deimos out
further and further.
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00:04:59,674 --> 00:05:01,091
Phobos, on the other hand...
93
00:05:01,134 --> 00:05:06,722
is rotating faster
than Mars rotates.
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00:05:06,764 --> 00:05:08,265
These small moons
were discovered...
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00:05:08,308 --> 00:05:13,312
by American astronomer
Asaph Hall in 1877.
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00:05:13,354 --> 00:05:16,481
He named Phobos
after the Greek god of fear...
97
00:05:16,524 --> 00:05:21,445
and Deimos
for the god of terror.
98
00:05:21,487 --> 00:05:25,115
Tom Duxbury was part
of the Mariner 9 mission...
99
00:05:25,158 --> 00:05:28,493
that first photographed
the two potato-shaped moons...
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00:05:28,536 --> 00:05:32,831
in November of 1971.
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00:05:32,874 --> 00:05:34,499
This was late at night...
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00:05:34,542 --> 00:05:36,960
on a cold, rainy, dark,
dreary day...
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and I looked at this...
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and I turned the picture
sideways.
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00:05:41,257 --> 00:05:52,976
It looked like a skull,
and it was such an eerie thing.
106
00:05:53,019 --> 00:05:55,437
Phobos is in a death spiral.
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00:05:55,480 --> 00:05:59,900
It orbits just 3,700 miles
from the Martian surface...
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00:05:59,942 --> 00:06:01,234
closer to its host planet...
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00:06:01,277 --> 00:06:04,112
than any moon
in our solar system.
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00:06:04,155 --> 00:06:06,198
If our own moon
were as close to the Earth...
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00:06:06,240 --> 00:06:11,703
as Phobos is to Mars,
it would look 20 times larger.
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00:06:11,746 --> 00:06:14,039
Its orbital period
would be in hours...
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not days like it is now,
but hours.
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00:06:16,709 --> 00:06:21,797
And at full moon,
it would fill the sky.
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00:06:21,839 --> 00:06:24,216
The daily tides, you know,
would rise and fall...
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00:06:24,258 --> 00:06:26,009
tens of feet
if not hundreds of feet...
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and so the Earth's moon...
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would eventually crash
into the Earth...
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00:06:30,306 --> 00:06:35,811
in such a situation.
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00:06:35,853 --> 00:06:38,563
Phobos' predicament
is caused by a process...
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00:06:38,606 --> 00:06:41,566
known as secular acceleration.
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00:06:41,609 --> 00:06:44,903
As Phobos races faster
than Mars rotates...
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00:06:44,946 --> 00:06:48,657
a tidal bump is raised
on the Martian surface.
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00:06:48,908 --> 00:06:52,828
In the process, Mars yanks
Phobos closer to its surface...
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00:06:52,870 --> 00:06:57,374
with each orbit.
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00:06:57,417 --> 00:06:59,418
The struggle between
Mars and Phobos...
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00:06:59,460 --> 00:07:04,381
is similar to the dynamics
of a simple game of tetherball.
128
00:07:04,424 --> 00:07:08,927
Imagine the ball as the moon,
the pole as the planet...
129
00:07:08,970 --> 00:07:11,346
and the rope between
the pole and the ball...
130
00:07:11,389 --> 00:07:17,602
as the planet's
gravitational pull.
131
00:07:17,645 --> 00:07:21,273
What we see
is that the gravity...
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00:07:21,315 --> 00:07:24,443
would pull the moon
in such a way...
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00:07:24,485 --> 00:07:25,694
that it speeds up.
134
00:07:25,736 --> 00:07:28,280
It goes faster and faster,
and it works its way...
135
00:07:28,322 --> 00:07:31,450
until it eventually
hits the pole.
136
00:07:31,492 --> 00:07:34,453
That's exactly what's
happening to Phobos.
137
00:07:34,495 --> 00:07:38,748
Phobos is going around Mars
faster than Mars rotates.
138
00:07:38,791 --> 00:07:40,083
That tidal interaction...
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00:07:40,126 --> 00:07:43,044
is pulling Phobos in
closer and closer...
140
00:07:43,087 --> 00:07:45,464
and speeding it up
in its orbit.
141
00:07:45,506 --> 00:07:46,965
In about 50 million years...
142
00:07:47,008 --> 00:07:49,676
we expect Phobos
to be pulled in so closely...
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00:07:49,719 --> 00:07:56,558
it will impact Mars and
disappear as a moon of Mars.
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00:07:56,601 --> 00:07:59,895
On the other hand, Deimos,
the further-out moon...
145
00:07:59,937 --> 00:08:02,481
is going slower
than Mars rotates.
146
00:08:02,523 --> 00:08:06,651
And so it's unwinding the string
in the opposite way...
147
00:08:06,694 --> 00:08:08,320
and what we see is Deimos...
148
00:08:08,362 --> 00:08:12,574
is going further
and further away from Mars.
149
00:08:12,617 --> 00:08:13,742
And eventually...
150
00:08:13,784 --> 00:08:16,703
Deimos will be pulled
away from Mars...
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00:08:16,746 --> 00:08:18,872
by the gravity of the sun.
152
00:08:18,915 --> 00:08:22,918
So, over time,
Mars will become moonless.
153
00:08:28,758 --> 00:08:32,177
Because Phobos outpaces
the rotation of Mars...
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00:08:32,220 --> 00:08:37,474
it appears to rise in the west
and set in the east.
155
00:08:37,517 --> 00:08:40,060
Instead of the planet
turning quickly under it...
156
00:08:40,102 --> 00:08:42,229
like our moon
and most other moons...
157
00:08:42,271 --> 00:08:45,649
and thus having it
rise in the east...
158
00:08:45,691 --> 00:08:46,691
and set in the west...
159
00:08:46,734 --> 00:08:49,528
it races ahead of the rotation
of the planet.
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00:08:49,570 --> 00:08:52,322
And so it comes up
on the western horizon...
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00:08:52,365 --> 00:08:59,996
and races ahead and sets
on the eastern horizon.
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00:09:00,039 --> 00:09:02,290
It will be another
50 millions years...
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00:09:02,333 --> 00:09:06,336
before Phobos
completely disappears.
164
00:09:06,379 --> 00:09:08,922
Before then,
it may prove useful...
165
00:09:08,965 --> 00:09:12,300
for the eventual
colonization of Mars.
166
00:09:12,343 --> 00:09:14,719
Science fiction writer
Arthur C. Clarke...
167
00:09:14,762 --> 00:09:16,221
speculated on this idea...
168
00:09:16,264 --> 00:09:19,683
in his book
"The Sands of Mars. "
169
00:09:19,725 --> 00:09:23,895
Although there is no real reason
to colonize Phobos itself...
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00:09:23,938 --> 00:09:29,276
its close proximity to Mars
makes it a natural waystation.
171
00:09:29,318 --> 00:09:30,735
From a gravity standpoint...
172
00:09:30,778 --> 00:09:33,530
it's much easier
to go to Phobos...
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which has no gravity...
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00:09:34,949 --> 00:09:37,325
than it is to fight
the gravity of Mars...
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00:09:37,368 --> 00:09:40,829
to get down to this surface.
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00:09:40,871 --> 00:09:43,081
From Galileo
to Stanley Kubrick...
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00:09:43,124 --> 00:09:45,750
the giant planets
of the outer solar system...
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00:09:45,793 --> 00:09:49,421
have tantalized our imagination
with their enormity.
179
00:09:49,463 --> 00:09:54,342
But in reality, exploring them
is tantamount to suicide.
180
00:09:54,385 --> 00:09:55,385
The overwhelming pressure...
181
00:09:55,428 --> 00:09:57,512
from Jupiter's
massive atmosphere...
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00:09:57,555 --> 00:10:02,100
would make it almost
impossible to function.
183
00:10:02,143 --> 00:10:04,019
But the moons
of these behemoths...
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00:10:04,270 --> 00:10:06,104
may provide a more
promising platform...
185
00:10:06,147 --> 00:10:11,276
for exploration
and even future colonization.
186
00:10:11,319 --> 00:10:14,029
Are these prisoners
of Jupiter's gravity...
187
00:10:14,071 --> 00:10:16,239
hostile worlds
with little chance...
188
00:10:16,282 --> 00:10:18,783
of sustaining organic life?
189
00:10:18,826 --> 00:10:20,785
Or might they provide
a safe haven...
190
00:10:20,828 --> 00:10:29,002
for future generations
of planetary explorers?
191
00:10:29,045 --> 00:10:31,546
Until recently,
very little was known...
192
00:10:31,589 --> 00:10:34,633
about the moons of the gas
and ice giants.
193
00:10:34,675 --> 00:10:37,010
Most of them remained
hidden in the glare...
194
00:10:37,053 --> 00:10:40,180
of their parent planets.
195
00:10:40,222 --> 00:10:43,975
Today, modern telescopes and
unmanned space exploration...
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00:10:44,018 --> 00:10:47,896
reveal a realm populated
by a host of moons...
197
00:10:47,938 --> 00:10:50,065
from planet-like
spherical worlds...
198
00:10:50,107 --> 00:10:56,446
to misshapen ones
barely 30 miles across.
199
00:10:56,489 --> 00:10:59,115
Jupiter, the largest planet
in the solar system...
200
00:10:59,158 --> 00:11:01,242
is a moon magnet.
201
00:11:01,285 --> 00:11:03,662
Nearly 4.5 billion years ago...
202
00:11:03,704 --> 00:11:09,167
it began as a massive gas cloud
collapsing in on itself.
203
00:11:09,210 --> 00:11:11,211
This process,
known as accretion...
204
00:11:11,253 --> 00:11:14,255
formed the beginnings
of the Jovian system.
205
00:11:14,298 --> 00:11:16,758
While nearly all the gas
and spinning material...
206
00:11:16,801 --> 00:11:19,094
went into forming
Jupiter itself...
207
00:11:19,136 --> 00:11:22,263
a very small percentage
clumped in small eddies...
208
00:11:22,306 --> 00:11:24,099
within Jupiter's orbit.
209
00:11:24,141 --> 00:11:25,392
These miniature accretions...
210
00:11:25,434 --> 00:11:26,851
solidified into Jupiter's
regular moons...
211
00:11:26,894 --> 00:11:32,691
lo, Europa, Ganymede,
and Callisto.
212
00:11:32,733 --> 00:11:35,151
As Jupiter coalesced,
its massive gravity...
213
00:11:35,194 --> 00:11:39,364
began adding to its menagerie
little remaining bits...
214
00:11:39,407 --> 00:11:43,243
from the birth
of the early solar system.
215
00:11:43,285 --> 00:11:48,456
The giant planets formed early
in a gas-rich environment...
216
00:11:48,499 --> 00:11:51,167
when there was lots
of little flotsam and jetsam...
217
00:11:51,210 --> 00:11:56,131
around the solar system still
to be captured into orbit.
218
00:11:56,173 --> 00:12:01,094
The number of Jupiter's moons
ranges from 60 to over 200...
219
00:12:01,137 --> 00:12:05,974
depending on who's counting.
220
00:12:06,016 --> 00:12:07,267
What's clear is...
221
00:12:07,309 --> 00:12:08,727
if you could stand
at the edge...
222
00:12:08,769 --> 00:12:10,895
of Jupiter's
gaseous atmosphere...
223
00:12:10,938 --> 00:12:12,439
and look to the heavens...
224
00:12:12,481 --> 00:12:16,943
you'd see a magnificent dance
of lunar objects.
225
00:12:16,986 --> 00:12:19,779
It would look pretty cool
to be able to see the moons.
226
00:12:19,822 --> 00:12:22,240
Every so often,
you'd see lo come by.
227
00:12:22,283 --> 00:12:24,576
Every second time
lo comes by...
228
00:12:24,618 --> 00:12:27,704
you'd see Europa
at the same time.
229
00:12:27,747 --> 00:12:29,497
And every four times
lo comes by...
230
00:12:29,540 --> 00:12:31,541
you'd see Ganymede.
231
00:12:31,584 --> 00:12:33,293
One member
of this Jovian cast...
232
00:12:33,335 --> 00:12:36,129
is so battered
by Jupiter's great mass...
233
00:12:36,172 --> 00:12:41,551
that it is literally bursting
from the inside out.
234
00:12:41,594 --> 00:12:45,597
In February of 2007,
the New Horizons spacecraft...
235
00:12:45,639 --> 00:12:47,640
eventually bound for Pluto...
236
00:12:47,683 --> 00:12:50,769
focused its cameras on lo.
237
00:12:50,811 --> 00:12:52,437
About the size of
Earth's moon...
238
00:12:52,480 --> 00:12:57,942
it orbits 263,000 miles
from Jupiter's surface.
239
00:12:57,985 --> 00:13:02,197
What sets lo apart
from the other Jovian moons...
240
00:13:02,239 --> 00:13:05,700
is its spectacular volcanism.
241
00:13:05,743 --> 00:13:07,202
New Horizons' cameras...
242
00:13:07,244 --> 00:13:10,079
captured detailed photos
of glowing lava...
243
00:13:10,122 --> 00:13:13,500
scattered across lo's surface.
244
00:13:13,876 --> 00:13:18,213
A huge 200-mile-high dust plume
rose above the surface...
245
00:13:18,255 --> 00:13:22,550
of the molten moon.
246
00:13:22,593 --> 00:13:25,261
lo, like all Jupiter's
regular moons...
247
00:13:25,304 --> 00:13:27,889
is named after a lover
of the god Jupiter...
248
00:13:27,932 --> 00:13:30,308
from Roman mythology.
249
00:13:30,351 --> 00:13:33,978
It was discovered by Galileo
in 1610...
250
00:13:34,021 --> 00:13:37,982
first photographed
by Pioneer I in 1974...
251
00:13:38,025 --> 00:13:41,361
and again by Voyager I
in 1979.
252
00:13:41,403 --> 00:13:44,155
Its pulsating activity
has puzzled...
253
00:13:44,198 --> 00:13:47,826
and intrigued scientists
for decades.
254
00:13:47,868 --> 00:13:51,830
Leaving lo is about
a ton per second of material...
255
00:13:51,872 --> 00:13:53,373
every second of every day.
256
00:13:53,415 --> 00:13:56,417
It's a phenomenal machine.
257
00:13:56,460 --> 00:13:57,544
I would like to go to lo...
258
00:13:57,586 --> 00:13:59,420
even though
it would be very dangerous...
259
00:13:59,463 --> 00:14:04,175
and hot and sulfurous.
260
00:14:04,218 --> 00:14:07,512
lo is too small to have
maintained a molten core...
261
00:14:07,555 --> 00:14:09,430
since its formation.
262
00:14:09,473 --> 00:14:11,182
Another mysterious process...
263
00:14:11,225 --> 00:14:14,644
must be responsible
for its heating.
264
00:14:14,687 --> 00:14:17,772
lo's entire interior
may be molten...
265
00:14:17,815 --> 00:14:21,568
because it's squeezed so much
as it's orbiting around Jupiter.
266
00:14:21,610 --> 00:14:24,988
This process is known
as tidal heating.
267
00:14:25,030 --> 00:14:26,739
The massive gravity
of Jupiter...
268
00:14:26,782 --> 00:14:32,787
is causing friction
at the inner core of lo.
269
00:14:32,830 --> 00:14:38,459
Much like a sculptor kneads
a cold lump of clay...
270
00:14:38,502 --> 00:14:46,217
Jupiter is endlessly creating
its own masterpiece.
271
00:14:46,260 --> 00:14:49,554
If a moon gets a little bit
of tidal heating...
272
00:14:49,597 --> 00:14:51,556
it becomes malleable.
273
00:14:51,599 --> 00:14:54,058
It can be stretched out
like clay...
274
00:14:54,101 --> 00:14:57,395
and deformed by the gravity
of the parent planet.
275
00:14:57,438 --> 00:14:59,272
The surface of the moon
is cold.
276
00:14:59,315 --> 00:15:03,067
It breaks like pulling
clay apart quickly. It'll break.
277
00:15:03,110 --> 00:15:05,069
But the interior,
where it's warm...
278
00:15:05,112 --> 00:15:07,864
can literally flow
and stretch...
279
00:15:07,907 --> 00:15:14,162
and be kneaded by the gravity
of the parent planet.
280
00:15:14,204 --> 00:15:17,916
Most regular moons
have circular orbits.
281
00:15:17,958 --> 00:15:19,542
To produce tidal heating...
282
00:15:19,585 --> 00:15:22,086
a moon must be
in a more oblong orbit...
283
00:15:22,129 --> 00:15:23,796
where the distance
from the host planet...
284
00:15:23,839 --> 00:15:27,884
changes radically
during a single revolution.
285
00:15:27,927 --> 00:15:30,595
The only way to produce
these eccentric orbits...
286
00:15:30,638 --> 00:15:34,515
is if another moon's gravity
disrupts it.
287
00:15:34,558 --> 00:15:37,310
When a moon
is in an eccentric orbit...
288
00:15:37,353 --> 00:15:38,770
a non-round orbit...
289
00:15:38,812 --> 00:15:43,107
it gets closer and farther
from its parent planet.
290
00:15:43,150 --> 00:15:44,776
When it does,
it gets squeezed.
291
00:15:44,818 --> 00:15:49,322
It gets pulled apart
when it's closer.
292
00:15:49,365 --> 00:15:51,532
lo is in orbital resonance...
293
00:15:51,575 --> 00:15:55,203
with its companion moons
Europa and Ganymede.
294
00:15:55,245 --> 00:15:57,330
While Jupiter and lo
struggle to find...
295
00:15:57,373 --> 00:15:59,624
a synchronistic
relationship...
296
00:15:59,667 --> 00:16:01,000
Europa and Ganymede...
297
00:16:01,043 --> 00:16:04,128
are yanking lo
in opposite directions.
298
00:16:04,171 --> 00:16:05,630
Jupiter yanks back...
299
00:16:05,673 --> 00:16:10,343
and lo gets stretched
and squeezed in the process.
300
00:16:10,386 --> 00:16:12,011
The tidal heating on lo...
301
00:16:12,054 --> 00:16:15,139
which is responsible
for its prodigious volcanoes...
302
00:16:15,182 --> 00:16:17,642
has a secondary side effect.
303
00:16:17,935 --> 00:16:20,728
It creates the largest
stationary visible object...
304
00:16:20,771 --> 00:16:22,647
in the solar system...
305
00:16:22,690 --> 00:16:30,488
a massive gas cloud
500 times the size of Jupiter.
306
00:16:30,531 --> 00:16:33,032
In 1990,
Professor Michael Mendillo...
307
00:16:33,075 --> 00:16:35,368
and his team
from Boston University...
308
00:16:35,411 --> 00:16:39,163
discovered a large gas cloud
spanning the huge distance...
309
00:16:39,206 --> 00:16:42,625
from one side of Jupiter
to the other.
310
00:16:42,668 --> 00:16:44,669
They were the first
to photograph...
311
00:16:44,712 --> 00:16:47,588
the entire nebula,
discover its origins...
312
00:16:47,631 --> 00:16:51,009
and the mechanism
that keeps it growing.
313
00:16:51,051 --> 00:16:52,635
Now, lo is small...
314
00:16:52,678 --> 00:16:54,887
so it doesn't have
much of an atmosphere.
315
00:16:54,930 --> 00:16:55,930
But these volcanoes...
316
00:16:55,973 --> 00:16:59,183
are continually
providing material...
317
00:16:59,226 --> 00:17:00,560
that could be an atmosphere.
318
00:17:00,602 --> 00:17:01,853
But you might ask...
319
00:17:01,895 --> 00:17:04,188
"Well, why doesn't it have
tremendous atmosphere...
320
00:17:04,231 --> 00:17:07,191
if all the volcanoes
have been going on for eons?"
321
00:17:07,234 --> 00:17:10,528
Well, it's because
the material escapes.
322
00:17:10,571 --> 00:17:12,864
The key gas is sodium.
323
00:17:12,906 --> 00:17:15,241
Even though it only
makes up five percent...
324
00:17:15,284 --> 00:17:17,744
of lo's ejected materials...
325
00:17:17,786 --> 00:17:21,497
it is easily detectable
by telescopes on Earth.
326
00:17:21,540 --> 00:17:24,042
Sodium emits an orange glow.
327
00:17:24,084 --> 00:17:28,087
In fact, sodium is commonly used
to illuminate streetlights...
328
00:17:28,130 --> 00:17:32,550
in many cities across the world.
329
00:17:32,593 --> 00:17:34,802
The sodium and the other
gas molecules...
330
00:17:34,845 --> 00:17:36,846
are pelted by light
from the sun...
331
00:17:36,889 --> 00:17:41,184
and electrons in Jupiter's
powerful magnetic field.
332
00:17:41,226 --> 00:17:43,561
Electrons and protons
are knocked off...
333
00:17:43,604 --> 00:17:46,814
some of these particles
and ionized.
334
00:17:46,857 --> 00:17:48,399
Now in plasma form...
335
00:17:48,442 --> 00:17:50,526
these ions
are taken on a ride...
336
00:17:50,569 --> 00:17:54,072
by Jupiter's
powerful magnetosphere.
337
00:17:54,114 --> 00:17:56,574
Its speed increases
dramatically...
338
00:17:56,617 --> 00:18:03,081
because it's been picked up
by the magnetic field.
339
00:18:03,123 --> 00:18:07,960
It's like they're taking
a ride on a cosmic carousel.
340
00:18:08,003 --> 00:18:11,589
The magnetic field lines
are the poles here.
341
00:18:11,632 --> 00:18:12,882
And then every now and then...
342
00:18:12,925 --> 00:18:16,677
a sodium atom gets picked up
along with this electron.
343
00:18:16,720 --> 00:18:19,889
And now, I'm in the Jupiter
plasma chorus...
344
00:18:19,932 --> 00:18:21,682
with all the other
ions and electrons...
345
00:18:21,725 --> 00:18:23,976
that have been captured
previously...
346
00:18:24,019 --> 00:18:26,395
and the ions
and the electrons recombine.
347
00:18:26,438 --> 00:18:29,774
The neutral is not confined
by the magnetic field...
348
00:18:29,817 --> 00:18:32,318
and it goes off
at a much higher speed...
349
00:18:32,361 --> 00:18:35,113
and that's enough
to escape from Jupiter.
350
00:18:35,155 --> 00:18:37,615
And they form the largest
visible cloud of gas...
351
00:18:37,658 --> 00:18:42,537
that's permanently
in the solar system.
352
00:18:42,579 --> 00:18:44,914
If we could see the nebula
with the naked eye...
353
00:18:44,957 --> 00:18:49,585
it would be the size of 12 moons
in the night sky.
354
00:18:49,628 --> 00:18:51,629
It is so enormous
that to view it...
355
00:18:51,672 --> 00:18:56,467
Mendillo and his team created
their own specialized telescope.
356
00:18:56,510 --> 00:18:59,220
Well, as it turns out,
to get a big field of view...
357
00:18:59,263 --> 00:19:01,139
all you need is
a small lens...
358
00:19:01,181 --> 00:19:05,476
like a pair of binoculars
gives you a big field of view.
359
00:19:05,519 --> 00:19:09,939
Even in 1991, the telescope
may have seemed ordinary...
360
00:19:09,982 --> 00:19:12,733
but its camera
was highly sophisticated...
361
00:19:12,776 --> 00:19:16,821
and, at the time,
revolutionary...
362
00:19:17,114 --> 00:19:18,948
the digital camera.
363
00:19:18,991 --> 00:19:20,992
Once you've got a picture
that's in numbers...
364
00:19:21,034 --> 00:19:23,494
you can do all kinds
of things with it.
365
00:19:23,537 --> 00:19:24,829
Mendillo and his team knew...
366
00:19:24,872 --> 00:19:27,707
that sodium existed
in the nebula.
367
00:19:27,749 --> 00:19:34,088
Sodium also exists
in the Earth's atmosphere.
368
00:19:34,131 --> 00:19:36,424
They were able to compare
digital photographs...
369
00:19:36,466 --> 00:19:39,093
of both Jupiter
and Earth's atmospheres...
370
00:19:39,136 --> 00:19:43,181
and bring forth an image
of the nebula.
371
00:19:43,223 --> 00:19:44,640
Well, that was very
difficult to do...
372
00:19:44,683 --> 00:19:47,226
if you just had two photographs
and pieces of paper.
373
00:19:47,269 --> 00:19:49,353
But now that we have
these digital cameras...
374
00:19:49,396 --> 00:19:55,026
we've revolutionized the way
that we can process images.
375
00:19:55,068 --> 00:19:57,111
Though lo would be
a fascinating...
376
00:19:57,154 --> 00:20:00,031
scientific and aesthetic
destination...
377
00:20:00,073 --> 00:20:03,659
its hostile environment
probably precludes that.
378
00:20:03,702 --> 00:20:06,579
Even landing an unmanned probe
would be difficult...
379
00:20:06,622 --> 00:20:11,083
among lo's convulsing fissures.
380
00:20:11,126 --> 00:20:13,044
But there's another moon
orbiting Jupiter...
381
00:20:13,086 --> 00:20:16,464
which may not only support
human exploration...
382
00:20:16,506 --> 00:20:20,468
but possibly support
its own alien life forms.
383
00:20:20,510 --> 00:20:22,261
Europa is one
of the most fascinating...
384
00:20:22,304 --> 00:20:25,806
and enigmatic objects
in our solar system...
385
00:20:25,849 --> 00:20:29,310
really unlike anyplace else
in the solar system...
386
00:20:29,353 --> 00:20:34,190
and for that matter,
unlike anything on Earth.
387
00:20:34,233 --> 00:20:36,067
The surface features
are such...
388
00:20:36,109 --> 00:20:37,526
that there are cracks
in the surface...
389
00:20:37,569 --> 00:20:40,696
there's mottled terrain, there's chaotic
terrain...
390
00:20:40,739 --> 00:20:44,659
and it looks like icebergs
in some areas.
391
00:20:44,701 --> 00:20:48,412
We know Europa
is an alien moon.
392
00:20:48,455 --> 00:20:51,999
Could it be home
to alien life forms as well?
393
00:20:54,711 --> 00:20:58,965
Europa orbits 400,000 miles
from Jupiter's surface...
394
00:20:59,007 --> 00:21:01,676
about double
the distance of lo.
395
00:21:01,718 --> 00:21:03,761
And like its convulsive
cousin...
396
00:21:03,804 --> 00:21:09,517
it too is molded
by gravitational tides.
397
00:21:09,559 --> 00:21:11,560
Jupiter has the greatest effect.
398
00:21:11,603 --> 00:21:13,896
Its mass,
like a persistent lover...
399
00:21:13,939 --> 00:21:17,400
pulls the reluctant moon
toward its surface.
400
00:21:17,442 --> 00:21:19,443
Europa resists
with its own gravity...
401
00:21:19,486 --> 00:21:21,821
and they form
a kind of symbiosis...
402
00:21:21,863 --> 00:21:25,992
hundreds of thousands of miles
above the gas giant.
403
00:21:26,034 --> 00:21:28,953
But it's not just Jupiter
tugging at Europa.
404
00:21:28,996 --> 00:21:31,622
Little lo
and larger cousin Ganymede...
405
00:21:31,665 --> 00:21:34,625
pull at Europa
from different directions.
406
00:21:34,668 --> 00:21:36,627
It's the same
orbital resonance...
407
00:21:36,670 --> 00:21:41,048
that has such a dramatic
effect on lo.
408
00:21:41,091 --> 00:21:44,468
However, the results
are far different on Europa.
409
00:21:44,511 --> 00:21:46,637
Europa's surface is cold...
410
00:21:46,680 --> 00:21:50,850
minus 550 degrees fahrenheit
in some places...
411
00:21:50,892 --> 00:21:52,476
yet there is heating.
412
00:21:52,519 --> 00:21:54,812
And what rises
to the surface of Europa...
413
00:21:54,855 --> 00:22:01,694
is also what makes the moon
so exciting: water.
414
00:22:01,737 --> 00:22:04,947
This water, actually
a kind of glacial ice...
415
00:22:04,990 --> 00:22:07,158
is rising
from an underground ocean...
416
00:22:07,200 --> 00:22:09,660
and oozing out
onto the surface...
417
00:22:09,703 --> 00:22:13,831
repaving it as a Zamboni
does an ice rink.
418
00:22:13,874 --> 00:22:16,250
Europa's ocean
is thought to be shallow...
419
00:22:16,293 --> 00:22:23,132
only about 10 or 15 miles
below the surface.
420
00:22:23,175 --> 00:22:26,177
Water was the cradle
of life on Earth.
421
00:22:26,219 --> 00:22:31,474
Could the same be true
on Europa or other moons?
422
00:22:31,767 --> 00:22:35,144
Icy satellite oceans could be
the most common habitat...
423
00:22:35,187 --> 00:22:37,521
that exists in the universe.
424
00:22:37,564 --> 00:22:39,940
Earths might be
relatively rare...
425
00:22:39,983 --> 00:22:44,695
but icy satellites
are probably plentiful.
426
00:22:44,738 --> 00:22:49,200
In February of 2007,
the New Horizons spacecraft...
427
00:22:49,242 --> 00:22:50,451
on its way to Pluto...
428
00:22:50,494 --> 00:22:52,870
and the outer reaches
of the solar system...
429
00:22:52,913 --> 00:22:55,206
managed to fly
close enough to Europa...
430
00:22:55,248 --> 00:22:59,085
to send back
some startling pictures.
431
00:22:59,127 --> 00:23:02,963
Seen only as the sun is rising
or setting behind Europa...
432
00:23:03,006 --> 00:23:05,633
are enormous
geological patterns...
433
00:23:05,675 --> 00:23:08,803
that have been dubbed
crop circles.
434
00:23:08,845 --> 00:23:10,888
They are very large.
435
00:23:10,931 --> 00:23:11,972
If you were to, you know...
436
00:23:12,015 --> 00:23:14,392
try to drive across
one of the circles...
437
00:23:14,434 --> 00:23:17,478
you would very, you know,
gently go in and travel down...
438
00:23:17,521 --> 00:23:21,232
to a location that's
a few hundred feet lower...
439
00:23:21,274 --> 00:23:23,025
than the surface
you came up from...
440
00:23:23,068 --> 00:23:25,528
and then rise back up.
441
00:23:25,570 --> 00:23:27,780
The resemblance
of Europa's crop circles...
442
00:23:27,823 --> 00:23:31,409
to the mysterious ones that dot
the countryside here on Earth...
443
00:23:31,451 --> 00:23:33,911
ends when you consider
their size.
444
00:23:33,954 --> 00:23:39,125
Each one is 2,000 to 3,000
miles in diameter.
445
00:23:39,167 --> 00:23:42,503
They're too shallow and uniform
to be impact craters.
446
00:23:42,546 --> 00:23:46,715
Asteroids and comets come
in different sizes and shapes.
447
00:23:46,758 --> 00:23:50,886
Europa's crop circles are
remarkably similar geologically.
448
00:23:50,929 --> 00:23:52,555
Although nothing
has been proven...
449
00:23:52,597 --> 00:23:54,890
it seems
the great mass of Jupiter...
450
00:23:54,933 --> 00:23:58,978
may once again be the culprit.
451
00:23:59,020 --> 00:24:00,104
The speculation is...
452
00:24:00,147 --> 00:24:02,940
that the icy covering
surrounding Europa...
453
00:24:02,983 --> 00:24:05,651
is not tethered
to the core of the moon.
454
00:24:05,694 --> 00:24:08,612
Rather, it's floating above
the subsurface ocean...
455
00:24:08,655 --> 00:24:11,574
like a spherical iceberg.
456
00:24:11,616 --> 00:24:14,994
The polar region may be
somehow shaped by Jupiter...
457
00:24:15,036 --> 00:24:17,830
and then over hundreds
of thousands of years...
458
00:24:17,873 --> 00:24:20,791
slowly tugged
toward the equator.
459
00:24:20,834 --> 00:24:23,377
This forms a line
of small circle depressions...
460
00:24:23,420 --> 00:24:27,965
dropping from the polar region
toward the equator.
461
00:24:28,008 --> 00:24:29,216
If Europa's ice crust...
462
00:24:29,259 --> 00:24:32,136
has similar structure
to icebergs on Earth...
463
00:24:32,179 --> 00:24:36,182
most of it would be
under the ocean's surface.
464
00:24:36,224 --> 00:24:40,352
This has huge implications
for future exploration.
465
00:24:40,395 --> 00:24:42,354
It means there has to be
something like eight...
466
00:24:42,397 --> 00:24:46,150
or nine times that amount of ice
underneath them to allow...
467
00:24:46,193 --> 00:24:50,237
that kind of a large-scale
topography to exist.
468
00:24:50,280 --> 00:24:53,073
The iceberg theory
lays to rest the belief...
469
00:24:53,116 --> 00:24:56,577
that Europa's subsurface ocean
can be easily tapped...
470
00:24:56,620 --> 00:24:58,162
through a thin crust.
471
00:24:58,205 --> 00:25:00,372
Radar mapping
and ultraviolet data...
472
00:25:00,415 --> 00:25:02,541
will prove to be
even more important...
473
00:25:02,584 --> 00:25:03,792
before a Europa lander...
474
00:25:03,835 --> 00:25:07,171
can make its way
down to the surface.
475
00:25:07,214 --> 00:25:09,965
Future explorers will have
to search out hot spots...
476
00:25:10,008 --> 00:25:12,009
in places where
this mysterious ocean...
477
00:25:12,052 --> 00:25:14,512
has welled up
through the surface...
478
00:25:14,554 --> 00:25:20,476
and from there try to find
a way to dip into it.
479
00:25:20,519 --> 00:25:22,770
Those explorers
may choose instead...
480
00:25:22,812 --> 00:25:25,689
to set up a base of operations
on Ganymede...
481
00:25:25,732 --> 00:25:27,858
Jupiter's largest moon.
482
00:25:27,901 --> 00:25:30,277
As Phobos might serve
Martian exploration...
483
00:25:30,320 --> 00:25:31,737
as a waystation...
484
00:25:32,030 --> 00:25:36,534
Ganymede might do the same
for the Jovian system.
485
00:25:36,576 --> 00:25:38,410
Larger than
the planet Mercury...
486
00:25:38,453 --> 00:25:40,829
its gravity is closer
to that of Earth's...
487
00:25:40,872 --> 00:25:44,500
than any of Jupiter's moons.
488
00:25:44,543 --> 00:25:46,126
And though
it's in orbital residence...
489
00:25:46,169 --> 00:25:48,295
with both lo and Europa...
490
00:25:48,338 --> 00:25:51,507
it's far enough away from
Jupiter to be less affected...
491
00:25:51,550 --> 00:25:55,636
by the gas giant's
relentless tides.
492
00:25:55,679 --> 00:25:57,263
And at Ganymede,
you could, say...
493
00:25:57,305 --> 00:25:58,597
park in some nice,
big crater...
494
00:25:58,640 --> 00:26:01,559
and build your domed,
protected region...
495
00:26:01,601 --> 00:26:04,353
protected from
the charged particles...
496
00:26:04,396 --> 00:26:05,896
in the Jovian system...
497
00:26:05,939 --> 00:26:08,816
and make a pretty safe
place to study...
498
00:26:08,858 --> 00:26:11,986
not just Ganymede itself
and its magnetic field...
499
00:26:12,028 --> 00:26:14,238
and its interior
and its geology...
500
00:26:14,281 --> 00:26:17,575
but the Jupiter system
as a whole.
501
00:26:17,617 --> 00:26:20,369
Ganymede is the only moon
in the solar system...
502
00:26:20,412 --> 00:26:22,413
with its own magnetic field.
503
00:26:22,455 --> 00:26:23,622
To have this distinction...
504
00:26:23,665 --> 00:26:25,332
Ganymede must have
sufficient mass...
505
00:26:25,875 --> 00:26:27,543
and a hot inner core.
506
00:26:27,961 --> 00:26:29,420
Its mass is obvious...
507
00:26:29,462 --> 00:26:30,963
but where the heat
is coming from...
508
00:26:31,006 --> 00:26:35,175
is a bit of a mystery.
509
00:26:35,218 --> 00:26:39,597
Ganymede is affected by both
lo and Europa's tidal forces.
510
00:26:39,639 --> 00:26:42,099
But the measurements
on its orbit indicate...
511
00:26:42,142 --> 00:26:45,269
that it's round enough to avoid
the squashing and stretching...
512
00:26:45,312 --> 00:26:48,731
that its smaller cousins
endure from Jupiter.
513
00:26:48,773 --> 00:26:50,065
The thought is...
514
00:26:50,108 --> 00:26:52,860
maybe something happened
in Ganymede's past...
515
00:26:52,902 --> 00:26:55,112
to change
its orbit slightly...
516
00:26:55,155 --> 00:26:59,033
and maybe its eccentricity
got kind of haywire...
517
00:26:59,075 --> 00:27:00,159
for a little while...
518
00:27:00,201 --> 00:27:02,911
and generated a lot of heat
within Ganymede...
519
00:27:02,954 --> 00:27:04,705
and caused the core
to be hot.
520
00:27:04,748 --> 00:27:05,831
We don't really know.
521
00:27:05,874 --> 00:27:07,458
What we do know...
522
00:27:07,500 --> 00:27:09,460
is that New Horizons'
recent flyby...
523
00:27:09,502 --> 00:27:10,878
of the Jovian system...
524
00:27:10,920 --> 00:27:13,881
gave us a tantalizing glimpse
of the wonders that await us...
525
00:27:13,923 --> 00:27:16,717
on Jupiter's alien moons.
526
00:27:16,760 --> 00:27:18,594
Scientists look forward
to the day...
527
00:27:18,637 --> 00:27:21,138
a lander touches down
on one of these moons...
528
00:27:21,181 --> 00:27:23,599
and starts to uncover
the secrets...
529
00:27:23,642 --> 00:27:28,145
of these mysterious worlds.
530
00:27:28,188 --> 00:27:31,649
Another icy moon orbits
the gas giant Saturn.
531
00:27:31,691 --> 00:27:34,818
It's too small to hold
onto its own atmosphere...
532
00:27:34,861 --> 00:27:35,986
but that doesn't stop it...
533
00:27:36,029 --> 00:27:40,366
from sapping the atmosphere
of its parent planet.
534
00:27:40,408 --> 00:27:42,660
Enceladus,
even though quite small...
535
00:27:42,702 --> 00:27:46,538
is named after a tribe of giants
in Greek mythology.
536
00:27:46,581 --> 00:27:48,499
Like lo and Europa...
537
00:27:48,541 --> 00:27:50,167
Enceladus
has an eccentric orbit...
538
00:27:50,210 --> 00:27:52,878
around its parent planet
Saturn.
539
00:27:52,921 --> 00:27:54,338
The tidal forces of Saturn...
540
00:27:54,381 --> 00:27:57,007
squeeze and knead
this tiny moon...
541
00:27:57,050 --> 00:28:01,053
and create heat
at its core.
542
00:28:01,346 --> 00:28:02,304
But unlike lo...
543
00:28:02,347 --> 00:28:04,640
it doesn't regurgitate
molten material...
544
00:28:04,683 --> 00:28:07,935
it coalesces
into a massive gas cloud.
545
00:28:07,977 --> 00:28:09,687
Water doesn't well up
to the surface...
546
00:28:09,729 --> 00:28:11,939
as it does on icy Europa.
547
00:28:11,981 --> 00:28:16,276
No, Enceladus actually
spits plumes of icy water...
548
00:28:16,319 --> 00:28:18,487
into the atmosphere of Saturn.
549
00:28:18,530 --> 00:28:19,905
So we don't call it
a volcano.
550
00:28:19,948 --> 00:28:21,532
It's more like a geyser.
551
00:28:21,574 --> 00:28:24,410
The water vapor
is then in orbit...
552
00:28:24,452 --> 00:28:26,078
around the little tiny moon...
553
00:28:26,121 --> 00:28:28,455
or because it's near Saturn...
554
00:28:28,498 --> 00:28:31,959
Saturn's gravity can pull it
into the planet.
555
00:28:32,001 --> 00:28:35,045
Interested by their work
on the torus of lo...
556
00:28:35,088 --> 00:28:37,715
Michael Mendillo and his team
at Boston University...
557
00:28:37,757 --> 00:28:40,134
began to consider
Enceladus' effect...
558
00:28:40,176 --> 00:28:42,761
on Saturn's atmosphere.
559
00:28:42,804 --> 00:28:45,556
And it turns out that water
is a wonderful catalyst...
560
00:28:45,598 --> 00:28:49,768
to have the ions
and electrons recombine.
561
00:28:49,811 --> 00:28:53,188
Before Cassini, scientists
relied on computer models...
562
00:28:53,231 --> 00:28:57,818
to determine atmospheric
conditions surrounding Saturn.
563
00:28:57,861 --> 00:28:59,653
They indicated that Saturn
should have...
564
00:28:59,696 --> 00:29:02,197
a very robust ionosphere.
565
00:29:02,240 --> 00:29:05,159
Surprisingly,
Cassini's data indicated...
566
00:29:05,201 --> 00:29:07,327
that Saturn's ionosphere
was only 10 percent...
567
00:29:07,370 --> 00:29:10,122
of what computer models
had predicted.
568
00:29:10,165 --> 00:29:13,584
It seems that the icy water
ejected from Enceladus...
569
00:29:13,626 --> 00:29:15,794
is neutralizing
the charged particles...
570
00:29:15,837 --> 00:29:18,839
in Saturn's ionosphere.
571
00:29:18,882 --> 00:29:23,427
Commence liftoff.
572
00:29:23,470 --> 00:29:25,929
Scientists had learned
quite by accident...
573
00:29:25,972 --> 00:29:31,143
the effect water can have
on Earth's atmosphere.
574
00:29:31,186 --> 00:29:35,773
In 1973, when Nasa launched
its Skylab workshop...
575
00:29:35,815 --> 00:29:39,193
it launched its last
gigantic Saturn V rocket...
576
00:29:39,235 --> 00:29:40,694
the moon rocket.
577
00:29:40,737 --> 00:29:42,613
And it had never
had a launch...
578
00:29:42,655 --> 00:29:44,531
that allowed
the space vehicle...
579
00:29:44,574 --> 00:29:47,785
to keep its engine burning
as high as the ionosphere.
580
00:29:47,827 --> 00:29:49,369
Well, this gigantic engine...
581
00:29:49,412 --> 00:29:51,872
dumped a ton per second
of water vapor...
582
00:29:51,915 --> 00:29:54,124
which comes out of
a giant rocket motor...
583
00:29:54,167 --> 00:29:55,292
into the ionosphere.
584
00:29:55,335 --> 00:29:59,129
And the ionosphere nearly
vanished on that day.
585
00:29:59,172 --> 00:30:02,007
It blew a gaping hole
in Earth's ionosphere...
586
00:30:02,050 --> 00:30:04,301
the top layer
of the atmosphere...
587
00:30:04,344 --> 00:30:07,346
a hole that took the sun's
ionizing radiation...
588
00:30:07,388 --> 00:30:11,058
24 hours to repair.
589
00:30:11,100 --> 00:30:13,060
However, on Saturn...
590
00:30:13,102 --> 00:30:14,478
where Enceladus
continuously dumps...
591
00:30:14,521 --> 00:30:18,106
six tons of water per minute
into its atmosphere...
592
00:30:18,149 --> 00:30:23,362
the long-term effects
have been significant.
593
00:30:23,404 --> 00:30:25,322
There's no worry that Enceladus
will strip away...
594
00:30:25,365 --> 00:30:28,826
its parent planet's
ionosphere completely...
595
00:30:28,868 --> 00:30:32,621
but this tiny moon,
only 300 miles in diameter...
596
00:30:32,664 --> 00:30:35,791
has gotten the attention
of the scientific community...
597
00:30:35,834 --> 00:30:39,461
and Saturn itself.
598
00:30:39,504 --> 00:30:42,297
While we prepare probes
to Phobos and Europa...
599
00:30:42,340 --> 00:30:45,342
and study data
from Enceladus and lo...
600
00:30:45,385 --> 00:30:47,344
an entirely new set of moons...
601
00:30:47,387 --> 00:30:50,597
has literally just come into the picture.
602
00:30:53,518 --> 00:30:57,020
Before the 1990s,
most astronomers agreed...
603
00:30:57,063 --> 00:31:00,482
that there were only 34 moons
in the solar system.
604
00:31:00,525 --> 00:31:03,694
Most of those were regular
moons like our own...
605
00:31:03,736 --> 00:31:06,530
spherical bodies
that orbit their host planet...
606
00:31:06,573 --> 00:31:08,532
in the same direction
it rotates.
607
00:31:08,575 --> 00:31:10,367
But a handful
of these satellites...
608
00:31:10,410 --> 00:31:14,955
were what's known
as irregular moons.
609
00:31:14,998 --> 00:31:17,916
These freakish moons
follow elongated orbits.
610
00:31:17,959 --> 00:31:19,668
Their orbits are often tilted...
611
00:31:19,711 --> 00:31:21,545
and they rotate
in the opposite direction...
612
00:31:21,588 --> 00:31:24,006
of their host planets.
613
00:31:24,048 --> 00:31:28,176
They look like flying potatoes
or splinters or misshapen lumps.
614
00:31:28,219 --> 00:31:30,804
They've been hard
to find before now...
615
00:31:30,847 --> 00:31:32,180
because they're very small...
616
00:31:32,223 --> 00:31:38,103
and they're also
usually very dark.
617
00:31:38,146 --> 00:31:40,647
The advent
of digital photography...
618
00:31:40,690 --> 00:31:42,482
and the use
of light-sensitive optics...
619
00:31:42,525 --> 00:31:46,737
changed the lunar terrain
within a decade.
620
00:31:46,779 --> 00:31:48,447
Dr. Brett Gladman...
621
00:31:48,489 --> 00:31:50,908
from the University
of British Columbia...
622
00:31:50,950 --> 00:31:54,328
discovered his first
irregular moon in 1997...
623
00:31:54,370 --> 00:31:57,247
at the Palomar Observatory.
624
00:31:57,290 --> 00:32:00,042
Since then, Dr. Gladman
has brought to light...
625
00:32:00,084 --> 00:32:05,213
17 previously hidden objects
in the solar system.
626
00:32:05,256 --> 00:32:07,925
So you detect objects
in the outer solar system...
627
00:32:07,967 --> 00:32:09,885
by observing them move...
628
00:32:09,928 --> 00:32:12,179
relevant to the background
stars and galaxies...
629
00:32:12,221 --> 00:32:13,931
which are stationary.
630
00:32:13,973 --> 00:32:16,391
So if you take
a picture of the sky...
631
00:32:16,434 --> 00:32:17,601
and you wait an hour...
632
00:32:17,644 --> 00:32:19,519
and you take another
picture of the sky...
633
00:32:19,604 --> 00:32:22,648
none of the stars in the galaxy
will have moved...
634
00:32:22,690 --> 00:32:26,026
but distant objects
in the outer solar system...
635
00:32:26,069 --> 00:32:28,946
will displace
by a visible amount...
636
00:32:28,988 --> 00:32:30,864
between the two pictures.
637
00:32:30,907 --> 00:32:32,157
And so by comparing
the two pictures...
638
00:32:32,200 --> 00:32:38,080
you can see, as we have here,
a moving target.
639
00:32:38,122 --> 00:32:41,166
The object could be a comet
or an asteroid...
640
00:32:41,209 --> 00:32:44,294
or, if it orbits a planet
in a retrograde fashion...
641
00:32:44,337 --> 00:32:47,798
a new irregular moon.
642
00:32:47,840 --> 00:32:50,467
Another important distinction
between regular moons...
643
00:32:50,510 --> 00:32:53,095
and their irregular
counterparts...
644
00:32:53,137 --> 00:32:55,681
irregular moons are captured.
645
00:32:55,723 --> 00:32:57,432
That is, they formed...
646
00:32:57,475 --> 00:32:59,017
independently
of their host planet...
647
00:32:59,060 --> 00:33:00,978
and most likely
were part of the debris...
648
00:33:01,020 --> 00:33:05,440
that originally formed
our solar system.
649
00:33:05,483 --> 00:33:08,735
Phoebe, the largest irregular
moon orbiting Saturn...
650
00:33:08,778 --> 00:33:11,405
is a classic example.
651
00:33:11,447 --> 00:33:14,783
Phoebe orbits Saturn
very far out.
652
00:33:14,826 --> 00:33:17,577
It has a very elliptical
and very inclined orbit.
653
00:33:17,620 --> 00:33:21,498
It orbits
in a retrograde direction.
654
00:33:21,541 --> 00:33:23,750
Voyager images suggested...
655
00:33:23,793 --> 00:33:25,961
that this thing looks like
it could be an asteroid...
656
00:33:26,004 --> 00:33:29,423
and so people thought maybe
it is a captured asteroid.
657
00:33:29,465 --> 00:33:34,052
Now we know from Cassini
it's a very waterized-rich body.
658
00:33:34,095 --> 00:33:36,847
That pretty much rules out
the asteroid belt.
659
00:33:36,889 --> 00:33:39,850
The thinking is that Phoebe
could very well have come...
660
00:33:39,892 --> 00:33:41,018
from the Kuiper Belt...
661
00:33:41,060 --> 00:33:45,981
way out in the outer reaches
of the solar system.
662
00:33:46,274 --> 00:33:49,234
The Kuiper Belt is thought
to be the debris left over...
663
00:33:49,277 --> 00:33:51,069
after the solar system formed.
664
00:33:51,112 --> 00:33:54,990
It revolves around the sun
beyond the orbit of Pluto.
665
00:33:55,033 --> 00:33:56,867
However, another theory...
666
00:33:56,909 --> 00:34:02,748
suggests something
altogether different.
667
00:34:02,790 --> 00:34:05,375
It's much more likely
that Phoebe formed...
668
00:34:05,418 --> 00:34:07,586
in an independent orbit
around the sun...
669
00:34:07,628 --> 00:34:11,798
and then was captured into orbit
around Saturn...
670
00:34:11,841 --> 00:34:13,383
whereas most of
the other objects...
671
00:34:13,426 --> 00:34:15,469
that formed
near Saturn's distance...
672
00:34:15,511 --> 00:34:17,012
were either accreted
by Saturn...
673
00:34:17,055 --> 00:34:20,599
or ejected
from the solar system.
674
00:34:20,641 --> 00:34:23,477
Phoebe would then be made
of the planetary debris...
675
00:34:23,519 --> 00:34:26,480
that was floating around Saturn
at the time of its birth.
676
00:34:26,522 --> 00:34:29,775
And possibly it;s made up
of different material...
677
00:34:29,817 --> 00:34:33,028
than some of the irregular
moons orbiting Jupiter.
678
00:34:33,071 --> 00:34:34,404
If this is the case...
679
00:34:34,447 --> 00:34:38,158
astrogeologists may be able
to discern and compare...
680
00:34:38,201 --> 00:34:39,367
the different ingredients...
681
00:34:39,410 --> 00:34:42,954
that birthed
these two gas giants.
682
00:34:42,997 --> 00:34:45,624
Three main theories
currently exist...
683
00:34:45,666 --> 00:34:48,835
as to how Phoebe and its other
irregular counterparts...
684
00:34:48,878 --> 00:34:50,587
lost their independence.
685
00:34:50,630 --> 00:34:52,923
Two suggest the irregulars
were captured...
686
00:34:52,965 --> 00:34:55,300
as the solar system
was still forming...
687
00:34:55,343 --> 00:34:57,302
and the planets were
still an accreting blob...
688
00:34:57,345 --> 00:34:59,429
of gas and debris.
689
00:34:59,472 --> 00:35:02,390
The gas-drag theory
is the most straightforward.
690
00:35:02,433 --> 00:35:06,144
Thick gases were swirling
around the accreting planet...
691
00:35:06,187 --> 00:35:08,188
when a comet, asteroid...
692
00:35:08,231 --> 00:35:10,315
or a shattered
combination of both...
693
00:35:10,358 --> 00:35:13,777
passed through
the gaseous mixture.
694
00:35:13,820 --> 00:35:15,529
We know that
the giant planets...
695
00:35:15,571 --> 00:35:18,031
built their regular
satellite systems...
696
00:35:18,074 --> 00:35:21,910
in a large accretion disc
around each of the planets...
697
00:35:21,953 --> 00:35:23,745
sort of like a mini
little solar system...
698
00:35:23,788 --> 00:35:25,789
forming around each planet.
699
00:35:25,832 --> 00:35:28,458
And the gas and dust
that was in that disc...
700
00:35:28,501 --> 00:35:31,628
can also serve
in its outer regions...
701
00:35:31,671 --> 00:35:33,547
as a source of friction...
702
00:35:33,589 --> 00:35:37,008
where passing planetesimals
formed independently...
703
00:35:37,051 --> 00:35:41,096
are slowed down a little bit
and captured into orbit.
704
00:35:41,139 --> 00:35:44,266
The second theory is really
a variation on the first.
705
00:35:44,308 --> 00:35:47,310
It's sometimes called
the pull-down theory.
706
00:35:47,353 --> 00:35:49,312
Here, instead of an object
being caught...
707
00:35:49,355 --> 00:35:52,482
by simply passing through
the accreting gases...
708
00:35:52,525 --> 00:35:54,317
it is unsuspectingly pulled...
709
00:35:54,360 --> 00:35:56,194
into the forming
planet's orbit...
710
00:35:56,237 --> 00:35:59,948
by its growing
gravitational pull.
711
00:35:59,991 --> 00:36:01,992
The gas-drag and the pull-down
theories of capture...
712
00:36:02,034 --> 00:36:04,661
work well for both
Jupiter and Saturn...
713
00:36:04,704 --> 00:36:06,872
because their mixture
of ingredients...
714
00:36:06,914 --> 00:36:13,879
was massive enough to slow down
these passing objects.
715
00:36:13,921 --> 00:36:18,341
But what about the icy giants
Neptune and Uranus?
716
00:36:18,384 --> 00:36:22,179
Because of the extreme cold,
they formed much more slowly...
717
00:36:22,221 --> 00:36:23,763
and it's difficult to believe...
718
00:36:23,806 --> 00:36:26,558
that their icy accretion mixture
contained enough mass...
719
00:36:26,601 --> 00:36:31,813
to snare a passing piece
of the solar system.
720
00:36:31,856 --> 00:36:36,318
Yet both icy giants have
their own irregular moons...
721
00:36:36,360 --> 00:36:41,740
hence, a third theory:
three-body interaction.
722
00:36:41,991 --> 00:36:43,033
We discover
that many of the objects...
723
00:36:43,075 --> 00:36:44,701
are actually
more than one object.
724
00:36:44,744 --> 00:36:46,453
They're usually two objects...
725
00:36:46,495 --> 00:36:50,165
often that because they're both
more or less the same size...
726
00:36:50,208 --> 00:36:53,210
as the other
in a binary relationship.
727
00:36:53,252 --> 00:36:54,711
Instead of being a big object...
728
00:36:54,754 --> 00:36:58,298
with a small object going in
an orbit around it like this...
729
00:36:58,341 --> 00:37:00,759
it's two more or less
similar-sized objects...
730
00:37:00,801 --> 00:37:02,677
going around a common orbit.
731
00:37:02,720 --> 00:37:05,805
Between the two of them
is called the barycenter.
732
00:37:05,848 --> 00:37:07,390
A binary pair exists...
733
00:37:07,433 --> 00:37:09,559
when two objects
of the same size...
734
00:37:09,602 --> 00:37:11,519
are tight enough
to the barycenter...
735
00:37:11,562 --> 00:37:16,149
to prevent a third larger object
from splitting them apart.
736
00:37:16,192 --> 00:37:17,734
But when one
of the binary pair...
737
00:37:17,777 --> 00:37:20,278
is significantly larger
than the other...
738
00:37:20,321 --> 00:37:22,155
the more massive
third object...
739
00:37:22,198 --> 00:37:25,784
has a greater chance
of separating them.
740
00:37:25,826 --> 00:37:28,411
The smaller one will tend
to have the much bigger orbit...
741
00:37:28,454 --> 00:37:30,872
swing out further.
742
00:37:30,915 --> 00:37:32,540
This brings
the smaller object...
743
00:37:32,583 --> 00:37:35,168
close enough to the planet
to be captured...
744
00:37:35,211 --> 00:37:41,508
while its partner is slung out
into an independent orbit.
745
00:37:41,550 --> 00:37:45,553
One bizarre moon seems
to defy classification.
746
00:37:45,596 --> 00:37:49,057
Triton orbits Neptune
in a retrograde fashion...
747
00:37:49,100 --> 00:37:51,268
counter to Neptune's rotation.
748
00:37:51,310 --> 00:37:53,436
That would make it
an irregular moon...
749
00:37:53,479 --> 00:37:55,146
except that it's spherical...
750
00:37:55,189 --> 00:37:57,357
and orbits
close to the equator...
751
00:37:57,400 --> 00:38:00,277
with an almost perfectly
round circumference...
752
00:38:00,319 --> 00:38:07,033
a classical description
of a regular moon.
753
00:38:07,076 --> 00:38:10,203
It also spews out
mysterious icy plumes...
754
00:38:10,246 --> 00:38:12,372
with some indication
that it once was...
755
00:38:12,415 --> 00:38:16,334
or possibly still is
volcanically active.
756
00:38:20,381 --> 00:38:23,967
Before Voyager 2 ventured
into the outer solar system...
757
00:38:24,010 --> 00:38:26,636
Neptune's moon Triton
was assumed to be...
758
00:38:26,679 --> 00:38:28,972
a geologically dead
ball of rock...
759
00:38:29,015 --> 00:38:32,475
about the size
of our own moon.
760
00:38:32,518 --> 00:38:34,811
When Voyager
beamed back photographs...
761
00:38:34,854 --> 00:38:36,771
revealing a world
with mountains...
762
00:38:36,814 --> 00:38:39,983
fault lines, and fissures...
763
00:38:40,026 --> 00:38:42,152
indicative
of tectonic movement...
764
00:38:42,194 --> 00:38:45,697
as well as a surprisingly
thick atmosphere...
765
00:38:45,740 --> 00:38:49,326
scientists were amazed.
766
00:38:49,368 --> 00:38:51,244
Geologic forces
usually associated...
767
00:38:51,287 --> 00:38:54,080
with much warmer
and larger planets...
768
00:38:54,123 --> 00:38:56,416
might be occurring
on a frozen moon...
769
00:38:56,459 --> 00:38:59,002
slightly smaller
than our own.
770
00:38:59,045 --> 00:39:02,881
Voyager detected
no active volcanoes in 1989.
771
00:39:02,923 --> 00:39:05,842
However, like Saturn's
moon Enceladus...
772
00:39:05,885 --> 00:39:10,972
geysers periodically erupted
from the planet's surface.
773
00:39:11,015 --> 00:39:12,682
What's really stunning
about Triton...
774
00:39:12,725 --> 00:39:14,225
is not just that it has...
775
00:39:14,268 --> 00:39:16,936
some unique geological
processes occurring...
776
00:39:16,979 --> 00:39:18,355
but the fact
that they're happening...
777
00:39:18,397 --> 00:39:22,108
even though Triton
is an irregular moon.
778
00:39:22,151 --> 00:39:24,444
Most large moons
in the solar system...
779
00:39:24,487 --> 00:39:26,696
are regular satellites...
780
00:39:26,739 --> 00:39:29,532
with the very important
exception of Triton...
781
00:39:29,825 --> 00:39:31,242
Neptune's largest moon...
782
00:39:31,285 --> 00:39:33,620
which orbits the wrong way.
783
00:39:33,662 --> 00:39:37,999
So Triton is thought to have
been a captured object.
784
00:39:38,042 --> 00:39:41,252
A captured moon that acts
like a regular one.
785
00:39:41,295 --> 00:39:43,296
How did an object
the size of Triton...
786
00:39:43,339 --> 00:39:44,672
slow down enough...
787
00:39:44,715 --> 00:39:47,884
not to either pass through
Neptune's atmosphere...
788
00:39:47,927 --> 00:39:52,514
or collide directly
into the icy planet?
789
00:39:57,436 --> 00:39:58,770
There's no sure bet...
790
00:39:58,813 --> 00:40:02,190
but some theories
carry better odds.
791
00:40:02,233 --> 00:40:04,859
Much like gamblers
at the roulette wheel...
792
00:40:04,902 --> 00:40:06,986
Triton and Neptune
played the odds...
793
00:40:07,029 --> 00:40:10,573
and trusted to luck.
794
00:40:10,616 --> 00:40:12,742
Place your bets.
Get lucky now.
795
00:40:12,785 --> 00:40:15,078
In roulette, there are
several ways to bet.
796
00:40:15,121 --> 00:40:17,163
Each one carries
different odds.
797
00:40:17,206 --> 00:40:18,957
And like most
games of chance...
798
00:40:18,999 --> 00:40:22,335
the longer the odds,
the greater the payoff.
799
00:40:22,378 --> 00:40:24,629
20 black, 20 black even.
800
00:40:24,672 --> 00:40:26,631
There are at least
three possible ways...
801
00:40:26,674 --> 00:40:29,300
Triton could've been
captured by Neptune.
802
00:40:34,515 --> 00:40:37,058
All three hypotheses
are physically possible...
803
00:40:37,101 --> 00:40:40,228
but the first one,
the idea of gas drag...
804
00:40:40,271 --> 00:40:41,271
is the least likely...
805
00:40:41,313 --> 00:40:43,690
simply because
the period of time...
806
00:40:43,732 --> 00:40:46,734
which Neptune had
a disc of gas and dust...
807
00:40:46,777 --> 00:40:49,612
which could've captured
a proto Triton object...
808
00:40:49,655 --> 00:40:51,781
it was a very short
period of time...
809
00:40:51,824 --> 00:40:54,868
and so the window of opportunity
was very small.
810
00:40:54,910 --> 00:40:56,995
So that's like betting
on the green zero...
811
00:40:57,037 --> 00:40:59,998
on the roulette table.
812
00:41:00,040 --> 00:41:03,251
More likely is the possibility
that the proto Triton...
813
00:41:03,294 --> 00:41:04,961
sometime in
the solar system history...
814
00:41:05,004 --> 00:41:08,965
crashed into a set
of a regular...
815
00:41:09,008 --> 00:41:10,341
middle-sized icy satellites...
816
00:41:10,384 --> 00:41:13,678
and it was the collision
which gave us Triton.
817
00:41:13,721 --> 00:41:16,764
And that's like betting
on the first third...
818
00:41:16,807 --> 00:41:18,057
of the numbers
on the roulette table...
819
00:41:18,100 --> 00:41:19,642
so you have, like,
a one-in-three chance...
820
00:41:19,685 --> 00:41:22,729
of that taking place.
821
00:41:22,771 --> 00:41:26,316
Your best bet is to bet
on the even numbers.
822
00:41:26,358 --> 00:41:27,609
There you have
a one-in-two chance...
823
00:41:27,651 --> 00:41:28,818
of things happening.
824
00:41:28,861 --> 00:41:32,447
And the best bet for the capture
of Triton right now...
825
00:41:32,490 --> 00:41:35,116
is this binary capture
hypothesis because there...
826
00:41:35,159 --> 00:41:38,161
we know there are
probably thousands of objects...
827
00:41:38,204 --> 00:41:40,538
that had existed
in the Kuiper Belt...
828
00:41:40,581 --> 00:41:42,165
that would have
the right size...
829
00:41:42,208 --> 00:41:46,044
and be partnered with
another even larger object...
830
00:41:46,086 --> 00:41:50,840
and Neptune
could capture one of them.
831
00:41:50,883 --> 00:41:52,842
No one knows for sure
which number paid...
832
00:41:52,885 --> 00:41:55,136
in the early days
of the solar system...
833
00:41:55,179 --> 00:41:57,222
when Neptune captured Triton.
834
00:41:57,264 --> 00:42:00,016
However, once Triton
began orbiting Neptune...
835
00:42:00,059 --> 00:42:01,726
in an irregular fashion...
836
00:42:01,769 --> 00:42:05,813
it started obliterating anything
that got in its way.
837
00:42:05,856 --> 00:42:10,318
Neptune doesn't have a very
regular system of satellites.
838
00:42:10,361 --> 00:42:11,861
It's thought
that the capture of Triton...
839
00:42:11,904 --> 00:42:14,405
disrupted what would've
otherwise been...
840
00:42:14,448 --> 00:42:16,449
a nice regular system...
841
00:42:16,492 --> 00:42:19,827
like the other
large planets have.
842
00:42:20,120 --> 00:42:22,872
It's as if Triton was angry
at losing its freedom...
843
00:42:22,915 --> 00:42:26,376
and took it out on Neptune's
other hapless moons.
844
00:42:26,418 --> 00:42:31,089
But where did
this headstrong moon come from?
845
00:42:31,131 --> 00:42:33,091
Data from Voyager 2 indicates...
846
00:42:33,133 --> 00:42:36,427
that Triton's density
nearly matches Pluto's.
847
00:42:36,470 --> 00:42:37,804
This suggests a kinship...
848
00:42:37,846 --> 00:42:41,808
that no other regular moon
can claim.
849
00:42:41,850 --> 00:42:43,768
It's suspected
that Pluto and Triton...
850
00:42:43,811 --> 00:42:48,106
are both objects that originated
in the Kuiper Belt.
851
00:42:48,148 --> 00:42:49,148
The outer solar system...
852
00:42:49,191 --> 00:42:50,775
consisted of
these large objects...
853
00:42:50,818 --> 00:42:53,278
going every which way,
essentially.
854
00:42:53,320 --> 00:42:56,281
And some of them formed
giant planets themselves...
855
00:42:56,323 --> 00:42:58,032
and some of them
were tossed out further...
856
00:42:58,075 --> 00:43:01,786
where they sit today
in the Kuiper Belt.
857
00:43:01,829 --> 00:43:03,580
Collisions, accretions...
858
00:43:03,622 --> 00:43:05,206
and even captures
have diminished...
859
00:43:05,249 --> 00:43:07,500
what was once
a major thoroughfare...
860
00:43:07,543 --> 00:43:10,753
of planetary
building materials.
861
00:43:10,796 --> 00:43:11,921
Early in solar system
history...
862
00:43:11,964 --> 00:43:14,716
the Kuiper Belt had
far more larger objects...
863
00:43:14,758 --> 00:43:16,884
that may have once had
a cumulative mass...
864
00:43:16,927 --> 00:43:18,845
of 50 Earths...
865
00:43:18,887 --> 00:43:20,597
whereas the current
Kuiper Belt mass...
866
00:43:20,639 --> 00:43:23,016
is much less
than one Earth.
867
00:43:23,058 --> 00:43:24,767
What's left
of the Kuiper Belt...
868
00:43:24,810 --> 00:43:27,103
is as old
as the solar system itself.
869
00:43:27,146 --> 00:43:29,522
The material that makes up
the binary objects...
870
00:43:29,565 --> 00:43:32,650
shards of collisions,
and even some alien moons...
871
00:43:32,693 --> 00:43:36,613
hasn't changed
in over four billion years.
872
00:43:36,655 --> 00:43:37,989
It's amazing
how really different...
873
00:43:38,032 --> 00:43:40,950
all the moons of the outer
solar system are.
874
00:43:40,993 --> 00:43:42,368
When I first got interested
in astronomy...
875
00:43:42,411 --> 00:43:43,494
as a kid in the 1960s...
876
00:43:43,537 --> 00:43:45,038
we hadn't seen
any of these moons.
877
00:43:45,080 --> 00:43:46,914
They were little dots
in your telescope...
878
00:43:46,957 --> 00:43:48,333
and so we had no idea...
879
00:43:48,375 --> 00:43:50,126
how radically different
they could be.
880
00:43:50,169 --> 00:43:51,461
But I think the most
shocking thing...
881
00:43:51,503 --> 00:43:52,754
was how, you know,
much variety there is...
882
00:43:52,796 --> 00:43:54,088
in the solar system.
883
00:43:54,131 --> 00:43:56,132
I think that blew me
and everybody else away...
884
00:43:56,175 --> 00:43:59,719
who lived through
that period.
885
00:43:59,762 --> 00:44:01,095
As we travel back home...
886
00:44:01,138 --> 00:44:04,182
from the frigid outskirts
of our solar system...
887
00:44:04,224 --> 00:44:06,726
awed by the vastness
of the universe...
888
00:44:06,769 --> 00:44:08,978
and the majesty
of the planets...
889
00:44:09,021 --> 00:44:11,439
it's worth it to pause
and take notice...
890
00:44:11,482 --> 00:44:14,108
of the small worlds
in the shadows.
891
00:44:14,151 --> 00:44:18,154
Those alien moons that were once
considered afterthoughts...
892
00:44:18,197 --> 00:44:20,156
hold mysteries just waiting...
893
00:44:20,199 --> 00:44:24,202
for human curiosity
to solve.
71280
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