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She has traveled nearly
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four billion kilometers.
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Delivered a probe to the
surface of a toxic moon.
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And produced science nine years longer
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than originally planned.
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She discovered flowing liquids
where none were expected.
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Phantasmagorical structures
on a planet's icy rings.
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A weirdly breathing magnetosphere.
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And a possible abode of life.
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00:00:53,340 --> 00:00:56,710
On a tiny world with a
startling atmosphere.
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00:01:01,820 --> 00:01:05,940
Now, after 20 years in
space, controllers have sent
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the Cassini spacecraft
into a daring spiral
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to end her remarkable journey.
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00:01:13,990 --> 00:01:16,730
Streaking along Saturn's upper atmosphere
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at more than 124,000 kilometers per hour,
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Cassini streams data and
images back to Earth,
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until heat and turbulence tear her apart.
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Three, two, one.
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00:01:53,290 --> 00:01:56,180
And liftoff of the Cassini spacecraft
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on a billion mile trek to Saturn.
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On the evening
of October 15th, 1997,
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a powerful Titan 4B booster leaves
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launch complex 40 at the
Kennedy Space Center.
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All systems go.
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The product of two decades
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of intense collaboration between NASA
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and the European Space Agency,
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in particular the Italian Space Agency.
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And the
solid rocket boosters
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have been jettisoned.
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Some on Earth
have protested this moment.
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They fear that if the launch
fails, Cassini's nuclear
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electric generator will
spread radioactive plutonium.
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No nukes in
space, no nukes in space.
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As she glides
outward on a nearly seven-year
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transit to Saturn, scientists organize
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their investigations based
on past probes' findings.
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Their questions nest within one another,
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like the giant planet's concentric rings.
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Does Saturn have a solid surface?
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00:03:14,860 --> 00:03:18,460
Or do its clouds thicken
down to extreme densities,
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perhaps creating exotic forms of matter?
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Like metallic hydrogen.
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00:03:32,490 --> 00:03:34,150
Is there a rocky core?
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00:03:36,470 --> 00:03:38,360
Why are the rings so bright?
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How old are they?
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00:03:46,200 --> 00:03:50,060
What's going on beneath the
thick orange clouds of Titan,
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Saturn's largest moon?
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How are Saturn's moons and rings related?
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00:04:07,120 --> 00:04:09,420
What will this giant planet tell us
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about the evolution of
solar systems, and of life?
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00:04:21,380 --> 00:04:24,860
At its distance of nearly a
billion and half kilometers
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from the sun, Saturn's orbit
lasts 29.5 Earth years.
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00:04:33,160 --> 00:04:35,160
Over the past Saturn year,
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Earth has added some 2.5 billion people.
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Average life expectancy rose
from age 64 to almost 72.
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The internet has exploded.
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It now has almost four billion users,
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with the half the world's
population now online.
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00:05:05,730 --> 00:05:09,920
In the time of Cassini,
our world has been consumed
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with new ways of communicating,
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00:05:13,650 --> 00:05:14,560
connecting,
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00:05:16,960 --> 00:05:17,793
working,
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00:05:20,290 --> 00:05:21,123
living,
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and seeing each other.
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Saturn is the Roman name for Chronos,
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the Greek God of time,
who ate his children
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in a fit of jealousy.
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In myth, as in the ever-changing universe,
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time is the devourer of all things.
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To catch up with Saturn,
mission planners have sent
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Cassini on a series of fly-bys,
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each time hitching a ride
on the planet's gravity
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to speed her on her way.
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00:06:15,210 --> 00:06:18,780
Pioneer 11 flew by Saturn in 1979.
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Voyager One in 1980.
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And Voyager Two in 1981.
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Cassini will become the
first craft to orbit Saturn,
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captured by Saturn's
gravity on June 30th, 2004.
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00:06:50,130 --> 00:06:53,740
Cassini's prime mission
was to be four years,
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but she will remain healthy far longer.
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Her assignments will be extended twice,
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an additional two-year equinox mission,
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and a seven-year solstice mission.
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Yet Cassini's entire exploration
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will span less than half a Saturn year.
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From late winter
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through early summer.
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00:07:23,300 --> 00:07:28,130
The Saturn system lies 9.5
astronomical units from the sun.
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That's nearly 10 times
farther out than Earth.
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The whole grand clockworks speeds along
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at 34,821 kilometers every hour,
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more than 10 times faster than
a bullet fired from a gun.
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The planet spins fast,
rotating about its axis
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once every 10 hours and 39 minutes.
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So while a year on Saturn
lasts only Earth 11,000 days,
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it's about 24,500 Saturn days.
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Made up mostly of hydrogen and helium,
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00:08:12,590 --> 00:08:15,600
Saturn is the least
dense of all the planets.
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It's often said, if you could
find a bathtub big enough,
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Saturn would float.
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00:08:23,210 --> 00:08:26,950
That's not quite accurate,
but its density is lower
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than that of the liquid
water in Earth's oceans.
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00:08:32,220 --> 00:08:33,500
And it's big.
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You could pour 764 Earths
into the volume of Saturn.
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This mission is officially
named Cassini-Huygens,
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honoring two remarkable men
of 17th-century science.
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The French-Italian
Giovanni Domenico Cassini,
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also known as Jean Dominique Cassini,
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00:09:00,180 --> 00:09:02,640
and the Dutch Christiaan Huygens.
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00:09:04,240 --> 00:09:07,020
Key players in the scientific revolution,
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00:09:07,020 --> 00:09:10,350
they collaborated and competed
throughout their lives.
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In the process, transforming
astrology into astrophysics.
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As director of the Paris Observatory,
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Cassini built and refined
long-tube refractor telescopes.
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00:09:30,270 --> 00:09:33,620
But Huygens found a way to
remove the cumbersome tube,
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inventing the so-called air telescope,
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and its better engineered eyepiece.
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00:09:45,350 --> 00:09:50,350
In 1665, Cassini co-discovered
Jupiter's great red spot,
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and used it to time the
big planet's rotation.
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00:09:59,100 --> 00:10:01,967
Huygens, applying Galileo's ideas,
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00:10:01,967 --> 00:10:04,850
invented the pendulum clock
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00:10:04,850 --> 00:10:07,530
and developed a balanced spring watch,
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00:10:07,530 --> 00:10:11,140
both pivotal innovations
in the study of space time.
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00:10:14,800 --> 00:10:18,250
Cassini published maps of
surface markings on Mars,
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00:10:19,330 --> 00:10:22,100
though Huygens had
actually seen them first.
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00:10:24,000 --> 00:10:26,710
And Huygens pegged the
length of the Martian day
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00:10:26,710 --> 00:10:29,440
at 24 and one-half hours,
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00:10:29,440 --> 00:10:33,710
just seven minutes shy of the
correct figure we use today.
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00:10:35,980 --> 00:10:40,403
By getting parallax observations
of Mars, Cassini was
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00:10:40,403 --> 00:10:44,220
the first to estimate the
size of our solar system.
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00:10:47,520 --> 00:10:51,480
And Cassini used Galileo's
method of measuring time
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by watching eclipses of Jupiter's moons
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00:10:54,540 --> 00:10:57,410
to lay out lines of longitude on Earth.
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00:11:00,490 --> 00:11:03,980
Endeavoring to perfect the
geometry of optical lenses,
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00:11:05,210 --> 00:11:08,440
Huygens developed the
wave theory of light,
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00:11:08,440 --> 00:11:11,780
setting the stage for
today's quantum mechanics.
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00:11:14,670 --> 00:11:18,300
Cassini explained the
so-called zodiacal light,
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00:11:18,300 --> 00:11:21,300
seen by astronomers as
the reflection of sunlight
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00:11:21,300 --> 00:11:24,140
off dust in the plane of the solar system.
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00:11:25,672 --> 00:11:28,140
Toward the end of his
life, Huygens determined
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00:11:28,140 --> 00:11:31,130
liquid water to be a
key factor in searching
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00:11:31,130 --> 00:11:35,360
for extraterrestrial life,
a quest now undertaken
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00:11:35,360 --> 00:11:39,764
by the Cassini spacecraft
and its Huygens probe.
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00:11:51,240 --> 00:11:55,880
We've known Saturn as the
ringed planet since 1655,
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when Cristiaan Huygens
explained what Galileo
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had seen 45 years earlier.
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00:12:03,330 --> 00:12:06,650
But if you were standing
on most of Saturn's moons,
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you would have a hard time
actually seeing the rings.
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00:12:11,180 --> 00:12:14,550
Because most moons ride in the ring plane,
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you could only view them edge on.
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00:12:18,260 --> 00:12:21,490
From the right, watch tiny Prometheus,
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just 86 kilometers across,
pass behind big Tethys,
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1,062 kilometers side.
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00:12:32,676 --> 00:12:35,600
Little Pandora scoots
through from left to right.
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00:12:42,240 --> 00:12:46,310
Here, medium sized Mimas,
traveling 14 kilometers
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00:12:46,310 --> 00:12:49,710
per second, glides in
front of the larger Rhea,
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at eight kilometers per second.
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00:13:18,510 --> 00:13:20,070
When Cassini launched,
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00:13:21,190 --> 00:13:24,686
18 moons were known to orbit Saturn,
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and 13 more were suspected.
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By the end of Cassini's mission,
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astronomers will confirm 53,
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with another nine marked as conditional.
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Only one of them is huge.
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Titan.
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In 1655, Christiaan Huygens
was the first to observe Titan.
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00:13:54,210 --> 00:13:59,060
Giovanni Domenico Cassini
discerned Iapetus in 1671,
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Rhea in 1672,
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Dione in 1684,
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and Tethys in 1684.
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00:14:11,470 --> 00:14:15,000
The skywatching siblings
William and Caroline Herschel
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found Mimas and Enceladus in 1789.
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00:14:22,750 --> 00:14:25,930
In 1848, Hyperion was spotted
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by the father-son team of
William and George Bond
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00:14:30,430 --> 00:14:32,580
in the U.S. and William
Lassell in the U.K.
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Phoebe was the first moon to be discovered
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through photography, by
the American astronomer
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William Henry Pickering in 1898.
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00:14:44,660 --> 00:14:48,530
Some of Saturn's moons are
probably captured objects,
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particularly those in
retrograde orbits like Phoebe.
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They orbit backwards, in
the opposite direction
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from the rotation of the planet.
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00:15:02,010 --> 00:15:04,780
Each Saturnian moon is a unique jewel
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in the majestic planet's
elaborate necklace.
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Before Cassini, no one suspected Enceladus
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to be anything other than a
dead ball of rock and ice.
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00:16:10,980 --> 00:16:14,510
But scientific sleuthing led
to a remarkable discovery.
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Enceladus is about 482
kilometers in diameter.
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00:16:23,620 --> 00:16:27,330
It would fit neatly between
Los Angeles and San Francisco.
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00:16:30,400 --> 00:16:35,000
The first good closeup,
taken by Voyager Two in 1981,
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00:16:35,000 --> 00:16:37,220
showed the globe was remarkably bright
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00:16:37,220 --> 00:16:38,750
and free of craters.
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00:16:41,520 --> 00:16:46,050
In fact, Enceladus is the
whitest body in the solar system.
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The first hints of a more complex story
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come from Cassini's magnetometer.
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00:16:54,770 --> 00:16:56,680
The moon's magnetic signature
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00:16:57,590 --> 00:16:59,400
looks more like that of a comet.
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00:17:01,880 --> 00:17:05,560
Field lines are bent around
Enceladus' south pole.
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00:17:07,490 --> 00:17:10,430
A closer fly-by shows
the southern polar region
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00:17:10,430 --> 00:17:12,610
has been recently resurfaced.
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00:17:14,490 --> 00:17:17,670
Cassini's infrared
spectrometer indicates the area
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00:17:17,670 --> 00:17:20,910
is about 100 degrees warmer
than the rest of the moon.
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00:17:22,420 --> 00:17:25,860
And that heat signature
aligns with four prominent
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00:17:25,860 --> 00:17:30,020
tiger stripes appearing across
the moon's southern terrain.
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00:17:31,610 --> 00:17:33,920
They turn out to be fissures,
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00:17:33,920 --> 00:17:36,040
cracks in the icy surface.
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00:17:36,990 --> 00:17:41,270
Each about 150 kilometers long
and about one kilometer wide.
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00:17:42,630 --> 00:17:45,950
Scientists name them Alexandria,
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00:17:45,950 --> 00:17:49,350
Cairo, Baghdad and Damascus.
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00:17:50,920 --> 00:17:54,230
From each, jets of water
vapor and water ice
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00:17:54,230 --> 00:17:55,920
shoot out into space.
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00:18:06,740 --> 00:18:10,440
Cassini eventually locates
more than 100 of these geysers.
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00:18:16,074 --> 00:18:18,171
Mission planners arrange more fly-bys
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00:18:18,171 --> 00:18:21,800
and in October of 2015,
navigate within 50 kilometers
216
00:18:21,800 --> 00:18:25,830
of Enceladus' South Pole,
and right through the jets,
217
00:18:25,830 --> 00:18:29,640
giving the instruments a
chance to taste and smell them.
218
00:18:31,620 --> 00:18:34,050
It's mostly water ice.
219
00:18:34,050 --> 00:18:38,670
There's also some ammonia,
methane and carbon dioxide,
220
00:18:38,670 --> 00:18:41,390
key compounds associated with life.
221
00:18:43,130 --> 00:18:47,340
And hydrogen gas, which
microbes, if there are any,
222
00:18:47,340 --> 00:18:49,840
could be using as a source of energy.
223
00:18:51,910 --> 00:18:55,870
Some of the particles are
salty, like frozen sea spray,
224
00:18:55,870 --> 00:18:58,290
flavored by sodium and potassium.
225
00:19:02,210 --> 00:19:05,660
The science team imagines
that a large subsurface ocean
226
00:19:05,660 --> 00:19:07,760
lies beneath the icy crust.
227
00:19:09,680 --> 00:19:13,610
As it sloshes around, carbon
dioxide makes it fizzy,
228
00:19:13,610 --> 00:19:15,000
like bottled soda.
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00:19:16,240 --> 00:19:18,710
When it finds a path to lower pressure,
230
00:19:18,710 --> 00:19:21,620
through the cracks of the tiger stripes,
231
00:19:21,620 --> 00:19:25,390
it sprays out into space like
champagne when the cork pops.
232
00:19:28,680 --> 00:19:31,240
Most of these salty
water particles fall back
233
00:19:31,240 --> 00:19:35,550
to the ground as snow,
decorating and repairing
234
00:19:35,550 --> 00:19:37,380
the surface of Enceladus.
235
00:19:41,030 --> 00:19:44,450
But some escape Enceladus' weak gravity.
236
00:19:47,820 --> 00:19:52,179
So Enceladus rides a misty
ring of its own creation.
237
00:19:58,300 --> 00:20:00,960
Were the moon to shut off its water jets,
238
00:20:00,960 --> 00:20:03,780
this e-ring would dissipate completely
239
00:20:03,780 --> 00:20:05,130
within a few hundred years.
240
00:20:08,610 --> 00:20:12,060
Tracking and modeling icy
tendrils made by interacting
241
00:20:12,060 --> 00:20:15,630
geyser jets lets researchers calculate
242
00:20:15,630 --> 00:20:19,110
how much mass Enceladus is
pumping into Saturn's rings.
243
00:20:27,720 --> 00:20:30,930
Enceladus orbits in resonance
with the moon Dione.
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00:20:34,370 --> 00:20:37,520
Their dance is thought to
heat their rocky cores.
245
00:20:40,120 --> 00:20:43,710
It's likely that Dione too
has a subsurface ocean.
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00:20:46,030 --> 00:20:48,710
Dione's big crater, Creusa,
247
00:20:48,710 --> 00:20:51,820
paints bright rays at least 500 kilometers
248
00:20:51,820 --> 00:20:54,412
across the moon's surface,
giving researchers
249
00:20:54,412 --> 00:20:57,480
a marker of geologic time.
250
00:20:58,960 --> 00:21:02,470
Craters younger than
Creusa disturb the rays.
251
00:21:02,470 --> 00:21:04,300
Older ones underlie them.
252
00:21:06,410 --> 00:21:10,280
Water is pulled down into
the hot cores of these moons,
253
00:21:11,210 --> 00:21:14,240
reemerging as steam through the sea floor.
254
00:21:16,070 --> 00:21:18,380
We know this because Cassini has detected
255
00:21:18,380 --> 00:21:20,290
tiny silicate particles
256
00:21:20,290 --> 00:21:22,680
that can only form in boiling water.
257
00:21:25,640 --> 00:21:30,640
In Earth's oceans, hydrothermal
vents, called black smokers
258
00:21:30,971 --> 00:21:35,971
and white smokers, are oases for life.
259
00:21:38,540 --> 00:21:41,100
The churning hot water provides energy
260
00:21:41,100 --> 00:21:44,060
and sets nutrient
particles swirling around.
261
00:21:50,910 --> 00:21:53,940
Is the same thing happening
beneath the ice crystal crusts
262
00:21:53,940 --> 00:21:56,470
of Saturn's snow globe moons?
263
00:21:58,490 --> 00:22:03,120
To find out, future missions
must look for amino acids,
264
00:22:03,120 --> 00:22:07,410
fatty, acids, long carbon chain molecules,
265
00:22:07,410 --> 00:22:12,110
and perhaps microorganisms
hitchhiking on the ice crystals,
266
00:22:13,780 --> 00:22:17,040
blasted far from the
undersurface ocean depths.
267
00:22:21,430 --> 00:22:25,360
Many astrobiologists
are fascinated by Titan,
268
00:22:25,360 --> 00:22:27,980
because it is very cold,
269
00:22:27,980 --> 00:22:32,980
about minus 180 celsius, yet it is wet.
270
00:22:33,230 --> 00:22:36,500
If anything lives on or inside Titan,
271
00:22:36,500 --> 00:22:39,830
it is almost surely not
related to life on Earth.
272
00:22:42,654 --> 00:22:45,336
Titan is about the same diameter and mass
273
00:22:45,336 --> 00:22:46,430
as the planet Mercury.
274
00:22:47,378 --> 00:22:49,280
And Titan's surface
gravity is about the same
275
00:22:49,280 --> 00:22:54,130
as Earth's moon, but
unlike Mercury or the moon,
276
00:22:54,130 --> 00:22:59,130
Titan has a thick atmosphere,
even thicker than Earth's.
277
00:22:59,420 --> 00:23:02,400
And scientists don't yet know why.
278
00:23:05,370 --> 00:23:08,350
It's the second-largest
moon in the solar system.
279
00:23:09,360 --> 00:23:12,970
At 5,150 kilometers in diameter,
280
00:23:12,970 --> 00:23:15,610
only Jupiter's Ganymede is wider.
281
00:23:18,470 --> 00:23:22,061
Titan is so much larger than
the rest of Saturn's moons,
282
00:23:22,061 --> 00:23:24,480
it may have formed from the collision
283
00:23:24,480 --> 00:23:26,812
of several of its siblings.
284
00:23:55,600 --> 00:23:58,840
By mission's end, Cassini will have flown
285
00:23:58,840 --> 00:24:01,800
by Titan 127 times.
286
00:24:03,610 --> 00:24:05,240
Each pass gives the craft
287
00:24:05,240 --> 00:24:07,820
a gravitational acceleration equivalent
288
00:24:07,820 --> 00:24:10,760
to almost 1,000 kilos of extra fuel.
289
00:24:13,700 --> 00:24:17,980
When the two Voyagers sailed
past in 1980 and 1981,
290
00:24:19,210 --> 00:24:23,200
they saw only this orange,
smog-enshrouded globe.
291
00:24:26,920 --> 00:24:30,560
American and European
scientists were so intrigued,
292
00:24:30,560 --> 00:24:33,090
they began sketching out what would become
293
00:24:33,090 --> 00:24:34,860
the Cassini-Huygens mission.
294
00:24:38,726 --> 00:24:43,070
23 years later, an international team
295
00:24:43,070 --> 00:24:45,650
commands the release of the Huygens probe,
296
00:24:47,370 --> 00:24:48,940
to land on Titan.
297
00:25:00,882 --> 00:25:03,910
January 14th, 2005.
298
00:25:06,910 --> 00:25:09,170
The European-built Huygens probe
299
00:25:10,390 --> 00:25:14,130
aero brakes into Titan's
atmosphere with its heat shield,
300
00:25:17,180 --> 00:25:18,640
deploys a parachute
301
00:25:20,430 --> 00:25:21,760
and floats down
302
00:25:23,060 --> 00:25:25,110
for over two and a half hours
303
00:25:26,150 --> 00:25:28,610
through a nitrogen-laden atmosphere.
304
00:25:33,980 --> 00:25:36,950
Its camera reveals an eerie landscape.
305
00:25:44,280 --> 00:25:47,770
Huygens lands softly in a
slushy bank of frozen methane,
306
00:25:51,670 --> 00:25:54,460
along the shoreline of a hydrocarbon lake.
307
00:25:58,300 --> 00:26:01,930
Huygens continues transmitting
data for another half-hour
308
00:26:01,930 --> 00:26:06,670
after landing, sending back
images of rounded pebbles
309
00:26:06,670 --> 00:26:09,660
probably made of hard frozen water ice.
310
00:26:11,660 --> 00:26:15,470
Humanity has placed its
imprint on yet another world.
311
00:26:18,270 --> 00:26:21,650
The flowing liquid on Titan is methane,
312
00:26:21,650 --> 00:26:24,700
which acts there as water does on Earth.
313
00:26:26,800 --> 00:26:29,180
In the range of Titan's temperatures,
314
00:26:29,180 --> 00:26:32,080
methane can exist in all three states,
315
00:26:33,500 --> 00:26:36,020
solid, liquid and gas.
316
00:26:37,780 --> 00:26:40,500
It is not impossible that a form of life
317
00:26:40,500 --> 00:26:42,680
could be evolving on this moon,
318
00:26:42,680 --> 00:26:46,410
feeding on the constant
rain of hydrocarbons,
319
00:26:46,410 --> 00:26:49,110
a true second Genesis,
320
00:26:49,110 --> 00:26:52,500
completely separate from
our earthly tree of life.
321
00:26:54,680 --> 00:26:57,420
Since Voyager first glimpsed Titan,
322
00:26:57,420 --> 00:27:00,230
researchers have speculated
that liquid ocenas
323
00:27:00,230 --> 00:27:01,780
grace its surface.
324
00:27:03,760 --> 00:27:07,420
But dense orange smog
has withheld the truth.
325
00:27:08,760 --> 00:27:12,120
This haze collects when
the sun's ultraviolet light
326
00:27:12,120 --> 00:27:14,960
breaks up methane in the high atmosphere,
327
00:27:14,960 --> 00:27:18,330
forming long molecular
chains that grow large enough
328
00:27:18,330 --> 00:27:19,830
to fall from the sky.
329
00:27:23,010 --> 00:27:26,020
These methane byproducts form snow drifts
330
00:27:26,020 --> 00:27:29,820
into a huge network of dunes
around Titan's equator.
331
00:27:34,000 --> 00:27:37,680
Cassini's camera was outfitted
with near-infrared filters
332
00:27:37,680 --> 00:27:42,160
to peer through the orange fog
to verify bodies of liquid.
333
00:27:44,010 --> 00:27:47,970
Images come back of relatively flat areas,
334
00:27:47,970 --> 00:27:50,180
but are they truly oceans?
335
00:27:52,874 --> 00:27:54,980
Or perhaps just methane slush?
336
00:27:56,020 --> 00:27:57,300
Or thick tar?
337
00:27:59,970 --> 00:28:02,540
The answer comes from Cassini's visible
338
00:28:02,540 --> 00:28:04,930
infrared-mapping spectrometer.
339
00:28:04,930 --> 00:28:07,970
It catches a specular reflection,
340
00:28:07,970 --> 00:28:10,430
a bright spot of sunlight bouncing off
341
00:28:10,430 --> 00:28:12,520
a clearly liquid surface.
342
00:28:14,480 --> 00:28:17,850
With Cassini's radar, flat surfaces,
343
00:28:17,850 --> 00:28:20,440
lakes and seas, appear dark,
344
00:28:20,440 --> 00:28:22,590
unless they are ruffled by waves.
345
00:28:24,050 --> 00:28:27,750
Titan indeed has oceans, ponds and pools
346
00:28:27,750 --> 00:28:32,660
of liquid hydrocarbons,
ethane, methane and propane.
347
00:28:35,000 --> 00:28:37,970
Strangely, they form
mostly in Titan's northern
348
00:28:37,970 --> 00:28:39,790
hemisphere, near the pole.
349
00:28:41,860 --> 00:28:44,580
Saturn's eccentric orbit is to blame.
350
00:28:45,550 --> 00:28:49,990
Northern summer is warmer than
southern summer on Saturn,
351
00:28:49,990 --> 00:28:52,270
but because of the way Titan is tipped,
352
00:28:52,270 --> 00:28:55,220
its southern summer is more severe,
353
00:28:55,220 --> 00:28:58,683
so all the southern
liquid methane evaporates
354
00:28:58,683 --> 00:29:00,870
and rains out in the north.
355
00:29:03,300 --> 00:29:07,150
Over time, the whole system flips.
356
00:29:07,150 --> 00:29:10,570
In 15,000 years, Titan's lakes will all
357
00:29:10,570 --> 00:29:12,460
be in the Southern Hemisphere.
358
00:29:14,070 --> 00:29:17,340
This one, named Ligeia Mare, is larger
359
00:29:17,340 --> 00:29:19,220
than Lake Superior on Earth.
360
00:29:20,190 --> 00:29:23,730
It's probably 150 meters deep in spots.
361
00:29:24,880 --> 00:29:27,600
Mysterious, frothy islands appear,
362
00:29:27,600 --> 00:29:29,640
bubbling up from under the surface.
363
00:29:31,400 --> 00:29:33,710
Titan holds a store of hydrocarbons
364
00:29:33,710 --> 00:29:37,225
about 10 times larger than all Earth's
365
00:29:37,225 --> 00:29:39,910
petroleum and natural
gas reserves combined.
366
00:29:46,400 --> 00:29:49,820
Hovering 300 kilometers
over Titan's South Pole,
367
00:29:51,010 --> 00:29:54,610
a huge persistent toxic
cloud of frozen hydrogen
368
00:29:54,610 --> 00:29:56,880
cyanide rotates ominously.
369
00:29:58,080 --> 00:30:00,470
This vortex seems to develop when Titan's
370
00:30:00,470 --> 00:30:03,400
Southern Hemisphere
enters its autumn season.
371
00:30:07,060 --> 00:30:10,020
Titan thrusts its methane up into space
372
00:30:10,020 --> 00:30:12,100
at a frightening rate.
373
00:30:12,100 --> 00:30:14,750
The atmospheric supply can't last longer
374
00:30:14,750 --> 00:30:16,730
than about 20 million years.
375
00:30:18,136 --> 00:30:20,940
Something must be
replenishing it, but what?
376
00:30:23,050 --> 00:30:25,650
Cassini's radar spots the answer.
377
00:30:27,270 --> 00:30:30,560
Mountains, some up to a kilometer tall.
378
00:30:32,580 --> 00:30:35,000
These may be cryovolcanos.
379
00:30:38,180 --> 00:30:41,240
Some could be active
today, spewing methane
380
00:30:41,240 --> 00:30:42,410
from within the moon.
381
00:30:46,440 --> 00:30:49,620
Cassini's radio science tools show Titan's
382
00:30:49,620 --> 00:30:53,950
whole body flexing in
response to Saturn's gravity.
383
00:30:53,950 --> 00:30:57,280
That makes it warm enough
inside to melt ice.
384
00:30:58,620 --> 00:31:01,370
Unlike the subsurface oceans of Enceladus,
385
00:31:01,370 --> 00:31:04,760
with its rocky ocean floors, Titan's ocean
386
00:31:04,760 --> 00:31:08,640
is probably sandwiched
between layers of water ice.
387
00:31:09,920 --> 00:31:12,980
So if there's an underground marine layer,
388
00:31:12,980 --> 00:31:15,640
it may be sealed off
from the hot chemistry
389
00:31:15,640 --> 00:31:20,640
of geothermal vents and any
chance of nurturing life forms.
390
00:31:23,970 --> 00:31:27,660
Even after Cassini-Huygens,
we still don't know
391
00:31:27,660 --> 00:31:31,770
how old Titan is, where it came from,
392
00:31:32,670 --> 00:31:35,380
or how long it's had an active atmosphere.
393
00:31:41,100 --> 00:31:45,340
Clues point to a cataclysmic
event in the Saturn system,
394
00:31:45,340 --> 00:31:47,980
perhaps 100 million years ago,
395
00:31:49,110 --> 00:31:52,380
that either created Titan
from smaller bodies,
396
00:31:53,400 --> 00:31:56,360
or energized a barren, frozen Titan
397
00:31:56,360 --> 00:31:57,950
into an active system.
398
00:32:00,140 --> 00:32:03,371
Possibly like the primitive Earth.
399
00:32:11,300 --> 00:32:14,880
To find out, we'll have to go back,
400
00:32:16,400 --> 00:32:18,560
float longer through the haze,
401
00:32:21,190 --> 00:32:23,120
sail the hydrocarbon seas
402
00:32:25,990 --> 00:32:28,510
and soar through the nitrogen skies
403
00:32:30,780 --> 00:32:31,613
of Titan.
404
00:32:47,191 --> 00:32:49,780
To Galileo in 1610, the ringed planet
405
00:32:49,780 --> 00:32:53,511
appeared as three stars,
with two small ones
406
00:32:53,511 --> 00:32:57,260
touching one large,
prompting Galileo to declare
407
00:32:57,260 --> 00:32:59,970
that Saturn must have ears.
408
00:33:03,170 --> 00:33:06,920
But in 1655, using more advanced optics,
409
00:33:06,920 --> 00:33:09,900
Christiaan Huygens unmasked the apparition
410
00:33:09,900 --> 00:33:13,230
as a flat ring circling
a spherical planet.
411
00:33:16,200 --> 00:33:19,280
20 years later, Giovanni Domenico Cassini
412
00:33:19,280 --> 00:33:22,560
discerned that it was not
one ring, but several,
413
00:33:22,560 --> 00:33:23,940
with gaps between them.
414
00:33:26,810 --> 00:33:30,360
The widest gap was later
named the Cassini Division.
415
00:33:31,770 --> 00:33:35,930
We now know that it's
4,800 kilometers wide
416
00:33:35,930 --> 00:33:37,390
and far from empty.
417
00:33:42,830 --> 00:33:47,670
In 1859, Scottish mathematician
James Clark Maxwell
418
00:33:47,670 --> 00:33:50,870
showed that the rings are not solid discs
419
00:33:50,870 --> 00:33:53,650
but composed of many smaller granules.
420
00:33:57,610 --> 00:34:00,500
Each tiny fleck, pebble and boulder
421
00:34:00,500 --> 00:34:03,560
revolves around the
planet in its own orbit,
422
00:34:03,560 --> 00:34:06,610
jockeying for position
among trillions of others.
423
00:34:08,890 --> 00:34:12,300
Though all are flying several
kilometers per second,
424
00:34:12,300 --> 00:34:14,970
they jostle one another only very gently.
425
00:34:37,640 --> 00:34:40,090
The concentric rings are given letters.
426
00:34:42,010 --> 00:34:46,370
A through G, in their order of discovery.
427
00:34:51,840 --> 00:34:55,010
Material riding close
into Saturn's cloud tops
428
00:34:55,010 --> 00:34:59,100
in the D ring whips around
Saturn in about four hours.
429
00:35:00,320 --> 00:35:02,850
But particles in the distance F ring
430
00:35:02,850 --> 00:35:05,120
take at least four times longer.
431
00:35:09,680 --> 00:35:12,470
It wasn't until the Cassini's
inspection that we learned
432
00:35:12,470 --> 00:35:14,670
just how flat the rings are.
433
00:35:15,690 --> 00:35:19,350
Incredibly, they are only
10 meters thick on average.
434
00:35:21,890 --> 00:35:24,650
From top to bottom, only about as tall
435
00:35:24,650 --> 00:35:26,410
as a three-story building.
436
00:35:29,100 --> 00:35:33,840
These rings are 30 million
times wider than they are high.
437
00:35:37,450 --> 00:35:40,260
And ring material can ripple up and down,
438
00:35:42,140 --> 00:35:44,290
crafting temporary corrugations.
439
00:35:46,580 --> 00:35:48,940
Many intricate wave patterns can be seen
440
00:35:48,940 --> 00:35:51,370
across the broad ring plane.
441
00:35:51,370 --> 00:35:54,380
Each one is conjured by
a specific gravitational
442
00:35:54,380 --> 00:35:56,600
resonance with a Saturnian moon.
443
00:35:59,160 --> 00:36:02,630
Though the basic physics of
the ring system is simple,
444
00:36:02,630 --> 00:36:06,110
it's mostly the product
of gravity and collisions,
445
00:36:06,110 --> 00:36:08,150
the intricate structure of the rings
446
00:36:08,150 --> 00:36:10,920
is hard to mathematically model,
447
00:36:10,920 --> 00:36:14,510
even after 13 years of
Cassini observations.
448
00:36:17,580 --> 00:36:20,900
The pressure of sunlight,
and forces from Saturn's
449
00:36:20,900 --> 00:36:24,900
magnetic field, can push or pull smaller,
450
00:36:24,900 --> 00:36:27,300
less massive ring particles around.
451
00:36:29,960 --> 00:36:32,870
The mission team flies a
series of special orbits
452
00:36:32,870 --> 00:36:35,900
that put the rings
between Cassini and Earth.
453
00:36:38,270 --> 00:36:41,090
By beaming radio signals of
three different wavelengths
454
00:36:41,090 --> 00:36:44,280
through the ring material,
researchers build up
455
00:36:44,280 --> 00:36:46,780
a color map of particle sizes.
456
00:36:47,940 --> 00:36:50,870
Red areas hold more big particles.
457
00:36:52,030 --> 00:36:55,050
Blue regions contain
mostly smaller grains.
458
00:36:56,640 --> 00:36:59,970
Radio waves, shown in the
bottom half of this image,
459
00:36:59,970 --> 00:37:04,060
reveal finer structure than
photos taken in visible light.
460
00:37:05,990 --> 00:37:09,290
Most particles are
small, from tiny crystals
461
00:37:09,290 --> 00:37:14,290
smaller than a dust
grain, up to pebble sized.
462
00:37:14,350 --> 00:37:17,530
Less common are ice
rocks and large boulders,
463
00:37:17,530 --> 00:37:19,380
up to the size of houses.
464
00:37:21,030 --> 00:37:24,230
A few are the size of mountains.
465
00:37:24,230 --> 00:37:28,250
Moons in the act of
forming, or falling apart.
466
00:37:29,970 --> 00:37:32,700
Grabbing an average size
ring particle would feel
467
00:37:32,700 --> 00:37:34,780
something like closing your hand around
468
00:37:34,780 --> 00:37:37,660
a thick layer of very cold whipped cream
469
00:37:37,660 --> 00:37:41,040
to find a glob of solid
ice cream deep inside.
470
00:37:43,950 --> 00:37:47,060
The packing of particles
varies between rings.
471
00:37:52,270 --> 00:37:54,610
Very little light gets through the B ring
472
00:37:54,610 --> 00:37:57,110
of crowded snowballs.
473
00:37:57,110 --> 00:37:59,640
An astronaut would have
to dig her way through it.
474
00:38:01,440 --> 00:38:03,610
The A ring is less congested.
475
00:38:05,290 --> 00:38:09,460
And the G ring is very
diffuse, like fog or smoke.
476
00:38:15,150 --> 00:38:17,780
The Cassini mission
confirms the rings are made
477
00:38:17,780 --> 00:38:20,150
of almost pure water ice.
478
00:38:21,320 --> 00:38:24,610
But tiny quantities of
simple organic compounds
479
00:38:24,610 --> 00:38:26,380
tint and shade them.
480
00:38:29,170 --> 00:38:31,040
The astronomer Carl Sagan called
481
00:38:31,040 --> 00:38:35,720
these colorful chemicals
tholins, Greek for muddy.
482
00:38:42,030 --> 00:38:44,710
Crossing Saturn's dark side,
483
00:38:44,710 --> 00:38:48,250
Cassini's camera picks up the true colors
484
00:38:48,250 --> 00:38:52,680
and intricate complexity of
the ring plane's variations.
485
00:39:07,800 --> 00:39:11,980
Subtle gravitational effects
fashioned by the many moons
486
00:39:11,980 --> 00:39:13,990
sculpt the ring material.
487
00:39:17,380 --> 00:39:22,380
Small moons, this one's named
Pan, orbit within the rings.
488
00:39:25,350 --> 00:39:28,470
They seem to sweep clear
their lanes of travel.
489
00:39:34,070 --> 00:39:37,010
The moon Mimas, gravitationally
combing the ring's
490
00:39:37,010 --> 00:39:40,450
particles, causes the
large Cassini Division.
491
00:39:45,090 --> 00:39:48,040
Other rings are herded
into form by so-called
492
00:39:48,040 --> 00:39:52,811
shepherd moons, like
Prometheus and Pandora.
493
00:40:10,420 --> 00:40:13,470
Tiny Daphnis, just
eight kilometers across,
494
00:40:14,560 --> 00:40:17,380
pushes a wave of ring material
495
00:40:17,380 --> 00:40:19,870
like the bow wave of a boat on a lake.
496
00:40:22,830 --> 00:40:26,740
Daphnis bobs up and down
like a merry-go-round horse,
497
00:40:26,740 --> 00:40:29,690
gravitationally pulling
particles into dune-like
498
00:40:29,690 --> 00:40:32,200
mounds three kilometers tall.
499
00:40:35,950 --> 00:40:40,330
It has plowed a 35-kilometer-wide
furrow in the ring field,
500
00:40:40,330 --> 00:40:42,200
called the Keeler Division.
501
00:40:44,740 --> 00:40:49,740
The larger Pan forges the
325-kilometer Encke Gap
502
00:40:49,900 --> 00:40:54,480
in Saturn's A ring, giving it a wavy edge.
503
00:40:54,480 --> 00:40:58,780
And Pan's gravity inspires
a spiral wake of particles.
504
00:41:02,130 --> 00:41:06,044
Based on that gap, researchers
predicted Pan's existence
505
00:41:06,044 --> 00:41:10,810
in the late 19th century,
long before it was first seen.
506
00:41:14,080 --> 00:41:18,000
But no on anticipated
Pan's remarkable shape.
507
00:41:21,070 --> 00:41:22,490
And it's not unique.
508
00:41:24,390 --> 00:41:28,320
The slightly wider moon Atlas
has a similar structure.
509
00:41:31,660 --> 00:41:35,650
Both wear skirts of gravitationally
attracted icy crystals.
510
00:41:37,690 --> 00:41:41,260
Certain small satellites
on eccentric orbits
511
00:41:41,260 --> 00:41:43,740
repeatedly crash through the F ring,
512
00:41:44,780 --> 00:41:47,580
leaving behind sets of disruptive splashes
513
00:41:47,580 --> 00:41:49,410
as evidence of their passing.
514
00:41:53,190 --> 00:41:57,260
Other minuscule moonlets,
too small to be seen,
515
00:41:57,260 --> 00:42:00,450
fashion propellor-shaped resonant waves
516
00:42:00,450 --> 00:42:04,042
in the snowy rings falling around Saturn.
517
00:42:18,710 --> 00:42:21,930
The ever-evolving complexity
of these ring circles
518
00:42:23,540 --> 00:42:26,350
moves like a musical score,
519
00:42:26,350 --> 00:42:28,355
playing in silence.
520
00:42:41,560 --> 00:42:45,420
Once every 14 years, the ring plane lies
521
00:42:45,420 --> 00:42:47,750
exactly edge on to the sun.
522
00:42:50,200 --> 00:42:52,800
Cassini was present for one such equinox.
523
00:42:56,560 --> 00:42:59,020
In essence, the sunlight on the rings
524
00:43:00,020 --> 00:43:02,450
has been switched off, and they cast
525
00:43:02,450 --> 00:43:05,050
no shadows on Saturn.
526
00:43:05,050 --> 00:43:07,320
They are only visible
because Saturn reflects
527
00:43:07,320 --> 00:43:08,620
some light on them,
528
00:43:08,620 --> 00:43:11,670
here digitally multiplied many times.
529
00:43:13,490 --> 00:43:16,160
Only the F ring, which is slightly tilted
530
00:43:16,160 --> 00:43:18,730
from the others, catches any sunlight.
531
00:43:21,100 --> 00:43:23,450
But because the rings are so thin,
532
00:43:23,450 --> 00:43:25,230
any tall structure within them
533
00:43:25,230 --> 00:43:27,960
throws its shadow onto the ring plane.
534
00:43:34,130 --> 00:43:37,200
Thus, in the outermost edge of the B ring,
535
00:43:37,200 --> 00:43:39,080
a surprise appears.
536
00:43:39,080 --> 00:43:43,700
Hundreds of long shadows
mark a field of icy spikes.
537
00:43:44,822 --> 00:43:48,210
Geometry dictates these points must range
538
00:43:48,210 --> 00:43:50,450
up to a kilometer or so in height.
539
00:43:52,000 --> 00:43:56,140
Like icebergs growing in a
sea of mostly empty space,
540
00:43:56,140 --> 00:43:58,930
these thorn-like clumps may be molded
541
00:43:58,930 --> 00:44:00,300
by the invisible fingers
542
00:44:01,266 --> 00:44:03,816
of a gravitational resonance
with one of the moons.
543
00:44:05,170 --> 00:44:08,890
Or they may be drawn out
by static electricity
544
00:44:08,890 --> 00:44:11,620
inspired by Saturn's magnetic field.
545
00:44:14,860 --> 00:44:17,710
Some of Saturn's rings
are constantly morphing,
546
00:44:20,040 --> 00:44:23,570
while others are stoically
consistent year after year.
547
00:44:37,410 --> 00:44:39,980
How old are these bright, icy rings?
548
00:44:42,090 --> 00:44:45,970
They may have formed in
the last 100 million years,
549
00:44:45,970 --> 00:44:49,400
when icy moons or comets collided
550
00:44:49,400 --> 00:44:51,820
or were torn apart by Saturn's gravity.
551
00:44:54,740 --> 00:44:57,480
Or they might be as old as Saturn,
552
00:44:57,480 --> 00:45:00,660
the leftover debris of
the solar system's birth.
553
00:45:02,600 --> 00:45:06,480
Cassini may yet find the true answer.
554
00:45:12,410 --> 00:45:14,970
Looking down at Saturn's North Pole,
555
00:45:14,970 --> 00:45:18,520
Cassini gets a spectacular
view of the globe's jet stream.
556
00:45:20,540 --> 00:45:23,990
Some resonance of the wind
energies banks the stream
557
00:45:23,990 --> 00:45:27,122
into a six-sided shape, the hexagon.
558
00:45:32,320 --> 00:45:35,730
Apparently, an eastward-flowing
shallow jet stream
559
00:45:35,730 --> 00:45:39,010
is bumped by occasional storms.
560
00:45:39,010 --> 00:45:41,620
The jet reacts by settling into the most
561
00:45:41,620 --> 00:45:46,620
stable geometric shape, six roughly sides.
562
00:45:51,790 --> 00:45:56,280
This polar monsoon is about
32,000 kilometers wide.
563
00:45:57,980 --> 00:46:01,040
You could fit two and
a half Earths into it.
564
00:46:04,160 --> 00:46:07,530
Its winds blow faster the
closer they get to the pole.
565
00:46:11,010 --> 00:46:14,324
Up to 540 kilometers per hour.
566
00:46:42,750 --> 00:46:46,700
Why kill Cassini in a
ball of atmospheric fire?
567
00:46:48,050 --> 00:46:50,930
The international scientific
community has agreed
568
00:46:50,930 --> 00:46:53,850
to avoid any possibility of contaminating
569
00:46:53,850 --> 00:46:58,750
Saturn's moons, especially
Enceladus and Titan.
570
00:47:02,040 --> 00:47:06,590
Cassini is warm inside,
essentially room temperature.
571
00:47:08,580 --> 00:47:11,600
Any microbes that found
their way in during assembly
572
00:47:12,830 --> 00:47:14,670
could have easily survived.
573
00:47:16,420 --> 00:47:20,330
And Cassini's RTG will
remain hot for decades.
574
00:47:22,440 --> 00:47:26,490
If she was allowed to
accidentally crash on Enceladus,
575
00:47:26,490 --> 00:47:29,120
Cassini might easily melt her way down
576
00:47:29,120 --> 00:47:31,970
through the ice into
the underground ocean.
577
00:47:34,040 --> 00:47:38,200
Back in 2009, studies had
showed Cassini had enough fuel
578
00:47:38,200 --> 00:47:41,460
to go beyond Saturn to
explore the ice giants
579
00:47:41,460 --> 00:47:43,020
Uranus or Neptune.
580
00:47:45,070 --> 00:47:47,300
She could have been sent back to Jupiter.
581
00:47:49,660 --> 00:47:52,790
Or outward to visit a
population of comet-like
582
00:47:52,790 --> 00:47:55,650
asteroids known as the Centaurs.
583
00:47:59,320 --> 00:48:03,470
But to get all the science
possible from the Saturn system,
584
00:48:03,470 --> 00:48:05,690
Cassini would have to die here.
585
00:48:08,600 --> 00:48:11,330
That led trajectory designers at JPL
586
00:48:11,330 --> 00:48:14,940
to develop a jewel of orbital dynamics,
587
00:48:14,940 --> 00:48:16,410
the Solstice Mission.
588
00:48:17,880 --> 00:48:21,470
The plan optimizes
repeated fly-bys of Titan.
589
00:48:23,470 --> 00:48:25,920
The route features high orbits to look
590
00:48:25,920 --> 00:48:27,700
at the poles and the rings.
591
00:48:29,080 --> 00:48:32,590
Long loops to map the
planet's magnetic fields.
592
00:48:33,810 --> 00:48:37,380
Flattened equatorial
orbits to check out moons.
593
00:48:41,230 --> 00:48:44,000
And ending at the peak of northern summer
594
00:48:45,890 --> 00:48:49,330
to mirror Cassini's
arrival in southern summer.
595
00:48:51,750 --> 00:48:55,479
Between the two, scientists
can infer the full cycle
596
00:48:55,479 --> 00:48:57,590
of Saturn's seasons.
597
00:49:00,410 --> 00:49:02,780
The science based on Cassini's data
598
00:49:04,150 --> 00:49:06,101
will go on for decades.
599
00:49:20,780 --> 00:49:24,310
Nudging Cassini's speed by
just eight meters per second
600
00:49:25,200 --> 00:49:27,330
is enough to begin her death spiral.
601
00:49:28,920 --> 00:49:32,130
The craft makes repeated
dives between the innermost
602
00:49:32,130 --> 00:49:35,790
ring material and the roiling atmosphere.
603
00:49:41,399 --> 00:49:42,980
These maneuvers would have
been far too dangerous
604
00:49:42,980 --> 00:49:45,480
to contemplate when Cassini was designed.
605
00:49:47,770 --> 00:49:51,870
Along the way, the
spacecraft maps fluctuations
606
00:49:51,870 --> 00:49:54,650
in Saturn's gravity and magnetic fields.
607
00:49:56,350 --> 00:50:00,020
And samples icy particles
flowing in from its rings.
608
00:50:02,900 --> 00:50:06,650
Until the very end,
Cassini beams science data
609
00:50:06,650 --> 00:50:09,124
and images directly to Earth.
610
00:50:15,920 --> 00:50:20,020
Finally, on September 15th, 2017,
611
00:50:20,870 --> 00:50:24,940
as the Cassini spacecraft
streaks along Saturn's clouds,
612
00:50:26,330 --> 00:50:29,850
its high-gain antenna
shifts away from Earth.
613
00:50:34,080 --> 00:50:35,440
The signal fades.
614
00:50:38,180 --> 00:50:39,710
And she is gone.
49246
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