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Lift off of Messenger on Nasa's
mission to Mercury.
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00:00:08,740 --> 00:00:11,660
♪ They'll say
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00:00:11,700 --> 00:00:15,540
♪ No-one can see us
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00:00:15,580 --> 00:00:19,420
♪ That we're estranged
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♪ And all alone
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00:00:22,620 --> 00:00:25,700
♪ They believe
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♪ Nothing can reach us
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00:00:29,520 --> 00:00:32,970
♪ And pull us out of
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♪ The boundless gloom
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♪ They're wrong
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♪ They're wrong
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♪ They're wrong. ♪
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00:01:09,300 --> 00:01:11,140
Far, far away...
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00:01:16,820 --> 00:01:18,100
beyond Mars...
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00:01:20,700 --> 00:01:24,820
past the storms of Jupiter,
and the rings of Saturn...
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00:01:26,740 --> 00:01:28,820
conditions become very different.
17
00:01:31,900 --> 00:01:36,660
Temperatures plummet,
and distances between worlds
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00:01:36,700 --> 00:01:40,740
are measured not in millions,
but in billions of kilometres.
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00:01:43,300 --> 00:01:46,460
Here lie the most mysterious
planets of them all.
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00:01:51,420 --> 00:01:52,460
Uranus.
21
00:01:54,540 --> 00:01:57,740
A pale blue marble
hanging in the dark,
22
00:01:57,780 --> 00:01:59,820
frozen depths of space.
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00:02:03,460 --> 00:02:05,380
And, further out...
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the solar system's final
true planet...
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00:02:12,460 --> 00:02:14,340
Neptune.
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00:02:17,060 --> 00:02:21,540
Beyond, we thought we'd only ever
find tiny, lifeless worlds...
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00:02:23,060 --> 00:02:24,420
frozen to the core.
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00:02:28,860 --> 00:02:30,860
How wrong we were.
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00:02:57,300 --> 00:03:00,820
We live at a time when our
civilisation has unprecedented
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00:03:00,860 --> 00:03:04,340
reach, and we have a near-permanent
presence at Mars,
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both in orbit and on the surface,
and we've had spacecraft orbiting
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00:03:08,660 --> 00:03:14,020
Mercury, Venus, Jupiter and Saturn
for extended periods.
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00:03:14,060 --> 00:03:18,460
But, once we get beyond Saturn,
things become much more difficult.
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00:03:18,500 --> 00:03:20,940
The distances are vast.
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00:03:20,980 --> 00:03:23,180
Travel times are measured
not in one months,
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00:03:23,220 --> 00:03:27,420
but in years, decades, even.
And that means that we've only
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00:03:27,460 --> 00:03:30,300
visited the outer planets once.
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00:03:31,980 --> 00:03:36,320
Each visit is a voyage
into the unknown, as we strive
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00:03:36,360 --> 00:03:40,700
to reach the most distant planetary
systems ever visited.
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00:03:42,980 --> 00:03:46,740
And, when we do get there, our
spacecraft are travelling so fast
41
00:03:46,780 --> 00:03:49,180
that they fly straight through,
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00:03:49,220 --> 00:03:52,220
only spending
a few hours in the system.
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00:03:52,260 --> 00:03:56,840
But those few hours of precious data
have allowed us to begin
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00:03:56,880 --> 00:04:01,460
to understand the mysteries that lie
there on the outer edges
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00:04:01,500 --> 00:04:02,900
of the solar system.
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We have ignition
and we have liftoff.
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Reports coming back indicate
those twin, large, solid motors
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are functioning perfectly.
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00:04:31,180 --> 00:04:34,820
Our first mission into the dark
was only possible thanks to some
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help from the planets themselves.
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Each planet orbits
at a different speed.
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And, for most of the time,
they're scattered around the Sun.
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00:04:58,820 --> 00:05:02,340
But once every 175 years...
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something rather wonderful
happens.
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00:05:10,620 --> 00:05:12,540
The outer planets align...
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creating a path...
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00:05:17,420 --> 00:05:20,860
that leads from Earth past Jupiter
and Saturn...
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all the way to Uranus and Neptune.
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Voyager 2 had been launched
at precisely the right moment
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00:05:50,340 --> 00:05:53,620
to take advantage of this rare
planetary alignment.
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00:06:03,540 --> 00:06:07,140
It arrived at Jupiter
in a little under two years.
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00:06:11,060 --> 00:06:13,020
Two and a half times more massive
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00:06:13,060 --> 00:06:15,580
than all the other planets
combined...
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00:06:17,260 --> 00:06:20,580
Jupiter gave Voyager
a gravitational kick.
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00:06:31,780 --> 00:06:34,420
Another two years on,
and Voyager witnessed
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00:06:34,460 --> 00:06:37,660
one of the most beautiful sights
in the solar system.
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The icy rings of
another gas giant...
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Saturn.
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00:07:01,380 --> 00:07:03,740
And, then, on and on...
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00:07:07,260 --> 00:07:09,180
further into the darkness.
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00:07:27,380 --> 00:07:31,900
Almost nine years after leaving
Earth, Voyager approached
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an entirely new class of planet.
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00:07:45,580 --> 00:07:49,520
Just like Jupiter and Saturn,
the planet's upper atmosphere
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00:07:49,560 --> 00:07:53,500
is composed mostly of swirling
hydrogen and helium gas.
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00:08:01,060 --> 00:08:05,380
And hidden beneath lies
an exotic, icy mix of methane,
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00:08:05,420 --> 00:08:07,020
ammonia and water.
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00:08:17,420 --> 00:08:22,340
But, unlike the other gas giants,
Uranus is almost featureless.
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00:08:26,460 --> 00:08:29,100
For all the time that Voyager
stared at the planet,
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00:08:29,140 --> 00:08:32,460
it saw just ten cloud formations.
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00:08:35,580 --> 00:08:37,420
And we soon discovered why.
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00:08:43,220 --> 00:08:47,780
Uranus, at -224 degrees Celsius,
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is the coldest planet
in the solar system.
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The first of the ice giants,
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in a permanent state of deep freeze.
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00:09:06,740 --> 00:09:09,500
Voyager spent just
six hours with Uranus...
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00:09:11,300 --> 00:09:15,460
and, as its gaze widened,
it took in the entire system.
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00:09:27,100 --> 00:09:28,700
Just like Saturn...
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Uranus has rings.
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The rings are so dark, so faint,
that they're very difficult
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to see from Earth.
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00:09:57,340 --> 00:10:00,500
In fact, we didn't
discover them until 1977.
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00:10:01,540 --> 00:10:04,660
They must be made of some kind of
material that doesn't reflect
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a lot of sunlight back,
and we don't know what that is.
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00:10:07,820 --> 00:10:10,700
It can't be water ice
like the rings of Saturn,
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because they would be much brighter.
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00:10:12,820 --> 00:10:16,620
They're also extremely
delicate and thin,
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and, again, that's a great mystery,
cos you'd expect the particles
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to collide and the rings
to spread out over time.
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That doesn't happen.
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00:10:35,340 --> 00:10:38,180
So, something must be holding
those rings in place,
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and the answer can be seen
in this photograph
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taken by Voyager 2.
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You can see a bright, thin ring,
which is known as the epsilon ring,
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and, above it and below it,
you can see two moons.
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The inner one is called Cordelia,
and the outer one is called Ophelia.
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00:10:56,860 --> 00:11:00,700
Now, the thing you need to know
about orbits, a moon or a ring
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particle that's orbiting closer
to a planet is moving more slowly
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00:11:04,620 --> 00:11:08,100
than a moon or ring particle
that's orbiting further away.
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00:11:08,140 --> 00:11:11,460
And, so, if there's a particle
in the epsilon ring that maybe
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has a collision, loses a bit
of energy and starts to drop down,
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then Cordelia tends to accelerate
that particle back up into the ring
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again to speed it up
by its gravitational influence.
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Whereas, if it's a particle on the
outer edge of the epsilon ring,
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it gets a bit more energy
and raises up in altitude,
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then Ophelia tends to slow it down,
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and, so, it falls back
into the ring again.
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And, by that mechanism,
these moons keep the ring nice
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and neat around Uranus,
and, for that reason,
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these moons have become
known as shepherd moons.
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00:11:57,500 --> 00:12:00,040
Now, we haven't discovered
any more shepherd moons.
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00:12:00,080 --> 00:12:02,620
Voyager was only in
the system for a few hours.
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00:12:05,020 --> 00:12:08,700
But we assume that they're there,
orbiting around Uranus,
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00:12:08,740 --> 00:12:11,380
keeping the other rings
precisely in place.
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00:12:17,020 --> 00:12:21,100
The missing moons are not the only
mysterious thing about the planet.
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Uranus orbits the Sun
in a unique way,
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a consequence of events
that happened long ago.
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Uranus was born from the vast cloud
of material
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that surrounded the young Sun.
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00:13:05,100 --> 00:13:07,540
Over time, this material grew
together
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under the influence of gravity...
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forming each of the planets...
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all orbiting in the same
anticlockwise direction
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as the primordial cloud
of gas and dust.
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This rotation remains to this day.
135
00:13:44,060 --> 00:13:46,980
Almost all the planets spin
on their axis in the same
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anticlockwise direction.
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But, for reasons we don't
yet fully understand,
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Venus and Uranus spin on their axes
in the opposite direction.
139
00:14:08,100 --> 00:14:10,780
And Uranus is even more curious.
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00:14:15,580 --> 00:14:18,740
The entire planet is on its side.
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00:14:28,420 --> 00:14:32,740
It's not known for certain why
Uranus spins in this way.
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00:14:32,780 --> 00:14:35,140
But it seems likely
that, at some point,
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probably in the distant past,
it was hit by another planet,
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possibly the size of
Earth or even larger,
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00:14:42,340 --> 00:14:45,740
which knocked the planet over,
and, indeed, modern computer
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00:14:45,780 --> 00:14:49,260
simulations suggest
that when you do that to a planet,
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all the moons follow,
and you end up with the planet
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and its system of moons,
and now its rings,
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sort of corkscrewing
around the Sun on its side.
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00:15:45,980 --> 00:15:50,940
Voyager had taken us to the most
distant planets we had ever visited.
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00:15:59,340 --> 00:16:06,220
And, now, an almost unthinkable
distance of 1.6 billion kilometres
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00:16:06,260 --> 00:16:11,220
of icy cold space
lay between the spacecraft
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and its next encounter.
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00:16:35,900 --> 00:16:39,260
The size and scale of the solar
system is impossible to imagine.
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00:16:41,100 --> 00:16:45,860
But, when we scale everything down,
then it becomes easier to visualise.
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The Sun is 1.4 million
kilometres in diameter.
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But scale that down by a factor
of around 600 million,
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and it becomes the size
of that light.
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00:16:58,500 --> 00:17:01,980
And the Earth, Mars and the rocky
planets
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are about that big on this scale.
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And the distances are,
I think, even more remarkable.
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00:17:10,060 --> 00:17:12,760
So, Mercury, the closest
planet to the Sun,
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would be all the way
over there by the sea.
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So, this would be where
Mercury orbits.
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00:17:28,780 --> 00:17:32,620
And Mercury is 96 metres away.
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It's about just under
a centimetre in diameter.
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00:17:37,660 --> 00:17:40,940
And the next planet, Venus,
is somewhere over there.
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We'd fly past Venus about
180 metres away from the Sun.
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And then head onwards
and outwards towards the Earth.
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00:18:05,540 --> 00:18:09,780
Here, at the Earth's orbit,
the true scale of our fragility
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and isolation becomes apparent.
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The Sun there, 250 metres away
with the twinkling stars
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00:18:19,860 --> 00:18:23,660
of the galaxy beyond,
and here's the Earth.
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Two centimetres across.
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On that pebble, all of
human history play out.
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At around 380 metres,
we pass by Mars,
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00:18:42,340 --> 00:18:46,580
the last of the rocky planets,
and then onwards into the darkness.
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00:19:10,140 --> 00:19:13,180
Crossing the harbour
takes us to the fringes
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of the outer solar system.
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00:19:17,900 --> 00:19:20,260
And, now, the distances
and the sizes
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00:19:20,300 --> 00:19:22,340
are beginning to get really big.
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00:19:26,380 --> 00:19:29,180
Jupiter, the largest planet
in the solar system,
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is over ten times the diameter
of our Earth, and there's the Sun,
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1.3km across the harbour.
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00:19:58,580 --> 00:20:01,780
At almost twice the distance
from the Sun to Jupiter,
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00:20:01,820 --> 00:20:03,060
we reach Saturn.
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00:20:04,820 --> 00:20:07,980
2.4km on our scale.
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00:20:09,860 --> 00:20:13,980
And we really are now entering
the twilight of the solar system.
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00:20:14,020 --> 00:20:18,140
Light levels are like early morning
or late evening here on Earth,
190
00:20:18,180 --> 00:20:20,740
but we can still see Saturn
in the night sky,
191
00:20:20,780 --> 00:20:24,260
because the planet and its rings
are highly reflective.
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00:20:30,860 --> 00:20:35,860
As far again as all the rocky
planets, and Jupiter and Saturn,
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00:20:35,900 --> 00:20:37,420
we reach Uranus.
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00:20:43,660 --> 00:20:48,380
3 billion kilometres from the Sun,
and we begin to fully appreciate
195
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the distances Voyager
had travelled...
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00:20:55,860 --> 00:20:58,940
on its journey to the farthest
reaches of the solar system.
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00:21:14,540 --> 00:21:18,660
Journey's end, Neptune,
a ball of gas about
198
00:21:18,700 --> 00:21:21,260
7.5 centimetres across.
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00:21:21,300 --> 00:21:25,820
7.4km away
from the Sun on this scale.
200
00:21:32,540 --> 00:21:37,380
And we are still down there
on the island in Reykjavik harbour.
201
00:21:38,460 --> 00:21:43,780
Little, microscopic ants crawling
around on the surface of a pebble.
202
00:22:08,700 --> 00:22:12,660
It had taken 12 years,
but Voyager had finally crossed
203
00:22:12,700 --> 00:22:16,660
the great expanse of space
between Earth and the most
204
00:22:16,700 --> 00:22:18,460
distant planetary system.
205
00:22:33,540 --> 00:22:34,580
Neptune.
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00:22:38,340 --> 00:22:43,940
17 times the mass of the Earth,
and even more massive than Uranus.
207
00:23:02,100 --> 00:23:06,580
But, in contrast to its sister
planet, Neptune's atmosphere
208
00:23:06,620 --> 00:23:08,460
is bursting with activity.
209
00:23:22,500 --> 00:23:26,740
What we found was a planet
of extreme weather,
210
00:23:26,780 --> 00:23:32,180
where high altitude winds whip white
methane clouds around at speeds
211
00:23:32,220 --> 00:23:34,820
of over 2,000km/h.
212
00:23:34,860 --> 00:23:38,020
Those are the highest wind speeds
anywhere in the solar system.
213
00:23:51,700 --> 00:23:54,220
And Voyager saw a great, dark spot,
214
00:23:54,260 --> 00:23:56,780
not unlike Jupiter's
great, red spot.
215
00:23:59,020 --> 00:24:03,260
A storm system the size of Earth,
that, when we looked only four
216
00:24:03,300 --> 00:24:06,380
or five years later,
we found had vanished.
217
00:24:10,420 --> 00:24:13,900
But, over the years,
we've observed more storms raging
218
00:24:13,940 --> 00:24:15,060
over the planet.
219
00:24:21,540 --> 00:24:24,860
It's one of the great mysteries
of planetary exploration,
220
00:24:24,900 --> 00:24:29,220
why a planet so far from the Sun,
with so little energy falling
221
00:24:29,260 --> 00:24:33,580
into its atmosphere from sunlight,
can have the most extreme winds
222
00:24:33,620 --> 00:24:34,780
in the solar system.
223
00:24:36,340 --> 00:24:39,540
And Voyager made yet
another puzzling discovery.
224
00:24:43,220 --> 00:24:47,700
Although further from the Sun,
the planet is warmer than Uranus.
225
00:24:52,260 --> 00:24:55,060
The source of this extra
heat remains a mystery.
226
00:24:59,380 --> 00:25:03,460
But, for some reason, Neptune emits
over two and a half times
227
00:25:03,500 --> 00:25:05,820
the heat it receives from the Sun.
228
00:25:09,940 --> 00:25:14,580
And this internal heat helps
to explain the ferocious storms.
229
00:25:18,500 --> 00:25:21,460
As the heat makes its way
from the core of the planet
230
00:25:21,500 --> 00:25:23,100
and out into space...
231
00:25:27,540 --> 00:25:29,740
it churns up the entire
atmosphere...
232
00:25:32,140 --> 00:25:36,140
creating winds unlike anything
seen elsewhere in the solar system.
233
00:25:42,100 --> 00:25:45,580
The probable reason that wind
speeds can be so high
234
00:25:45,620 --> 00:25:49,380
is because there's no solid surface
on a planet like Neptune.
235
00:25:49,420 --> 00:25:53,780
It's exotic liquids further down,
and gases further up.
236
00:25:53,820 --> 00:25:55,940
But there's no rocky surface.
237
00:25:55,980 --> 00:26:00,240
There are no mountains
and continents to break up the flow
238
00:26:00,280 --> 00:26:04,540
of atmospheric gases,
and, so, the winds can just whip
239
00:26:04,580 --> 00:26:07,340
around the planet
at supersonic speeds.
240
00:26:24,580 --> 00:26:28,980
Voyager 2 had almost completed its
grand tour of the solar system.
241
00:26:45,500 --> 00:26:47,860
But before it began
its lonely journey
242
00:26:47,900 --> 00:26:49,860
out into interstellar space...
243
00:26:54,220 --> 00:26:56,540
it had one, last world to visit.
244
00:27:06,740 --> 00:27:12,180
Triton, a vast moon covered
in a sheen of frozen nitrogen.
245
00:27:14,660 --> 00:27:18,300
We expected it to be a silent,
still world,
246
00:27:18,340 --> 00:27:21,980
but Voyager was in
for one, last surprise.
247
00:27:56,540 --> 00:27:59,460
But, when Voyager arrived,
248
00:27:59,500 --> 00:28:04,520
we saw geological activity
on that frozen world.
249
00:28:04,560 --> 00:28:09,350
We saw geysers erupting up
into space 8km high,
250
00:28:09,390 --> 00:28:14,180
and then carrying dark material
100km downwind.
251
00:28:22,340 --> 00:28:26,740
Now, the key to understanding
what process caused those eruptions
252
00:28:26,780 --> 00:28:31,180
was that we noticed that the geysers
tended to erupt on a place
253
00:28:31,220 --> 00:28:34,300
on Triton's surface
below the faint Sun,
254
00:28:34,340 --> 00:28:37,340
even though it's so many
billions of miles away.
255
00:28:37,380 --> 00:28:42,340
What's happening is the sunlight
is falling on the thin layer
256
00:28:42,380 --> 00:28:47,340
of nitrogen ice, going through,
and heating up a layer of darker
257
00:28:47,380 --> 00:28:49,820
particles a metre below the surface.
258
00:28:52,940 --> 00:28:55,620
A difference of just
four degrees Celsius
259
00:28:55,660 --> 00:28:58,940
is enough for the heat
to radiate up
260
00:28:58,980 --> 00:29:03,780
and vaporise the frozen nitrogen,
creating gas.
261
00:29:07,940 --> 00:29:10,540
That gas is under pressure,
and, ultimately,
262
00:29:10,580 --> 00:29:12,820
it punches through the nitrogen ice
263
00:29:12,860 --> 00:29:17,380
carrying those dark particles up and
making the geysers of Triton.
264
00:29:22,540 --> 00:29:25,180
In the furthest reaches
of the solar system,
265
00:29:25,220 --> 00:29:29,220
the faint light of the Sun
is still enough to power the most
266
00:29:29,260 --> 00:29:31,380
distant of geological wonders.
267
00:29:36,220 --> 00:29:40,540
But this can't explain the rest
of Triton's mysterious features.
268
00:29:50,420 --> 00:29:53,940
Terrain on this scale could only
be created
269
00:29:53,980 --> 00:29:56,460
by a much more powerful force.
270
00:30:01,180 --> 00:30:05,740
And a clue seems to be lurking
in Triton's odd orbit.
271
00:30:12,660 --> 00:30:15,460
Unlike every other large moon
in the solar system,
272
00:30:15,500 --> 00:30:20,740
Triton orbits in the opposite
direction to the spin of the planet.
273
00:30:20,780 --> 00:30:22,780
And that means it's highly unlikely
274
00:30:22,820 --> 00:30:25,580
that Triton and Neptune formed
at the same time.
275
00:30:25,620 --> 00:30:29,780
If you formed a planet and a moon
out of the same collapsing cloud
276
00:30:29,820 --> 00:30:33,820
of gas and dust, then they tend
to spin and orbit in the same
277
00:30:33,860 --> 00:30:37,060
direction as the spin
of the initial dust cloud,
278
00:30:37,100 --> 00:30:42,100
so, the most likely explanation
for that is that Triton is a visitor
279
00:30:42,140 --> 00:30:46,380
to the Neptunian system, that,
unlike Voyager, never left.
280
00:30:56,580 --> 00:31:00,300
One theory is that, billions of
years ago,
281
00:31:00,340 --> 00:31:02,780
Triton was not a moon at all.
282
00:31:07,860 --> 00:31:11,540
It grew up in a region
of space way beyond Neptune...
283
00:31:15,300 --> 00:31:17,100
the Kuiper belt.
284
00:31:23,500 --> 00:31:27,860
Here, trillions of frozen lumps
of water, ammonia
285
00:31:27,900 --> 00:31:30,300
and methane circle the Sun.
286
00:31:34,100 --> 00:31:37,980
The frozen leftovers from
the formation of the solar system.
287
00:31:46,860 --> 00:31:50,500
Perhaps Triton ended up on the inner
edge of this region...
288
00:31:57,340 --> 00:31:59,180
and ventured close enough
289
00:31:59,220 --> 00:32:02,060
to Neptune to be drawn
in by its gravity...
290
00:32:05,980 --> 00:32:10,460
until, eventually, it was plucked
from the Kuiper belt,
291
00:32:10,500 --> 00:32:15,140
and forever trapped in orbit
around the distant, blue planet.
292
00:32:24,740 --> 00:32:29,060
Today, Triton orbits in a nice,
regular circle around Neptune,
293
00:32:29,100 --> 00:32:31,220
but it wouldn't have
started out that way.
294
00:32:31,260 --> 00:32:33,540
When it was first captured,
it would have glanced
295
00:32:33,580 --> 00:32:37,260
past the planet and ended
up in a wide, elliptical orbit,
296
00:32:37,300 --> 00:32:41,220
sometimes being far away from
the planet, and sometimes close.
297
00:32:41,260 --> 00:32:44,400
That means that, as Triton
orbited around Neptune,
298
00:32:44,440 --> 00:32:47,540
the gravitational pull
was constantly changing,
299
00:32:47,580 --> 00:32:51,220
and that stretches and squashes
the moon, and heats up
300
00:32:51,260 --> 00:32:53,020
the interior by friction.
301
00:32:53,060 --> 00:32:55,020
It's a process called tidal heating.
302
00:32:58,500 --> 00:33:01,940
The molten interior would
have exploded up through cracks
303
00:33:01,980 --> 00:33:04,020
and faults in Triton's crust...
304
00:33:05,620 --> 00:33:08,660
creating the ragged surface
we see today.
305
00:33:10,740 --> 00:33:13,180
And what you're left
with is a cooling moon,
306
00:33:13,220 --> 00:33:17,780
orbiting in a circle the wrong
way around the planet,
307
00:33:17,820 --> 00:33:21,380
the dramas of its past
hidden from view.
308
00:33:21,420 --> 00:33:25,420
All that remains are the geysers,
powered by the faint light
309
00:33:25,460 --> 00:33:30,100
of the Sun, painting dark streaks
across the now-quiescent surface.
310
00:33:42,140 --> 00:33:45,020
Voyager had fulfilled its mission,
311
00:33:45,060 --> 00:33:48,660
and now headed onwards,
out of the solar system...
312
00:33:51,420 --> 00:33:54,460
where it would never
encounter another planet.
313
00:34:05,220 --> 00:34:09,020
But, elsewhere, another world
awaited our arrival...
314
00:34:11,740 --> 00:34:13,940
far out in the darkness.
315
00:34:17,940 --> 00:34:22,140
Mission... And lift off of Nasa's
New Horizons spacecraft
316
00:34:22,180 --> 00:34:27,220
on a decade-long voyage to visit
the planet Pluto and then beyond.
317
00:34:45,380 --> 00:34:47,220
The New Horizons spacecraft,
318
00:34:47,260 --> 00:34:50,100
on its way to the very edge
of our solar system.
319
00:35:01,700 --> 00:35:04,820
Our ambition to learn
more about a small,
320
00:35:04,860 --> 00:35:09,380
intriguing world depended
on the success of New Horizons.
321
00:35:16,900 --> 00:35:20,420
As the tiny probe,
less than three metres in length,
322
00:35:20,460 --> 00:35:22,460
was sent out into the abyss...
323
00:35:28,380 --> 00:35:32,420
most of its electronics
and all nonessential systems
324
00:35:32,460 --> 00:35:34,500
were shut down to save power.
325
00:35:37,220 --> 00:35:43,340
It would hibernate for almost its
entire 4.8 billion kilometre trek.
326
00:35:53,500 --> 00:35:57,100
Whilst New Horizons continued
its voyage to Pluto,
327
00:35:57,140 --> 00:36:00,740
a controversy arose here on Earth
about the definition
328
00:36:00,780 --> 00:36:02,300
of Pluto itself.
329
00:36:02,340 --> 00:36:05,340
See, we always knew
that Pluto is small,
330
00:36:05,380 --> 00:36:09,820
smaller than Neptune's moon Triton,
but it was discoveries made
331
00:36:09,860 --> 00:36:13,780
in the vicinity of Pluto
by the Hubble Space Telescope
332
00:36:13,820 --> 00:36:17,100
that really challenged
its status as a planet.
333
00:36:21,340 --> 00:36:26,660
From Earth, Pluto, far away on
the inner edge of the Kuiper belt,
334
00:36:26,700 --> 00:36:30,060
is so distant that, even with
Hubble, it appears
335
00:36:30,100 --> 00:36:32,540
as nothing more than a fuzzy image.
336
00:36:35,820 --> 00:36:38,020
But Pluto was not alone.
337
00:36:40,300 --> 00:36:43,260
We began to detect
other distant objects.
338
00:36:56,260 --> 00:36:59,300
Then, Hubble discovered
that another world
339
00:36:59,340 --> 00:37:01,540
is almost the same
size as Pluto.
340
00:37:09,900 --> 00:37:14,220
The discovery of these new worlds
has forced us to reconsider
341
00:37:14,260 --> 00:37:16,580
what we mean by the word "planet".
342
00:37:20,740 --> 00:37:24,820
The International Astronomical Union
has a three-part definition
343
00:37:24,860 --> 00:37:27,580
of a planet. Firstly, it has to
orbit the Sun,
344
00:37:27,620 --> 00:37:29,500
and Pluto certainly does that.
345
00:37:29,540 --> 00:37:32,340
It goes round once every 248 years.
346
00:37:32,380 --> 00:37:37,260
Secondly, it has to be massive
enough for gravity to sculpt it
347
00:37:37,300 --> 00:37:42,040
almost into a sphere, and Pluto
indeed is almost spherical.
348
00:37:42,080 --> 00:37:46,820
But, thirdly, it has to clear
its own orbit around the Sun,
349
00:37:46,860 --> 00:37:50,520
and that's essentially
a mass constraint as well.
350
00:37:50,560 --> 00:37:54,220
It has to have enough
gravity to throw things out
351
00:37:54,260 --> 00:37:56,100
from its orbital path.
352
00:37:56,140 --> 00:37:58,660
And that's where Pluto falls down.
353
00:37:58,700 --> 00:38:01,500
Now, why that extra idea?
354
00:38:01,540 --> 00:38:04,980
Well, ultimately,
it's because if Pluto is big enough
355
00:38:05,020 --> 00:38:08,460
to be a planet, then Eris is big
enough to be a planet,
356
00:38:08,500 --> 00:38:11,260
and Makemake is big
enough to be a planet,
357
00:38:11,300 --> 00:38:15,740
and tens or even potentially
hundreds of objects out there
358
00:38:15,780 --> 00:38:18,280
are big enough to be planets.
359
00:38:18,320 --> 00:38:20,510
Now, does it really matter?
360
00:38:20,550 --> 00:38:22,700
Well, I don't think so.
361
00:38:22,740 --> 00:38:28,180
Ultimately, Pluto is a world, and,
therefore, we should explore it.
362
00:38:42,100 --> 00:38:46,260
And, in July 2015,
that's exactly what we did.
363
00:38:52,340 --> 00:38:56,940
After nine years of flight,
New Horizons awoke.
364
00:38:58,780 --> 00:39:00,540
Copy that.
365
00:39:00,580 --> 00:39:03,220
We are locked by telemetry
with the phase path.
366
00:39:36,540 --> 00:39:42,180
We had our first glimpse of the most
distant world ever visited.
367
00:40:29,500 --> 00:40:31,980
Pluto is beautiful.
368
00:40:32,020 --> 00:40:35,180
And, far from being a frigid,
featureless world,
369
00:40:35,220 --> 00:40:38,380
it turns out that it
has all the characteristics
370
00:40:38,420 --> 00:40:40,820
of a dynamic, living planet.
371
00:40:40,860 --> 00:40:45,940
And, yes, it is cold on the surface,
about -230 degrees Celsius.
372
00:40:45,980 --> 00:40:49,000
I'd be walking
over solid nitrogen.
373
00:40:49,040 --> 00:40:52,020
But the blotches
that could be made out
374
00:40:52,060 --> 00:40:56,420
in the grainy Hubble Space Telescope
images turned out to be
375
00:40:56,460 --> 00:41:00,260
a tremendous variety
of geological form and structure.
376
00:41:06,380 --> 00:41:10,260
But by far the most recognisable
feature is the region known
377
00:41:10,300 --> 00:41:11,540
as Tombaugh Regio,
378
00:41:11,580 --> 00:41:15,260
or to give it its more popular
name, Pluto's Heart.
379
00:41:21,020 --> 00:41:24,740
The western lobe of the heart
is called Sputnik Planitia.
380
00:41:30,500 --> 00:41:35,380
A giant plain of frozen nitrogen,
methane and carbon monoxide...
381
00:41:38,220 --> 00:41:41,500
that stretches for a million
square kilometres.
382
00:41:46,220 --> 00:41:50,300
And, at its edge, lies a range
of mountains made of pure,
383
00:41:50,340 --> 00:41:53,420
frozen water ice...
384
00:41:53,460 --> 00:41:57,820
that rise up to 6km
above the plain.
385
00:42:02,900 --> 00:42:06,500
But there's something
very strange about the region,
386
00:42:06,540 --> 00:42:10,580
something that sets it apart
from the rest of this dwarf planet.
387
00:42:15,180 --> 00:42:18,620
The surface of Pluto is covered
in craters, the scars
388
00:42:18,660 --> 00:42:21,660
of impacts that have taken place
over many billions of years,
389
00:42:21,700 --> 00:42:23,820
just like the surface of our moon.
390
00:42:23,860 --> 00:42:29,780
Except, if you look on Sputnik
Planitia, it is absolutely smooth.
391
00:42:29,820 --> 00:42:33,500
There are no craters there at all,
not a single one.
392
00:42:35,900 --> 00:42:39,140
From space, the lack
of craters is striking.
393
00:42:40,660 --> 00:42:44,260
And, the closer you look,
the stranger the mystery gets.
394
00:42:53,580 --> 00:42:57,940
Detailed imagery beamed back
by New Horizons revealed a network
395
00:42:57,980 --> 00:43:00,540
of hexagon and pentagon shapes...
396
00:43:06,060 --> 00:43:09,220
that crisscross the frozen
nitrogen surface.
397
00:43:20,660 --> 00:43:24,980
A clue to what might be happening
can be seen in these images.
398
00:43:25,020 --> 00:43:29,020
Those kind of patterns are found
elsewhere in nature.
399
00:43:29,060 --> 00:43:31,900
Here, for example,
on the surface of the Sun.
400
00:43:33,860 --> 00:43:37,540
Or here, in a liquid that's
been heated from below.
401
00:43:39,060 --> 00:43:42,220
These patterns are
characteristic of convection.
402
00:43:42,260 --> 00:43:45,740
There's a heat source which is
causing material to rise up,
403
00:43:45,780 --> 00:43:50,020
and then it cools and falls back
again, and in those circulating
404
00:43:50,060 --> 00:43:53,460
convection currents, you tend to get
patterns like this.
405
00:43:56,380 --> 00:43:59,940
So, what could be happening below
the surface of Sputnik Planitia
406
00:43:59,980 --> 00:44:04,100
is that there is a heat source deep
down which is melting the nitrogen
407
00:44:04,140 --> 00:44:08,260
ice and causing it to rise,
cool and then fall again,
408
00:44:08,300 --> 00:44:12,460
and those convection currents
are constantly resurfacing the area.
409
00:44:17,340 --> 00:44:22,180
That a small world like Pluto is
still active was a huge surprise.
410
00:44:26,420 --> 00:44:28,740
Our best theory of how this could be
411
00:44:28,780 --> 00:44:31,620
is that somewhere deep
in its interior...
412
00:44:33,740 --> 00:44:38,100
there are radioactive elements
that generate heat as they decay.
413
00:44:42,420 --> 00:44:46,740
This heat warms a sunless,
half-frozen ocean of water
414
00:44:46,780 --> 00:44:51,100
that has existed for billions of
years beneath the surface of Pluto.
415
00:45:02,300 --> 00:45:05,220
Now, the evidence from Sputnik
Planitia that there is still
416
00:45:05,260 --> 00:45:09,420
an internal heat source, and studies
of other geological features
417
00:45:09,460 --> 00:45:12,940
on Pluto, have led some scientists
to suggest that
418
00:45:12,980 --> 00:45:15,820
that ocean of water
might still be there.
419
00:45:20,820 --> 00:45:22,660
And the relatively warm ocean
420
00:45:22,700 --> 00:45:26,220
could explain the lack of craters
on Sputnik Planitia.
421
00:45:30,380 --> 00:45:35,780
The entire area is constantly
being repaved as the nitrogen
422
00:45:35,820 --> 00:45:37,980
surface is slowly turned over.
423
00:45:49,060 --> 00:45:52,580
But why all this activity
here and nowhere else?
424
00:45:56,780 --> 00:46:00,220
Perhaps Pluto's heart is the site
of a huge impact...
425
00:46:03,220 --> 00:46:07,220
that, long ago, punched a large
hole in the surface,
426
00:46:07,260 --> 00:46:10,140
almost down
to the vast ocean beneath.
427
00:46:12,900 --> 00:46:17,100
A hole that's slowly filled
with soft nitrogen ice...
428
00:46:19,500 --> 00:46:23,540
that now gently churns
just above a warmer ocean.
429
00:46:26,340 --> 00:46:27,660
Imagine that.
430
00:46:27,700 --> 00:46:31,160
An ocean billions of
miles away from the Sun,
431
00:46:31,200 --> 00:46:34,660
on the frozen frontier
of the solar system.
432
00:46:34,700 --> 00:46:37,540
On this most surprising of worlds,
433
00:46:37,580 --> 00:46:40,420
there may still be
an ocean of water.
434
00:46:50,380 --> 00:46:55,100
New Horizons' closest encounter
with Pluto lasted just hours...
435
00:47:03,500 --> 00:47:06,420
during which only one
hemisphere was visible...
436
00:47:08,500 --> 00:47:10,900
leaving the other side a mystery.
437
00:47:29,900 --> 00:47:33,060
Pluto held a final surprise.
438
00:47:33,100 --> 00:47:37,260
As New Horizons turned its camera
back for one, last look...
439
00:47:41,060 --> 00:47:44,580
it captured an image
of Pluto's atmosphere,
440
00:47:44,620 --> 00:47:46,300
glowing in the dark.
441
00:47:52,620 --> 00:47:56,940
A thin, blue sky over
a hidden ocean of water...
442
00:47:58,340 --> 00:48:01,620
4.8 billion kilometres from Earth.
443
00:48:28,820 --> 00:48:30,420
We've come a long way.
444
00:48:32,420 --> 00:48:35,500
After just half a century
of space exploration...
445
00:48:37,460 --> 00:48:40,340
we've reached every one of
the planets in the solar system...
446
00:48:45,140 --> 00:48:47,100
and begun to tell their story.
447
00:48:57,460 --> 00:49:00,620
What's emerging is a tale
of never-ending change...
448
00:49:02,980 --> 00:49:04,940
of dramatic origins...
449
00:49:09,220 --> 00:49:10,700
moments of hope...
450
00:49:16,380 --> 00:49:18,060
and loss.
451
00:49:31,220 --> 00:49:34,620
Where just eight motes of rock,
ice and gas...
452
00:49:36,220 --> 00:49:39,100
set against the dark backdrop
of space...
453
00:49:40,540 --> 00:49:45,740
have conspired together to
produce life on at least one world.
454
00:49:58,980 --> 00:50:01,780
"Why do we explore?"
some people ask.
455
00:50:01,820 --> 00:50:05,780
Shouldn't we deal with the problems
here on Earth before committing time
456
00:50:05,820 --> 00:50:10,260
and energy and resources
to exploring the stars?
457
00:50:10,300 --> 00:50:14,740
Well, I think focusing
entirely on our mote of dust
458
00:50:14,780 --> 00:50:17,620
would be a profound mistake.
459
00:50:17,660 --> 00:50:21,020
It would mean that we've taken
the decision to sit huddled
460
00:50:21,060 --> 00:50:23,940
in a tiny corner
of the solar system,
461
00:50:23,980 --> 00:50:25,340
wondering what we're doing here.
462
00:50:27,700 --> 00:50:31,660
It would mean that we've taken
the decision to fight amongst
463
00:50:31,700 --> 00:50:34,860
ourselves for ever-more-precious
resources,
464
00:50:34,900 --> 00:50:38,820
confined below a thin shell
of air on a small rock,
465
00:50:38,860 --> 00:50:42,700
rather than following the
three-dimensional path marked out
466
00:50:42,740 --> 00:50:44,820
by the lights in the night.
467
00:50:53,860 --> 00:50:56,940
We live in
a solar system of wonders,
468
00:50:56,980 --> 00:51:01,180
of planets of storms and moons
of ice and landscapes and vistas
469
00:51:01,220 --> 00:51:05,120
that stir the imagination
and enrich the soul,
470
00:51:05,160 --> 00:51:09,060
a system of limitless resources,
limitless beauty
471
00:51:09,100 --> 00:51:10,860
and limitless potential.
472
00:51:13,100 --> 00:51:16,620
A system that we've only
just begun to explore...
473
00:51:19,500 --> 00:51:23,780
in a journey that has already
rewarded us with so much.
474
00:51:49,540 --> 00:51:53,700
Pluto was the most distant world
that Nasa had ever planned to visit.
475
00:51:54,860 --> 00:51:58,740
Ten, nine, eight, seven...
476
00:51:58,780 --> 00:52:02,540
The launch of New Horizons
was incredibly dramatic.
477
00:52:04,500 --> 00:52:06,780
Mission... And liftoff.
478
00:52:06,820 --> 00:52:09,420
And it just shoots up so fast.
479
00:52:09,460 --> 00:52:11,660
It's the fastest launch
ever from Earth.
480
00:52:11,700 --> 00:52:13,620
About ten miles per second.
481
00:52:18,660 --> 00:52:22,500
In order to ensure that it was going
to last for the decade across space
482
00:52:22,540 --> 00:52:25,220
and actually work there,
they built in a lot of redundancy.
483
00:52:25,260 --> 00:52:27,660
There were sort of two of
everything, computers
484
00:52:27,700 --> 00:52:29,460
and the guidance systems,
485
00:52:29,500 --> 00:52:31,760
and they figured out
how to hibernate.
486
00:52:31,800 --> 00:52:34,060
The first spacecraft
that hibernated.
487
00:52:35,820 --> 00:52:39,020
To put the spacecraft largely
to sleep let the spacecraft
488
00:52:39,060 --> 00:52:40,860
just silently coast,
489
00:52:40,900 --> 00:52:44,540
then we could extend the life
of the electronics.
490
00:52:46,620 --> 00:52:49,180
No spacecraft mission had ever
really used hibernation
491
00:52:49,220 --> 00:52:52,580
as a day-to-day way
to cross the solar system.
492
00:52:55,340 --> 00:52:56,940
As the spacecraft slept,
493
00:52:56,980 --> 00:52:59,820
it sped away from Earth
towards its destination...
494
00:53:01,220 --> 00:53:03,300
to a world that had lain hidden
495
00:53:03,340 --> 00:53:06,700
amongst the stars for almost
all of human history.
496
00:53:08,460 --> 00:53:13,140
The discovery of Pluto was in 1930,
when Clyde Tombaugh,
497
00:53:13,180 --> 00:53:14,660
a Kansas farm boy,
498
00:53:14,700 --> 00:53:19,540
was using the telescope at
the Lowell Observatory in Arizona.
499
00:53:19,580 --> 00:53:21,140
Every clear night,
500
00:53:21,180 --> 00:53:24,020
Clyde would go out and take images
501
00:53:24,060 --> 00:53:27,460
of the sky on photographic plates,
and when it was cloudy
502
00:53:27,500 --> 00:53:29,980
or during the day,
he would compare those plates.
503
00:53:30,020 --> 00:53:34,620
And Clyde Tombaugh noticed
that there was this little speck
504
00:53:34,660 --> 00:53:36,100
moving across the stars.
505
00:53:36,140 --> 00:53:40,220
And, then, in 1930,
Clyde Tombaugh discovered Pluto.
506
00:53:41,580 --> 00:53:44,460
But Tombaugh would never
see Pluto up close.
507
00:53:47,020 --> 00:53:51,540
He died nine years before
the launch of New Horizons,
508
00:53:51,580 --> 00:53:53,340
at the age of 90.
509
00:53:54,500 --> 00:53:58,820
He had asked if a mission ever
did get launched some of his ashes
510
00:53:58,860 --> 00:54:01,260
could be sent on the journey.
511
00:54:01,300 --> 00:54:06,340
And to think that Clyde's ashes,
you know, flew by Pluto,
512
00:54:06,380 --> 00:54:09,580
and, you know, he was finally
visiting the place
513
00:54:09,620 --> 00:54:12,100
that he discovered,
that was pretty cool.
514
00:54:20,060 --> 00:54:21,100
Wow!
515
00:54:22,260 --> 00:54:26,420
Now, I mean, Pluto was a shock
and a revelation in so many ways.
516
00:54:26,460 --> 00:54:28,580
Our jaws just dropped to the floor.
517
00:54:30,220 --> 00:54:34,220
This amazing world that we would
never have known about,
518
00:54:34,260 --> 00:54:36,300
unless we sent
a spacecraft out there.
519
00:54:48,220 --> 00:54:51,620
But New Horizons didn't stop
after its flyby of Pluto.
520
00:54:54,900 --> 00:54:57,460
It continued on
for three more years,
521
00:54:57,500 --> 00:54:59,820
ever deeper into the Kuiper belt.
522
00:55:01,420 --> 00:55:03,660
The temperatures out there
are almost absolute zero,
523
00:55:03,700 --> 00:55:06,420
so everything is so well preserved.
524
00:55:07,940 --> 00:55:10,500
The Kuiper belt completely
changed everything.
525
00:55:10,540 --> 00:55:14,500
It's an archaeological dig,
if you will, into the early history
526
00:55:14,540 --> 00:55:17,260
of our solar system,
so it's a scientific wonderland.
527
00:55:19,620 --> 00:55:21,460
On New Year's Day, 2019,
528
00:55:21,500 --> 00:55:25,540
New Horizons had reached
the centre of the region...
529
00:55:28,060 --> 00:55:32,460
and was about to encounter the
most distant object ever visited.
530
00:55:48,460 --> 00:55:51,420
This object may be the most
primitive object
531
00:55:51,460 --> 00:55:53,780
ever encountered by a spacecraft.
532
00:55:54,780 --> 00:55:59,540
By looking at Ultima Thule today,
we think we're looking back in time
533
00:55:59,580 --> 00:56:01,660
to the origin of the solar system.
534
00:56:13,980 --> 00:56:18,860
Ultima Thule's formation was perhaps
just one of the countless collisions
535
00:56:18,900 --> 00:56:20,980
that formed the planets themselves.
536
00:56:27,540 --> 00:56:31,580
But, somehow, it escaped
and was flung far out
537
00:56:31,620 --> 00:56:33,100
into the Kuiper belt.
538
00:56:34,420 --> 00:56:37,460
The worlds out there,
which are billions of miles
539
00:56:37,500 --> 00:56:42,940
from the Sun, there are so many
mysteries kept in these objects,
540
00:56:42,980 --> 00:56:45,820
and we can really go out
and explore them, and start
541
00:56:45,860 --> 00:56:47,980
to understand these mysteries.
542
00:56:49,860 --> 00:56:53,780
Like every mission before it,
New Horizons has helped write
543
00:56:53,820 --> 00:56:55,340
the story of the planets.
544
00:57:00,580 --> 00:57:03,780
A story that we're only just
beginning to tell.
545
00:57:06,860 --> 00:57:10,100
The planets of our solar system,
they're in our back yard.
546
00:57:10,140 --> 00:57:12,620
We have the technology
to be able to go
547
00:57:12,660 --> 00:57:14,620
and stand on these surfaces.
548
00:57:16,460 --> 00:57:19,580
To be able to go out there
and be able to continue doing
549
00:57:19,620 --> 00:57:22,700
something that is very natural
and intrinsic to all of us,
550
00:57:22,740 --> 00:57:26,460
and that is answering the big
questions and exploring the unknown.
551
00:57:31,580 --> 00:57:34,020
I feel as though we're absolutely
just at the beginning
552
00:57:34,060 --> 00:57:36,380
of planetary exploration.
553
00:57:36,420 --> 00:57:39,500
There's a lot of exploration
left for us.
554
00:57:48,220 --> 00:57:51,020
Journey through our solar system
with this free poster
555
00:57:51,060 --> 00:57:52,740
produced by the Open University,
556
00:57:52,780 --> 00:57:55,940
and discover more about its
planets and moons.
557
00:57:57,380 --> 00:57:59,820
Order your free copy by calling...
558
00:58:04,300 --> 00:58:05,740
Or go to...
559
00:58:10,260 --> 00:58:12,900
And follow the links
to the Open University.
47709
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