All language subtitles for How.The.Universe.Works.S09E04.Secrets.Of.The.Sun.1080p.AMZN.WEB-DL.DDP2.0.H.264-alfaHD_track4_[eng]

NARRATOR: There's a violent star
at the centre of our solar system.

The immense power,
the roiling, boiling surface,

the massive plumes. It's ridiculous.

And our planet is at its mercy.

There are explosions and big giant

eruptions of plasma
that head straight to Earth.

We have to understand these better
to protect ourselves.

The sun is a churning cauldron
of nuclear reactions.

Revealing its inner workings
was once mission impossible,

but not anymore.

We've recruited
this network of spies, if you will.

We've build a fleet of spacecraft
that monitor the sun 24 hours a day.

With the sun
under close surveillance,

we just might have what it takes
to defend our planet.

September 6th, 2017,

a flash of ultraviolet
and X-ray light

erupts from the sun

sending a burst
of radiation toward Earth.

We call it a solar flare.

Flares are huge explosions
on the surface of the sun,

throwing light out into solar system

and absolutely baking
anything in its path.

These are really powerful events
erupting from the sun,

and we are fundamentally
in the line of fire.

The flare is so intense
it causes radio blackouts

across the side of the Earth
facing the sun...

..and the timing
could not have been worse.

The problem was, at this time,

there were hurricanes
in the Atlantic bearing down
on the Caribbean,

and there were people trying
to get in there and rescue folks.

Radio communication
between disaster relief teams

goes down for most of the day.

Space weather and Earth weather
combine to create chaos.

OLUSEYI:
It's not just an academic exercise.

Your very lifestyle
depends on understanding

how the sun behaves.

We need to be able to predict
what the sun is going to do next,

and to do that,
we need to have eyes on the sun,

as many eyes as we can get.

MAN OVER RADIO:
Three, two, one.

That's why NASA has put
together an elite unit.

We have ignition,
and we have lift-off.

Lift-off. And lift-off
on an international mission
of solar physics.

A fleet of daring spacecraft.

We humans have come a long way.
If you go back a few thousand years,

people were worshiping the sun,

and today,
we've built a fleet of spacecraft

that monitor the sun
24 hours a day,

observing it from every angle,
predicting what it's gonna do next.

That's nuts.

Leading the pack is the
Solar Dynamics Observatory, or SDO.

It keeps a telescopic eye on flares
blasting out from the sun's surface.

24 hours a day,
the SDO probe is on the lookout.

It's constantly vigilant.

Looks at the sun in a lot
of different wavelengths

in exquisite detail
so that we can see exactly

what sort of high energy events
are happening on the sun.

The record for the longest
service goes to SOHO,

our sentinel monitoring the sun

and its faint outer atmosphere.

The Solar and Heliospheric
Observatory, or SOHO,

is the old hand at studying the sun.
It's been up there for 25 years,

observing not just the sun itself,
but the environment around it.

Instead of looking directly at it,
it actually blocks out
most of the light

so that we can see
all these beautiful structures
that surround the sun.

And then there's the new recruit,
the Parker Solar Probe

our scout going deep behind
enemy lines.

The Parker Solar Probe
is going to give us

the closest look at the sun
that we have ever had

in the history of humanity.

We're flying so close to the sun

we're flying through the gases
of its atmosphere.

Twenty-nine other craft
make up the fleet,

each with their own role to play.

This fleet of spacecraft
that we have,

the overall mission is
to observe the sun scientifically,

learn about its behaviour,
but also importantly

to learn about the effects
that it has on Earth.

Our lookout probe,
the Solar Dynamics Observatory,
or SDO, spots something hellish.

Today's forecast for the sun
is predicted to be
10,000 degrees Fahrenheit

with winds of up to 600 m/s.

And a pretty decent chance of rain.

You don't wanna be in this rainstorm

cos your umbrella
isn't gonna help you.

Solar rain isn't water,
it's plasma, hot plasma.

Rather than a solid, liquid, or gas,

the entire sun is made up of
a strange fourth state of matter...

..plasma.

We're familiar with
three forms of matter,

you know, solid, holds its shape.

Liquid, flows.
A plasma is very much like a gas,

except the atoms in the gas have had
their electrons stripped off.

Rip those electrons off,
it's not an atom any more,

it's an ion and a free electron,
and we call that state plasma.

Plasma may sound weird

but we find it closer to home
than you might think.

There is plasma on Earth,
it just doesn't last very long.

So, for example,
when you see a lightning strike,

the glow from that
is coming from ionized air, plasma.

Plasma is just simply
gas that's very hot,

so hot it's lost
some of its electrons

and become electrically charged.

And the wonderful thing about plasma

is that once it has
that electric charge,

you can direct it
with a magnetic field.

And the sun has the most
powerful magnetic field

in the solar system.

It twists and flows
through the entire star.

The sun's magnetic field
is incredibly complicated.

There are lots of loops
of magnetic lines

coming out of the sun's surface.

As you go above the surface,
the magnetic field

begins to control
where the gas can go,

and you get these beautiful loops
and other structures above the sun

that are just showing you
where the magnetic field is.

The SDO spacecraft's jaw-dropping
videos of rain on the sun

show plasma flowing along huge
looping magnetic field lines

that have punched through
the sun's surface.

Because the surface
of the sun is a plasma

and these loops of magnetic fields
are coming out of it,

it draws that plasma up,

which then cools and rains down
as a plasma rain.

Tracking these loops
of magnetic field and plasma

could help explain solar flares...

..and it could give us some warning.

September 2017...

..minutes before the devastating
mid-hurricane radio blackout,

our solar lookout
spotted an explosion

on the surface of the sun.

Suddenly, you have this tremendous
flow of energy

and an explosive release of it,
and we call this a solar flare.

This is SDO's
specialty of observation.

The craft tracked the magnetic loops
above the sun's surface.

They were highly unstable.

BASRI: SDO takes very detailed
pictures of where the flows are.

You can actually see gas flowing
from one place to another.

You can see the...
You can see the magnetic loops.

PLAIT: These magnetic flux loops

are kind of like wires
carrying electricity.

When they're on their own,
they're fine,

but if they get too close,
they can connect and short-circuit,

and then you get a tremendous
release of energy.

The Ghostbusters
were really onto something.

Don't cross the streams.

The contact between magnetic loops

released an epic explosion
of high energy light.

(EXPLODES)

This radiation altered
our planet's atmosphere.

Radio waves jammed,
causing blackouts

at the worst possible moment.

PLAIT: Solar flares
are happening on the sun

90 million mi away.
Who cares, right?

Well, think of it this way,

a really good solar flare
could be the equivalent of,

oh, say, 10 million
hydrogen bombs going off.

How's that sound?

Solar flares happen a lot
and they do affect us.

They have affected us in the past
and they will again in the future.

But the sun's twisting
magnetic fields do more

than just disrupt
our communications.

When we see flares,
we gotta keep an eye out on those.

But sometimes
there's something even bigger.

The sun launches huge clouds
of plasma across the solar system.

All of that material
can come to the Earth

and really mess things up here,

blow out our power grid,
destroy our satellites,

even physically harm
our astronauts in orbit.

Can the solar fleet safeguard Earth?

November 5th, 2018,

an explosive cloud of plasma
hits the Parker Solar Probe

as it orbits just 15 million mi
from the sun.

We have this fleet of spacecraft
out there viewing the sun

and they're also
under attack by the sun.

There are explosions
coming from its surface.

It's not just light,
but explosions of hot plasma.

And the Parker Solar Probe
got blasted and yet it survived.

A huge blast of high-energy
charged particles

launches into the solar system
at millions of miles an hour...

..a coronal mass ejection.

But our solar scout
is prepared for the onslaught.

PLAIT: The Parker Solar Probe
gets very close to the sun

and it has a heat shield
to protect it.

But if it gets hit
by a coronal mass ejection,

it has to be protected
against that as well,

and so it's been radiation-hardened
to survive such an impact.

Could these blasts
pose a danger to our planet?

A coronal mass ejection
accelerates the subatomic particles,

and it's not
a little bit of particles.

It could be up to
a billion tons of them

screaming across
the solar system at high speed,

and this is something
we need to take very seriously.

To understand these dangerous
blasts of plasma...

..we have to look at their source...

..an area around the sun
known as the corona.

The sun's corona is kind of
like its atmosphere.

You can think of the sun itself
as being a ball of gas,

and then outside of that
is this ethereally thin gas

stretching out
for millions of miles.

The corona is
a difficult thing to study

because the surface of the sun
is so bright, it blocks our view.

We can only see the corona
during a total solar eclipse,

when the moon
blocks the sun's bright glare.

And in 2017, we caught a break.

The total solar eclipse
in August of 2017

was my third total solar eclipse.

Er, and I'll never get tired
of seeing them.

It's a magic, amazing event.

Over the course of the day,
the moon slowly slipped

in front of the sun,
and we got more and more excited.

And that moment of totality
when the moon blocked the sun

and we saw the corona
stretching out,

that was life-changing.

That was one of the most beautiful
things have ever seen in my life.

OLUSEYI: Seeing a total
solar eclipse is surreal.

You see them in movies,
you see them on television,

but to see one in real life

and to see the corona
emerge in the darkness

once the sun's disc
is covered by the moon,

it's almost like being in a movie.

The solar corona
is made up of the same plasma

as the surface of the sun...

..except it's even hotter...

..and reaches far out into space.

It's very tenuous,
it's very faint, though,

and so from here on the Earth,
there's not a ghost of a chance

of seeing it in the daytime sky.

You're blinded
by the light of the sun.

It's trillions of times
more intense.

PLAIT: You can only see it
during a solar eclipse,

when the moon blocks
the bright surface of the sun

and allows that
fainter light to be seen.

The problem
is the moment of totality,

when the corona reveals itself,
only lasts for a few minutes.

Astronomers, though,
we're impatient.

We don't want to wait
for a total solar eclipse,

which only happens
once or twice a year,

so we figured out a way
to make an artificial one,

and it's really simple.

One member of the solar fleet
has it covered.

Our solar sentinel, SOHO,
creates its own eclipse

by obscuring the blinding sun

with a circular plate in front
of the probe's camera.

Sometimes the best solution
is the simplest solution.

You know, instead of trying
to make a sensor

that could actually see the full
dynamic range of the sun's light,

you know, why not just block out
the light that we don't need?

In July 2012,

SOHO spotted
a huge chunk of the corona

blasting off into the solar system.

Seconds earlier, another probe

monitoring the solar surface
spotted a bright flare.

Were these events connected?

If a flare goes off,
it can disrupt those loops,

and if you get
the right kind of disruption,

the whole thing can just blow open,

and then you have
a tremendous amount of

billions of tons of hydrogen
blown off into interplanetary space,

and that's a coronal mass ejection.

Coronal mass ejections
are solar flares on steroids.

If a solar flare was a firecracker,

a coronal mass ejection
is more like an atom bomb.

And if a coronal mass ejection
comes our way, it hits hard.

The first thing it does is it
compresses Earth's magnetic field,

and then it wraps around the Earth

and this causes the magnetic field
itself to rearrange, reconnect,

and streams of particles

travel down those magnetic fields
toward our poles,

and impact the atmosphere.

Our shields are up, but they're able
to penetrate our shields,

our shield being
our own magnetic field.

Once they breach our defences,

the particles of a coronal
mass ejection can wreak havoc.

In August of 1972,

tensions were running high
in Vietnam.

Two dozen sea mines
detonated at the same time

when their magnetic
sensors were tripped.

A satellite was lost because
of the electromagnetic pulse

that ripped through it.

And an Air Force sensor
detected what looked like

a nuclear explosion
somewhere here on the planet.

Fortunately, scientists quickly
found the real culprit.

A coronal mass ejection

had ripped through
the Earth's magnetic field

and triggered magnetic sensors.

The crisis soon deescalated.

PLAIT: The sun
is an immense ball of plasma

860,000 mi across.

We are not going
to be able to stop it

from doing whatever it wants to do.

What we can do is learn to predict
what's going to happen,

so we're doing that now.

Our new fleet of solar observers
are our first line of defence.

PLAIT: The sun is a little
over 90 million mi from Earth.

It takes light a little over eight
minutes to get from there to here.

As rapidly as a coronal
mass ejection is traveling,

it still takes a few days
to get here.

LANZA: We can watch the sun to see
is there going to be an event?

Or is an event starting?

And the satellites can then tell us,
"Hey, you better be careful.

"You might need to batten down
the hatches on Earth."

But there may be an earlier clue
the fleet can watch out for,

vast dark regions moving across

the solar surface called sun spots.

BASRI: We know that this is
the wind-up before the release.

This thing is getting ready to blow.

In March of 1989,

a solar eruption caused
blackouts across Canada...

..and malfunctions
on board the Space Shuttle.

WOMAN: We've been
seeing some erratic

pressure signatures
out of tank three

as well as some manifold
pressure spikes in that system.

11 years later, the sun emitted
a flare that was so powerful

it blinded
the solar fleet's sensors.

11 years after that,
the Earth had a near miss

with the most powerful coronal mass
ejection ever recorded.

The sun has a very predictable

but actually quite
mysterious cycle of activity.

It gets very, very active
every 11 years,

and then it settles back down
to a more peaceful existence.

This 11-year cycle has astronomers
scratching their heads.

One thing we do know
is that violent solar events

seem to be preceded by dark
patches on the solar surface...

..sun spots.

Sun spots are large areas
on the surface of the sun,

much bigger than the Earth,

that are caused by incredibly
strong magnetic fields

disrupting the flow of plasma.

And every 11 years, these dark spots
grow in number...

..like clouds gathering
before a storm.

When you start seeing
more and more sunspots,

there's an expectation
that you're gonna see more intense

and more frequent solar flares.

But what drives this 11-year cycle?

It's kind of ironic that one of
the most predictable things

about the sun is also
the most mysterious.

SUTTER: We've been puzzling over
the sunspot cycle for generations.

And now, finally, we have spacecraft

headed to the sun
to try to give us some answers.

The SOHO, SDO, and STEREO Spacecraft

monitor the sun's atmosphere
using ultraviolet telescopes.

They spot flashes
of high-energy ultraviolet light

moving across the sun.

These waves of light
could be connected

to the cycle of sun spots...

..and to the sun's outburst,

because everything
we see on the sun's surface

is controlled by violent processes
deep in its interior.

The sun is a very simple onion.

At the very, very centre
is the core,

where the nuclear fusion happens.

A layer surrounding that
is known as the radiative zone,

where most of the energy
gets pushed out through radiation.

Then surrounding that is something
called the convective zone,

where there's great plumes
and chains of plasma

moving up and down, up and down.

But, unlike an onion,
the layers spin.

THALLER: There are currents
inside the sun

that we don't see from the surface.

Layers of the sun deep down inside

are rotating at different rates
than the layers above.

BASRI: So it turns out the inner
part of the sun is rotating

at maybe three times more rapidly
than the outer part of the sun.

We also can see
on the outer part of the sun

that the equator is rotating
more rapidly than the whole.

These layers of plasma
grinding against each other

generate the sun's enormously
powerful magnetic field

and give rise to sun spots,
plasma loops, and solar flares.

This differential rotation
takes the field

and starts twisting it
around the sun,

so as the magnetic gets too twisted,
it starts knotting up

and these knots start bubbling up
to the surface

and that's what we're seeing
actually with the sun spots.

And that's why you see
all these wonderful loops

and prominences coming off the sun.

Once the magnetic fields
start twisting and interacting,

they can direct the plasma
into vast rivers and loops

both above and below
the surface of the sun.

Why these events flare up
every 11 years is a mystery...

..but now new observations
from the solar fleet

could provide a clue about
what triggers the solar cycle...

..giant moving magnetic fields
beneath the sun's surface.

We think that
the ultraviolet light flickers

are telling us
where the magnetic field is.

In the course of the 11-year cycle,
the sun's magnetic fields

begin to move down from the poles,
closer and closer to the equator.

As the magnetic field lines
move through the star,

they carry huge amounts of
plasma with them.

The magnetic field lines
act like shepherds

for the plasma
underneath the surface,

and they push plasma down
to the equator of the sun.

The magnetic fields
trap enormous amounts of
plasma,

like water behind a dam

until eventually the floodgates open
and the plasma comes rushing out.

When the magnetic fields meet,
they cancel each other out

and release the plasma,
which goes as a tsunami wave

back to the poles.

When that plasma rebounds
from the equator

and hits the magnetic field
coming down from the poles,

the mid-latitudes, you get a huge
burst of magnetic activity.

Magnetic activity that
triggers sun spots and loops

also explains the 11-year cycle.

We think that this relationship
between the magnetic fields,

the ultraviolet flickers
and the plasma

drives the 11-year cycle.

We think this is what's
actually doing the work.

The solar cycle
has wound down for now

but once the next plasma
tsunami rushes through the sun,

our star will kick start
into action again.

Over the next few years,
we're going to see more sun spots,

more activity, more flares,
more ejections,

and more space weather
that we have to deal with.

Our fleet of solar spies
is poised and ready.

But flares
and coronal mass ejections

are not the only solar attacks

we have to shield ourselves against.

There's a strange, invisible force

flowing through
the entire solar system.

There is this great wind
of high-energy particles
from the sun,

a million mph wind.

And it can be deadly.

In November 2019,

the solar fleet watched
as Mercury sailed across the sun.

Mercury is the closest planet
to our sun in our solar system,

so it's on the front line
receiving all of this radiation,

an incredible amount of energy,
and it's such a tiny planet.

Temperatures on the innermost
planet's surface

reach 800 degrees Fahrenheit...

..but scientists discovered
something unexpected on Mercury...

..frozen pools of water
hidden in its craters.

It's one of the last places
in the solar system

you might expect to find ice,
on Mercury,

one of the hottest planets
in the solar system.

Despite the overall
really high temperatures

across the whole planet,
there are regions,

like, typically deep within craters,
that are permanently shadowed,

so there's never direct sunlight
on those regions of Mercury

and you can keep things
as cold as ice in those craters.

But where did the ice come from?

When we first saw
that there was ice on Mercury,

we thought something
must have brought it there,

something like a comet,
which is made out of ice.

But there's a new idea
that maybe the materials

that make this ice
are actually coming from the sun.

The sun creating ice
sounds strange...

..but recent research shows
it's not as crazy as it seems.

We often think of space
as being empty but, in fact,

we are bathed in a wind,
a million-mph wind,

of high energy particles
from the sun all the time,

the solar wind.

A stream of subatomic particles
called protons

constantly flow out
from the sun in all directions...

..bombarding the planets
of our solar system.

HOWETT: The solar wind is so strong
when it hits Mercury

that it can break down
some of the minerals and rocks

on its surface into their
constituent parts.

And those parts, especially if
they have oxygen in them,

can go to reform and form water

which, if it forms
in the right place,

can then stick around.

Protons in the solar wind
combine with oxygen

to form water molecules.

They condense and freeze in craters
which never see sunlight...

..so even on the sun's
closest neighbour, ice builds up.

But the solar wind
doesn't stop at Mercury.

The solar wind
has a tremendous impact

on the worlds of our solar system.

We think it's responsible
for the planet Venus

becoming this hellhole of heat.

Up until as recently
as 700 million years ago...

..Venus was a lush water world
with conditions suitable for life.

But the solar wind blasted
away the water vapor

and oxygen from Venus's atmosphere,

leaving carbon dioxide to dominate,

trapping the sun's heat and causing
surface temperatures to skyrocket.

Mars was once habitable, too,

but the solar wind quickly
took care of that as well.

We believe that billions
of years ago,

Mars had an atmosphere
and it had oceans and rivers

and it looked a lot like Earth.
It was gorgeous.

But that solar wind stripped away
the Martian atmosphere

and turned it into the barren
wasteland that it is today.

And Earth is in
the line of fire, too.

It's bombarded every day
with solar wind particles.

So how has life survived?

THALLER: One of the things
we really take for granted

is how well protected
we are here on the Earth.

The atmosphere absorbs
a lot of harmful things

from space and from the sun as well,

but also our magnetic field
deflects the solar wind around us

and we still have an atmosphere.

And when the charged
particles come from the sun,

the magnetic field line
strap those charged particles

and redirect them
to the poles of the planet.

The physical effect,
the direct physical effect

of getting bombarded
by these particles,

they can generate
the Aurora Borealis,

the Northern Lights, and these
are spectacular and beautiful.

Auroras are beautiful,
but they're also the front line

in the battle between Earth
and the solar wind.

Without our protective shield,

we'd suffer the same fate
as Venus or Mars.

But there's a mystery
surrounding the solar wind.

One of the things
we know about the solar wind

is that it is hugely energetic,
million miles an hour.

What gives it that energy?

Astronomers think
the source of the solar wind

lies in the inner corona...

..the atmosphere of the sun revealed
by our solar sentinel, SOHO.

SOHO's data shows
that near the sun's surface,

the wind speed is close to zero...

..but by the time the wind
gets to the outer corona,

it accelerates to 720,000 mph.

Something happens mysterious

between the surface of the sun
and the corona

that gives a punch
to the solar wind.

To investigate,
we need to visit the corona...

..so NASA sent a scout
on a daring mission

behind enemy lines.

The Parker Solar Probe,
that's a daredevil.

This is designed
to dive bomb the sun.

The sun exerts a hostile influence

on the planets of our solar system.

The solar wind.

It's fast, it's lethal,
but we don't know how it works.

We have spacecraft
between us and the sun

that can actually see
what's coming toward us,

but what scientists have never
been able to explain is

what actually accelerates
the wind away from the sun?

This has been one of the biggest
mysteries of the sun so far.

For decades,
we had no way of solving it...

..until now.

There are some really wonderful
moments when you're a scientist.

And I was actually at the launch
of the Parker Solar Probe,

standing right next
to Dr Eugene Parker,
who it was named after.

MAN: Lift-off
of the Parker Solar Probe.

Long ago, he had proposed the sun
probably had a wind of particles

that affected the Earth,
and people basically laughed at him,

but he was proven right over time.

And as that giant Delta rocket
slowly went up from the pad,

he and I both got to bebathed
in that light and smile.

There has been no spacecraft
ever in human history

to fly through the corona,
the very atmosphere, of the sun.

Didn't work out well for Icarus

and we hope it works out
well for Parker.

The thing about going near the sun
is the closer you go to it,

the closer your temperature
gets to its surface temperature,

and its surface temperature
is 6,000 degrees,

which vaporises metal easily.
(CHUCKLES)

Surviving close to the sun
is a big ask...

..but reaching the sun,
that's an even bigger
challenge.

It's very hot.
It tends to melt your spacecraft.

That's the obvious problem.

A less obvious problem is
it's just hard to get there.

This is something that is very hard
for most people to grasp.

There have been
suggestions of, you know,

let's send all our nuclear waste
and trash into the sun or whatever,

and it turns out
to be very difficult

to drop anything into the sun.

The reason is the Earth is circling
around the sun at 67,000 mph.

That's good cos that means
we don't drop into the sun,

we stay at the same distance.

But if you do wanna drop
into the sun,

you have to lose that velocity,
and that's a lot of velocity.

To lose speed, the Parker
Solar Probe swings by Venus

performing a gravitational
slingshot in reverse.

THALLER: Now,
usually a gravitational slingshot

gives us more velocity,

so if we're flying out to Pluto,
for example,

we might whip the spacecraft
around the planet Jupiter.

It actually takes the spacecraft
and gravitationally

slingshots it forward,
making it go faster.

What we do with the Parker
Solar Probe is the opposite.

We're gonna use
a gravitational slingshot,

but not to speed it up,
to slow it down.

Parker's gravitational maneuverers
send the craft on a trajectory

inside the sun's extended corona...

..closer to the sun
than any spacecraft before it.

This probe actually dives
really deep toward the sun,

so it's actually going through
some of these coronal material

and can actually observe it directly
in a way that other probes can't.

Using its extreme
ultraviolet telescope,

Parker spots
vast dark regions below.

There's really interesting regions
called coronal holes,

where you can see
literally deeper into the sun.

Coronal holes
are areas of the sun's corona

where the atmosphere
is cooler and less dense.

And when the probe passes over
a hole in the corona, it gets more,

it gets a bigger blaster
of the solar wind.

These coronal holes appear
to be the source of the solar wind.

We think it's through these holes

that the solar wind
is able to escape the sun.

The big question is
how does the solar wind

actually accelerate away
from the sun?

It seems to defy logic.

You would think that,
as something leaves the source,

it would start to slow down,
or at least stay the same speed,

but this doesn't. It gets faster.

THALLER: Something is
accelerating the solar wind.

It gets faster and hotter
as it moves away

from the surface of the sun,
and the mechanism is a mystery.

To solve the mystery,

our solar scout
dives close to the sun...

..not to see what's going on,
but to listen.

(HOLLOW RUMBLING)

That sounded spooky.
That sounded really spooky.

For something
that's so big and powerful,

it's very gentle sounding.
It really, you know,

disguises the fact
that it's incredibly destructive

and would kill me in an instant.
(LAUGHS)

These strange sounds
could actually reveal

what gives the solar wind
its destructive power.

Fluctuations in the sun's
magnetic field generate waves

that roll through the particles
of the solar wind.

These acoustic waves
transport particles with them,

they give them energy.

Think about a surfer actually
going down the surface of a wave,

going faster
and faster all the time.

These waves could be
what accelerates

the particles in the solar wind

from zero to 720,000 mph...

..giving them the momentum they need
to reach far into the solar system.

The solar winds
travel just incredible distances.

You know, they go past the Earth,
past Jupiter.

They've even been seen past Pluto.

THALLER: It really does
pack a wallop,

even all the way at the edge
of our solar system.

One thing that really
surprised me is that Pluto,

there are bits of its atmosphere

being blasted off
by the solar wind all the time.

Tons of atmosphere a day
are being lost from Pluto.

The solar wind is powerful enough
to blast past the planets...

..to the very edges
of our solar system.

But how far does that wind reach?

For 40 years, the oldest members
of the solar fleet

have been on a long-range
reconnaissance mission to find out.

The Voyager program,
it was a wonderful idea,

a grand tour
of the outer solar system

in the latter part of the 1970s.

There was a magic period
of time there where one spacecraft,

by doing gravity slingshots
past the planets,

could visit every planet,

and, er, in the process, of course,
that flings the spacecraft

out of the solar system
at very high speeds.

At this distance, our sun is just
a slightly brighter point of light,

a set against thousands
of other points of light.

It is just lonely out there.

In fact, both Voyagers
have travelled so far now

that they've effectively reached
the outer edges of our solar system,

that boundary zone
where the sun's influence wanes

and the stars take over.

Over 11 billion mi away,

the Voyager probes cross over
into interstellar space.

But have they reached the edge
of the solar wind?

Voyager 2, it was able to sample
the environment around it

and found the usual mix
of solar wind particles give way

to a different flavour of particles
with different energies,

the general interstellar
mix of particles

that are just hanging out
in our galaxy.

The solar wind actually smashes into

and shocks up against the gas
of the interstellar medium.

We had discovered the edge
of our solar system

and it was much more dramatic,

much more active
than we anticipated.

Interstellar space
is violent and dangerous,

teeming with lethal radiation.

Supernova blasts
and colliding neutron stars

send cosmic rays across the galaxy,
straight toward our solar system.

But these deadly threats
are stopped in their tracks.

THALLER: We really do live inside
kind of a protective bubble

that's being blown
by the solar wind.

As the solar wind moves out
into our solar system,

it carries with it
the sun's magnetic field.

That magnetic field protects us
from the highest energy particles

the universe can come up with,
cosmic rays.

In some cases, a single proton
can have as much energy

as a 100-mph fast ball.

Without this protective bubble,
called the heliosphere,

cosmic protons
would smash through your cells,

damaging your DNA.

Ironically, the solar wind is deadly

but without it, we wouldn't be here.

Like we saw with Mars,
the solar wind has the ability

to wipe out life on Earth.

But out there in the furthest
reaches of our solar system,

it's defending life on Earth.

So in a way, it's a giver of life
and it takes life, a yin and a yang.

And now, for the first time,

the Voyager probes have looked back

at the heliosphere
from the outside...

revealing what
our solar system looks like

as it moves through space.

Something that we lose sight of
sitting here on Earth

watching the sun around,
watching the planets go round,

is that the sun itself
is actually hurtling through space

really, really fast on an orbit
around the centre of our galaxy.

If our sun
were perfectly stationary,

then the heliosphere
would be a perfect sphere.

But because it's moving,

it's ploughing through
that interstellar medium,

and so that makes one end shorter
and the other end longer,

and new research is showing

it's even more
complicated than that,

where we might have, like,
a double tail, almost like a...

A buttery croissant
surrounding the sun.

Our sun shapes our world

and protects us from the dangers
of interstellar space.

It's the engine that drives
the entire solar system...

..and now, for the first time,

our fleet of solar spacecraft
shows us how it works.

We're pretty familiar
with the sun, right?

You see it during the day,
lights up the Earth,

provides us with heat,
but observing it with
all these other satellites,

all these observatories,
has shown us a side of the sun

that we knew nothing about.

We have this whole fleet
of spacecraft orbiting the sun,

taking observations in all these
different wavelengths,

X-ray, ultraviolet,
optical, infra-red.

They tell us about
the functioning of the sun

from its outer atmosphere
down to its deep core,

and give us a window into its...
its functions and its evolution.

Put them all together
and we finally have an understanding

of our source of life itself.