Original subtitles

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.