Original subtitles

NARRATOR: There's a violent star at the center

of our solar system.

The immense power, the roiling, boiling surface,

the massive plumes.

It's ridiculous.

NARRATOR: 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.

NARRATOR: 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 built a fleet of spacecraft that

monitor the Sun 24 hours a day.

NARRATOR: With the Sun under close surveillance,

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

[explosion]

September 6, 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 the 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.

NARRATOR: The flare up 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.

NARRATOR: Radio communication between disaster relief teams

goes down for most of the day.

Space weather and Earth weather combined to create chaos.

HAKEEM 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 in order to do that, we need to have eyes on the Sun,

as many eyes as we can get.

RADIO VOICE: 3, 2, 1.

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

RADIO VOICE: We have ignition.

And we have liftoff.

NEWSCASTER VOICES: Liftoff.

And liftoff.

On an international mission of the solar physics.

NARRATOR: A fleet of daring spacecraft.

We humans have come a long way.

If you go back a few thousand years,

people were worshipping 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 going to do next.

That's nuts.

NARRATOR: 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 probe is on the lookout.

It's constantly vigilant.

PHIL PLAIT: It looks at the Sun and 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.

NARRATOR: The record for the longest service

goes to SOHO, our sentinel monitoring the Sun

and its faint outer atmosphere.

PHIL PLAIT: The Solar and Heliosphere

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.

NINA LANZA: Instead of looking directly at it,

it actually blocks out most of the lights

that we can see all these beautiful structures

that surround the Sun.

NARRATOR: And then there's the new recruit...

The Parker Solar Probe.

Our scout going deep behind enemy lines.

PAUL M. SUTTER: 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.

DAN DURDA: We're flying so close to the Sun,

we're flying through the gases of its atmosphere.

NARRATOR: 29 other craft make up the fleet,

each with their own role to play.

PHIL PLAIT: This fleet of spacecraft

that we have, the overall mission is to observe the Sun

scientifically, learn about its behavior, but also importantly,

to learn about the effects that it has on Earth.

NARRATOR: Our look-out probe, the Solar

Dynamics Observatory, or SDO, spots something hellish.

PHIL PLAIT: Today's forecast for the Sun

is predicted to be 10,000 degrees Fahrenheit with winds

of up to 600 miles per second.

And a pretty decent chance of rain.

You don't want to be in this rainstorm

because your umbrella isn't going to help you.

Solar rain isn't water.

It's plasma.

Hot plasma.

NARRATOR: Rather than a solid, liquid, or gas,

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

Plasma.

MICHELLE THALLER: 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.

NARRATOR: And the Sun has the most powerful magnetic field

in the solar system.

It twists and flows through the entire star.

PHIL PLAIT: The Sun's magnetic field

is incredibly complicated.

There are lots of loops of magnetic lines coming

out of the Sun's surface.

GIBOR BASRI: 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.

NARRATOR: 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.

PHIL PLAIT: 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.

NARRATOR: 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 lookouts spotted an explosion

on the surface of the Sun.

PHIL PLAIT: 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.

NARRATOR: The craft tracked the magnetic loops

above the Sun's surface.

They were highly unstable.

SDO takes very detailed pictures

of where the flows are.

You can actually see gas flowing from one place.

You can see the magnetic loops.

This 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 on to something.

Don't cross the streams.

NARRATOR: The contact between magnetic loops released an epic

explosion of high-energy light.

This radiation altered our planet's atmosphere.

Radio waves jammed, causing blackouts

at the worst possible moment.

PHIL PLAIT: Solar flares are happening on the Sun

90 million miles 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 bonds 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.

NARRATOR: But the Sun's twisting magnetic fields

do more than just disrupt our communications.

And when we see flares, we've got

to keep an eye out on those.

But sometimes, there's something even bigger.

NARRATOR: The Sun launches huge clouds of plasma

across the solar system.

PHIL PLAIT: 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.

NARRATOR: Can the solar fleet safeguard Earth?

November 5, 2018.

An explosive cloud of plasma hits

the Parker Solar Probe as it orbits just

15 million miles from the Sun.

We have this fleet of spacecraft

out there viewing the Sun.

And they are also under attack by the Sun.

There are explosions coming from its surface.

Is not just light, but explosions of hot plasma.

And the Parker Solar Probe got blasted.

And yet it survived.

NARRATOR: 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 scouts is prepared for the onslaught.

PHIL 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.

NARRATOR: Could these blasts pose a danger to our planet?

A coronal mass ejection accelerates

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.

NARRATOR: To understand these dangerous blasts of plasma, we

have to look at their source...

An area around the Sun known as the corona.

PHIL PLAIT: 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.

NARRATOR: 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.

Astronomers, though, we're impatient.

We don't want to have 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.

NARRATOR: 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,

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

NARRATOR: 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?

GIBOR BASRI: 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.

NARRATOR: Coronal mass ejections are solar flares on steroids.

If a solar flare was a firecracker,

coronal mass ejection is more like an atom bomb.

NARRATOR: 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 are able to penetrate our shields.

Our shield being our own magnetic field.

NARRATOR: Once they breach our defenses,

the particles of a coronal mass ejection can wreak havoc.

In August of 1972, tensions were running high in Vietnam.

[bombs exploding]

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.

NARRATOR: 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 de-escalated.

PHIL PLAIT: The Sun is an immense ball of plasma

860,000 miles 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.

NARRATOR: Our new fleet of solar observers

are our first line of defense.

PHIL PLAIT: The Sun is a little over

90 million miles 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.

We can watch the Sun to see is there going to be an event,

or is an event starting?

And these satellites can then tell

us, hey, you better be careful.

You might need to batten down the hatches on Earth.

NARRATOR: But there may be an earlier clue

the fleet can watch out for.

Vast, dark regions moving across the solar surface

called sunspots.

HAKEEM OLUSEYI: We know that this is

the wind up before the release.

This thing is getting ready to blow.

NARRATOR: In March of 1989, a solar eruption

caused blackouts across Canada and malfunctions

on board the space shuttle.

RADIO VOICE: We've been seeing some erratic pressure

signatures out of tank 3, as well as some manifold pressure

spikes in that system.

NARRATOR: 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 more of a peaceful existence.

NARRATOR: 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.

Sunspots.

HAKEEM OLUSEYI: Sunspots 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.

NARRATOR: 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

going to see more intense and more frequent solar flares.

NARRATOR: 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.

PAUL M. 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.

NARRATOR: 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 sunspots and to the Sun's outbursts.

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 center 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.

NARRATOR: But unlike an onion, the layers spin.

MICHELLE THALLER: There are currents inside the Sun

we don't see from the surface.

Layers of the Sun deep down inside

are rotating at different rates than the layers above.

GIBOR 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 pole.

NARRATOR: These layers of plasma grinding against each other

generate the Sun's enormously powerful magnetic field

and give rise to sunspots, plasma loops, and solar flares.

This differential rotation takes the field

and starts twisting it around the Sun.

So as the magnetic field 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 sunspots.

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.

NARRATOR: 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.

NARRATOR: 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.

NARRATOR: 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 polls.

MICHELLE THALLER: When that plasma

rebounds from the equator and hits the magnetic field coming

down from the poles at the mid latitudes,

you get a huge burst of magnetic activity.

NARRATOR: Magnetic activity that triggers sunspots 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.

NARRATOR: 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 start to see more sunspots, more activity, more flares,

more ejections, and more space weather

that we have to deal with.

NARRATOR: 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 mile-an-hour wind.

NARRATOR: And it can be deadly.

[explosion]

In November 2019, the solar fleet watched as Mercury

sailed across the Sun.

JESSIE CHRISTIANSEN: 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.

NARRATOR: 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.

KEVIN WALSH: Despite the overall really

high temperatures across the whole planet,

there are regions...

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.

NARRATOR: 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.

NARRATOR: The Sun creating ice sounds strange.

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

MICHELLE THALLER: We often think of space as being empty.

But in fact, we are bathed in a wind, a million

mile-an-hour wind of high-energy particles from the Sun

all the time.

The solar wind.

NARRATOR: A stream of subatomic particles

called protons constantly flow out

from the Sun in all directions, bombarding the planets

of our solar system.

CARLY 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.

NARRATOR: Protons in the solar wind combined with oxygen

to form water molecules.

They condense and freeze in craters

which never see sunlight.

So even on the Sun's closest neighbor, ice builds up.

But the solar wind doesn't stop at Mercury.

The solar wind has a tremendous impact

on the world's of our solar system.

We think it's responsible for the planet Venus

becoming this hell hole of heat.

NARRATOR: 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.

PAUL M. SUTTER: We believe that billions of years

ago, Mars had an atmosphere, and it had oceans, and rivers.

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.

NARRATOR: And Earth is in the line of fire too.

It's bombarded every day with solar wind particles.

So how has life survived?

MICHELLE 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 lines trap those

charged particles and redirect them

to the poles of the planet.

PHIL PLAIT: 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.

NARRATOR: 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 is a mystery surrounding the solar wind.

One of the things we know about the solar wind

is that it is hugely energetic.

A million miles-an-hour.

What gives it that energy?

NARRATOR: 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 win gets to the outer corona,

it accelerates to 720,000 miles-an-hour.

Something happens mysterious between the surface of the Sun

and the corona that gives a punch to the solar wind.

NARRATOR: 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.

[explosion]

NARRATOR: 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.

MICHELLE THALLER: We have spacecraft between us

and the Sun that can actually see what's coming towards us

and how it will impact 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.

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

Until now.

There really are some of these 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 the probe is named after.

NEWSCASTER VOICE: Liftoff of the Parker Solar Probe.

MICHELLE THALLER: 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 be bathed 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.

GIBOR BASRI: 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 vaporizes metal easily.

NARRATOR: 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 I think that it's very hard for most people

to grasp.

There have been suggestions of, you

know, let's send all our nuclear waste into the Sun,

or our trash, or whatever.

And it turns out to be very difficult to drop

anything into the Sun.

NARRATOR: The reason is the Earth

is circling around the Sun at 67,000 miles-an-hour.

That's good because that means we don't drop in to the Sun.

We stay at the same distance.

But if you do want to drop into the Sun,

you'd have to lose that velocity.

And that's a lot of velocity.

NARRATOR: To lose speed the Parker Solar Probe

swings by Venus, performing a gravitational slingshot

in reverse.

MICHELLE 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 go faster.

The thing that we have to do with Parker Solar Probe

is the opposite.

We're going to use a gravitational slingshot,

but not to speed it up...

To slow it down.

NARRATOR: Parker's gravitational maneuvers

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.

NARRATOR: 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.

NARRATOR: Coronal holes are areas of the Sun's coronavirus

where the atmosphere is cooler and less dense.

And when the probe passes over a hole in the coronavirus it

gets a bigger blast of the solar wind.

NARRATOR: These coronal holes appear to be

the source of the solar wind.

And we think it's through these holes

that the solar wind is able to escape the Sun.

NARRATOR: 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 probably start to slow down, or at least

stay the same speed.

But this doesn't.

It gets faster.

MICHELLE 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.

NARRATOR: To solve the mystery, our solar scout

dives close to the Sun...

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

[strange noises]

That sounded spooky.

That sounded really spooky.

You know, 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.

NARRATOR: 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

that give them energy.

Think about a surfer actually going

down the surface of a wave, going

faster and faster all the time.

NARRATOR: These waves could be what accelerates the particles

in the solar wind from 0 to 720,000 miles-an-hour,

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.

MICHELLE THALLER: It really does pack a wallop, even all the way

at the edge of our solar system.

One of the things 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.

NARRATOR: The solar wind is powerful enough

to blast past the planets to the very edges of our solar system.

When we sent members of the solar fleet to investigate,

we witnessed a battle between the Sun and interstellar space.

A battle that could decide the fate of our planet.

[explosion]

The Sun blasts the solar system with a storm of particles.

The solar wind.

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.

In fact, both Voyagers have traveled 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.

NARRATOR: Over 11 billion miles 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 flavor 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 discovered the edge of our solar system.

And it was much more dramatic, much more active

than we anticipated.

NARRATOR: 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.

MICHELLE THALLER: We really do live inside kind

of a protective bubble that's being blown by the solar wind.

You see, 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 mile-an-hour fastball.

NARRATOR: 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.

PHIL PLAIT: 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.

NARRATOR: 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 go around, watching the planets go around,

is that the Sun itself is actually hurtling through space

really, really fast on an orbit around the center

of our galaxy.

If our Sun were perfectly stationary,

then the heliosphere would be a perfect sphere.

But because it's moving, it's plowing

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 buttery croissant surrounding the Sun.

NARRATOR: 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 all the time 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.

JESSIE CHRISTIANSEN: We have this whole fleet of spacecraft

orbiting the Sun taking observations in all

of these different wavelengths.

X-ray, ultraviolet, optical, infrared.

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 functions and its evolution.

Put them all together, and we finally have an understanding

of our source of life itself.