Original subtitles

- [Narrator] Before Earth, before the sun,

before anything we know, there was only gas and dust,

cold, drifting, ancient,

a swirling, chaotic cloud adrift in the Milky Way.

From this darkness, a masterpiece would emerge,

our solar system.

- The formation of our solar system is a fantastic example

of this cycle of life, and death, and rebirth.

- [Narrator] It begins with the cataclysmic end

of primordial stars.

(explosion booming)

These explosions tear through the galaxy-seeding space

with heavy elements.

And from their ashes, a molecular cloud takes shape.

For tens of millions of years, it slumbers,

still and silent,

until a cosmic event spurs a chain reaction.

Gravity stirs.

The collapse begins.

At its core, heat and pressure rise until the sun is born.

Around it, a disk of dust and gas

begins to gather and collide,

slowly evolving into the planets, moons,

and asteroids we know today.

It's a story written over billions of years,

one of unimaginable scale and breathtaking complexity,

a cosmic clockwork that somehow, against all odds,

settled into balance.

- Our solar system is incredibly unique,

and it's very reasonable to expect

that there is not a perfect analog out there

for us to explore.

- The origins of our solar system,

we have an idea of how the sun and the planets formed

purely based off of being able to observe other stars

and where they are in their evolution.

- But there's still quite a few unanswered questions

about exactly how our sun formed

and how the planets and moons around the sun formed.

- [Narrator] The clues lay scattered across the galaxy,

remnants of ancient collisions,

stellar winds, and the very structure of the cosmos.

(majestic music)

(gentle music)

(lighthearted music)

(lighthearted music)

Throughout the vast reaches of our galaxy,

billions of stellar systems exist in chaotic turmoil,

planets with wildly eccentric orbits,

stars pulsating unpredictably,

cosmic environments hostile to life.

Yet here we are, orbiting a remarkably stable star

at precisely the right distance,

in a system of astonishing equilibrium.

- A stellar system contains at least a star, maybe two,

and it also has all of its revolving bodies around it.

And all of the objects

that are bound by gravity to that star

are part of the system.

- Our solar system consists of the sun

and everything that orbits around the sun,

so primarily our planets, and then there's also moons,

and asteroids, and comets, and other small bodies.

- [Narrator] In the disk surrounding our star,

the eight planets keep the system in steady calibration.

Jupiter's immense gravity acts as a cosmic shield,

deflecting dangerous impacts from beyond,

while the Earth and its moon orbit in the perfect proximity

and rhythm for the emergence of the only known life form

in our cosmos.

Earth is perfectly set right inside this habitable zone

where we can have liquid water

that allows life to thrive the way it does.

We don't know how common this is in the universe,

but the fact that Earth

does sit exactly within this habitable zone

is just a luck of the draw.

- [Narrator] The planetary arrangement defies probability,

rocky inner worlds, gas giants in the middle distance,

ice worlds beyond.

At our system's heart is our sun,

which shines with metronomic regularity,

generating a heartbeat that has remained stable

for billions of years.

- The sun itself is a medium-sized star.

It's not the most common,

but it is sort of a fairly typical

sort of medium-sized star.

- It didn't have to be this way, though.

We're quite fortunate.

If we were in a system with a more massive star,

so more massive than the sun,

then those more massive stars don't live as long.

And conversely, we could be around a much smaller star.

Most of the stars in the Milky Way

are less massive than the sun.

And you might think, oh, well, low mass stars,

if they have a long lifetime,

maybe that would be a good place to live.

But it turns out that a low mass star is also,

they tend to be really active,

which means they have more storms

and more magnetic activity,

which could be dangerous for life on a planet.

- [Narrator] This arrangement, so familiar to us,

is exceedingly rare

among the thousands of other systems we've discovered.

- When we look at exoplanetary system,

they don't necessarily look like the solar system.

- What is necessary to trigger the collapse

of a giant molecular cloud

and give rise to a solar system like ours?

(lighthearted music)

(explosion booming)

- [Narrator] This harmony did not emerge

from a peaceful process.

Our solar system's history is one of extraordinary violence,

a story of collisions, migrations,

and near catastrophes that, against incredible odds,

produced the cosmic sanctuary we inhabit today.

- There are all sorts of things we don't know

about how the solar system formed.

We don't know exactly what cloud of gas we formed in.

We don't know who our sort of birth partners

or siblings are.

So a lot of the details of how the sun formed

are still unknown.

- And so certainly the formation of our solar system

is maybe it's the moment zero, right?

It's that time where it all begins.

And so I think understanding that is incredibly important

to understanding how we came to be.

- [Narrator] Long before the first star flickered to life,

our solar system existed

as a molecular cloud of gas and dust,

light-years wide and millions of suns in mass.

- The gas in our galaxy comes in different forms.

The densest parts of the gas distribution

are, they sort of look like kind of amorphous clouds.

We call them molecular clouds.

- [Narrator] Rather than holding water,

these clouds are filled with molecules like hydrogen.

And it's within these frigid cradles

where new stars are born.

In addition to holding the raw material for new stars,

they also contain stars of the past,

the dust of dead stellar bodies

that will nourish the next generation.

- Without this diversity of elements

that can then form all sorts of molecules,

it would have been impossible to generate

all that diversity we know on Earth.

And even us as human, we are made out of this stardust.

97% of our body is made out of it.

- [Narrator] This molecular cloud

hangs in delicate equilibrium for eons,

a silent, dark giant.

This is the universe's primordial soup,

the raw ingredients for the emergence of everything we know.

So how did such a structure, cold and seemingly inert,

set the stage for creation?

(enigmatic music)

To answer this question,

let's take a look at the Orion Nebula.

It exists in the depths of the Milky Way,

a cloud of molecular hydrogen and cosmic dust

where new worlds awaken.

Here, thousands of young stars illuminate the gas.

This is not a static masterpiece

but a dynamic work in progress,

a place where the universe tells an epic tale of creation.

- The Orion Nebula

is the closest massive star-forming region

to our solar system,

located a merely 1,500 light-years away.

- It's full of hundreds or thousands of stars,

including some very massive stars.

Some of them are going to end their lives soon and explode.

But we also see young stars being born in the region.

- What's really important

about actually observing star formation

is it allows us to sort of look into the sun's past.

So we're not able to actually,

you know, research the sun's formation on its own,

but we can use other stars and their formation processes

to make that sort of connection

and understand how the sun must have formed

by using that other star formation

as an analog to the solar system.

- The Orion Nebula serves as a fantastic testbed

for understanding the star formation process,

which consequently feeds

into our understanding of the planet formation process.

Our understanding of star and planet formation together

gives rise to our understanding of where we came from,

where the solar system came from.

- [Narrator] The wild spectacle of Orion's nascent stars

offers a glimpse into our own origins,

hinting at the forces that shaped the dawn

of our solar system.

- Because it's so bright,

we can actually see the Orion Nebula with our naked eye.

The light that we're seeing coming from the nebula

is really high energy radiation

from the newest generation of stars

that have recently formed.

- One reason why we might feel so connected

to the Orion Nebula

is firstly because it's something we can see

on the night sky with the naked eye, right?

It's something that humanity,

different cultures have been able to tell stories about.

In addition to that, it marks the birth place for stars.

It's a place where baby stars are forming.

And so when we think about our own sun,

it provides us the opportunity

to see how these types of stars are formed

and how they evolved in their early days.

(rhythmic music)

- [Narrator] The Orion Nebula

is composed of a complex, layered structure,

reflecting the dynamic nature of star formation.

This is a sprawling cosmic cloud,

primarily composed of hydrogen,

the most abundant element in the universe.

Along with trace amounts of other molecules and elements,

this hydrogen exists at extremely low temperatures,

often just a few degrees above absolute zero.

Interspersed throughout this cloud

are microscopic dust grains,

which shield hydrogen from the harsh ultraviolet radiation

that would otherwise dissociate it.

Because of this, beneath Orion's icy veil,

infant stars blaze.

- One important place near the center of the Orion Nebula

is the Trapezium Cluster.

And when we look at this Trapezium Cluster,

we can see that extremely massive stars are being born.

We call these O and B type stars.

It's a naming system astronomers have for stars.

These are the most massive stars that form.

- [Narrator] These celestial newborns

range from fierce blue giants 20 times the sun's mass

to tiny red dwarfs barely large enough to ignite.

Some spin wildly,

while others produce blinding flares of light,

a full spectrum of stellar possibilities

that offer us a window into our sun's turbulent youth.

Within the nebula,

the dark silhouette reveal protoplanetary disks,

the precursors to planetary systems.

- A protoplanetary disk is a flattened ring of gas and dust

orbiting around a newly formed star.

And it's within protoplanetary disks

that we expect the planet formation process to take place.

- [Narrator] Within the cloud's core,

a delicate equilibrium exists between chaos and order.

Here, turbulence churns gas at staggering speeds,

forging the cosmic architecture

that will dictate the destiny of stars.

- This disk is formed of tiny little particles

that are orbiting the star.

And you can see it as a soup of tiny particles

that are going in all directions,

but roughly with a general rotation motion around the stars.

But at a very small scale,

there's a lot of bumping between the particles.

- Giant molecular clouds are turbulent places,

with gas churning around

at hundreds of kilometers per second,

which creates regions of lower density and higher density.

And it's that turbulence that carves out gaps and ridges

within the giant molecular cloud that eventually seed

the locations of star formation throughout.

- [Narrator] From this chaos emerge filaments,

thread-like structures spanning vast distances

that use gravity to channel gas

into the dense cores where stars ignite.

- Molecular clouds are complex structures.

They have their own internal structure

and their own internal phases.

In particular, we've seen that the gas in them

often forms long filamentary structures.

And stars seem to tend to form in those filaments.

- [Narrator] Like stellar assembly lines,

each knot in these filaments allows gravity to take hold

and birth a new star.

(gentle music)

As gravity pulls gas in,

the fierce ultraviolet radiation from massive stars nearby

also carves away its surrounding material,

sculpting nebula's ever changing landscape.

Newly formed OB stars give off immense amounts

of ultraviolet radiation that produces these bright bubbles

around newly formed stars.

Those bubbles exert a pressure on the surrounding gas,

which again can enhance the density of the molecular cloud

in small regions that, if they reach a critical density,

will collapse to form new stars.

- [Narrator] Magnetic fields also guide this process.

Filaments often align with these fields,

working together to shape the cloud structure.

Without this cosmic choreography,

stars might form too erratically or not at all.

(suspenseful music)

Yet for all their power, turbulence, gravity,

and magnetic fields alone may not tell the full story.

For our solar system to exist, equilibrium had to break.

A spark was needed to ignite the chain reaction

that birthed the sun.

(dramatic music)

(collision booming)

(dramatic music)

(explosion booming)

The collapse of the giant molecular cloud

that formed our solar system 4.6 billion years ago

represents a critical turning point.

Although we understand the outcome,

the initiating event remains a subject of debate.

What triggered this collapse?

For eons, our molecular cloud finds itself

in a cosmic standoff.

Thermal pressure from the hot gas within pushes outward,

while gravity pulls inward,

and then the balance starts to break.

Deep within, dense regions grow colder, heavier,

until they cross a critical threshold and gravity wins.

- A molecular cloud is a big puffy ball of gas and dust,

but it's not all one uniform density.

There are regions that are a little bit more dense

and regions that are a little bit under-dense.

And what we know from understanding gravity

is you can reach a critical threshold.

It's given the technical name, a Jeans mass.

But essentially it's this critical threshold

that if you have enough mass in a given volume,

it's going to collapse to make a star.

So if you have a region that is massive enough,

gravity is gonna win out over any internal motions,

over any rotation.

- [Narrator] High density regions

will eventually reach a tipping point.

Too much mass in one place and gravity becomes unstoppable.

Suddenly, gas surges inward,

spinning faster as it contracts.

The angular momentum flattens the chaos into a disk.

At its heart, a protostar flickers to life.

But what exactly tipped the scales,

increasing the clouds density

and triggering the birth of our solar system?

(dramatic music)

Was it chaos alone

or did this collapse require a more violent push?

- Molecular clouds are the nurseries of star formation,

and some region of them has to collapse under gravity

to make new stars.

And that could be just by chance,

a region has a mass above a threshold

and it collapses and makes stars.

But it could also be triggered

by some nearby dramatic event like a supernova explosion.

(suspenseful music)

- [Narrator] In the silent abyss of space,

death ignites life.

A dying star in its final cataclysmic act

unleashes a shockwave that tears across the light years,

a force capable of obliterating worlds, or birthing them.

- Supernova are this end of life event

that occurs at the end of a massive star's life.

- Really massive stars

are incredibly efficient at burning through their fuel.

- [Narrator] But their gas tank has a limit.

As they burn through the hydrogen within their core,

the resulting energy escapes out into space.

When a giant star finally runs out of fuel,

the core implodes, crushed by its own weight,

like a building collapsing inward.

(dramatic music)

- This results in a massive collapse

of material down to the core

that produces an immense shockwave

that propagates back through the shell of the star

and ejects material in an explosive supernova.

You can think of it as a basketball

with a tennis ball on top and dropping the two.

When they hit the ground, the basketball will bounce up

maybe a few feet,

whereas the energy within the basketball

will send the tennis ball much higher into the air.

- So when a supernova goes off,

it sends out this blast wave into space.

- [Narrator] The shockwave ripples outward

at 30 million kilometers an hour,

fast enough to circle Earth almost once in a second.

The star's outer layers are blown away,

scattering metals and dust into space,

seeds for future stars, planets, and even life.

It's possible this material slams into our molecular cloud.

Gas and dust spiral inward, a chaotic ballet of gravity

culminating in the birth of a protostar.

Without that initial spark,

the stellar engine may never have roared to life.

But is this what really happened?

(dramatic music)

An unexpected witness may offer a clue.

When the Allende meteorite explodes over Mexico in 1969,

it scatters fragments of our solar system's infancy

across the desert.

More than space debris, this is a celestial time capsule

that's been frozen in space for 4.6 billion years.

- They contain some of the first solids

that formed in our solar system.

And so when you're holding it,

it does actually feel quite powerful

because what you're holding

is literally the oldest thing you could ever hold.

(lighthearted music)

- [Narrator] Its minerals reveal fascinating insights

into the violent processes of stellar birth.

- The fragments of it have been studied extensively,

and this is where we detected the specific isotope

of elements like iron, and aluminum, and others.

- [Narrator] The fragments hold Iron-60,

a radioactive isotope that shouldn't exist

in 4.6 billion-year-old rocks,

that is, unless they are remnants of a stellar death nearby.

Their presence is a definitive clue, a smoking gun,

supporting the theory that a supernova shockwave slammed

into our molecular cloud.

This cosmic impact dispersed heavy elements

and initiated the collapse that birthed our solar system.

- When we look at the chemical composition,

a very special isotope that we see in the solar system,

we notice the presence of Iron-60, Aluminum-26.

These isotope are known to be emitted

and being part of the supernova explosions.

- [Narrator] Might this suggest that a supernova's fury

reached us just as our molecular cloud began to stir?

There could be a hint.

427 light-years away,

we find a snapshot of a similar explosive birth,

which may illuminate how our solar system came to be.

In the constellation Ophiuchus,

massive stars meet swift, violent ends,

their supernova shockwaves

tearing through neighboring clouds.

- Within this star-forming region,

we've studied the chemistry of the material,

and we see there's quite a lot of Aluminum-26.

That's an isotope of aluminum

that we know is produced in abundance

in supernova explosions.

But it's also pretty short lived.

So the fact that we're seeing it

means that a supernova went off really recently.

- [Narrator] These radioactive elements

mark the fleeting moments between a star's death

and another solar system's birth.

- The star formation in that region

is clearly being enriched by a recent supernova explosion.

- This region contains all sorts of area

that are forming stars.

And within these regions,

there are hundreds and thousands of stars

that are at different evolution stage.

- [Narrator] Stars in Ophiuchus rarely emerge alone.

They are born in clusters, like cosmic families,

their beginnings and destinies intertwined.

- But it is important to remember

that these regions are extremely young.

And although we see them all bound together

by gravity and close to each other,

they're not meant to stay like that forever.

(dramatic music)

- [Narrator] Over millions of years,

the bonds loosen and the stars slowly drift apart,

each carrying a piece of their shared origin

into the wider galaxy.

And when they die,

often in spectacular supernova explosions,

they scatter essential elements like carbon, oxygen,

and radioactive material into the space around them.

This seeds their surroundings

with the raw ingredients for planets,

and eventually life itself.

Could this have been the origin story of our sun,

born in a clan and nursed by a sibling's death?

While a shockwave

may have set the story of our sun into motion,

growing and maintaining a stable solar system

over billions of years comes with chaos, collisions,

migrations, and gravitational forces

that are constantly reshaping it.

- After the birth of our protosun,

gravity takes over, and gas and dust spiral inward,

creating a spinning disk.

The disk rotation concentrates material at its center,

where intense pressure and heat begin to build.

Trillions of dust grains and gas molecules collide, merge,

and fragment in this environment.

It's a cosmic arena where dust particles

are constantly in motion, like bumper cars in a ring,

and each collision is a chance for growth or destruction.

(dramatic music)

- Dust particles tend to travel

a little bit faster than the gas.

So they're trying to move through this gas,

but they're feeling this drag force

because they're trying to move through a dense medium.

That causes them to lose some orbital angular momentum.

So in addition to their orbit,

these dust particles also start to drift in toward the star.

(dramatic music)

- [Narrator] These dust grains begin to stick together,

gradually forming larger bodies known as planetesimals.

In protoplanetary disks, like the one surrounding HL Tauri,

a young star about 450 light years away,

we witness this process unfold in real time.

- Whenever you think of a protostar forming,

there should be this disk of material around it,

and that's where we think planets will form.

So that's called a protoplanetary disk,

that disk of material spinning around the star.

- When we look at a system

that is forming planets, protoplanets,

we see not a very uniform disk,

but rather a disk that contains rings,

or areas that are empty,

and others that are brighter

that still contain a lot of dust.

- These gaps were long believed to be the sites

of ongoing giant planet formation,

giant planets that formed and carved out gaps

in the dust distribution of protoplanetary disks,

like the one around HL Tau.

- [Narrator] In this turbulent disk,

multiple forces are at work.

Gravity pulls inward,

while the outward pressure of gas and dust resists collapse.

Meanwhile, magnetic fields and solar wind

sculpt the disk's structure,

influencing the paths of forming planets.

It's almost certain that these gaps

are the locations of planet formation,

because any solid material

that you need to go into forming protoplanets,

that material is going to pile up at the edge of these gaps,

create an over density of solids

that is more easily collapsible into protoplanetary cores.

- [Narrator] As the disk evolves,

it sets the stage for the birth of new worlds.

But to promise the sustenance of such protoplanets,

our early protostar would require a growth spurt.

For millions of years, the protostar swells,

feeding on the swirling disk's gas.

Deep within its core, temperature builds,

soaring to 15 million degrees Celsius.

This is the moment where hydrogen nuclei,

like unlit matches, are waiting to spark a fusion.

When the core of the protostar

reaches a critical temperature and pressure,

the reaction will begin.

- The sun is really fundamentally a big ball of gas

held together by gravity.

What gravity likes to do is to pull things together.

So picture that you have this forming star.

It's a big ball of gas.

It's collapsing under gravity.

What happens in the center of that object

as it's collapsing under gravity?

It gets hotter and hotter and hotter.

And eventually, at the center of the sun

and the center of every star,

you reach a temperature that is so high,

millions of degrees, where nuclear fusion can happen.

- By crushing the atoms very close to each other,

you would think that fusing them is an easy thing to do,

but atoms don't necessarily want to fuse together.

- [Narrator] Hydrogen nuclei have positive charges

that should repel each other.

However, at the smallest scales,

the universe doesn't allow the classic laws of physics.

On the quantum level, there's a strange phenomenon

that allows hydrogen particles to slip through barriers

that would otherwise block them.

At the core of the sun, hydrogen miraculously fuses together

and the stars turn on, seemingly achieving the impossible.

This is nuclear fusion.

- Nuclear fusion is where you take the nuclei of atoms,

light atoms, bring them together,

and they make a heavier atom.

And through that process,

you actually generate a ton of energy.

- In the process of nuclear fusion,

we're converting mass itself into energy.

And that conversion of mass into energy

involves the speed of light.

E is equal to MC squared.

Speed of light is a big number.

And if you square it, you get an even bigger number.

And that means just a little bit of mass

converts into a huge amount of energy.

- [Narrator] Each second,

the sun converts 600 million tons of hydrogen

into helium at its core,

releasing energy equivalent to a billion nuclear bombs.

With its first breath of fusion,

the sun erupts into brilliance.

Violent solar winds,

charged particles racing at 1.6 million kilometers per hour,

scour the inner solar system, vaporizing dust and gas.

The sun's ignition illuminates our neighborhood of space.

And what transpires within its core

will set the stage for everything we see today.

- Once the sun ignites hydrogen in its core,

it starts to undergo a steady rate of nuclear fusion

that produces enough energy to hold the sun up

against the inward force of gravity.

And this balance between the outward thermal pressure

driven by nuclear fusion and gravity

is what will hold the sun up for about 10 billion years.

- [Narrator] It's a key piece of the puzzle

and understanding the unique conditions

that led to our solar system's formation

and the emergence of life.

(lighthearted music)

So why does our sun burn steadier

and quieter than most stars?

- A star's lifetime is dictated by its mass.

Very low mass stars will live for billions,

if not trillions of years,

whereas very massive stars

might only live for a few million years.

The distinction is mass equals temperature,

and temperature sets the rate

at which you burn through your fuel.

Massive stars will burn through their reservoir of hydrogen

extremely quickly, like a huge bonfire.

- [Narrator] Take Betelgeuse, for example,

a colossal red supergiant in the constellation Orion.

This star is around 700 times the size of the sun,

its brightness pulsating wildly through the cosmos.

At the relatively youthful age of 10 million years old,

Betelgeuse is a star that will live fast and die young.

(dramatic music)

- When you're lighting a bonfire,

you have a lot of wood in there,

a lot of fuel that you're burning,

but it burns a lot brighter,

and it burns through that fuel much quicker,

where a less massive star, for example, is like a candle,

where you're sort of lighting the wick

and it slowly burns through that wick

and the wax that's within.

- [Narrator] Our sun occupies a rare middle ground

in nearly every quality.

This mediocrity proves crucial for a long life.

If our sun had formed as a smaller mass red dwarf star,

like many of those in Orion,

it would burn for trillions of years,

but at a terrible cost.

- At the other end of the mass scale,

there are very small stars, say red dwarf stars,

that are cool at their surface,

and therefore they have a redder color,

and that do burn hydrogen in their core

but are burning it at a much slower rate.

And those stars can exist for hundreds of billions of years,

unlike the sun which can only exist for billions of years.

You might imagine that life, for instance,

would have a long time to evolve

in planetary systems around stars like that.

- But their atmosphere is extremely active.

They have flares, which means that they erupt strongly

due to their magnetic field.

- So those might be a hazard to life on planets around them.

By comparison, the sun is a much quieter

and more stable environment.

- [Narrator] Though relatively stable,

our sun does, however, harbor some volatility.

Solar flares and coronal mass ejections erupt unpredictably.

Surrounding the sun's core is a turbulent sea of plasma,

a superheated state of matter

where atoms are stripped of their electrons.

This layer, nearly 200,000 kilometers thick,

is called the convection zone.

Here, heat from deep within the sun

rises through huge churning currents.

Hot plasma surges towards the surface,

where it cools before sinking back down.

- Heat transport within the sun

happens via a different mechanism

depending on where you are inside the sun.

Deep within the sun, it's hot enough

that heat is transported via radiation,

and the sun is said to have a radiative core,

on top of which sits a convective envelope.

As you travel through the sun from its surface

at about 5,700 kelvin

all the way down to the base of this convective zone,

it heats up to about 2 million Kelvin.

And that extreme temperature difference drives convection,

like heating a pot of water on your stove.

- [Narrator] This activity manifests

as a roiling sea of granules covering the sun's surface,

bright fleeting cells where superheated plasma erupts,

cools, and retreats in mere minutes.

Zoom out and these merge into super granules,

colossal swirls that could swallow Earth twice over.

(dramatic music)

This relentless churn doesn't just transport heat,

it also generates electric currents

that weave the sun's magnetic fields into existence.

- Different layers of the sun rotate at different speeds.

And that combination of the rotation and the convection

is able to turn mechanical movement energy

of these charged particles, this plasma,

into a magnetic field that looks a lot like your bar magnet,

with a north, south.

The sun is a giant bar magnet.

- [Narrator] Deep inside the sun,

one spinning layer meets another,

both moving at a different pace.

This clashing force twists and stretches the magnetic field,

amplifying its power

and extending its reach far into the solar system.

Yet even with all of this magnetic might,

our sun is relatively calm

compared to other stars, such as red dwarfs.

- Red dwarfs are highly active stars

that release powerful flares at unexpected times.

And these flares

release immense amounts of high energy radiation

that can drive atmospheric processes on planets

and even strip planets of their atmospheres.

So if our sun were a red dwarf,

this would have drastic consequences

on the properties of planets throughout the solar system.

(bright music)

- [Narrator] If the Earth

orbited a dim and cool red dwarf star,

it would be much closer for life to emerge,

putting it directly in the star's firing line.

- The Earth at its current orbital distance

would be far too cold to be habitable.

You'd have to be much closer to the star

in order to have the right temperature for liquid water

to exist on your surface.

- [Narrator] Yet too close to a red dwarf

and its atmosphere could be stripped away entirely.

Our sun's comparatively weaker convection

is a crucial factor in Earth's habitability.

It has enough turbulence to sustain solar activity,

but not so much as to produce the extreme flares

seen on red dwarfs.

But it's not just the quieter temperature of the sun

that allows our solar system to thrive.

It's also the strange contradiction

in the way that it moves.

(lighthearted music)

(gentle music)

For the Sun's equator to complete a single rotation,

it takes 25 Earth days.

This is a seemingly slow crawl

when compared to the fast spins of the outer worlds.

- The Earth spins on its axis once a day.

The sun spins on its axis closer to once a month,

once every 25 days at the equator.

We might think,

all right, well, the sun's a much bigger system.

Maybe that has something to do with it.

Its equator is a much bigger equator.

But if we look at other bodies in the solar system,

for instance, Jupiter and Saturn,

they have rotation periods of less than an Earth day,

about half an Earth day or less.

So really, the planets spin much, much faster than the sun.

- [Narrator] The sun's rotation

creates just the right balance of solar wind and radiation.

- A structure like the sun, that has a magnetic field,

sort of gets connected

to all the ionized material around it.

It gets connected to the disk of material around it.

If that disk is spinning, then it could, in principle,

spin the sun up.

But the transfer could also work the other way.

If the sun is spinning faster than the disk,

it would start pulling the disk material around it.

And that could lead to a transfer of spin

or angular momentum outwards in the system,

from the sun into the disk material.

- [Narrator] If the sun was spinning faster,

its magnetic field would also grow more powerful,

thereby bombarding the planets

with intense storms of stellar particles.

And this rapid rotation

is exactly what we would expect to see.

But instead, the sun turns at a surprisingly slow pace.

- We've talked about a gas cloud collapsing down.

Usually, the gas it forms from has a little bit of spin.

And while the cloud can get rid of its energy

through radiation,

it can't get rid of that angular momentum.

There's no easy way to do that.

So the angular momentum is sort of stuck in the system.

- The amount of spin angular momentum

that an individual object has

is related to how fast it's spinning,

as well as how its mass is actually distributed.

Think of a figure skater spinning on ice.

When they bring their arms out, they rotate more slowly,

compared to when they bring their arms in

and spin quite rapidly.

The same is true when you're forming stars.

As that material is brought inward to small distances,

the object has to spin up to conserve spin angular momentum.

- [Narrator] As the cloud that formed the sun collapsed,

the majority of its angular momentum

should have been transferred primarily to our star.

But our solar system today seems to defy this logic.

- Despite the sun having about 99%

of the solar system's total mass,

it only has about 0.6% of its total spin angular momentum.

- [Narrator] This is one of the greatest mysteries

of our cosmic origins, the angular momentum paradox.

(rhythmic music)

Theoretical models and observations

of young sun-like stars suggest that the Sun's spin

was significantly faster in its infancy than it is today,

estimating it could have completed a rotation in a few days.

- If the sun hadn't lost its angular momentum,

it would be a much more active and much more violent star.

It would have these very powerful convection currents.

It would be dragging and shearing magnetic fields.

As a result, there would be a lot more solar activity,

flares, solar storms, and a much stronger solar wind.

So it really wouldn't be a very favorable environment

for life or for planets.

- [Narrator] But angular momentum is a property

that cannot be destroyed, only transferred.

- So the question is,

where did all the rest of that angular momentum go?

- [Narrator] We may find a clue in Herbig-Haro 211,

a young star system 1,000 light years away,

which showcases how newborn stars lose spin

by launching powerful jets of gas into space.

So when you look at a protoplanetary star,

we often find specific objects that look peculiar.

We call them Herbig-Haro objects.

And they have jets that are directed away from their pole.

- [Narrator] As a cloud of gas collapses into a star,

it spins faster, like an ice skater pulling in their arms.

But too much spin can stop the star from growing.

To fix this, young stars fire off twin jets

at hundreds of kilometers per second.

These jets act like escape valves,

carrying away extra spin

while allowing the star to keep pulling in material.

- As it's accreting material and growing in mass,

it has to spin up to conserve angular momentum.

And one of the ways these newly formed stars

are able to shed some of that spin angular momentum

is releasing bipolar jets

that carry that material away,

along with that excess angular momentum.

- [Narrator] As a star matures and starts to form a disk,

another mechanism may step in, magnetic braking.

- Our sun has this strong magnetic field.

And as the sun is forming

and it's building its magnetic field,

there's also all this debris around it.

That magnetic field

can tie in to the material around the forming sun,

and that can cause a braking effect

that can slow down the spin of the sun.

So some of that angular momentum from the sun

gets distributed through magnetic interactions

to the protoplanetary disk.

- [Narrator] The stronger the magnetic field

and faster its spin, the more momentum the sun loses.

Over millions of years, this complex interaction

leaves the sun rotating slowly,

while the outer disk and future planets gain momentum.

- If the sun were still spinning as rapidly

as we believed it was when it first formed,

the sun itself would be a much more active star.

Flares would be more frequent,

coronal mass ejections would be much more frequent,

and this would again have very detrimental effects

on the atmospheric evolution of the planets that orbit it.

(dramatic music)

- [Narrator] Today, the sun's light

illuminates a diverse planetary family,

rocky inner worlds, massive gas giants,

and distant, icy realms.

- The story of our solar system

began with the death of something else,

and potentially it began with the death of a star

and this massive explosion

that might have triggered the collapse of a cloud

that in the process of collapsing

would go on to create our sun,

and eventually the planets,

including the one we live on today.

- [Narrator] Following the sun's ignition,

its protoplanetary disk continues as a chaotic cosmic arena,

housing relentless collisions, mergers, and fragmentations.

The radiation and solar wind from the igniting sun

begins to sculpt a disk,

pushing gas and smaller particles outwards.

This leads to the formation of larger bodies,

the planet's first building blocks.

- When looking into a protoplanetary disk,

at first it's only dust grains

and very, very small particles.

As they collide, some of them end up fusing together.

And by being glued and increasing their mass,

the probability that any other subsequent collision

is also accreted or added to the object is higher.

And this accretion process lasts a very long time

and will ultimately lead to the final mass of the object.

(collision booming)

- [Narrator] The vast cosmos

is a gallery of planetary systems,

each a unique work of art.

Most of these systems exist in chaotic extremes,

hot Jupiters scorching inner worlds

or super-Earths crowding the habitable zone.

Our system's architectures stand apart, a cosmic unicorn.

- We used to think that planetary systems

would probably often wind up looking

like the one we live in,

fairly stable orbits, a collection of terrestrial planets.

But the more we've discovered other systems,

the more we see

that there are many, many different possibilities.

- Earth's habitability hinges

on a series of extraordinary coincidences.

- [Narrator] In this interstellar lottery,

Earth struck gold.

Yet for every Earth, there are countless barren worlds,

a stark reminder

of the sheer improbability of our existence.

- When we look out to the stars,

what we have in our backyard is uncommon.

- I think the question at the back of everyone's mind

is always, how likely was it to end up in this situation?

And I think we wanna know that for two reasons.

First of all,

because there are a lot of other stars out there

and we'd like to know if those other stars

might have planets like our planet's life,

like we have in our solar system.

But I think it also just gives people

a very different perspective on the universe,

to know that we're either an exceptionally rare case

or that we're quite common.

- [Narrator] The universe is a vast, interconnected web.

The same forces that birthed stars can also destroy them.

(dramatic music)

This duality is a reminder

of the cosmos's unpredictable power.

- The sun will continue shining for much, much longer

than a massive star would,

and it has already burned for more than 4 billion years now.

It will continue to burn for another 5 billion years.

- Massive stars, when they reach the end of their life,

may start to run out of fuel,

blow up in these extraordinary supernova explosions.

Those explosions are actually kind of rare, though.

Stars have to be quite massive.

Most stars in the universe

end their lives in slightly less dramatic ways.

So stars like our sun

do not end their lives as supernova explosions.

They end their lives

by becoming what are called red giant stars,

shedding their outer layers

in a beautiful process called a planetary nebula.

- When the planetary nebula is released,

it'll eventually get integrated

into the surrounding interstellar medium,

the same material that is going

into forming the next generation of stars.

So effectively, stars like our sun

are recycling their own material for the next generation.

- [Narrator] Transience is in the nature

of all celestial bodies.

Our existence is a fleeting moment

in the universe's grand narrative.

The balance between creation and destruction

is a delicate dance, one that has given us life,

but also reminds us of our place

within the infinite expanse of space.

From the vast molecular cloud where our story begins

to the fiery birth of our sun

and the forces that shaped our planetary neighborhood,

peeling back the layers of our cosmic history

helps us understand the story of how we got here.

- At the end of the day, when we look out into the heavens,

the reason why we are captivated by what we see

is because I think instinctually at our core,

we are trying to understand our role in the bigger universe.

Why are we here?

What is our destiny?

What is our purpose?

And you can't really address those questions

without factoring in where we come from.

(dramatic music)

- [Narrator] As we study the stars,

peering into the depths of space to glimpse our own past,

we are reminded that even in this seemingly random void,

patterns emerge.

(dramatic music continues)

Our solar system, the unique haven of life,

is a testament to the power of these cosmic forces.

It's a reminder

that we are not simply inhabitants of a planet,

but participants in a story

that began billions of years ago,

and continues to unfold today.

(majestic music)