Space's Deepest Secrets

The history of our solar system

is the history of us,

but how well do we really understand our cosmic roots?

To understand where we are now,

we need to understand where we were at the beginning.

Remarkable new evidence

threatens to rewrite almost everything we thought we knew

about the birth of our planetary backyard.

The history of the solar system

isn't as neat as eight planets formed

and now they're the same eight planets today.

Anything that challenges the status quo

and our thinking about that is profound.

It profoundly changes our sense of how we got to be.

Did one of the largest stars

that ever lived give birth to the Sun?

Was our solar system home to two stars, not just one?

And did supersized planets once roam

where the Earth sits today?

There were planets that probably got ejected

from the solar system entirely.

There may have been planets that were actually

thrown into the Sun.

This is the all-new birth story of our solar system,

and the race to rewrite history.

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Today, across the world, scientists are grappling

to solve a serious problem.

Their best theories for how our solar system formed

just don't add up.

Understanding the history of our solar system

really is the story of our origin.

We happen to be here today on this planet,

because this planet formed from the raw ingredients

that formed our solar system.

For decades, scientists have known

that the Sun and the planets

were born out of the same cloud of gas and dust

that collapsed under gravity 4.5 billion years ago.

But that collapse needed an extra ingredient

to get things started.

Somehow the cloud has to collapse.

Something has to give it a shove,

make one area denser than another,

and then gravity can take its course

and bring things together, and begin to form

our sun and the planets.

But it doesn't just happen spontaneously.

There needs to be a trigger.

According to the conventional theory,

that trigger was a supernova...

An exploding star.

The supernova sends a shock wave of material

blasting through space.

It smashes into a nearby cloud of gas and dust,

forcing it to collapse.

A new star, our sun, sparks into life.

And the remaining swirls of gas and dust

condense into planets.

Our solar system is born.

The supernova trigger theory has reigned supreme for decades,

but remarkable new evidence now threatens to override it.

At the university of California,

Ed Young hunts for cast-iron evidence

to support the supernova trigger theory.

He studies some of the rarest rocks on Earth.

Meteorites that are as old as the Sun.

I'm pulling out this particular meteorite.

It's a meteorite that fell in Australia in 1960.

It's about 4.5 billion years old, very ancient.

This rock is pretty much as old as the age of the solar system.

Ed looks for chemicals inside these early rocks.

These chemicals could prove a supernova shock wave

really did trigger the formation of our solar system.

The solar system formed by the triggering event

being a supernova, then this rock would contain

some of the material that was spewed out

by the supernova at the time of the explosion.

When a supernova explodes,

it sends out radiation in every direction,

and that radiation encounters other stuff,

and the fingerprint of the supernova

is left on everything it touches.

Ed looks for traces of a chemical

that forms in the abundance in supernova shock waves.

It's called iron-60.

We use this instrument to measure

with great precision the various elements

that make up that meteorite.

If we find evidence for iron-60,

then we have possible evidence for a supernova nearby

at the time the solar system formed,

because supernovae form the iron-60.

The team prepares the sample.

They grind the meteorite,

setting its primordial grains free

after 4.5 billion years of imprisonment.

Then, they dissolve the grains in acid

and finally, place the sample

inside a machine to measure its chemical composition.

The machine heats the sample to extreme temperatures,

smashing it into its component chemicals.

We walked our sample over to this mass spectrometer.

It has a plasma that's as hot as the surface of the Sun,

and so it's a very efficient way

of analyzing ratios of elements that we put in there.

After just a few minutes,

the results flash up on Ed's screen.

They list the type and abundance

of every chemical in the meteorite.

But how much of the supernova marker, iron-60, will he find?

The slope of this line indicates

a modest amount of iron-60 in the early solar system.

Less than had previously been estimated.

The result is a surprising setback

for the supernova trigger theory.

The fact that this slope is lower

and the amount of iron-60 that implies

is less than previously thought,

tends to argue against the notion

that there was a supernova exploding

right near where the solar system was born

at the time it was forming.

Ed's results suggest that a supernova

can't have triggered the formation of our solar system.

If the violent winds of a supernova

didn't provide the trigger...

What did?

Now that we know that iron-60 is not a smoking gun,

we have to start rethinking the origins of other isotopes

that were present in the early solar system.

Ed goes back to his results.

He searches for unusual levels of other chemical elements.

One stands out...

Aluminum-26.

Unlike iron-60, aluminum-26 can be formed

by other ways... Ways other than a supernova.

Aluminum-26 is commonly produced

by oversized stars.

But there's only one monster

with the power to kickstart the birth of a solar system.

A giant Wolf-Rayet star,

50 times the size of the Sun.

The most massive, brightest breed of star in the universe.

Hidden under the surface, it's a cosmic chemical factory,

fusing atoms of hydrogen together

to produce heavier elements like oxygen and aluminum

but, crucially, not iron-60.

This stellar furnace creates so much heat

it unleashes winds of nearly five million miles per hour,

which slam into the surrounding clouds of cosmic gas and dust,

sweeping them away from the star

and piling them up into a dense,

chemically-rich shell of material,

trillions of miles wide.

If a supernova didn't explode and collapse the cloud

that made the Sun, what could have?

Well, maybe it was a very, very high-mass, luminous star.

There's a type of star like that called a Wolf-Rayet star,

and they are incredibly violent, blasting out radiation.

Wolf-Rayet stars are extremely rare.

Of the two billion stars in the milky way,

astronomers have only spotted 600

of these spectacular, bloated objects.

They are very, very massive stars

that are almost ripping themselves apart with winds.

Winds of high energy charged particles.

The winds of a Wolf-Rayet star

are almost like a slow explosion of the star,

and because that's the case,

you don't get these radioactive iron elements,

so the fingerprint of the Wolf-Rayet is very different

than that of the supernova.

Did the ferocious winds from a Wolf-Rayet star

trigger the creation of our solar system?

The theory ticks a number of boxes,

with one exception.

The clouds of gas that give birth to stars

are normally very cold,

but Wolf-Rayet stars and the winds they throw out into space

are scorching hot.

Far too hot to form a star like the Sun.

But could the chemical-rich shell

that surrounds these massive stars hold a clue?

At the university of Chicago,

astrophysicist Vikram Dwakadas,

part of a team that uses computer simulations

to peer inside giant Wolf-Rayet stars.

He wants to know if the outer shell of one of these stars

might have triggered the creation of our solar system.

The solar system cannot be formed too close to the star

because these stars are very hot.

The Wolf-Rayet star is very small out here.

It's a single point at the center,

and in fact, this single point is still about a few times,

up to 15 times the size of our sun.

Then this medium out here

could go up to about 10 billion times the size of our sun.

Vikram believes the distant outer shells of Wolf-Rayet stars

have all the raw chemicals needed to build a solar system.