Space's Deepest Secrets

One day, future humans must leave Earth

for a new home among the stars.

Finding another habitable world

is not just a science-fiction dream.

It has to do with the survival of humanity.

Today, astronomers are laying the groundwork

for our move to a new Earth.

But the more alien worlds they discover,

the more they learn how deadly the cosmos really is.

The universe has this one rule

when it comes to life... Kill it all.

To pinpoint our new home,

astronomers must unlock why space is so savage.

What unleashed one of the most powerful blasts of energy

ever seen to fry a promising alien world?

You would be dead so fast, you wouldn't even know it.

How did our cruel Sun destroy Earth's sister planet?

It just didn't make it,

and it became this inhospitable hellscape.

We dive through waves of deadly radiation

and plunge into suffocating atmospheres

to reveal the raw, destructive power of the cosmos.

captions paid for by discovery communications

Humanity's days on Earth are numbered.

The Sun's brightness will increase by 10%

over the next one billion years.

This extra heat will boil away Earth's oceans

and incinerate all life on our planet.

Our fate is written in the stars,

we must leave and find a new home

in another part of the galaxy,

To ancient people,

the Earth seemed absolutely eternal.

It must have always been here and always will be here.

We know planets change.

They live, and then they die.

Our galaxy stretches 100,000 light-years across.

Where in this huge expanse

is somewhere that can support complex life?

Planets are formed from the leftover debris

from star formation.

We have over 400 billion stars in our galaxy.

That means we could have trillions of planets.

Astronomers call these alien worlds exoplanets.

In 2016, exoplanet hunters make an exciting discovery.

They find a rocky planet that is roughly the same size as Earth.

The planet orbits Proxima Centauri,

the closest star to our Sun.

They named the planet Proxima B.

It is just 4.2 light-years from Earth,

and it is in just the right spot

to potentially support complex life, like humans.

Finding Proxima B was a game changer,

because not only is it a planet in the habitable zone

of its star, it's the closest star to us.

So this means that we could potentially go there.

This changes the future directions of science on Earth.

The habitable zone is the sweet spot around a star,

where temperatures are right for liquid water to exist

on the surface of a planet.

If you're too close to the star, that water is gonna boil away.

If you're too far, it's going to freeze.

And if you're in that zone,

you can have liquid water on your surface.

The signs look good that Proxima B

might have what it takes to be a home for humans in the future.

But what astronomers see next puts the celebrations on hold.

2018, violent waves of radiation slam into Proxima B.

The blast wipes out hopes that the planet can support life.

This is one of the biggest high-energy events

involving an exoplanet that we've ever been able to witness.

What could have caused such a huge release of energy?

Astronomers attempt to unlock the mystery.

They examine the prime suspect...

The star that Proxima B orbits... Proxima Centauri.

Astronomers measure the light output

from thousands of stars in our galaxy.

A sudden increase in starlight is evidence

that the star is releasing a stellar flare.

A stellar flare is an explosion of intense radiation

that erupts from a star's outer layers.

Proxima Centauri is a red dwarf star.

Astronomers discover that this type of star

emits around 80,000 times more flares

than a star like our Sun.

Observations also reveal that each flare

is around a thousand times more powerful

than the average type of flare that our Sun emits.

Small red stars have gigantic flares.

They're so huge,

they actually double the brightness of the star.

That means the flare is as bright as the star is.

So imagine if the Sun did that.

Imagine if the Sun doubled its brightness right now.

That wouldn't be good.

The evidence is clear.

A super powerful flare from Proxima Centauri

fried Proxima B.

Splitting open the star reveals why it is so volatile.

Proxima Centauri is so small that its core touches

the churning layer of hydrogen that surrounds it.

The extreme heat in the core

drives streams of superheated plasma

to the surface like a furiously boiling pot of water.

Huge eruptions of plasma spew from the star

with the force of a billion hydrogen bombs.

The flares fan out through space.

They slam into Proxima B

and extinguish any chance

that the planet can support life.

Proxima Centauri discharges

mega flares like this three times a year.

These extreme flares will wipe out the ozone layer

of every planet in the habitable zone of the star.

The Earth has a layer of protective ozone

in its atmosphere

that absorbs ultraviolet light from the Sun, which is great

because that kind of light is harmful to life on Earth.

The problem with Proxima Centauri

is that it is a flare star.

And if Proxima Centauri B has an ozone layer,

it'll get destroyed by this constant barrage

of high-energy radiation.

The destruction of this layer ruins any chance

that humans could one day live on Proxima B.

The kind of light that these flares emit

is the kind of light that we use to sterilize surfaces.

A DNA molecule would just be completely destroyed.

A new Earth must orbit a stable star

to support complex life.

The hunt for our next home continues.

Can three newly discovered planets

in the same system

sustain humans on a thin boundary between fire and ice?

And can a Jupiter-sized alien planet unlock the mystery

of why habitable worlds are so hard to find?

Humans must leave Earth

before our Sun incinerates our world

and forge a future on a planet in another part of the galaxy.

Today, astronomers lay the groundwork

for our eventual move to a new planet.

In 2017, they discover an extraordinary system

40 light-years away from Earth.

A dwarf star called Trappist-1

sits at the center of the system.

Around it orbits seven rocky planets

and all of them are a similar size to Earth.

The planets are so close to Trappist-1

that a year on these worlds

lasts between 2 and 19 Earth days.

Three of the planets fall inside the habitable zone

of the system.

Could one of these worlds be our future home?

There are times as a scientist

where you discover something out there that, honestly,

if it wasn't right in front of our eyes,

I would not believe that it exists.

And the Trappist-1 system absolutely blows me away.

Telescopes analyze the system in more detail.

They reveal it is likely

that these planets have unusual orbits.

They do not spin around their star in the same way

as Earth revolves around the Sun.

Instead, many astronomers think that the same sides

of all seven planets face their star.

They call this tidal locking.

You can witness an example of tidal locking in action

really close to the Earth.

Just look up in the night sky and look at the moon.

You only ever see one side of it.

One face is always pointed toward the Earth.

This is because the moon is tidally locked to the Earth.

And what that means is that the time it takes for the moon

to spin once on its own rotational axis

is exactly equal to the time

that it takes to orbit the Earth once.

The close proximity of these planets to their star

unlocks why this happens in the Trappist-1 system.

The star Trappist-1 is 20,000 times more massive

than its orbiting planets,

and its immense gravity grips them as they huddle in close.

The star's gravity warps each planet,

pulling out a huge bulge of rock on the side facing the star.

The star tugs on the bulge like a handle,

gently slowing the rotation of the planet.

After millions of years, the planet slows down so much

that one side remains locked, always facing the star.

Living on a tidally locked world

in the Trappist-1 system

poses a big challenge for future humans.

The rotation of Earth ensures that no part of the planet

gets too hot or too cold to support life.

It's the spin of our home planet

that allows it to actually harbor life.

It's this spin that evenly distributes thermal energy

across our planet's surface

and creates conditions hospitable for life itself.

But tidal locking turns the Trappist-1 planets

into super extreme worlds of two halves.

It's likely that every planet in the Trappist-1 system