Original subtitles

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Imagine an alien world,

a scorched, barren landscape, hot enough to boil water.

Where mysterious holes on the battle-scarred surface

host a labyrinth of tunnels,

each wide enough to house a city.

This world is dead,

yet it breathes life into its nearest planetary neighbour.

This extraterrestrial place is closer than you might imagine.

This is our moon.

Look at our solar system from an alien visitor's perspective.

What would surprise you?

What would make you look twice?

The intriguing answer -

our oversized moon.

If you look at our moon

and compare it to all of the other moons in our solar system,

it's actually quite odd.

It's huge.

Way bigger than any other moon in the solar system

compared to its planet.

It's a giant moon.

It's almost like we're a binary planet,

two objects orbiting around each other to some degree.

Our planet-sized moon is unique in the solar system.

And this battle-scarred giant serves as our guardian angel.

Its immense gravity raises the tides

that breathe life into the Earth's oceans.

The Moon stabilises the tilt of our planet,

regulating the climate and seasons.

Without the Moon, humans may never have evolved.

We owe everything to our moon,

yet its formation is one of the greatest

unsolved mysteries of planetary science.

There are many theories for the origin of our supersized moon,

but they all start the same way,

with the formation of the inner solar system 4.6 billion years ago.

When the solar system first formed,

it would've looked very different from the way it looks now.

Instead of having a few planets and mostly empty space

surrounding the sun, you would've had a disc.

And this disc would've been thick,

it would've been composed of gas and dust and rocky bodies.

The infant sun sparks into life,

blowing away the clouds of gas that are closest to it.

Over time, the rocky fragments that are left behind

clump together to form dozens of new planets,

many more than we now see today.

These fledgling worlds jostle for position,

crossing paths as they struggle to find stable orbits.

Is it possible that one of these planets

was destined to become our moon?

There have been a lot of ideas about

where our oversized moon came from.

One idea was just that it was wandering around

in our solar system and we captured it.

According to the capture theory,

a wayward planet passed a little too close to the early Earth

and our planet's immense gravity seized hold of it.

The planet then settled into orbit around the Earth

and became the Moon we see today.

This theory seemed to tick all the boxes...

..but scientists needed proof.

If it was really true that the Moon was a captured planet,

its constituents should be different from the Earth.

It was something that formed in a different place from the Earth

and then got captured,

so you would expect them to be made of different stuff.

To prove the theory, scientists needed to compare

the Moon's earliest rocks with similar samples found on Earth.

The best rock for comparison is anorthosite,

a volcanic rock that could only have formed

when the newly born Moon was still molten.

On Earth, an anorthosite forms in highly geologically active places,

like Iceland.

This is what we want.

You see this anorthosite, how white it is.

Anorthosite forms in a different way than normal basalt.

Um...you can almost think of it like the white foam

on the head of a dark beer, sort of floating up to the top.

So in a magma environment,

this would form and then just float up to the top of a...

of a magma sea.

Getting a sample of anorthosite from the Moon was crucial,

because darker rocks could've had their chemistry

altered by asteroid impacts.

We really had to have a piece of this anorthosite rock,

because we couldn't learn about the origin of the Moon

from the dark materials.

We had to have, you know, that genesis rock

to tell us about the origin of the Moon.

In the 1970s, Apollo astronauts collected samples

and brought them back to Earth for comparison.

The results shocked the scientific world.

What they found was that the composition of the Moon

was almost exactly the same

as the composition of the crust of the Earth.

So this idea that the Moon was a captured planet

from elsewhere in the solar system was out.

There was no way that was true.

PHIL: The rocks looked very Earth-like in many respects

and that was a puzzle.

With the captured-planet theory blown out of the water,

planetary scientists went back to the drawing board.

Scientists said, "Look, we've got to get together and figure this out."

And they went to a conference together in Kona, Hawaii,

all the top scientists in planetary science,

and they hammered out all of the leading ideas.

A lot of people think scientists don't have an imagination,

we're just robots looking at things and analysing. It's not like that.

If you want to figure out how something like the Moon came to be,

you have to have a wild imagination and try all these crazy ideas,

but they have to be constrained by reality.

They locked themselves into a room together

and emerged from that meeting and said, "Yes, this can work."

Scientists switched their attention

to the water contents of the Moon rocks.

They were surprisingly dry.

Something must've heated up the Moon to unimaginable temperatures,

and we were led to think that it must be some sort of collision.

A new theory emerged around the possibility

of a catastrophic collision,

4.5 billion years ago.

But it wasn't an impact into the Moon...

..it was an impact into the Earth.

There was a crazy idea that the Earth formed,

and while it was still young, another planet-sized object,

something about the size of Mars, came in and hit the Earth.

It blew off a huge amount of material,

which then coalesced and formed the Moon.

This is a pretty cool idea.

It was ground-breaking, I guess, literally.

Scientists name the Mars-sized planet Theia

and modelled how the impact would've played out.

4.5 billion years ago,

Theia clips the Earth with a glancing blow.

The impact throws molten debris far into space,

forming a ring of burning rock around the Earth.

If we could travel back in time

and somehow stand on the surface of the Earth

when the Moon was forming, it would've been amazing.

A bright ring of fire was stretching across the sky.

And here in the sky would've been a bright ball of magma,

glowing, with all kinds of shrapnel and small rocks

being attracted to that point because of the immense gravity.

This was the proto-Moon,

the thing that would eventually become the Moon

we have in our sky today.

Our moon forms in under a year.

Its crust is almost chemically identical to Earth's,

because they share a common origin.

This impact idea, as weird as it sounds,

actually does the best job explaining everything

that we see about the Moon.

The impact hypothesis becomes the leading theory

for the origin of our oversized Moon.

But when space probes journey to the far side of the Moon,

they discover something that throws the theory into chaos.

The Moon has a dark secret...

..it was born with a twin.

*

*

Take a look at the Moon tonight

and you might see a face, or perhaps a rabbit,

or a tree, depending on your culture.

Myths and legends surround the patterns

etched on the surface of the Moon.

But what can these marks tell us about the origins

of our oversized guardian?

What we call the Man in the Moon

is actually just a series of light and dark patches

on the Moon's surface.

And of course, people are programmed to recognise faces everywhere

so that's why we see this, you know, face.

These dark patches appear to be unique to the Moon.

Centuries ago, astronomers thought

they were seeing enormous oceans of liquid water.

We now know the dark stains

are actually ancient floods of volcanic lava.

Planetary geologist Jani Radebaugh

captures a bird's-eye view of similar features on Hawaii,

using her research kite-cam.

These lava flows we're standing on are identical

to the things we would see if we were standing

on the dark patches of the Moon.

They are dark in colour, they're made of basalt

and they flowed out in vast lava flows across the surface.

It turns out the dark plains of lava on the Moon are battle scars...

..evidence of a violent past.

Four billion years ago, asteroids rained down

on the newly formed Moon, tearing into the surface.

Where the fractured crust is thinnest,

molten lava seeps from the Moon's hot interior.

Spreading out in giant pools...

..and solidifying to form the scars we see today from Earth.

Strangely, although the Moon rotates, the Earth's gravity holds onto it so tightly

that the same face points towards us at all times,

making the features on the far side of the Moon a complete mystery.

For all of history, the far side of the Moon

was invisible to the Earth.

It's the backside, you can't see it.

In 1959, the Soviet spacecraft Lunar 3

flew past the Moon's far side

and photographed it for the first time.

Astronomers expected to see the same familiar dark and light patches,

but they were in for a big surprise.

When scientists saw the pictures, they were shocked.

The far side looked completely different than the near side.

It's saturated with craters. It just was such a huge dichotomy.

Nobody was expecting that at all.

The far side still had massive impact craters,

but it was uniformly pale.

It seemed like no dark lava had bled out onto the surface at all.

But why?

The only solution we could come up with is

there's a difference in thickness between the crust of the near side

and the crust of the far side.

That the backside must be so thick

that lavas are not able to come up through them

and erupt out onto the surface.

Instead, on the front side, where it's very thin,

lavas can easily come up through cracks

and flow out onto the surface.

Recent NASA missions confirm the crust on the back of the Moon

is around 26 kilometres thicker than the crust on the front.

The far side is thicker.

It's not like, "Oh, part of it is and part of it isn't."

No, really, the other side of the Moon has a thicker crust

than the near side. That's bizarre.

So one of the biggest mysteries in planetary science

over the last about 50 years is, you know,

"Why is the crust of the far side so thick?"

The impact theory doesn't really cover that.

It just forms the Moon but it doesn't say

why one side should be so different than the other one,

unless something strange happened.

The new age of supercomputer modelling brought about

the first credible explanation.

The impact of Theia could've made two moons, not one.

And this double birth might also explain our double-sided moon.

According to the theory, 4.5 billion years ago,

there were two moons in the night sky.

The smaller moon chases its larger sibling,

gradually getting closer.

Eventually, the two moons collide and slowly mould together.

The smaller moon covers the far side of the larger moon,

creating a new, much thicker crust.

Not all impacts are high-speed,

super-violent events that eject material everywhere.

Instead of just "Wham", smacking into it,

it would've just merged with it, just been pulled apart

and smeared out over the Moon.

Essentially, when you look at one half of the Moon,

you see more of one body, and when you look at the other side,

you see more of the other body.

They're kind of wrapped around the first body

and so it's thicker on that side.

Two moons become one.

The evidence for this cosmic collision seems to add up,

inside supercomputers, at least...

..but not all astronomers are convinced.

Some believe there's an alternative explanation.

And their proof lies on an alien planet

that's being cooked alive.

480 light years from our solar system,

a rocky, Earth-like planet orbits a sun-like star...

..but this is no place for life.

COROT-7b is a sun-grazer.

This bizarre exoplanet orbits 60 times closer to its star

than the Earth does to the Sun.

Their close proximity locks one face of the planet

to its fiery companion,

just like the Moon is locked to the Earth.

The result is a cosmic barbecue.

Temperatures soar to over 1,600 degrees Celsius

on the near side of the planet,

reducing the rocky surface to a boiling ocean of liquid magma.

By contrast, the shaded far side of the planet

has a cool, solid crust.

This overcooked exoplanet is the inspiration for a surprising

new theory about the formation of our moon's lopsided crust.

It's the brainchild of a pair of young researchers

with no background in lunar science.

Because I work in exoplanets, I knew very little

about lunar geology when this whole thing started.

In 2011, Jason Wright was discussing

sun-grazing exoplanets with colleagues,

when conversation turned to the mystery of the Moon's half-and-half crust.

And then I remembered that the Moon, when it formed,

was very close to the Earth and the Earth would've been

extremely hot after the impact that formed the Moon.

And in fact, the geometry is almost exactly the same

as the COROT-7b system.

That got me thinking, "Well, maybe something similar

happened to the Moon."

Jason theorises that the hot Earth cooked

the near side of the Moon,

just like stars cooked sun-grazing planets.

So if you imagine that the Moon is forming,

this big, hot ball of the Earth is hanging in its sky,

on the far side of the Moon, it would be quite cool.

The near side of the Moon is kept hot by the molten Earth.

Vast clouds of mineral vapour stream from the hot surface,

feeding a cloud that surrounds the Moon.

On the cool side, these minerals condense

and rain down, building a thicker crust.

It's a nice idea, but it only works

if the Moon locks one face to the Earth straight after it forms.

Jason asked grad student Arpita Roy to see if that was even possible.

When Jason first came to me with the idea,

he was very excited about it and he believed it was a big deal.

The calculation to check the tidal-locking of the Moon

was pretty easy to do.

Um...the number was so small that we were surprised.

It was on the order of 100 days,

which is very, very quick in astronomical timescales.

Arpita's breakthrough means that the near side of the Moon

locked to the Earth while our planet was still molten,

supporting Jason's theory of a cooked moon.

It's still very new, but the theory is gaining momentum.

In science, if you have two ideas that explain something equally well,

you kind of want to go with the one that has more natural outcome.

This broiling-Earth idea is a natural outcome

of what we know must have happened.

Thankfully for us, the surface of the Earth is a lot cooler today.

But the inside is still hot,

thanks to the radioactive decay of metals,

deep inside the core of the Earth.

This rising heat drives the volcanism

and geological activity we see on the surface today.

There are mountain ranges being pushed up

and other mountain ranges being subducted into the ocean.

The crust of the Earth is continuously changing.

The Moon doesn't have a radioactive core,

so scientists have always assumed that its centre is cold

and its geology is dead.

But a series of unexplained observations suggest that once again,

we're wrong about the Moon.

One of the big questions we've been trying to answer over the last few decades is,

"Is there any activity on the Moon left at all?"

For hundreds of years, astronomers have reported

strange bursts of light coming from the Moon.

Others have witnessed reddish glows that lasted

for minutes at a time.

Could these rare sightings show

that the Moon's geological heart is still beating?

The Moon is small enough that over four billion years,

it should've cooled all the way through.

And yet there's still some things that we see that, maybe,

kind of, sort of indicate that there's still stuff

going on inside of it.

Aristarchus is a volcanic region

in the northwest of the Moon's nearside.

Astronomers have reported over 700 glowing lights here

in the last 50 years.

Even Neil Armstrong saw something strange here

from the window of the Apollo 11 lander.

(RADIO BEEPS) NEIL: Hey, Houston.

I'm looking north up towards Aristarchus now

and uh...there's an area there that is

considerably more illuminated than...than the surroundings.

A slight amount of fluorescence to it, quite bright.

(RADIO BEEPS)

Uh...roger, 11. We copy. (RADIO BEEPS)

What's going on in Aristarchus?

Smoking volcanoes like this one in Hawaii

have given planetary scientists a potential answer.

Because where there's smoke, there should be fire.

You know, one clue to how these events are happening

on the Moon is where they're found.

They're actually found in a very special location on the Moon

and it's very much like what we're standing on right now.

Aristarchus is covered in vast plains of volcanic ash,

and some scientists believe this fine material

is responsible for the strange bursts of light we see from Earth.

The kind of ash that I'm holding right here is a little bit damp,

because there's been a recent rainfall in the region.

Whereas the material we'd be holding on Aristarchus

would be extremely fine.

Gases escaping from this active volcano

carry particles of fine volcanic ash and steam into the air.

Sunlight brightens the plume, making it visible for miles.

Perhaps something similar could happen on the Moon.

There's gas that comes out of the vent,

picks up the very fine lunar dust

and spreads it out across the landscape

so that we can see it illuminated by sunlight.

If the theory's true,

it means the Moon's volcanoes are still active.

Something like this is just kind of so mind-boggling that

it's hard for us to wrap our minds

around the fact that the Moon actually could still be alive today.

I mean, we've thought for many years that the Moon is cold and dead,

but maybe these are happening now

and that means that the Moon is not dead, the Moon is alive.

That's very exciting.

We thought we understood the Moon...

..but each time scientists peel back the layers,

they find another secret.

And perhaps the biggest of all...

..is that without the Moon, we wouldn't be here.

*

*

The Moon and the Earth were born together.

They have dramatically shaped each other's evolution.

And we now think that life, too, was given

a head-start by the presence of our oversized moon.

This is the Earth 4.4 billion years ago,

around the time scientists think life on Earth got started.

The newly formed Moon sits just 24,000 kilometres away,

appearing much larger in the sky than it does today.

Its gravity raises enormous tides in the Earth's warm, young oceans.

In that era, the tides were not measured in feet,

they were measured in miles.

You'd have these massive tsunamis

that would wash up on land and then wash back into the sea.

The Moon's gravity creates tides

by drawing Earth's oceans up towards it in a bulge of water.

And as the Earth spins, this bulge washes onto land as a tide.

The closer the Moon, the bigger the pull of gravity

and the stronger the tide.

Some scientists think that the warm rock pools these

giant early tides left behind formed the perfect mixing bowl

for the ingredients of life to come together.

The good thing about a tidal pond is that environments change.

Water comes in, brings nutrients, goes away,

the nutrients concentrate.

So that may have been a process

that concentrated the stuff life needed

in a way that led to life.

4.4 billion years ago, onrushing tides stirred up

organic molecules from the surface of the Earth.

As the tides receded, these chemicals were left behind

in shallow rock pools, which then evaporated in the heat of the sun,

concentrating their chemical contents.

And perhaps the first life was born inside this rich organic soup.

If we had tiny, little moons around the Earth like Mars does,

then we never would've had the massive tides that carry

materials and energy up onto the beach environment,

where life really might've gotten a foothold.

And so we wouldn't have had the minerals,

we wouldn't have had the energy and maybe we wouldn't have had life.

Did the Moon create life on Earth?

The jury's out, but one thing is certain -

intelligent life takes time to evolve.

At least four billion years in our case.

We've gradually changed from simple single cells

to the kind of organism that can question its own origins.

And it's the Moon that's provided the stability for life to evolve

by holding the Earth's axial tilt steady for over four billion years.

The Moon locked that tilt into place and has actually stabilised our rotational axis

and made sure the seasons are mostly the same,

century after century, millennia after millennia.

When we look at the tilt of the Earth,

it's been about the same for the time that

complex life has existed, and this is really important.

As we progress out of single-cell, simple organisms

to much more complex organisms,

greater stability really helps that.

How different would things have been without the Moon?

Just look at Mars to see the devastating effects

of an unstable tilt.

Mars actually had a tilt that is as far as 60 degrees.

That means that there was actually...

it was cold at the equators on Mars and it was warm around the poles.

And so that's really a difficult environment

for life to arise and grow.

When we look at Mars, we see that its axial tilt has swung around

to such a degree that it's inhibited life.

If the Earth had swung that chaotically,

ice ages would have come and gone like seasons.

Life would have needed to start from scratch over and over again,

never having time to evolve into complex organisms.

Mars serves as an indicator that our supersized moon

may have been instrumental

in the development of intelligent life on Earth.

And increasingly, scientists believe similar cosmic partnerships

are the key to finding other intelligent life in the universe.

When we're looking at exoplanets and we're wondering

which one of these could have civilizations, advanced life forms,

and there's a bunch that had a big moon and a bunch that didn't.

I would say, "Let's first look at the ones with a moon,

if for no other reason than we know that on this world

we have a big moon and we have advanced life."

As we're looking out beyond our solar system,

we're looking into the galaxy, looking for exoplanets that might be habitable,

maybe we should be looking for an object that has

a supersized moon in the right location around its star.

It might be the perfect place to look for life.

Scientists have discovered over 1,000 exoplanets

orbiting stars in our galactic backyard...

..by measuring the dip in brightness as the planet passes in front of its parent star.

An exomoon should also cause a tiny extra dip in brightness.

Current technology can't pick out this double-dip,

but a future generation of space telescopes

could potentially reveal large moons in the Milky Way.

And perhaps then we'll be able to narrow down our search

for a second Earth.

If we ever want to see these distant exoplanets up close,

we'll need a cheap, reliable route into space...

..and the Moon could be the key to making this dream a reality.

One of the greatest barriers to conquering space

is the enormous amount of fuel required to escape

Earth's gravitational pull.

But the Moon's gravity is six times weaker.

A lunar launchpad could become a gateway to the stars.

So if we establish a base, uh...on the Moon, for example,

now we need very little energy to get off of the Moon and to go

and explore other bodies from there.

What would it take to build a lunar Cape Canaveral?

(INDISTINCT RADIO CHATTER)

The biggest hurdle is keeping the ground crew alive.

One of the biggest dangers of being on the surface of the Moon

is you're not protected by a magnetic field.

On the Moon, you don't have that.

If there's a big solar storm, the flux of high-energy particles

would hit astronauts with so much energy

they would break down the cells and destroy our DNA.

The Moon is also hit with radiation

that originates from far outside our solar system.

Distant supernovas throw out charged particles

called cosmic rays, at close to the speed of light.

On Earth, our atmosphere blocks most of the incoming rays.

But on the Moon, astronauts are in the firing line...

..and many have reported seeing tiny flashes,

as cosmic rays smash through their optic nerve.

Incoming space rocks are another major hazard on the Moon.

On the Moon, there's no atmosphere,

so something the size of a grain of sand

is moving at speeds multiple times the speed of a bullet.

And if that hits your colony, it can put a pretty good hole in the wall.

Yet another obstacle to long-term survival on the Moon

is the extremes of temperature.

One of the things we don't really think about

about the air around us, is it actually redistributes heat.

On the Moon, you have no air.

So if you have your hand

and half of it is in sunlight and half is in shadow,

you've got a 400-degree difference there.

The best protection from all of these long-term problems

is a thick layer of rock.

But a recent discovery suggests

future astronauts won't need to dig to build their shelters underground.

*

*

This remarkable hole on the surface of the Moon,

called a skylight, is the size of a football pitch.

We are seeing big openings to massive cave systems

that might form the perfect base for lunar exploration.

Skylights are the entrances to a network of vast tunnels

which potentially run for miles under the surface of the Moon.

There are already underground caverns there.

And they're not carved by water, these are carved by lava.

Similar natural tunnels called lava tubes

exist on Earth in volcanic regions like Iceland.

So we're in the bottom of a hole that's formed

uh...from a collapsed lava tube.

Now, we know that on the surface of the Moon,

there are holes like this.

And if all indications are correct,

they also lead to giant lava tubes, just like this one.

Lava tubes form when flowing rivers of molten rock

start to cool.

The surface solidifies first, insulating the hot lava

below that continues to flow, carving out long underground tunnels.

Living in a tube like this actually wouldn't be that crazy.

In fact, this is a big tube, it's quite large,

but the ones on the Moon are 10 times bigger than this.

On the Moon, lava tubes run beneath hundreds of metres of solid rock,

protecting the tunnels from radiation,

micrometeorites and keeping the temperature stable.

A lava tube like this on the Moon would be nice and stable,

and perhaps never get much colder than the coldest caves on Earth.

Astronauts on the Moon could seal themselves inside

tubes like this by adding airlocks.

If we were able to colonise a lava tube under the lunar surface,

we could adjust the environment.

We could pump in air, we could make the temperature right.

You could get out and walk around in this vast subterranean tunnel.

You could have an entire city down there,

lighting up the walls of the lunar terrain.

A lava tube would be a great first lunar station.

I mean, it's like a ready-made home for us.

In the future, when we have colonies on the Moon,

they may very well be inside of these lava tubes.

It'll be dark all the time, you're in a cavern,

it'll have to be lit.

But you don't have to worry about

enclosing your domes or anything like that,

it's already a sealed, self-sufficient environment.

You fill it with air and you can live in it, outside.

It'd be pretty amazing. Uh...you're in one-sixth gravity,

you don't necessarily need a spacesuit.

That would be fantastic.

If you want to go out on the surface, which you would have to,

yeah, you have to wear a spacesuit and be able to protect yourself.

But I think living in one of these colonies

would be really astonishing.

You could... you could fly.

You could have wings. You could make wings and flap and fly.

There have been science-fiction novels written about this.

I would love to see this someday.

I think that would be an amazing future to look forward to.

Scientists think that these lunar space stations

could be self-sufficient.

There are craters that are always shaded

and they contain water ice.

And so that is really exciting, because we didn't realise

that there was actually still water on the Moon.

We thought the Moon was just bone-dry for many years,

that was the mantra.

And now we're finding out

that contained in soil, contained inside of crater walls

that are permanently shadowed, there is lots and lots of water ice.

Water is the perfect resource for a lunar launchpad.

As well as drinking it, you can split water with electricity

to create oxygen to breathe and hydrogen to use as a fuel.

When you think about it,

rocket fuel is made of liquid hydrogen and liquid oxygen,

and, hey, those are the components of water.

The Moon's craters hold around six billion tons of water ice.

That's enough to launch 20 rockets into space every day

for over 100 years.

For over four billion years, the Moon has driven our evolution,

shaped our climate, and in the future,

its resources will allow us to conquer space.

But it's not going to be around forever.

Sometimes when we talk about things that are reliable,

we say there's nothing as reliable as the rising of the sun, right?

We can think of the Moon in the same way.

It goes through its phases. It's there night after night,

year after year.

But it turns out, the Moon is actually moving away from the Earth,

and that's due to the interaction of the Moon

and the Earth's tidal bulge.

The bulge of water pulled up by gravity

sits slightly ahead of the Moon

because the Earth spins faster than the Moon orbits.

The Moon pulls, by gravity, on that bulge

and slows the Earth's rotation.

Over billions of years, that has slowed the Earth's rotation a lot.

We used to be spinning a lot more rapidly,

probably more than twice as fast as we do now.

The Moon's attraction to the bulge

has the opposite effect on its own orbit,

speeding it up.

This increased speed makes the Moon's orbit wider,

pushing it further and further away.

It's a very small amount, so it's only about 3.8 centimetres,

which is about an inch-and-a-half a year.

Over billions of years, the Moon will shrink to a dot

in the night sky and the Earth's spin will become so slow

that the Moon will appear to freeze above our heads.

There will come a time where the Earth is actually locked.

One side of the Earth faces one side of the Moon

and the two of them will go around in lockstep.

So there'll be one place on Earth where you can see the Moon.

So you might imagine you'd have to go on some kind of uh...

vacation to actually see the Moon at that point in time,

but that's going to be a long from now.

So...so, you know, um... I wouldn't start booking

your tickets quite yet. (CHUCKLING)

Is this the long-term future of our moon?

Some scientists envision a more dramatic ending -

a death by fire that will destroy the Moon and, quite possibly,

all life on Earth, too.

The process begins with the expansion of the sun.

The actual future history of the Earth-Moon system

will depend upon the sun...

..and it could produce remarkable effects.

As the sun gets older, it expands,

filling the inner solar system with a dense solar wind.

This wind will impede the Moon.

So as the Moon orbits around the Earth, there'll be drag,

there'll just be more stuff in space for the Moon to push against.

So the Moon has been moving away from the Earth

for billions of years, maybe at that point, it'll start coming back.

This new inward trajectory is a death spiral.

The Moon eventually is going to spiral closer and closer.

And then, because of the gravitational forces,

the tidal forces are gonna be so strong,

it's going to essentially explode.

18,000 kilometres above the surface of the Earth,

the Moon reaches a point of no return...

..the gravitational pull of the Earth finally overwhelms it.

And you'll see it shaking, you'll see it quaking.

It'll be stretched way out and it'll be stretched sort of

toward us and away from us, it'll be hard to tell.

But eventually, you'll see that actually breaking apart,

an entire world being shattered by the gravity of Earth.

The fractured remains of the Moon

create a Saturn-like ring of rocky debris.

Having a ring around the Earth would be a phenomenal sight,

I would love to see that.

You would look up and you would be able to see the ring,

it would be at an angle to the Earth.

If you were at the right place on the Earth,

you'd be able to see it broad, stretching across the sky.

I don't know if you'd be able to see it during the day, but at night,

it would be one of the most spectacular sights I can imagine.

But the beauty soon turns to terror,

as pieces of the ring rain down on Earth.

I mean, it's going to be an awesome sight, a terrifying sight.

I mean, the whole sky is going to be filled with

raining meteors just showering through the sky

and they're going to be huge.

Eventually, all that of material will be incorporated into the Earth,

and now these two siblings, separated at birth,

now are finally again one body.

From the fiery inferno, a new Earth is born...

..but this world is sterile.

The Moon's presence allowed life to arise on the Earth,

and the Moon's presence will also destroy life on Earth.

The Moon giveth and the Moon taketh away.

So that's kind of a neat storyline,

although maybe not so great for us. (CHUCKLES)

It's pretty sad to imagine the Earth without the Moon.

We're partners, we've affected each other's development.

Seeing the Moon in the sky is something that gives me joy

every single time, that has never gotten old.

We can't help but show affection towards it.

It's there every night staring at us and, of course,

romances have been written about it and will continue

to be written about it.

Life on Earth may not have existed without the Moon,

but certainly, without it, even if it did,

it'd be much less romantic.

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