The moon... Earth's nearest neighbor,
but one of the most mysterious objects in the solar system.
If you actually want to look at one of the greatest mysteries
of the universe right now, just look up at the moon.
For decades, scientists were sure
they'd solved many of the moon's deepest secrets.
But now, new evidence suggests that nearly everything
we thought we knew about the moon could be wrong.
We might need to completely rethink
our understanding of the formation of the moon.
Imagine if you could have looked up at the night sky
and saw two moons.
That would've been lit!
♪♪
Why is our moon so big?
Why does it look so strange?
And why is the nearside
so totally different from the far side?
♪♪
Today, pioneering technology could finally reveal answers.
Z is preparing to fire.
This is the inside story
of the race to unravel
the mysteries of our moon.
♪♪
Captions by vitac... www.vitac.com
captions paid for by discovery communications
♪♪
The moon...
Since mankind first looked up to the sky,
it's been there, looking back.
It remains the only place beyond our home planet
where humans have set foot.
That's one small step for a man,
one giant leap for mankind.
Without it, life as we know it probably wouldn't exist.
The moon has been the earth's companion for 4.5 billion years.
It drives the motions of the tides,
and the motions of the tides
are intricately linked to the cycle of life on earth.
The moon is vital for life on earth.
The moon is there
in the sense of a satellite of planet earth,
but it's there, also, in a sense of allowing life as we know it
to have the features that we experience.
As important as the moon is,
scientists now know that it's also extremely weird.
The first clue is its surprising size.
If there were an alien astronomer
from another solar system,
I think they would come to our planet
and look up at the moon with astonishment.
There's something about our moon
that makes it incredibly strange.
It's just too darn big.
Of all the major planets in the solar system,
earth has the biggest moon
relative to the size of the planet,
and that's very, very strange.
Large moons are rare amongst the rocky planets
in our solar system.
♪♪
Mercury and Venus have no moons at all.
♪♪
Mars has two tiny moons, deimos and phobos,
many hundreds of times smaller than their host planet.
It's thought they were once asteroids
that Mars ensnared with its gravitational pull.
But earth's moon is a freak.
Over 2,100 miles across,
weighing in at 77 million trillion tons,
it's more than a quarter the size of earth,
far too big to be a captured asteroid.
How did we get this giant cosmic companion?
Scientists think that the moon must have been formed
by an event of extraordinary violence.
When you look at the surface of the moon,
one thing you can see is that it's been hit a lot,
but maybe it was created from the biggest hit.
For over 30 years, one theory for the nature
of this violent birth has ruled supreme.
It's called the giant-impact hypothesis.
The main idea of how the moon formed
was that something came in, smacked the earth,
bits flew everywhere, and they eventually recondensed,
forming the moon as we see it today.
4.5 billion years ago,
when earth is still a scorched ball of hot rock,
another young planet called theia
comes too close for comfort.
As it strikes the edge of the earth at an angle,
traveling at more than 26,000 miles per hour,
theia rips off the top of the earth.
The debris forms a ring...
and over time,
the fragments fuse together into a ball of scorching rock
that eventually becomes our moon.
♪♪
Scientists want to investigate
if this established theory is correct.
If the giant-impact hypothesis is true,
then we should be able to find evidence.
So they revisit clues
first gathered over 45 years ago.
In the 1960s and '70s,
Apollo astronauts collected over 830 pounds of moon rocks.
That Boulder's gonna roll.
Man, that is hard.
Just don't stub your toe.
Scientists think that these rocks
could hold the answer...
It's orange!
As to whether the conventional theory
of how the moon formed is right.
♪♪
Edward young is a geochemist.
He's got his hands on a precious sample of moon rock.
♪♪
We get samples like this from Johnson space center.
We request a milligram or less.
That's all we need, really, to make an analysis.
This particular sample comes from the Apollo 16 mission.
It was brought back by the astronauts.
If the conventional theory is correct,
and theia collided with the earth in a glancing blow,
then the moon should be mostly made out of theia.
It means that moon rock should be chemically different
than earth rock.
Ed designs experiments to test this prediction.
In his lab, ed has the largest and highest resolution
mass spectrometer of its kind in the world.
The machine analyzes the oxygen the rocks contain.
Every solar system body
has its fingerprint of molecular weight of oxygen.
Theia should've been different from earth,
and if theia is mostly in the moon,
we should expect to see the moon having a slightly different
molecular weight of oxygen than the earth.
Ed's colleague uses a laser
to prepare a sample for analysis.
The laser melts the rock
and causes it to react with a chemical
within the chamber, releasing oxygen gas.
What most people don't think about is that rock
is mostly oxygen. It's 90%, by volume, oxygen,
and it's about half, by weight, oxygen.
And so when we heat the sample
and melt the sample with the laser beam,
that leaves us, when we're all done,
with just oxygen remaining as oxygen gas,
and the oxygen gas is what we analyze.
The oxygen acts as a unique identifier,
the chemical fingerprint of the rock.
Ed compares the chemical fingerprint of the moon rocks
to earth rocks.
The big question... Are they different as predicted?
Well, in this plot, we're looking at our results
for samples from the earth and samples from the moon.
And on this axis of this plot,
we're seeing the real fingerprint of the oxygen
that makes up these bodies.
If the collision that formed the moon left more
theia in the moon than it did in the earth,
we would expect there to be an offset,
and what we're seeing on this plot
is that there's no resolvable difference
between the terrestrial samples from the earth
and the lunar samples.
The result is surprising.
The moon and earth rocks
have virtually identical chemical fingerprints.
It flies in the face of the conventional theory
of how the moon formed.
♪♪
You have this object, theia,
that impacts with this other object, earth,
and then in the end, you have two objects,
the earth and the moon,
that are now combinations of earth and theia.
The problem is, is that we can't find evidence of theia.
It's like stumbling upon
a site of a massive collision
between what you know is two cars,
but you can't find the other car.
So is the entire theia hypothesis
just plain wrong, or does the standard theory
just need reworking for the earth and the moon
to end up with virtually identical chemical fingerprints?
One scientist might just have the answer.
Nothing comes close to realizing
that you've found something
that no one has ever thought of before.
And she's ready to put a radical new idea to the test.
♪♪
The moon...
One of the strangest objects in the solar system.
Astronomers are in a race to unlock the secrets
of its mysterious origin.
They are convinced the conventional model
for how the moon formed is flawed.
But is it completely wrong?
Astrophysicist Sarah Stewart believes that the basic idea
of the giant-impact hypothesis is still correct,
but with one crucial difference.
Instead of hitting the earth in a glancing blow,
theia could've slammed right into it.
The energy of the collision partially vaporizes
the two planets,
mixing them together to create a superheated cloud
of liquefied rock and gas called a synesthesia.
As the seething mass cools,
droplets of molten rock fuse together
and gradually grow bigger.
Over just a few decades,
material from the two vaporized planets
keeps merging and mixing,
and the synesthesia shrinks until it gives birth to the moon
and, crucially, a rebuilt earth made from the same material.
There are scientists now that think when two planets collide,
the first thing that you're left over with
is a giant doughnut of extremely hot rock.
We're talking rock that's been vaporized.
And out of this one object,
this one big doughnut of gaseous rock,
two things formed.
In the very core of this was the earth,
basically the remnant of these two planets that collided,
and farther out in this hot doughnut of gas,
that was where the moon formed.
♪♪
At sandia national laboratories,
Sarah uses the z machine
to put the new synesthesia idea to the test.
♪♪
The z machine produces short bursts of electrical energy
of phenomenal intensity found nowhere else on earth.
It was originally built to study the physics of nuclear weapons.
Sarah wants to use the power of the z machine to prove
that a big enough impact could turn earth and theia
into a giant churning cloud of vaporized rock.
In this chamber,
we are recreating planet formation in the lab.
The experiments are extremely energetic,
and so part of the massive chamber
is to contain all of the debris from the explosion.
Sarah smashes materials together
inside the z machine and measures the point
at which they vaporize.
Earth is represented by a tiny sample of mineral
that's mounted onto a block.
Theia is represented by a metal plate.
That strikes the target.
That generate a shock wave that travels through the sample,
earth, and we can determine when the material begins to vaporize.
When the z machine fires,
it releases a pulse of electricity,
1,000 times greater than a lightning bolt.
Attention building 983. Z is preparing to fire.
The electrical energy generates a force
that smashes the sample and target together
at more than 100 times the speed of sound.
This creates a mini earthquake that shakes the entire site.
Will the results seal the fate of Sarah's new idea?
♪♪
The hot-off-the-press results is that 20% to 30% of the earth
was vaporized enough
to generates a synesthesia as we predicted.
The data indicates that theia colliding with earth
could've created a single, churning cloud
of vaporized rock,
a synesthesia.
It's in this highly vaporized synesthesia
that the moon forms and leads to the chemical similarity
between the earth and the moon.
♪♪
The synesthesia idea is that instead of just throwing
the stuff up into orbit after the impact,
the rock on the surface of the earth actually vaporized,
and the earth was spinning very rapidly,
and just wound up forming sort of a doughnut shape.
Now this actually solves a lot of problems.
It actually shows how the rocks on the moon
could be similar in many ways to the earth.
They all formed out of the same cloud of debris.
The new synesthesia idea
is gaining significant traction
because it may also help to explain
another of the moon's strangest mysteries.
Since the moon landings, scientists have known
that moon rocks have mysteriously low amounts
of particular elements, such as sodium and potassium.
Planets like the earth and Mars are rich in these chemicals,
so why not the moon?
The earth and the moon are almost chemically identical,
but not quite.
The moon has less potassium and sodium in it
than the earth does, and that's really weird.
You expect them to be the same.
♪♪
Geoscientist Catherine macris
thinks that the synesthesia theory
could finally solve this decades-old mystery.
I like to go in the lab and sort of create my own moon.
And with the help of the mini moon she created,
she's ready to put the synesthesia theory
to the test.
♪♪
Geoscientist Catherine macris
is trying to finally solve a decades-old mystery.
If the moon is formed from the same cloud
of debris as the earth,
why does it have low levels of certain elements?
Catherine thinks a curious quirk of the synesthesia theory
may have allowed the earth
to steal the moon's sodium and potassium.
The quirk has all to do with temperature
and the order in which in the earth and the moon form.
Hidden deep inside the swirling clouds of the synesthesia,
the embryonic moon takes shape first.
As it grows, its gravity sucks in more
and more of the superheated molten rock around it.
The surface of the young moon becomes so hot,
sodium and potassium evaporate back into the cloud.
They drift away into the synesthesia
in a trail of vapor.
♪♪
As the synesthesia cloud cools, it shrinks,
eventually forming the earth,
complete with the moon's missing sodium and potassium.
Catherine wants to test this idea.
Her experiment recreates the high temperatures
in the synesthesia
to see this affects the chemical makeup of the moon.
We have a 400-watt co2 laser.
This is the laser, right here.
It's very big and powerful.
The laser is actually pointing straight up right now,
but I have some mirrors or lenses here
that actually send it straight down here
so that it's shooting right inside of this chamber here.
Catherine puts a miniature synthetic moon
into the metal chamber.
The sample's chemical makeup
is similar to that of the embryonic moon
when it starts to grow in a synesthesia.
When it melts, it's going to be a little, tiny ball of magma,
basically, floating and spinning.
The embryonic mini moon levitates
on a jet of gas,
just like it's on an air-hockey table,
and Catherine uses the laser to heat it up.
As the temperature rises,
the embryonic mini moon starts to glow.
♪♪
We can see that it's getting hotter and hotter.
It reaches over 3,600 degrees fahrenheit.
This is the same temperature
as the outer edge of a synesthesia cloud.
A trail of vapor suddenly bursts
from the surface of the mini moon.
Catherine thinks this smoke may include
the vital sodium and potassium missing from the real moon.
♪♪
It started out being a really dark brown,
and we can see that it changed color.
Right now, what we're seeing is that it's a very,
very, very pale yellow, and it's also gotten smaller.
Further tests confirm that the chemical makeup
of the miniature embryonic moon has been altered.
It contains less sodium and potassium.
The red line represents potassium.
The blue lines represents sodium,
and what we see is that the longer we heat the melt,
the more of this material is evaporated and then lost,
and so what we are left with is a moon
that has less of those elements.
♪♪
One of the amazing things about this idea
is that the moon would've formed before the earth.
In the very outer parts of the cloud,
the smaller moon formed,
and maybe as much as 1,000 years later,
things finally settled down in the core of the cloud
to make our planet.
So in the synesthesia debris cloud,
the earth and the moon would've had
slightly different formation times,
with the moon forming just prior to the earth.
And because they would've formed at different times,
the earth is able to steal the sodium and potassium
from the moon,
and this could explain their chemical differences.
The brand-new synesthesia theory
could be scientists' best explanation
for how earth's moon was born 4.5 billion years ago.
It explains why the moon and earth
share almost identical chemical fingerprints,
and, crucially, why the moon has less potassium and sodium.
But scientists still want to know
why the moon looks the way it does.
The familiar dark patches that cover the nearside of the moon
are unique in the solar system.
What are they, and what forces created them?
And is it possible
that the earth once had two moons in the sky?
Imagine if you could've looked up at the night sky
and saw two moons.
That would've been lit!
♪♪
A new generation of scientists
are challenging the established theory of how the moon was born.
But one mystery remains unsolved.
The familiar dark splotches that cover the nearside of the moon
are unique in the solar system.
What made the man in the moon,
and why don't we see similar features on other moons?
We think of our solar system
as just being eight planets, right?
But in reality, many of those planets have many moons,
and those moons happen to be
some of the most fascinating places in the solar system.
You've got io, you know,
the solar system's greatest hellscape.
You've got Enceladus, which has beautiful plumes.
You've got titan, which rains liquid methane.
And then you have our moon.
Our moon is unique.
If you've ever seen "the man in the moon," right?
That face that you see on the nearside of the moon.
That doesn't happen on all moons in the solar system.
Even more mysteriously,
the dark rocks that make up the man in the moon
are almost completely absent from the far side.
All of those dark splotches that we see on the nearside,
they're not on the other side.
There's a huge difference in geology between the far side
and the nearside of the moon, and that is really peculiar.
♪♪
Noah Petro works
at NASA's Goddard space flight center.
He's dedicated his career
to solving the moon's greatest mysteries.
♪♪
Noah is a project scientist
on NASA's lunar reconnaissance orbiter mission.
Launched in 2009, this robot spacecraft
has been orbiting the moon ever since,
mapping its surface.
Noah thinks that the data from this lunar probe
could help explain how the man in the moon was created.
♪♪
What we have up here is a view of what's happening
with the lunar reconnaissance orbiter,
and so what we have in this display
is a sense of what the spacecraft is seeing,
what the spacecraft is doing.
Right now, lro is just about as close to the south pole
as it's gonna get.
We're passing about 2 degrees away from the south pole,
and in a moment, lro will start passing
over the far side of the moon.
Noah's spacecraft is equipped
with a special instrument that scans the moon in infrared,
a type of radiation invisible to our eyes.
The scans show that the man in the moon
is made of rocks that are rich in iron,
different from the rest of the white lunar crust.
The areas in dark red and orange
are areas that have lots of iron at the surface.
The areas in blue have little or no iron at the surface.
The iron-rich rocks
are a type of solidified lava known as basalt.
The results confirm what's been known
since the Apollo moon landings.
The nearside of the moon is covered
in these massive pools of volcanic rock
that have erupted and flowed onto the lunar surface,
covering much of the nearside.
The earth's most active volcanoes
spew iron-rich lava onto the surface.
♪♪
The moon's dark patches are made in just the same way,
but on a whole different scale.
Some of these lava floods are the size of an entire country.
It's an extraordinary revelation.
For hundreds of millions of years,
one side of the moon burned with volcanic fire...
while the other side was almost completely undisturbed.
Why?
Those dark patches on the moon, those are pools of hardened,
cooled lava that flowed up 4 billion years ago,
and they're largely confined to one side of the moon,
the side that faces the earth, and this is a real mystery.
These lava pools that are hundreds of miles across
are weird.
It's not clear where they come from.
♪♪
Peter Schultz looks for clues in the moon's geological scars.
Boy, I've been interested in the moon
since I was a kid with my telescope, seeing the craters.
I didn't understand.
How come there were so many craters on the moon?
Peter thinks that a giant asteroid collision
may have led to the lava plains on the nearside of the moon,
and to prove it, he's taking aim with one of NASA's largest guns.
We're going to fire a projectile down here
at 22 times the speed of sound,
and we do this with a combination of gases
and gunpowder.
The gunpowder explodes, sends a piston down,
compresses hydrogen gas up to about 1 million times
the atmospheric pressure of the air we breathe.
When that happens, and it's let loose,
it sends the projectile down this tube into the chamber.
That's when we see the magic happen.
Peter thinks that a single asteroid strike
could've weakened one side of the moon,
making it more prone to volcanic floods,
but the asteroid would've had to be huge,
hundreds of miles across.
♪♪
Peter believes he's found evidence of one asteroid strike
big enough to fit the bill.
But there's a problem...
It's on the wrong side of the moon.
♪♪
Planetary scientist Peter Schultz
is hoping to solve one of the moon's greatest mysteries.
What led to the dark areas of lava
that cover the nearside of the the moon,
and why are they confined to only that side?
The answer, he believes, is tied to evidence
of a giant asteroid strike found on the opposite side.
Here's the moon. This is the nearside.
This is the side that has all these lava plains covering it,
very smooth, not very many craters.
But there's only one big impact on the moon that we know today,
and that's on the other side,
and this is the south pole-aitken basin,
almost larger than the radius of the moon.
The south pole-aitken basin, 1,550 miles wide
and almost 5 miles deep.
It is the largest impact crater on the moon
and one of the largest in the solar system.
Peter wants to investigate if the giant asteroid
that created this enormous crater
could also critically damage the moon on the opposite side.
♪♪
He uses the NASA ames gun to recreate the birth
of the massive south pole-aitken basin.
♪♪
Here is what we're gonna hit,
and we're gonna hit it with this tiny glass sphere.
We're going to put it on just like a golf tee
and slam it at really high speeds.
♪♪
The team loads the gun with 100 grams of gunpowder
and place the surrogate moon in position.
♪♪
With the gun locked and loaded,
a pump sucks air out of the chamber
to recreate the conditions of outdoor space,
- and it's ready to fire. - Here we go.
♪♪
5.32 k.
Very good.
Footage from the high-speed camera reveals what happened.
The impact to the bottom of the sphere creates a shock wave
that travels right through to the other side.
Where the wave fronts converge,
they crack the body of the sphere.
So here comes the projectile.
It hits right here, and the shock wave begins,
and then the shock wave converges,
and it's inside the sphere.
And nothing is one the surface on the opposite side.
It's all of it on the inside,
and then everything begins to fail,
and it gets this crack that comes all the way up.
♪♪
Peter thinks that this shock wave is crucial...
Ha!
It explains how a massive impact on one side of the the moon
could've created deep cracks on the opposite side.
Ooh. Look at that.
The shock waves started here, propagated through,
and caused all this damage that's on the inside,
but it went from the inside-out
so that when you look at the backside...
you can see this whole portion just popped right off.
But the south pole-aitken impact
alone can't explain
the full story of the man in the moon,
because it took another cosmic event
to turn the cracks into floods of lava.
Four point three billion years ago,
a huge asteroid strikes the far side of the moon.
Violent shock waves travel through the moon.
Where the shock waves converge,
they cause the inside of the moon to crack,
but the man in the moon doesn't yet show his face.
A few hundred million years later, asteroids rain down,
puncturing the weakened crust and releasing oceans of lava.
As the lava cools, it solidifies,
finally turning into the dark basalt rock
that makes up the man in the moon.
Collisions within our solar system
are the way that we have a moon at all.
We think that the moon was formed by a giant collision
and that, perhaps, collisions are part of
how the moon evolves subsequently.
Without collisions, we wouldn't have a moon
and certainly not a moon that looks the way it does.
Scientists solve the mystery
of why the nearside of the moon looks the way it does,
but what about the side of the moon
that we can't see from earth?
♪♪
New evidence suggests that the far side
may hide an even darker past.
For the longest time, the far side of the moon
was just a matter for Sci-Fi.
We had no idea what was on the far side of the moon.
We couldn't see it, and so, of course,
everyone's mind always goes to aliens.
That's clearly where they were hiding.
I think the far side of the moon
has always had this wonderful poetic aspect to it.
It's very intriguing.
People even called it the dark side of the moon,
and it turns out, there was a mystery
waiting for us there the entire time.
Is this so-called dark side
the secret burial site
of the moon's long-lost sibling?
♪♪
Scientists are edging closer
to revealing the secret history of our moon,
but perhaps the biggest mystery of all
is the one that lies hidden from earth,
the far side of the moon.
The far side of the moon has always been intriguing,
mostly because we couldn't see it from the earth.
An interesting thing about the moon
is that it always keeps the same side facing the earth,
and this is a normal result of close-orbiting bodies.
The moon is tidally locked to the earth,
and that means that as it rotates around our planet,
it always shows the same face towards the planet
as it goes around.
♪♪
Scientists get their first glimpse
of the far side of the moon in the late 1950s.
Although the Americans landed a human on the moon first,
it was actually the Soviets who were able to explore
the moon really thoroughly before the Americans could.
They actually sent a probe around
to the far side of the moon,
the side we can never see from earth,
and discovered something really weird.
In stark contrast to the lowlands of the nearside,
the far side is deeply cratered and mountainous.
It's an alien landscape.
♪♪
Data from NASA's moon mission grail
reveals something even more mysterious.
On the lowlands of the nearside of the moon,
the crust is little more than 15 miles deep.
♪♪
But on the mountainous far side...
It's up to 2 1/2 times thicker.
That means the the moon is lopsided.
It's an astonishing revelation that only adds to the mystery.
What created the mountainous far side of the moon
and gave it its superthick crust?
♪♪
Erik asphaug is a planetary geologist.
He believes he can solve the mystery.
His idea is inspired by a comet.
So this here is comet 67p.
It's mostly dirt and ice mixed together.
And what you can see
is it's really two objects stuck together.
There's the neck.
There's the head.
There's the body.
There's layers all over this object.
Comet 67p is made from two comets
that collided to become one.
Is it possible that the moon
is also an amalgamation of two different bodies?
Erik's idea is incredible.
For tens of millions of years,
the earth may have had two moons...
A large moon and a smaller twin sister.
Erik thinks that this smaller moon
could've merged with its larger sibling
to create the far side of the moon's thick crust,
♪♪
But why didn't two moons colliding
smash each other to pieces?
♪♪
Erik carries out numerical modeling to investigate.
He thinks the speed on the collision is key.
In this kind of collision that we modeled,
it's basically two objects orbiting the earth
in the same orbit falling into each other,
so they don't come in with a lot of speed.
It's completely different physics,
and that's what we found out with our modeling.
You can think of it almost as a gargantuan landslide.
Erik thinks that the two moons collide
at an incredibly slow speed,
about a tenth of the speed of a typical asteroid collision.
♪♪
Instead of blasting out a crater,
the small sister moon flattens out like a cosmic pancake...
Spreading itself across the surface
and making the crust much thicker.
If this two-moon theory is right,
then the thick crust of the mountainous far side
is the remnants of earth's long-lost second moon.
♪♪
If you had a time machine and went back
to 100 or 50 million years after the earth formed,
and you looked up,
you would see a big moon in the sky and a littler moon,
and eventually, that little moon would smash into it.
I can't imagine.
I can't imagine how awesome that would be,
to see that up in the sky.
♪♪
When you hear the word "collision,"
you think of something very violent and dramatic
and over in an instant.
And instead, if there really was a smaller moon
colliding slowly with our moon,
it was more of a gravitational snuggle-up.
It happened over a long period of time.
Scientists are beginning to shed light
on the many mysteries of the moon...
explaining its violent birth and its equally violent history.
Amazingly, something as close and obvious as the moon
is actually one of the most mysterious objects
in the entire universe.
It's very rare for one big idea to explain everything,
so we add more to it, and now we have
a much more layered and nuanced understanding
of how the moon formed,
but there are still some weird things about the moon
that we have to explain.
♪♪
Born when a planet the size of Mars
crashes into earth,
a second companion moon slams into its surface
to create the mountainous far side...
♪♪
And a massive asteroid collision
marks the beginning of what becomes the man in the moon.
♪♪
The moon may have one of the most exciting stories
in the universe.
♪♪