Original subtitles

WILLIAM SHATNER: A future space station

synchronized to planet Earth,

the potential for life buried under miles of ice

and rogue moons that could wipe out life as we know it.

We're all familiar with the moon that hangs in our night sky

and controls the ebb and flow of life on our planet.

But Earth's moon is only one of hundreds in the solar system,

each of them a mysterious and often bizarre world.

Could these alien moons offer a key to exploring outer space

and perhaps to finding a new home for humanity?

Well, that is what we'll try and find out.

♪ ♪

Apollo 17, NASA's final voyage to the Moon,

completes its mission to collect Moon rocks

and perform gravity and seismic activity experiments.

After spending 75 hours on the Moon's surface

and exploring more than 22 miles in the lunar rover,

astronauts Jack Schmitt and Eugene Cernan

prepare for their journey home.

As Commander Cernan approaches the lunar module,

he readies himself to take the last human steps on the Moon.

(high-pitched beep)

SHATNER: In just over a decade, NASA's Apollo program

had successfully developed and executed

a space exploration mission

that allowed 12 people to walk on Earth's moon.

But how much do we really know

about the giant gray sphere that hangs in our sky?

What, precisely, is a moon?

And just what makes it different from our planet

or other planets in the universe?

PASCAL LEE: A planet is a large object

that's going independently around a star.

And so, what a moon is,

is an object that is not going directly around a star

but around a planet

as the planet itself goes around the star.

So the Earth, for example, has a very large moon.

Many of the planets in our solar system have moons.

Every one of these objects are little worlds of their own.

(thunder crashes)

VERONICA BRAY: A lot of people think

of moons as like our moon.

It's kind of black-and-white,

cold, dead, geologically inactive.

But it's relatively boring

compared to what we know of some other moons.

For example, Pan looks like a flying saucer

or a-a ravioli.

Hyperion looks like a sea sponge,

with all of these strange pits in its surface.

And then we look at Jupiter's moon Io,

which is the most volcanically active body in the solar system,

covered with yellows and oranges.

We know of something like 300 moons in the solar system today,

and we are always discovering more.

Each of these objects

has a unique and distinctive geology,

it's a different color, it has a different history.

Each one is kind of a puzzle piece

in understanding the solar system.

SHATNER: You could say that many of the bizarre moons

that circle our neighboring planets

make the Earth's moon seem rather dull.

But a closer look reveals that our gray companion

is the perfect partner

for creating a thriving environment on our planet.

The size, proximity and singularity of our moon

make our home world quite unique.

Earth is the only terrestrial planet in the solar system

that has a major moon.

Mercury and Venus don't have moons.

Mars has some little captured moons.

We are unique in that we are a terrestrial planet

that has this moon that is huge.

The Moon is very unusual in that it is

about one quarter the size of the Earth in terms of diameter.

It's very big, compared to planet Earth.

Our moon is humungous.

Even the largest moons of our solar system--

when we look at Ganymede and Titan,

the large worlds of Jupiter and Saturn--

they're nothing in comparison to the size of those giant planets.

And then we look at the Moon,

and it is huge compared to the Earth.

SHATNER: It turns out that this solitary, large moon

has helped make our planet the livable world that it is.

LEE: The Moon's motion around the Earth is so regular

that cultures have created calendars,

in many cases, reliant on the cycles of the Moon.

It's a timepiece, in terms of when is a good time

to grow crop, to plant, to harvest.

The other thing is that the Moon has

a physical influence on the Earth.

BRAY: If we didn't have the large moon that we have,

we would have much more wobble of our spin axis,

which would lead to more extreme seasons.

We also wouldn't have tides.

So, that has implications

for the development of life on Earth.

Life wouldn't have been able to develop

from the seas to the land so easily

if we didn't have a moon.

REBECCA BOYLE: we are very lucky that we have our moon here

to stabilize our spin,

to stabilize the tilt of our planet on its axis

and stabilize its own rotation around the sun.

And the Moon is one of the things

that keeps us safe from the gravitational bullying

of Jupiter or other planets.

It safeguards the climate of Earth through this action.

We're very lucky to have a large moon stabilizing us.

SHATNER: While the Moon plays an instrumental role

in the balance of life on Earth,

this may not have always been the case,

because there is evidence

that our moon may have once had a twin.

At the University of California, Santa Cruz,

planetary scientist Erik Asphaug publishes a study theorizing

that the Earth once had not one but two moons.

Our planet having a single moon seems like an eternal constant,

ever since humans first looked up at the sky.

But could this incredible theory about a second moon

actually be true?

As familiar as the Moon is,

one of the lingering big mysteries about the Moon is,

how did it form?

Where does it come from?

The prevailing theory

is that the Moon formed when,

actually, a larger object, larger than the Moon,

hit the Earth very early in the Earth's history.

This is known as the giant-impact theory.

BEN McGEE: The modern understanding of how our moon formed

is that giant impact sprayed out a bunch of debris

that would later coalesce to form our moon.

But there is a newer idea

that says maybe, out of that debris,

we formed not one moon but two.

SHATNER: The idea of two moons orbiting around the Earth is fascinating,

but if this theory is correct, where's the evidence?

Whatever happened to our second moon?

McGEE: There's an intriguing idea called the big splat concept,

that the little sister moon, trailing behind the major one,

it kind of trailed after our moon in the same orbit,

minding its own business.

But slowly, since the Moon was so much bigger,

its gravity had taken over,

and it would slowly pull this smaller moon in.

And in slow-motion, basically,

smashed into the far side and ends up creating

many of the characteristics we see today,

where our moon's two sides--

one facing Earth and one facing away--

are very geologically different.

RENU MALHOTRA: It's conceivable that the Earth had two moons in the past.

It's conceivable it had multiple moons in the past.

And we are at a stage when all of that evolution has finished,

and having a single large moon is probably

the most stable outcome.

McGEE: We take for granted that Earth has one giant moon,

but we're actually very lucky that the Earth

has a moon as big as we do.

So, this just goes to show how unique our moon is,

almost like a twin-planet system, the Earth and Moon,

which is lucky for us, because we rely

on the environment that the Moon helped create here on Earth.

SHATNER: While the Moon does an excellent job

of making Earth habitable for humans,

the lunar face we gaze at each night

also hides a dark side.

What can 21st-century technology tell us about the hidden spaces

and possible resources our moon may hold

that could change the course of space exploration

as we know it?

SHATNER: In a historic mission,

China launches the Chang'e-6 spacecraft

from the island of Hainan.

The purpose of this unmanned vessel is to bring back

the first ever rock and soil samples

from the far side of the Moon,

an area we cannot see from here on Earth.

The lunar farside has been fascinating to people

for a long time.

Our first look was in 1959 from a Russian spacecraft

that got some very fuzzy pictures of the back.

Since then, of course, the flights of Apollo

and other robotic missions, we've completely mapped

both sides of the Moon.

But there's a lot of mystery around it

because it faces away from us all the time.

DE KLEER: The Moon is what we call

tidally locked to the Earth.

And what that means is that it's always facing

the same side to the Earth.

And so, of course, when you look up at the Moon in the sky,

you always see the same pattern on it,

and that is because you're always looking at what we call

the near side of the Moon.

And interestingly, the near side and the far side of the Moon

look very different from one another.

McGEE: One of the reasons the Apollo missions went to

the near side of the Moon first is because you can see it.

And if you can see that side with your eyes,

it means you can also see it with a radio antenna.

It means we could talk.

This is one of the reasons why

we didn't send astronauts to the farside.

There would be no way to communicate with them.

So it can be very risky trying to go to the farside

in just figuring out--

how do you get information to and from

if it's always pointed away from the Earth?

When Apollo 17 left-- that was 1972--

it was half a century ago,

and humans haven't been back since.

And when you look at everything

that humans were able to do during Apollo,

that only amounts to about two weeks of total stay time.

All in, only 12 people have ever walked on the Moon.

There's so much we have yet to explore.

There are so many mysteries about the Moon

that are yet unanswered.

SHATNER: While no human has touched

the lunar surface in over 50 years,

scientists are using new tools to explore the Moon,

from its dark side to what lies below its rocky crust.

Could there be resources deep underground

that could make the Moon a prime outpost

for future space travel?

At the SETI Institute,

planetary scientist Pascal Lee and his team

release a stunning discovery.

Near the north pole of the Moon, Lee notices strange pits

that he believes could be the entrance

to giant underground caverns.

I went on a manual search, so to speak,

uh, for caves near the Moon's polar regions.

I started with the north pole,

spiraled to lower latitudes.

And sure enough, inside Philolaus Crater,

we found a series of these little dots

that look like a string of collapsed lava tube roofs.

It was a eureka moment because it was like a wish come true.

We were seeing exactly what we were looking for.

SHATNER: According to experts,

several hundred such pits exist on the Moon

and each one could be the entrance

to massive underground caves where lava used to flow.

But it's what we might find inside those caves

that could change the course of space exploration.

It's so important to explore a place like Philolaus

or some of these other craters where we found caves

because there are regions that are permanently shadowed.

That's why they're so cold.

And lava tubes and caves could be a place

where ice would accumulate over time

and be collected

and therefore be a place where you could harvest them.

There's a lot at stake in finding water ice on the Moon.

PYLE: Where you have water ice,

you can make rocket fuel, you can make breathable oxygen,

you can make drinkable water.

But the big one really is rocket fuel.

It's very, very expensive to launch fuel off Earth,

and you have to burn fuel to carry fuel off our planet.

It's much easier once you've extracted these fuels

from the water that's there in the form of ice on the Moon.

And now the solar system is your backyard.

SHATNER: Perhaps even more intriguing is that lava tubes and caves

may also provide humans a place to live.

The surface of the Moon is extremely harsh.

You are subject to ionizing radiation from deep space.

You go underground, it's an entirely different realm.

You're now shielded from space radiation.

I'm also curious to see what else they might offer.

There are other possible resources that could be found.

Minerals.

Who knows what the underground world will reveal to us?

SHATNER: It's exciting to think that our single moon

could hold resources that could take us farther into space.

But there are planets in our solar system

that have dozens of moons.

And scientists have good reason to believe

that some of them may harbor

the building blocks of life.

SHATNER: A team of international astronomers

announces a stunning discovery.

They've located a whopping 62 new moons

around the ringed planet of Saturn.

This new discovery raises Saturn's count

to a remarkable 145 moons,

well ahead of Jupiter and its 95 moons.

Together, these two giants possess

most of the moons in the solar system.

In terms of the number of moons in the solar system,

the vast majority of them are

small objects that are orbiting either Jupiter or Saturn.

And that's simply because

the gravity of those planets is so high.

Jupiter and Saturn are the largest planets

in the solar system, and so they have the easiest time

capturing small objects that are flying through the solar system.

SHATNER: In the grip of Jupiter and Saturn's orbits

are giant moons covered completely in ice.

These include Ganymede, the largest known moon,

and Callisto, which is as large as the planet Mercury.

But what's really intriguing about these icy moons

is that scientists believe some of them could harbor life.

NASA reveals that its upcoming mission

to Jupiter's icy moon of Europa, the Europa Clipper orbiter,

will carry a one-millimeter-thick metal plate

engraved with various messages about water.

Why water?

Because experts believe Europa contains

a vast ocean up to 100 miles deep

under a layer of ice that is 15 miles thick.

KAKU: Underneath the ice,

there is a liquid water ocean for Europa

larger in volume than the size of the Earth's ocean.

This is amazing.

Who would have thought that there could be

another ocean in our solar system

bigger than our own ocean

orbiting around Jupiter?

The spacecraft, in addition to its scientific payloads,

actually has a plate that contains

a bunch of engravings,

much like Voyager and Pioneer had plaques

that were designed to maybe communicate

to the rest of the universe things that the scientific team

thought might be important to send out into the solar system.

One of those is the picture of the sound waves

of people saying the word "water"

in more than 100 languages.

Another is a scientific diagram of what water is

and how it absorbs light.

The search for water is what connects us and this mission

to the rest of our solar system.

BRAY: All life as we know it needs water,

so the search for life

in our solar system or beyond

becomes the quest to find liquid water.

And the indication that there's a subsurface ocean

inside Europa, it gave us this potential location

for life to have formed.

We are hopeful for bacterial life.

We're looking for the basics.

PYLE: We think there's a very good chance

that there's gonna be life there.

It could be anything from the earliest microbes

to whales living in there-- we just don't know.

But we may find out in the next decade or two.

SHATNER: While discovering water on Europa is intriguing,

could there be a place in our solar system

where a liquid other than water might produce life?

The Cassini spacecraft launches the Huygens probe towards Titan,

Saturn's largest moon

and the only moon in the solar system

that has a significant atmosphere.

Three weeks later, as the probe descends,

its video camera captures what is truly another world.

The video is spectacular.

It's like you're parachuting down on Earth

because you're coming through the clouds.

You can see the haze layers part.

And as the Huygens lander is getting closer to the ground,

we start to be able to make out these river systems

and lakes.

And the view that we get

from the surface is extremely Earth-like.

It's pebbles and rocks.

Except these aren't made of rock, they're made of ice.

SHATNER: While the Huygens probe reveals

a surprisingly Earth-like surface

covered with mountains of ice,

there's one feature that is not of this Earth:

large pools of liquid methane

on Titan's surface.

On Earth, methane is an abundant greenhouse gas

in the atmosphere.

But on Titan,

could it be a source of life?

BRAY: The observation of

methane lakes

and river systems on Titan

has some people thinking,

we use water on Earth for our life,

life as we know it.

Is it possible to have a life

that is based off a different liquid?

So, liquid methane?

The surface of Titan is a really dynamic place,

and there's a lot of questions about

what's going on down there.

SHATNER: Could there be alien life-forms

in the methane lakes of Titan?

It seems fantastical,

but early observation of these lakes revealed

something extraordinary.

DE KLEER: One of the mysteries

when we first landed on Titan's surface

is that when we took repeated radar images of

the same lakes on Titan,

there were these features in the lakes

that changed over time and kind of came and went,

and they're called these magic islands.

McGEE: Scientists started calling them, informally,

"magic islands" that would appear and disappear at will.

The most recent research makes it

look like those islands aren't islands at all,

but instead they're nitrogen and ethane and methane

bubbling up from the interior.

It really makes you wonder,

having material bubbling up,

well, that only invites the question,

what's actually going on down there?

SHATNER: Could these strange bubbles

come from some undiscovered form of life?

Well, the only way to know

may be to dive deep into Titan's lakes.

Its largest lakes are just incredible in scale.

Kraken Mare, which is the largest

body of liquid on Titan, is enormous.

It's twice the size of all the Great Lakes put together.

But we haven't really explored below the surfaces of them.

LAU: It really begs for exploration.

We could build a submarine

that we could put into one of these lakes on Titan

and have it go explore around the lake,

maybe even looking for possible signs of life

at the bottom of the lake.

Finding life-forms on faraway moons covered in ice

could change everything we thought we knew

about our solar system.

But on the other hand,

moons could also wipe out

every trace of life on a planet

when they become unstable

and go rogue.

SHATNER: At the U.S. Naval Observatory,

using the largest refracting telescope in the world,

a frustrated astronomer named Asaph Hall

nearly abandons his search for the moons of Mars.

Fortunately, his wife, mathematician Angeline Stickney,

encourages Hall to persist.

LEE: The moons of Mars

were discovered by American astronomer Asaph Hall.

His wife really, in my view, deserves equal credit because

he actually had all but given up,

and it's only at her insistence

that, in the end, he was able to discover

moons around Mars by spotting little dots of light.

SHATNER: Hall names the two moons Phobos and Deimos,

meaning "fear" and "terror,"

after the sons of the Greek god of war.

Little does Hall know

these names will prove prophetic,

because Phobos is doomed to,

one day, bring destruction to its home planet.

LEE: Phobos is drifting towards Mars,

and at this point, we're catching Phobos

almost at the last minute of its life.

It's going to, first of all, break up

and turn into a ring of debris around Mars.

And then, if it doesn't burn up,

it's gonna crash somewhere along the equator of Mars.

50 million years from now,

who knows where humanity will be,

but if we are living on Mars,

we are gonna have a shower of debris.

BRAY: So, at some point in the future,

if we have a human presence there at the time,

Phobos will eventually rain down onto Mars,

causing significant devastation.

SHATNER: While it's an extraordinarily long time from now,

the prospect of Phobos crashing into the Red Planet

could mean the end of any human settlement

we've managed to place on Mars by then.

But this scenario isn't the only one

that can turn a moon

into a dangerous object.

LAU: Moons aren't just static worlds orbiting around planets.

Many of them are very dynamic

in how their orbits change over time.

We have this concept that there might even be

rogue moons, moons that have been

pulled away from their orbit around the planet

for various reasons.

BRAY: The idea of a rogue moon is that

an otherwise happy and stable moon

can be perturbed by the close proximity

of the star in that star system

or another planetary body,

and it will pull that moon from its orbit.

SHATNER: As it turns out, when a moon

leaves its planet and goes rogue,

it spells disaster.

At UCLA, theoretical physicist Brad Hansen

publishes a remarkable paper

suggesting that moons located throughout the galaxy

may be going rogue

and colliding with planets.

BRAD HANSEN: Some moons

can eventually spiral out to the point where

they're no longer bound to their parent planet,

but rather simply become another asteroid

orbiting the original parent star.

So they have very similar orbits

to the original planet, and so they're gonna

keep coming back again and again

until, eventually, they come back and impact the planet.

SHATNER: According to Hansen's study, rogue moons that have been

ripped from their orbit can be catastrophic

when they whip around a star

and slam into their home planet.

BRAY: Usually moons are significantly smaller

than the planets that they orbit.

And so, in that case, the impact

of this theoretical rogue moon,

it wouldn't destroy that planet,

but it is big enough to sterilize it.

A mass extinction event

could be caused by the impact of a rogue moon into a planet.

SHATNER: A planet getting taken out by a collision

with its own rogue moon is unsettling.

And it begs the question,

could our moon ever lose

its gravitational bond with Earth

and crash into our planet?

KAKU: When you think of the Moon,

you think of something that's eternal,

something that's been there since time immemorial.

But then you begin to realize that the orbit of the Moon

is actually not so stable.

It's actually leaving us

at about the rate of one and a half inches per year.

So this means that it will eventually reach a point where

it's just about to leave the planet Earth.

MAHOLTRA: If it goes too far,

the Moon's orbit could become unstable

and then become unbound.

It could leave the orbit around the Earth.

That instability is very difficult to compute.

Many possibilities are there.

The potential for chaos is always there.

HANSEN: We talk about how the dinosaurs

underwent extinction through an asteroid collision

that was estimated to be about 10 kilometers in size.

The Moon is

thousands of kilometers in size,

so it would be a genuine global catastrophe

if something the size of the Moon hit the Earth.

SHATNER: While the ultimate fate of our moon

is something we may not be able to predict,

what about other moons,

both inside and outside our solar system?

How concerned should we be

about the possibility of rogue moons reaching us

from other corners of the galaxy?

McGEE: Rogue moons probably happen more often than we think

out there in the cosmos.

Whether or not we end up having to worry about

our own moon becoming rogue,

it doesn't mean we don't have to

keep looking for rogue moons

from elsewhere in the solar system.

And it's something we're gonna have to deal with,

probably, in our own solar system's future.

When moons become dangerous objects

flying through the solar system,

we're pretty much helpless to stop them.

Perhaps the solution to protecting Earth,

and even venturing deeper into space,

is by building our own

man-made moon.

SHATNER: The Soviet Union launches

a revolutionary piece of technology

that will change the course of the 20th century:

a polished aluminum device named Sputnik.

It is the very first artificial satellite in history,

and is, by most definitions, a man-made moon.

NEWSMAN (over radio): Today a new moon is in the sky.

A 23-inch metal sphere placed in orbit by a Russian rocket.

The launch of the Sputnik satellite by the USSR

was a watershed moment for us

in changing the way we looked at moons.

The Sputnik satellite itself was characterized

as a new moon, a baby moon, in newspapers at the time.

It caused panic in the United States because

this meant that the USSR was always watching.

PYLE: Sputnik was really the first artificial moon.

It was the first thing orbiting the Earth

besides our natural moon,

and it was a metal ball about this big around.

A little bigger than a basketball.

And it beeped as it went around the Earth

every 90 minutes.

And that's about all it did.

But you would've thought the world was coming to an end.

The press was rife with headlines about

"Reds Orbit Artificial Moon."

It was sighted over San Francisco.

It's the end of the world.

And it really got the West riled up.

This fairly innocuous little metal sphere

was really the kickoff for the whole space race.

And that's what ultimately took us to the Moon.

SHATNER: Today, we're surrounded by thousands of artificial moons

called satellites, orbiting the Earth.

But shortly after the launch of Sputnik, one Soviet scientist

suggested an artificial moon might already exist...

and be orbiting around the planet Mars.

At the Sternberg Astronomical Institute,

renowned Ukrainian astrophysicist

Iosif Shklovsky makes a shocking proposal.

Shklovsky suggests that Phobos, one of Mars' two moons,

could be hollow, and artificially constructed

from a thin sheet of metal.

From the size of Phobos, and the rate at which Phobos was

migrating towards Mars, Shklovsky determined that

Phobos could be something that was almost hollow

and just had a very thin shell.

Close to what we might call the density

of an empty can of soda.

Shklovsky proposed that Phobos might actually be

a station or ship built

by an extraterrestrial civilization on Mars.

It could be the last vestige of an alien civilization

still in orbit around the planet.

Now, that, of course, was an extraordinary claim.

SHATNER: Nearly 20 years later, in 1976,

NASA's Viking 1 spacecraft performed

an up-close flyby of Mars,

and sent back photographic evidence that Phobos was,

in fact, a dry and dusty natural moon.

Even though we now know that Phobos is definitely not

a Martian station or a spaceship from a Martian civilization,

I think this was sort of the dawn of the era of

thinking of gigantic stations,

where a civilization

could actually create objects, mechanisms,

vessels that could be of cosmic or astronomical proportions,

to the point of being the size of a little world.

McGee: It may sound bizarre to consider building an artificial moon,

but honestly, every single satellite we've sent up

is an artificial tiny moon.

The Sputnik satellite itself was small.

It was about two and a half feet in diameter,

but its implications were profound.

Now you have larger structures,

like the space station Mir we had for a while,

or the International Space Station we currently have.

Those are, like, a football field in length.

They're getting much bigger.

PYLE: There can be some practical uses for artificial moons.

I think one of the most profound suggestions

has been from Buzz Aldrin himself,

second man to walk on the Moon,

who suggested something called the lunar cycler.

And these are moon-sized objects

that could be artificially constructed.

You can use them for fuel depots,

you can use them for reprovisioning stops.

They could be facilities for people on their way

deeper into the solar system.

And so you have this big,

comfortable, well-protected, enormous facility

moved into a long, permanent, looping orbit

between the Earth and Mars, or Earth and the Moon.

CHARLES ADLER: In 1976, Gerald O'Neill,

a physicist at Princeton University, speculated about

building what are called now O'Neill cylinders,

where long cylinders could be spun around

so that centrifugal force

could approximate the experience

of gravity inside the structures

to house people living in these huge space stations

built in orbit around Earth, or around the other planets.

But if you want something that is moon-sized,

you're getting into the realm of billions

or trillions or quadrillions of dollars.

It's going to be very, very expensive, and currently

out of the reach of today's technology.

But it may be that in the future these things

actually become possibilities.

SHATNER: While building a moon-sized space station

might be currently out of reach, turning the Earth's moon

into a destination for humans is closer than ever.

The big question is

how will we survive on the Moon?

SHATNER: The crew of Imagination 1 completes a six-day mission

inside a sealed Moon simulator known as SAM,

or Space Analog for the Moon and Mars.

Their mission: to simulate what life might be like

for humans living on the Moon.

TRENT TRESCH: SAM is a hermetically-sealed research habitat

that demonstrates what it would be like

to live on another celestial body,

like the Moon or Mars.

You're actually able to move around

and even bounce around as if you were on the surface of the Moon.

At this point in time, with the NASA Artemis missions

and others, we're looking at going back

to the Moon and establishing long-term habitation.

It is so exciting that we are going back to the Moon,

hopefully within this decade.

SHATNER: While SAM is used for scientific research

into how we can survive on the Moon,

another chief goal of the project

is getting everyday people

involved in space exploration.

Enter... Imagination 1.

JULIE JOHNSON: In the case of Imagination 1,

our crew was, uh, made up

of four different professional artists,

and our mission was to demonstrate

what artists can bring

to a scientific endeavor like space flight.

When we imagine going to the Moon and living there

for a more extended amount of time,

it will be important that we have people

from all kinds of different backgrounds, because

the more perspectives we can have,

the better decisions I think we can make.

SHATNER: No matter what an astronaut's background is,

the experience in such a lunar simulator

gives just a glimpse

of what a truly alien experience

living on the Moon will be.

When the moment comes that we actually

pull down on that handle for that outer door...

...sealing ourselves off hermetically from the outside,

there's this real sense of separation,

a sense that you've left what you know behind.

And there are many things that feel different

living in a space that's pressurized.

In the space suit,

you don't have the same kind of fine motor control

that you would normally.

There's a sense of separation from the way

you normally would move through the world.

TRESCH: There's gonna be a lot of difficulties

that the first inhabitants are gonna experience.

A lot of our dreams and excitement and aspirations

about long-term habitation in space

come really from those two weeks that we set foot

on the Moon in the '60s and '70s.

The Moon as an alien place is really a foreign place.

There's still a lot to be discovered and to be understood.

And I think there's just an excitement

around that discovery.

It's still just a foreign land.

SHATNER: The prospect of finally living on the Earth's moon is exciting.

But our moon is just one of many equally thrilling

and terrifying alien worlds

waiting for us to encounter.

The moons of our solar system are a key part of exploration,

mostly because, if we want to go to places,

we can't land on gas giants, but we can land on their moons.

And so, the moons provide us with this solid surface

where we can land,

potentially as a jumping-off point for

further space adventures.

DE KLEER: The population of moons,

and especially the moons of the gas giant planets,

but even including the moons

of Earth and Mars, are such a

diverse population of objects.

And this is something we've only appreciated

in the past few decades, just how

unique and interesting

each of these objects is.

SHOWALTER: Every moon has a story to tell.

Every moon, you can look at it and say,

"How did it get there? What is it made of?"

Every one tells the history of how it came to be where it is.

LEE: All of a sudden, we have this

incredible number of places we could go explore,

not just the planets themselves, but their families of moons.

The Earth's moon is a reference

to which we can now also compare other moons

and see how alien they are in the solar system.

Today, we're closer than ever to constructing

a permanent base on Earth's moon.

Is this an important first step that will eventually lead us

to reaching alien moons?

And if so, what will we find

when we get to these strange, new worlds?

It's exciting to think about.

But for now, these exotic and faraway moons

remain unexplored

and unexplained.

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