All language subtitles for The.UnXplained.Mysteries.of.the.Universe.S01E06.1080p.WEB.h264-EDITH_track3_[eng]

WILLIAM SHATNER:
Futuristic plans to create

an ecosystem on Mars.

A source of life found
on the edge of our solar system.

And galactic probes that hunt
for humanity's next home.

By nature, we humans
are curious creatures.

We want to boldly go
into uncharted territories

to make new discoveries.

So, as the next era
of space exploration begins,

what will we find
when we reach other planets?

Will they be places where
humanity can create a new home?

And what dangers will we face

when we try to conquer
these new frontiers?

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

Astronaut Neil Armstrong
positions himself on a ladder

just a few feet
from the surface of the moon.

It is the first time
an astronaut has been exposed

to the dangers
of the lunar environment.

SHATNER:
Alone in a temperature capable
of freezing skin on contact,

and with no oxygen
outside his spacesuit,

if something goes wrong,
a painful death

is all but guaranteed
for the astronaut.

SHATNER:
Carefully, Armstrong
prepares for one of the most

extraordinary accomplishments
in human history.

SHATNER:
And with that step, Apollo 11

put a man on the moon

and claimed
humanity's next frontier.

Throughout human history,

the combination of intelligence
and innate curiosity

has compelled us
to look beyond Earth

and imagine life
in the universe.

And for nearly a hundred years,

human ingenuity
has allowed us to explore

the most dangerous frontier
we have ever encountered.

Space-- it's not just
the next frontier of humanity.

It is the ultimate frontier.

And it is way more dangerous

than anything humanity has
ever encountered in the past.

If you think about
all the classic dangers

of the Old West
and ramp it up by a hundred,

you're still not even there

at the dangers
presented by space.

SHATNER:
If space is so dangerous,
one can't help but wonder:

why leave Earth at all?

Isn't it basically perfect
for life as we know it?

The Earth is special
in a number of ways.

We have liquid water
on the surface.

We have plate tectonics.

We have an atmosphere
which is thick enough

that it is meaningful
for life on Earth.

It is also thin enough
that it's not completely opaque.

We can see the night sky
when the Sun sets.

All of these things are,

galactically speaking,
not guaranteed.

SUTTER:
As far as we know,

we are the only place
in the solar system

where all that
special combinations

came right into the same place.

But as beautiful

and special as Earth is,

it's also fragile.

We only have
one planet to live on.

And we face innumerable
existential threats,

some of them human-caused,

and some that are
totally out of our hands

like a supernova explosion...

...or a solar flare

or an asteroid impact.

The more places we live,

the more we can ensure

the longevity
of the human species

far into the future.

SHATNER:
Is it our instinct for survival
that compels us

to look to the stars
for a new home?

Or does our innate curiosity to
understand the world around us

help us look past
the dangers we face

when exploring outer space?

Humans have explored
much of the Earth.

We've been in the sky some,

we've been around the Earth

a gajillion times in orbit.

And a few times,

we've spent an incredibly
short amount of time

going to and setting foot
on the Moon and coming back.

And that's it.

That's a tiny,
tiny, tiny little corner.

It's a nice corner to be in,

but it's a tiny corner
of what's there.

And so people are always
wondering, "What comes next?"

SHATNER:
As we consider new frontiers
beyond Earth,

just where could humans
actually consider going?

Are there really planets
that we could explore

without being killed
in the process?

The first places humans
might settle off world

in the solar system are what
we call the rocky planets.

And that's because
they have a place to stand

and they have resources
we can access.

That would include Mercury,
Venus and Mars.

SHATNER:
Mercury, named after the fleet-
footed Roman deity Mercurius,

is the closest planet
to our Sun.

But as a place to explore,
it may not even be possible.

In fact, of the dozens of probes
sent out to our solar system,

only two
have ever been to Mercury.

And they didn't even land.

In the case of Mercury,

uh, it's simply
too close to the Sun,

which has turned it
into a nightmare.

SUTTER:
Mercury is just
downright awful

because in the daytime
it has temperatures

over 800 degrees on the surface.

But because
there's no atmosphere,

its night side plunges

to almost
-300 degrees Fahrenheit.

So no matter what,

you're always
going to be miserable.

SHATNER:
While our solar system's
first planet

seems impossible to explore,

what about Venus,
our closest neighbor?

At first glance, Venus
looks like the prime candidate

for exploration
and human habitation.

It's very close to us.

It's roughly
the same size of the Earth.

It has an atmosphere,

but if hell could be a planet,

it would be Venus.

The atmosphere of Venus
is over a hundred times thicker

than Earth's atmosphere.

And we're talking
temperatures topping

900 degrees Fahrenheit.

That is hot enough to melt lead.

That is no place to call home.

SHATNER:
While it seems clear
the surface of Venus

is no place
for a human settlement,

some at NASA suspect
we might be able

to manage living
above the surface.

In the clouds.

If you go up about 30 miles
in the Venusian clouds,

you get to temperatures that
are more or less Earth-like,

and radiation levels
that are safe.

And so some have proposed

that you could have airships

floating through
this cloud layer,

potentially hosting
human explorers

and maybe in the future,
even hosting human habitation.

There are
conceptual NASA missions

that would float
through the clouds of Venus

to do scientific exploration.

SHATNER:
Though fascinating,

the idea of living
in the clouds of Venus

seems firmly seated
in science fiction for now.

And so, with Mercury
and Venus ruled out,

there appears to be
just one rocky planet left:

Mars.

But even Mars
is a challenging proposition.

There's a lot of things
about Mars

that would make it
extremely difficult

for humans to live there,
to work there.

And yet we do currently have
the technology.

We could send humans
to Mars right now.

We can do it.

It really just requires
the want, the ambition

and the funding
to make it happen.

SHATNER:
Could Mars be the next giant
leap in human space exploration?

The answer is yes.

And while getting there
may be possible,

surviving will be
its own dangerous challenge.

Mars. It is the most studied
planet in our solar system.:

As of August 2023,

more than 50 Mars missions
have been launched

by countries around the globe.

What is it about the Red Planet

that draws such international
interest and attention?

BATYGIN:
Mars is popular
first and foremost

because it's the thing
that's kind of within reach.

The rest of the universe
seems immutable

and distant
and sort of out there.

Mars is just
on that boundary between

reachable and completely alien.

LEE: It has a landscape
that speaks to us.

It looks like
the pristine deserts

that we have on the Earth.

Mars looks like a place

that would be quite manageable
for us to inhabit.

And there's this romance

that is tied to this
frontier-like landscape

that is drawing us towards it.

SHATNER:
Atop an Atlas-D booster,
the Mariner 4 spacecraft

launches on
an eight-month journey to Mars.

Its mission is to take the first
pictures of the Red Planet.

Mariner 4
and other Mariner spacecraft

would spend more than a decade
collecting data

on our neighboring planets
Mercury, Venus

and Mars.

PYLE:
In the early 1960s,

the space race was
just beginning to heat up.

America's answer to that
was the Mariner program

with a standardized
spacecraft form.

So you could build a number
of different kinds

of spacecraft
that were more or less alike.

You could send them to Mercury,
you could send them to Mars,

you could send them to Venus.

And the idea behind
the Mariner spacecraft

was primarily to get the first
look at these worlds close-up.

SHATNER: Prior to Mariner 4's
arrival to the Red Planet,

our knowledge of
the Martian surface was limited

to conjecture and speculation.

Did it have water?

Did it have life?

Could there even be Martians
looking back at us?

If humans were ever going
to set foot on the planet,

we'd need answers
to these questions.

PYLE: Mariner 4 to Mars was
a big moment for astronomers

and for the public
at large because,

for easily a hundred years,

we thought
Mars might have animals.

We thought it might have oceans.

Some people thought
it might actually have people.

Then Mariner 4 flies past
in 1965...

...and our world
spins on a dime.

PYLE: This whole
imaginary red Martian empire

is just crushed to dust.

And we realize this place
is just like the Moon.

It has a little bit
more atmosphere,

it's got more color to it.

But it is just this bleak
and rocky environment.

And there's nothing else there.

SHATNER: Even though Mars was
a barren, desert landscape,

scientists were encouraged
to expand exploration efforts.

And what they found
in over six decades

of intensive research could be

the next frontier
for human civilization.

TRAVIS TAYLOR: When we look
at the Red Planet above us,

we see that there could be ice.

There could be liquid water.

There's carbon dioxide
and dry ice there.

And there could be an atmosphere
if there was a little bit

more energy added
to Mars just the right way.

So, perhaps it also might
offer us a future place

to go as a new safe haven
or expansion of humanity

out into the solar system
and into the stars.

And so hopefully one day,
we're gonna follow up

those probes with actual people

to go there and do some
investigating and exploring.

SHATNER:
Exploring the Martian frontier,
however, will not be easy.

In fact, it will be much
more dangerous than the Moon.

Because it's one thing
to get there.

But surviving a hostile planet

may be harder than we think.

If you were to wander onto
the surface of Mars unprotected,

there are five things
that will kill you.

Within seconds, you're dead

from the low
atmospheric pressure.

If that didn't kill,
you within minutes,

you would be dead from the fact
that the Martian atmosphere

is made of carbon dioxide
instead of oxygen.

We are brain dead within
a few minutes without oxygen.

The third thing that will
kill you is the temperature.

The temperature
is extremely cold,

-80 degrees Fahrenheit.

You are a frozen popsicle
to the bone by sundown.

If that didn't kill you,

the fourth thing
would be the dust.

It's gonna clog your lungs.

It's abrasive.

It's gonna tear up
the tissues of your lungs.

Within a few weeks, you are dead

from just being in contact
with the dust.

And, finally,
if that didn't kill you,

space radiation.

You don't have
a thick atmosphere

and you have no magnetic field.

You are exposed to radiation.

You're dead within several
months to a few years.

SHATNER:
It makes you wonder:

if Mars is so uninhabitable,

why bother going at all?

Well, some scientists think it's
possible to transform the planet

far beyond
the dry desert it is today.

If we want to live on Mars

the same way
that we live on Earth--

where we can just walk outside,

take a breath of fresh air,
grow plants, have crops,

you know, do all the normal
things that we do on the Earth--

we have to completely change

the character of that planet.

We have to turn it into
something more like the Earth.

And this process is known
as terraforming.

MICHIO KAKU:
The terraforming process
would begin in steps.

The first step,
of course, is the ice caps.

Realize that there's
plenty of water on Mars,

but most of it is frozen.

We can redirect satellites
to beam solar energy

down to the polar ice caps
to melt them,

so that water will once
again flow through the planet

and make it possible
to have agriculture.

Then we can begin the process
of constructing materials

out of the soil

so that we can begin the process

of creating cities on Mars.

And then the last process
would be

to make sure that
there's enough oxygen

so that we could then
breathe on the Red Planet.

BATYGIN:
While being an ambitious idea,

to say the very least,
terraforming is

one that requires
extraordinary resources.

We, in a way, are doing this
to the Earth right now.

Emission of carbon
into the atmosphere

is terraforming the Earth.

All of the industry
that we have on our planet--

that's changing the temperature
of the atmosphere

by one, two degrees per decade.

And so to make Mars livable,
we would have to change

the atmospheric temperature
by hundreds of degrees.

So the amount
of investment and...

just resources required
to do that are unfathomable.

TAYLOR: Those are the kinds
of things that will take,

hundreds to thousands
of years to do.

You're not gonna terraform
Mars overnight,

but it could be done.

Transforming the Red Planet
into an Earth-like world

is a tantalizing prospect.

Even if it will
take decades to achieve.

But what if we didn't
have to wait that long?

What if the planet Pluto--

long thought to be frozen,
dead, and lifeless--

turns out to be anything but?

24-year-old astronomer
Clyde Tombaugh

has spent the last few weeks
tediously searching

the sky for a theoretical planet
known only

as Planet X.

Yet all attempts to observe it
up to this point have failed.

So what was Tombaugh
going to do differently?

BROWN: He had the insight that
you take a picture of the sky,

come back the next night,
take another picture of the sky.

And you see something move
that's in our solar system.

But he had to do it by hand,
move them both around

and look for anything
that moved.

SHATNER: It's an extraordinarily
tedious process,

but it pays off

when he spots a tiny,
barely visible dot

hiding in a sea of stars.

It was
a ridiculously meticulous,

incredible job that he just

went through the sky
until he found this one

little thing
that was one night here...

...the next night here,
and that was Pluto.

SHATNER:
Instantly, Tombaugh expanded

our definition
of the solar system.

As knowledge of Pluto spread
through the cosmic community,

scientists wanted to know,
"What sort of planet was it?"

Could it have water?
Could it have life?

For the remainder
of the 20th century...

...Pluto was about
as mysterious to us

as it was in 1930.

SUTTER:
Our best image of Pluto came
from the Hubble Space Telescope.

At the time, our most powerful,
most advanced

observatory ever designed.

And all we have is

a tiny little fuzzy patch

that really doesn't look
much like anything.

SHATNER:
By 2006, Pluto's planetary
status is downgraded

to a dwarf planet
based on its small size

and weak orbital dominance.

But that same year,

NASA launches an interplanetary

space probe called New Horizons,

designed to explore
the strange planet

on the edge of the solar system

and beyond.

New Horizons was the first
mission sent to explore Pluto.

To take images, to figure out

what the surface
was made out of,

to study its atmosphere,

to study its moons.

And then go on to explore
the rest of the Kuiper Belt.

The Kuiper Belt is a huge
donut-shaped ring

that orbits outside of Neptune.

And it's like the asteroid belt,
but much farther out.

SHATNER:
On the second floor of
the Applied Physics Laboratory,

Kelsi Singer and her team
anxiously await

the first photo of Pluto
from New Horizons.

Will it be icy or rocky?

Colorful or gray?

They could only guess
at the answers.

SINGER:
We had no idea

what the details
of the surface looked like.

The best pictures
were just blurry blotches

of bright and dark.

Because we didn't have
any good photos of the surface,

we thought that Pluto
might be just a cold,

inactive, dead world.

SHATNER:
After taking over nine years
to reach the dwarf planet,

the New Horizons probe sends
the first photos of Pluto

back to Earth,

and scientists are stunned

by what they see.

SINGER:
Seeing the images coming
back from Pluto was

definitely one of
the most exciting things

I've done in my life.

No one else had seen Pluto,

and the pictures
that we got back

showed a surface
that looked nothing like

anywhere else
in the solar system.

When we first started to
be able to see

the real surface of Pluto,

and we were getting
the images back,

we could see this
weird mountainous terrain,

and we found that
the surface of Pluto

was much more active

than we expected.

SHATNER:
One image in particular would
stand out from all the rest.

It's an iconic image
that would make huge waves

around the world

known as the heart photo.

BROWN:
When people see
this heart of Pluto,

it's this region that,
of course,

happens to be shaped
like a... like a heart.

But this is the crater.

It was a former impact crater.

Something came in and
smacked Pluto really hard,

left this big basin,
this big crater,

and that crater filled up

with nitrogen ice.

SUTTER:
There are boulders
the size of Mount Everest

made of water ice

floating on that glacial field.

It is alive

and it is dynamic.

SHATNER:
The heart photo confirmed that,

far from being
a cold, dead wasteland,

Pluto might have one of the most
basic requirements for life.

BROWN:
It would not be surprising

if Pluto had an ocean
on the inside.

It would be many hundreds
of kilometers down,

but probably there.

SUTTER:
All life that we know of
requires liquid water.

So, if there is liquid water,

there is the potential for life.

It's crazy to think about.

There might be living creatures

hiding underneath
the surface of Pluto.

SHATNER:
Creatures on Pluto?

It hardly seems logical

and yet we can't rule it out.

Does this also mean
human exploration

could one day be possible?

Perhaps.
But the dangers

will be very real.

SUTTER:
Pluto is so distant
from the Sun,

the surface temperature
of Pluto--

we're talking somewhere around
-360 degrees Fahrenheit.

That is colder than anything

we can experience on the Earth.

And to give you a sense
of how long it would take

for a human mission
to reach Pluto,

we're talking somewhere like

20 to 30 years to
reach that destination.

KAKU:
Some people have looked
at Pluto and said

that, well,
perhaps Pluto could be

a station for astronauts

going into deep space.

Perhaps there's
liquid oceans there.

Perhaps it has a warm interior.

This, of course,
is still speculation,

but that's the target
for looking for life

in the solar system.

So, maybe.

If Pluto,

the most distant planet
in our solar system,

can still surprise us,

then it begs the question

what is waiting to be
discovered on planets

that are much closer?

Well, a space probe
recently revealed that,

of all places,

Jupiter may hold the key

to Earth's survival.

SHATNER:
At Lockheed Martin's
Waterton Canyon facility,

NASA's Juno orbiter
is being assembled

just weeks before
its launch to explore

the fifth planet
from the Sun: Jupiter.

Many scientists believe that

the large moons orbiting
the biggest planet

in our solar system
may be the best place to

find life in outer space,

and one day
host humans as well.

But to have any chance
of exploring these moons,

we must understand

the giant beast
that guards them.

Jupiter itself is
one of the gas giants.

It is practically the gas giant.

It makes up most of
the mass of our solar system

outside of the Sun.

McGEE:
Jupiter's gravity is so strong

that it acts like a cosmic
vacuum cleaner in a way,

stripping asteroids,
rogue worlds,

and swallowing them up
without even blinking.

In 1994, there was a comet--

Shoemaker-Levy 9--
that smashed into Jupiter.

And it was strung
into pieces before it hit,

and each of those
pieces exploded,

creating a mushroom cloud
the size of the Earth.

And Jupiter didn't notice.

SHATNER: Jupiter's
immense size and gravity

also creates its greatest
threat to human life:

radiation.

LAU:
Jupiter is spinning

really fast, it's moving
a lot of material around

in its magnetic field.

It's bombarding
its moons and other areas

with all of this radiation.

And so, for any human being,

Jupiter would be
a horrendous place to live.

SHATNER:
The punishing effects
of Jupiter's radiation

was a top concern for
scientists and engineers

as they developed
the Juno space probe

in the early 2000s.

Could a spacecraft be built
that could withstand

Jupiter's powerful wrath?

Jupiter, with its
massive magnetic field,

collects particles
that fly by it

and get generated by its moons.

And then it speeds them up
with its magnetic field.

And then it has these belts
of high energy particles--

radiation-- that are just there.

And electronics that
we develop and build

are highly susceptible
to damage

or upsets
from that radiation.

JENNIFER DELAVAN:
The Juno mission is really
the first mission to Jupiter

to stay there for
an appreciable amount of time.

All the other missions
were simple flyby missions--

one shot and you're done.

You really do need to

be prepared for
the radiation environment,

and it really will affect

the memory on board
the spacecraft,

and you really will
have to come up with

ways to work around that.

SHATNER:
And so, as the Juno spacecraft
nears completion,

everyone at
Lockheed Martin is on edge.

The craft must be built
and operated perfectly

if it is to survive.

But now, just weeks
before launch,

the craft has a serious problem,

and the team in charge
of Juno's construction

is running out of time.

COX:
The biggest challenge we had was

one of the avionics boxes.

We were doing
the last test in thermal,

and the worst thing happened

that you could have happen
on a box, which is,

it was running well,

it malfunctioned badly
for five minutes,

and then it started
working fine again.

You got to understand
why that happened

to make sure it's not gonna
happen again in the mission.

I didn't know
what we were gonna do.

So we thought it over,

and I recommended
to let us keep trying to

solve the problem
for a month or two.

Thankfully, in the end,

we figured out what happened

and we were able to fix it,

and then we were able to
get that box to the spacecraft.

Literally, we gave it to them

on a Monday night, it was on
the spacecraft Tuesday morning,

it was in
the final environmental test

on Friday type of thing.

If we would have not solved
that problem successfully,

I'm not sure if we would have
made the launch date.

SHATNER:
On August 5, 2011,

Juno successfully launched

and began its
five-year journey to Jupiter.

Remarkably, the probe survived

its encounter with
the giant planet

and, in 2016,
began its assignment

to collect data on
Jupiter's thermal radiation,

gravitational and
polar magnetic fields,

and the circulation patterns
in its atmosphere.

Before Juno,
the poles of the planet

were something
we had never seen before.

And so it was a mystery to

the science community
as a whole

as to what was
going on up there.

And so Juno has flown
across those poles

and uncovered new mysteries
of what is causing

the swirling storms
that we see in the images

and just the makeup
of the planet.

SHATNER:
The incredible, first-ever
pictures of Jupiter's poles

showed giant, swirling storms,

similar to
the famous Great Red Spot

near Jupiter's equator.

The spacecraft also got a look
beneath these giant storms,

but what it found
was troubling, to say the least.

Especially if you were a human

thinking about taking
a look around.

SUTTER:
Juno discovered that

the Great Red Spot
is enormously thick.

We're talking
around 200 miles deep.

Compare that to
the biggest storms on the Earth,

which are only
a few miles thick,

this thing is a monster.

If you plunge yourself
down into the depths,

you quickly experience
pressures and temperatures

beyond anything you could
possibly imagine on the Earth.

It is just a rough place to be.

SHATNER:
Juno confirmed that
the moons of Jupiter

may be as close as
human exploration may ever get

to the mighty
and dangerous planet.

And that Jupiter
may not always be

the so-called protector
of Earth,

as we commonly thought.

Jupiter has tremendous
gravitational influence.

So it's often portrayed
as Earth's protector,

vacuuming up material

that would otherwise careen
through the inner solar system,

but it could also fling things
and potentially hit Earth.

BATYGIN:
As the theory of planet
formation has come

into sharper and sharper focus,

it has become
progressively clear

that Jupiter played
the role

of a great architect

of the large-scale structure
of our solar system.

But Jupiter can both
act as our protector

as well as
the harbinger of our demise.

Whether Jupiter is our cosmic
protector or our worst enemy,

the fact remains that human
settlement there is impossible.

So, if we want
to live on another planet,

where should we go?

Some believe
that our next frontier

is light-years away in a world

beyond our solar system.

SHATNER:
Scientist Georgina Dransfield
and a group of experts

publish a stunning new find.

They have discovered a planet
about the size of Earth...

...orbiting a nearby star.

There's a recent discovery.
It's very exciting.

It's an exoplanet
called TOI 715 b,

located roughly
137 light-years away.

And it's exciting because
it's very Earth-like:

It's 1.5 times the size,
three times the mass.

And in astronomical terms,

that's almost
identical to Earth.

An exoplanet is simply a planet

that orbits another star.

And these exoplanets
get their names

from their parent stars.

SHATNER:
Since discovering
the first exoplanet in 1995,

scientists have confirmed
over 5,000 planets

orbiting distant stars.

While this may sound like
a lot of worlds to explore,

almost all of them
appear to be uninhabitable.

However,
TOI 715 b...

...may be different.

Most of the exoplanets

that we have discovered
so far are gigantic.

We're talking Saturn size,
Jupiter size, and even bigger

because those are
the easiest ones to spot.

But this exoplanet
is very interesting.

It's what's called
a Super-Earth.

It's larger than the Earth,
but not by very much.

SHATNER:
A Super-Earth, similar in size
to our own planet?

What's even more intriguing

is that astronomers
may have found

multiple Earth-like planets.

McGEE:
One of the most exciting aspects
of the discovery

is that astronomers may not
have discovered one planet

that's Earth-like
and potentially habitable,

but two,
and one that might even be

more like the Earth
than the first.

So we need more measurements
to find out,

but it's looking like a really
high target for exploration.

SUTTER:
Galactically speaking,

TOI 715 b

is right next door.

It's only 137 light-years away.

Most exoplanets we've discovered

are thousands
of light-years away.

The Milky Way galaxy itself

stretches
for 100,000 light-years.

So 137 is like nothing.

SHATNER:
137 light-years
may be close, cosmically,

but it's not exactly
a trip around the block.

After all, just one light-year

spans about 5.8 trillion miles.

Which begs the question:

If we're trying to find
habitable planets for humans,

why look beyond
our solar system at all?

The worlds of our solar system
are beautiful, dynamic places,

places we want to explore,
but we didn't evolve there.

Life didn't evolve there,
as far as we know so far.

And so maybe our solar system
isn't the best place

to look for human settlement
in the future.

We have
many hundreds of billions,

maybe even trillions of planets
in our own galaxy.

And so that suggests that maybe
there are some other worlds

that are far more Earth-like,

far more tangible places
for us to one day

send humans
for large-scale settlement,

for large-scale inhabitation.

SHATNER:
While exploring the planets
of distant stars

sounds fascinating,
our ability to one day

travel in deep space
will remain theoretical

for a very long time to come.

And if we are ever able
to overcome the challenges

of radiation exposure

or travelling
at the speed of light,

perhaps the most dangerous
obstacle for human explorers

will be time itself.

If we really are sending humans
at close to the speed of light,

due to relativity,
they'll be traveling

so close to the speed of light
to get there

in relevant timescales

that the people back on Earth,

the things happening
back on Earth,

will be happening a lot faster.

And so their family
will be aging a lot quicker.

Chances are if we go
to someplace like Vega

25 light years away,

by the time
the humans get there,

most of their relatives
will be gone.

SHATNER:
Essentially, the closer you get

to traveling
at the speed of light,

the faster the people
back home on Earth will age.

It's a harrowing thought,
landing on a distant world

and having no way
to get a message back home.

But then you realize

there's no one alive
to receive it anyway.

This is perhaps
the ultimate danger

of this final frontier.

Fortunately, for now,

Earth continues to be
just the right place

for human life in the universe.

But some scientists are posing
an intriguing question.

Is it possible Earth
wasn't our home to begin with?

SHATNER:
As far as we know,
Earth is the only place

we humans have ever called home.

Our species has thrived
on this extraordinary planet

for hundreds
of thousands of years.

So why is it that
while we inhabit a place

so perfectly suited for life,

we are the only
living creatures we know

that are determined
to leave the planet?

SUSAN KARLIN:
If you think about it,

humans are the only ones
who will put ourselves

in these crazy positions
of going into space,

going into areas
where it's clearly not safe.

LAU:
For many of us, that next step
of humans going out

and not only exploring,

but settling
in these other worlds,

some of which
are very dangerous to us,

is in some ways
that next evolution,

that next step
in our development.

SCHWIETERMAN:
I think a quote from
a Soviet rocket scientist,

Konstantin Tsiolkovsky,
is appropriate.

And he said that "Earth
is the cradle of humanity,

but one can't remain
in the cradle forever."

SHATNER:
Could this drive to explore
these dangerous frontiers

and perhaps live
on another planet one day

come not merely
from human curiosity,

but perhaps
from a more primal urge?

What if Earth was never
our home to begin with?

There are a lot
of interesting ideas

on-on where
life on Earth originated.

Um, some of the more
interesting ones that I-I like

are that it actually
started on Mars,

that Earth was a difficult place
to have originally started out

because it was cold,
it was totally frozen.

And Mars
seems to be more habitable,

had wet environments.

Maybe it started on Mars.

Meteorite came in,
blasted off Mars,

landed on the Earth

and we're just contaminants
here on the Earth.

KAKU:
We now realize
that meteors can also bring

DNA and different kinds
of organic materials

to the planet Earth.

Some people think now
that the solar system

is like a ping pong game

with different
kinds of asteroids

going, hopping between
different kinds of planets.

SHATNER:
It's a fascinating thought
that maybe Martians do exist.

They're just... us.

If that's true,

then it truly is no wonder
we are such pioneers

driven to exploring the cosmos.

Pick any frontier,
whether it's the oceans

or new continents, new land,
something over the horizon,

these all call to humans as,
in a way, a means of survival.

And in the same way,
space is next.

That is our next frontier.

There are hazards lurking

that we're gonna want
to get ahead of.

But our drive is to see
what's over the next horizon

and try and prepare
for what's coming,

even if we don't know
what's there yet.

So, it's part of the human soul.

With everything we're learning
about other planets,

it seems that the day we
actually set foot on one of them

is closer than ever.

But as we start to explore
these distant worlds,

we have to ask ourselves:

What risks
are we willing to take?

What waits for us
on these dangerous frontiers?

We simply don't know.

So, until we are able
to make that journey,

the answers will remain...

unexplained.

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