Original subtitles

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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