For 25 years,
astronomers have been scouring the night sky,
looking for a holy grail,
the ultimate hope... A planet like our own.
They've found thousands of other worlds,
but most are nothing like we expected...
And many are truly bizarre.
The universe has a vivid imagination.
Orphan planets without stars,
worlds made from diamond
and perhaps even giant eyeballs
circling their suns.
If humans ever get to visit a planet like this,
we're gonna lose our darn minds.
Could any of these worlds be an earth-like twin
with earth-like life?
Or is there really no place like home?
Have you ever dreamed about
traveling out of this world?
My name is Mike Massimino,
and I turned that fantasy into a reality
when I space-walked to repair the Hubble space telescope.
Great job, Mike!
Now as we expand our knowledge
of our solar system from Mercury to the cosmic unknowns,
I want to take you on a personal journey to...
Captions by vitac... www.Vitac.Com
captions paid for by discovery communications
"the planets."
Welcome to "the planets."
I'm Mike Massimino.
I've been lucky enough to go into space,
and I can tell you, looking down on earth
is a once-in-a-lifetime experience.
But is earth a once-in-a-lifetime planet?
We know there are other solar systems
with their own planets, but is there another earth...
Or something even stranger?
Over 400 years ago,
a brave philosopher first posed the question,
if the stars in the night sky are like our sun,
could they have planets, too?
The modern hunt for exoplanets...
Alien worlds orbiting distant stars...
Began in earnest in the 1990s.
Pioneering astronomers expected to find planetary systems
much like our own.
But from the very first,
what they found shocked the world of science.
We're finding planets that I would've thought,
if I saw in a movie, I'd go, "oh, yeah."
That's... that's cute. That makes for a pretty scene.
"But come on. That's not really gonna happen."
And then, boom, we're finding 'em.
The shocks came early.
The very first confirmed planet
found outside our solar system
wasn't orbiting anything like our sun.
It was orbiting one of the most violent
and mysterious objects in the universe:
A pulsar.
It defied logic.
If you were to wake me up
in the middle of the night and say,
"where's the last place you would ever,
ever, ever find planets?"
I probably would've said, "orbiting a pulsar."
A pulsar is honestly one of
the most dramatic things the universe offers.
A teaspoonful of the star
has about as much mass as mount Everest.
And they can rotate hundreds of times a second.
Can you imagine a monster like that?
Pulsars are incredibly compact.
Imagine roughly the entire mass of the sun
squeezed down to an object no bigger than Manhattan.
As they spin, pulsars spit out light
and beams of radiation.
But it's the birth of these violent stars
that makes them such an unlikely home for planets
because pulsars are born in the cosmic fires
of supernova explosions.
These explosions are so powerful
that if one occurs near an ordinary planet
like the earth,
it would be vaporized in the blast.
Finding planets orbiting a pulsar after
a supernova explosion
is like going to the site of a devastating earthquake
and then finding a China shop
with all the plates and everything...
Everything is perfectly intact, not a scratch on 'em.
It just doesn't make any sense.
For a planet to survive a supernova blast,
it would have to be made of incredibly tough material.
But what?
A clue came in 2011,
when astronomers found a strange planet
closely orbiting a rapidly spinning pulsar
in the Serpens constellation.
The planet is big,
3,000 times the size of the pulsar it orbits.
But the real surprise is its composition.
The planet appears to be very rich in carbon
but so dense it could only be in diamond form.
If you told me 20 years ago we'd be talking about a...
A giant diamond orbiting pulsar,
I would ask, uh, "what were we drinking?"
The diamond planet
could be one of the most spectacular places
in the universe,
shining like a 37,000-mile-wide dirty disco ball.
For planetary geologist Jani Radebaugh,
the closest thing we have to the surface
of the diamond planet here on earth
is the shimmering black volcanic flood plain in Iceland.
Imagine we're standing on the surface of a diamond planet.
You can see that it's really flat, really uniform.
And yet it's a little bit shiny.
I think it would be really beautiful.
However beautiful, a diamond planet
is not a place you want to visit.
The planet's immense density exerts a gravitational
pull over 15 times stronger
than that on the earth,
making life extremely uncomfortable for any visitors.
So we're standing on a very high-mass body.
This means that the gravity is extremely large.
It's so big that we'd probably
just be squished flat to a paste.
So how did the diamond planet form?
Scientists believe there can only be one explanation.
It must've started life as a star
but one in a binary partnership
with a much larger companion.
We're actually sort of rare.
Our solar system only has one star.
Most solar systems have more than one.
And the stars orbit around each other.
Billions of years ago,
the diamond planet is a yellow star,
much like our sun.
Its much larger binary partner quickly
burns through its fuel supply
and then explodes in a violent supernova,
leaving behind a remnant, a pulsar.
The sun-like star is big enough to survive the blast.
But billions of years later,
it, too, runs out of fuel and dies,
leaving behind a burnt-out core known as a white dwarf.
The gravity of the pulsar starts
to steal the lighter elements,
hydrogen and helium,
from the outer layers of the white dwarf
until pretty much all that's left are
the molecules of carbon
the dead star produced during its lifetime.
The pressures in the leftover ball
are so intense that the carbon crystallizes,
turning it into a compacted diamond.
But it turns out these cosmic diamonds aren't forever.
The gravity of the pulsar pulls on the diamond planet,
hauling inwards on a slow
and ever-decreasing death spiral.
At some point, as it gets closer and closer to that pulsar,
it's feeling a harder and harder gravitational stretching.
When it gets very close, that force will get so strong,
it will rip that planet apart.
Imagine the view
as a 10-thousand-billion- billion-billion-karat diamond
is ripped to pieces.
Gravity cannot hold the body together anymore.
And it... it basically gets torn apart.
And now, what you have is a... A shower of diamonds.
I mean, that sounds amazing.
But what exoplanet hunters
really want to find are worlds like our own.
Astronomers, in general, are looking for exoplanets
because they're cool.
But come on. We're human beings.
And we want to find another planet like earth.
And in 2016, astronomers are shocked
when they discover a potentially earth-like planet
orbiting our closest neighboring star.
Stunned scientists wonder,
will this new exoplanet
have what it takes to give birth to life,
intelligent life,
even civilizations?
So we know there are other planets
orbiting other stars in space.
Could any of those planets actually support life?
The chances are better than you think...
Once you expand the definition of "life."
Take a look at the night sky.
We now know that planets probably surround
almost every point of light you see.
But there's more.
For every star we can see,
there are countless others too dim
for our eyes to pick out.
These are the red dwarfs,
far smaller than the sun
but home to planets by the truckload.
And many of these worlds
are made from rock like the earth.
There are more red dwarfs
than any other kind of star in the galaxy.
And these stars have planets, too.
So the most common type of planet in our galaxy
is one that lives around a red dwarf.
Of the billions of red dwarfs in the milky way,
more than one in 20 have planets
that orbit at just the right distance
for liquid water to collect on the surface.
Any closer, the temperature would be too hot,
and the surface water would boil.
Any farther away and the water would freeze.
It's often called the Goldilocks zone
because it's just right for oceans to form,
just as they did on the earth.
Could one of these warm, wet worlds
provide a habitat for life like us?
And that's something that we've always wanted
to know the answer to: Are we alone?
These rocky, wet planets
may seem like dead ringers for the earth.
But there's a catch.
Many red-dwarf worlds
orbit so closely to their demo stars
that the same side of the planet
would always face inwards,
held in place forever by the star's immense gravity.
Scientists call this phenomenon tidal locking.
We're all familiar with the fact that the earth spins on its axis
and gives us night and day.
But if you move in closer to a star, eventually,
the gravitational interaction will stop that rotation.
One side of the planet will always face the star.
One side will always face away.
And you're tidally locked.
If you land on this planet and look around,
you're gonna see stuff that's very different depending on
where you are.
If you're on the point on the planet
that is underneath the star
so that, when you look up, that star is straight up,
that's where it's always gonna be.
It never rises. It never sets.
It never moves.
That's where the star is.
Now, if you're on the other side of the planet,
it's always nighttime... You look up,
you never see your host star in the sky.
In 2016, astronomers discovered
a potentially earth-like planet
orbiting the sun's closest neighboring star,
Proxima Centauri.
The planet, dubbed Proxima B,
sits close enough to its host
to have oceans like the earth.
But scientists suspect its tidally locked.
The result: Proxima B may be staring at its parent star
like a giant eyeball.
The night side is a dark, frozen wilderness,
the day side, a sunblasted desert.
But between the two lies hope for life.
A long, thin strip of land in permanent dusk wraps
around the planet like a ribbon.
Jani Radebaugh pictures an eerie twilight zone
where dark glaciers melt
to fill vast lagoons
just as earth's glaciers do during the summer.
Basically, we would have liquid water
flowing off of these glaciers, pouring off the glaciers
and heading out into the wasteland...
And icebergs calving off into this beautiful bay.
We've got liquid water.
We've got energy from this burning sun.
And so this is exactly the kinda place
where we would look for life.
A ring of hope for life on a planet
orbiting the sun's nearest neighbor.
Could Proxima B really be home to alien civilizations?
Until we go there, the jury's out.
But red dwarfs burn for trillions of years.
And they outnumber the other stars
in the sky three to one.
If advanced alien civilizations
really are out there,
the planets of red dwarf stars
could be ideal places to find them.
Let's say that we were sitting on a planet around
one of these red dwarfs, maybe a trillion years from now.
We could still be sitting here.
We've never seen a red dwarf die.
And so if that's true, then there's plenty of time
for life to have gotten started.
So not only do we have microbial life,
but maybe even more complex life
and then take it a step further.
We might even have intelligent life in these locations.
It's amazing that even tiny stars
can have potentially habitable rocky planets,
no matter how weird these worlds may turn out to be.
But when astronomers turn their telescopes
to bigger stars,
the surprises keep coming.
These sun-sized stars have planets, too.
And some of them could be the weirdest yet.
Imagine a gas planet
so black it appears to be eating light.
I was one of only 16 astronauts
that got to space-walk on the amazing Hubble space telescope.
The Hubble has provided astronomers
with lots of answers... and even more questions.
Take the recently-discovered dark knight,
a planet so dark, it appears to be eating
all the light around it.
How does that work?
For over two decades,
astronomers have scanned the heavens for alien worlds.
And they've found them
pretty much everywhere they've looked.
They hope to discover multiple planets
just like the earth.
But instead, they've uncovered
a galaxy filled with the bizarre.
When you search for all of these exoplanets,
you can see that the universe has a vivid imagination.
Some of them have super gravity.
Others have two stars and not one.
In 2011, astronomer David kipping
was reviewing data on a gas giant
that was closely orbiting a distant star.
As he studied the brightness of the parent star,
he found something really weird.
It looked like the orbiting planet was eating light.
When I first saw this data,
I actually thought we'd made a mistake.
I thought, "we must've screwed up in our analysis."
David was measuring the brightness of the star
as it went from its day side to its night side.
It had been predicted that the brightness
would drop significantly.
But instead, there was only a tiny drop in the light levels.
The only explanation was that the planet
was barely reflecting any light at all.
This planet, Tres-2b,
reflects less than 1% of the light which hits it.
That's darker than a piece of coal
that you might hold in your hand.
And it's darker than virtually any material
you will ever encounter in your life.
And for that reason, we started
to nickname this planet the dark knight.
Black objects appear black
because they absorb most of the light that hits them.
The more light an object absorbs,
the blacker it appears.
But the dark knight is so intensely black,
it almost appears to be eating the light around it.
And this weird planet has another secret:
It sits so close to its star
that its atmosphere reaches
incredible temperatures...
2,000 degrees Fahrenheit,
hot enough to melt gold.
Could the dark knight's scorching atmosphere
help explain its weird,
ultra-dark appearance?
There is some very alien chemistry
happening in the atmosphere of this exoplanet.
You're gonna have vaporous sodium,
vaporous potassium,
maybe even titanium oxide in the atmosphere.
These substances are solid on earth.
But here, it is so hot, they are gases.
And these gases, like sodium,
are excellent absorbers of light,
creating the dark knight's weirdly shadowy appearance.
Normally, this absorption
is limited to a very narrow color
such as yellow light.
But this planet is so hot
that that absorption feature gets broadened out.
And this absorption feature then spans
the entire visible wavelength of light.
And the planet basically looks extremely dark.
Planets like the dark knight
fascinate astronomers because
these star-skimming giant planets
aren't expected to form so close to their star.
When young stars burst into life,
they blow away the gas
and dust that surrounds them,
leaving little material behind to build gas planets
the size of Jupiter.
Instead, the dark knight must've started life far away
from the heat of its star,
where ice and gas was abundant,
and then gradually spiraled inwards
to its current position.
We think these hot Jupiters form much
like the planets in our solar system.
You have a massive planet
that's orbiting very far from the star,
building up material from this disc of gas
and dust swirling around the star.
But as it's moving through this disc of material,
it's slamming into it.
And that's acting like a drag.
So very slowly, over millions of years,
it's going to spiral into the star,
get closer and closer and closer.
And what you're left with is a massive planet
orbiting very close to its star, a hot Jupiter.
Tres-2b most likely started life
looking much like Jupiter does today,
bright in color
and with a raging, stormy atmosphere.
But as it moved closer to its hot star,
the planet's atmosphere began to cook.
It blackened and became the dark knight.
So this shows us how dynamic
planetary systems must be.
Planets migrate.
Where we see planets today
may not be where they formed.
In fact, we're pretty sure it's not where they formed.
Thanks to strange worlds like Tres-2b,
we now know for sure that gas giant planets
can drift in towards their star.
But could the opposite be true?
Could they sometimes drift out?
Astronomers turn their telescopes
to the spaces between stars.
And they're amazed to find scores
of exoplanets set adrift in open space.
And one of these lonely orphan worlds
could be the weirdest exoplanet we've ever seen.
Planets exist in solar systems,
orbiting around a host star, right?
Not always.
We now know there are rogue planets...
Independent planets that jump ship,
tumbled out of their solar systems,
and now travel on their own across the cosmos.
So what's it like on a planet that has no star?
2013... A group of astronomers
scan the night sky for a mysterious class of object
called a brown dwarf.
Brown dwarfs are failed stars,
too small for fusion
to fully ignite in their cores.
But these dim, gassy balls do radiate some heat,
allowing the astronomers to pick them out
with infrared telescopes.
A star is just a big ball of hydrogen
that happens to have enough mass that the interior
gets hot enough inside to start a nuclear reaction.
Now, the universe is perfectly capable of producing things
that just didn't quite have enough mass
to get those nuclear reactions going.
And we call that a brown dwarf.
The astronomers get a hit
on their infrared detectors.
But it's not what they were expecting.
The object they see is too low-mass
to be a brown dwarf.
It had to be a gas planet.
But its host star was nowhere to be seen.
The planet appeared to be set adrift in open space.
The astronomers had stumbled across
one of the most mysterious objects in the galaxy:
A lonely, orphaned, rogue planet.
A planet, by definition,
in some sense, you might've thought,
is something that orbits a star.
These are planets that don't have a star.
Our galaxy could be home to billions of
rogue planets wandering across interstellar space.
Without a star to keep them warm,
you'd expect rogue planets to be cold.
But the planet discovered in 2013 is seriously weird.
It's hot.
The clouds in the planet's deep,
gassy atmosphere burn at over 1,400 degrees Fahrenheit.
It's hard to imagine a more hostile place to visit.
This thing almost certainly has incredible weather,
tremendous storms,
huge parcels of hot air rising and cold air falling.
Not only that, we found that, in a lot of these objects,
if they're hot enough,
iron and other metals can be vaporized.
As they cool though, this stuff can rain out.
And you can imagine droplets of molten iron
falling out of the sky.
This is not a great place to, you know, buy a condo.
Diving deep below the searing clouds,
pressure builds
until the crush of gravity is so great,
hydrogen gases transform into a weird liquid metal.
But where did this planet come from?
And how did it get so hot?
The planet's scorching heat reminds scientists
of infant gas giants in the hot,
violent crossfire
of a newly forming planetary system.
Is it possible this rogue planet
was actually a baby thrown from its nursery
by its jealous planetary siblings?
Planets obviously form in the vicinity of a star.
But, you know, they're in a nest with other planets.
And when they get too close in the early days,
their gravitational tugs
will usually slow one of the planets down
and speed the other planet up.
And if it speeds up enough,
that planet can escape the interstellar system
altogether and go out into the depths of space-Ace-Ace.
An orphan baby gas giant cast out into the cosmos.
But this world may not be truly alone.
It could have companion moons.
In our solar system,
families of icy moons swing around Jupiter
and Saturn on elliptical orbits.
And scientists have discovered icy exteriors
that cover vast liquid water oceans.
As we've seen in the moons in our solar system,
uh, they can be very active.
If they're icy, the gravitational interaction
with their host planet can stretch them
and squeeze them and heat them up.
These so-called tidal forces could power
hot volcanic vents just like the vents
found deep in the earth's oceans.
On our planet, ocean vents support
all kinds of strange life
without the benefit of sunlight.
Could something similar be happening
on the tidally-heated moon of a rogue planet?
You could have these moons kind of snuggled up
around this exoplanet,
keeping warm through its gravity.
So even with no star around,
there's still possibility for life.
Weird rogue planets allow us
to dream of interstellar alien life.
But it's hard to imagine these deep-sea creatures
developing into advanced,
complex, intelligent life
on the meager energy of volcanic vents.
To find evidence of civilizations,
we need to look elsewhere.
And it's just possible the weird behavior
of a distant star
has provided our first clue
that these advanced civilizations
could really exist.
What would it take for scientists
to entertain the possibility that there might be
other intelligent life in the universe?
Well, a few years ago,
astronomers noticed something blocking the light
of a rather ordinary star,
and they haven't been able to fully explain what it is.
And that has opened the door to some intriguing theories.
We used to think our galaxy
was only filled with stars.
We now know those stars have planets, too,
hundreds of billions of them.
Astronomers call these alien worlds exoplanets.
Since 2009, a planet-hunting space observatory
called Kepler has revolutionized
the search for exoplanets,
locating more than all
the telescopes on earth combined.
Kepler's success is due to its ability
to keep watch on 150,000 stars simultaneously.
If Kepler spots the light from one of those stars dimming
just for a moment,
an exoplanet could be crossing its path.
And the greater the drop detected,
the bigger the exoplanet could be.
But in 2011 and 2013,
Kepler spots dips in brightness
that are off the scale.
The mystery star is dubbed tabby's star,
named for the astronomer
who investigated its strange behavior.
And that behavior has forced scientists to consider
a completely universe-changing possibility.
The tabby star is really interesting because we know
there's an object that's orbiting it,
and it's blocking a really large amount of the light.
That's how we know it's there.
But it's much more than a planet typically would block.
If you have a Jupiter-sized planet
orbiting a normal star,
you block a percent of the light.
It's a very, very small dip.
But with tabby's star, what we're seeing are huge dips
where 20% of the light is being blocked.
If Kepler's readings are right,
something huge is moving around tabby's star.
And there's an outside chance
that something is the remnants of a planet
taken apart by aliens
and repurposed as a giant solar power plant.
What really advanced societies
would do is just take apart some worthless planet,
like Neptune in our own solar system,
and rebuild it as a giant sphere
outside the orbit of their planet,
collect all that sunlight and then use that.
The best energy source anywhere is your star.
So you might build giant structures
to actually harvest the energy.
Freeman Dyson called this a Dyson sphere.
Could we have found a Dyson sphere?
If the remains of an exoplanet
are blocking the light from tabby's star,
the aliens have been busy.
Their megastructure would need to be vast to account
for the dimming seen by scientists.
A Dyson sphere is the stuff of Sci-Fi dreams.
But how can we prove it's real?
Astronomers at SETI turn their telescopes to tabby's star
in the hopes of eavesdropping on the radio chatter
of its alien builders.
As soon as we heard about tabby's star,
we swung the antennas
of our Allen telescope array in the direction of that star.
And we spent about a week or two actually looking at it
over a wide range of the radio dial,
looking for any signals. Well, we didn't find any.
We also used a telescope down in Panama
to look for flashing laser lights.
We didn't find those either.
If a type of Dyson sphere
is being constructed around tabby's star,
its workforce is suspiciously quiet.
Every big claim requires big proof.
Just seeing a change in a light profile
is interesting and is intriguing
but is not compelling
and is not evidence to me yet.
I think that just tells us
we have to keep looking and keep learning.
But if it's not aliens repurposing a planet,
what else could be causing the dramatic dimming in light?
Could it be stellar activity?
Could it be there's a disc around the star?
Could it be disintegrating planets?
But probably, right now, the leading contender
is a family of comets which are orbiting this star
and causing these dips.
Comets are vast, dirty snowballs left over
from the formation of planetary systems.
But if a giant cluster
of comets exists around tabby's star,
they could appear a whole lot bigger.
If they get close to their star,
that ice can heat up,
turn into a gas and expand.
And that expanding cloud
can then be much larger than a planet.
We see that in our own solar system.
And it could be something like that that's blocking the star.
A vast cloud of comets could be
blocking the light from tabby's star.
But there's a problem: It's unlikely there would be enough
comets to account for these dips.
And the infrared signature
hasn't been anything out of the ordinary.
So either we've missed it.
That dust disperses relatively rapidly, which is possible,
or there's something more going on here
than just comets breaking up.
None of the current theories
can fully solve the mystery of tabby's star.
So for now, an alien megastructure built
from a planet remains an intriguing,
if distant, possibility.
We've seen worlds made of diamond,
planets where molten iron rains from the sky,
and, perhaps now,
the first signs of alien intelligence.
But there's another planet in the galaxy
that could be the weirdest of them all,
because, no matter how hard we look,
we simply can't find another to match it.
We know our home planet is a special place.
It has just the right mixture of warmth,
stability, and elements that make life possible.
But with the chance
that billions of other planets could exist,
why haven't we found another that's close to being like ours?
It turns out creating earth may have been
even more complicated than we think.
Our hunt for exoplanets
has revealed a galaxy filled
with bizarre planetary systems
and strange alien worlds.
But the biggest surprise is how few of these worlds
look like our planet, the earth.
So far, we haven't found many, if any, solar systems
that are kind of identical to ours.
We always assumed there'd be small planets
on the inside, big planets on the outside like...
Like our own solar system. We don't find too many of those.
What we have found is that
the most common type of planet around other stars
is what's called a super earth.
These super earths
have atmospheres that are too thick,
creating pressures too high to support life like us.
So why does our small planet,
with its exposed continents and relatively thin atmosphere,
appear to be so rare?
A new, radical idea suggests the earth
could be a second-generation planet,
built from the remains of a demolition derby
between giant rocky worlds
that once dominated the early solar system.
There may have been planets before the ones
we know that were destroyed,
that were kicked out or sent careening into the sun.
That makes the earth a second-generation planet.
We may have had brothers and sisters
that we never knew about.
Imagine the scene... 4.6 billion years ago,
the planets in our solar system begin to form
from a vast disc of dust and debris.
Giant Jupiter is the first to form.
And it settles into a distant orbit.
Where the earth sits today,
a band of super earths are born,
vast worlds up to 10 times the mass of the earth
and with thick crushing atmospheres.
The gravity of these giant,
inhospitable worlds dominates
the inner solar system,
preventing smaller, earth-sized planets
from forming...
That is, until Jupiter joins the party.
We believe that this first generation of planets
was driven onto the surface of the young sun
by the migration of our big bully
in the solar system... Jupiter.
A few million years
after the birth of the solar system,
the gravity of the protoplanetary disc
slows Jupiter down,
and it starts to spiral in towards the sun.
As it moves inwards,
it pushes waves of asteroids
and debris towards the super earths.
The incoming debris disturbs
the orbits of the giant planets.
Some may smash each other to pieces.
Others are sent hurtling into the sun.
Once the planetary carnage is over,
Jupiter is tugged back out
by the gravity of the newly formed Saturn.
The solar system that is left behind is a place
that's depleted in solid material and gaseous material.
It is a place where...
Where debris will coalesce
over hundreds of millions of years
into the terrestrial planets that we have today.
Planetary building starts over
in the inner solar system.
But the new planets feed on scraps,
growing much smaller than their predecessors,
with thinner atmospheres and lower pressures.
Among them is our own planet, the earth,
a second-generation planet prime for life.
For so long, we've been trying to identify
all the different factors
that make life likely on a planet.
We know that it has to be warm, it has to be stable.
Well, maybe we've got a new one now.
Maybe being a second-generation planet
is one of the advantages we need to look for.
If this is true, the incredible birth story
of our planet could offer a reason
why we don't see other worlds
out there teeming with intelligent life.
Perhaps the earth is the planet
that broke the rules.
What we're seeing is that our own solar system
may be the exception.
And when you look at our solar system,
what's the weirdest planet?
Well, the weirdest planet would have to be earth.
Right now, earth seems to be
the oddball in the universe
because we haven't found life in the universe.
But we continue to search.
And hopefully, we'll prove ourselves wrong.
Eventually,
amongst the billions of worlds out there,
we might find another planet
that beat the odds,
gave birth to life,
nurtured intelligence
and created a civilization smart enough
not to extinguish itself.
Only then will we know
whether the earth is truly unique.