For thousands of years, we've wondered if we're alone in the cosmos.
Life - is it a one time event...
..or is it something that's occurred lots of times throughout the universe?
And, at this very moment, new discoveries are bringing us closer to the answers.
We are right on the cusp of being able to say life exists somewhere else.
All of our searching is leading to one ultimate goal..
finding intelligent life somewhere in the vastness of the universe.
lf we could discover an advanced civilisation,
it would be clearly the greatest discovery of humanity,
beating out fire.
Get ready, because the known universe is about to take you on a hunt for life out there.
Over the next hour, we'll show you how the hunt for alien life has dramatically changed
over the past few decades.
The lessons we're learning at the bottom of our oceans
and in Yellowstone's acid pits
are giving us dramatic insight into how life came to be on our planet.
And it's helping us understand and imagine how life might emerge on an alien world.
We'll take you on a journey to faraway planets,
where amazing creatures may roam the lands.
Creatures that make the wildest science fiction movies look like reality shows.
And, finally, we'll show you how new technologies are being used to search for,
and possibly communicate with, advanced alien civilisations.
so is Earth the only planet where life has emerged in this vast cosmos?
Are we alone?
Or are we part of something bigger-
a web of life that stretches light years through the universe?
Are we alone?
And it ties into all the big questions: How did we get here? Where are we going?
Are we a part of a bigger picture?
But for many years the question was taboo to science.
Before the mid-1 990s,
it was considered somewhat embarrassing to even address the question,
because looking for alien life seems a little frighteningly close to science fiction.
For decades, the furthest we got in looking for aliens was imagining them on the silver screen.
MAN: What is your name?
After all, alien life needs a home.
And we hadn't even found a planet outside our own solar system.
scientists, in fact, never talked about planets around other stars.
There was no way to detect them
and so it was one of those domains of science that you couldn't answer,
and, therefore, you didn't talk about it.
ln 1 995, astronomers discovered a planet orbiting a star 50 light years from Earth.
And since then, they've found hundreds more.
For the first time in human history, we realised that our sun,
with its eight major planets that go around it,
is just one type of a planetary system, one example of billions.
These discoveries are exciting,
but don't expect to be contacting extraterrestrial life on these planets any time soon.
While it's been a spectacular ride in the last decade to find these planets,
most of them are giant planets.
Most of the worlds we've found are gas giants,
which probably couldn't support life.
You can't stand on them. There's no hard surface.
They're large balls of hydrogen and helium gas,
like Jupiter and saturn.
We found a few rocky planets with hard surfaces,
but they're many times more massive than Earth
and contain the most hostile environments you could ever imagine.
One such planet, Corot 7B, orbits so close to its star
that surface temperatures reach as high as 1,600 degrees Celsius.
sunrise here does not bring the sound of birdsong.
lnstead, it's an armageddon of volcanic explosions.
Those planets are all going to be so hot, you can't develop something as complex as life.
scientists have gone back to the drawing board looking to find worlds capable of supporting life,
small rocky planets like Earth.
We don't know that life has to evolve on the surface of small, rocky planets.
But we know it did once, here on Earth.
And so, it's a reasonable place to start the search.
Earth is important because we know that this little planet had everything needed to create life.
And if a distant world has similar conditions,
there's at least a possibility life could emerge there, too.
lf you were to give a biologist a piece of paper
and say, ''Write down on every line something you need for life.''
They'll say you need an energy source,
you need oxygen, you need water, you need carbon, you need organic compounds,
you need amino acids, you need all this stuff.
There's a long list of factors that make our Earth special and perfectly suited for life.
But the most important is its distance from our energy source - the sun.
At 1 49 million kilometres away, the Earth is at just the right place for water to exist as a liquid.
so why is liquid water important?
lmagine a world so much hotter than the Earth that there are no oceans,
no liquid water at all on its surface.
such a place would be like a desert.
Without water, there's nothing to let the grains of sand interact.
And in the same way, without water, there's nothing to allow the atoms -
the carbon and oxygen and trace elements -
to form the molecules that would give rise to the chemistry of life.
On the other hand, on a world much colder than the Earth,
water can only exist as ice, and we have another problem.
This frozen block of sand has all of the grains of sand locked together.
They can't move around and interact,
just the same way that on a frozen world,
the atoms and molecules can't move around and interact
to form the chemistry necessary for life.
But if temperatures and conditions are just right, like here on Earth, you get liquid water.
The water allows the sand grains to flow together and intermingle
and form more complex structures.
ln the same way, water acts like a cocktail mixer,
allowing the atoms and molecules to come together
and ultimately form the building blocks of life.
All that water was perfect for breeding life.
Lots of it.
lt's estimated that since the emergence of Earth's first life form,
1 00 billion species have existed on the planet.
Millions are alive right now,
and that fact alone tells scientists a lot as they comb the cosmos for alien life.
lf we look for life in the universe
we have to understand it will come in different shapes and sizes.
And the same thing occurs here on Earth.
Take this handful of dirt.
lt's not just dirt, there's a lot going on in here.
There's an earthworm.
Go in a little more...
..and there are these tiny little mites.
Zoom in further...
..and there are these little creatures called protozoa.
And smaller still...
..there's bacteria, billions of them.
so you see, there really are a lot of living things in a handful of dirt
and we should probably remember that if we ever go digging around on alien worlds.
Life isn't always something you can see with the naked eye.
ln these piles of dirt lie the secrets to our origins.
And scientists are keeping that in perspective when they search for life in the cosmos.
You have to be looking for that bacterium first, because that's gonna be far more common.
lf we don't find that, the chance of finding these tall, elegant, grey, ET guys
is gonna be highly diminished.
so are there other Earths out there capable of supporting extraterrestrial life,
or even bacteria?
We're closer than ever to finding the answers,
because scientists have picked up the scent in this cosmic hunt.
ln the hunt for alien life,
scientists are focusing their efforts on finding small, rocky planets like Earth.
But searching for another Earth is like trying to find a needle in a million haystacks.
Because, from trillions of kilometres away,
these small planets get lost in the blinding glare of their star's brightness.
The sad truth of the matter is that Earth-like planets are mere cosmic specks of dust,
and, therefore, detecting them is really quite hard.
Hard, but not impossible.
Every now and again, the planet passes directly between us and the star.
And if it does that, it's like a little eclipse
and the starlight drops.
lt gets darker because the planet is blocking the light from that star.
And it turns out we can see that.
With this in mind, scientists built one of the world's most sensitive telescopes
and launched it into space.
The mission, called Kepler, may not help us find extra terrestrial life
but it could help us find its home.
Kepler will simply do one thing unbelievably well -
measure the brightnesses of 1 00,000 stars over and over and over,
looking for a few of those 1 00,000 stars that dim.
seeing the tiniest dim from a small planet travelling in front of a star
thousands of light years away isn't easy to imagine,
but the Kepler telescope is one of the most sensitive cameras ever built.
To give you an idea just how sensitive Kepler is,
l'm gonna demonstrate using this massive World War ll searchlight.
The brightness of that searchlight represents the extreme luminosity of stars
and l'm gonna use this tiny marble to represent the planet.
When this planet passes in front of the star,
it blocks out a tiny fraction of the light,
dimming the star by a very small amount.
And that's exactly what the Kepler spacecraft can detect.
Kepler can detect a .01 per cent change in a star's luminosity.
But even if it spots a dimming star, there's still another problem.
When Kepler sees a star that dims,
it could be due to a speck of dust that crossed in front of the telescope.
There's a possibility of binary stars -
two stars that orbit each other,
thereby dimming the stars as one blocks the other.
To make sure Kepler's truly found a planet,
scientists are using one of the largest Earth-based telescopes for confirmation.
This telescope will also determine the planet's mass and distance from its star.
scientists are most interested in the small, rocky worlds
that sit in what's called the Goldilocks Zone.
Remember how important liquid water is to life?
lf a planet is in the Goldilocks Zone, it's not too close and not too far from its star.
lt'sjust right.
And it's possible for water to flow there as a liquid.
We obviously sit in the Goldilocks Zone,
but in our solar system, Mars and Venus also do,
but we've yet to find life on either of those two planets.
Knowing if a planet is inhabitable is not as straightforward as saying,
''Oh, we found a planet the size of the Earth
and it's 90 million miles from a sun-like star.''
Venus is uninhabitable and Mars is uninhabitable.
Why is Venus such a harsh, hideous environment,
some 600 degrees Celsius or so?
And, of course, the answer for Venus, sadly,
is that some greenhouse effect, global warming, has overtaken Venus.
When it formed over four billion years ago,
Venus had water, and probably vast oceans on its surface.
But there was also a lot of the greenhouse gas water vapour in the atmosphere,
which blanketed and heated the planet.
And as Venus got hotter,
more and more water from its surface evaporated into the atmosphere,
trapping the heat even more.
On Earth, much of the greenhouse gas carbon dioxide is chemically bound to the rocks.
And it was this way on young Venus, too.
But when it got to about 400 degrees Celsius,
this carbon dioxide started baking out of the rocks and into the atmosphere.
With an atmosphere of water vapour and carbon dioxide,
this cycle kept going and going
and the runaway greenhouse effect has left Venus dry, lifeless,
and a scorching 480 degrees Celsius.
Even if it weren't that hot,
the atmospheric pressure at the surface is 90 times the Earth's atmospheric pressure,
so you'd be crushed.
And it has sulphuric acid rain.
You know, Venus is basically, by every definition, Hell.
And yet, if you were to detect Venus orbiting another star,
you might suspect it would have Earth-like conditions.
Mars also lies in the Goldilocks Zone,
but it has the opposite problem of Venus.
lt doesn't have enough greenhouse gases to trap in heat
and it's become a cold, barren, desert world.
We have two examples of how planets have gone astray
and we have to wonder how many other ways are there
that a planet can fail to be habitable.
With so many ways a habitable planet can be rendered uninhabitable,
Kepler's findings are crucial,
because the more potential homes it finds,
the better the chance life might exist outside our little Earth.
ln five years, we will know for certain, from Kepler's results,
how frequent Earth-like planets are.
lt will do this by only looking at 1 00,000 stars out of at least 200 billion in our galaxy.
But how is it possible to calculate the number of Earth-like planets orbiting other stars
without looking at all the stars?
lt's like asking how many blades of grass are there on this soccer field.
l could either get down on my hands and knees here
and spend the rest of my life counting every single one
or l could do what Kepler's going to do, which we call sampling.
We have a little grid - two inches by two inches on each side.
All l have to do now is count the number of blades of grass in that little two-inch square
and then multiply by the number of squares that would cover this whole field.
Let's do it. One, two, three...
24, 25, 26, 27...
33, 34, 35...
47... l wonder if l counted that one.
207.
207 blades of grass in a two inch by two inch patch.
Now, let's get out the calculator here and see what that means.
207 divided by two inches by two inches
means 52 blades of grass per square inch.
Now we need the number of square inches in this field.
lt's 1 80 by 360.
Wow, that's almost 1 0 million square inches in this field.
so, multiply that by 52 -
half a billion blades of grass and l only had to count 207.
lf Kepler does find Earth-like planets,
this method of sampling will bring us one step closer to understanding
how many habitable homes are in our galaxy.
Even if one out of a thousand stars in the Milky Way galaxy has a planet like the Earth
that means there are millions and millions of Earths orbiting other stars.
so if you ask me: ls there life out there?
it seems awfully likely.
ln the grand scope of the cosmos,
we've considered ourselves pretty lucky to be at just the right spot
and to have all the right ingredients for life to emerge.
But is it really luck?
Or does life find a way?
There are new discoveries showing us there might just be another recipe for life to emerge.
We have a general idea of what conditions are crucial for life to thrive on a planet.
We know liquid water plays a role,
and we know life needs an energy source.
For us, that's our sun.
And for a long time, scientists believed that every single life form on Earth
got their energy from our star.
That was until an underwater explorer, who discovered the Titanic,
also helped discover something else deep in the ocean.
By far, the most important discovery l've ever made was not the Titanic.
lt was when we discovered this whole new life system on our planet.
We thought all life needed access to sunlight,
but working with the Wood's Hole Oceanographic lnstitute,
Bob Ballard found a thriving ecosystem where there was no sunlight.
There were creatures we'd never seen before.
One of the dominant organisms was what we call a tube worm
and these were 6, 8 feet tall,
and they had human-like blood.
And when they wanted to respirate,
they would stick out the tube,
basically their lung.
Prior to that discovery, we thought that all life on the Earth owed its existence to the sun.
Without sunlight, there was something else giving this life energy.
lt was coming from deep inside the Earth's core.
something called black smokers, or hydrothermal vents,
were bringing up minerals from deep underground.
And this was an amazing discovery
because the temperature coming out of the bottom of the ocean
was 650 degrees Fahrenheit.
Hot enough to melt lead.
Amazingly, this life thrived in an extremely hostile environment,
which meant we needed to expand our narrow view of where life might be found.
We have to understand that life will evolve
under conditions which seem horribly hostile, horribly alien.
And yet, it not only evolves and works,
it thrives and has a whole ecosystem that depends on these bizarre environments.
And the bizarre environments didn't stop at the bottom of the ocean.
Life is found in the worst environments you could imagine.
Like the boiling hot springs of Yellowstone national park.
The hot springs at Yellowstone can be PH1 , just like battery acid...
..and 1 94 degrees.
lf you went into this, it would dissolve you.
Dr Mark Young is an astrobiologist looking very closely at Yellowstone's hot springs.
He thinks these acid pits may be one of our biggest clues to understanding
how life emerged on Earth.
Three billion years ago, planet Earth was much more like what we see in Yellowstone -
boiling acid, very high temperatures,
where life was dependent not so much on photosynthesis,
but on the chemicals that are found
and the gases that come out of the boiling hot springs like Yellowstone.
Those pits in Yellowstone are just nasty.
ln fact, the acid in them can dissolve just about anything.
l have some acid here that's a little more concentrated than you'll find in Yellowstone,
but the results will be the same.
Now watch what happens to this penny when l drop it in the acid.
l'm gonna put this bell jar over to control the environment.
The green colour is copper coming from the penny
and a noxious fume is being emitted.
And that's an oxide of nitrogen that is very hazardous,
and l'm glad l have it in a bell jar.
What amazes me is that scientists are finding life aplenty in environments similar to that,
and that just goes to show that life can flourish in even the harshest conditions.
We're finding micro-organisms not only living in these hot springs but flourishing.
Wherever there's liquid water -
no matter the amount of light, the temperature, the acidity - life thrives.
This revolutionary discovery is opening us up to the possibility that life may exist
in places we never thought possible.
Even under the surfaces of planets or nearby moons.
What's incredible is that it turns out that even in our own little solar system,
there are diversity places where there could be life.
ln 2008, a probe visited to the Martian surface,
the Phoenix Mars Lander,
and it made an amazing discovery.
Phoenix dug down into the dirt,
and after only a couple of inches, uncovered crystals of frozen water.
The key question is; how far down does the water persist beneath the surface
and if you go far enough, is the pressure and temperature high enough
that the water would be liquid, not in the form of ice?
And there's a very good suggestion, l think, that there are, in fact, liquid aquifers.
We might be able to drill down and find the evidence, if any, of life on Mars at this moment.
And scientists are also excited about what they believe to be an ocean
underneath the surface of Jupiter's frozen moon, Europa.
sure, it's cold and solid in the form of ice on the surface,
but almost certainly, beneath the ice on Europa is a vast ocean,
hundreds, if not thousands, of kilometres thick.
Europa sits well outside the Goldilocks Zone,
but just like at the bottom of Earth's oceans,
hydrothermal vents could be the energy source needed for life to emerge.
Those ocean depths could be home to some bizarre life forms -
huge tubeworms feeding on the minerals coming from inside Europa's core.
There's no telling what kind of life may exist in Europa's ocean.
But one of the most fascinating places in our solar system is saturn's largest moon, Titan.
Titan's atmosphere and surface features are similar to Earth's 3.5 billion years ago.
Titan is one of the larger moons in the solar system
and the only one to have a substantial atmosphere.
And the atmosphere has lots of methane in it.
And it's cold enough that the methane precipitates and drops, like raindrops,
and falls out onto the surface of Titan.
Not liquid water, but liquid methane.
On Earth, methane is a flammable gas,
but the temperatures on Titan are so cold, minus 1 80 degrees Celsius,
that the methane can form liquid.
Titan actually has lakes, rain and rivers made of liquid natural gas, liquid methane.
That probably isn't quite as good as water, but at least it's a medium.
Things can flow around, begin to form bonds.
Fluid is where it's at.
The idea that life can emerge from a different kind of liquid
is adding a whole new dimension to our search.
lt's possible that life elsewhere in the universe can thrive with other liquids, not just water,
and so we have to keep our eyes open.
Other environments very different from that on the Earth could harbour life.
New discoveries constantly shift our perspective on where alien life might exist.
And as we continue investigating the clues to this cosmic mystery,
we have to remember to keep an open mind.
Because life out there might be stranger than Hollywood could have ever dreamt up.
The hunt for life in the cosmos is intensifying.
New discoveries have opened us up to the possibility that life could exist
closer than we ever imagined, right in our own solar system.
But even if that doesn't pan out,
there are billions of stars out there just like our sun
with potentially billions of planets harbouring life, like Earth.
lt's completely reasonable to think that there's life out there.
There's just so many possibilities - billions of stars and billions of galaxies,
and dah-duh, dah-duh, dah-duh.
surely there's life out there.
Finding life, even primitive microbial life,
would change our place in the universe by telling us that we're not alone.
And it would most likely be an indication
that we're getting closer to finding an intelligent civilisation.
lt would be really fun if we could find an alien that could, you know, send me an email
or twitter or whatever, all day long,
but the profound question is life or nonlife.
Once we have the microbial, we have the potential for intelligence.
But if we don't have a life form at all, we don't have the potential for anything.
What if we do find complex life out there?
What would it look like?
Would it be anything like what we see in Hollywood movies?
lt is humorous that Hollywood depicts aliens more or less the same way.
There's a Klingon here and a Romulan there
and there's slanty eyes and, you know, big old brains and so on.
Any sort of alien that resembles a human is ludicrous - two eyes, a nose, and a mouth.
There's no reason an alien would have to be adapted this way.
Over hundreds of millions of years,
all the creatures of our planet have adapted to their environment,
so the chemistries are similar,
which means your genetic makeup isn't all that different from an earthworm, or even your pet.
Basically, all animals are worms.
We're worms - we've got a head, we've got a tail.
We're long and skinny and that's how we move forward. Dinosaurs are worms.
What people don't understand is that evolution is not a road map.
Humans are not at the top of the evolutionary ladder.
We're not the end point, the goal of evolution, or anything like that.
We're accidents, we're random.
We eat through our mouths but we breathe through our mouths and we can choke on food.
That's a terrible design. lt's an accident of evolution.
Maybe aliens evolved differently. Maybe they don't need to breathe.
Maybe they can get oxygen in some other way.
Anything like that can go, as long as it makes sense for the environment.
so life on another planet would adapt to its environment
and could be stranger than you could ever imagine.
lt's fun to speculate about how life might evolve
under conditions that are very different from those here on the earth.
lf you lived on a planet with twice the gravity of Earth,
there'd be a lot more pull on your body
and you'd come crashing down twice as hard if you fell.
so perhaps creatures there would have stronger, stockier bodies
with more legs closer to the ground.
A planet with very little gravity would be like our moon or Mars.
l can imagine a creature on a low gravity planet as being...long and spindly.
Life on a low gravity planet might be tall and thin, with long legs.
lf life evolved on a very dense planet where the atmosphere is soupy or water-like,
you could see creatures as big as whales or elephants actually flying,
not through the air, but through this liquid-like atmosphere.
l think we are currently ignorant, actually, about the real realistic diversity of life elsewhere.
Life in the universe may be incredibly diverse.
But could it all have come from the same place?
Panspermia is the idea espoused at the beginning of the classic Battlestar Galactica
that life here began out there.
The building blocks of life on our planet may have originated elsewhere
and were transported here when a meteorite collided with Earth.
Comets have a lot of organic materials on them.
some meteorites have amino acids in them.
These are the building blocks, the precursors, of life.
so at least the building blocks of life could have come from space.
lt seems unimaginable because life, or the building blocks of life,
would have had to survive an impact with our planet.
Here at NAsA's Ames Research Center in northern California,
astronomer Peter schultz and his team are testing to see if this theory of Panspermia
is even remotely possible.
lt's good.
Here l've got the projectile that is embedded with some organics.
so the real question is; will this survive if we hammer it at a high speed?
We're gonna be firing this at around three-and-a-half kilometres per second.
This would be about the speed of something surviving entry into the atmosphere.
schultz will create a high-speed impact using NAsA's vertical gun,
which will fire the projectile at 1 6,000 kilometres per hour,
that's ten times faster than a bullet.
This is a pretty special gun.
lt uses a lot of gunpowder but then compresses hydrogen gas,
and then it's released, and then the hydrogen gas expands.
When it expands, the projectile continues on down into the impact chamber
and that's when things happen.
This is where it all happens. This is the impact chamber.
The projectile's gonna come through this hole, slam into this target,
which is about two feet across - this is just ordinary sand -
and we'll see if it survives.
With the vertical gun loaded
and the impact chamber set,
it's time to test and see if the organic material laced onto the projectile
can survive a high-speed impact.
This drives me nuts.
(Buzzer)
Oh! OK.
This was...gorgeous.
Whoa!
l...l hope there's stuff left.
The key now is to go back in there, dig out these pieces
and see if we can find any survivors, literally survivors.
We gotta go see what we did.
Oh, what a mess. Oh, this is dynamite.
schultz scours the impact chamber, hunting for remnants of the projectile.
This is like looking for your lost contact on a beach.
Let's see what we have.
Oh, that is so sweet.
We did the experiment, we collected some pieces.
We showed that we actually got solid pieces that survived impact,
and embedded within that solid piece are amino acids.
You can see it here in this image.
You can see the fracturing, but even though it's fractured, it's not melted.
Panspermia is not that far-fetched after all.
lt says you can transport the seeds of life, if not life itself, from one planet to another.
However life began on our planet, it eventually evolved to develop intelligence.
And ultimately, our goal is to see if that's happened somewhere else in the universe.
What we're really looking for is, you know, spock.
We're looking for another civilisation that's either like us or not like us, but is clearly intelligent.
That's the Holy Grail of the search for extraterrestrial intelligence.
With so many stars and so many planets out there,
it would truly be a surprise if intelligent life did not exist somewhere in the universe,
perhaps even nearby in our own galaxy.
With the closest stars light years away, is it possible to actually travel there?
Or will first contact be made some other way?
Right now, in our own Milky Way galaxy alone,
there may be numerous intelligent alien civilisations.
But why haven't we contacted or been contacted by any of them?
First of all, there's a lot of empty space out there.
The very nearest star to us is four light years away.
They could send us a signal, in four years' time it would get here,
and then we could reply eight years later to them.
That's the closest star.
What about communicating with people across the galaxy
where there are tens of thousands or a hundred thousand light years in between?
lf we wanted to pop over and borrow a cup of sugar,
it would take some 700,000 years for us to bring the sugar home.
so that's a very big problem.
With the nearest star 400 trillion kilometres away,
our current technology could get us there in, say, 1 00,000 years,
so travelling to see an alien civilisation clearly isn't going to work.
But how about we just call them up?
After all, radio signals travel at the speed of light.
lf we are going to communicate with aliens,
that's gonna be the most boring conversation we've ever had,
because if they're beaming radio waves at us and they're 1 00 light years away,
and they say, ''Hey, how's the weather down there on Earth?''
lt takes a hundred years to get here and we say,
''Hey, it's fine. How are things there on Globnarp?''
Another hundred years back and forth. lt's a century travel time.
That's a boring conversation.
The chances that two intelligent civilisations have the ability to communicate,
the desire to communicate, and are around long enough to communicate
makes this cosmic chat even tougher.
so we've been intelligent in the sense we've had the same brain size for about 1 00,000 years.
Yet we've only been able to communicate for the past 50 years -
a tiny fraction, meaning if another civilisation communicated with us 200 years ago,
we would have missed the signal altogether.
There can be a lot of miscommunications when trying a cosmic chat.
We could think of communicating with an alien civilisation as like a game of cosmic catch.
The stadium...is the galaxy.
And the ball is our message.
so if we send the ball out into the stadium, odds are nobody's there to receive it.
Of course, we could luck out and actually send our message towards an alien civilisation.
But what if that civilisation was technologically 500 years or more behind where we are?
Well, that would be like throwing a baseball to a baby.
(Cries)
Of course, if everything is just right
and there is another technological civilisation out there capable of receiving our message...
Here you go.
Well, that would be our first contact with an extraterrestrial civilisation.
since it would be a long time before we could have a face-to-face conversation,
the best thing we can do for now isjust to listen.
At the search for Extraterrestrial lntelligence, seth shostack is doing just that.
These are the individual antennas of the Allen telescope array.
lt's one of the most powerful observatories in the world
and, in fact, the kind of thing that could check out millions of star systems.
lf you can check out a few million star systems,
you have a really good chance of finding a signal from ET.
Radio waves or TV signals have recognisable patterns,
so shostack and other scientists are listening for deliberate signals from an alien planet.
These telescopes listen to hundreds of thousands to millions of stars at the same time
and they do it 24 hours a day.
These distances between stars are enormously vast.
Most interstellar visiting is gonna be via signalling, not by actual visiting.
And what are we broadcasting out into the cosmos?
Television transmissions have been travelling away from the earth
for about 50 years.
l Love Lucy and Gilligan's lsland have been broadcast to the galaxy,
travelling at the speed of light,
and they are our emissaries, they are our diplomats to the galaxy.
Our ultra-high frequency and microwave radio signals
have been expanding into space at the speed of light.
These radio, radar, and television signals fill a sphere nearly 1 00 light years in diameter,
so any civilisation within 1 00 light years of Earth
might be hearing our voices or watching our television shows.
We're sending transmissions out into the cosmos,
but suppose we detect a signal from an alien civilisation.
How would we respond?
lt's something we've thought about a lot.
The United Nations has even drawn up a manifesto about what we would do.
When the day comes that we pick up a transmission from an alien civilisation,
we as a species, frankly, will face our greatest challenge ever, l think.
lt raises the question, who represents Earth?
Who represents the Homo sapiens?
And l think the only way to decide this will be with some very seriously thought-out process.
But if we do pick up a signal from an alien race,
not everyone thinks it's such a good idea to answer back.
There will be those who, l think, understandably, will argue that we humans should remain hidden
in the great galactic tall grasses,
because, of course, maybe they're hungry, for example,
and would like some hors d'oeuves.
Would aliens really want to do us harm?
Probably not.
Aliens we contact will at least have learned to live with themselves peacefully.
For them to exist in any numbers in the galaxy,
they would have to have long lifetimes as intelligent, technological,
communicating civilisations.
We are closer than ever to finding answers to one of mankind's greatest questions..
Are we alone?
There is something in us that wants to find our place.
What is our purpose? Maybe that purpose is just to be nice to each other
and just to seek and explore and to discover.
We are exploring and every discovery we make will help us understand our very existence.
We want to be a part of something bigger than ourselves.
We know deep down that our lives are flickering moments of glory.
We would like to know that there's a higher purpose,
that we're a part of something bigger.
Are we simply one small piece in the cosmicjigsaw puzzle
or are we truly the only special beings in this vast universe?
Finding the answer could be mankind's greatest challenge.