Original subtitles

(mellow music)

- [Narrator] We are finding more and more exoplanets,

more and more locations for liquid water,

and the possibility for life as we know it.

But, where are the alien civilizations?

Where are the technologically advanced creatures?

Why can't we find signs of other sentient beings?

Where are their signals out there, amongst the stars?

Perhaps the answer to that age old question,

are we alone in the galaxy, is a yes.

(dramatic music)

(eerie music)

American astronomer and astrophysicist Frank Drake

established the Search for Extraterrestrial Intelligence,

or SETI back in 1960.

(eerie music)

Listening to the stars and the noisy galaxy,

trying to find signals that are deliberate,

messages from other planets,

where life has evolved an intelligence,

a technological civilization like our own,

able to comprehend the vastness of space.

Like us, looking for the answer to that age old question,

are we alone?

(eerie music)

There are 3,700 known exoplanets so far.

NASA's tests is going to find lots more.

The European CHEOPS mission will specifically

study the known exoplanets

and look for more around our brighter stellar neighbors.

(eerie music)

Multiple planetary systems and terrestrial,

Earth-like planets are coming up trumps

and we've only been looking for 15 years.

We have been looking and listening

for nearly 60 years now, with zero results.

No radio signals,

no laser or other light flashes in our direction,

no attempts at communication that we can detect.

So, where are all the aliens?

(eerie music)

Well, it's a complicated question.

Stars that can harbor Earth-like planets?

Viable exoplanets that can sustain liquid water?

As for life, how long does it take to generate life?

Then, how long to evolve into intelligent life?

Will that intelligent life become technological?

How long will an advanced civilization survive?

Tough questions when you only have Earth as your example.

(eerie music)

Then, there is the time factor.

The universe is 13.8 billion years old.

Our star, the Sun, is 4.6 billion years old,

and probably a 3rd or 4th generation star.

Earth is 4.543 billion years old.

Our moon is just the right size

to stabilize Earth's rotation

and provide ocean tides and sea currents.

(eerie music)

Life on Earth is at least 3.5 billion years old.

Several major climactic and asteroid interventions

steered the evolutionary cart, leading to us.

Homo sapiens, 200,000 years.

Our civilization began around 6,000 years.

The Industrial Age is just over 200 years.

The ability to send signals into space, maybe 100 years.

Powerful radio signals, television signals,

radar, and laser light, say, 50 years.

Being generous, our signals have traveled out

in a sphere with a radius of 100 light years.

(mellow music)

That's about 1/1000th of the width of the Milky Way,

which is 105,700 light years across.

(mellow music)

The nearest galaxy is Andromeda,

at 220,000 light years away.

(mellow music)

How long will we continue to broadcast?

In other words, how long

will our technological society last?

Some think not so very long.

We have to be realists.

There will not be too many terrestrial-like planets

with liquid water and an atmosphere to support life,

nurture that life to evolve over billions of years

into a sentient species that may just develop technology

and an understanding of the cosmos,

to want to listen out and respond to a signal from space.

(mellow music)

There is, most likely, life out there,

but it's not talking to us yet.

(dramatic music)

(mellow music)

Let's crunch some numbers.

We'll take the arbitrary figure of 100 light years,

where a sufficiently advanced society

could detect our radio signals.

(mellow music)

They then work out where the signal came from,

and dispatch a response.

This could take a few years to achieve.

Then that signal will take up to 100 years

to get back to us.

100 light years in kilometers roughly equals

nine plus 14 zeros after it.

(mellow music)

What stars are within that reach?

We're only looking at main sequence stars,

ones that are stable and long lived,

moving through various stages

of their lifetime of billions of years.

(mellow music)

So, we have 3,868 stars to choose from,

plus a few more very dim ones we haven't found yet.

(mellow music)

Exoplanet hunters have been targeting the dimmer,

smaller stars called red dwarfs, or, M-type stars,

because it is much easier to detect planets around them.

There are 2,026 stars of that class in our region.

They have also been looking at the slightly larger,

orange K-type main sequence stars,

because of their spectral and luminosity qualities,

astronomers favor them for having

habitable goldilocks regions.

(mellow music)

There are 947 and counting,

though there are only 155 within 50 light years.

Then there's the G-type stars.

Our sun is a G-type,

so they are highly regarded for habitable zones.

There are 512 of them.

(mellow music)

F-types are slightly larger than our sun,

303 are nearby, and several have known planets.

A-type, which are young stars,

a mere 100 million years old, and again,

have been found to harbor Jupiter-like gas planets; 76.

(mellow music)

B-type are giant blue stars, and rare, only 4 in our region.

And, supergiant O-types are hot,

and hostile, and nowhere near us.

(mellow music)

So, how many exoplanets?

3,700 confirmed exoplanets so far.

(mellow music)

Five Mercury-sized rocky worlds,

72 Mars-sized,

701 Earth-sized, terrestrials,

(mellow music)

982 called Super Earths,

799 Neptune-type gaseous worlds,

and 1,217 Jupiter-sized gas planets.

So, that gives a current total of

1,683 Earth-like, rocky planets.

(mellow music)

How many of these rocky worlds

could harbor liquid water on their surface?

Well, there is the habitable, or goldilocks zone,

around these stars, where the planets receive

the right amount of solar flux, where water is liquid.

Too close and the water would boil away,

too far and it will freeze,

making life more difficult to evolve.

(mellow music)

So, scientists have estimated there are

17 definitely within this zone,

but three are outside our distance limit of 100 light years,

so that leaves 14.

Plus, another 13 terrestrials that could seed life,

but be very harsh and unforgiving to it.

That makes 27 candidates

capable of harboring life as we know it.

(dramatic music)

- Life could be incredibly common,

because there are lots of planets out there,

or, it could be an incredibly rare event

that only happens on one in a billion planets in a galaxy.

We really just don't know, so,

whenever I get asked that question, my answer is,

I don't have an opinion yet, I'll need some more evidence.

(dramatic music)

(mellow music)

- [Narrator] TRAPPIST-1, an M-type dwarf star

at 39.6 light years distance,

contains a solar system of seven terrestrial planets,

and it a major contender for harboring liquid water;

they're all Earth-sized candidates.

(mellow music)

Other multi-planet systems in our region include HR 8832,

55 Cancri, and 61 Virginis.

The names just roll of the tongue,

each with at least three planets orbiting it.

(mellow music)

- Well, looking at exoplanets,

these planets around other stars,

is a bit like detective work.

They're so small next to a bright star,

that it's hard to tease out information

unless you do it incrementally.

So, what we can tell right now is that

these planets are, in fact, similar to Earth in size,

and we can tell that some of them

may be similar to Earth in its composition,

doing crude studies of the density of these planets.

We're also using the Hubble Space Telescope right now

to do followup observations of the atmospheres

of some of these planets to see

the composition of the atmosphere and wondering,

and trying to find out if maybe there might be

water in the atmospheres, to see if they are

similar to our own Earth's atmospheres.

(mellow music)

- [Narrator] With names like TRAPPIST, YZ Ceti, Gliese 876,

HD 219134,

and Wolf-1060,

these exo-worlds sound ponderous and uninteresting.

(mellow music)

But, one day they may be given more appealing names,

because these are worlds with great potential.

(mellow music)

Elements such as hydrogen, helium, carbon and oxygen

abound throughout the universe,

so we might assume that they are available to such planets

and therefore water would be plentiful.

(mellow music)

Even worlds completely covered in water are feasible.

These basic elements also make up

the active ingredients for life.

(mellow music)

Elements and amino acids are commonplace,

so microbial life could emerge

on all these target planets quite readily.

(mellow music)

- Now, we strongly suspect, based on an example of one,

our Earth, that the laws of biology

work the same everywhere too.

And by that I mean, the laws

that Charles Darwin discovered for us.

We think that based on these laws

that evolution can drive life to greater complexity

and ultimately to intelligence.

It's the smart thing to do.

(mellow music)

- [Narrator] As with Earth, it could take

billions of years for evolution to create

ever greater complexity, and eventually, intelligence.

(mellow music)

On Earth, most highly intelligent creatures

are of the mammalian family,

but the octopus developed its intelligence

through an entirely separate route.

(mellow music)

This would indicate that intelligence

has many chances of evolving on these worlds.

(mellow music)

So, why are there no similar

technological societies among these 27 candidate planets?

What could be stopping intelligent creatures

from developing technology, radios, and space ships?

(mellow music)

There are several possible answers.

(dramatic music)

(mellow music)

Earth has had major climactic disasters

that nearly wiped out life completely.

Perhaps a similar disaster was successful

on one of these other world and killed it.

But, even with these events

befalling some of our candidate planets,

there should still be 25 or more potential civilizations.

(dramatic music)

- So, you'd think there'd be plenty of opportunities

for life to evolve somewhere else,

and maybe swing by the Earth or at least call on the radio.

But we haven't found any alien monoliths,

or beer cans,

(audience laughs)

or cigarette ends, and we have not heard them

tweeting on the radio either.

So, where are they?

There are lots of theories about that,

but I'm gonna concentrate on the more plausible ones.

First of all, there's the water trap.

Maybe the worlds that have water on them are all ocean,

for the most part, and if that's the case,

you can't discover combustion, you can't make metals,

so you can't make a radio or a spaceship.

If our dolphin friends lived on an ocean planet,

they would be stuck where they are,

in the stone age forever.

(dramatic music)

Or, maybe on a planet that has dry land but no metals,

or very few metals.

Same problem.

You can't develop a technology.

And, how about the difficulty of interstellar travel?

Maybe it's just too hard.

It looks like a real challenge for us.

It could be a couple of hundred years before we try that.

Maybe it's just to hard.

(audience laughs)

And then, there's another theory,

which is, that we could be the first.

We could be the first intelligence to evolve

in this part of the galaxy.

Someone has to be.

We could be the elder race.

So, here's a time history of Earth.

When you look at all the time that life has been here,

nearly 4 billion years, humans have only been around

for a couple of thousand years,

civilization for about 6,000 years,

depending how you count it,

and our technical era only for 200 years.

When you look at this picture, it is obvious

that the most likely first alien lifeforms

that we discover will not be intelligent.

They'll be somewhere back here, equivalent to life on Earth

during the first three billion years of evolution.

Similarly, nearby life on an exoplanet

is probably plodding its way up the evolutionary ladder.

Remember how long it took us to get where we are,

where we could even think about life elsewhere.

(dramatic music)

- [Narrator] We Earthlings have the prime real estate

in our solar system.

We may well be alone for the moment

in our section of the galaxy,

the only ones with space travel.

(dramatic music)

If so, we need to take care of our planet

and our civilization and stick around long enough

to see other intelligences and civilizations emerge

over the coming millions of years,

on those 25 nearby planets.

(dramatic music)