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Thank you to Draper and its Hack The Moon initiative for supporting PBS Digital Studios.

People have always dreamed of ways to be closer to the stars.

Thats what brought us here to Mauna Kea in Hawaii.

From this spot, we can stand nearer to the sky, and see farther and clearer than almost

anywhere else on Earth

to wonder what and perhaps even who is out there.

On Earth and in space, advanced telescopes have stared for weeks even months into patches

of sky

and theyve seen that other stars are surrounded by planets of their own.

At least a planet for every star.

But what sort of planets are they?

Astronomers have learned that our galaxy is home to many kinds of planet/sun systems:

from hot Jupiters to warm Neptunes, even super-Earths of lava and diamond.

These planets have expanded our view of where life may be possible.

But what drives astronomers to study them is to find an answer that ultimate question:

Is life abundant or are we unique?

Were standing in front of two of the most sensitive, precise, and advanced ground telescopes

ever constructed - the Keck Observatory.

These instruments, and others that are being designed, will allow scientists, for the first

time, to characterize these far-off exoplanets, to paint a detailed picture of their sizes,

their orbits, even the chemicals in their atmospheres, to understand where and how life

might exist.

Combined with knowledge from biology, physics, and chemistry, were learning a great deal

about how life and planets coevolve.

We call it the science of astrobiology.

Decades before we discovered the first exoplanet, one scientist asked what wed

need to know in order to know whether another intelligent, technological civilization is, or was, or

might one day be out there.

That scientist was a young radio astronomer named Frank Drake.

He gave us a way to estimate the number of technological civilizations that are out there.

N* tells us how often stars are born.

Its now known around one star per year born in the Milky Way, so we put a1there.

f sub p is the fraction of stars with planets,

which we now believe is 1, or at least 1 planet for every star.

Solar systems are the rule, not the exception.

n sub p is the estimate of how many planets orbit their stars at distances that allow

for liquid water.

We think is many as 1 in 5 planets sit in these so-calledhabitable zones”, or

a value for n sub p of 0.2.

In all, there may be as many as 40 billion Earth-sized planets orbiting in the habitable

zones of Sun-like stars and red dwarfs in the Milky Way.

Now so far, our discoveries have filled nearly half of the equation and expanded what is possible,

but the Drake Equation is still incomplete.

We dont yet know how many host life (f sub L) if any of that life is intelligent (f sub i)

if its built a civilization (f sub c), or how long that civilization might

last so that we might find it.

When astronomers are searching for maybe that ultimate question of is life abundant or is

it unique, what sorts of actual experiments are they doing here to try and get at that question?

Well the first thing you have to do is to find the planets, right?

And so thats one of the things that Keck does wonderfully well and many other telescope

facilities, is we find them, either by transiting when the planet goes in front of its star

and dips the light down a bit, or through the radial velocity method.

Or through direct imaging with Keck adaptive optics.

So youve gotta find the planets, thats step one.

Step two is are the planets at a distance from their host star where water could be

liquid on the surface?

And then you want to know something about the atmosphere of that planet.

And thats when things get really, really hard.

Because to be able to measure the atmosphere of that planet you either have to have an

extremely precise measurement of the star before and during these eclipses, or you have

to be able to measure the light thats bouncing off of that planet, and measure the chemistry

in its atmosphere.

And both of those things require extremely precise instrumentation, very, very large

telescopes, and just sheer force of will to keep in the game.

This telescope is amazing.

Each of its 36 hexagonal mirror segments is polished so smooth, if they were the size

of the Earth, their largest imperfections would only be three feet high.

And twice every second, these segments position are adjusted by an accuracy of

4 nanometers or 1/25,000th of a human hair.

The next phase of exoplanet exploration will be the search for biosignatures, these are telltale

chemical signs like oxygen or methane in those far-away atmospheres.

These will be detectable from future space telescopes and giant ground-based observatories

planned on Earth.

Then comes the big question:

How many of them actually show hints of life in their atmosphere?

And are we being fooled?

Just because you see ozone and methane and carbon dioxide and water vapor in the atmosphere,

is that a slam dunk for life?

Not necessarily.

We want to be able to do that, and then we want to get at the essence of your question

which is, if we look at a hundred planets, and theyre all in the habitable zone, and

we see nothing, then thats told you something statistically.

If you look at a hundred planets, and fifty of them or sixty of them have something, that

tells you something really amazing about the universe.

So we need to have the power and the precision to go after as many planets as possible, but

at the same time just by exploring Earth, were finding out that life is thriving

in places where we thought impossible.

So when you combine those two things and when you think about solar systems which are radically

unlike ours, the mind really starts to stretch out and think that life could really be abundant

out there in the universe and we should stop being so Earth-centric sometimes when we think

about that.

But if the cosmos is so vast, and full of so many places where life and intelligence

may arise, then where are they?

Perhaps there's someGreat Filterwhich prevents other life-bearing planets from reaching our

level of civilization.

Maybe the appearance of even simple life on habitable worlds is so unlikely that biology

itself is the Great Filter.

Or while life is common, maybe the emergence of even simple intelligence is rare.

But there is another option: maybe the Great Filter lies in technological civilizations themselves.

In the millennia since human civilization started, our most important discovery is the

one thats enabled us to burn 100 million years of stored energy to power our technological growth:

fossil fuels.

As a rule, it takes energy to build and grow a technological civilization and harnessing

massive amounts of energy has some impact on a civilizations environment.

Over there is the place where we measure the planets atmospheric carbon dioxide concentration.

Its just crossed 415 parts per million for the first time since humans came into


Now as evidenced by the measurements taken there, human activities are changing our planets

climate, and those changes may have dire consequences for us.

Were not the first life form to change the climate on the Earth.

Billions of years ago, ancient microbes breathed the first oxygen into the atmosphere, making

possible life as we know it today.

But the result of that shift was the death of massive amounts of Earths early life,

to whom oxygen was poisonous.

Its an environmental shift that completely changed the course of how life unfolded on

this planet.

Are we now about to shift the course of life on Earth again?

Is self-destruction in the process of harnessing energy an inherent risk in the development

of all civilizations, human or alien?

Whether or not we are ever able to find another technological civilization might depend on

the question of if civilizations can harness energy without destroying their own future.

So, as we build ourselves up to be closer to the stars, we should at least ask:

will the same be true of us?

Whether there's life outside of our solar system is one of the biggest questions we've

ever asked, but so is whether there's life in the solar system.

Check it out the next episode with Dianna from Physics Girl.

Thanks you to Draper and its Hack the Moon initiative for supporting PBS Digital Studios.

You know the story of the astronauts who landed on the moon.

Now you can log on to to discover the story

of the male and female engineers who guided them there and back safely.

Hack the Moon chronicles the engineers and technologies

behind the Apollo missions.

Brought to you by Draper the site is full of images and videos and stories

about the people who hacked the moon.

PBS is bringing you the Universe with the Summer of Space, which includes six incredible, new

science and history shows airing on PBS and streaming on and the PBS video app.

Watch it all on

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