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People have always dreamed of ways to be closer
to the stars.
That’s 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 they’ve 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?
We’re 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, we’re 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 we’d
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.
It’s now known around one star per year born in the Milky Way, so we put a “1” there.
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-called “habitable 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 don’t yet know how many host life (f
sub L) if any of that life is intelligent (f sub i)
if it’s 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 that’s 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 you’ve gotta find the planets, that’s
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 that’s 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 that’s 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 segment’s
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 they’re all in the habitable zone, and
we see nothing, then that’s 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,
we’re 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 some “Great Filter” which 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 that’s 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 civilization’s environment.
Over there is the place where we measure the
planet’s atmospheric carbon dioxide concentration.
It’s just crossed 415 parts per million
for the first time since humans came into
existence.
Now as evidenced by the measurements taken
there, human activities are changing our planet’s
climate, and those changes may have dire consequences for us.
We’re 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 Earth’s early life,
to whom oxygen was poisonous.
It’s 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 wehackthemoon.com 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 PBS.org and the PBS video app.
Watch it all on pbs.org/summerofspace
