-
I'm here to tell you about
the real search for alien life.
-
Not little green humanoids
arriving in shiny UFOs,
-
although that would be nice.
-
But it's the search for planets
-
orbiting stars far away.
-
Every star in our sky is a sun.
-
And if our sun has planets --
-
Mercury, Venus, Earth, Mars, etc.
-
Surely those other stars should
have planets also
-
-- and they do.
-
And in the last two decades,
-
astronomers have found
thousands of exoplanets.
-
Our night sky is literally
teeming with exoplanets.
-
We know, statistically speaking,
-
that every star has at least one planet.
-
And in the search for planets,
-
and in the future, planets
that might be like earth,
-
we're able to help address
-
some of the most amazing
and mysterious questions
-
that have faced humankind for centuries.
-
Why are we here?
-
Why does our universe exist?
-
How did earth form and evolve?
-
How and why did life originate
and populate our planet?
-
The second question that
we often think about is:
-
Are we alone?
-
Is there life out there?
-
Who is out there?
-
You know, this question
has been around
-
for thousands of years,
-
since at least the time
of the Greek philosophers.
-
But, I'm here to tell you
just how close we're getting
-
to finding out the answer
to this question.
-
It's the first time in human history
-
that this really is within reach for us.
-
Now when I think about
the possibilities
-
for life out there,
-
I think of the fact that our sun
-
is but one of many stars.
-
This is a photograph of a real galaxy,
-
we think our milky way
looks like this galaxy.
-
It's a collection of bound stars.
-
But our milky way is one of
hundreds of billions of stars
-
and our galaxy is one of upwards
of hundreds of billions of galaxies.
-
Knowing that small planets
are very common,
-
you can just do the math.
-
And there are just so many stars
and so many planets out there,
-
that surely, there must be life
somewhere out there.
-
Well, the biologists get furious
with me for saying that,
-
because we have absolutely no evidence.
-
for life beyond earth, yet.
-
Well, if we were able to look
at our galaxy from the outside
-
and zoom in to where our sun is,
-
we see a real map of the stars.
-
And the highlighted stars are
those with known exoplanets.
-
This is really just
the tip of the iceberg.
-
Here, this animation is zooming in
onto our solar system.
-
And you'll see here the planets
-
as well as some spacecraft
that are also orbiting our sun.
-
Now if we can imagine going to
the west coast of North America,
-
and looking out at the night sky,
-
here's what we'd see on a spring night.
-
And you can see
the constellations overlaid
-
and again, so many stars with planets.
-
There's a special patch of the sky
-
where we have thousands of planets.
-
This is where the Kepler Space Telescope
focused for many years.
-
Let's zoom in and look at
one of the favorite exoplanets.
-
This star is called Kepler-186f.
-
It's a system of about five planets.
-
And by the way, most of these exoplanets,
-
we don't know too much about.
-
We know their size, and their orbit
and things like that.
-
But there's a very special planet
here called Kepler-186f,
-
this planet is in a zone that is not
too far from the star,
-
so that the temperature may be
just right for life.
-
Here, the artist conniption
is just zooming in
-
and showing you what that planet
might be like.
-
So, many people have this
romantic notion of astronomers
-
going to the telescope
on a lonely mountaintop
-
and looking at the spectacular night sky
-
through a big telescope.
-
But actually, we just work on
our computers like everyone else
-
and we get our data by email
or by loading from a database.
-
So instead of coming here
to tell you about
-
the somewhat tedious nature
of the data and data analysis
-
and the complex computer models we make,
-
I have a different way to try
to explain to you
-
some of the things that we're
thinking about exoplanets.
-
Here's a travel poster:
-
"Kepler-186f,
-
Where the grass is always redder
on the other side."
-
That's because Kepler-186f
orbits a red star,
-
and we're just speculating that
perhaps the plants there,
-
if there is vegetation that
does photosynthesis,
-
it has different pigments and looks red.
-
"Enjoy the gravity on HD 40307g, "
-
a super-earth.
-
This planet is more massive than earth
-
and has a higher surface gravity.
-
"Relax on Kepler-16b,
-
where your shadow always has company."
-
We know of a dozen planets
that orbit two stars,
-
and there's likely many more out there.
-
If we could visit one of those planets,
-
you literally would see two sunsets
-
and have two shadows.
-
So actually, science fiction
got some things right,
-
Tatooine from Star Wars.
-
And I have a couple of other
favorite exoplanets
-
to tell you about.
-
This one is Kepler-10b,
-
it's a hot, hot planet.
-
It orbits over 50 times
closer to its star
-
than the earth does to our sun.
-
And actually, it's so hot
-
we can't visit any of these planets,
-
but if we could,
-
we would melt long before
we got there.
-
We think the surface is hot enough
to melt rock
-
and has liquid lava lakes.
-
We use 1214b,
-
this planet,
-
we know the mass and the size
-
and it has a fairly low density,
-
it's somewhat warm.
-
We actually don't know really
anything about this planet.
-
One possibility is that
it's a water world,
-
like a scaled-up version of one
of Jupiter's icy moons
-
that might be 50 percent water by mass.
-
In this case, it would have
a thick steam atmosphere
-
overlaying an ocean,
-
not of liquid water,
-
but of an exotic form of water,
-
a superfluid --
-
not quite a gas, not quite a liquid.
-
Under that wouldn't be rock,
-
but a form of high pressure ice,
like (word)
-
So out of all these planets out there,
-
and the variety is
just simply astonishing,
-
we mostly want to find the planets
-
that are Goldie Locks planets,
we call them,
-
not too big, not too small
-
not too hot, not too cold --
-
just right for life.
-
But to do that, we'd have to
be able to look
-
at the planet's atmosphere
-
because the atmosphere acts
like a blanket
-
trapping heat --
-
the greenhouse effect.
-
We have to be able to asses
the greenhouse gasses
-
on other planets.
-
Well, science fiction got
some things wrong.
-
The Star Trek Enterprise had to travel
vast distances
-
at incredible speeds
to orbit other planets
-
so that First officer Spok
could further analyze
-
the atmosphere and see
if the planet
-
was habitable or if
there were lifeforms there.
-
Well, we don't need
to travel at warp speeds
-
to see other planets' atmospheres,
-
although I don't want to dissuade
any budding engineers
-
from figuring out how to do that.
-
We actually can and do study
planet atmospheres
-
from here, from earth orbit.
-
This is a picture, a photograph
-
of the Hubble Space Telescope
-
taken by the shuttle Atlantis
as it was departing
-
after the last human space
flight to Hubble.
-
They installed a new camera, actually,
-
that we use for exoplanet atmospheres.
-
And so far, we've been able to study
dozens of exoplanet atmospheres,
-
about six of them in great detail.
-
But those are not small planets like earth.
-
They're big, hot planets
-
that are easy to see.
-
We're not ready,
-
we don't have the right technology yet
-
to study small exoplanets.
-
But nevertheless,
-
I wanted to try to explain to you
-
how we study exoplanet atmospheres.
-
I want you to image, for a moment,
a rainbow.
-
And if we could look
at this rainbow closely,
-
we would see that some
dark lines are missing.
-
And here's our sun,
-
the white light of our sun split up,
-
not by raindrops, but by a spectrograph.
-
And you can see all these dark, vertical lines.
-
Some are narrow, some are wide,
-
some are shaded at the edges.
-
And this is how astronomers have studied
objects in the heavens
-
literally, for over a century.
-
So here, each different atom and molecule
-
has a special set of lines,
-
a fingerprint, if you will.
-
And that's how we study
exoplanet atmospheres.
-
And, I'll just never forget
when I started working
-
on exoplanet atmospheres
20 years ago,
-
how many people told me,
-
"This will never happen,
-
we'll never be able to study them.
-
Why are you bothering?"
-
And that's why I'm pleased
to tell you about
-
all the atmospheres studied now,
-
and this is really a whole field
of its own.
-
So when it comes to other planets,
other earths,
-
in the future when we can observe them,
-
what kind of gasses would be looking for?
-
Well, you know, our own earth has oxygen
in the atmosphere
-
to 20 percent by volume.
-
That's a lot of oxygen.
-
But without plants
and photosynthetic life,
-
there would be no oxygen,
virtually no oxygen
-
in our atmosphere.
-
So oxygen is here because of life
-
and our goal then is to look for gasses
-
in other planet atmospheres,
-
gasses that don't belong,
-
that we might be able to attribute to life.
-
But which molecules should
we search for?
-
I actually told you how diverse
exoplanets are,
-
we expect that to continue in the future
-
when we find other earths.
-
And that's one of the main things
I'm working on now,
-
I have a theory about this.
-
It reminds me that nearly everyday,
-
I receive an email --
-
email or emails--
-
from someone with a crazy theory
about physics, gravity
-
or cosmology or some such.
-
Please don't email me
one of your crazy theories.
-
Well, I have my own crazy theory.
-
But, who does the MIT professor go to?
-
Well I emailed a Nobel Laureate
in physiology and medicine
-
and he said, "Sure, come and talk to me."
-
So I brought my two biochemistry frirnds
-
and we went to talk to him
about our crazy theory.
-
And that theory was that life produces
all small molecules,
-
so many molecules.
-
Like, everything I could think of,
-
but not being a chemist.
-
Think about it:
-
carbon dioxide, carbon monoxide,
-
molecular hydrogen, molecular nitrogen,
-
methane, methal choloride (?) --
-
so many gasses,
-
they also exist for other reasons,
-
but just life even produces ozone.
-
So we go to talk to him about this,
-
and immediately, he shot down
the theory.
-
He found an example that didn't exist.
-
So, we went back to the drawing board
-
and we actually think we have
found something
-
very interesting in another field.
-
But back to exoplanets,
-
the point is that life produces
so many different types of gases,
-
literally thousands of gasses.
-
And so what we're doing now
is just trying to figure out
-
on which types of exoplanets,
-
which gasses could be attributed to life.
-
And so when it comes time
-
that we find gasses on exoplanet
atmospheres,
-
that we won't know if they're
being produced
-
by intelligent aliens or by trees,
-
or earth(?) swamp,
-
or even just by simple, single celled
microbial life.
-
And so working on the models
-
and thinking about biochemistry
-
it's all well and good.
-
But a really big challenge ahead of us
-
is how.
-
How are we going to find these planets?
-
They're actually many ways to find planets,
-
several different ways.
-
But the one that I'm most focused on
-
is how can we open a gateway
-
so that in the future,
-
we can find hundreds of earths.
-
We have a real shot
at finding signs of life.
-
And actually, I just finished
leading a two-year project
-
in this very special phase
of a concept
-
we call the star shade.
-
And the star shade is very
specially shaped screen
-
and the goal is to fly that star shade
-
so it blocks out the light of a star
-
so that a telescope can see
the planets directly.
-
Here, you can see myself
and two team members
-
holding up one small part of the star shade.
-
It's shaped like a giant flower,
-
and this is one of the prototype petals.
-
The concept is that a star shade
and telescope launch together,
-
with the petals unfurling
from the stowed position.
-
The central trust would expand,
-
with the petals snapping into place.
-
Now, this has to be made very precisely,
-
literally, the petals to microns
-
and they have to deploy to millimeters.
-
And this hole structure would have to fly
-
tens of thousands of kilometers
away from the telescope,
-
it's about tens of meters in diameter.
-
And the goal is to block out
the starlight to incredible percussion
-
so that we'd be able to see
the planets directly.
-
It has to be a very special shape
-
because of the physics of defraction.
-
Now this is a really project
that we worked on,
-
literally, you would not believe how hard.
-
Just so you believe that it's
not just in movie format,
-
here's a real photograph
of a second generation
-
star shade deployment
test bed in the lab.
-
And in this case,
-
I just want you to know,
-
that that central trust
has heritage left over
-
from large radio deployables in space.
-
So after all of that hard work
-
where we try to think of all
the crazy gasses
-
that might be out there,
-
we build the very
complicated space telescopes,
-
what are we going to find?
-
Well, in the best case,
-
we will find an image
of another eco-earth.
-
Here's earth as a pale blue dot.
-
This is actually a real photograph
of earth
-
taken by the Voyager I spacecraft,
-
four billion miles away.
-
And that red light is just scattered light
in the camera optics.
-
But what's so awesome to consider
is that
-
if there are intelligent aliens
orbiting on a planet
-
around a star near to us
-
and they build complicated
space telescopes
-
of a kind we're trying to build,
-
all they'll see is this pale blue dot,
-
a pinprick of light.
-
And so sometimes when I pause
to think about
-
my professional struggle
and huge ambition,
-
it's hard to think about that
in contrast
-
to the vastness of the universe.
-
But nonetheless, I am devoting
the rest of my life
-
to finding another earth.
-
And I can guarantee that in
the next generation
-
of space telescopes,
-
and the second generation,
-
we will have the capability to find
and identity other earths.
-
And the capability to split up
the starlight
-
so that we can look for gasses
-
and assess the greenhouse gasses
in the atmosphere,
-
estimate the surface temperature,
-
and look for signs of life.
-
But there's more,
-
in this case of searching
for other planets like earth,
-
we are making a new kind of map
-
of the nearby stars and
of the planets orbiting them,
-
including stars that actually might be
-
inhabitable by humans.
-
And so I envision that our descendants,
-
hundreds of years from now,
-
will embark on an interstellar journey
-
to other worlds.
-
And they will look back at all of us
-
as the generation who first found
the earth-like worlds.
-
Thank you.
-
(Applause)
-
June Cohen: And I give you,
for a question,
-
Rosetta Mission manager Fred Jansen.
-
Fred Jansen: You mentioned halfway through
-
that the technology to actually look
at the spectrum
-
of an exoplanet-like earth
is not there yet.
-
When do you expect this will be there
-
and what's needed?
-
Sara Seager: Well actually,
what we expect is what
-
we call our next-generation
Hubble telescope.
-
And this is called the
James Webb Space Telescope,
-
and that will launch in 2018
-
and that's what we're going to do,
-
we're going to look at
a speicla kind of planet
-
called transient exoplanets,
-
and that will be our first shot
-
at studying small plants
for gasses that might indicate
-
the planet is habitable.
-
JC: I'm going to ask you one
follow-up question, too, Sara,
-
as the generalist.
-
So I am really struck by the notion
in your career
-
of the opposition you faced,
-
that when you began thinking about
exoplanets,
-
there was extreme skepticism
in the scientific community
-
that they existed,
-
and you proved them wrong.
-
What did it take to take that on?
-
SS: Well, the thing is that
as scientists,
-
we're supposed to be skeptical.
-
It's our job to make sure that
what the other peson is saying
-
makes sense or not.
-
But being a scientist,
-
I think you've seen it
from this session,
-
it's like being an explorer.
-
You have this immense curiosity,
-
this stubbornness,
-
this sort of resolute will
that you will go forward
-
no matter what people say.
-
JC: I love that.
Thank you, Sara.
-
(Applause)