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 ice-nine.
So out of all these planets out there,
and the variety is just simply astonishing,
we mostly want to find the planets
that are Goldielocks planets, we call them,
not too big, not too small
not too hot, not too cold --
but 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 analyze
the atmosphere to 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 planet 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 imagine, 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 so 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 of gravity
or cosmology or some such.
Please don't email me one of your crazy theories.
Well, I had 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 friends
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 when 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 Starshade.
And the Starshade is very specially shaped screen
and the goal is to fly that Starshade
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 Starshade.
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 precision
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
Starshade deployment test bed in the lab.
And in this case,
I just wanted 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,
and we build the very complicated space telescopes
that might be out there,
what are we going to find?
Well, in the best case,
we will find an image of another exo-earth.
Here's earth as a pale blue dot.
This is actually a real photograph of earth
taken by the Voyager 1 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 that 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)