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I'm here to tell you
about the real search for alien life.

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Not little green humanoids
arriving in shiny UFOs,

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although that would be nice.

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But it's the search for planets
orbiting stars far away.

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Every star in our sky is a sun.

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And if our sun has planets --

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Mercury, Venus, Earth, Mars, etc.,

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surely those other stars
should have planets also,

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and they do.

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And in the last two decades,

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astronomers have found
thousands of exoplanets.

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Our night sky is literally
teeming with exoplanets.

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We know, statistically speaking,

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that every star has at least one planet.

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And in the search for planets,

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and in the future,
planets that might be like Earth,

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we're able to help address

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some of the most amazing
and mysterious questions

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that have faced humankind for centuries.

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Why are we here?

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Why does our universe exist?

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How did Earth form and evolve?

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How and why did life originate
and populate our planet?

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The second question
that we often think about is:

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Are we alone?

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Is there life out there?

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Who is out there?

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You know, this question has been around
for thousands of years,

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since at least the time
of the Greek philosophers.

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But I'm here to tell you
just how close we're getting

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to finding out the answer
to this question.

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It's the first time in human history
that this really is within reach for us.

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Now when I think about the possibilities
for life out there,

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I think of the fact that our sun
is but one of many stars.

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This is a photograph of a real galaxy,

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we think our Milky Way
looks like this galaxy.

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It's a collection of bound stars.

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But our [sun] is one
of hundreds of billions of stars

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and our galaxy is one of upwards
of hundreds of billions of galaxies.

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Knowing that small planets
are very common,

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you can just do the math.

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And there are just so many stars
and so many planets out there,

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that surely, there must be life
somewhere out there.

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Well, the biologists get furious
with me for saying that,

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because we have absolutely no evidence
for life beyond Earth yet.

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Well, if we were able to look
at our galaxy from the outside

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and zoom in to where our sun is,

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we see a real map of the stars.

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And the highlighted stars
are those with known exoplanets.

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This is really just
the tip of the iceberg.

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Here, this animation is zooming in
onto our solar system.

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And you'll see here the planets

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as well as some spacecraft
that are also orbiting our sun.

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Now if we can imagine going
to the West Coast of North America,

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and looking out at the night sky,

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here's what we'd see on a spring night.

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And you can see
the constellations overlaid

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and again, so many stars with planets.

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There's a special patch of the sky
where we have thousands of planets.

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This is where the Kepler Space Telescope
focused for many years.

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Let's zoom in and look
at one of the favorite exoplanets.

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This star is called Kepler-186f.

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It's a system of about five planets.

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And by the way, most of these exoplanets,
we don't know too much about.

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We know their size, and their orbit
and things like that.

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But there's a very special planet
here called Kepler-186f.

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This planet is in a zone
that is not too far from the star,

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so that the temperature
may be just right for life.

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Here, the artist's conception
is just zooming in

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and showing you what that planet
might be like.

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So, many people have this
romantic notion of astronomers

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going to the telescope
on a lonely mountaintop

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and looking at the spectacular night sky
through a big telescope.

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But actually, we just work
on our computers like everyone else,

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and we get our data by email
or downloading from a database.

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So instead of coming here to tell you

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about the somewhat tedious nature
of the data and data analysis

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and the complex computer models we make,

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I have a different way
to try to explain to you

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some of the things
that we're thinking about exoplanets.

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Here's a travel poster:

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"Kepler-186f:

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Where the grass is always redder
on the other side."

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That's because Kepler-186f
orbits a red star,

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and we're just speculating
that perhaps the plants there,

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if there is vegetation
that does photosynthesis,

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it has different pigments and looks red.

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"Enjoy the gravity on HD 40307g,

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a Super-Earth."

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This planet is more massive than Earth

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and has a higher surface gravity.

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"Relax on Kepler-16b,

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where your shadow always has company."

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(Laughter)

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We know of a dozen planets
that orbit two stars,

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and there's likely many more out there.

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If we could visit one of those planets,

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you literally would see two sunsets

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and have two shadows.

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So actually, science fiction
got some things right.

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Tatooine from Star Wars.

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And I have a couple of other
favorite exoplanets

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to tell you about.

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This one is Kepler-10b,

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it's a hot, hot planet.

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It orbits over 50 times closer to its star

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than our Earth does to our sun.

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And actually, it's so hot,

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we can't visit any
of these planets, but if we could,

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we would melt long before we got there.

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We think the surface
is hot enough to melt rock

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and has liquid lava lakes.

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Gliese 1214b.

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This planet, we know the mass and the size

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and it has a fairly low density.

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It's somewhat warm.

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We actually don't know
really anything about this planet,

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but one possibility
is that it's a water world,

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like a scaled-up version
of one of Jupiter's icy moons

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that might be 50 percent water by mass.

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And in this case, it would have
a thick steam atmosphere

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overlaying an ocean,

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not of liquid water,

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but of an exotic form
of water, a superfluid --

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not quite a gas, not quite a liquid.

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And under that wouldn't be rock,

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but a form of high-pressure ice,

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like ice IX.

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So out of all these planets out there,

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and the variety
is just simply astonishing,

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we mostly want to find the planets
that are Goldilocks planets, we call them.

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Not too big, not too small,

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not too hot, not too cold --

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but just right for life.

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But to do that,
we'd have to be able to look

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at the planet's atmosphere,

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because the atmosphere
acts like a blanket trapping heat --

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the greenhouse effect.

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We have to be able to assess
the greenhouse gases

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on other planets.

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Well, science fiction
got some things wrong.

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The Star Trek Enterprise

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had to travel vast distances
at incredible speeds

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to orbit other planets

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so that First Officer Spock
could analyze the atmosphere

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to see if the planet was habitable

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or if there were lifeforms there.

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Well, we don't need
to travel at warp speeds

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to see other planet atmospheres,

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although I don't want to dissuade
any budding engineers

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from figuring out how to do that.

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We actually can and do study
planet atmospheres

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from here, from Earth orbit.

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This is a picture, a photograph
of the Hubble Space Telescope

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taken by the shuttle Atlantis
as it was departing

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after the last
human space flight to Hubble.

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They installed a new camera, actually,

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that we use for exoplanet atmospheres.

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And so far, we've been able to study
dozens of exoplanet atmospheres,

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about six of them in great detail.

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But those are not
small planets like Earth.

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They're big, hot planets
that are easy to see.

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We're not ready,

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we don't have the right technology yet
to study small exoplanets.

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But nevertheless,

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I wanted to try to explain to you
how we study exoplanet atmospheres.

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I want you to imagine,
for a moment, a rainbow.

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And if we could look
at this rainbow closely,

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we would see that some
dark lines are missing.

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And here's our sun,

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the white light of our sun split up,

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not by raindrops, but by a spectrograph.

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And you can see
all these dark, vertical lines.

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Some are very narrow, some are wide,

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some are shaded at the edges.

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And this is actually how astronomers
have studied objects in the heavens,

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literally, for over a century.

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So here, each different atom and molecule

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has a special set of lines,

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a fingerprint, if you will.

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And that's how we study
exoplanet atmospheres.

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And I'll just never forget
when I started working

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on exoplanet atmospheres 20 years ago,

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how many people told me,

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"This will never happen.

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We'll never be able to study them.
Why are you bothering?"

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And that's why I'm pleased to tell you
about all the atmospheres studied now,

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and this is really a field of its own.

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So when it comes to
other planets, other Earths,

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in the future when we can observe them,

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what kind of gases
would we be looking for?

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Well, you know, our own Earth
has oxygen in the atmosphere

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to 20 percent by volume.

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That's a lot of oxygen.

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But without plants
and photosynthetic life,

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there would be no oxygen,

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virtually no oxygen in our atmosphere.

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So oxygen is here because of life.

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And our goal then is to look for gases
in other planet atmospheres,

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gases that don't belong,

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that we might be able
to attribute to life.

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But which molecules should we search for?

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I actually told you
how diverse exoplanets are.

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We expect that to continue in the future

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when we find other Earths.

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And that's one of the main things
I'm working on now,

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I have a theory about this.

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It reminds me that nearly every day,

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I receive an email or emails

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from someone with a crazy theory
about physics of gravity

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or cosmology or some such.

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So, please don't email me
one of your crazy theories.

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(Laughter)

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Well, I had my own crazy theory.

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But, who does the MIT professor go to?

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Well, I emailed a Nobel Laureate
in Physiology or Medicine

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and he said, "Sure, come and talk to me."

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So I brought my two biochemistry friends

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and we went to talk to him
about our crazy theory.

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And that theory was that life
produces all small molecules,

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so many molecules.

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Like, everything I could think of,
but not being a chemist.

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Think about it:

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carbon dioxide, carbon monoxide,

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molecular hydrogen, molecular nitrogen,

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methane, methyl chloride --

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so many gases.

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They also exist for other reasons,

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but just life even produces ozone.

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So we go to talk to him about this,

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and immediately, he shot down the theory.

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He found an example that didn't exist.

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So, we went back to the drawing board

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and we think we have found something
very interesting in another field.

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But back to exoplanets,

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the point is that life produces
so many different types of gases,

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literally thousands of gases.

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And so what we're doing now
is just trying to figure out

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on which types of exoplanets,

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which gases could be attributed to life.

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And so when it comes time
when we find gases

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in exoplanet atmospheres

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that we won't know
if they're being produced

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by intelligent aliens or by trees,

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or a swamp,

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or even just by simple,
single-celled microbial life.

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So working on the models

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and thinking about biochemistry,

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it's all well and good.

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But a really big challenge
ahead of us is: how?

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How are we going to find these planets?

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There are actually many ways
to find planets,

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several different ways.

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But the one that I'm most focused on
is how can we open a gateway

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so that in the future,

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we can find hundreds of Earths.

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We have a real shot
at finding signs of life.

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And actually, I just finished
leading a two-year project

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in this very special phase

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of a concept we call the starshade.

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And the starshade
is a very specially shaped screen

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and the goal is to fly that starshade

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so it blocks out the light of a star

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so that the telescope
can see the planets directly.

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Here, you can see myself
and two team members

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holding up one small part
of the starshade.

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It's shaped like a giant flower,

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and this is one of the prototype petals.

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The concept is that a starshade
and telescope could launch together,

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with the petals unfurling
from the stowed position.

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The central truss would expand,

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with the petals snapping into place.

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Now, this has to be made very precisely,

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literally, the petals to microns

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and they have to deploy to millimeters.

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And this whole structure would have to fly

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tens of thousands of kilometers
away from the telescope.

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It's about tens of meters in diameter.

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And the goal is to block out
the starlight to incredible precision

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so that we'd be able to see
the planets directly.

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And it has to be a very special shape,

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because of the physics of defraction.

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Now this is a real project
that we worked on,

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literally, you would not believe how hard.

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Just so you believe
it's not just in movie format,

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here's a real photograph

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of a second-generation
starshade deployment test bed in the lab.

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And in this case,
I just wanted you to know

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that that central truss
has heritage left over

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from large radio deployables in space.

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So after all of that hard work

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where we try to think of all the crazy
gases that might be out there,

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and we build the very
complicated space telescopes

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that might be out there,

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what are we going to find?

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Well, in the best case,

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we will find an image
of another exo-Earth.

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Here is Earth as a pale blue dot.

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And this is actually
a real photograph of Earth

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taken by the Voyager 1 spacecraft,

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four billion miles away.

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And that red light is just scattered light
in the camera optics.

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But what's so awesome to consider

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is that if there are intelligent aliens

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orbiting on a planet
around a star near to us

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and they build complicated
space telescopes

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of the kind that we're trying to build,

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all they'll see is this pale blue dot,

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a pinprick of light.

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And so sometimes, when I pause to think

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about my professional struggle
and huge ambition,

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it's hard to think about that

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in contrast to the vastness
of the universe.

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But nonetheless, I am devoting
the rest of my life

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to finding another Earth.

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And I can guarantee

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that in the next generation
of space telescopes,

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in the second generation,

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we will have the capability
to find and identity other Earths.

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And the capability
to split up the starlight

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so that we can look for gases

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and assess the greenhouse gases
in the atmosphere,

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estimate the surface temperature,

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and look for signs of life.

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But there's more.

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In this case of searching
for other planets like Earth,

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we are making a new kind of map

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of the nearby stars
and of the planets orbiting them,

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including [planets] that actually might be
inhabitable by humans.

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And so I envision that our descendants,

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hundreds of years from now,

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will embark on an interstellar
journey to other worlds.

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And they will look back at all of us

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as the generation who first found
the Earth-like worlds.

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Thank you.

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(Applause)

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June Cohen: And I give you,
for a question,

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Rosetta Mission Manager Fred Jansen.

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Fred Jansen: You mentioned halfway through

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that the technology
to actually look at the spectrum

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of an exoplanet like Earth
is not there yet.

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When do you expect this will be there,

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and what's needed?

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Actually, what we expect is what we call
our next-generation Hubble telescope.

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And this is called the James Webb
Space Telescope,

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and that will launch in 2018,

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and that's what we're going to do,

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we're going to look
at a special kind of planet

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called transient exoplanets,

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and that will be our first shot
at studying small planets

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for gases that might indicate
the planet is habitable.

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JC: I'm going to ask you
one follow-up question, too, Sara,

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as the generalist.

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So I am really struck
by the notion in your career

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of the opposition you faced,

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that when you began thinking
about exoplanets,

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there was extreme skepticism
in the scientific community

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that they existed,

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and you proved them wrong.

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What did it take to take that on?

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SS: Well, the thing is that as scientists,

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we're supposed to be skeptical,

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because our job to make sure
that what the other person is saying

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actually makes sense or not.

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But being a scientist,

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I think you've seen it from this session,

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it's like being an explorer.

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You have this immense curiosity,

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this stubbornness,

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this sort of resolute will
that you will go forward

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no matter what other people say.

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JC: I love that. Thank you, Sara.

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(Applause)