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  • 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 [sun] 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's conception 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 downloading 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."

  • (Laughter)

  • 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 our 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.

  • Gliese 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,

  • but 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.

  • And 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.

  • And under that wouldn't be rock,

  • but a form of high-pressure ice,

  • like ice IX.

  • So out of all these planets out there,

  • and the variety is just simply astonishing,

  • we mostly want to find the planets that are Goldilocks 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 assess the greenhouse gases

  • 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 Spock 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 very narrow, some are wide,

  • some are shaded at the edges.

  • And this is actually 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 field of its own.

  • So when it comes to other planets, other Earths,

  • in the future when we can observe them,

  • what kind of gases would we 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 gases in other planet atmospheres,

  • gases 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 every day,

  • I receive an email or emails

  • from someone with a crazy theory about physics of gravity

  • or cosmology or some such.

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

  • (Laughter)

  • Well, I had my own crazy theory.

  • But, who does the MIT professor go to?

  • Well, I emailed a Nobel Laureate in Physiology or 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, methyl chloride --

  • so many gases.

  • 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 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 gases.

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

  • on which types of exoplanets,

  • which gases could be attributed to life.

  • And so when it comes time when we find gases

  • in exoplanet atmospheres

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

  • by intelligent aliens or by trees,

  • or a swamp,

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

  • 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?

  • There are 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,