3 moons and a planet that could have alien life | James Green

356,771 views ・ 2016-09-07

TED


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Is there life beyond Earth in our solar system?
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Wow, what a powerful question.
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You know, as a scientist --
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planetary scientist --
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we really didn't take that very seriously until recently.
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Carl Sagan always said,
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"It takes extraordinary evidence for extraordinary claims."
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And the claims of having life beyond Earth
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need to be definitive,
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they need to be loud
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and they need to be everywhere for us to be able to believe it.
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So how do we make this journey?
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What we decided to do
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is first look for those ingredients for life.
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The ingredients of life are:
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liquid water --
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we have to have a solvent,
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can't be ice, has to be liquid.
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We also have to have energy.
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We also have to have organic material --
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things that make us up,
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but also things that we need to consume.
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So we have to have these elements
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in environments for long periods of time
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for us to be able to be confident that life,
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in that moment when it starts,
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can spark and then grow and evolve.
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Well, I have to tell you that early in my career,
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when we looked at those three elements,
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I didn't believe that they were beyond Earth
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in any length of time and for any real quantity.
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Why? We look at the inner planets.
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Venus is way too hot -- it's got no water.
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Mars -- dry and arid.
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It's got no water.
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And beyond Mars,
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the water in the solar system is all frozen.
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But recent observations have changed all that.
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It's now turning our attention to the right places
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for us to take a deeper look
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and really start to answer our life question.
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So when we look out into the solar system,
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where are the possibilities?
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We're concentrating our attention on four locations.
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The planet Mars
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and then three moons of the outer planets:
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Titan, Europa and small Enceladus.
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So what about Mars?
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Let's go through the evidence.
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Well, Mars we thought was initially moon-like:
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full of craters, arid and a dead world.
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And so about 15 years ago,
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we started a series of missions to go to Mars
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and see if water existed on Mars in its past
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that changed its geology.
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We ought to be able to notice that.
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And indeed we started to be surprised right away.
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Our higher resolution images show deltas and river valleys and gulleys
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that were there in the past.
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And in fact,
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Curiosity --
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which has been roving on the surface now for about three years --
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has really shown us that it's sitting in an ancient river bed,
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where water flowed rapidly.
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And not for a little while,
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perhaps hundreds of millions of years.
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And if everything was there,
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including organics,
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perhaps life had started.
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Curiosity has also drilled in that red soil
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and brought up other material.
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And we were really excited when we saw that.
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Because it wasn't red Mars,
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it was gray material,
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it's gray Mars.
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We brought it into the rover,
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we tasted it,
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and guess what?
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We tasted organics --
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carbon, hydrogen, oxygen,
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nitrogen, phosphorus, sulfur --
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they were all there.
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So Mars in its past,
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with a lot of water,
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perhaps plenty of time,
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could have had life,
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could have had that spark,
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could have grown.
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And is that life still there?
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We don't know that.
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But a few years ago
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we started to look at a number of craters.
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During the summer,
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dark lines would appear down the sides of these craters.
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The more we looked,
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the more craters we saw,
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the more of these features.
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We now know more than a dozen of them.
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A few months ago the fairy tale came true.
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We announced to the world that we know what these streaks are.
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It's liquid water.
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These craters are weeping during the summer.
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Liquid water is flowing down these craters.
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So what are we going to do now --
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now that we see the water?
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Well, it tells us that Mars has all the ingredients necessary for life.
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In its past it had perhaps two-thirds of its northern hemisphere --
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there was an ocean.
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It has weeping water right now.
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Liquid water on its surface.
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It has organics.
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It has all the right conditions.
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So what are we going to do next?
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We're going to launch a series of missions
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to begin that search for life on Mars.
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And now it's more appealing than ever before.
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As we move out into the solar system,
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here's the tiny moon Enceladus.
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This is not in what we call the traditional habitable zone,
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this area around the sun.
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This is much further out.
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This object should be ice over a silicate core.
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But what did we find?
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Cassini was there since 2006,
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and after a couple years looked back after it flew by Enceladus
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and surprised us all.
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Enceladus is blasting sheets of water out into the solar system
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and sloshing back down onto the moon.
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What a fabulous environment.
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Cassini just a few months ago also flew through the plume,
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and it measured silicate particles.
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Where does the silica come from?
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It must come from the ocean floor.
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The tidal energy is generated by Saturn,
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pulling and squeezing this moon --
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is melting that ice,
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creating an ocean.
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But it's also doing that to the core.
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Now, the only thing that we can think of
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that does that here on Earth as an analogy ...
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are hydrothermal vents.
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Hydrothermal vents deep in our ocean were discovered in 1977.
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Oceanographers were completely surprised.
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And now there are thousands of these below the ocean.
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What do we find?
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The oceanographers, when they go and look at these hydrothermal vents,
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they're teeming with life,
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regardless of whether the water is acidic or alkaline --
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doesn't matter.
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So hydrothermal vents are a fabulous abode for life here on Earth.
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So what about Enceladus?
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Well, we believe because it has water
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and has had it for a significant period of time,
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and we believe it has hydrothermal vents
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with perhaps the right organic material,
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it is a place where life could exist.
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And not just microbial --
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maybe more complex because it's had time to evolve.
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Another moon, very similar,
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is Europa.
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Galileo visited Jupiter's system in 1996
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and made fabulous observations of Europa.
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Europa, we also know, has an under-the-ice crust ocean.
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Galileo mission told us that, but we never saw any plumes.
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But we didn't look for them.
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Hubble,
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just a couple years ago,
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observing Europa,
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saw plumes of water
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spraying from the cracks in the southern hemisphere,
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just exactly like Enceladus.
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These moons,
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which are not in what we call a traditional habitable zone,
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that are out in the solar system,
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have liquid water.
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And if there are organics there,
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there may be life.
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This is a fabulous set of discoveries
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because these moons have been in this environment like that
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for billions of years.
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Life started here on Earth, we believe, after about the first 500 million,
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and look where we are.
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These moons are fabulous moons.
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Another moon that we're looking at is Titan.
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Titan is a huge moon of Saturn.
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It perhaps is much larger than the planet Mercury.
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It has an extensive atmosphere.
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It's so extensive --
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and it's mostly nitrogen with a little methane and ethane --
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that you have to peer through it with radar.
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And on the surface, Cassini has found liquid.
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We see lakes ...
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actually almost the size of our Black Sea in some places.
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And this area is not liquid water;
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it's methane.
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If there's any place in the solar system where life is not like us,
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where the substitute of water is another solvent --
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and it could be methane --
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it could be Titan.
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Well, is there life beyond Earth in the solar system?
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We don't know yet,
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but we're hot on the pursuit.
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The data that we're receiving is really exciting
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and telling us --
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forcing us to think about this in new and exciting ways.
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I believe we're on the right track.
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That in the next 10 years, we will answer that question.
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And if we answer it,
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and it's positive,
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then life is everywhere in the solar system.
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Just think about that.
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We may not be alone.
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Thank you.
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(Applause)
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