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So as an astronomer,
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when I look at the sky with other people,
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they always ask me,
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"What is your favorite place in the universe?
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What is your favorite galaxy?
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What is your favorite planet?"
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Earth. That's right.
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This is a very special place, even for an astronomer.
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We look at a lot of places,
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but there's only one that we know of in the whole universe
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that we can live on.
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It's an amazing planet,
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there is an amazing number of things happening,
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some of them, you are hearing about it today.
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That's the only place in the universe
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where we know that there is life,
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so that makes it extremely special.
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What I'm going to talk to you about
00:00:47
is this great adventure in astronomy that is happening
00:00:50
where we are actually actively looking
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for other places like this.
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It's impossible to imagine the number of possibilities,
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what happens on those other planets
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that can be habitable.
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So that's what I'm going to tell you about.
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So, the first thing we have to think of
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is, well, what makes a planet habitable?
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And, the easiest thing to do
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is to look at our own solar system.
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We have multiple examples.
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The first thing we learn is that size matters.
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We can't have a planet that's too small or too big.
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If we look at a planet that is too small,
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it doesn't have an atmosphere.
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The moon, technically not a planet,
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but a good example for this,
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it doesn't hold an atmosphere.
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Jupiter - very, very big -
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and it actually is mostly composed of gas,
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it has no surface you can stand on.
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The Earth is just right.
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The second thing that we learned
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is that the planet has to be
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at the right distance from its star.
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If the planet is too close to its star,
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That's the case for Venus.
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Here I have a picture that was taken by a spacecraft
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