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  • So as an astronomer,

  • when I look at the sky with other people,

  • they always ask me,

  • "What is your favorite place in the universe?

  • What is your favorite galaxy?

  • What is your favorite planet?"

  • My answer is

  • Earth. That's right.

  • This is a very special place, even for an astronomer.

  • We look at a lot of places,

  • but there's only one that we know of in the whole universe

  • that we can live on.

  • It's an amazing planet,

  • there is an amazing number of things happening,

  • some of them, you are hearing about it today.

  • That's the only place in the universe

  • where we know that there is life,

  • so that makes it extremely special.

  • What I'm going to talk to you about

  • is this great adventure in astronomy that is happening

  • where we are actually actively looking

  • for other places like this.

  • It's impossible to imagine the number of possibilities,

  • what happens on those other planets

  • that can be habitable.

  • So that's what I'm going to tell you about.

  • So, the first thing we have to think of

  • is, well, what makes a planet habitable?

  • And, the easiest thing to do

  • is to look at our own solar system.

  • We have multiple examples.

  • The first thing we learn is that size matters.

  • We can't have a planet that's too small or too big.

  • If we look at a planet that is too small,

  • it doesn't have an atmosphere.

  • The moon, technically not a planet,

  • but a good example for this,

  • is too small,

  • it doesn't hold an atmosphere.

  • Jupiter - very, very big -

  • and it actually is mostly composed of gas,

  • it has no surface you can stand on.

  • The Earth is just right.

  • The second thing that we learned

  • is that the planet has to be

  • at the right distance from its star.

  • If the planet is too close to its star,

  • it's too hot.

  • That's the case for Venus.

  • Here I have a picture that was taken by a spacecraft

  • that landed on Venus,

  • and the surface, although it's rocky and quite familiar to us

  • compared to Earth,

  • it's really too hot.

  • At the opposite end, if a planet is too far from the star,

  • it is too cold.

  • That's the case for Mars.

  • So, we need to look for planets

  • that are at the right distance from their star

  • and also of the right size.

  • So, one other thing,

  • you know, you might think, "Oh, this is really hard

  • because the planet has to be just right.

  • It only happened once in our solar system."

  • But when you look at the sky at night,

  • and here's a video that I took actually from Hawaii,

  • a dark place where you can see a lot of stars,

  • the first thing you notice is that there are a lot of stars.

  • So, the odds are in our favor,

  • even if a small fraction of the stars

  • have habitable planets.

  • There are a lot of stars.

  • On a moonless night, in a dark site,

  • if you count the stars in the sky

  • and you count five stars per second,

  • it would take you 15 minutes to count

  • all of the stars in the sky.

  • That is a tiny fraction of the stars in our galaxy.

  • If you count all the stars in our galaxy,

  • and you also count at five stars per second,

  • it would take you more than 1,000 years

  • to count all the stars in our galaxy.

  • And then, if you manage

  • to count the galaxies in the universe,

  • if you count five galaxies per second,

  • it would take you also more than 1,000 years

  • to count all of the galaxies in the universe.

  • So the numbers are just astronomical,

  • there's a lot of opportunities for exoplanets.

  • There has to be a large number of exoplanets

  • along which there are,

  • on which there could be life.

  • So this is very exciting.

  • So let's imagine that maybe only 1 in 100 stars

  • has the right kind of planet,

  • and I think this is pessimistic.

  • If you could visit one of those planets per second,

  • it'll take you sixty years

  • to actually visit all of them in our galaxy alone.

  • That's, I think, one second is not enough to study them.

  • So, there's a few hundred of us in this room.

  • If we divided the task and each of us basically took

  • a couple of minutes to study each planet,

  • it would take us a life time to do this.

  • Meet back again and tell those amazing stories

  • of what we would have seen

  • in maybe some TED senior event.

  • So, why is it hard?

  • Why don't we have pictures of exoplanets with aliens on them?

  • Well, here's an example.

  • This is a picture that was taken

  • by the Cassinni spacecraft as it was orbiting Saturn.

  • It's actually behind Saturn,

  • so what you see is the sun

  • that is blocked by Saturn.

  • And if you look very, in detail,

  • if you have very sharp eyesight,

  • you will see all of us.

  • We're all on that picture.

  • Here is where we are.

  • Um, so that's what Earth starts to look like

  • when we look at it from far away.

  • Now, we have to do the same thing around other stars,

  • and the planet is very close to the star.

  • So this is zooming in to us.

  • All of us are on that little dot

  • at the time the picture was taken.

  • So, what I work on is inventing optics, tricks to actually do this,

  • to take images of planets around those other stars.

  • This is my easiest coronagraph.

  • We call this optic tricks, "coronagraph".

  • This is the easiest one I ever built.

  • I just put my thumb in front of the sun

  • and then you can see things around it.

  • That's what we're trying to do,

  • but we need to do it much better

  • than what I did in this picture.

  • And, there are two things we need to do:

  • we need a much better eye,

  • call them telescopes,

  • and we need more fancy, clever ways to do it

  • than putting a thumb.

  • So as an example, one of the projects I work on

  • is for the Subaru Telescope,

  • which you can see here in this picture.

  • It's a very large telescope,

  • so I replace my eye by a large telescope.

  • And, the other thing that we do

  • is the coronagraph is not just a stupid thumb,

  • it's this very complicated thing

  • that's shown in that picture

  • that I would love to have time to tell you about.

  • Just to give you a sense for size,

  • this arrow points to a door on the side of the telescope,

  • and if you have very sharp eyes,

  • you can see that there is a railing going around the telescope,

  • so it's a really big eye.

  • So, I think the most exciting thing for me

  • is actually to look at the night sky,

  • to see all these stars and wonder,

  • "Well, are there people on planets around those stars?"

  • Because there must be amazing things happening

  • around those stars that we don't know yet.

  • During your life time, we will start

  • to actually figure out those things.

  • And the most exciting thing for me

  • is to think about, maybe,

  • beings on those stars looking back at our star

  • and wondering the same thing.

  • So I think the future will be extremely exciting

  • because we are starting to figure out those things

  • and amazing range of possibilities

  • is, I think, even wider than our imagination.

  • Thank you.

So as an astronomer,

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A2 US TED-Ed planet count telescope galaxy star

【TED-Ed】The search for other Earth-like planets - Olivier Guyon

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    稲葉白兎 posted on 2015/01/25
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