WEBVTT

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So I'm pretty sure that I'm not
the only one in this room

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who at some point have found myself

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you know, looking up towards the stars,

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and wondered, you know, are we it,

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or are there other living planets
out there, such as our own?

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I guess it is possible
that I'm then the only person

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who has obsessed enough
about that question

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to make it my career.

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But moving on.

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How do we get to this question?

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Well I would argue the first thing to do

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is to turn our eyes back down from the sky

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to our own planet, the Earth.

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And think about just how lucky
did the Earth have to be

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to be the living planet it is.

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Well, it had to be
at least somewhat lucky.

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Had we been sitting closer to the Sun

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or a bit further away

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any water that we have had
would have boiled off or frozen over.

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And I mean, it's not a given
that a planet has water on it.

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So had we been a dry planet

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there would not have been
a lot of life on it.

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And even if we had had all the water
that we have today,

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if that water had not been accompanied

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by the right kind of chemicals
to get life going,

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we would have a wet planet,
but just as dead.

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So with so many things that can go wrong,

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what are the chances that they go right?

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What are the chances that the planet forms

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with at least the basic ingredients needed

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to have an [unclear] of life happening?

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Well, let's explore that together.

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So if you're going to have
a living planet,

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the first thing you're going to need

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is a planet.

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(Laughter)

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But not any planet will do.

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You're probably going to need
a rather specific and Earth-like planet.

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A planet that is rocky,

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so you can have both oceans and land,

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and it's sitting neither too close
nor too far away from its star

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but at the just right temperature.

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And it's just right
for liquid water that is.

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So how many of these planets
do we have in our galaxy?

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Well, one of the great discoveries
of the past decades

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is that planets are incredibly common.

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Almost every star
has a planet around them.

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Some have many.

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And among these planets,

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on the order of a few percent
are Earth-like enough

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that we would consider them
potentially living planets.

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So having the right kind of planet
is actually not that difficult

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when we consider that there's
about 100 billion stars in our galaxy.

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So that gives you about a billion
potential living planets.

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But it's not enough to just be
at the right temperature

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or have the right overall composition.

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You also need the right chemicals.

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And what the second and important
ingredient to make a living planet is,

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I think it's pretty intuitive,

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it's water.

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After all, we did define our planet
as being potentially living

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if it had the right temperature
to keep water liquid.

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And I mean, here on Earth
life is water-based.

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But more generally,

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water is just really good
as a meeting place for chemicals.

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It is a very special liquid.

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So this is our second ingredient,
our second basic ingredient.

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Now the third ingredient

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I think is probably
a little bit more surprising.

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I mean, we are going to need
some organics in there, right,

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since we are thinking about organic life.

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But the organic molecule

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that seems to be at the center
of the chemical networks

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that can produce biomolecules
is hydrogen cyanide.

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So for those of you who know
what this molecule is like,

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you know it's something
that's good idea to stay away form.

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But it turns out

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that what's really, really bad
for advanced life forms

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such as yourselves,

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is really, really good
to get the chemistry started,

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the right kind of chemistry
that can lead to origins of life.

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So now we have our three
ingredients that we need,

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you know, the temperate planet,

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water and hydrogen cyanide.

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So how often do these three come together?

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How many temperate planets
are there out there

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that have water and hydrogen cyanide?

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Well, in an ideal world,

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we would now turn one of our telescopes

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towards one of these temperate planets

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and check for ourselves.

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Just, do these planets have water
and cyanides on them?

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Unfortunately, we don't yet
have large enough telescopes to do this.

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We can detect molecules
in the atmospheres of some planets.

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But these are large planets

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sitting often pretty close to their star,

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nothing like these, you know,
just right planets

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that we're talking about here,

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which are much smaller and further away.

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So we have to come up with another way.

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And the other way that we have
conceived of and then followed

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is to instead of looking
for these molecules

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in the planets when they exist,

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is to look for them in the material
that's forming new planets.

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So planets form in discs
of dust and gas around young stars.

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And these discs get their material

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from the interstellar medium.

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Turns out that the empty space
you see between stars

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when you are looking up towards them,
asking existential questions,

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is not as empty as it seems,

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but actually full of gas and dust,

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which can, you know,
come together in clouds

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then collapse to form these discs,
stars and planets.

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And one of the things we always see
when we do look at these clouds

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is water.

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You know, I think we have a tendency
to think about water

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as something that's,
you know, special to us.

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Water is one of the most abundant
molecules in the universe,

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including in these clouds,

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these star and planet-forming clouds.

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And not only that,

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water is also a pretty robust molecule,

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it's actually not that easy to destroy.

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So a lot of this water
that is in interstellar medium

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will survive the [unclear] dangers,
collapse, journey from clouds

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to disc, to planets.

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So water is alright.

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That second ingredient
is not going to be a problem.

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Most planets are going to form
with some access to water.

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So what about hydrogen cyanide?

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Well, we also see cyanides
and other similar organic molecules

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in these interstellar clouds.

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But here, we're less certain
about the molecules surviving,

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going from the cloud to the disc.

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They're just a bit more delicate,
a bit more fragile.

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So if we're going to know
that this hydrogen cyanide

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is sitting in the vicinity
of new planets forming,

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we'd really need to see it
in the disc itself,

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in these planet-forming discs.

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So about a decade ago,

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I started a program
to look for this hydrogen cyanide

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and other molecules
in these planet-forming discs.

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And this is what we found.

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So good news, in these six images,

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those bright pixels represent emission

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originating from hydrogen cyanide

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in planet-forming discs
hundreds of light years away

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that have made it to our telescope,

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onto the detector

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and then allowing us to see it like this.

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So the very good news

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is that these discs do indeed have
hydrogen cyanide in them.

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That last, more elusive ingredient.

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Now the bad news is that we don't know
where in the disc it is.

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If we look at these,

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I mean, no one can say
they are beautiful images,

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even at the time when we got them.

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You see the pixel size is pretty big

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and it's actually bigger
than these discs themselves.

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So each pixel here

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represents something that's much bigger
than our solar system.

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And that means

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that we don't know where in the disc
the hydrogen cyanide is coming from.

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And that's a problem,

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because these temperate planets,

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they can't access hydrogen
cyanide just anywhere,

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but it must be fairly close
to where they assemble

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for them to have access to it.

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So to bring this home,

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let's think about an analogous example.

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That is, of cypress growing
in the United States.

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So let's say hypothetically

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that you've returned from Europe

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where you have seen
beautiful Italian cypresses,

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and you want to understand, you know,

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does it make sense to import them
to the United States.

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Could you grow them here?

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So you talk to the cypress experts,

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they tell you that there is indeed

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a band of not-too-hot, not-too-cold
across the United States

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where you could grow them.

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And if you have a nice,
high-resolution map or image like this,

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it's quite easy to see
that this cypress strip

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overlaps with a lot of green
fertile land pixels.

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Even if I start degrading
this map quite a bit,

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making it lower and lower resolution,

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it's still possible to tell

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that there's going to be some fertile land
overlapping with this strip.

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But what about if the whole United States

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is incorporated into a single pixel?

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If the resolution is that low.

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What do you do now,

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how do you now tell whether you can grow
cypresses in the United States?

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Well the answer is you can't.

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I mean, there's definitely
some fertile land there,

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or you wouldn't have
that green tint to the pixel,

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but there's just no way of telling

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whether any of that green
is in the right place.

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And that is exactly the problem
we were facing

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with our single-pixel
images of these discs

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[unclear] hydrogen cyanide.

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So what we need is something analogous

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to those low-resolution maps
that I just showed you

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to be able to tell whether there's overlap

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between where the hydrogen cyanide is

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and where these planets
can access it as they are forming.

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So coming to the rescue a few years ago

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is this new, amazing,
beautiful telescope ALMA,

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the Atacama Large Millimeter
and submillimeter Array

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in northern Chile.

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So ALMA is amazing in many different ways,

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but the one that I'm going to focus on

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is that, as you can see,
I call this one telescope,

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but you can there are actually
many dishes in this image.

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And this is a telescope that consists
of 66 individual dishes

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that all work in unison.

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And that means that you have a telescope

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that is the size of the largest distance
that you can put these dishes

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away from one another.

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Which in ALMA's case are a few miles.

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So you have a more
than mile-sized telescope.

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And when you have such a big telescope,

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you can zoom in on really small things,

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including making maps of hydrogen cyanide

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in these planet-forming discs.

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So when ALMA came online a few years ago,

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that was one of the first things

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that I proposed that we use it for.

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And what does a map of hydrogen cyanide
look like in a disc?

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Is the hydrogen cyanide
at the right place?

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And the answer is that it is.

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So this is a map.

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You see the hydrogen cyanide emission
being spread out across the disc.

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First of all, it's almost everywhere,

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which is very good news.

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But you have a lot
of extra bright emission

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coming from close to the star
towards the center of the disc.

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And this is exactly
where we want to see it.

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This is close to where
these planets are forming.

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And this is not what we see
just towards one disc,

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here are three more examples.

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You can see they all show the same thing,

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lots of bright, hydrogen cyanide emission

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coming from close
to the center of the star.

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For full disclosure,
we don't always see this.

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There are discs where we see the opposite.

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Where there's actually a hole
in their emission towards the center.

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So this is the opposite
of what we want to see, right.

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This is not places
where we could research

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if there is any hydrogen cyanide around

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where these planets are forming.

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But in most cases,

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we just don't detect hydrogen cyanide,

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but we detect it in the right place.

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So what does all this mean?

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Well I told you in the beginning

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you know, that we have lots
of these temperate planets,

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maybe billion or so of them,

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that could have life develop on them

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if they have the right ingredients.

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And I've also shown that

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we think a lot of the time
the right ingredients are there, right,

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we have water, we have hydrogen cyanide,

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there will be other
organic molecules as well

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coming with the cyanides.

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This means that planets
with the most basic ingredients for life

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are likely to be incredibly
common in our galaxy.

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And if all it takes for life to develop

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is to have these basic
ingredients available,

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there should be a lot
of living planets out there.

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But that is of course a big if.

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And I would say the challenge
of the next decades,

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for both astronomy and chemistry,

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is to figure out just how often

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we go from having
a potentially living planet

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to having an actually living one.

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Thank you.

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(Applause)