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Anjali Tripathi: Why Earth may someday look like Mars
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Every minute, 400 pounds of hydrogen and almost 7 pounds of helium escape from Earth's atmosphere into outer space. Astrophysicist Anjali Tripathi studies the phenomenon of atmospheric escape, and in this fascinating and accessible talk, she considers how this process might one day (a few billion years from now) turn our blue planet red.
Anjali Tripathi - Astrophysicist
Anjali Tripathi explores planets to uncover the processes that make and destroy them. Full bio
Anjali Tripathi explores planets to uncover the processes that make and destroy them. Full bio
Double-click the English transcript below to play the video.
00:12
So when you look out
at the stars at night,
at the stars at night,
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it's amazing what you can see.
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It's beautiful.
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But what's more amazing
is what you can't see,
is what you can't see,
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because what we know now
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is that around every star
or almost every star,
or almost every star,
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there's a planet,
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or probably a few.
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So what this picture isn't showing you
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are all the planets that we know about
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out there in space.
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But when we think about planets,
we tend to think of faraway things
we tend to think of faraway things
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that are very different from our own.
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But here we are on a planet,
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and there are so many things
that are amazing about Earth
that are amazing about Earth
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that we're searching far and wide
to find things that are like that.
to find things that are like that.
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And when we're searching,
we're finding amazing things.
we're finding amazing things.
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But I want to tell you
about an amazing thing here on Earth.
about an amazing thing here on Earth.
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And that is that every minute,
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400 pounds of hydrogen
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and almost seven pounds of helium
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escape from Earth into space.
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And this is gas that is going off
and never coming back.
and never coming back.
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So hydrogen, helium and many other things
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make up what's known
as the Earth's atmosphere.
as the Earth's atmosphere.
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The atmosphere is just these gases
that form a thin blue line
that form a thin blue line
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that's seen here from
the International Space Station,
the International Space Station,
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a photograph that some astronauts took.
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And this tenuous veneer around our planet
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is what allows life to flourish.
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It protects our planet
from too many impacts,
from too many impacts,
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from meteorites and the like.
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And it's such an amazing phenomenon
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that the fact that it's disappearing
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should frighten you,
at least a little bit.
at least a little bit.
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So this process is something that I study
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and it's called atmospheric escape.
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So atmospheric escape
is not specific to planet Earth.
is not specific to planet Earth.
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It's part of what it means
to be a planet, if you ask me,
to be a planet, if you ask me,
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because planets, not just here on Earth
but throughout the universe,
but throughout the universe,
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can undergo atmospheric escape.
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And the way it happens actually tells us
about planets themselves.
about planets themselves.
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Because when you think
about the solar system,
about the solar system,
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you might think about this picture here.
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And you would say, well,
there are eight planets, maybe nine.
there are eight planets, maybe nine.
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So for those of you
who are stressed by this picture,
who are stressed by this picture,
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I will add somebody for you.
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(Laughter)
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Courtesy of New Horizons,
we're including Pluto.
we're including Pluto.
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And the thing here is,
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for the purposes of this talk
and atmospheric escape,
and atmospheric escape,
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Pluto is a planet in my mind,
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in the same way that planets
around other stars that we can't see
around other stars that we can't see
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are also planets.
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So fundamental characteristics of planets
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include the fact that they are bodies
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that are bound together by gravity.
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So it's a lot of material
just stuck together
just stuck together
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with this attractive force.
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And these bodies are so big
and have so much gravity.
and have so much gravity.
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That's why they're round.
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So when you look at all of these,
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including Pluto,
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they're round.
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So you can see that gravity
is really at play here.
is really at play here.
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But another fundamental
characteristic about planets
characteristic about planets
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is what you don't see here,
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and that's the star, the Sun,
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that all of the planets
in the solar system are orbiting around.
in the solar system are orbiting around.
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And that's fundamentally driving
atmospheric escape.
atmospheric escape.
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The reason that fundamentally stars
drive atmospheric escape from planets
drive atmospheric escape from planets
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is because stars offer planets
particles and light and heat
particles and light and heat
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that can cause the atmospheres to go away.
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So if you think of a hot-air balloon,
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or you look at this picture
of lanterns in Thailand at a festival,
of lanterns in Thailand at a festival,
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you can see that hot air
can propel gasses upward.
can propel gasses upward.
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And if you have enough energy and heating,
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which our Sun does,
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that gas, which is so light
and only bound by gravity,
and only bound by gravity,
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it can escape into space.
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And so this is what's actually
causing atmospheric escape
causing atmospheric escape
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here on Earth and also on other planets --
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that interplay
between heating from the star
between heating from the star
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and overcoming the force
of gravity on the planet.
of gravity on the planet.
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So I've told you that it happens
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at the rate of 400 pounds
a minute for hydrogen
a minute for hydrogen
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and almost seven pounds for helium.
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But what does that look like?
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Well, even in the '80s,
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we took pictures of the Earth
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in the ultraviolet
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using NASA's Dynamic Explorer spacecraft.
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So these two images of the Earth
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show you what that glow
of escaping hydrogen looks like,
of escaping hydrogen looks like,
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shown in red.
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And you can also see other features
like oxygen and nitrogen
like oxygen and nitrogen
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in that white glimmer
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in the circle showing you the auroras
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and also some wisps around the tropics.
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So these are pictures
that conclusively show us
that conclusively show us
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that our atmosphere isn't just
tightly bound to us here on Earth
tightly bound to us here on Earth
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but it's actually
reaching out far into space,
reaching out far into space,
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and at an alarming rate, I might add.
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But the Earth is not alone
in undergoing atmospheric escape.
in undergoing atmospheric escape.
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Mars, our nearest neighbor,
is much smaller than Earth,
is much smaller than Earth,
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so it has much less gravity
with which to hold on to its atmosphere.
with which to hold on to its atmosphere.
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And so even though Mars has an atmosphere,
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we can see it's much thinner
than the Earth's.
than the Earth's.
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Just look at the surface.
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You see craters indicating
that it didn't have an atmosphere
that it didn't have an atmosphere
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that could stop those impacts.
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Also, we see that it's the "red planet,"
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and atmospheric escape plays a role
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in Mars being red.
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That's because we think
Mars used to have a wetter past,
Mars used to have a wetter past,
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and when water had enough energy,
it broke up into hydrogen and oxygen,
it broke up into hydrogen and oxygen,
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and hydrogen being so light,
it escaped into space,
it escaped into space,
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and the oxygen that was left
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oxidized or rusted the ground,
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making that familiar
rusty red color that we see.
rusty red color that we see.
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So it's fine to look at pictures of Mars
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and say that atmospheric escape
probably happened,
probably happened,
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but NASA has a probe that's currently
at Mars called the MAVEN satellite,
at Mars called the MAVEN satellite,
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and its actual job
is to study atmospheric escape.
is to study atmospheric escape.
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It's the Mars Atmosphere
and Volatile Evolution spacecraft.
and Volatile Evolution spacecraft.
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And results from it have already
shown pictures very similar
shown pictures very similar
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to what you've seen here on Earth.
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We've long known that Mars
was losing its atmosphere,
was losing its atmosphere,
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but we have some stunning pictures.
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Here, for example,
you can see in the red circle
you can see in the red circle
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is the size of Mars,
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and in blue you can see the hydrogen
escaping away from the planet.
escaping away from the planet.
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So it's reaching out more than 10 times
the size of the planet,
the size of the planet,
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far enough away that it's
no longer bound to that planet.
no longer bound to that planet.
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It's escaping off into space.
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And this helps us confirm ideas,
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like why Mars is red,
from that lost hydrogen.
from that lost hydrogen.
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But hydrogen isn't
the only gas that's lost.
the only gas that's lost.
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I mentioned helium on Earth
and some oxygen and nitrogen,
and some oxygen and nitrogen,
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and from MAVEN we can also look
at the oxygen being lost from Mars.
at the oxygen being lost from Mars.
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And you can see
that because oxygen is heavier,
that because oxygen is heavier,
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it can't get as far as the hydrogen,
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but it's still escaping
away from the planet.
away from the planet.
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You don't see it all confined
into that red circle.
into that red circle.
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So the fact that we not only see
atmospheric escape on our own planet
atmospheric escape on our own planet
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but we can study it elsewhere
and send spacecraft
and send spacecraft
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allows us to learn
about the past of planets
about the past of planets
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but also about planets in general
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and Earth's future.
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So one way we actually
can learn about the future
can learn about the future
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is by planets so far away
that we can't see.
that we can't see.
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And I should just note though,
before I go on to that,
before I go on to that,
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I'm not going to show you
photos like this of Pluto,
photos like this of Pluto,
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which might be disappointing,
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but that's because we don't have them yet.
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But the New Horizons mission
is currently studying atmospheric escape
is currently studying atmospheric escape
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being lost from the planet.
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So stay tuned and look out for that.
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But the planets
that I did want to talk about
that I did want to talk about
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are known as transiting exoplanets.
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So any planet orbiting a star
that's not our Sun
that's not our Sun
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is called an exoplanet,
or extrasolar planet.
or extrasolar planet.
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And these planets that we call transiting
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have the special feature
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that if you look
at that star in the middle,
at that star in the middle,
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you'll see that actually it's blinking.
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And the reason that it's blinking
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is because there are planets
that are going past it all the time,
that are going past it all the time,
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and it's at special orientation
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where the planets are blocking
the light from the star
the light from the star
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that allows us to see that light blinking.
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And by surveying the stars
in the night sky
in the night sky
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for this blinking motion,
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we are able to find planets.
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This is how we've now been able
to detect over 5,000 planets
to detect over 5,000 planets
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in our own Milky Way,
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and we know there are
many more out there, like I mentioned.
many more out there, like I mentioned.
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So when we look at the light
from these stars,
from these stars,
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what we see, like I said,
is not the planet itself,
is not the planet itself,
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but you actually see
a dimming of the light
a dimming of the light
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that we can record in time.
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So the light drops as the planet
decreases in front of the star,
decreases in front of the star,
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and that's that blinking
that you saw before.
that you saw before.
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So not only do we detect the planets
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but we can look at this light
in different wavelengths.
in different wavelengths.
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So I mentioned looking at the Earth
and Mars in ultraviolet light.
and Mars in ultraviolet light.
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If we look at transiting exoplanets
with the Hubble Space Telescope,
with the Hubble Space Telescope,
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we find that in the ultraviolet,
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you see much bigger blinking,
much less light from the star,
much less light from the star,
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when the planet is passing in front.
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And we think this is because you have
an extended atmosphere of hydrogen
an extended atmosphere of hydrogen
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all around the planet
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that's making it look puffier
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and thus blocking
more of the light that you see.
more of the light that you see.
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So using this technique,
we've actually been able to discover
we've actually been able to discover
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a few transiting exoplanets
that are undergoing atmospheric escape.
that are undergoing atmospheric escape.
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And these planets
can be called hot Jupiters,
can be called hot Jupiters,
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for some of the ones we've found.
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And that's because
they're gas planets like Jupiter,
they're gas planets like Jupiter,
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but they're so close to their star,
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about a hundred times closer than Jupiter.
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And because there's all this
lightweight gas that's ready to escape,
lightweight gas that's ready to escape,
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and all this heating from the star,
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you have completely catastrophic rates
of atmospheric escape.
of atmospheric escape.
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So unlike our 400 pounds per minute
of hydrogen being lost on Earth,
of hydrogen being lost on Earth,
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for these planets,
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you're losing 1.3 billion
pounds of hydrogen every minute.
pounds of hydrogen every minute.
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So you might think, well,
does this make the planet cease to exist?
does this make the planet cease to exist?
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And this is a question
that people wondered
that people wondered
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when they looked at our solar system,
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because planets
closer to the Sun are rocky,
closer to the Sun are rocky,
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and planets further away
are bigger and more gaseous.
are bigger and more gaseous.
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Could you have started
with something like Jupiter
with something like Jupiter
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that was actually close to the Sun,
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and get rid of all the gas in it?
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We now think that if you start
with something like a hot Jupiter,
with something like a hot Jupiter,
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you actually can't end up
with Mercury or the Earth.
with Mercury or the Earth.
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But if you started with something smaller,
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it's possible that enough gas
would have gotten away
would have gotten away
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that it would have
significantly impacted it
significantly impacted it
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and left you with something very different
than what you started with.
than what you started with.
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So all of this sounds sort of general,
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and we might think about the solar system,
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but what does this have to do
with us here on Earth?
with us here on Earth?
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Well, in the far future,
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the Sun is going to get brighter.
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And as that happens,
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the heating that we find from the Sun
is going to become very intense.
is going to become very intense.
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In the same way that you see
gas streaming off from a hot Jupiter,
gas streaming off from a hot Jupiter,
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gas is going to stream off from the Earth.
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And so what we can look forward to,
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or at least prepare for,
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is the fact that in the far future,
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the Earth is going to look more like Mars.
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Our hydrogen, from water
that is broken down,
that is broken down,
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is going to escape
into space more rapidly,
into space more rapidly,
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and we're going to be left
with this dry, reddish planet.
with this dry, reddish planet.
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So don't fear, it's not
for a few billion years,
for a few billion years,
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so there's some time to prepare.
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(Laughter)
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But I wanted you
to be aware of what's going on,
to be aware of what's going on,
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not just in the future,
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but atmospheric escape
is happening as we speak.
is happening as we speak.
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So there's a lot of amazing science
that you hear about happening in space
that you hear about happening in space
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and planets that are far away,
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and we are studying these planets
to learn about these worlds.
to learn about these worlds.
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But as we learn about Mars
or exoplanets like hot Jupiters,
or exoplanets like hot Jupiters,
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we find things like atmospheric escape
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that tell us a lot more
about our planet here on Earth.
about our planet here on Earth.
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So consider that the next time
you think that space is far away.
you think that space is far away.
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Thank you.
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(Applause)
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ABOUT THE SPEAKER
Anjali Tripathi - AstrophysicistAnjali Tripathi explores planets to uncover the processes that make and destroy them.
Why you should listen
Even though Anjali Tripathi worked on NASA's Mars rovers in high school, the California native never expected to become an astronomer. Unlike the earthquakes she researched early on, astronomy seemed unconnected from daily life. As she has since discovered, exploring distant planets has a lot to do with life itself -- including the fate of the air we breathe. Using some of the most powerful telescopes and supercomputers, Tripathi studies how seemingly permanent planets change over time. She has pioneered the characterization of planet-forming environments and developed computer simulations to trace the 3D structure of planet atmospheres that are shrinking due to evaporation.
A natural teacher, Tripathi makes complex science concepts relevant and easy to understand. She believes that everyone can understand science -- even rocket science. She has partnered with the Smithsonian, Teach for America and others to increase scientific literacy and spread enthusiasm for the subject. Her engaging and humorous talks feature real world connections and unusual props, including a fully functioning Mars Pathfinder rover or full-size solar car.
Tripathi earned degrees in physics and astronomy from M.I.T., the University of Cambridge and Harvard University. Recognized as a promising American leader with a commitment to public service, Tripathi is a 2016-17 White House Fellow.
Anjali Tripathi | Speaker | TED.com