WEBVTT

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I'm really glad to be here.

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I'm glad you're here,

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because that would be a little weird.

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I'm glad we're all here.

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And by "here," I don't mean here.

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Or here.

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But here.

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I mean Earth.

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And by "we," I don't mean
those of us in this auditorium,

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but life,

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all life on Earth --

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(Laughter)

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from complex to single-celled,

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from mold to mushrooms

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to flying bears.

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(Laughter)

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The interesting thing is,

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Earth is the only place
we know of that has life --

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8.7 million species.

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We've looked other places,

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maybe not as hard
as we should or we could,

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but we've looked and haven't found any;

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Earth is the only place
we know of with life.

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Is Earth special?

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This is a question I've wanted
to know the answer to

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since I was a small child,

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and I suspect 80 percent
of this auditorium

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has thought the same thing
and also wanted to know the answer.

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To understand whether
there are any planets --

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out there in our solar system or beyond --

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that can support life,

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the first step is to understand
what life here requires.

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It turns out, of all of those
8.7 million species,

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life only needs three things.

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On one side, all life
on Earth needs energy.

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Complex life like us derives
our energy from the sun,

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but life deep underground
can get its energy

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from things like chemical reactions.

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There are a number
of different energy sources

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available on all planets.

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On the other side,

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all life needs food or nourishment.

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And this seems like a tall order,
especially if you want a succulent tomato.

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(Laughter)

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However, all life on Earth
derives its nourishment

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from only six chemical elements,

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and these elements can be found
on any planetary body

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in our solar system.

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So that leaves the thing
in the middle as the tall pole,

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the thing that's hardest to achieve.

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Not moose, but water.

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(Laughter)

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Although moose would be pretty cool.

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(Laughter)

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And not frozen water, and not water
in a gaseous state, but liquid water.

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This is what life needs
to survive, all life.

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And many solar system bodies
don't have liquid water,

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and so we don't look there.

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Other solar system bodies
might have abundant liquid water,

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even more than Earth,

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but it's trapped beneath an icy shell,

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and so it's hard to access,
it's hard to get to,

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it's hard to even find out
if there's any life there.

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So that leaves a few bodies
that we should think about.

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So let's make the problem
simpler for ourselves.

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Let's think only about liquid water
on the surface of a planet.

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There are only three bodies
to think about in our solar system,

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with regard to liquid water
on the surface of a planet,

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and in order of distance from the sun,
it's: Venus, Earth and Mars.

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You want to have an atmosphere
for water to be liquid.

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You have to be very careful
with that atmosphere.

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You can't have too much atmosphere,
too thick or too warm an atmosphere,

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because then you end up
too hot like Venus,

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and you can't have liquid water.

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But if you have too little atmosphere
and it's too thin and too cold,

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you end up like Mars, too cold.

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So Venus is too hot, Mars is too cold,

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and Earth is just right.

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You can look at these images behind me
and you can see automatically

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where life can survive
in our solar system.

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It's a Goldilocks-type problem,

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and it's so simple
that a child could understand it.

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However,

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I'd like to remind you of two things

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from the Goldilocks story
that we may not think about so often

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but that I think are really relevant here.

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Number one:

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if Mama Bear's bowl is too cold

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when Goldilocks walks into the room,

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does that mean it's always been too cold?

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Or could it have been just right
at some other time?

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When Goldilocks walks into the room
determines the answer

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that we get in the story.

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And the same is true with planets.

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They're not static things. They change.

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They vary. They evolve.

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And atmospheres do the same.

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So let me give you an example.

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Here's one of my favorite
pictures of Mars.

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It's not the highest resolution image,
it's not the sexiest image,

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it's not the most recent image,

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but it's an image that shows riverbeds
cut into the surface of the planet;

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riverbeds carved by flowing, liquid water;

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riverbeds that take hundreds or thousands
or tens of thousands of years to form.

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This can't happen on Mars today.

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The atmosphere of Mars today
is too thin and too cold

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for water to be stable as a liquid.

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This one image tells you
that the atmosphere of Mars changed,

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and it changed in big ways.

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And it changed from a state
that we would define as habitable,

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because the three requirements
for life were present long ago.

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Where did that atmosphere go

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that allowed water
to be liquid at the surface?

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Well, one idea is it escaped
away to space.

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Atmospheric particles
got enough energy to break free

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from the gravity of the planet,

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escaping away to space, never to return.

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And this happens with all bodies
with atmospheres.

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Comets have tails

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that are incredibly visible reminders
of atmospheric escape.

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But Venus also has an atmosphere
that escapes with time,

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and Mars and Earth as well.

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It's just a matter of degree
and a matter of scale.

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So we'd like to figure out
how much escaped over time

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so we can explain this transition.

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How do atmospheres
get their energy for escape?

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How do particles get
enough energy to escape?

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There are two ways, if we're going
to reduce things a little bit.

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Number one, sunlight.

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Light emitted from the sun can be absorbed
by atmospheric particles

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and warm the particles.

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Yes, I'm dancing, but they --

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(Laughter)

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Oh my God, not even at my wedding.

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(Laughter)

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They get enough energy
to escape and break free

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from the gravity of the planet
just by warming.

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A second way they can get energy
is from the solar wind.

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These are particles, mass, material,
spit out from the surface of the sun,

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and they go screaming
through the solar system

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at 400 kilometers per second,

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sometimes faster during solar storms,

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and they go hurtling
through interplanetary space

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towards planets and their atmospheres,

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and they may provide energy

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for atmospheric particles
to escape as well.

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This is something that I'm interested in,

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because it relates to habitability.

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I mentioned that there were two things
about the Goldilocks story

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that I wanted to bring to your attention
and remind you about,

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and the second one
is a little bit more subtle.

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If Papa Bear's bowl is too hot,

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and Mama Bear's bowl is too cold,

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shouldn't Baby Bear's bowl be even colder

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if we're following the trend?

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This thing that you've accepted
your entire life,

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when you think about it a little bit more,
may not be so simple.

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And of course, distance of a planet
from the sun determines its temperature.

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This has to play into habitability.

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But maybe there are other things
we should be thinking about.

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Maybe it's the bowls themselves

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that are also helping to determine
the outcome in the story,

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what is just right.

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I could talk to you about a lot
of different characteristics

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of these three planets

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that may influence habitability,

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but for selfish reasons related
to my own research

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and the fact that I'm standing up here
holding the clicker and you're not --

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(Laughter)

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I would like to talk
for just a minute or two

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about magnetic fields.

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Earth has one; Venus and Mars do not.

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Magnetic fields are generated
in the deep interior of a planet

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by electrically conducting
churning fluid material

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that creates this big old magnetic field
that surrounds Earth.

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If you have a compass,
you know which way north is.

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Venus and Mars don't have that.

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If you have a compass on Venus and Mars,

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congratulations, you're lost.

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(Laughter)

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Does this influence habitability?

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Well, how might it?

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Many scientists think
that a magnetic field of a planet

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serves as a shield for the atmosphere,

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deflecting solar wind particles
around the planet

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in a bit of a force field-type effect

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having to do with electric charge
of those particles.

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I like to think of it instead
as a salad bar sneeze guard for planets.

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(Laughter)

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And yes, my colleagues
who watch this later will realize

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this is the first time in the history
of our community

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that the solar wind has been
equated with mucus.

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(Laughter)

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OK, so the effect, then, is that Earth
may have been protected

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for billions of years,

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because we've had a magnetic field.

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Atmosphere hasn't been able to escape.

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Mars, on the other hand,
has been unprotected

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because of its lack of magnetic field,

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and over billions of years,

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maybe enough atmosphere
has been stripped away

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to account for a transition
from a habitable planet

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to the planet that we see today.

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Other scientists think
that magnetic fields

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may act more like the sails on a ship,

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enabling the planet to interact
with more energy from the solar wind

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than the planet would have been able
to interact with by itself.

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The sails may gather energy
from the solar wind.

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The magnetic field may gather
energy from the solar wind

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that allows even more
atmospheric escape to happen.

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It's an idea that has to be tested,

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but the effect and how it works

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seems apparent.

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That's because we know

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energy from the solar wind
is being deposited into our atmosphere

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here on Earth.

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That energy is conducted
along magnetic field lines

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down into the polar regions,

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resulting in incredibly beautiful aurora.

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If you've ever experienced them,
it's magnificent.

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We know the energy is getting in.

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We're trying to measure
how many particles are getting out

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and if the magnetic field
is influencing this in any way.

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So I've posed a problem for you here,

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but I don't have a solution yet.

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We don't have a solution.

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But we're working on it.
How are we working on it?

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Well, we've sent spacecraft
to all three planets.

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Some of them are orbiting now,

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including the MAVEN spacecraft
which is currently orbiting Mars,

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which I'm involved with
and which is led here,

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out of the University of Colorado.

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It's designed to measure
atmospheric escape.

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We have similar measurements
from Venus and Earth.

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Once we have all our measurements,

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we can combine all these together,
and we can understand

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how all three planets interact
with their space environment,

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with the surroundings.

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And we can decide whether magnetic fields
are important for habitability

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or not.

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Once we have that answer,
why should you care?

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I mean, I care deeply ...

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And financially as well, but deeply.

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(Laughter)

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First of all, an answer to this question

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will teach us more
about these three planets,

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Venus, Earth and Mars,

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not only about how they interact
with their environment today,

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but how they were billions of years ago,

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whether they were habitable
long ago or not.

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It will teach us about atmospheres

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that surround us and that are close.

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But moreover, what we learn
from these planets

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can be applied to atmospheres everywhere,

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including planets that we're now
observing around other stars.

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For example, the Kepler spacecraft,

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which is built and controlled
here in Boulder,

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has been observing
a postage stamp-sized region of the sky

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for a couple years now,

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and it's found thousands of planets --

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in one postage stamp-sized
region of the sky

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that we don't think is any different
from any other part of the sky.

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We've gone, in 20 years,

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from knowing of zero planets
outside of our solar system,

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to now having so many,

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that we don't know
which ones to investigate first.

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Any lever will help.

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In fact, based on observations
that Kepler's taken

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and other similar observations,

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we now believe that,

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of the 200 billion stars
in the Milky Way galaxy alone,

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on average, every star
has at least one planet.

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In addition to that,

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estimates suggest there are somewhere
between 40 billion and 100 billion

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of those planets
that we would define as habitable

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in just our galaxy.

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We have the observations of those planets,

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but we just don't know
which ones are habitable yet.

00:12:19.159 --> 00:12:22.765
It's a little bit like
being trapped on a red spot --

00:12:22.789 --> 00:12:23.960
(Laughter)

00:12:23.984 --> 00:12:25.216
on a stage

00:12:26.178 --> 00:12:29.740
and knowing that there are
other worlds out there

00:12:31.042 --> 00:12:33.818
and desperately wanting to know
more about them,

00:12:35.174 --> 00:12:39.108
wanting to interrogate them and find out
if maybe just one or two of them

00:12:39.132 --> 00:12:40.742
are a little bit like you.

00:12:42.244 --> 00:12:44.803
You can't do that.
You can't go there, not yet.

00:12:44.827 --> 00:12:48.820
And so you have to use the tools
that you've developed around you

00:12:48.844 --> 00:12:50.139
for Venus, Earth and Mars,

00:12:50.163 --> 00:12:52.976
and you have to apply them
to these other situations,

00:12:53.000 --> 00:12:57.696
and hope that you're making
reasonable inferences from the data,

00:12:57.720 --> 00:13:00.838
and that you're going to be able
to determine the best candidates

00:13:00.862 --> 00:13:03.261
for habitable planets,
and those that are not.

00:13:04.139 --> 00:13:06.854
In the end, and for now, at least,

00:13:06.878 --> 00:13:09.665
this is our red spot, right here.

00:13:10.376 --> 00:13:13.712
This is the only planet
that we know of that's habitable,

00:13:13.736 --> 00:13:16.927
although very soon we may
come to know of more.

00:13:16.951 --> 00:13:19.687
But for now, this is
the only habitable planet,

00:13:19.711 --> 00:13:21.013
and this is our red spot.

00:13:21.976 --> 00:13:23.396
I'm really glad we're here.

00:13:24.507 --> 00:13:25.682
Thanks.

00:13:25.706 --> 00:13:28.937
(Applause)