TED2015
Fred Jansen: How to land on a comet
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As manager of the Rosetta mission, Fred Jansen was responsible for the successful 2014 landing of a probe on the comet known as 67P/Churyumov-Gerasimenko. In this fascinating and funny talk, Jansen reveals some of the intricate calculations that went into landing the Philae probe on a comet 500 million kilometers from Earth -- and shares some incredible photographs taken along the way.
Fred Jansen - Space explorer
As manager of the Rosetta mission, Fred Jansen is in charge of the project that could be instrumental in uncovering clues to the origins of life on Earth. Full bio
As manager of the Rosetta mission, Fred Jansen is in charge of the project that could be instrumental in uncovering clues to the origins of life on Earth. Full bio
Double-click the English transcript below to play the video.
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I'd like to take you on the epic quest
of the Rosetta spacecraft.
of the Rosetta spacecraft.
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To escort and land the probe on a comet,
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this has been my passion
for the past two years.
for the past two years.
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In order to do that,
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I need to explain to you something
about the origin of the solar system.
about the origin of the solar system.
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When we go back
four and a half billion years,
four and a half billion years,
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there was a cloud of gas and dust.
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In the center of this cloud,
our sun formed and ignited.
our sun formed and ignited.
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Along with that, what we now know
as planets, comets and asteroids formed.
as planets, comets and asteroids formed.
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What then happened, according to theory,
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is that when the Earth had cooled down
a bit after its formation,
a bit after its formation,
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comets massively impacted the Earth
and delivered water to Earth.
and delivered water to Earth.
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They probably also delivered
complex organic material to Earth,
complex organic material to Earth,
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and that may have bootstrapped
the emergence of life.
the emergence of life.
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You can compare this to having
to solve a 250-piece puzzle
to solve a 250-piece puzzle
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and not a 2,000-piece puzzle.
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Afterwards, the big planets
like Jupiter and Saturn,
like Jupiter and Saturn,
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they were not in their place
where they are now,
where they are now,
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and they interacted gravitationally,
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and they swept the whole interior
of the solar system clean,
of the solar system clean,
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and what we now know as comets
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ended up in something
called the Kuiper Belt,
called the Kuiper Belt,
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which is a belt of objects
beyond the orbit of Neptune.
beyond the orbit of Neptune.
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And sometimes these objects
run into each other,
run into each other,
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and they gravitationally deflect,
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and then the gravity of Jupiter
pulls them back into the solar system.
pulls them back into the solar system.
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And they then become the comets
as we see them in the sky.
as we see them in the sky.
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The important thing here to note
is that in the meantime,
is that in the meantime,
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the four and a half billion years,
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these comets have been sitting
on the outside of the solar system,
on the outside of the solar system,
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and haven't changed --
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deep, frozen versions of our solar system.
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In the sky, they look like this.
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We know them for their tails.
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There are actually two tails.
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One is a dust tail,
which is blown away by the solar wind.
which is blown away by the solar wind.
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The other one is an ion tail,
which is charged particles,
which is charged particles,
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and they follow the magnetic field
in the solar system.
in the solar system.
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There's the coma,
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and then there is the nucleus,
which here is too small to see,
which here is too small to see,
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and you have to remember
that in the case of Rosetta,
that in the case of Rosetta,
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the spacecraft is in that center pixel.
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We are only 20, 30, 40 kilometers
away from the comet.
away from the comet.
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So what's important to remember?
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Comets contain the original material
from which our solar system was formed,
from which our solar system was formed,
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so they're ideal to study the components
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that were present at the time
when Earth, and life, started.
when Earth, and life, started.
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Comets are also suspected
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of having brought the elements
which may have bootstrapped life.
which may have bootstrapped life.
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In 1983, ESA set up
its long-term Horizon 2000 program,
its long-term Horizon 2000 program,
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which contained one cornerstone,
which would be a mission to a comet.
which would be a mission to a comet.
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In parallel, a small mission to a comet,
what you see here, Giotto, was launched,
what you see here, Giotto, was launched,
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and in 1986, flew by the comet of Halley
with an armada of other spacecraft.
with an armada of other spacecraft.
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From the results of that mission,
it became immediately clear
it became immediately clear
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that comets were ideal bodies to study
to understand our solar system.
to understand our solar system.
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And thus, the Rosetta mission
was approved in 1993,
was approved in 1993,
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and originally it was supposed
to be launched in 2003,
to be launched in 2003,
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but a problem arose
with an Ariane rocket.
with an Ariane rocket.
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However, our P.R. department,
in its enthusiasm,
in its enthusiasm,
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had already made
1,000 Delft Blue plates
1,000 Delft Blue plates
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with the name of the wrong comets.
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So I've never had to buy any china since.
That's the positive part.
That's the positive part.
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(Laughter)
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Once the whole problem was solved,
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we left Earth in 2004
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to the newly selected comet,
Churyumov-Gerasimenko.
Churyumov-Gerasimenko.
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This comet had to be specially selected
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because A, you have to
be able to get to it,
be able to get to it,
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and B, it shouldn't have been
in the solar system too long.
in the solar system too long.
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This particular comet has been
in the solar system since 1959.
in the solar system since 1959.
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That's the first time
when it was deflected by Jupiter,
when it was deflected by Jupiter,
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and it got close enough
to the sun to start changing.
to the sun to start changing.
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So it's a very fresh comet.
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Rosetta made a few historic firsts.
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It's the first satellite to orbit a comet,
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and to escort it throughout
its whole tour through the solar system --
its whole tour through the solar system --
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closest approach to the sun,
as we will see in August,
as we will see in August,
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and then away again to the exterior.
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It's the first ever landing on a comet.
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We actually orbit the comet
using something which is not
using something which is not
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normally done with spacecraft.
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Normally, you look at the sky and you know
where you point and where you are.
where you point and where you are.
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In this case, that's not enough.
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We navigated by looking
at landmarks on the comet.
at landmarks on the comet.
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We recognized features --
boulders, craters --
boulders, craters --
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and that's how we know where we are
respective to the comet.
respective to the comet.
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And, of course, it's the first satellite
to go beyond the orbit of Jupiter
to go beyond the orbit of Jupiter
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on solar cells.
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Now, this sounds more heroic
than it actually is,
than it actually is,
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because the technology
to use radio isotope thermal generators
to use radio isotope thermal generators
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wasn't available in Europe at that time,
so there was no choice.
so there was no choice.
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But these solar arrays are big.
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This is one wing, and these are not
specially selected small people.
specially selected small people.
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They're just like you and me.
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(Laughter)
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We have two of these wings,
65 square meters.
65 square meters.
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Now later on, of course,
when we got to the comet,
when we got to the comet,
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you find out that 65 square meters of sail
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close to a body which is outgassing
is not always a very handy choice.
is not always a very handy choice.
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Now, how did we get to the comet?
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Because we had to go there
for the Rosetta scientific objectives
for the Rosetta scientific objectives
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very far away -- four times the distance
of the Earth to the sun --
of the Earth to the sun --
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and also at a much higher velocity
than we could achieve with fuel,
than we could achieve with fuel,
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because we'd have to take six times as
much fuel as the whole spacecraft weighed.
much fuel as the whole spacecraft weighed.
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So what do you do?
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You use gravitational flybys, slingshots,
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where you pass by a planet
at very low altitude,
at very low altitude,
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a few thousand kilometers,
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and then you get the velocity
of that planet around the sun for free.
of that planet around the sun for free.
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We did that a few times.
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We did Earth, we did Mars,
we did twice Earth again,
we did twice Earth again,
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and we also flew by two asteroids,
Lutetia and Steins.
Lutetia and Steins.
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Then in 2011, we got so far from the sun
that if the spacecraft got into trouble,
that if the spacecraft got into trouble,
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we couldn't actually
save the spacecraft anymore,
save the spacecraft anymore,
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so we went into hibernation.
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Everything was switched off
except for one clock.
except for one clock.
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Here you see in white the trajectory,
and the way this works.
and the way this works.
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You see that from
the circle where we started,
the circle where we started,
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the white line, actually you get
more and more and more elliptical,
more and more and more elliptical,
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and then finally we approached the comet
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in May 2014, and we had to start
doing the rendezvous maneuvers.
doing the rendezvous maneuvers.
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On the way there, we flew by Earth and we
took a few pictures to test our cameras.
took a few pictures to test our cameras.
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This is the moon rising over Earth,
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and this is what we now call a selfie,
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which at that time, by the way,
that word didn't exist. (Laughter)
that word didn't exist. (Laughter)
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It's at Mars. It was taken
by the CIVA camera.
by the CIVA camera.
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That's one of the cameras on the lander,
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and it just looks under the solar arrays,
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and you see the planet Mars
and the solar array in the distance.
and the solar array in the distance.
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Now, when we got out
of hibernation in January 2014,
of hibernation in January 2014,
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we started arriving at a distance
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of two million kilometers
from the comet in May.
from the comet in May.
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However, the velocity
the spacecraft had was much too fast.
the spacecraft had was much too fast.
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We were going 2,800 kilometers an hour
faster than the comet, so we had to brake.
faster than the comet, so we had to brake.
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We had to do eight maneuvers,
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and you see here,
some of them were really big.
some of them were really big.
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We had to brake the first one
by a few hundred kilometers per hour,
by a few hundred kilometers per hour,
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and actually, the duration of that
was seven hours,
was seven hours,
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and it used 218 kilos of fuel,
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and those were seven nerve-wracking
hours, because in 2007,
hours, because in 2007,
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there was a leak in the system
of the propulsion of Rosetta,
of the propulsion of Rosetta,
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and we had to close off a branch,
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so the system was actually
operating at a pressure
operating at a pressure
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which it was never designed
or qualified for.
or qualified for.
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Then we got in the vicinity of the comet,
and these were the first pictures we saw.
and these were the first pictures we saw.
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The true comet rotation period
is 12 and a half hours,
is 12 and a half hours,
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so this is accelerated,
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but you will understand that
our flight dynamics engineers thought,
our flight dynamics engineers thought,
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this is not going to be
an easy thing to land on.
an easy thing to land on.
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We had hoped for some kind
of spud-like thing
of spud-like thing
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where you could easily land.
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But we had one hope: maybe it was smooth.
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No. That didn't work either. (Laughter)
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So at that point in time,
it was clearly unavoidable:
it was clearly unavoidable:
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we had to map this body
in all the detail you could get,
in all the detail you could get,
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because we had to find an area
which is 500 meters in diameter and flat.
which is 500 meters in diameter and flat.
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Why 500 meters? That's the error
we have on landing the probe.
we have on landing the probe.
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So we went through this process,
and we mapped the comet.
and we mapped the comet.
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We used a technique
called photoclinometry.
called photoclinometry.
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You use shadows thrown by the sun.
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What you see here is a rock
sitting on the surface of the comet,
sitting on the surface of the comet,
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and the sun shines from above.
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From the shadow, we, with our brain,
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can immediately determine
roughly what the shape of that rock is.
roughly what the shape of that rock is.
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You can program that in a computer,
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you then cover the whole comet,
and you can map the comet.
and you can map the comet.
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For that, we flew special trajectories
starting in August.
starting in August.
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First, a triangle
of 100 kilometers on a side
of 100 kilometers on a side
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at 100 kilometers' distance,
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and we repeated the whole
thing at 50 kilometers.
thing at 50 kilometers.
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At that time, we had seen the comet
at all kinds of angles,
at all kinds of angles,
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and we could use this technique
to map the whole thing.
to map the whole thing.
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Now, this led to a selection
of landing sites.
of landing sites.
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This whole process we had to do,
to go from the mapping of the comet
to go from the mapping of the comet
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to actually finding
the final landing site, was 60 days.
the final landing site, was 60 days.
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We didn't have more.
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To give you an idea,
the average Mars mission
the average Mars mission
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takes hundreds of scientists
for years to meet
for years to meet
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about where shall we go?
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We had 60 days, and that was it.
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We finally selected the final landing site
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and the commands were prepared
for Rosetta to launch Philae.
for Rosetta to launch Philae.
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The way this works is that Rosetta
has to be at the right point in space,
has to be at the right point in space,
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and aiming towards the comet,
because the lander is passive.
because the lander is passive.
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The lander is then pushed out
and moves towards the comet.
and moves towards the comet.
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Rosetta had to turn around
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to get its cameras to actually look
at Philae while it was departing
at Philae while it was departing
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and to be able to communicate with it.
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Now, the landing duration
of the whole trajectory was seven hours.
of the whole trajectory was seven hours.
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Now do a simple calculation:
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if the velocity of Rosetta is off
by one centimeter per second,
by one centimeter per second,
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seven hours is 25,000 seconds.
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That means 252 meters wrong on the comet.
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So we had to know the velocity of Rosetta
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much better than
one centimeter per second,
one centimeter per second,
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and its location in space
better than 100 meters
better than 100 meters
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at 500 million kilometers from Earth.
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That's no mean feat.
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Let me quickly take you through
some of the science and the instruments.
some of the science and the instruments.
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I won't bore you with all the details
of all the instruments,
of all the instruments,
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but it's got everything.
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We can sniff gas,
we can measure dust particles,
we can measure dust particles,
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the shape of them, the composition,
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there are magnetometers, everything.
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This is one of the results from
an instrument which measures gas density
an instrument which measures gas density
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at the position of Rosetta,
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so it's gas which has left the comet.
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The bottom graph
is September of last year.
is September of last year.
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There is a long-term variation,
which in itself is not surprising,
which in itself is not surprising,
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but you see the sharp peaks.
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This is a comet day.
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You can see the effect of the sun
on the evaporation of gas
on the evaporation of gas
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and the fact that the comet is rotating.
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So there is one spot, apparently,
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where there is a lot of stuff coming from,
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it gets heated in the Sun,
and then cools down on the back side.
and then cools down on the back side.
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And we can see
the density variations of this.
the density variations of this.
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These are the gases
and the organic compounds
and the organic compounds
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that we already have measured.
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You will see it's an impressive list,
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and there is much, much,
much more to come,
much more to come,
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because there are more measurements.
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Actually, there is a conference
going on in Houston at the moment
going on in Houston at the moment
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where many of these results are presented.
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Also, we measured dust particles.
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Now, for you, this will not
look very impressive,
look very impressive,
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but the scientists were thrilled
when they saw this.
when they saw this.
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Two dust particles:
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the right one they call Boris,
and they shot it with tantalum
and they shot it with tantalum
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in order to be able to analyze it.
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Now, we found sodium and magnesium.
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What this tells you is this is
the concentration of these two materials
the concentration of these two materials
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at the time the solar system was formed,
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so we learned things about
which materials were there
which materials were there
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when the planet was made.
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Of course, one of the important
elements is the imaging.
elements is the imaging.
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This is one of the cameras of Rosetta,
the OSIRIS camera,
the OSIRIS camera,
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and this actually was the cover
of Science magazine
of Science magazine
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on January 23 of this year.
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Nobody had expected
this body to look like this.
this body to look like this.
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Boulders, rocks -- if anything, it looks
more like the Half Dome in Yosemite
more like the Half Dome in Yosemite
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than anything else.
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We also saw things like this:
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dunes, and what look to be,
on the righthand side, wind-blown shadows.
on the righthand side, wind-blown shadows.
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Now we know these from Mars,
but this comet doesn't have an atmosphere,
but this comet doesn't have an atmosphere,
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so it's a bit difficult to create
a wind-blown shadow.
a wind-blown shadow.
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It may be local outgassing,
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stuff which goes up and comes back.
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We don't know, so there is
a lot to investigate.
a lot to investigate.
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Here, you see the same image twice.
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On the left-hand side,
you see in the middle a pit.
you see in the middle a pit.
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On the right-hand side,
if you carefully look,
if you carefully look,
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there are three jets coming out
of the bottom of that pit.
of the bottom of that pit.
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So this is the activity of the comet.
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Apparently, at the bottom of these pits
is where the active regions are,
is where the active regions are,
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and where the material
evaporates into space.
evaporates into space.
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There is a very intriguing crack
in the neck of the comet.
in the neck of the comet.
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You see it on the right-hand side.
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13:46
It's a kilometer long,
and it's two and a half meters wide.
and it's two and a half meters wide.
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Some people suggest that actually,
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when we get close to the sun,
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the comet may split in two,
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and then we'll have to choose,
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which comet do we go for?
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The lander -- again, lots of instruments,
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mostly comparable except for the things
which hammer in the ground and drill, etc.
which hammer in the ground and drill, etc.
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But much the same as Rosetta, and that is
because you want to compare
because you want to compare
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what you find in space
with what you find on the comet.
with what you find on the comet.
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These are called
ground truth measurements.
ground truth measurements.
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These are the landing descent images
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that were taken by the OSIRIS camera.
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You see the lander getting further
and further away from Rosetta.
and further away from Rosetta.
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On the top right, you see an image
taken at 60 meters by the lander,
taken at 60 meters by the lander,
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60 meters above the surface of the comet.
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The boulder there is some 10 meters.
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So this is one of the last images we took
before we landed on the comet.
before we landed on the comet.
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Here, you see the whole sequence again,
but from a different perspective,
but from a different perspective,
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and you see three blown-ups
from the bottom-left to the middle
from the bottom-left to the middle
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of the lander traveling
over the surface of the comet.
over the surface of the comet.
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14:54
Then, at the top, there is a before
and an after image of the landing.
and an after image of the landing.
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The only problem with the after image is,
there is no lander.
there is no lander.
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But if you carefully look
at the right-hand side of this image,
at the right-hand side of this image,
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we saw the lander still there,
but it had bounced.
but it had bounced.
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It had departed again.
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15:11
Now, on a bit of a comical note here
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is that originally Rosetta was designed
to have a lander which would bounce.
to have a lander which would bounce.
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That was discarded because
it was way too expensive.
it was way too expensive.
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Now, we forgot, but the lander knew.
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15:23
(Laughter)
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During the first bounce,
in the magnetometers,
in the magnetometers,
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you see here the data from them,
from the three axes, x, y and z.
from the three axes, x, y and z.
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Halfway through, you see a red line.
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At that red line, there is a change.
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What happened, apparently,
is during the first bounce,
is during the first bounce,
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somewhere, we hit the edge of a crater
with one of the legs of the lander,
with one of the legs of the lander,
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15:44
and the rotation velocity
of the lander changed.
of the lander changed.
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15:47
So we've been rather lucky
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15:49
that we are where we are.
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This is one of
the iconic images of Rosetta.
the iconic images of Rosetta.
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It's a man-made object,
a leg of the lander,
a leg of the lander,
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standing on a comet.
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16:01
This, for me, is one of the very best
images of space science I have ever seen.
images of space science I have ever seen.
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(Applause)
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One of the things we still have to do
is to actually find the lander.
is to actually find the lander.
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The blue area here
is where we know it must be.
is where we know it must be.
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We haven't been able to find it yet,
but the search is continuing,
but the search is continuing,
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as are our efforts to start getting
the lander to work again.
the lander to work again.
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16:26
We listen every day,
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16:28
and we hope that between now
and somewhere in April,
and somewhere in April,
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the lander will wake up again.
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16:32
The findings of what
we found on the comet:
we found on the comet:
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This thing would float in water.
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16:38
It's half the density of water.
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So it looks like
a very big rock, but it's not.
a very big rock, but it's not.
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16:43
The activity increase we saw
in June, July, August last year
in June, July, August last year
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was a four-fold activity increase.
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By the time we will be at the sun,
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there will be 100 kilos
a second leaving this comet:
a second leaving this comet:
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gas, dust, whatever.
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That's 100 million kilos a day.
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Then, finally, the landing day.
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I will never forget -- absolute madness,
250 TV crews in Germany.
250 TV crews in Germany.
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The BBC was interviewing me,
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2019
17:11
and another TV crew
who was following me all day
who was following me all day
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were filming me being interviewed,
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and it went on like that
for the whole day.
for the whole day.
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The Discovery Channel crew
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actually caught me
when leaving the control room,
when leaving the control room,
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and they asked the right question,
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and man, I got into tears,
and I still feel this.
and I still feel this.
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For a month and a half,
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I couldn't think about
landing day without crying,
landing day without crying,
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and I still have the emotion in me.
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With this image of the comet,
I would like to leave you.
I would like to leave you.
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Thank you.
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(Applause)
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ABOUT THE SPEAKER
Fred Jansen - Space explorerAs manager of the Rosetta mission, Fred Jansen is in charge of the project that could be instrumental in uncovering clues to the origins of life on Earth.
Why you should listen
Fred Jansen manages the European Space Agency’s Rosetta mission, which guided a probe into orbit around a comet and dispatched a lander to its surface -- both firsts in space exploration. Although the lander Philae could not accomplish its full mission before going into hibernation, the data it’s already gathered will immeasurably multiply our knowledge of comets and their contributions to the ingredients of life on Earth.
In addition to his work with the Rosetta Mission, Jansen oversees the ESA’s XMM-Newton, an orbiting x-ray space observatory delving into the most elusive secrets of the universe, including black holes and dark matter.
Fred Jansen | Speaker | TED.com