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I'd like to take you on the epic quest
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.

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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.

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When we go back
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.

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Along with that, what we now know
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,

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comets massively impacted the Earth
and delivered water to Earth.

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They probably also delivered
complex organic material to Earth,

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and that may have bootstrapped
the emergence of life.

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You can compare this to having
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,

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they were not in their place
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,

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and what we now know as comets

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ended up in something
called the Kuiper Belt,

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which is a belt of objects
beyond the orbit of Neptune.

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And sometimes these objects
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.

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And they then become the comets
as we see them in the sky.

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The important thing here to note
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,

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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.

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The other one is an ion tail,
which is charged particles,

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and they follow the magnetic field
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,

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and you have to remember
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.

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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,

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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.

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Comets are also suspected

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of having brought the elements
which may have bootstrapped life.

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In 1983, ESA set up
its long-term Horizon 2000 program,

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which contained one cornerstone,
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,

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and in 1986, flew by the comet of Halley
with an armada of other spacecraft.

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From the results of that mission,
it became immediately clear

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that comets were ideal bodies to study
to understand our solar system.

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And thus, the Rosetta mission
was approved in 1993,

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and originally it was supposed
to be launched in 2003,

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but a problem arose
with an Ariane rocket.

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However, our P.R. department,
in its enthusiasm,

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had already made
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.

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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.

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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,

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and B, it shouldn't have been
in the solar system too long.

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This particular comet has been 
in the solar system since 1959.

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That's the first time
when it was deflected by Jupiter,

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and it got close enough
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 --

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closest approach to the sun,
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

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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.

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In this case, that's not enough.

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We navigated by looking
at landmarks on the comet.

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We recognized features --
boulders, craters --

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and that's how we know where we are
respective to the comet.

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And, of course, it's the first satellite
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,

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because the technology
to use radio isotope thermal generators

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wasn't available in Europe at that time,
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.

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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.

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Now later on, of course,
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.

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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

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very far away -- four times the distance
of the Earth to the sun --

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and also at a much higher velocity
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.

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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,

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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.

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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,

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and we also flew by two asteroids,
Lutetia and Steins.

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Then in 2011, we got so far from the sun
that if the spacecraft got into trouble,

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we couldn't actually
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.

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Here you see in white the trajectory,
and the way this works.

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You see that from
the circle where we started,

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the white line, actually you get
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.

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On the way there, we flew by Earth and we
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)

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It's at Mars. It was taken
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.

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Now, when we got out
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.

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However, the velocity
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.

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We had to do eight maneuvers,

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and you see here,
some of them were really big.

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We had to brake the first one
by a few hundred kilometers per hour,

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and actually, the duration of that
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,

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there was a leak in the system
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

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which it was never designed
or qualified for.

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Then we got in the vicinity of the comet,
and these were the first pictures we saw.

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The true comet rotation period
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,

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this is not going to be
an easy thing to land on.

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We had hoped for some kind
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:

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we had to map this body
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.

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Why 500 meters? That's the error
we have on landing the probe.

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So we went through this process,
and we mapped the comet.

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We used a technique
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,

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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.

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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.

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For that, we flew special trajectories
starting in August.

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First, a triangle
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.

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At that time, we had seen the comet
at all kinds of angles,

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and we could use this technique
to map the whole thing.

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Now, this led to a selection
of landing sites.

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This whole process we had to do,
to go from the mapping of the comet

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to actually finding
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

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takes hundreds of scientists
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.

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The way this works is that Rosetta
has to be at the right point in space,

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and aiming towards the comet,
because the lander is passive.

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The lander is then pushed out
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

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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.

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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,

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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,

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and its location in space
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.

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I won't bore you with all the details
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,

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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

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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.

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There is a long-term variation,
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

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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.

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And we can see
the density variations of this.

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These are the gases
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,

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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

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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,

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but the scientists were thrilled
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

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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

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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

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when the planet was made.

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Of course, one of the important
elements is the imaging.

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This is one of the cameras of Rosetta,
the OSIRIS camera,

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and this actually was the cover
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.

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Boulders, rocks -- if anything, it looks
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.

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Now we know these from Mars,
but this comet doesn't have an atmosphere,

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so it's a bit difficult to create
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.

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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.

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On the right-hand side,
if you carefully look,

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there are three jets coming out
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,

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and where the material
evaporates into space.

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There is a very intriguing crack
in the neck of the comet.

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You see it on the right-hand side.

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It's a kilometer long,
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.

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But much the same as Rosetta, and that is
because you want to compare

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what you find in space
with what you find on the comet.

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These are called
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.

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00:14:16,436 --> 00:14:20,244
On the top right, you see an image
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.

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Here, you see the whole sequence again,
but from a different perspective,

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and you see three blown-ups
from the bottom-left to the middle

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of the lander traveling
over the surface of the comet.

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Then, at the top, there is a before
and an after image of the landing.

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The only problem with the after image is,
there is no lander.

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But if you carefully look
at the right-hand side of this image,

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we saw the lander still there, 
but it had bounced.

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It had departed again.

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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.

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00:15:06,937 --> 00:15:09,510
That was discarded because
it was way too expensive.

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Now, we forgot, but the lander knew.

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00:15:11,784 --> 00:15:13,388
(Laughter)

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00:15:13,388 --> 00:15:15,895
During the first bounce,
in the magnetometers,

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you see here the data from them,
from the three axes, x, y and z.

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Halfway through, you see a red line.

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00:15:21,931 --> 00:15:23,765
At that red line, there is a change.

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What happened, apparently,
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,

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and the rotation velocity
of the lander changed.

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So we've been rather lucky

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that we are where we are.

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00:15:39,485 --> 00:15:43,154
This is one of
the iconic images of Rosetta.

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It's a man-made object,
a leg of the lander,

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standing on a comet.

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00:15:49,028 --> 00:15:54,159
This, for me, is one of the very best
images of space science I have ever seen.

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(Applause)

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00:15:59,340 --> 00:16:03,191
One of the things we still have to do
is to actually find the lander.

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The blue area here
is where we know it must be.

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00:16:06,887 --> 00:16:10,505
We haven't been able to find it yet,
but the search is continuing,

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as are our efforts to start getting
the lander to work again.

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We listen every day,

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and we hope that between now
and somewhere in April,

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the lander will wake up again.

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The findings of what
we found on the comet:

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This thing would float in water.

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It's half the density of water.

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00:16:28,875 --> 00:16:31,893
So it looks like
a very big rock, but it's not.

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00:16:31,893 --> 00:16:35,539
The activity increase we saw
in June, July, August last year

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was a four-fold activity increase.

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00:16:37,930 --> 00:16:39,673
By the time we will be at the sun,

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there will be 100 kilos
a second leaving this comet:

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00:16:44,246 --> 00:16:45,802
gas, dust, whatever.

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00:16:45,802 --> 00:16:48,333
That's 100 million kilos a day.

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00:16:49,603 --> 00:16:51,978
Then, finally, the landing day.

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I will never forget -- absolute madness,
250 TV crews in Germany.

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00:16:57,366 --> 00:16:59,385
The BBC was interviewing me,

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00:16:59,385 --> 00:17:02,357
and another TV crew
who was following me all day

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00:17:02,357 --> 00:17:04,493
were filming me being interviewed,

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00:17:04,493 --> 00:17:06,931
and it went on like that
for the whole day.

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00:17:06,931 --> 00:17:08,742
The Discovery Channel crew

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00:17:08,742 --> 00:17:11,064
actually caught me
when leaving the control room,

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00:17:11,064 --> 00:17:13,177
and they asked the right question,

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00:17:13,177 --> 00:17:16,802
and man, I got into tears,
and I still feel this.

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00:17:16,802 --> 00:17:18,485
For a month and a half,

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00:17:18,485 --> 00:17:21,319
I couldn't think about
landing day without crying,

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00:17:21,319 --> 00:17:24,034
and I still have the emotion in me.

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00:17:24,034 --> 00:17:26,983
With this image of the comet,
I would like to leave you.

335
00:17:26,983 --> 00:17:29,096
Thank you.

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00:17:29,096 --> 00:17:33,975
(Applause)