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  • I'd like to take you on the epic quest of the Rosetta spacecraft.

  • To escort and land the probe on a comet,

  • this has been my passion for the past two years.

  • In order to do that,

  • I need to explain to you something about the origin of the solar system.

  • When we go back four and a half billion years,

  • there was a cloud of gas and dust.

  • In the center of this cloud, our sun formed and ignited.

  • Along with that, what we now know as planets, comets and asteroids formed.

  • What then happened, according to theory,

  • is that when the Earth had cooled down a bit after its formation,

  • comets massively impacted the Earth and delivered water to Earth.

  • They probably also delivered complex organic material to Earth,

  • and that may have bootstrapped the emergence of life.

  • You can compare this to having to solve a 250-piece puzzle

  • and not a 2,000-piece puzzle.

  • Afterwards, the big planets like Jupiter and Saturn,

  • they were not in their place where they are now,

  • and they interacted gravitationally,

  • and they swept the whole interior of the solar system clean,

  • and what we now know as comets

  • ended up in something called the Kuiper Belt,

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

  • And sometimes these objects run into each other,

  • and they gravitationally deflect,

  • and then the gravity of Jupiter pulls them back into the solar system.

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

  • The important thing here to note is that in the meantime,

  • the four and a half billion years,

  • these comets have been sitting on the outside of the solar system,

  • and haven't changed --

  • deep, frozen versions of our solar system.

  • In the sky, they look like this.

  • We know them for their tails.

  • There are actually two tails.

  • One is a dust tail, which is blown away by the solar wind.

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

  • and they follow the magnetic field in the solar system.

  • There's the coma,

  • and then there is the nucleus, which here is too small to see,

  • and you have to remember that in the case of Rosetta,

  • the spacecraft is in that center pixel.

  • We are only 20, 30, 40 kilometers away from the comet.

  • So what's important to remember?

  • Comets contain the original material from which our solar system was formed,

  • so they're ideal to study the components

  • that were present at the time when Earth, and life, started.

  • Comets are also suspected

  • of having brought the elements which may have bootstrapped life.

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

  • which contained one cornerstone, which would be a mission to a comet.

  • In parallel, a small mission to a comet, what you see here, Giotto, was launched,

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

  • From the results of that mission, it became immediately clear

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

  • And thus, the Rosetta mission was approved in 1993,

  • and originally it was supposed to be launched in 2003,

  • but a problem arose with an Ariane rocket.

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

  • had already made 1,000 Delft Blue plates

  • with the name of the wrong comets.

  • So I've never had to buy any china since. That's the positive part.

  • (Laughter)

  • Once the whole problem was solved,

  • we left Earth in 2004

  • to the newly selected comet, Churyumov-Gerasimenko.

  • This comet had to be specially selected

  • because A, you have to be able to get to it,

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

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

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

  • and it got close enough to the sun to start changing.

  • So it's a very fresh comet.

  • Rosetta made a few historic firsts.

  • It's the first satellite to orbit a comet,

  • and to escort it throughout its whole tour through the solar system --

  • closest approach to the sun, as we will see in August,

  • and then away again to the exterior.

  • It's the first ever landing on a comet.

  • We actually orbit the comet using something which is not

  • normally done with spacecraft.

  • Normally, you look at the sky and you know where you point and where you are.

  • In this case, that's not enough.

  • We navigated by looking at landmarks on the comet.

  • We recognized features -- boulders, craters --

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

  • And, of course, it's the first satellite to go beyond the orbit of Jupiter

  • on solar cells.

  • Now, this sounds more heroic than it actually is,

  • because the technology to use radio isotope thermal generators

  • wasn't available in Europe at that time, so there was no choice.

  • But these solar arrays are big.

  • This is one wing, and these are not specially selected small people.

  • They're just like you and me.

  • (Laughter)

  • We have two of these wings, 65 square meters.

  • Now later on, of course, when we got to the comet,

  • you find out that 65 square meters of sail

  • close to a body which is outgassing is not always a very handy choice.

  • Now, how did we get to the comet?

  • Because we had to go there for the Rosetta scientific objectives

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

  • and also at a much higher velocity than we could achieve with fuel,

  • because we'd have to take six times as much fuel as the whole spacecraft weighed.

  • So what do you do?

  • You use gravitational flybys, slingshots,

  • where you pass by a planet at very low altitude,

  • a few thousand kilometers,

  • and then you get the velocity of that planet around the sun for free.

  • We did that a few times.

  • We did Earth, we did Mars, we did twice Earth again,

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

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

  • we couldn't actually save the spacecraft anymore,

  • so we went into hibernation.

  • Everything was switched off except for one clock.

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

  • You see that from the circle where we started,

  • the white line, actually you get more and more and more elliptical,

  • and then finally we approached the comet

  • in May 2014, and we had to start doing the rendezvous maneuvers.

  • On the way there, we flew by Earth and we took a few pictures to test our cameras.

  • This is the moon rising over Earth,

  • and this is what we now call a selfie,

  • which at that time, by the way, that word didn't exist. (Laughter)

  • It's at Mars. It was taken by the CIVA camera.

  • That's one of the cameras on the lander,

  • and it just looks under the solar arrays,

  • and you see the planet Mars and the solar array in the distance.

  • Now, when we got out of hibernation in January 2014,

  • we started arriving at a distance

  • of two million kilometers from the comet in May.

  • However, the velocity the spacecraft had was much too fast.

  • We were going 2,800 kilometers an hour faster than the comet, so we had to brake.

  • We had to do eight maneuvers,

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

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

  • and actually, the duration of that was seven hours,

  • and it used 218 kilos of fuel,

  • and those were seven nerve-wracking hours, because in 2007,

  • there was a leak in the system of the propulsion of Rosetta,

  • and we had to close off a branch,

  • so the system was actually operating at a pressure

  • which it was never designed or qualified for.

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

  • The true comet rotation period is 12 and a half hours,

  • so this is accelerated,

  • but you will understand that our flight dynamics engineers thought,

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

  • We had hoped for some kind of spud-like thing

  • where you could easily land.

  • But we had one hope: maybe it was smooth.

  • No. That didn't work either. (Laughter)

  • So at that point in time, it was clearly unavoidable:

  • we had to map this body in all the detail you could get,

  • because we had to find an area which is 500 meters in diameter and flat.

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

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

  • We used a technique called photoclinometry.

  • You use shadows thrown by the sun.

  • What you see here is a rock sitting on the surface of the comet,

  • and the sun shines from above.

  • From the shadow, we, with our brain,

  • can immediately determine roughly what the shape of that rock is.

  • You can program that in a computer,

  • you then cover the whole comet, and you can map the comet.

  • For that, we flew special trajectories starting in August.

  • First, a triangle of 100 kilometers on a side

  • at 100 kilometers' distance,

  • and we repeated the whole thing at 50 kilometers.

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

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

  • Now, this led to a selection of landing sites.

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

  • to actually finding the final landing site, was 60 days.

  • We didn't have more.

  • To give you an idea, the average Mars mission

  • takes hundreds of scientists for years to meet

  • about where shall we go?

  • We had 60 days, and that was it.

  • We finally selected the final landing site

  • and the commands were prepared for Rosetta to launch Philae.

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

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

  • The lander is then pushed out and moves towards the comet.

  • Rosetta had to turn around

  • to get its cameras to actually look at Philae while it was departing

  • and to be able to communicate with it.

  • Now, the landing duration of the whole trajectory was seven hours.

  • Now do a simple calculation:

  • if the velocity of Rosetta is off by one centimeter per second,

  • seven hours is 25,000 seconds.

  • That means 252 meters wrong on the comet.

  • So we had to know the velocity of Rosetta

  • much better than one centimeter per second,

  • and its location in space better than 100 meters

  • at 500 million kilometers from Earth.

  • That's no mean feat.

  • Let me quickly take you through some of the science and the instruments.

  • I won't bore you with all the details of all the instruments,

  • but it's got everything.

  • We can sniff gas, we can measure dust particles,

  • the shape of them, the composition,

  • there are magnetometers, everything.

  • This is one of the results from an instrument which measures gas density

  • at the position of Rosetta,

  • so it's gas which has left the comet.

  • The bottom graph is September of last year.

  • There is a long-term variation, which in itself is not surprising,

  • but you see the sharp peaks.

  • This is a comet day.

  • You can see the effect of the sun on the evaporation of gas

  • and the fact that the comet is rotating.

  • So there is one spot, apparently,

  • where there is a lot of stuff coming from,

  • it gets heated in the Sun, and then cools down on the back side.

  • And we can see the density variations of this.

  • These are the gases and the organic compounds

  • that we already have measured.

  • You will see it's an impressive list,

  • and there is much, much, much more to come,

  • because there are more measurements.

  • Actually, there is a conference going on in Houston at the moment

  • where many of these results are presented.

  • Also, we measured dust particles.

  • Now, for you, this will not look very impressive,

  • but the scientists were thrilled when they saw this.

  • Two dust particles:

  • the right one they call Boris, and they shot it with tantalum

  • in order to be able to analyze it.

  • Now, we found sodium and magnesium.

  • What this tells you is this is the concentration of these two materials

  • at the time the solar system was formed,

  • so we learned things about which materials were there

  • when the planet was made.

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

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

  • and this actually was the cover of Science magazine