0:00:00.717,0:00:05.514 I'd like to take you on the epic quest[br]of the Rosetta spacecraft. 0:00:05.514,0:00:09.540 To escort and land the probe on a comet, 0:00:09.540,0:00:12.730 this has been my passion[br]for the past two years. 0:00:13.450,0:00:14.545 In order to do that, 0:00:14.545,0:00:18.015 I need to explain to you something[br]about the origin of the solar system. 0:00:18.015,0:00:20.238 When we go back[br]four and a half billion years, 0:00:20.238,0:00:21.957 there was a cloud of gas and dust. 0:00:21.957,0:00:26.484 In the center of this cloud,[br]our sun formed and ignited. 0:00:26.484,0:00:32.195 Along with that, what we now know[br]as planets, comets and asteroids formed. 0:00:32.195,0:00:35.608 What then happened, according to theory, 0:00:35.608,0:00:39.625 is that when the Earth had cooled down[br]a bit after its formation, 0:00:39.625,0:00:44.396 comets massively impacted the Earth[br]and delivered water to Earth. 0:00:45.082,0:00:49.516 They probably also delivered[br]complex organic material to Earth, 0:00:49.516,0:00:52.906 and that may have bootstrapped[br]the emergence of life. 0:00:52.906,0:00:56.366 You can compare this to having[br]to solve a 250-piece puzzle 0:00:56.366,0:00:59.570 and not a 2,000-piece puzzle. 0:00:59.570,0:01:03.053 Afterwards, the big planets[br]like Jupiter and Saturn, 0:01:03.053,0:01:05.631 they were not in their place[br]where they are now, 0:01:05.631,0:01:08.278 and they interacted gravitationally, 0:01:08.278,0:01:11.830 and they swept the whole interior[br]of the solar system clean, 0:01:11.830,0:01:13.432 and what we now know as comets 0:01:13.432,0:01:15.545 ended up in something[br]called the Kuiper Belt, 0:01:15.545,0:01:19.213 which is a belt of objects[br]beyond the orbit of Neptune. 0:01:19.213,0:01:22.906 And sometimes these objects[br]run into each other, 0:01:22.906,0:01:25.971 and they gravitationally deflect, 0:01:25.971,0:01:30.428 and then the gravity of Jupiter[br]pulls them back into the solar system. 0:01:30.428,0:01:34.120 And they then become the comets[br]as we see them in the sky. 0:01:34.120,0:01:37.394 The important thing here to note[br]is that in the meantime, 0:01:37.394,0:01:39.693 the four and a half billion years, 0:01:39.693,0:01:42.875 these comets have been sitting[br]on the outside of the solar system, 0:01:42.875,0:01:44.290 and haven't changed -- 0:01:44.290,0:01:47.193 deep, frozen versions of our solar system. 0:01:47.193,0:01:49.282 In the sky, they look like this. 0:01:49.282,0:01:51.233 We know them for their tails. 0:01:51.233,0:01:52.904 There are actually two tails. 0:01:52.904,0:01:56.759 One is a dust tail,[br]which is blown away by the solar wind. 0:01:56.759,0:02:00.404 The other one is an ion tail,[br]which is charged particles, 0:02:00.404,0:02:03.143 and they follow the magnetic field[br]in the solar system. 0:02:03.143,0:02:04.292 There's the coma, 0:02:04.292,0:02:07.199 and then there is the nucleus,[br]which here is too small to see, 0:02:07.199,0:02:09.689 and you have to remember[br]that in the case of Rosetta, 0:02:09.689,0:02:11.866 the spacecraft is in that center pixel. 0:02:11.866,0:02:15.976 We are only 20, 30, 40 kilometers[br]away from the comet. 0:02:15.976,0:02:18.297 So what's important to remember? 0:02:18.297,0:02:23.166 Comets contain the original material[br]from which our solar system was formed, 0:02:23.166,0:02:25.526 so they're ideal to study the components 0:02:25.526,0:02:29.791 that were present at the time [br]when Earth, and life, started. 0:02:29.791,0:02:31.673 Comets are also suspected 0:02:31.673,0:02:35.944 of having brought the elements[br]which may have bootstrapped life. 0:02:35.944,0:02:40.309 In 1983, ESA set up[br]its long-term Horizon 2000 program, 0:02:40.309,0:02:44.233 which contained one cornerstone,[br]which would be a mission to a comet. 0:02:44.233,0:02:49.123 In parallel, a small mission to a comet,[br]what you see here, Giotto, was launched, 0:02:49.123,0:02:55.329 and in 1986, flew by the comet of Halley[br]with an armada of other spacecraft. 0:02:55.329,0:02:58.900 From the results of that mission,[br]it became immediately clear 0:02:58.900,0:03:04.087 that comets were ideal bodies to study[br]to understand our solar system. 0:03:04.087,0:03:08.599 And thus, the Rosetta mission[br]was approved in 1993, 0:03:08.599,0:03:12.234 and originally it was supposed[br]to be launched in 2003, 0:03:12.234,0:03:14.858 but a problem arose[br]with an Ariane rocket. 0:03:14.858,0:03:17.923 However, our P.R. department,[br]in its enthusiasm, 0:03:17.923,0:03:20.145 had already made[br]1,000 Delft Blue plates 0:03:20.145,0:03:22.535 with the name of the wrong comets. 0:03:22.535,0:03:26.102 So I've never had to buy any china since.[br]That's the positive part. 0:03:26.102,0:03:27.821 (Laughter) 0:03:27.821,0:03:29.701 Once the whole problem was solved, 0:03:29.701,0:03:32.882 we left Earth in 2004 0:03:32.882,0:03:35.970 to the newly selected comet,[br]Churyumov-Gerasimenko. 0:03:35.970,0:03:38.826 This comet had to be specially selected 0:03:38.826,0:03:41.480 because A, you have to[br]be able to get to it, 0:03:41.480,0:03:44.261 and B, it shouldn't have been[br]in the solar system too long. 0:03:44.261,0:03:48.208 This particular comet has been [br]in the solar system since 1959. 0:03:48.208,0:03:51.523 That's the first time[br]when it was deflected by Jupiter, 0:03:51.523,0:03:54.500 and it got close enough[br]to the sun to start changing. 0:03:54.500,0:03:56.151 So it's a very fresh comet. 0:03:56.611,0:03:59.502 Rosetta made a few historic firsts. 0:03:59.502,0:04:02.018 It's the first satellite to orbit a comet, 0:04:02.018,0:04:05.640 and to escort it throughout[br]its whole tour through the solar system -- 0:04:05.640,0:04:08.938 closest approach to the sun,[br]as we will see in August, 0:04:08.938,0:04:11.259 and then away again to the exterior. 0:04:11.259,0:04:13.860 It's the first ever landing on a comet. 0:04:13.860,0:04:17.552 We actually orbit the comet[br]using something which is not 0:04:17.552,0:04:19.001 normally done with spacecraft. 0:04:19.001,0:04:22.636 Normally, you look at the sky and you know[br]where you point and where you are. 0:04:22.636,0:04:24.772 In this case, that's not enough. 0:04:24.772,0:04:28.070 We navigated by looking[br]at landmarks on the comet. 0:04:28.070,0:04:30.545 We recognized features --[br]boulders, craters -- 0:04:30.545,0:04:34.562 and that's how we know where we are[br]respective to the comet. 0:04:34.562,0:04:39.091 And, of course, it's the first satellite[br]to go beyond the orbit of Jupiter 0:04:39.091,0:04:40.292 on solar cells. 0:04:40.292,0:04:42.619 Now, this sounds more heroic[br]than it actually is, 0:04:42.619,0:04:47.715 because the technology[br]to use radio isotope thermal generators 0:04:47.715,0:04:51.013 wasn't available in Europe at that time,[br]so there was no choice. 0:04:51.013,0:04:52.590 But these solar arrays are big. 0:04:52.590,0:04:55.865 This is one wing, and these are not[br]specially selected small people. 0:04:55.865,0:04:57.699 They're just like you and me. 0:04:57.699,0:05:00.090 (Laughter) 0:05:00.090,0:05:04.291 We have two of these wings,[br]65 square meters. 0:05:04.291,0:05:07.310 Now later on, of course,[br]when we got to the comet, 0:05:07.310,0:05:10.839 you find out that 65 square meters of sail 0:05:10.839,0:05:16.481 close to a body which is outgassing[br]is not always a very handy choice. 0:05:16.481,0:05:18.525 Now, how did we get to the comet? 0:05:18.525,0:05:22.193 Because we had to go there[br]for the Rosetta scientific objectives 0:05:22.193,0:05:26.001 very far away -- four times the distance[br]of the Earth to the sun -- 0:05:26.001,0:05:30.111 and also at a much higher velocity[br]than we could achieve with fuel, 0:05:30.111,0:05:34.430 because we'd have to take six times as[br]much fuel as the whole spacecraft weighed. 0:05:34.430,0:05:35.840 So what do you do? 0:05:35.840,0:05:39.323 You use gravitational flybys, slingshots, 0:05:39.323,0:05:42.690 where you pass by a planet[br]at very low altitude, 0:05:42.690,0:05:44.455 a few thousand kilometers, 0:05:44.455,0:05:49.168 and then you get the velocity[br]of that planet around the sun for free. 0:05:49.168,0:05:51.211 We did that a few times. 0:05:51.211,0:05:53.690 We did Earth, we did Mars,[br]we did twice Earth again, 0:05:53.690,0:05:57.658 and we also flew by two asteroids,[br]Lutetia and Steins. 0:05:58.318,0:06:02.983 Then in 2011, we got so far from the sun[br]that if the spacecraft got into trouble, 0:06:02.983,0:06:06.792 we couldn't actually[br]save the spacecraft anymore, 0:06:06.792,0:06:08.765 so we went into hibernation. 0:06:08.765,0:06:12.103 Everything was switched off[br]except for one clock. 0:06:12.103,0:06:15.614 Here you see in white the trajectory,[br]and the way this works. 0:06:15.614,0:06:18.057 You see that from[br]the circle where we started, 0:06:18.057,0:06:21.873 the white line, actually you get[br]more and more and more elliptical, 0:06:21.873,0:06:24.822 and then finally we approached the comet 0:06:24.822,0:06:29.187 in May 2014, and we had to start[br]doing the rendezvous maneuvers. 0:06:29.187,0:06:33.784 On the way there, we flew by Earth and we[br]took a few pictures to test our cameras. 0:06:33.784,0:06:35.962 This is the moon rising over Earth, 0:06:35.962,0:06:37.917 and this is what we now call a selfie, 0:06:37.917,0:06:41.609 which at that time, by the way,[br]that word didn't exist. (Laughter) 0:06:41.609,0:06:44.580 It's at Mars. It was taken[br]by the CIVA camera. 0:06:44.580,0:06:46.762 That's one of the cameras on the lander, 0:06:46.762,0:06:49.177 and it just looks under the solar arrays, 0:06:49.177,0:06:53.450 and you see the planet Mars[br]and the solar array in the distance. 0:06:53.450,0:06:59.118 Now, when we got out[br]of hibernation in January 2014, 0:06:59.118,0:07:00.903 we started arriving at a distance 0:07:00.903,0:07:03.736 of two million kilometers[br]from the comet in May. 0:07:03.736,0:07:07.845 However, the velocity[br]the spacecraft had was much too fast. 0:07:07.845,0:07:13.906 We were going 2,800 kilometers an hour[br]faster than the comet, so we had to brake. 0:07:13.906,0:07:15.763 We had to do eight maneuvers, 0:07:15.763,0:07:18.340 and you see here,[br]some of them were really big. 0:07:18.340,0:07:24.364 We had to brake the first one[br]by a few hundred kilometers per hour, 0:07:24.364,0:07:28.674 and actually, the duration of that[br]was seven hours, 0:07:28.674,0:07:31.622 and it used 218 kilos of fuel, 0:07:31.622,0:07:35.572 and those were seven nerve-wracking [br]hours, because in 2007, 0:07:35.572,0:07:38.762 there was a leak in the system[br]of the propulsion of Rosetta, 0:07:38.762,0:07:40.909 and we had to close off a branch, 0:07:40.909,0:07:43.487 so the system was actually[br]operating at a pressure 0:07:43.487,0:07:46.785 which it was never designed[br]or qualified for. 0:07:47.795,0:07:52.704 Then we got in the vicinity of the comet,[br]and these were the first pictures we saw. 0:07:52.704,0:07:55.277 The true comet rotation period[br]is 12 and a half hours, 0:07:55.277,0:07:57.366 so this is accelerated, 0:07:57.366,0:08:00.617 but you will understand that[br]our flight dynamics engineers thought, 0:08:00.617,0:08:04.471 this is not going to be[br]an easy thing to land on. 0:08:04.471,0:08:09.115 We had hoped for some kind[br]of spud-like thing 0:08:09.115,0:08:11.281 where you could easily land. 0:08:11.281,0:08:14.572 But we had one hope: maybe it was smooth. 0:08:14.572,0:08:18.310 No. That didn't work either. (Laughter) 0:08:18.310,0:08:21.003 So at that point in time,[br]it was clearly unavoidable: 0:08:21.003,0:08:24.534 we had to map this body[br]in all the detail you could get, 0:08:24.534,0:08:29.687 because we had to find an area[br]which is 500 meters in diameter and flat. 0:08:29.687,0:08:34.286 Why 500 meters? That's the error[br]we have on landing the probe. 0:08:34.286,0:08:37.467 So we went through this process,[br]and we mapped the comet. 0:08:37.467,0:08:39.834 We used a technique[br]called photoclinometry. 0:08:39.834,0:08:42.064 You use shadows thrown by the sun. 0:08:42.064,0:08:45.151 What you see here is a rock[br]sitting on the surface of the comet, 0:08:45.151,0:08:48.077 and the sun shines from above. 0:08:48.077,0:08:50.236 From the shadow, we, with our brain, 0:08:50.236,0:08:53.880 can immediately determine[br]roughly what the shape of that rock is. 0:08:53.880,0:08:55.922 You can program that in a computer, 0:08:55.922,0:09:00.176 you then cover the whole comet,[br]and you can map the comet. 0:09:00.176,0:09:03.856 For that, we flew special trajectories[br]starting in August. 0:09:03.856,0:09:06.765 First, a triangle[br]of 100 kilometers on a side 0:09:06.765,0:09:08.428 at 100 kilometers' distance, 0:09:08.428,0:09:11.432 and we repeated the whole [br]thing at 50 kilometers. 0:09:11.432,0:09:15.079 At that time, we had seen the comet[br]at all kinds of angles, 0:09:15.079,0:09:19.752 and we could use this technique[br]to map the whole thing. 0:09:19.752,0:09:23.019 Now, this led to a selection[br]of landing sites. 0:09:23.019,0:09:27.279 This whole process we had to do,[br]to go from the mapping of the comet 0:09:27.279,0:09:30.844 to actually finding[br]the final landing site, was 60 days. 0:09:30.844,0:09:32.230 We didn't have more. 0:09:32.230,0:09:34.350 To give you an idea,[br]the average Mars mission 0:09:34.350,0:09:38.134 takes hundreds of scientists[br]for years to meet 0:09:38.134,0:09:40.201 about where shall we go? 0:09:40.201,0:09:42.359 We had 60 days, and that was it. 0:09:42.359,0:09:45.402 We finally selected the final landing site 0:09:45.402,0:09:50.455 and the commands were prepared[br]for Rosetta to launch Philae. 0:09:50.455,0:09:54.830 The way this works is that Rosetta[br]has to be at the right point in space, 0:09:54.830,0:09:57.653 and aiming towards the comet,[br]because the lander is passive. 0:09:57.653,0:10:01.330 The lander is then pushed out[br]and moves towards the comet. 0:10:01.330,0:10:03.120 Rosetta had to turn around 0:10:03.120,0:10:07.677 to get its cameras to actually look[br]at Philae while it was departing 0:10:07.677,0:10:10.146 and to be able to communicate with it. 0:10:10.146,0:10:14.720 Now, the landing duration[br]of the whole trajectory was seven hours. 0:10:14.720,0:10:17.507 Now do a simple calculation: 0:10:17.507,0:10:21.546 if the velocity of Rosetta is off[br]by one centimeter per second, 0:10:21.546,0:10:25.888 seven hours is 25,000 seconds. 0:10:25.888,0:10:30.253 That means 252 meters wrong on the comet. 0:10:30.253,0:10:33.597 So we had to know the velocity of Rosetta 0:10:33.597,0:10:36.104 much better than[br]one centimeter per second, 0:10:36.104,0:10:40.168 and its location in space[br]better than 100 meters 0:10:40.168,0:10:43.372 at 500 million kilometers from Earth. 0:10:43.372,0:10:45.740 That's no mean feat. 0:10:45.740,0:10:50.129 Let me quickly take you through[br]some of the science and the instruments. 0:10:50.129,0:10:53.565 I won't bore you with all the details[br]of all the instruments, 0:10:53.565,0:10:55.214 but it's got everything. 0:10:55.214,0:10:58.348 We can sniff gas,[br]we can measure dust particles, 0:10:58.348,0:11:00.600 the shape of them, the composition, 0:11:00.600,0:11:03.108 there are magnetometers, everything. 0:11:03.108,0:11:06.707 This is one of the results from[br]an instrument which measures gas density 0:11:06.707,0:11:08.565 at the position of Rosetta, 0:11:08.565,0:11:10.794 so it's gas which has left the comet. 0:11:10.794,0:11:13.278 The bottom graph[br]is September of last year. 0:11:13.278,0:11:16.575 There is a long-term variation,[br]which in itself is not surprising, 0:11:16.575,0:11:18.456 but you see the sharp peaks. 0:11:18.456,0:11:20.546 This is a comet day. 0:11:20.546,0:11:24.656 You can see the effect of the sun[br]on the evaporation of gas 0:11:24.656,0:11:27.604 and the fact that the comet is rotating. 0:11:27.604,0:11:29.312 So there is one spot, apparently, 0:11:29.312,0:11:31.459 where there is a lot of stuff coming from, 0:11:31.459,0:11:34.756 it gets heated in the Sun,[br]and then cools down on the back side. 0:11:34.756,0:11:38.262 And we can see[br]the density variations of this. 0:11:38.262,0:11:42.395 These are the gases[br]and the organic compounds 0:11:42.395,0:11:44.090 that we already have measured. 0:11:44.090,0:11:45.878 You will see it's an impressive list, 0:11:45.878,0:11:48.362 and there is much, much,[br]much more to come, 0:11:48.362,0:11:50.308 because there are more measurements. 0:11:50.308,0:11:53.656 Actually, there is a conference[br]going on in Houston at the moment 0:11:53.656,0:11:56.117 where many of these results are presented. 0:11:56.827,0:11:58.448 Also, we measured dust particles. 0:11:58.448,0:12:01.250 Now, for you, this will not[br]look very impressive, 0:12:01.250,0:12:04.523 but the scientists were thrilled[br]when they saw this. 0:12:04.523,0:12:05.940 Two dust particles: 0:12:05.940,0:12:08.934 the right one they call Boris,[br]and they shot it with tantalum 0:12:08.934,0:12:11.048 in order to be able to analyze it. 0:12:11.048,0:12:13.439 Now, we found sodium and magnesium. 0:12:13.439,0:12:17.688 What this tells you is this is[br]the concentration of these two materials 0:12:17.688,0:12:20.404 at the time the solar system was formed, 0:12:20.404,0:12:23.771 so we learned things about[br]which materials were there 0:12:23.771,0:12:26.859 when the planet was made. 0:12:26.859,0:12:29.577 Of course, one of the important[br]elements is the imaging. 0:12:29.577,0:12:32.943 This is one of the cameras of Rosetta,[br]the OSIRIS camera, 0:12:32.943,0:12:35.938 and this actually was the cover[br]of Science magazine 0:12:35.938,0:12:38.608 on January 23 of this year. 0:12:38.608,0:12:42.046 Nobody had expected[br]this body to look like this. 0:12:42.046,0:12:45.644 Boulders, rocks -- if anything, it looks[br]more like the Half Dome in Yosemite 0:12:45.644,0:12:48.151 than anything else. 0:12:48.151,0:12:50.729 We also saw things like this: 0:12:50.729,0:12:55.651 dunes, and what look to be,[br]on the righthand side, wind-blown shadows. 0:12:55.651,0:12:59.575 Now we know these from Mars,[br]but this comet doesn't have an atmosphere, 0:12:59.575,0:13:02.454 so it's a bit difficult to create[br]a wind-blown shadow. 0:13:02.454,0:13:04.439 It may be local outgassing, 0:13:04.439,0:13:06.622 stuff which goes up and comes back. 0:13:06.622,0:13:09.803 We don't know, so there is[br]a lot to investigate. 0:13:09.803,0:13:11.893 Here, you see the same image twice. 0:13:11.893,0:13:14.410 On the left-hand side,[br]you see in the middle a pit. 0:13:14.410,0:13:16.627 On the right-hand side,[br]if you carefully look, 0:13:16.627,0:13:19.858 there are three jets coming out[br]of the bottom of that pit. 0:13:19.858,0:13:22.155 So this is the activity of the comet. 0:13:22.155,0:13:26.172 Apparently, at the bottom of these pits[br]is where the active regions are, 0:13:26.172,0:13:28.935 and where the material[br]evaporates into space. 0:13:28.935,0:13:32.545 There is a very intriguing crack[br]in the neck of the comet. 0:13:32.545,0:13:34.541 You see it on the right-hand side. 0:13:34.541,0:13:38.237 It's a kilometer long,[br]and it's two and a half meters wide. 0:13:38.237,0:13:40.483 Some people suggest that actually, 0:13:40.483,0:13:42.551 when we get close to the sun, 0:13:42.551,0:13:44.409 the comet may split in two, 0:13:44.409,0:13:46.089 and then we'll have to choose, 0:13:46.089,0:13:48.341 which comet do we go for? 0:13:48.341,0:13:51.514 The lander -- again, lots of instruments, 0:13:51.514,0:13:56.855 mostly comparable except for the things[br]which hammer in the ground and drill, etc. 0:13:56.855,0:14:00.732 But much the same as Rosetta, and that is[br]because you want to compare 0:14:00.732,0:14:04.238 what you find in space[br]with what you find on the comet. 0:14:04.238,0:14:06.931 These are called[br]ground truth measurements. 0:14:06.931,0:14:10.162 These are the landing descent images 0:14:10.162,0:14:12.210 that were taken by the OSIRIS camera. 0:14:12.210,0:14:16.436 You see the lander getting further[br]and further away from Rosetta. 0:14:16.436,0:14:20.244 On the top right, you see an image[br]taken at 60 meters by the lander, 0:14:20.244,0:14:23.100 60 meters above the surface of the comet. 0:14:23.100,0:14:25.514 The boulder there is some 10 meters. 0:14:25.514,0:14:30.228 So this is one of the last images we took[br]before we landed on the comet. 0:14:30.228,0:14:33.786 Here, you see the whole sequence again,[br]but from a different perspective, 0:14:33.786,0:14:37.971 and you see three blown-ups[br]from the bottom-left to the middle 0:14:37.971,0:14:42.156 of the lander traveling[br]over the surface of the comet. 0:14:42.156,0:14:46.342 Then, at the top, there is a before[br]and an after image of the landing. 0:14:46.342,0:14:50.269 The only problem with the after image is,[br]there is no lander. 0:14:50.269,0:14:53.540 But if you carefully look[br]at the right-hand side of this image, 0:14:53.540,0:14:57.569 we saw the lander still there, [br]but it had bounced. 0:14:57.569,0:14:59.230 It had departed again. 0:14:59.230,0:15:02.317 Now, on a bit of a comical note here 0:15:02.317,0:15:06.937 is that originally Rosetta was designed[br]to have a lander which would bounce. 0:15:06.937,0:15:09.510 That was discarded because[br]it was way too expensive. 0:15:09.510,0:15:11.784 Now, we forgot, but the lander knew. 0:15:11.784,0:15:13.388 (Laughter) 0:15:13.388,0:15:15.895 During the first bounce,[br]in the magnetometers, 0:15:15.895,0:15:19.725 you see here the data from them,[br]from the three axes, x, y and z. 0:15:19.725,0:15:21.931 Halfway through, you see a red line. 0:15:21.931,0:15:23.765 At that red line, there is a change. 0:15:23.765,0:15:27.690 What happened, apparently,[br]is during the first bounce, 0:15:27.690,0:15:32.416 somewhere, we hit the edge of a crater[br]with one of the legs of the lander, 0:15:32.416,0:15:35.236 and the rotation velocity[br]of the lander changed. 0:15:35.236,0:15:37.209 So we've been rather lucky 0:15:37.209,0:15:39.485 that we are where we are. 0:15:39.485,0:15:43.154 This is one of[br]the iconic images of Rosetta. 0:15:43.154,0:15:47.077 It's a man-made object,[br]a leg of the lander, 0:15:47.077,0:15:49.028 standing on a comet. 0:15:49.028,0:15:54.159 This, for me, is one of the very best[br]images of space science I have ever seen. 0:15:54.159,0:15:59.340 (Applause) 0:15:59.340,0:16:03.191 One of the things we still have to do[br]is to actually find the lander. 0:16:03.191,0:16:06.887 The blue area here[br]is where we know it must be. 0:16:06.887,0:16:10.505 We haven't been able to find it yet,[br]but the search is continuing, 0:16:10.505,0:16:14.270 as are our efforts to start getting[br]the lander to work again. 0:16:14.270,0:16:16.012 We listen every day, 0:16:16.012,0:16:18.570 and we hope that between now[br]and somewhere in April, 0:16:18.570,0:16:20.308 the lander will wake up again. 0:16:20.308,0:16:22.445 The findings of what[br]we found on the comet: 0:16:23.795,0:16:26.251 This thing would float in water. 0:16:26.251,0:16:28.875 It's half the density of water. 0:16:28.875,0:16:31.893 So it looks like[br]a very big rock, but it's not. 0:16:31.893,0:16:35.539 The activity increase we saw[br]in June, July, August last year 0:16:35.539,0:16:37.930 was a four-fold activity increase. 0:16:37.930,0:16:39.673 By the time we will be at the sun, 0:16:39.673,0:16:44.246 there will be 100 kilos[br]a second leaving this comet: 0:16:44.246,0:16:45.802 gas, dust, whatever. 0:16:45.802,0:16:48.333 That's 100 million kilos a day. 0:16:49.603,0:16:51.978 Then, finally, the landing day. 0:16:51.978,0:16:57.366 I will never forget -- absolute madness,[br]250 TV crews in Germany. 0:16:57.366,0:16:59.385 The BBC was interviewing me, 0:16:59.385,0:17:02.357 and another TV crew[br]who was following me all day 0:17:02.357,0:17:04.493 were filming me being interviewed, 0:17:04.493,0:17:06.931 and it went on like that[br]for the whole day. 0:17:06.931,0:17:08.742 The Discovery Channel crew 0:17:08.742,0:17:11.064 actually caught me[br]when leaving the control room, 0:17:11.064,0:17:13.177 and they asked the right question, 0:17:13.177,0:17:16.802 and man, I got into tears,[br]and I still feel this. 0:17:16.802,0:17:18.485 For a month and a half, 0:17:18.485,0:17:21.319 I couldn't think about[br]landing day without crying, 0:17:21.319,0:17:24.034 and I still have the emotion in me. 0:17:24.034,0:17:26.983 With this image of the comet,[br]I would like to leave you. 0:17:26.983,0:17:29.096 Thank you. 0:17:29.096,0:17:33.975 (Applause)