0:00:02 > 0:00:03Yeah, three minutes to go.
0:00:05 > 0:00:09On Friday scientists and the world's media gathered to watch
0:00:09 > 0:00:13the end of one of the most ambitious space missions ever attempted.
0:00:14 > 0:00:17In a last daring manoeuvre, the Rosetta spacecraft would
0:00:17 > 0:00:19accelerate towards the surface of a comet.
0:00:21 > 0:00:24So we really feel the sense of,
0:00:24 > 0:00:27yeah, we're getting closer and closer.
0:00:27 > 0:00:30This final stage of the mission was designed to give us
0:00:30 > 0:00:33the most detailed pictures we've ever seen of a comet's nucleus.
0:00:33 > 0:00:36This must be data from very close to the comet.
0:00:36 > 0:00:39This is a few tens of metres now, isn't it?
0:00:39 > 0:00:44And give us a new insight into the origins of the solar system.
0:00:44 > 0:00:47But these pictures came at a price -
0:00:47 > 0:00:49the inevitable death of the spacecraft
0:00:49 > 0:00:52as it crashed into the comet's surface.
0:00:53 > 0:00:56Tonight on The Sky At Night special,
0:00:56 > 0:00:59we take you behind the scenes in mission control
0:00:59 > 0:01:03for the final triumph and tragedy of the Rosetta mission.
0:01:03 > 0:01:05And so this is the end of the Rosetta mission.
0:01:05 > 0:01:08- Thank you and goodbye.- Good man.
0:01:38 > 0:01:41Well, it's early Friday morning here at Esoc
0:01:41 > 0:01:43and the good news is that everything went well overnight.
0:01:43 > 0:01:46Rosetta fired its engine and it's now
0:01:46 > 0:01:48on a collision course with the comet.
0:01:48 > 0:01:51Even better, it's already sending back pictures.
0:01:51 > 0:01:54This one is a wide-field view of the head of the comet,
0:01:54 > 0:01:57the area that the probe will impact in just a few hours.
0:01:57 > 0:01:58But look at this -
0:01:58 > 0:02:00a high-resolution view of the landscape
0:02:00 > 0:02:04taken from just 15km up, which came back this morning.
0:02:04 > 0:02:09And on an image like this the resolution is about 1.5 metres.
0:02:09 > 0:02:12By the end of today we're hoping to have images that show things
0:02:12 > 0:02:15that are just a centimetre or so across. It's incredible.
0:02:15 > 0:02:19From here on in, it's all about that countdown to the final impact.
0:02:22 > 0:02:24As well as covering Rosetta's final plunge
0:02:24 > 0:02:28into 67P/Churyumov-Gerasimenko,
0:02:28 > 0:02:32we'll be looking at some of the crucial discoveries from the mission.
0:02:33 > 0:02:36What we're seeing here are the structures that may lead to form
0:02:36 > 0:02:40not only the comet, but possibly everything else in the solar system.
0:02:42 > 0:02:45We'll be finding out what happened to the Philae lander,
0:02:45 > 0:02:48which was lost on the surface in 2014.
0:02:49 > 0:02:52And I get into an argument about what a comet smells like.
0:02:52 > 0:02:54It's quite perfumed.
0:02:54 > 0:02:56I get more hints of urine.
0:02:58 > 0:03:03Back on Friday morning, almost 500 million miles away,
0:03:03 > 0:03:05between the asteroid belt and the orbit of Jupiter,
0:03:05 > 0:03:09Rosetta was closing in on the surface of the comet.
0:03:10 > 0:03:13Just a few hours before impact, I caught up with the mission's
0:03:13 > 0:03:15project scientist, Matt Taylor.
0:03:17 > 0:03:19When I talk to people about coming out here
0:03:19 > 0:03:22to see you and to see the team for this,
0:03:22 > 0:03:23the first question I got this,
0:03:23 > 0:03:25"Well, why are they crashing it?"
0:03:25 > 0:03:29Couldn't you have just left Rosetta in orbit and kept taking data
0:03:29 > 0:03:31or even left it there for the future?
0:03:31 > 0:03:33People seem reluctant to let it go.
0:03:33 > 0:03:35Yeah. I mean, that's the thing.
0:03:35 > 0:03:37People have claimed ownership, which is right,
0:03:37 > 0:03:40cos many people have paid for this with their taxes.
0:03:40 > 0:03:43Now, Rosetta's been in space since 2004,
0:03:43 > 0:03:45but this spacecraft is old.
0:03:45 > 0:03:47There were some issues with thrusters,
0:03:47 > 0:03:49the reaction wheels are getting on,
0:03:49 > 0:03:51so you're not guaranteeing it will come out of hibernation again.
0:03:51 > 0:03:54And why do it now? Why the timing at the end of September?
0:03:54 > 0:03:56We're already at very low data rates.
0:03:56 > 0:03:59The power's down, the comet will start to go behind the sun,
0:03:59 > 0:04:02with respect to Earth, the data rate just drops through the floor.
0:04:02 > 0:04:06Very soon we're at nothing, so there's no science to be done.
0:04:06 > 0:04:09We do it now, we go out with a bang, basically.
0:04:09 > 0:04:11So that's the science answer.
0:04:11 > 0:04:16As a person who's been involved in the mission, it will be sad to see.
0:04:16 > 0:04:18It's sad, but let's go out when everything's working.
0:04:18 > 0:04:22I keep on making this analogy with certain rock bands
0:04:22 > 0:04:26from the '60s and '70s who continue to get wheeled out on stage,
0:04:26 > 0:04:27they're a bit rheumatic in the hands,
0:04:27 > 0:04:30they're not carrying the tune any more.
0:04:30 > 0:04:31We didn't want that of Rosetta -
0:04:31 > 0:04:34- to come back out of hibernation and be... - HE MOANS
0:04:34 > 0:04:37It's really good now. Let's end on a high.
0:04:37 > 0:04:40Let's end on the maximum capability of this mission.
0:04:40 > 0:04:43Just squeeze the last bit out of what is
0:04:43 > 0:04:46a monumental achievement and get that best science.
0:04:46 > 0:04:50And so what happens with the impact of the crash?
0:04:50 > 0:04:51What's the sequence of events?
0:04:51 > 0:04:54It's 20km from the surface and we just have this
0:04:54 > 0:04:56clean trajectory down to the surface.
0:04:56 > 0:04:58And then once we get below 2km
0:04:58 > 0:05:00that's the golden period because
0:05:00 > 0:05:01we've never been that close before.
0:05:01 > 0:05:04That's the region where the coma grows, where it accelerates.
0:05:04 > 0:05:06It's the acceleration region.
0:05:06 > 0:05:08We've been probing it from a remote sensing point of view,
0:05:08 > 0:05:11but now we're going to actually fly through it, sample it, taste it.
0:05:11 > 0:05:14It's going to be nuts to actually get to that region
0:05:14 > 0:05:16and understand how this thing works.
0:05:16 > 0:05:18All right, it's one set of observations,
0:05:18 > 0:05:19but it's never been done before.
0:05:19 > 0:05:21When it happens you'll be in full rock mode,
0:05:21 > 0:05:24- cheering it as it goes down? - You know what? I don't know.
0:05:24 > 0:05:26I really can't tell you what I feel.
0:05:26 > 0:05:28I really can't tell you at the moment.
0:05:28 > 0:05:29It's just complete mixed emotions.
0:05:29 > 0:05:31Yeah, I'll be in tears probably,
0:05:31 > 0:05:33- blubbing like anything. - We'll find out.
0:05:33 > 0:05:35I don't know how I'm going to think about it,
0:05:35 > 0:05:37but we will find out shortly.
0:05:37 > 0:05:39- Matt, thanks a lot.- Cool. Thank you.
0:05:42 > 0:05:47It's believed that comets like 67P formed 4.6 billion years ago
0:05:47 > 0:05:49in the Kuiper belt -
0:05:49 > 0:05:52the realm of icy bodies at the edge of the solar system.
0:05:52 > 0:05:55And they have been unchanged ever since.
0:05:56 > 0:06:00One of the great promises of Rosetta was that, by studying
0:06:00 > 0:06:02the composition of the comet, it would tell us about conditions
0:06:02 > 0:06:04in the early solar system.
0:06:06 > 0:06:08This last part of the mission was designed to help us
0:06:08 > 0:06:11answer those questions.
0:06:11 > 0:06:14Rosetta's trajectory was carefully planned to take it towards
0:06:14 > 0:06:18some of the most fascinating and mysterious features on the comet.
0:06:18 > 0:06:20They're called pits, and they may offer us
0:06:20 > 0:06:24a glimpse into 67P's distant past.
0:06:26 > 0:06:30To find out more I went to talk to comet expert Alan Fitzsimmons.
0:06:32 > 0:06:36So, Alan, what are these pits and why are we so interested in them?
0:06:36 > 0:06:38Well, the pits are openings,
0:06:38 > 0:06:43large cavern-like structures we see in the surface of the comet.
0:06:43 > 0:06:46We see them in various regions, but we see in particular
0:06:46 > 0:06:48quite a few in the Ma'at region
0:06:48 > 0:06:51at the top or the head of the comet.
0:06:51 > 0:06:55In fact, this is where we're going to land Rosetta.
0:06:55 > 0:06:58Now, if we go back to this picture here and zoom up, we can see,
0:06:58 > 0:07:03for example, we've got one, two, three pits and possibly also
0:07:03 > 0:07:07a pit where one half of the wall has collapsed and disappeared over time.
0:07:07 > 0:07:09So how are these pits formed?
0:07:09 > 0:07:13We actually believe now that these are sinkholes.
0:07:13 > 0:07:17They're caverns - sub-surface caverns that have been exposed
0:07:17 > 0:07:19over time by the roofs collapsing.
0:07:19 > 0:07:22These are regions where there used to be sub-surface ice,
0:07:22 > 0:07:27but the ice has disappeared at some point in the past.
0:07:27 > 0:07:31We can see that happening in this pit or this sinkhole right here
0:07:31 > 0:07:35because we can see that the sunlight is illuminating this bottom rim here
0:07:35 > 0:07:37and if we bring up the contrast
0:07:37 > 0:07:42we can see the jets of material coming from the edge of this pit.
0:07:42 > 0:07:45So is that what we see in the tail of a comet?
0:07:45 > 0:07:46Are these gases escaping?
0:07:46 > 0:07:49We think that this is the process that is going on and could be
0:07:49 > 0:07:53the major way that comets lose the material, lose the gas and the dust
0:07:53 > 0:07:57we see streaming in the ground-based telescope images of the comet.
0:07:57 > 0:07:59We know perhaps how they're formed -
0:07:59 > 0:08:02why is Rosetta landing so close to them?
0:08:02 > 0:08:05Well, because these pits extend so far below the surface
0:08:05 > 0:08:09they give us an insight into the previous history of the comet.
0:08:09 > 0:08:13If we look at this pit here we can see this kind of granular structure,
0:08:13 > 0:08:16or texture, to the walls of the pit.
0:08:16 > 0:08:20We call these structures dragon eggs or goose bumps.
0:08:20 > 0:08:21So what sort of size are these?
0:08:21 > 0:08:23Well, although they look small in this image,
0:08:23 > 0:08:25they're actually quite sizeable.
0:08:25 > 0:08:28They're about a metre to three metres across in reality.
0:08:28 > 0:08:31But, importantly, we see them wherever we can see
0:08:31 > 0:08:34exposed surfaces going into the interior.
0:08:34 > 0:08:37And the implication therefore is that these objects
0:08:37 > 0:08:40are all the way through the comet.
0:08:40 > 0:08:43So it looks as if this is the stuff that the comet is actually made of?
0:08:43 > 0:08:47Absolutely. This must be the stuff that came together to form the comet
0:08:47 > 0:08:494.5 billion years ago.
0:08:49 > 0:08:51If that's true then what we're seeing here
0:08:51 > 0:08:54are the structures that may have led to form not only the comet,
0:08:54 > 0:08:57but possibly everything else in the solar system.
0:08:57 > 0:08:59- So these are the building blocks of the solar system?- Absolutely.
0:08:59 > 0:09:04And that's why it's so important to get as close up a view as we can get,
0:09:04 > 0:09:07and that's why Rosetta is being aimed towards these pits.
0:09:07 > 0:09:09A very fitting end for Rosetta.
0:09:09 > 0:09:11- I'm hoping that you get the data you need.- Me too.
0:09:13 > 0:09:15Back in Darmstadt,
0:09:15 > 0:09:18we were beginning to see the first of those detailed views.
0:09:20 > 0:09:23This composite image of the landing site shows the craft
0:09:23 > 0:09:25homing in on the pits.
0:09:26 > 0:09:30I went to mission control to meet Andrea Accomazzo, one of the team
0:09:30 > 0:09:35responsible for shepherding Rosetta through its final journey.
0:09:35 > 0:09:36It's lovely to see you again.
0:09:36 > 0:09:39Can you tell us what's happening in mission control today?
0:09:39 > 0:09:42Well, what we're doing right now is just monitoring the spacecraft.
0:09:42 > 0:09:43There's nothing else we have to do
0:09:43 > 0:09:46and there's actually nothing else we can do.
0:09:46 > 0:09:48We've done our last manoeuvre last night,
0:09:48 > 0:09:51so the spacecraft is heading down towards the comet.
0:09:51 > 0:09:54This morning we had to update some commands - some instruction,
0:09:54 > 0:09:57if you want - for the spacecraft to do exactly what we want it to do.
0:09:57 > 0:10:00But then that's it. Now it's game over for control.
0:10:00 > 0:10:03How difficult is this last manoeuvre?
0:10:03 > 0:10:07What has been extremely difficult is what we have been doing the last six weeks.
0:10:07 > 0:10:09We've been flying much closer to the comet
0:10:09 > 0:10:13and there's no uniformity of the shape, therefore of the gravitational field.
0:10:13 > 0:10:16- The fact it looks like a duck. - Indeed.
0:10:16 > 0:10:18And then every day we are flying over a different mountain,
0:10:18 > 0:10:21if you want, and the gravitational pull was different,
0:10:21 > 0:10:24so every time we had to re-estimate and this was a very challenging.
0:10:24 > 0:10:27What will you be looking for when the landing actually happens?
0:10:27 > 0:10:31On this screen we actually see the output of the spectrum analysers
0:10:31 > 0:10:35in the antenna receiving the signal of Rosetta.
0:10:35 > 0:10:38So it's a representation of the signal received by Rosetta.
0:10:38 > 0:10:41And the moment this signal will disappear it will tell us
0:10:41 > 0:10:43that Rosetta has landed on the comet.
0:10:43 > 0:10:45How does that feel?
0:10:45 > 0:10:49Well, when the spike goes away for sure I will be a bit sad.
0:10:49 > 0:10:51I have no doubts.
0:10:51 > 0:10:53But I guess I will share the feelings with all the colleagues
0:10:53 > 0:10:56who have spent maybe 20 years working together for this project.
0:10:56 > 0:10:59- But afterwards it's time for a party.- OK.
0:10:59 > 0:11:01Well, we've got a couple of hours to go, so good luck,
0:11:01 > 0:11:05I hope all goes well and we'll see you on the other side.
0:11:05 > 0:11:07Thanks. Thanks, see you later.
0:11:07 > 0:11:12In just a few hours everyone would be nervously watching this waveform.
0:11:12 > 0:11:15It was the spacecraft's heartbeat.
0:11:15 > 0:11:19And when that spike disappeared we would know that Rosetta was no more.
0:11:24 > 0:11:27Mission control is important, but the scientific heart
0:11:27 > 0:11:31of the mission is a separate room where the imaging teams are sitting
0:11:31 > 0:11:33analysing the data as it arrives.
0:11:33 > 0:11:36And that's where we're going now to see the latest images.
0:11:40 > 0:11:44This room is normally off limits, but we're allowed in briefly
0:11:44 > 0:11:48to talk to the man in charge of the imaging team, Holger Sierks.
0:11:48 > 0:11:50- Hey. How are you?- How you doing?
0:11:50 > 0:11:53- Good, good. Good seeing you.- Sorry to interrupt you. I know you're...
0:11:53 > 0:11:54- You're busy.- We're busy, yes.
0:11:54 > 0:11:57Have you got two minutes to show us what you've got?
0:11:57 > 0:12:01So that's an image taking at 7.5km altitude.
0:12:01 > 0:12:03It was just taken...
0:12:03 > 0:12:07Well, two hours and 40 minutes ago.
0:12:07 > 0:12:13So we are now below 8km and getting to the six now,
0:12:13 > 0:12:16so you really feel the sense of,
0:12:16 > 0:12:19yeah, we're getting closer and closer.
0:12:19 > 0:12:21- We have the latest image over there. - That's beautiful.
0:12:21 > 0:12:22So what are we looking at?
0:12:22 > 0:12:26- This is sort of the landscape that the Rosetta is flying over?- Yeah.
0:12:26 > 0:12:27That's the landscape.
0:12:27 > 0:12:30So we don't have the landing site in view yet there.
0:12:30 > 0:12:32We also have other close-ups,
0:12:32 > 0:12:35so we're following the descent of the space probe.
0:12:35 > 0:12:39And so we are just passing over the landscape
0:12:39 > 0:12:42and snapshotting the area beneath us.
0:12:42 > 0:12:45And as a photographer, how much of a challenge is it
0:12:45 > 0:12:48to make the camera work for this descent?
0:12:48 > 0:12:53I mean, it wasn't designed to take images this close to a comet.
0:12:53 > 0:12:55Yeah, it's a challenge in two ways.
0:12:55 > 0:12:57It's a challenge in exposure time.
0:12:57 > 0:13:00You would think at 700 million km distance it's all dark there,
0:13:00 > 0:13:04the sky is dark so you have to expose for long. It's not.
0:13:04 > 0:13:06So we're exposing 15 milliseconds.
0:13:06 > 0:13:10So it's very short exposure times to avoid motion smear
0:13:10 > 0:13:13and saturation of the images.
0:13:13 > 0:13:16And then of course we have to cope with the performance of the cameras.
0:13:16 > 0:13:19They are made for long-range shooting,
0:13:19 > 0:13:21not for very close shooting.
0:13:21 > 0:13:24So we have a few capabilities -
0:13:24 > 0:13:27changing the glass in the filters in the beam,
0:13:27 > 0:13:30so modifying the focus a little.
0:13:30 > 0:13:34But not as much as we would wish now for the descent.
0:13:34 > 0:13:38So we will get out of focus, we will do some magic here on this computer
0:13:38 > 0:13:43to deconvolve, to sharpen the images, but there is only so much we can do.
0:13:43 > 0:13:45So we are looking forward to seeing these images.
0:13:45 > 0:13:49- Yeah, well, we'll look forward to it too. You've got two hours, we'll leave you alone.- OK.
0:13:49 > 0:13:51But we'll catch you with the final images later. Good luck.
0:13:51 > 0:13:55- OK. Thanks a lot. We need it. - Yeah, yeah. Take care.
0:13:55 > 0:13:58As Rosetta got closer to the surface it was returning
0:13:58 > 0:14:01astonishingly detailed images,
0:14:01 > 0:14:04revealing cliffs and boulder fields,
0:14:04 > 0:14:08cracks and fractures of the surface geology.
0:14:08 > 0:14:12And surprisingly smooth dust-covered plains.
0:14:12 > 0:14:17It is a remarkably complex landscape for such a small body.
0:14:17 > 0:14:18That's amazing.
0:14:18 > 0:14:21Seeing the images streaming live from the spacecraft
0:14:21 > 0:14:23to here in Darmstadt is incredible.
0:14:23 > 0:14:26And they're such a wonderful set, too.
0:14:26 > 0:14:30I think what I am realising is how varied the surface of the comet is.
0:14:30 > 0:14:33As Rosetta is flying over it we're seeing beautiful scene
0:14:33 > 0:14:35after beautiful scene of landscape after landscape,
0:14:35 > 0:14:39and of course we've still got the highest resolution images
0:14:39 > 0:14:41still to come. Not too long to go now.
0:14:43 > 0:14:47Of course, this wasn't the first attempt to land on the surface of 67P.
0:14:50 > 0:14:55In 2014 the Philae lander had been released onto the comet.
0:14:55 > 0:14:59One of the key goals of the final weeks of Rosetta's mission
0:14:59 > 0:15:01was to find out what had happened to Philae.
0:15:03 > 0:15:06Because it had disappeared shortly after landing.
0:15:13 > 0:15:18Comet 67P is shaped like a large rubber duck.
0:15:18 > 0:15:21Philae was due to land here, on the top of the duck's head.
0:15:21 > 0:15:23And although it landed at exactly the right position
0:15:23 > 0:15:27the thrusters and the harpoons which were due to anchor it to the comet
0:15:27 > 0:15:30didn't fire, and so the lander bounced.
0:15:32 > 0:15:36Pictures from the camera shows how Philae had bounced twice
0:15:36 > 0:15:38on the comet's surface.
0:15:42 > 0:15:45The data from its instruments showed that it had drifted for
0:15:45 > 0:15:47two hours in the comet's low gravity
0:15:47 > 0:15:50before finally coming to a halt.
0:15:52 > 0:15:55The pictures from its onboard cameras revealed that it had
0:15:55 > 0:15:57wedged itself under a cliff.
0:16:00 > 0:16:02Philae had landed in the shade.
0:16:02 > 0:16:05And with no sunlight reaching its solar panels
0:16:05 > 0:16:09it could only operate as long as its batteries lasted.
0:16:09 > 0:16:11So, just three days after touchdown,
0:16:11 > 0:16:13Philae fell silent.
0:16:13 > 0:16:17But it had gathered enough data to work out roughly where it might be -
0:16:17 > 0:16:20this region here, called Abydos.
0:16:20 > 0:16:24But nobody knew its true location.
0:16:24 > 0:16:25Ever since then
0:16:25 > 0:16:29the mission scientists have been searching for Philae.
0:16:29 > 0:16:34In June 2015 the lander woke up briefly and made radio contact again
0:16:34 > 0:16:37but couldn't communicate its exact location.
0:16:37 > 0:16:41And until just a month ago there was still no sign of Philae.
0:16:43 > 0:16:48In September Rosetta began its closest approach to the comet,
0:16:48 > 0:16:51and much of the time of the Osiris camera was spent searching
0:16:51 > 0:16:53for where Philae was hiding.
0:16:53 > 0:16:56And on the 2nd September they got this photograph.
0:16:56 > 0:17:00And if you look very closely you can see the distinctive shape of
0:17:00 > 0:17:01the Philae lander.
0:17:03 > 0:17:06After being missing for nearly two years,
0:17:06 > 0:17:07Philae had been found.
0:17:10 > 0:17:12For scientists like Ian Wright,
0:17:12 > 0:17:14who had worked on the lander's instrument,
0:17:14 > 0:17:18it was a chance to look back at what the mission have achieved.
0:17:18 > 0:17:21There must have been an emotional reaction when you saw that
0:17:21 > 0:17:23image of Philae on the ground.
0:17:23 > 0:17:25I'm not one for crying,
0:17:25 > 0:17:29but it was really an emotional experience, yeah.
0:17:29 > 0:17:32Because we'd been looking at things over the last couple of years,
0:17:32 > 0:17:34little white dots, and someone says, "Oh, we found it."
0:17:34 > 0:17:36And you have a look at it and you think,
0:17:36 > 0:17:39"Well, I don't know. I don't really get that."
0:17:39 > 0:17:41But when you saw that image you said, "Nah, that's it.
0:17:41 > 0:17:43"I don't need convincing. That is really it."
0:17:43 > 0:17:45So that was great.
0:17:45 > 0:17:46That was a really great day.
0:17:46 > 0:17:50I would hate to be at this point now not having found it.
0:17:50 > 0:17:52I think that would be really terrible.
0:17:54 > 0:17:58Ian's instrument on Philae was a mass spectrometer called Ptolemy.
0:17:58 > 0:18:02It was designed to collect samples drilled from the surface
0:18:02 > 0:18:04and heat them in its ovens....
0:18:05 > 0:18:10..analysing the products to reveal what the comet was made of.
0:18:10 > 0:18:15But as Philae bounced, those initial plans went out of the window.
0:18:16 > 0:18:18We actually got to measure the surface chemistry
0:18:18 > 0:18:21at a couple of places, which wasn't planned.
0:18:21 > 0:18:22But, you know, unfortunately,
0:18:22 > 0:18:25because it landed on its side and the drill couldn't reach the surface
0:18:25 > 0:18:29we just couldn't actually extract a sample of that material.
0:18:29 > 0:18:31- You know, that's the way life goes.- Yeah.
0:18:31 > 0:18:34But, interestingly, as part of the whole journey from landing
0:18:34 > 0:18:36the first time, bouncing around,
0:18:36 > 0:18:39dust or whatever has collected in the oven
0:18:39 > 0:18:41and we're able to boil it out,
0:18:41 > 0:18:44just as we would have done if we'd actually drilled it.
0:18:44 > 0:18:47And what we expected to see was some water and CO2..
0:18:47 > 0:18:50- The main ingredients. Yeah.- Yeah.
0:18:50 > 0:18:52And actually, intriguingly,
0:18:52 > 0:18:54the water signal was relatively low.
0:18:54 > 0:18:58I mean, still the biggest signal, but nowhere near...
0:18:58 > 0:19:02It clearly showed that what we landed on was very dry.
0:19:02 > 0:19:06Comets are often called dirty snowballs.
0:19:06 > 0:19:09But the discovery that 67P contains less water
0:19:09 > 0:19:12and more dust than expected
0:19:12 > 0:19:15means we might have to come up with a new label.
0:19:15 > 0:19:18Icy dirt ball might be a better description.
0:19:19 > 0:19:22This was just one of the many surprising discoveries about
0:19:22 > 0:19:25the comet's make-up that the mission has made.
0:19:27 > 0:19:30When it comes to saying, "What was your highlight?
0:19:30 > 0:19:32"What was the thing that was, in a sense,
0:19:32 > 0:19:34"most amazing or most unexpected?"
0:19:34 > 0:19:38For me, it will be the detection of free oxygen, free O2.
0:19:39 > 0:19:41Free oxygen is plentiful on Earth,
0:19:41 > 0:19:45but only because it's produced by living organisms.
0:19:45 > 0:19:49It WAS thought to be very rare in the rest of the solar system.
0:19:52 > 0:19:56It does force us to rethink the whole notion about oxygen in
0:19:56 > 0:19:59planetary atmospheres as an indicator of life,
0:19:59 > 0:20:01because here it is in a comet.
0:20:01 > 0:20:05There's no chance that this has been formed by life on a comet.
0:20:05 > 0:20:10But what it does show us is that molecules like oxygen
0:20:10 > 0:20:13were incorporated into the comet at the time of its formation,
0:20:13 > 0:20:15it's been there ever since,
0:20:15 > 0:20:18and that goes against any kind of thinking that we have about this.
0:20:18 > 0:20:20And no-one expected this. I was taught...
0:20:20 > 0:20:24I remember being taught that in the early parts of solar system formation
0:20:24 > 0:20:27you use all the oxygen up, it reacts, you don't get O2,
0:20:27 > 0:20:28and yet here it is.
0:20:28 > 0:20:30It's a sign that we don't understand the chemistry.
0:20:30 > 0:20:33Absolutely. Chemistry is still more exciting than we imagine.
0:20:33 > 0:20:36- Ian, thank you very much. - OK. Thank you.
0:20:38 > 0:20:42But as well as learning about the composition of the comet,
0:20:42 > 0:20:44the data collected by Rosetta have also produced
0:20:44 > 0:20:48some remarkable new ways of experiencing 67P,
0:20:48 > 0:20:52as I discovered when I met planetary scientist Geraint Jones.
0:20:54 > 0:20:57As well as the instruments that's measuring the composition of
0:20:57 > 0:21:00the dust there's also several instruments looking at the
0:21:00 > 0:21:02composition of the gas coming off the comets.
0:21:02 > 0:21:04And one of these is Rosina,
0:21:04 > 0:21:07which is a very sophisticated mass spectrometer.
0:21:07 > 0:21:09It's measured the gas that's come off from the comet while
0:21:09 > 0:21:13Rosetta's been there and drawn up a very long list by now
0:21:13 > 0:21:15of all the gases that are there.
0:21:15 > 0:21:17So with this you can actually come up with an ingredients list
0:21:17 > 0:21:20- for what a comet's made of? - That's right, yeah.
0:21:20 > 0:21:22A colleague in the Open University, Colin Snodgrass, came up with
0:21:22 > 0:21:26the great idea of trying to simulate what this actually smells like.
0:21:26 > 0:21:30And this postcard actually smells roughly of what
0:21:30 > 0:21:33Rosetta sampled at the comet.
0:21:33 > 0:21:35- So this is the smell of 67P? - It is.
0:21:35 > 0:21:36So, please.
0:21:36 > 0:21:38OK, I'm going in.
0:21:40 > 0:21:42I must... I quite like the smell.
0:21:42 > 0:21:46It reminds me...of disinfectant, or it's quite perfumed.
0:21:46 > 0:21:48What does it smell like to you?
0:21:48 > 0:21:50Well, I must admit, I'm not too keen on it.
0:21:50 > 0:21:52So people have different reactions.
0:21:52 > 0:21:56Yeah, I get more hints of urine etc.
0:21:56 > 0:21:58- Actually, I'm not going to smell again!- Yeah.
0:21:58 > 0:22:02I suppose comets are the building blocks of the early solar system,
0:22:02 > 0:22:05so I guess this smells like the early solar system?
0:22:05 > 0:22:08That's right. So we know from the Apollo astronauts
0:22:08 > 0:22:10that the moon smells roughly of gunpowder.
0:22:10 > 0:22:11Now we've got the smell
0:22:11 > 0:22:13of somewhere else in the solar system, as well.
0:22:20 > 0:22:23Another great advantage of this mission is that it's been
0:22:23 > 0:22:27travelling alongside the comet for nearly two years,
0:22:27 > 0:22:30and that's given us an unprecedented opportunity
0:22:30 > 0:22:34to observe how 67P changes over time.
0:22:35 > 0:22:39We've always known that comets get more active
0:22:39 > 0:22:41as they get warmer.
0:22:41 > 0:22:44They only produce their dramatic tails as they approach the sun.
0:22:44 > 0:22:47But Rosetta has given us a ringside view to observe
0:22:47 > 0:22:49these processes in much more detail.
0:22:52 > 0:22:56When it first arrived in orbit around the comet in August 2014
0:22:56 > 0:23:00it was half a billion miles from the sun
0:23:00 > 0:23:03and the comet's nucleus was largely frozen and dormant.
0:23:05 > 0:23:08But as its orbit brought it closer to the sun,
0:23:08 > 0:23:10we can see it burst into life.
0:23:15 > 0:23:19These three images show a period of just 36 minutes
0:23:19 > 0:23:23on 29th July 2015.
0:23:23 > 0:23:26In this middle image we see a vast but short-lived jet
0:23:26 > 0:23:29bursting from the surface.
0:23:29 > 0:23:33It's caused by ice below the surface converting into gas
0:23:33 > 0:23:35and then shooting out into space.
0:23:37 > 0:23:40Other outbursts have been even more dramatic.
0:23:42 > 0:23:45On February 19th this year a huge event -
0:23:45 > 0:23:48thought to have been a landslide - caused a massive cloud of dust
0:23:48 > 0:23:50to erupt from the comet,
0:23:50 > 0:23:53resulting in a sixfold increase in brightness.
0:23:56 > 0:23:59It's this sort of sudden and rare event that would've been
0:23:59 > 0:24:02almost impossible to observe if we had not been studying the comet
0:24:02 > 0:24:04for a long period of time.
0:24:17 > 0:24:19But by Friday lunchtime
0:24:19 > 0:24:21Rosetta's adventure around 67P
0:24:21 > 0:24:23was rapidly coming to an end.
0:24:25 > 0:24:29This picture was taken just over 1km above the surface.
0:24:29 > 0:24:33And with the spacecraft descending at about a metre per second,
0:24:33 > 0:24:36it was only a matter of minutes until it hit the surface.
0:24:43 > 0:24:47I joined Matt Taylor to watch the end of this remarkable mission.
0:24:49 > 0:24:52That last 2km, we've never been there.
0:24:52 > 0:24:54So the stuff we're getting now is unbelievable.
0:24:54 > 0:24:57This trajectory, this impact, is giving us something that
0:24:57 > 0:24:59we couldn't get in any other way.
0:24:59 > 0:25:01So we're getting this because we're crashing it.
0:25:01 > 0:25:04So we're sacrificing the spacecraft to get this science.
0:25:04 > 0:25:07- What is the atmosphere in there at the minute?- It's horrible.
0:25:07 > 0:25:11This is the opposite of what they do all the time.
0:25:11 > 0:25:14They spend their life making sure spacecraft are safe
0:25:14 > 0:25:16and they've made this spacecraft do the opposite.
0:25:16 > 0:25:19You look at the people in that room that have spent their careers
0:25:19 > 0:25:21on this mission.
0:25:21 > 0:25:23When I was in the room you could feel it.
0:25:23 > 0:25:25You felt this deflation.
0:25:25 > 0:25:29How does this compare to watching Philae disappear onto the surface?
0:25:29 > 0:25:31HE SIGHS
0:25:31 > 0:25:34Well, Philae was landing and going to do something afterwards.
0:25:34 > 0:25:38This is, as soon as touches, there's no more. There's no more Rosetta.
0:25:38 > 0:25:41- Operationally, of course. We've got the science. - There's all this science.
0:25:41 > 0:25:44- Yeah, but for this there's nothing after.- Data's still coming down.
0:25:44 > 0:25:47So the carrier signal is still pretty strong.
0:25:47 > 0:25:49Three minutes to go.
0:25:51 > 0:25:54- This must be data from very close to the comet.- Yeah.
0:25:54 > 0:25:56This is good.
0:25:56 > 0:25:58This is a few tens of metres now, isn't it?
0:26:00 > 0:26:01It's still there.
0:26:05 > 0:26:07- Oh. - SPORADIC APPLAUSE
0:26:12 > 0:26:15We have LOS.
0:26:16 > 0:26:18That's it.
0:26:18 > 0:26:20He's just confirmed LOS.
0:26:20 > 0:26:23Signal's gone. And how do you feel?
0:26:24 > 0:26:27I just feel, actually, for that team the most.
0:26:27 > 0:26:30Because as a scientist working on this mission we've still got stuff to do,
0:26:30 > 0:26:34but they've had to do something that's so counterintuitive,
0:26:34 > 0:26:37so against what they do
0:26:37 > 0:26:39and this is cutting that team up.
0:26:39 > 0:26:42And so this is the end of the Rosetta mission.
0:26:42 > 0:26:44Thank you and goodbye.
0:26:44 > 0:26:45Congratulations.
0:26:45 > 0:26:47- It's been an amazing mission. - Thanks again.
0:26:47 > 0:26:49HE SIGHS DEEPLY
0:26:49 > 0:26:51- Are you all right?- Bugger.
0:26:56 > 0:26:58- Well done. - HE SIGHS
0:27:00 > 0:27:02- Thank you very much for that. - Thanks, mate.- I appreciate it.
0:27:02 > 0:27:04Give us a hug, you. Good man.
0:27:06 > 0:27:08Right, what's the next mission? No.
0:27:10 > 0:27:13There is only one mission. Let's see.
0:27:18 > 0:27:21Rosetta's last picture was this blurry image taken
0:27:21 > 0:27:24just 20 metres above the surface.
0:27:24 > 0:27:28Just a few seconds later it crashed into the comet
0:27:28 > 0:27:30and went quiet for ever.
0:27:31 > 0:27:35Over the coming weeks and months we can expect many more images
0:27:35 > 0:27:37from the descent to be released.
0:27:37 > 0:27:40We will see deep into the heart of the pits.
0:27:42 > 0:27:44All the data from the other instruments will help
0:27:44 > 0:27:49in revealing the comet's composition and history...
0:27:49 > 0:27:54and will help us understand the beginnings of the whole solar system.
0:27:54 > 0:27:56And so goodbye, Rosetta.
0:27:56 > 0:27:59The spacecraft may have finished its mission,
0:27:59 > 0:28:02but the journey of discovery it's launched us on
0:28:02 > 0:28:04will go on for many years to come.