Goodbye Rosetta: A Sky at Night Special The Sky at Night

Yeah, three minutes to go.

On Friday scientists and the world's media gathered to watch

the end of one of the most ambitious space missions ever attempted.

In a last daring manoeuvre, the Rosetta spacecraft would

accelerate towards the surface of a comet.

So we really feel the sense of,

yeah, we're getting closer and closer.

This final stage of the mission was designed to give us

the most detailed pictures we've ever seen of a comet's nucleus.

This must be data from very close to the comet.

This is a few tens of metres now, isn't it?

And give us a new insight into the origins of the solar system.

But these pictures came at a price -

the inevitable death of the spacecraft

as it crashed into the comet's surface.

Tonight on The Sky At Night special,

we take you behind the scenes in mission control

for the final triumph and tragedy of the Rosetta mission.

And so this is the end of the Rosetta mission.

-Thank you and goodbye.

-Good man.

Well, it's early Friday morning here at Esoc

and the good news is that everything went well overnight.

Rosetta fired its engine and it's now

on a collision course with the comet.

Even better, it's already sending back pictures.

This one is a wide-field view of the head of the comet,

the area that the probe will impact in just a few hours.

But look at this -

a high-resolution view of the landscape

taken from just 15km up, which came back this morning.

And on an image like this the resolution is about 1.5 metres.

By the end of today we're hoping to have images that show things

that are just a centimetre or so across. It's incredible.

From here on in, it's all about that countdown to the final impact.

As well as covering Rosetta's final plunge

into 67P/Churyumov-Gerasimenko,

we'll be looking at some of the crucial discoveries from the mission.

What we're seeing here are the structures that may lead to form

not only the comet, but possibly everything else in the solar system.

We'll be finding out what happened to the Philae lander,

which was lost on the surface in 2014.

And I get into an argument about what a comet smells like.

It's quite perfumed.

I get more hints of urine.

Back on Friday morning, almost 500 million miles away,

between the asteroid belt and the orbit of Jupiter,

Rosetta was closing in on the surface of the comet.

Just a few hours before impact, I caught up with the mission's

project scientist, Matt Taylor.

When I talk to people about coming out here

to see you and to see the team for this,

the first question I got this,

"Well, why are they crashing it?"

Couldn't you have just left Rosetta in orbit and kept taking data

or even left it there for the future?

People seem reluctant to let it go.

Yeah. I mean, that's the thing.

People have claimed ownership, which is right,

cos many people have paid for this with their taxes.

Now, Rosetta's been in space since 2004,

but this spacecraft is old.

There were some issues with thrusters,

the reaction wheels are getting on,

so you're not guaranteeing it will come out of hibernation again.

And why do it now? Why the timing at the end of September?

We're already at very low data rates.

The power's down, the comet will start to go behind the sun,

with respect to Earth, the data rate just drops through the floor.

Very soon we're at nothing, so there's no science to be done.

We do it now, we go out with a bang, basically.

So that's the science answer.

As a person who's been involved in the mission, it will be sad to see.

It's sad, but let's go out when everything's working.

I keep on making this analogy with certain rock bands

from the '60s and '70s who continue to get wheeled out on stage,

they're a bit rheumatic in the hands,

they're not carrying the tune any more.

We didn't want that of Rosetta -

-to come back out of hibernation and be...

-HE MOANS

It's really good now. Let's end on a high.

Let's end on the maximum capability of this mission.

Just squeeze the last bit out of what is

a monumental achievement and get that best science.

And so what happens with the impact of the crash?

What's the sequence of events?

It's 20km from the surface and we just have this

clean trajectory down to the surface.

And then once we get below 2km

that's the golden period because

we've never been that close before.

That's the region where the coma grows, where it accelerates.

It's the acceleration region.

We've been probing it from a remote sensing point of view,

but now we're going to actually fly through it, sample it, taste it.

It's going to be nuts to actually get to that region

and understand how this thing works.

All right, it's one set of observations,

but it's never been done before.

When it happens you'll be in full rock mode,

-cheering it as it goes down?

-You know what? I don't know.

I really can't tell you what I feel.

I really can't tell you at the moment.

It's just complete mixed emotions.

Yeah, I'll be in tears probably,

-blubbing like anything.

-We'll find out.

I don't know how I'm going to think about it,

but we will find out shortly.

-Matt, thanks a lot.

-Cool. Thank you.

It's believed that comets like 67P formed 4.6 billion years ago

in the Kuiper belt -

the realm of icy bodies at the edge of the solar system.

And they have been unchanged ever since.

One of the great promises of Rosetta was that, by studying

the composition of the comet, it would tell us about conditions

in the early solar system.

This last part of the mission was designed to help us

answer those questions.

Rosetta's trajectory was carefully planned to take it towards

some of the most fascinating and mysterious features on the comet.

They're called pits, and they may offer us

a glimpse into 67P's distant past.

To find out more I went to talk to comet expert Alan Fitzsimmons.

So, Alan, what are these pits and why are we so interested in them?

Well, the pits are openings,

large cavern-like structures we see in the surface of the comet.

We see them in various regions, but we see in particular

quite a few in the Ma'at region

at the top or the head of the comet.

In fact, this is where we're going to land Rosetta.

Now, if we go back to this picture here and zoom up, we can see,

for example, we've got one, two, three pits and possibly also

a pit where one half of the wall has collapsed and disappeared over time.

So how are these pits formed?

We actually believe now that these are sinkholes.

They're caverns - sub-surface caverns that have been exposed

over time by the roofs collapsing.

These are regions where there used to be sub-surface ice,

but the ice has disappeared at some point in the past.

We can see that happening in this pit or this sinkhole right here

because we can see that the sunlight is illuminating this bottom rim here

and if we bring up the contrast

we can see the jets of material coming from the edge of this pit.

So is that what we see in the tail of a comet?

Are these gases escaping?

We think that this is the process that is going on and could be

the major way that comets lose the material, lose the gas and the dust

we see streaming in the ground-based telescope images of the comet.

We know perhaps how they're formed -

why is Rosetta landing so close to them?

Well, because these pits extend so far below the surface

they give us an insight into the previous history of the comet.

If we look at this pit here we can see this kind of granular structure,

or texture, to the walls of the pit.

We call these structures dragon eggs or goose bumps.

So what sort of size are these?

Well, although they look small in this image,

they're actually quite sizeable.

They're about a metre to three metres across in reality.

But, importantly, we see them wherever we can see

exposed surfaces going into the interior.

And the implication therefore is that these objects

are all the way through the comet.

So it looks as if this is the stuff that the comet is actually made of?

Absolutely. This must be the stuff that came together to form the comet

4.5 billion years ago.

If that's true then what we're seeing here

are the structures that may have led to form not only the comet,

but possibly everything else in the solar system.

-So these are the building blocks of the solar system?

-Absolutely.

And that's why it's so important to get as close up a view as we can get,

and that's why Rosetta is being aimed towards these pits.

A very fitting end for Rosetta.

-I'm hoping that you get the data you need.

-Me too.

Back in Darmstadt,

we were beginning to see the first of those detailed views.

This composite image of the landing site shows the craft

homing in on the pits.

I went to mission control to meet Andrea Accomazzo, one of the team

responsible for shepherding Rosetta through its final journey.

It's lovely to see you again.

Can you tell us what's happening in mission control today?

Well, what we're doing right now is just monitoring the spacecraft.

There's nothing else we have to do

and there's actually nothing else we can do.

We've done our last manoeuvre last night,

so the spacecraft is heading down towards the comet.

This morning we had to update some commands - some instruction,

if you want - for the spacecraft to do exactly what we want it to do.

But then that's it. Now it's game over for control.

How difficult is this last manoeuvre?

What has been extremely difficult is what we have been doing the last six weeks.

We've been flying much closer to the comet

and there's no uniformity of the shape, therefore of the gravitational field.

-The fact it looks like a duck.

-Indeed.

And then every day we are flying over a different mountain,

if you want, and the gravitational pull was different,

so every time we had to re-estimate and this was a very challenging.

What will you be looking for when the landing actually happens?

On this screen we actually see the output of the spectrum analysers

in the antenna receiving the signal of Rosetta.

So it's a representation of the signal received by Rosetta.

And the moment this signal will disappear it will tell us

that Rosetta has landed on the comet.

How does that feel?

Well, when the spike goes away for sure I will be a bit sad.

I have no doubts.

But I guess I will share the feelings with all the colleagues

who have spent maybe 20 years working together for this project.

-But afterwards it's time for a party.

-OK.

Well, we've got a couple of hours to go, so good luck,

I hope all goes well and we'll see you on the other side.

Thanks. Thanks, see you later.

In just a few hours everyone would be nervously watching this waveform.

It was the spacecraft's heartbeat.

And when that spike disappeared we would know that Rosetta was no more.

Mission control is important, but the scientific heart

of the mission is a separate room where the imaging teams are sitting

analysing the data as it arrives.

And that's where we're going now to see the latest images.

This room is normally off limits, but we're allowed in briefly

to talk to the man in charge of the imaging team, Holger Sierks.

-Hey. How are you?

-How you doing?

-Good, good. Good seeing you.

-Sorry to interrupt you. I know you're...

-You're busy.

-We're busy, yes.

Have you got two minutes to show us what you've got?

So that's an image taking at 7.5km altitude.

It was just taken...

Well, two hours and 40 minutes ago.

So we are now below 8km and getting to the six now,

so you really feel the sense of,

yeah, we're getting closer and closer.

-We have the latest image over there.

-That's beautiful.

So what are we looking at?

-This is sort of the landscape that the Rosetta is flying over?

-Yeah.

That's the landscape.

So we don't have the landing site in view yet there.

We also have other close-ups,

so we're following the descent of the space probe.

And so we are just passing over the landscape

and snapshotting the area beneath us.

And as a photographer, how much of a challenge is it

to make the camera work for this descent?

I mean, it wasn't designed to take images this close to a comet.

Yeah, it's a challenge in two ways.

It's a challenge in exposure time.

You would think at 700 million km distance it's all dark there,

the sky is dark so you have to expose for long. It's not.

So we're exposing 15 milliseconds.

So it's very short exposure times to avoid motion smear

and saturation of the images.

And then of course we have to cope with the performance of the cameras.

They are made for long-range shooting,

not for very close shooting.

So we have a few capabilities -

changing the glass in the filters in the beam,

so modifying the focus a little.

But not as much as we would wish now for the descent.

So we will get out of focus, we will do some magic here on this computer

to deconvolve, to sharpen the images, but there is only so much we can do.

So we are looking forward to seeing these images.

-Yeah, well, we'll look forward to it too. You've got two hours, we'll leave you alone.

-OK.

But we'll catch you with the final images later. Good luck.

-OK. Thanks a lot. We need it.

-Yeah, yeah. Take care.

As Rosetta got closer to the surface it was returning

astonishingly detailed images,

revealing cliffs and boulder fields,

cracks and fractures of the surface geology.

And surprisingly smooth dust-covered plains.

It is a remarkably complex landscape for such a small body.

That's amazing.

Seeing the images streaming live from the spacecraft

to here in Darmstadt is incredible.

And they're such a wonderful set, too.

I think what I am realising is how varied the surface of the comet is.

As Rosetta is flying over it we're seeing beautiful scene

after beautiful scene of landscape after landscape,

and of course we've still got the highest resolution images

still to come. Not too long to go now.

Of course, this wasn't the first attempt to land on the surface of 67P.

In 2014 the Philae lander had been released onto the comet.

One of the key goals of the final weeks of Rosetta's mission

was to find out what had happened to Philae.

Because it had disappeared shortly after landing.

Comet 67P is shaped like a large rubber duck.

Philae was due to land here, on the top of the duck's head.

And although it landed at exactly the right position

the thrusters and the harpoons which were due to anchor it to the comet

didn't fire, and so the lander bounced.

Pictures from the camera shows how Philae had bounced twice

on the comet's surface.

The data from its instruments showed that it had drifted for

two hours in the comet's low gravity

before finally coming to a halt.

The pictures from its onboard cameras revealed that it had

wedged itself under a cliff.

Philae had landed in the shade.

And with no sunlight reaching its solar panels

it could only operate as long as its batteries lasted.

So, just three days after touchdown,

Philae fell silent.

But it had gathered enough data to work out roughly where it might be -

this region here, called Abydos.

But nobody knew its true location.

Ever since then

the mission scientists have been searching for Philae.

In June 2015 the lander woke up briefly and made radio contact again

but couldn't communicate its exact location.

And until just a month ago there was still no sign of Philae.

In September Rosetta began its closest approach to the comet,

and much of the time of the Osiris camera was spent searching

for where Philae was hiding.

And on the 2nd September they got this photograph.

And if you look very closely you can see the distinctive shape of

the Philae lander.

After being missing for nearly two years,

Philae had been found.

For scientists like Ian Wright,

who had worked on the lander's instrument,

it was a chance to look back at what the mission have achieved.

There must have been an emotional reaction when you saw that

image of Philae on the ground.

I'm not one for crying,

but it was really an emotional experience, yeah.

Because we'd been looking at things over the last couple of years,

little white dots, and someone says, "Oh, we found it."

And you have a look at it and you think,

"Well, I don't know. I don't really get that."

But when you saw that image you said, "Nah, that's it.

"I don't need convincing. That is really it."

So that was great.

That was a really great day.

I would hate to be at this point now not having found it.

I think that would be really terrible.

Ian's instrument on Philae was a mass spectrometer called Ptolemy.

It was designed to collect samples drilled from the surface

and heat them in its ovens....

..analysing the products to reveal what the comet was made of.

But as Philae bounced, those initial plans went out of the window.

We actually got to measure the surface chemistry

at a couple of places, which wasn't planned.

But, you know, unfortunately,

because it landed on its side and the drill couldn't reach the surface

we just couldn't actually extract a sample of that material.

-You know, that's the way life goes.

-Yeah.

But, interestingly, as part of the whole journey from landing

the first time, bouncing around,

dust or whatever has collected in the oven

and we're able to boil it out,

just as we would have done if we'd actually drilled it.

And what we expected to see was some water and CO2..

-The main ingredients. Yeah.

-Yeah.

And actually, intriguingly,

the water signal was relatively low.

I mean, still the biggest signal, but nowhere near...

It clearly showed that what we landed on was very dry.

Comets are often called dirty snowballs.

But the discovery that 67P contains less water

and more dust than expected

means we might have to come up with a new label.

Icy dirt ball might be a better description.

This was just one of the many surprising discoveries about

the comet's make-up that the mission has made.

When it comes to saying, "What was your highlight?

"What was the thing that was, in a sense,

"most amazing or most unexpected?"

For me, it will be the detection of free oxygen, free O2.

Free oxygen is plentiful on Earth,

but only because it's produced by living organisms.

It WAS thought to be very rare in the rest of the solar system.

It does force us to rethink the whole notion about oxygen in

planetary atmospheres as an indicator of life,

because here it is in a comet.

There's no chance that this has been formed by life on a comet.

But what it does show us is that molecules like oxygen

were incorporated into the comet at the time of its formation,

it's been there ever since,

and that goes against any kind of thinking that we have about this.

And no-one expected this. I was taught...

I remember being taught that in the early parts of solar system formation

you use all the oxygen up, it reacts, you don't get O2,

and yet here it is.

It's a sign that we don't understand the chemistry.

Absolutely. Chemistry is still more exciting than we imagine.

-Ian, thank you very much.

-OK. Thank you.

But as well as learning about the composition of the comet,

the data collected by Rosetta have also produced

some remarkable new ways of experiencing 67P,

as I discovered when I met planetary scientist Geraint Jones.

As well as the instruments that's measuring the composition of

the dust there's also several instruments looking at the

composition of the gas coming off the comets.

And one of these is Rosina,

which is a very sophisticated mass spectrometer.

It's measured the gas that's come off from the comet while

Rosetta's been there and drawn up a very long list by now

of all the gases that are there.

So with this you can actually come up with an ingredients list

-for what a comet's made of?

-That's right, yeah.

A colleague in the Open University, Colin Snodgrass, came up with

the great idea of trying to simulate what this actually smells like.

And this postcard actually smells roughly of what

Rosetta sampled at the comet.

-So this is the smell of 67P?

-It is.

So, please.

OK, I'm going in.

I must... I quite like the smell.

It reminds me...of disinfectant, or it's quite perfumed.

What does it smell like to you?

Well, I must admit, I'm not too keen on it.

So people have different reactions.

Yeah, I get more hints of urine etc.

-Actually, I'm not going to smell again!

-Yeah.

I suppose comets are the building blocks of the early solar system,

so I guess this smells like the early solar system?

That's right. So we know from the Apollo astronauts

that the moon smells roughly of gunpowder.

Now we've got the smell

of somewhere else in the solar system, as well.

Another great advantage of this mission is that it's been

travelling alongside the comet for nearly two years,

and that's given us an unprecedented opportunity

to observe how 67P changes over time.

We've always known that comets get more active

as they get warmer.

They only produce their dramatic tails as they approach the sun.

But Rosetta has given us a ringside view to observe

these processes in much more detail.

When it first arrived in orbit around the comet in August 2014

it was half a billion miles from the sun

and the comet's nucleus was largely frozen and dormant.

But as its orbit brought it closer to the sun,

we can see it burst into life.

These three images show a period of just 36 minutes

on 29th July 2015.

In this middle image we see a vast but short-lived jet

bursting from the surface.

It's caused by ice below the surface converting into gas

and then shooting out into space.

Other outbursts have been even more dramatic.

On February 19th this year a huge event -

thought to have been a landslide - caused a massive cloud of dust

to erupt from the comet,

resulting in a sixfold increase in brightness.

It's this sort of sudden and rare event that would've been

almost impossible to observe if we had not been studying the comet

for a long period of time.

But by Friday lunchtime

Rosetta's adventure around 67P

was rapidly coming to an end.

This picture was taken just over 1km above the surface.

And with the spacecraft descending at about a metre per second,

it was only a matter of minutes until it hit the surface.

I joined Matt Taylor to watch the end of this remarkable mission.

That last 2km, we've never been there.

So the stuff we're getting now is unbelievable.

This trajectory, this impact, is giving us something that

we couldn't get in any other way.

So we're getting this because we're crashing it.

So we're sacrificing the spacecraft to get this science.

-What is the atmosphere in there at the minute?

-It's horrible.

This is the opposite of what they do all the time.

They spend their life making sure spacecraft are safe

and they've made this spacecraft do the opposite.

You look at the people in that room that have spent their careers

on this mission.

When I was in the room you could feel it.

You felt this deflation.

How does this compare to watching Philae disappear onto the surface?

HE SIGHS

Well, Philae was landing and going to do something afterwards.

This is, as soon as touches, there's no more. There's no more Rosetta.

-Operationally, of course. We've got the science.

-There's all this science.

-Yeah, but for this there's nothing after.

-Data's still coming down.

So the carrier signal is still pretty strong.

Three minutes to go.

-This must be data from very close to the comet.

-Yeah.

This is good.

This is a few tens of metres now, isn't it?

It's still there.

-Oh.

-SPORADIC APPLAUSE

We have LOS.

That's it.

He's just confirmed LOS.

Signal's gone. And how do you feel?

I just feel, actually, for that team the most.

Because as a scientist working on this mission we've still got stuff to do,

but they've had to do something that's so counterintuitive,

so against what they do

and this is cutting that team up.

And so this is the end of the Rosetta mission.

Thank you and goodbye.

Congratulations.

-It's been an amazing mission.

-Thanks again.

HE SIGHS DEEPLY

-Are you all right?

-Bugger.

-Well done.

-HE SIGHS

-Thank you very much for that.

-Thanks, mate.

-I appreciate it.

Give us a hug, you. Good man.

Right, what's the next mission? No.

There is only one mission. Let's see.

Rosetta's last picture was this blurry image taken

just 20 metres above the surface.

Just a few seconds later it crashed into the comet

and went quiet for ever.

Over the coming weeks and months we can expect many more images

from the descent to be released.

We will see deep into the heart of the pits.

All the data from the other instruments will help

in revealing the comet's composition and history...

and will help us understand the beginnings of the whole solar system.

And so goodbye, Rosetta.

The spacecraft may have finished its mission,

but the journey of discovery it's launched us on

will go on for many years to come.