How to Catch a Comet The Sky at Night

This month we have a space spectacular.

After over a decade of chasing a comet through the solar system,

the space probe Rosetta finally reaches its target.

And we'll be reporting from the European Space Agency's

mission control in Germany.

Rosetta is one of the most exciting and ambitious missions ever

attempted, like something straight out of science fiction.

There's a six billion kilometre journey,

a rendezvous with a comet and then, if all goes well,

a landing on the surface using harpoons and grappling hooks.

It's a wonderful scientific mission but it is also a remarkable

feat of engineering and I'm going to meet the people

who are in control and find out how they're going to pull this off.

And here in the UK, we'll be discovering why comets are

so important to study and viewing one visible in our skies right now.

Welcome to The Sky At Night.

Welcome to the European Space Operations Centre

mission control in Darmstadt, Germany.

This is where Rosetta's most critical manoeuvres are planned

and then carried out.

We'll be getting a tour of the spacecraft itself

and a look at the latest images from Rosetta

which have given scientists one or two surprises.

And I'm here at the Open University in Buckinghamshire,

where one of the key instruments on the Rosetta lander

was designed and built. We'll be finding out more about comets

and how they're helping us unravel mysteries of Earth's past

and maybe looking into the origins of life itself.

And there's a comet visible right now in the night sky.

Pete Lawrence will be showing you how to find it

and how to take a great comet photo.

Comets are probably one of the most spectacular

and enigmatic objects we see in our night skies.

For millennia they have caused us to wonder,

"What are they and where do they come from?!"

Even 1,000 years ago we recognised their distinctive shape.

In the 11th century Bayeux Tapestry

Halley's Comet is carefully stitched,

showing three main parts to a comet.

A solid nucleus surrounded by a halo, called a coma,

and then a long streaming tail

With the advent of photography comets have provided breathtaking images

and revealed features that cannot be seen with the naked eye.

Multiple tails are often revealed on photos.

A very straight gas tail is caused by the solar wind

ionising gases as they are given off, making them glow.

It always points directly away from the sun.

The more familiar diffused, often curved tail is made up of dust

which streams behind the comet,

which is also slightly deflected by the solar wind.

Recently we've been able to get an even closer look at a comet.

In 1986, space probe Giotto took these remarkable images

as it flew past Halley's Comet.

In the past 30 years there have been a number of missions

that have flown past comets.

And what they've discovered is a central nucleus

one to ten kilometres wide.

Comets also are surprisingly black due to the high carbon content.

The carbon is mixing with ice and rock,

and as the comet approaches the sun,

that ice vaporises, producing a coma and the glorious comet's tail.

The tail can be very long indeed.

Comet Hyakutake's was about 360 million miles long

when it appeared in 1996.

When the Earth passes through the remains of a comet's tail,

the result is an often spectacular meteor shower

as dust particles burn up in the Earth's upper atmosphere.

It's only when comets approach the sun closely enough to become active

and brightly lit that they become visible to us.

To date we've detected over 4,000 comets

but we know that there are billions more out there.

We think they're the leftover detritus of the formation

of the solar system, some 4.5 billion years ago.

And, as such, we can use them as tiny time capsules,

giving us a window into our distant past.

Now we hope to get an unprecedented view of a comet,

the snappily named 67P/Churyumov-Gerasimenko,

was discovered in 1969

and it's what is known as one of the Jupiter family comets,

as they have been swung into their orbits by Jupiter's gravity.

Picked from obscurity, it has become a scientific celebrity

as the target for the Rosetta mission.

And with Rosetta approaching it, we're beginning to get images

of the comet for the first time and it's throwing up some big surprises.

Chris is in Germany, looking at the latest images hot off the press.

Letting me loose in ESA's mission control is a bit like letting

a child loose in a sweet shop.

Here, look what I've found.

This is a model of Rosetta and it's completely accurate.

The real thing weighed 2.9 tonnes on launch,

this one's not quite that big but you can see these long solar panels

which in real life are 32 metres long.

They need to be that size to capture the faint light of the sun and so

that Rosetta can be powered all the way out in the outer solar system.

It's got this beautiful communications antenna here.

This can point towards Earth so it can send its signals back to us

and then, on the back, all of the instruments.

This is the side that will face the comet. You can see here

in particular the two cameras of the OSIRIS imaging system.

Those will provide the scientific images

and they'll help us select a landing site for Philae.

This is the little lander that will somehow touch down on the comet.

On August 6th Rosetta went into orbit around the comet and so now

those cameras are providing vital images to help the team

choose their landing spot.

But, as Dr Holger Sierks shows me,

those images have provided quite a surprise already.

The early images taken, yes, the beginning of July

when it had just barely started to resolve were a surprise

and it looks like two bodies sticking together,

-so that was quite obvious right from the beginning.

-Yes.

The first days in early July.

The most recent ones I've seen make it look a bit like a rubber duck

or something like that, or at least a small head on a body.

Is that because it's two bodies that have stuck together

or could this shape have appeared some other way?

I like the rubber duck a lot.

We don't know it yet.

That is a surprise and we'll have to work to find out why

the body looks like this.

It could be two pieces right from the beginning,

it could also be a bigger block that just had

some eruptions sideways and just carved like the shape we see.

So, the duck, if that's what we're calling it,

-is about three kilometres across, something like that.

-Yes.

It must make planning what you're going to do with Rosetta harder, and

that planning depends on the images that your cameras are providing.

-It makes planning harder but also more fascinating.

-Yes.

And we are now in the process of laying out the mapping sequences.

Yes, and the rest of the mission depends on

-the quality of those maps as well?

-Yes.

And we will also remap because the shape is going to change.

We'll watch it on the way in, so to the closest point to the sun,

so we'll see the activity rise and the comet be more

and more active and then die out again,

calm down. We know that the comet is releasing dust

and we want to study these areas where the activity is formed,

where dust has moved away,

and so why is it happening here in this area and not in others?

The physics of comets is not well understood.

So the immediate task for OSIRIS is to produce a three-dimensional map

of the surface. Can you show us how far you've got with that?

I can show you the current state.

Just looking here at the shape model here,

it's hard to understand where you would safely put down this lander.

Is the obvious thing to go for this big flat face here?

-That seems safest to me.

-Yes, that is very obvious.

The tricky thing is the sun is coming up

so if you project the illumination condition into November you'll see

that it's not so favourable on the large side, on this bottom side.

You don't want to land in the dark.

And you don't want to land in the dark so landing will be a challenge.

I think that we'll do a good job, I am convinced about this,

and find a good spot, perhaps on the back of the duck, we'll see.

Yes, OK, well, we can shoot for the back of the duck then!

That's excellent.

With Rosetta now in orbit, every day we see new critical

and stunning surface detail on the comet

and with the lander due to be released in November,

we'll be keeping an eye on more pictures as they come in over the

next few months and as the landing site is chosen and confirmed.

Rosetta and the lander module carry more than 20

scientific instruments between them, which will be sending back data.

Here in the UK the Open University is home to the team

in charge of a key instrument on the Rosetta lander, that will

actually analyse the comet's samples.

Comets are fascinating because they give us a snapshot

into the ancient solar system and by looking at what they're made of

we can understand how our world was formed and maybe even how life began.

Dr Natalie Starkey is one of the comet research team here and

has been studying particles of dust from the Earth's upper atmosphere.

Amongst the normal dust and pollution

she finds particles which form the tails of comets.

So, this is one of the most interesting particles

I've analysed actually because it contains all sorts of material.

We've got amorphous material up in the top and also over to the right.

-That looks quite gloopy.

-Yes, exactly, it's kind of...

It's more organic kind of material.

Organic? That sounds interesting.

Yes, it's not life, so people will think of organic material as life,

but actually what we are talking about is carbon, hydrogen, nitrogen

oxygen bonds and it's kind of organic precursor material.

-Right.

-The rest of the particle is quite rocky.

So what sort of analysis do you do?

Well, we try and do everything

because this is a sample of space and we don't get many of them.

So how many have you done in your career so far?

I've measured about 50 so far, maybe five that are really,

really interesting, that can tell us a lot about the kind of time

we're looking into, this really early material.

-4.5 billion years ago.

-Exactly, exactly.

So we want to throw every single instrument at them that we have,

you know, all these really advanced techniques

because they're precious samples

and as we are analysing it, we are destroying it as we go...

-Taking bits off the top.

-Exactly.

-Yes.

But we are getting some numbers at the same time.

And the next images you have here show some of the beautiful

isotopic images we get.

So when you say isotope, what do you mean?

Well, an isotope is just a special type of an element really,

it just contains a different number of neutrons in it

so we're just looking at these very little variations.

So those isotope distributions, what do they tell us?

Well, what we can see from this particle is that actually

there's quite a lot of variation in this single piece of dust.

Actually, this allows us to trace not only time -

so when that comet might have formed, a little bit,

it doesn't give us a date but we can kind of relative times -

but also processes, kind of what happened to those isotope ratios

because they change depending on the temperature

-and the conditions that that comet formed under.

-I see.

-So isotopes are actually giving you a location and timescale.

-Exactly.

So we start to be able to place things relatively to each other

and what we find with particles like this really interesting one

is that it contains pieces that are a bit mixed so it's not just

all one composition, it didn't all form in one place,

this piece of comet actually contains other pieces of comet

that formed in different places all over the solar system.

And somehow it all came together.

It somehow came together at a later date so our understanding

of comet formation is really led by research like this.

When we use these particles from the stratosphere we don't know

from which particular comet they've come from, but one time

we've actually been into space and we've sampled a comet

and it was the Stardust mission which landed back on Earth in 2006,

it was a NASA mission and what they did was actually just fly through

the tail of the comet, so all the material coming off

they just collected this as impacting particles

into the collectors and this mission was really groundbreaking.

So, our very simple comet model is that they formed

far from the sun and they only contain material that formed

far from the sun, in the cold outer reaches of the solar system.

Which would make sense, if they formed there, that's the material.

Yes, but actually what Stardust showed us is that this comet called

Wild 2 contained material that was formed in the inner solar system

so it contained material that is very similar to what we see

in asteroids, so it's a little bit complicated.

We probably have asteroids at one end, comets at the other,

but now we think there's a bit of a continuum in between

and so we need to go and measure more comets to really find out

what this continuum is and what's going on really.

-So I guess that is where Rosetta comes in?

-Exactly.

In your ideal scenario, the dream wish now,

what would you like to get out of Rosetta?

For me it's all about the landing because I want to drill into that

comet and get some of the samples and find out what it's made of.

It will hopefully tell us how far from the sun potentially this comet

formed and what kind of processes it's undergone in its lifetime

so where all those little pieces that form that comet

actually formed themselves.

Whether it was in the inner solar system which will be

a bit of a surprise or whether it was way away from the sun,

so this is one of the things will help us

build up that picture of the comet and its life history, basically.

Well, very good luck for it all and I am really looking forward

-to seeing some of this data coming out.

-Thank you.

Every decade or so we get a spectacular comet passing close by

the sun and giving us a display that dominates the night sky.

But there are actually comets visible much more frequently

than that and Pete's here to show you how to see one

that's in the night sky right now.

Typically there are lots of faint comets visible in the night sky

but occasionally one will get bright enough so that they can be seen

with a small telescope, or even a pair of binoculars.

Now, there's one of those visible this month.

This particular comet is relatively easy to see

as long as you know where to look.

This newly discovered comet, called C/2014 E2 (Jacques),

can be found by locating the bright star Capella.

At this time of year it's the brightest star

in the north-eastern part of the sky.

At the start of the month the comet lies in a patch of sky

approximately one fist width at arm's length to the right of Capella.

By the 15th it'll have moved up the sky

to sit left of the star Mirphak in Perseus.

Look up from Mirphak and you'll eventually arrive at the W shape

constellation of Cassiopeia. During August the W appears on its side.

After the 15th the comet tracks up towards Segin,

the star that marks the left hand end of the W.

It's so close to it on the nights of the 22nd and 23rd of August

that a pair of binoculars pointed at the star

should include the comet in the same field of view.

At the end of August E2 (Jaques) moves into the constellation of

Cepheus and, although it should be fading,

will hopefully remain a binocular target.

OK, you should be able to see this comet quite easily

with just a pair of binoculars, but if you've got a digital SLR camera,

a decent lens, and a tripod, you can try taking a photograph of it

to get an even better view.

Put the ISO or sensitivity of your camera high

and use an exposure of 30 or more seconds,

open the lens wide and set your focus to infinity

and take a photo of what you think is the right area of sky.

Use a remote trigger if you can to avoid camera shake.

Now, hopefully, if you're in the right area of sky,

you should be able to pick out a little fuzzy blob.

Let's have a look.

Just like that.

And that should be the comet.

The comet nucleus itself is, of course, not only tiny

but incredibly black so all we're looking at is the sun's light

reflecting off the dust it's emitting and from glowing gases.

The fuzzy, diffuse nature of a comet does make it quite

difficult to find first of all because it looks much fainter

than a star, but once you have identified it in your photograph

the thing to do then is to centre up the frame

so you're pointing directly at the comet

and then use a lens with a longer focal length to get closer in.

I'm going to use a telescope for this one.

Now, as most comets move relative to the stars,

if you take a long exposure shot on a tracking mount,

which keeps up with the stars, the comet will appear blurred.

One way around this is to take shorter exposures and,

using image processing software, combine the images,

using the comet's head as the reference.

This will make the stars appear like dotted lines

but the comet will really shine through

and hopefully show its true colour, an astonishing green glow.

And that's a very characteristic colour, seen in a lot of comets.

That's due to the gases which surround the central core

of the comet, the nucleus,

and they're giving off this amazing green coloured light.

It's the sun's ultraviolet light that causes the gases,

mainly cyanogen and diatomic carbon, to fluoresce and it's one

of the features of comets only really picked up by photography.

Comets make fantastic photographic subjects

and if you do manage to get a long exposure shot of it, that'll pick out

some good detail and give you a great image to show off as well.

If you do get a nice photo, share it via our website...

..where you'll also find my guide on how to find E2 (Jaques).

Dix, neuf, huit, sept, six...

It's been more than ten years since Rosetta was blasted into space

at the start of an epic mission.

Decollage.

It's taken more than £1 billion of investment

and decades of scientific work.

So why does visiting a comet warrant so much investment?

And how on earth are we going to achieve the mission's objectives?

Chris has been finding out.

One of the questions this mission sets out to answer

is a surprising one.

Could this water, this precious liquid

that makes all life on Earth possible,

have been carried here from space on the icy asteroids and comets

which have bombarded the Earth over millennia?

We think of ourselves as the blue planet,

with vast amounts of liquid water,

but if all of our water were gathered into one place,

well, this image shows how little there really is on Earth.

Nevertheless, it would take perhaps 100 million comets

to bring us all this.

It seems ridiculous that all of Earth's water could have been

delivered from space and yet, in the early days, Earth would have been

a hot world - any water would have boiled off almost immediately.

And so water must have arrived on Earth and the other rocky planets

later and one of the leading theories is that it was delivered

during a period of heavy bombardment nearly four billion years ago,

as icy comets and asteroids slammed into the Earth.

We think there might have been enough comets hitting the Earth

to supply all of our water, but one of Rosetta's tasks

is to look for hard evidence that they really did.

Water can contain different kinds of hydrogen, different isotopes.

And the ratio of these isotopes gives Earth's water a distinct signature.

Rosetta will analyse the water on the comet to see

whether it shares that same distinctive signature,

real evidence that our water could have come from comets.

But that's not all,

Rosetta will also be looking for complex chemicals like amino acids

which form the basis of life, to find out whether these, too,

could have come from comets.

These are some of the most profound questions in science today and

that's why this particular mission is so exciting, and so ambitious.

To answer these big questions Rosetta has to do something

really new, land on the surface and drill down to analyse what

lies beneath, and before you can do that you have to catch the comet.

It's an incredible undertaking,

challenging in just about every respect

and it's made Rosetta a huge engineering project.

Now the most crucial moments are finally upon the team.

Andrea Accomazzo's been working on Rosetta

since the earliest design stages and is the flight director.

It is one of the most challenging space missions ever.

Nobody has ever gone to such an irregular body,

such an active body with the need of such a high accuracy of flying

the spacecraft around the body so it's definitely something new,

it's unique in the history of space flight and it's fantastic.

How do you go about rendezvousing with the comet?

What we wanted to do, we wanted to reach the comet and stop there

and start orbiting the comet

so we had to slow down the spacecraft compared to the comet and slowly

approach it and once we were close to it then we could start our mission.

At the end of our ten-years journey we now start exploring

a new world and we have to characterise it completely.

We don't know anything of this new world.

We have to characterise the gravity field first,

we have to characterise how it's rotating,

we know the shape, we have taken a couple of images but we have to

characterise it to a level such that we can then orbit and land.

And, of course, this is a changing body as well,

we expect the comet to become more active as it gets near the sun.

We have already seen some activity from the comet.

How do you have to take that into account?

It sounds like a scary place for a spacecraft to be.

Indeed, indeed, it is also a scary place to be with a spacecraft

which has huge solar arrays.

Fundamentally the comet is releasing material and gases

so we are going to a windy place with huge sails

and it's not easy to navigate around a body like this

but this is the mission we have and we will do it.

A lot of science will come from the main spacecraft

but the lander is very, very exciting. Tell us about that,

how is the lander going to touch down on the comet?

The lander, for sure, is the most fascinating part of this mission.

You can imagine we are landing on a body that is far away from the

Earth, a body that is so irregular so it definitely is the most

fascinating, and also technically it is the most challenging for us.

We have to release the lander when we are flying

in front of the comet which is a very bad region for the wind.

The wind is expected to be very high.

-Because that is where the sun's energy comes in.

-Right, right.

The sun is heating the surface of the comet

and it's blowing out a lot of gases.

We have to fly very fast in front of the comet, release the lander,

the lander will slowly fall onto the surface of the comet...

-Just pulled by the comet's gravity?

-Right.

It is pulled by the gravity of the comet.

There is no active system to slow down on the lander

and when it lands, it anchors itself, it has two harpoons underneath

and they will be fired onto the surface, hoping to hook it there.

And so the lander will do its thing, it will send back information,

but the mission goes on even after the landing.

What happens next?

The mission itself is spending 18 months at least around the comet.

There's much more we have to discover through the science instruments on board Rosetta.

So taking it together, it's 18 years of work for you,

what does it feel like to be this close to starting to get data back?

Well, when I started working on Rosetta in 1996 it looks so far away

the whole thing but my life has gone through, in my professional life

and my private life, has gone through this 18 years and now we are there

and it can't be anything better than what we are living right now.

Well, I hope it all goes well, we look forward to seeing the results.

-Thank you very much.

-Thanks.

The Rosetta probe is an astonishing piece of craftsmanship.

Here at the control centre they have what's called an engineering replica

of it, kept in pristine, space-like cleanliness

and used to test all of the software on board.

This engineering replica is obviously missing its solar panel wings,

but other than that it's the perfect way to admire

all of Rosetta's features.

The whole thing weighed 2.9 tonnes on launch.

But 1.6 tonnes of that was fuel.

24 tiny thrusters give precision control.

Rosetta itself carries 11 on-board instruments,

which all have to share the same power supply.

There are 12,000 separate electrical connections.

They alone took three years to build and all of them have to work.

Over the next three and a half months,

Rosetta will be working its way closer to the comet,

taking images and measurements with these instruments all the time,

helping us to understand what's going on

and trying to select a site for the all-important landing.

After nearly 20 years of work, I can't imagine what the team

here must be thinking as they get close to these historic moments.

We're going to explore a brave new world,

we're going to learn so much not just about this comet,

not just about the origins of the solar system,

but also about what happened a long time ago here on Earth.

It's a really, really exciting time.

Of course, we'll be following Rosetta's progress over the next

nail-biting couple of months as it spirals down towards the comet,

releasing the lander with its grappling hooks, ready for drilling.

And next month we'll be looking at new worlds

discovered on planets outside our solar system.

In the meanwhile, get outside and get looking for comets. Good night.

# Let's hitch a rocket to the moon

# Open out the throttle

# Steer towards the sun

# Rosetta's in her stride

# Surf the comet's tail on an astronomic trail

# Take the world along just for the ride

# Comet chaser! #