This remarkable object is one of the oldest surviving images of the
night sky, showing the moon in 1857,
not long after the process of photography had been invented.
It's a beautiful, fragile and wonderful thing.
But what it represented at the time was a spectacular
breakthrough in technology.
Since then, we've come a long way.
For the past 50 years,
we've been sending spacecraft around the solar system.
And they have been sending back the most amazing pictures.
On tonight's programme, we'll be revealing our choice
of the five most stunning images ever taken of the solar system.
We'll be investigating why these images were taken
and how they've transformed our understanding of these alien worlds.
Welcome to The Sky At Night.
Appropriately enough,
we're at the Natural History Museum's Other Worlds exhibition.
A collection of spectacular images of the solar system.
What's stunning about capturing images like these,
of other bodies within our solar system, is that it would have been
inconceivable just one generation ago.
Over the next half hour, we're going to bring you remarkable
and striking images from all over the solar system.
And we've chosen what we think are the five most significant,
based on three criteria.
Firstly, scientific interest.
Each image needs to reveal something about our solar system,
how it works or its history.
And secondly, they need to represent a technological advance,
a new way of seeing the solar system.
And finally, of course,
each image needs to be absolutely visually stunning.
There are literally thousands of images we could have chosen.
But we've settled on what we think are the top five.
We start by considering images of Saturn.
Saturn has always been considered to be the most beautiful planet
and since 2004, the Cassini space probe has been in orbit about it
and it has sent back some extraordinary pictures.
And our choice for the iconic picture of the Saturn system is this
breathtaking portrait of the planet and its rings.
To explain the intricacies of this stunning image,
I've been joined by Cassini imaging team's scientist Carl Murray.
Carl, this is an extraordinary image of the planet Saturn and its rings.
But there is so much here, can you guide me through?
Well, it's actually 141 different images all mosaicked together.
But taken in a very special geometry,
when the sun was eclipsed by Saturn.
So, we are in the shadow of Saturn,
the spacecraft is in the shadow of Saturn when the image was taken.
So, what we see is a kind of a unique view.
We can see, for example, this bright ring around the planet,
which is the sunlight being refracted through the atmosphere.
We can see the main rings themselves
and we start to see these other rings,
which are normally almost invisible to see.
But this geometry, this alignment with the sun allows us to see
these faint rings and learn something about them.
Yes, they seem to be so far out beyond the planet.
It's just a huge system. It is. In fact,
this whole image is covering about 600,000 kilometres across.
So, there's the planet, which is
about 60,000 kilometres across and then this vast,
main ring system here
and then these faint rings going out beyond that.
There's all sorts of colours going on here. Now, is this real data?
Or is it an artificial colour? The differences are real.
So, for example, the main rings you see,
we know are composed of water ice. We've known that for some time.
So, you would expect that to be essentially white,
but there are some contaminants in the rings as well.
So, there's a slight reddishness to the rings, which,
combined with the water ice gives this sort of yellowish colour.
But the photo reveals more than just the rings.
Elsewhere in the image, we see several of Saturn's 62 moons.
And the photograph also reveals how the formation of Saturn's
rings and moons are entwined.
This is the moon Enceladus.
So, this is active. We think there's liquid water,
possibly even a global ocean of liquid water underneath.
And this material is coming
out at pressure and going out to several hundred kilometres.
And then just, sort of, wandering around.
If you just look really closely, you can actually see
plumes of material coming out of the south polar region. Yes.
And that has created the entire E ring.
So, it shows this connection between rings and moons. Yeah.
And it seems to be quite a strong one.
So, moons forming rings and then, sometimes, rings forming moons?
Yes. I find that surprising.
I did too, when it was first proposed,
but we know that material naturally can accrete in the rings.
Supposing you get a large enough mass, then it could start
evolving, as it interacts with the ring material around it.
And, maybe, even escape from the rings and then move outwards.
And maybe catch up with another one that had ready escaped
and get larger. And they originally proposed it for small moons
and they think now maybe even the larger moons of Saturn
and indeed other giant planets could have formed in this way.
So, rings can lead to moons. If moons break up, they can lead
to rings. And it's a very interesting process that goes on.
Yeah, far more dynamic than I ever realised. Exactly.
Now, you have this, what I like to call
an accretion disc, with a large mass in the centre.
That all sounds very familiar. Yes, it's funny you should say that,
it's very similar to what we think that early solar system was like.
That there was a disc of material out of which the planets formed,
in that case.
And this is a disc that we can study in detail now.
We can see how things evolve now and then try
and extrapolate to what went on in the early solar system.
So, by studying the rings of Saturn,
we can actually look back to the formation of our whole solar system.
Well, I think that makes this an incredible, powerful picture.
Cos not only is it a beautiful picture of Saturn,
but it's giving us an understanding of our very own origin.
Well, thank you, that was fantastic. You're welcome.
Before we leave this astonishing photo,
consider the technology that was used to take it.
Cassini's black-and-white camera has a resolution of
just one megapixel,
a fraction of what you'll find in the average smartphone.
It's only by stitching the photos together
and applying filters that isolate particular wavelengths of light,
that it is possible to make these astonishing colour images.
Art and science, both served by the power of technology.
Our next photograph moves beyond art and science,
to touch the deepest human emotions
and it was captured by a camera even more primitive than Cassini's.
I'm remarkably lucky to be holding this thing in my hands.
It's a flight spare, a copy of the cameras that flew
on the Voyager 1 mission,
one of two spacecraft that were launched in 1977,
towards the outermost planets of the solar system.
It's the same technology that was used in the first video cameras.
And although it looks rather primitive now,
the Voyagers produced some of the most spectacular images
we'd ever seen.
As the Voyager probes flew out through the solar system
in the late '70s and '80s, they sent back amazing pictures.
There was detailed video of Jupiter
and its immense red-spot storm.
And the first close-up images of Jupiter's moons,
revealing Io to be volcanically active
and Europa's icy surface to be covered in mysterious stripes.
The probes flew past Saturn
and then became the first to photograph Uranus and Neptune.
We haven't picked any of those images -
instead we've chosen one taken on Valentine's Day, 1990 -
a time when Voyager 1 was more than six billion kilometres from the sun.
And, at the suggest of the famous planetary scientist Carl Sagan,
it turned to look back in the direction from which it had come
and it took this image.
And, at first, there's not much to see.
You see the blackness of space, a couple of streaks,
which are glare from the sun on the lens.
The sun must be up here somewhere.
But, if you look closer, you see this tiny, pale blue dot,
suspended in one of those sunbeams.
And that is the Earth, seen floating on its own,
amongst the blackness of space.
And no-one caught the emotional impact of that realisation
better than the man
whose idea the picture was.
And this is where we live, on a blue dot.
Consider again that dot.
That's here, that's home,
that's us.
On it, everyone you love,
everyone you know, everyone you ever
heard of, every human being who ever
was lived out their lives on a mote
of dust suspended in a sunbeam.
The Earth is a very small stage
in a vast cosmic arena.
Our third picture was taken 25 years after the pale blue dot,
by the next mission we sent to the outer reaches of the solar system.
Last summer, after a 9½-year journey,
the New Horizon space probe began its approach to Pluto,
a world many expected to be frozen and featureless.
Until then, our highest resolution images of the dwarf plant had
been little more than a fuzzy dot.
Now, we were getting increasingly detailed pictures and,
on the 14th of July, New Horizons
made its closest approach as it flew past Pluto.
For the mission's scientists, there was a nervous wait to see what,
if any, images had been captured by the space craft.
One of those scientists was Carly Howett.
It felt like being five again
and it was Christmas morning
and you knew that there were presents,
but until you actually see what's inside the box,
we didn't really know for sure whether the exposure times
that we'd set were right and all those sorts of things.
So, we were confident in our abilities,
but you're always a little bit nervous.
So, once we started getting the data on the ground,
we knew it was safe and we knew it was good.
And it was like Christmas morning over and over again.
Our third image is this spectacular image of Pluto
taken by New Horizons.
The dwarf planet snapped suddenly into focus
and it was unlike anything
that had been expected.
This image really revolutionised the way that we understood Pluto.
One of the first things that we saw in this image were the mountains.
There are mountains of water ice on Pluto.
They stand about 2½ miles high,
which, for a water ice mountain, is incredibly high.
We wouldn't get that on the Earth, water ice wouldn't be strong
enough, it would collapse under its own weight.
But, at Pluto's cold temperatures,
it's strong enough to maintain that weight.
On closer inspection, some of the mountains held even more surprises.
They have holes in.
And you only get holes in mountains if they're volcanoes.
And so, what we think is going on here is there are cryovolcanoes.
So, not volcanoes in the way that we're used to them,
on Hawaii, with hot rock and lava,
but rather volcanoes that would have emitted ice.
We don't see them being active now,
we don't see any outflow from them at the moment,
we don't know when they were last active,
but there's certainly enough strange terrain around them
to indicate that they must have been active in the near recent past.
But while some areas of Pluto were rugged and mountainous,
in others, such as the large heart-shaped Tombaugh Regio,
the ice was suspiciously smooth.
The left side was known as Sputnik Planum
and this is an interesting region,
because it's incredibly smooth.
But, when we zoom in, you can
see there's a lot of complicated structure in this region.
And you can see there's all of this structure in the cells itself.
But you can see how different this terrain is when you get
up against the bedrock, if you like, of the surrounding regions.
Now, the smoothness is very strange.
Everywhere is bombarded by meteorites,
these are called impact craters.
And so what is going on in this region of Pluto to eradicate
those impact craters? There's several ideas about this.
The prominent idea is that this is made of mostly nitrogen
and carbon monoxide.
These are quite soft and so
we don't think a lot of heat is needed to get these ices moving.
The heating that Pluto still has from its core is able to
circulate those ices.
So, if you had an impact here, it wouldn't take long before this
overturning eradicated any evidence for it.
So, this image really has revolutionised
our understanding of both Pluto and the outer solar system.
Before we got there, we knew something of its bulk
composition, but we didn't know about its complex geology.
And we certainly didn't think that it was geologically active.
This has huge implications,
not only for our understanding of Pluto and its evolution
and its composition, but also for other,
similar bodies in the outer solar system.
Before we reach our next photo, let's delve back
into the history of our attempts to photograph the solar system.
We've only been sending probes to the planets for 50 years.
But, as Pete Lawrence has been finding out,
the art of astrophotography is much, much older.
The technology found in digital cameras today has come
directly from astronomy.
In fact, the sensors, like the one I'm using here and the ones found in
digital cameras and smartphones are descended from those
developed by NASA for interplanetary spacecraft.
And the desire to take pictures of the sky has a long
history in helping develop photographic techniques.
In fact, even before they were taking photographs of people,
photographers were taking pictures of the sky.
The earliest photographs, called Daguerreotypes, were taken on
chemically-coated sheets of copper and developed using mercury fumes.
However, these weren't very sensitive
and could only capture the very brightest objects in the sky.
So, photographers and astronomers
came up with a series of new techniques.
I've come to the Observatory Science Centre, in Herstmonceux,
where astronomers have been imaging the sky for 150 years to try
out one of those old techniques.
This is Guy Paterson,
an artist who specialises in historic photographic methods.
Hi, Guy.
Hi. Nice to meet you. This looks quite interesting.
What's going on here?
We're going to attempt to get a shot of the moon,
using a very old process called wet plate collodion. Right.
So, what have you got to do then, to make this work?
OK, so, we're going to start off by putting on these protective gloves,
cos silver nitrate tends to stain anything organic for several
days if you use it. We have our plate,
it comes with a protective film over the surface we want to use.
So, we're going to peel that off.
So, I'm going to pour on the collodion. OK.
It's completely away from the sanitisation of using digital kit,
where you just press a button and the image appears on the back of it.
That's right. I think that's a lot of the appeal, actually,
you're completely in control of the situation.
If it goes well...
PETE LAUGHS
Right, so, now we're ready for it to go into the silver nitrate solution.
OK. And we lower it in there, carefully.
That makes it light sensitive after that point.
I guess the lights have got to go out now,
so that we can get the plate onto the back of the telescope.
That's right.
And try and capture a picture of that moon, which is
shining brightly out there, perfect for us.
Five, four, three, two, one.
And here is our plate. Nothing to see at the moment.
Now we're going to develop, which we do just pouring the solution on.
So, this takes about 15 seconds, you say? That's right.
Just stop the development by pouring water over it.
Finally. It's the moment of truth.
Oh, look at that.
So, now you've rinsed it off, is it OK to turn the lights back on?
Yeah, it should be absolutely fine. OK.
This is amazing and just how it used to be done.
The plate is actually quite small, but
when you look at it closely, you can see there's loads of detail on it.
And, to be honest, I'm actually quite surprised that this old
technology is able to produce something as sharp as this.
Quite amazing.
So far, we have seen three of our five images.
A portrait of the whole Saturn system,
a distant view of planet Earth
and a revolutionary image of Pluto.
Our next image may seem plain by comparison.
It's a picture of Gale Crater on the surface of Mars.
But this photo is special, because it shows with incredible accuracy
what it would be like to stand on the surface of another world.
It was taken by one of the most advanced pieces of equipment
we've ever sent into space.
The Curiosity Rover that was lowered onto
the surface of Mars in August 2012.
Amongst its suite of scientific instruments,
Curiosity is equipped with a camera mounted on a mast at head height.
This particular image was created by painstakingly assembling more
than 70 frames from that camera into a single high-resolution panorama.
The colours have been adjusted to render them
as close as possible to what our eyes would see.
It is the work of artist Michael Benson.
So, this is sort of a human eye view of the Martian surface. Yeah.
Exactly, and what I'm trying to achieve with a lot of these images,
most of these images, is to give people a sense of what it
might look like if we could actually go.
So, why is it important to let people see images like this?
I think that we, on Earth,
spend too much time in our self-absorbed concerns, you know?
I would surmise that it might be useful
if we looked up a little more and understood that we belong,
that the Earth belongs, to a suite of landscapes,
orbiting the same source of light, the sun.
Some of them very alien, sci-fi, you know, Jupiter.
And some of them are very close to what we might see...
I mean, they're very Earth-like in some ways. This one,
for example, it looks like Utah or Arizona.
And you can see this connection between Mars and our planet.
Those are the so-called terrestrial planets, those with hard surfaces
in the inner solar system. Yeah. So, that's part of what I'm trying
to convey with this work. So, this could be Earth, but it's not.
This is another planet, out there.
But the sky gives it away, doesn't it? Yes, that does look alien.
Yeah, yeah, yeah. Well, I think it gives everyone an opportunity to
stand on the surface of Mars and to me, that's a great achievement.
Thank you very much. Thank you. I appreciate it.
But, as awe-inspiring as this picture is,
there's a great deal more to it than its aesthetic appeal.
The primary purpose of imaging the planets is to provide
scientific value.
And in that one image of Gale Crater, there's an amazing
wealth of detail about the geological history of Mars.
I've come downstairs in the museum to find Dr Joe Michalski,
a planetary geologist who uses images from spacecraft to study
the geological past of Mars.
So, when I look at this image, I see a landscape
and I can imagine being there.
But, as a geologist, what do you get from images like this one?
Well, the first thing we think about is context.
The important thing here is that this is the floor of a huge
impact crater. Those craters, effectively,
are basins where sedimentary rocks accumulate from various processes.
Cos it's an old impact crater? Yeah, about four billion years old.
And the rocks within it are also old,
but 500 million years younger than that. So, a lot is going on there.
OK, so what should I be looking at, if I want to be a Martian geologist?
Where do we start? So, if you look at the top of the image,
that's the edge of Mount Sharp.
You can see layered rocks that are nearly horizontal.
Yeah, there's this, sort of, stripeyness to it.
Yeah, so those are rock beds, strata,
that formed probably through air-fall of volcanic ash or dust.
And that's accumulated over millions of years
and that's why it forms layers.
Then, beneath that, you can
see there are these other units that don't form as prominent topography.
The bluish and the light brown.
So, the fact that it does not form these big buttes tells me
that it's a softer unit. And, so,
if we were able to investigate the mineralogy of that, it might
be something that, for example, contains clay minerals or sulphates.
So, those are minerals that formed in water, but they're softer.
So, part of the evidence that there was some water here or some
dampness here is the fact that you have clay and these other things?
That's right. In between is this unit,
which is just composed of gravel and sand and dust.
Those are common deposits on Mars,
where you've got a little bit of fluvial activity.
That's river-like, right? Or water. Yeah, exactly.
So, when we look at this image, we see a landscape partly
shaped by water.
And the crater's 5km deep,
so should I be imagining a big, deep lake? Was the crater full of water?
As we've investigated this further, it seems that no,
it probably wasn't ever filled like that.
But, certainly, there was water here.
There were small lakes that came
and went at the scale of thousands of years.
It seems like a lot to a human, but geologically, it's a snapshot.
It's amazing to me how much you can tell from this one image,
but, of course, that's the beauty of these images of other worlds.
They're not just beautiful things to look at, they're data as well.
Yeah, that's right.
Every single image is packed with scientific information.
Joe, thank you very much. Thanks.
That brings us to our last image, which is
a bit different to our others, because even I haven't seen it yet.
It's only just been taken.
Via this NASA website I can access data from a satellite called
the Solar Dynamics Observatory, which sits 36,000km away
from Earth staring at the sun and sending its data back.
This is its most recent image, taken just ten minutes ago.
It's not the view of the sun we're used to,
it's not a featureless yellow disc.
This is the sun in the ultraviolet.
The Solar Dynamics Observatory captures images using
light in ten different wavelengths.
It reveals the sun to be a very different
beast from the featureless, golden disc we're used to seeing.
It shows the surface to be incredibly active,
bursting with flares and massive explosions of super-heated plasma.
This is the true face of our sun.
I never get tired of seeing the sun like this.
It's not just a boring, yellow disc, it's a dynamic and active world.
There are wonderful features in its atmosphere
and the disc itself is a turbulent, boiling mass of gas.
And we can see all of that because we're looking in the ultraviolet.
And that's one of the reasons we chose this image, it
demonstrates that by going beyond the light that our human eyes
are sensitive to, we can get much more information about the cosmos.
The Solar Dynamics Observatory actually images the sun once
every ten seconds,
giving us a real-time view of the star that allows us
to trace the source of its surface activity.
In some wavelengths, we can see dark sunspots on this surface.
But in other wavelengths, we can see that those dark spots
are the sites for the greatest solar activity.
Where arcs of plasma burst from the surface along the twisted
magnetic field lines of the sun.
And that's important,
because activity on the sun has a tremendous affect on the Earth.
The activity on the sun's surface creates what is known as
space weather.
The flares and ejections from the surface
send streams of charged particles shooting out into space.
If they hit the earth, they create quite an effect.
Causing aurorae, like the Northern and Southern Lights.
But those solar storms can also cause severe damage to the
electrics of satellites and even interrupt power supplies on Earth.
And that is why the Solar Dynamics Observatory images are so important.
It is hoped that the information embedded in these brilliant images
will give us an understanding on the causes
and variety of solar activity, helping us to predict
space weather and finding out when solar storms
are heading towards Earth.
So, that's it, our choices for the top five solar system photos.
And if you think we've missed something or if you disagree,
you can use Twitter to let us know.
But whatever your favourite images, you can agree, I'm sure,
that we've come a long way
since this wonderful image of the moon taken almost 160 years ago.
We really have.
And that's all we have time for this month.
Next month, we'll be joined by Stephen Hawking to explore
the recent discovery of gravitational waves
and what they can tell us about black holes.
In the meantime, get outside and get looking up.
Goodnight.