0:00:04 > 0:00:07This remarkable object is one of the oldest surviving images of the
0:00:07 > 0:00:11night sky, showing the moon in 1857,
0:00:11 > 0:00:15not long after the process of photography had been invented.
0:00:15 > 0:00:18It's a beautiful, fragile and wonderful thing.
0:00:18 > 0:00:21But what it represented at the time was a spectacular
0:00:21 > 0:00:23breakthrough in technology.
0:00:23 > 0:00:26Since then, we've come a long way.
0:00:26 > 0:00:28For the past 50 years,
0:00:28 > 0:00:32we've been sending spacecraft around the solar system.
0:00:32 > 0:00:36And they have been sending back the most amazing pictures.
0:00:36 > 0:00:40On tonight's programme, we'll be revealing our choice
0:00:40 > 0:00:44of the five most stunning images ever taken of the solar system.
0:00:44 > 0:00:47We'll be investigating why these images were taken
0:00:47 > 0:00:51and how they've transformed our understanding of these alien worlds.
0:00:51 > 0:00:53Welcome to The Sky At Night.
0:01:25 > 0:01:28Appropriately enough,
0:01:28 > 0:01:31we're at the Natural History Museum's Other Worlds exhibition.
0:01:31 > 0:01:34A collection of spectacular images of the solar system.
0:01:37 > 0:01:40What's stunning about capturing images like these,
0:01:40 > 0:01:43of other bodies within our solar system, is that it would have been
0:01:43 > 0:01:46inconceivable just one generation ago.
0:01:46 > 0:01:48Over the next half hour, we're going to bring you remarkable
0:01:48 > 0:01:51and striking images from all over the solar system.
0:01:51 > 0:01:55And we've chosen what we think are the five most significant,
0:01:55 > 0:01:56based on three criteria.
0:01:56 > 0:01:59Firstly, scientific interest.
0:01:59 > 0:02:02Each image needs to reveal something about our solar system,
0:02:02 > 0:02:04how it works or its history.
0:02:04 > 0:02:07And secondly, they need to represent a technological advance,
0:02:07 > 0:02:09a new way of seeing the solar system.
0:02:09 > 0:02:11And finally, of course,
0:02:11 > 0:02:15each image needs to be absolutely visually stunning.
0:02:15 > 0:02:20There are literally thousands of images we could have chosen.
0:02:20 > 0:02:24But we've settled on what we think are the top five.
0:02:25 > 0:02:28We start by considering images of Saturn.
0:02:31 > 0:02:35Saturn has always been considered to be the most beautiful planet
0:02:35 > 0:02:39and since 2004, the Cassini space probe has been in orbit about it
0:02:39 > 0:02:43and it has sent back some extraordinary pictures.
0:02:45 > 0:02:50And our choice for the iconic picture of the Saturn system is this
0:02:50 > 0:02:55breathtaking portrait of the planet and its rings.
0:03:02 > 0:03:05To explain the intricacies of this stunning image,
0:03:05 > 0:03:10I've been joined by Cassini imaging team's scientist Carl Murray.
0:03:10 > 0:03:14Carl, this is an extraordinary image of the planet Saturn and its rings.
0:03:14 > 0:03:17But there is so much here, can you guide me through?
0:03:17 > 0:03:21Well, it's actually 141 different images all mosaicked together.
0:03:21 > 0:03:23But taken in a very special geometry,
0:03:23 > 0:03:26when the sun was eclipsed by Saturn.
0:03:26 > 0:03:28So, we are in the shadow of Saturn,
0:03:28 > 0:03:32the spacecraft is in the shadow of Saturn when the image was taken.
0:03:32 > 0:03:34So, what we see is a kind of a unique view.
0:03:34 > 0:03:38We can see, for example, this bright ring around the planet,
0:03:38 > 0:03:41which is the sunlight being refracted through the atmosphere.
0:03:41 > 0:03:43We can see the main rings themselves
0:03:43 > 0:03:45and we start to see these other rings,
0:03:45 > 0:03:49which are normally almost invisible to see.
0:03:49 > 0:03:52But this geometry, this alignment with the sun allows us to see
0:03:52 > 0:03:56these faint rings and learn something about them.
0:03:56 > 0:03:59Yes, they seem to be so far out beyond the planet.
0:03:59 > 0:04:02- It's just a huge system. - It is. In fact,
0:04:02 > 0:04:06this whole image is covering about 600,000 kilometres across.
0:04:06 > 0:04:09So, there's the planet, which is
0:04:09 > 0:04:12about 60,000 kilometres across and then this vast,
0:04:12 > 0:04:13main ring system here
0:04:13 > 0:04:16and then these faint rings going out beyond that.
0:04:16 > 0:04:20There's all sorts of colours going on here. Now, is this real data?
0:04:20 > 0:04:24- Or is it an artificial colour? - The differences are real.
0:04:24 > 0:04:26So, for example, the main rings you see,
0:04:26 > 0:04:30we know are composed of water ice. We've known that for some time.
0:04:30 > 0:04:32So, you would expect that to be essentially white,
0:04:32 > 0:04:35but there are some contaminants in the rings as well.
0:04:35 > 0:04:38So, there's a slight reddishness to the rings, which,
0:04:38 > 0:04:41combined with the water ice gives this sort of yellowish colour.
0:04:41 > 0:04:44But the photo reveals more than just the rings.
0:04:44 > 0:04:48Elsewhere in the image, we see several of Saturn's 62 moons.
0:04:51 > 0:04:55And the photograph also reveals how the formation of Saturn's
0:04:55 > 0:04:56rings and moons are entwined.
0:04:58 > 0:05:00This is the moon Enceladus.
0:05:00 > 0:05:04So, this is active. We think there's liquid water,
0:05:04 > 0:05:06possibly even a global ocean of liquid water underneath.
0:05:06 > 0:05:08And this material is coming
0:05:08 > 0:05:11out at pressure and going out to several hundred kilometres.
0:05:11 > 0:05:14And then just, sort of, wandering around.
0:05:14 > 0:05:17If you just look really closely, you can actually see
0:05:17 > 0:05:20- plumes of material coming out of the south polar region.- Yes.
0:05:20 > 0:05:22And that has created the entire E ring.
0:05:22 > 0:05:25- So, it shows this connection between rings and moons.- Yeah.
0:05:25 > 0:05:28And it seems to be quite a strong one.
0:05:28 > 0:05:32So, moons forming rings and then, sometimes, rings forming moons?
0:05:32 > 0:05:34- Yes.- I find that surprising.
0:05:34 > 0:05:36I did too, when it was first proposed,
0:05:36 > 0:05:39but we know that material naturally can accrete in the rings.
0:05:39 > 0:05:43Supposing you get a large enough mass, then it could start
0:05:43 > 0:05:46evolving, as it interacts with the ring material around it.
0:05:46 > 0:05:50And, maybe, even escape from the rings and then move outwards.
0:05:50 > 0:05:53And maybe catch up with another one that had ready escaped
0:05:53 > 0:05:56and get larger. And they originally proposed it for small moons
0:05:56 > 0:06:00and they think now maybe even the larger moons of Saturn
0:06:00 > 0:06:03and indeed other giant planets could have formed in this way.
0:06:03 > 0:06:08So, rings can lead to moons. If moons break up, they can lead
0:06:08 > 0:06:11to rings. And it's a very interesting process that goes on.
0:06:11 > 0:06:14- Yeah, far more dynamic than I ever realised.- Exactly.
0:06:14 > 0:06:17Now, you have this, what I like to call
0:06:17 > 0:06:20an accretion disc, with a large mass in the centre.
0:06:20 > 0:06:23- That all sounds very familiar. - Yes, it's funny you should say that,
0:06:23 > 0:06:27it's very similar to what we think that early solar system was like.
0:06:27 > 0:06:30That there was a disc of material out of which the planets formed,
0:06:30 > 0:06:31in that case.
0:06:31 > 0:06:34And this is a disc that we can study in detail now.
0:06:34 > 0:06:38We can see how things evolve now and then try
0:06:38 > 0:06:40and extrapolate to what went on in the early solar system.
0:06:40 > 0:06:42So, by studying the rings of Saturn,
0:06:42 > 0:06:46we can actually look back to the formation of our whole solar system.
0:06:46 > 0:06:48Well, I think that makes this an incredible, powerful picture.
0:06:48 > 0:06:51Cos not only is it a beautiful picture of Saturn,
0:06:51 > 0:06:54but it's giving us an understanding of our very own origin.
0:06:54 > 0:06:57- Well, thank you, that was fantastic. - You're welcome.
0:06:57 > 0:07:00Before we leave this astonishing photo,
0:07:00 > 0:07:03consider the technology that was used to take it.
0:07:04 > 0:07:07Cassini's black-and-white camera has a resolution of
0:07:07 > 0:07:10just one megapixel,
0:07:10 > 0:07:14a fraction of what you'll find in the average smartphone.
0:07:14 > 0:07:17It's only by stitching the photos together
0:07:17 > 0:07:21and applying filters that isolate particular wavelengths of light,
0:07:21 > 0:07:26that it is possible to make these astonishing colour images.
0:07:26 > 0:07:29Art and science, both served by the power of technology.
0:07:31 > 0:07:35Our next photograph moves beyond art and science,
0:07:35 > 0:07:37to touch the deepest human emotions
0:07:37 > 0:07:42and it was captured by a camera even more primitive than Cassini's.
0:07:44 > 0:07:48I'm remarkably lucky to be holding this thing in my hands.
0:07:48 > 0:07:51It's a flight spare, a copy of the cameras that flew
0:07:51 > 0:07:53on the Voyager 1 mission,
0:07:53 > 0:07:56one of two spacecraft that were launched in 1977,
0:07:56 > 0:07:59towards the outermost planets of the solar system.
0:07:59 > 0:08:02It's the same technology that was used in the first video cameras.
0:08:02 > 0:08:04And although it looks rather primitive now,
0:08:04 > 0:08:07the Voyagers produced some of the most spectacular images
0:08:07 > 0:08:09we'd ever seen.
0:08:12 > 0:08:15As the Voyager probes flew out through the solar system
0:08:15 > 0:08:20in the late '70s and '80s, they sent back amazing pictures.
0:08:22 > 0:08:24There was detailed video of Jupiter
0:08:24 > 0:08:27and its immense red-spot storm.
0:08:29 > 0:08:32And the first close-up images of Jupiter's moons,
0:08:32 > 0:08:35revealing Io to be volcanically active
0:08:35 > 0:08:40and Europa's icy surface to be covered in mysterious stripes.
0:08:41 > 0:08:44The probes flew past Saturn
0:08:44 > 0:08:47and then became the first to photograph Uranus and Neptune.
0:08:50 > 0:08:53We haven't picked any of those images -
0:08:53 > 0:08:57instead we've chosen one taken on Valentine's Day, 1990 -
0:08:57 > 0:09:02a time when Voyager 1 was more than six billion kilometres from the sun.
0:09:02 > 0:09:06And, at the suggest of the famous planetary scientist Carl Sagan,
0:09:06 > 0:09:09it turned to look back in the direction from which it had come
0:09:09 > 0:09:11and it took this image.
0:09:12 > 0:09:15And, at first, there's not much to see.
0:09:15 > 0:09:17You see the blackness of space, a couple of streaks,
0:09:17 > 0:09:19which are glare from the sun on the lens.
0:09:19 > 0:09:21The sun must be up here somewhere.
0:09:21 > 0:09:25But, if you look closer, you see this tiny, pale blue dot,
0:09:25 > 0:09:27suspended in one of those sunbeams.
0:09:27 > 0:09:31And that is the Earth, seen floating on its own,
0:09:31 > 0:09:33amongst the blackness of space.
0:09:47 > 0:09:51And no-one caught the emotional impact of that realisation
0:09:51 > 0:09:52better than the man
0:09:52 > 0:09:55whose idea the picture was.
0:09:55 > 0:09:59And this is where we live, on a blue dot.
0:10:00 > 0:10:02Consider again that dot.
0:10:02 > 0:10:06That's here, that's home,
0:10:06 > 0:10:07that's us.
0:10:07 > 0:10:10On it, everyone you love,
0:10:10 > 0:10:13everyone you know, everyone you ever
0:10:13 > 0:10:16heard of, every human being who ever
0:10:16 > 0:10:19was lived out their lives on a mote
0:10:19 > 0:10:23of dust suspended in a sunbeam.
0:10:24 > 0:10:29The Earth is a very small stage
0:10:29 > 0:10:31in a vast cosmic arena.
0:10:38 > 0:10:43Our third picture was taken 25 years after the pale blue dot,
0:10:43 > 0:10:48by the next mission we sent to the outer reaches of the solar system.
0:10:49 > 0:10:53Last summer, after a 9½-year journey,
0:10:53 > 0:10:57the New Horizon space probe began its approach to Pluto,
0:10:57 > 0:11:01a world many expected to be frozen and featureless.
0:11:01 > 0:11:05Until then, our highest resolution images of the dwarf plant had
0:11:05 > 0:11:08been little more than a fuzzy dot.
0:11:08 > 0:11:12Now, we were getting increasingly detailed pictures and,
0:11:12 > 0:11:15on the 14th of July, New Horizons
0:11:15 > 0:11:20made its closest approach as it flew past Pluto.
0:11:20 > 0:11:24For the mission's scientists, there was a nervous wait to see what,
0:11:24 > 0:11:27if any, images had been captured by the space craft.
0:11:27 > 0:11:31One of those scientists was Carly Howett.
0:11:31 > 0:11:33It felt like being five again
0:11:33 > 0:11:35and it was Christmas morning
0:11:35 > 0:11:37and you knew that there were presents,
0:11:37 > 0:11:40but until you actually see what's inside the box,
0:11:40 > 0:11:42we didn't really know for sure whether the exposure times
0:11:42 > 0:11:45that we'd set were right and all those sorts of things.
0:11:45 > 0:11:48So, we were confident in our abilities,
0:11:48 > 0:11:50but you're always a little bit nervous.
0:11:50 > 0:11:52So, once we started getting the data on the ground,
0:11:52 > 0:11:54we knew it was safe and we knew it was good.
0:11:54 > 0:11:58And it was like Christmas morning over and over again.
0:11:58 > 0:12:02Our third image is this spectacular image of Pluto
0:12:02 > 0:12:04taken by New Horizons.
0:12:06 > 0:12:09The dwarf planet snapped suddenly into focus
0:12:09 > 0:12:11and it was unlike anything
0:12:11 > 0:12:13that had been expected.
0:12:14 > 0:12:19This image really revolutionised the way that we understood Pluto.
0:12:19 > 0:12:22One of the first things that we saw in this image were the mountains.
0:12:22 > 0:12:25There are mountains of water ice on Pluto.
0:12:25 > 0:12:27They stand about 2½ miles high,
0:12:27 > 0:12:30which, for a water ice mountain, is incredibly high.
0:12:30 > 0:12:33We wouldn't get that on the Earth, water ice wouldn't be strong
0:12:33 > 0:12:36enough, it would collapse under its own weight.
0:12:36 > 0:12:37But, at Pluto's cold temperatures,
0:12:37 > 0:12:40it's strong enough to maintain that weight.
0:12:40 > 0:12:45On closer inspection, some of the mountains held even more surprises.
0:12:45 > 0:12:46They have holes in.
0:12:46 > 0:12:49And you only get holes in mountains if they're volcanoes.
0:12:49 > 0:12:53And so, what we think is going on here is there are cryovolcanoes.
0:12:53 > 0:12:56So, not volcanoes in the way that we're used to them,
0:12:56 > 0:12:57on Hawaii, with hot rock and lava,
0:12:57 > 0:13:00but rather volcanoes that would have emitted ice.
0:13:00 > 0:13:02We don't see them being active now,
0:13:02 > 0:13:04we don't see any outflow from them at the moment,
0:13:04 > 0:13:06we don't know when they were last active,
0:13:06 > 0:13:09but there's certainly enough strange terrain around them
0:13:09 > 0:13:12to indicate that they must have been active in the near recent past.
0:13:12 > 0:13:17But while some areas of Pluto were rugged and mountainous,
0:13:17 > 0:13:20in others, such as the large heart-shaped Tombaugh Regio,
0:13:20 > 0:13:23the ice was suspiciously smooth.
0:13:23 > 0:13:26The left side was known as Sputnik Planum
0:13:26 > 0:13:27and this is an interesting region,
0:13:27 > 0:13:29because it's incredibly smooth.
0:13:29 > 0:13:31But, when we zoom in, you can
0:13:31 > 0:13:33see there's a lot of complicated structure in this region.
0:13:33 > 0:13:37And you can see there's all of this structure in the cells itself.
0:13:37 > 0:13:40But you can see how different this terrain is when you get
0:13:40 > 0:13:44up against the bedrock, if you like, of the surrounding regions.
0:13:44 > 0:13:47Now, the smoothness is very strange.
0:13:47 > 0:13:49Everywhere is bombarded by meteorites,
0:13:49 > 0:13:51these are called impact craters.
0:13:51 > 0:13:54And so what is going on in this region of Pluto to eradicate
0:13:54 > 0:13:57those impact craters? There's several ideas about this.
0:13:57 > 0:14:00The prominent idea is that this is made of mostly nitrogen
0:14:00 > 0:14:02and carbon monoxide.
0:14:02 > 0:14:04These are quite soft and so
0:14:04 > 0:14:08we don't think a lot of heat is needed to get these ices moving.
0:14:08 > 0:14:12The heating that Pluto still has from its core is able to
0:14:12 > 0:14:14circulate those ices.
0:14:14 > 0:14:17So, if you had an impact here, it wouldn't take long before this
0:14:17 > 0:14:21overturning eradicated any evidence for it.
0:14:21 > 0:14:23So, this image really has revolutionised
0:14:23 > 0:14:27our understanding of both Pluto and the outer solar system.
0:14:27 > 0:14:30Before we got there, we knew something of its bulk
0:14:30 > 0:14:33composition, but we didn't know about its complex geology.
0:14:33 > 0:14:36And we certainly didn't think that it was geologically active.
0:14:36 > 0:14:37This has huge implications,
0:14:37 > 0:14:40not only for our understanding of Pluto and its evolution
0:14:40 > 0:14:43and its composition, but also for other,
0:14:43 > 0:14:45similar bodies in the outer solar system.
0:14:51 > 0:14:55Before we reach our next photo, let's delve back
0:14:55 > 0:14:59into the history of our attempts to photograph the solar system.
0:15:00 > 0:15:04We've only been sending probes to the planets for 50 years.
0:15:04 > 0:15:06But, as Pete Lawrence has been finding out,
0:15:06 > 0:15:10the art of astrophotography is much, much older.
0:15:12 > 0:15:15The technology found in digital cameras today has come
0:15:15 > 0:15:17directly from astronomy.
0:15:17 > 0:15:21In fact, the sensors, like the one I'm using here and the ones found in
0:15:21 > 0:15:24digital cameras and smartphones are descended from those
0:15:24 > 0:15:28developed by NASA for interplanetary spacecraft.
0:15:28 > 0:15:31And the desire to take pictures of the sky has a long
0:15:31 > 0:15:35history in helping develop photographic techniques.
0:15:35 > 0:15:38In fact, even before they were taking photographs of people,
0:15:38 > 0:15:42photographers were taking pictures of the sky.
0:15:42 > 0:15:45The earliest photographs, called Daguerreotypes, were taken on
0:15:45 > 0:15:50chemically-coated sheets of copper and developed using mercury fumes.
0:15:50 > 0:15:52However, these weren't very sensitive
0:15:52 > 0:15:56and could only capture the very brightest objects in the sky.
0:15:56 > 0:15:59So, photographers and astronomers
0:15:59 > 0:16:02came up with a series of new techniques.
0:16:02 > 0:16:06I've come to the Observatory Science Centre, in Herstmonceux,
0:16:06 > 0:16:10where astronomers have been imaging the sky for 150 years to try
0:16:10 > 0:16:13out one of those old techniques.
0:16:13 > 0:16:15This is Guy Paterson,
0:16:15 > 0:16:19an artist who specialises in historic photographic methods.
0:16:19 > 0:16:20Hi, Guy.
0:16:20 > 0:16:23- Hi.- Nice to meet you. This looks quite interesting.
0:16:23 > 0:16:24What's going on here?
0:16:24 > 0:16:27We're going to attempt to get a shot of the moon,
0:16:27 > 0:16:31- using a very old process called wet plate collodion.- Right.
0:16:31 > 0:16:34So, what have you got to do then, to make this work?
0:16:34 > 0:16:38OK, so, we're going to start off by putting on these protective gloves,
0:16:38 > 0:16:43cos silver nitrate tends to stain anything organic for several
0:16:43 > 0:16:46days if you use it. We have our plate,
0:16:46 > 0:16:50it comes with a protective film over the surface we want to use.
0:16:50 > 0:16:52So, we're going to peel that off.
0:16:53 > 0:16:57- So, I'm going to pour on the collodion.- OK.
0:16:57 > 0:17:01It's completely away from the sanitisation of using digital kit,
0:17:01 > 0:17:04where you just press a button and the image appears on the back of it.
0:17:04 > 0:17:07That's right. I think that's a lot of the appeal, actually,
0:17:07 > 0:17:11you're completely in control of the situation.
0:17:11 > 0:17:12If it goes well...
0:17:12 > 0:17:14PETE LAUGHS
0:17:14 > 0:17:19Right, so, now we're ready for it to go into the silver nitrate solution.
0:17:19 > 0:17:23- OK.- And we lower it in there, carefully.
0:17:23 > 0:17:26That makes it light sensitive after that point.
0:17:26 > 0:17:28I guess the lights have got to go out now,
0:17:28 > 0:17:31so that we can get the plate onto the back of the telescope.
0:17:31 > 0:17:33That's right.
0:17:33 > 0:17:37And try and capture a picture of that moon, which is
0:17:37 > 0:17:40shining brightly out there, perfect for us.
0:17:40 > 0:17:46Five, four, three, two, one.
0:17:51 > 0:17:55And here is our plate. Nothing to see at the moment.
0:17:55 > 0:18:02Now we're going to develop, which we do just pouring the solution on.
0:18:03 > 0:18:08- So, this takes about 15 seconds, you say?- That's right.
0:18:08 > 0:18:13Just stop the development by pouring water over it.
0:18:13 > 0:18:16- Finally.- It's the moment of truth.
0:18:18 > 0:18:20Oh, look at that.
0:18:20 > 0:18:23So, now you've rinsed it off, is it OK to turn the lights back on?
0:18:23 > 0:18:26- Yeah, it should be absolutely fine. - OK.
0:18:30 > 0:18:34This is amazing and just how it used to be done.
0:18:34 > 0:18:37The plate is actually quite small, but
0:18:37 > 0:18:41when you look at it closely, you can see there's loads of detail on it.
0:18:41 > 0:18:44And, to be honest, I'm actually quite surprised that this old
0:18:44 > 0:18:48technology is able to produce something as sharp as this.
0:18:48 > 0:18:51Quite amazing.
0:18:51 > 0:18:54So far, we have seen three of our five images.
0:18:55 > 0:18:58A portrait of the whole Saturn system,
0:18:58 > 0:19:01a distant view of planet Earth
0:19:01 > 0:19:04and a revolutionary image of Pluto.
0:19:05 > 0:19:08Our next image may seem plain by comparison.
0:19:09 > 0:19:13It's a picture of Gale Crater on the surface of Mars.
0:19:14 > 0:19:19But this photo is special, because it shows with incredible accuracy
0:19:19 > 0:19:22what it would be like to stand on the surface of another world.
0:19:34 > 0:19:37It was taken by one of the most advanced pieces of equipment
0:19:37 > 0:19:39we've ever sent into space.
0:19:44 > 0:19:47The Curiosity Rover that was lowered onto
0:19:47 > 0:19:51the surface of Mars in August 2012.
0:19:51 > 0:19:54Amongst its suite of scientific instruments,
0:19:54 > 0:19:59Curiosity is equipped with a camera mounted on a mast at head height.
0:20:01 > 0:20:06This particular image was created by painstakingly assembling more
0:20:06 > 0:20:11than 70 frames from that camera into a single high-resolution panorama.
0:20:12 > 0:20:15The colours have been adjusted to render them
0:20:15 > 0:20:19as close as possible to what our eyes would see.
0:20:19 > 0:20:21It is the work of artist Michael Benson.
0:20:21 > 0:20:25- So, this is sort of a human eye view of the Martian surface.- Yeah.
0:20:25 > 0:20:30Exactly, and what I'm trying to achieve with a lot of these images,
0:20:30 > 0:20:33most of these images, is to give people a sense of what it
0:20:33 > 0:20:36might look like if we could actually go.
0:20:36 > 0:20:39So, why is it important to let people see images like this?
0:20:39 > 0:20:41I think that we, on Earth,
0:20:41 > 0:20:47spend too much time in our self-absorbed concerns, you know?
0:20:47 > 0:20:49I would surmise that it might be useful
0:20:49 > 0:20:52if we looked up a little more and understood that we belong,
0:20:52 > 0:20:54that the Earth belongs, to a suite of landscapes,
0:20:54 > 0:20:58orbiting the same source of light, the sun.
0:20:58 > 0:21:04Some of them very alien, sci-fi, you know, Jupiter.
0:21:04 > 0:21:06And some of them are very close to what we might see...
0:21:06 > 0:21:09I mean, they're very Earth-like in some ways. This one,
0:21:09 > 0:21:11for example, it looks like Utah or Arizona.
0:21:11 > 0:21:17And you can see this connection between Mars and our planet.
0:21:17 > 0:21:20Those are the so-called terrestrial planets, those with hard surfaces
0:21:20 > 0:21:26- in the inner solar system.- Yeah. - So, that's part of what I'm trying
0:21:26 > 0:21:31- to convey with this work.- So, this could be Earth, but it's not.
0:21:31 > 0:21:33This is another planet, out there.
0:21:33 > 0:21:36- But the sky gives it away, doesn't it?- Yes, that does look alien.
0:21:36 > 0:21:39- Yeah, yeah, yeah.- Well, I think it gives everyone an opportunity to
0:21:39 > 0:21:42stand on the surface of Mars and to me, that's a great achievement.
0:21:42 > 0:21:46- Thank you very much.- Thank you. - I appreciate it.
0:21:46 > 0:21:48But, as awe-inspiring as this picture is,
0:21:48 > 0:21:52there's a great deal more to it than its aesthetic appeal.
0:21:52 > 0:21:55The primary purpose of imaging the planets is to provide
0:21:55 > 0:21:58scientific value.
0:21:58 > 0:22:00And in that one image of Gale Crater, there's an amazing
0:22:00 > 0:22:04wealth of detail about the geological history of Mars.
0:22:06 > 0:22:11I've come downstairs in the museum to find Dr Joe Michalski,
0:22:11 > 0:22:16a planetary geologist who uses images from spacecraft to study
0:22:16 > 0:22:19the geological past of Mars.
0:22:20 > 0:22:23So, when I look at this image, I see a landscape
0:22:23 > 0:22:25and I can imagine being there.
0:22:25 > 0:22:28But, as a geologist, what do you get from images like this one?
0:22:28 > 0:22:30Well, the first thing we think about is context.
0:22:30 > 0:22:35The important thing here is that this is the floor of a huge
0:22:35 > 0:22:37impact crater. Those craters, effectively,
0:22:37 > 0:22:41are basins where sedimentary rocks accumulate from various processes.
0:22:41 > 0:22:45- Cos it's an old impact crater? - Yeah, about four billion years old.
0:22:45 > 0:22:47And the rocks within it are also old,
0:22:47 > 0:22:51but 500 million years younger than that. So, a lot is going on there.
0:22:51 > 0:22:54OK, so what should I be looking at, if I want to be a Martian geologist?
0:22:54 > 0:22:57- Where do we start?- So, if you look at the top of the image,
0:22:57 > 0:23:00that's the edge of Mount Sharp.
0:23:00 > 0:23:02You can see layered rocks that are nearly horizontal.
0:23:02 > 0:23:05Yeah, there's this, sort of, stripeyness to it.
0:23:05 > 0:23:08Yeah, so those are rock beds, strata,
0:23:08 > 0:23:11that formed probably through air-fall of volcanic ash or dust.
0:23:11 > 0:23:14And that's accumulated over millions of years
0:23:14 > 0:23:15and that's why it forms layers.
0:23:15 > 0:23:17Then, beneath that, you can
0:23:17 > 0:23:21see there are these other units that don't form as prominent topography.
0:23:21 > 0:23:23The bluish and the light brown.
0:23:23 > 0:23:27So, the fact that it does not form these big buttes tells me
0:23:27 > 0:23:30that it's a softer unit. And, so,
0:23:30 > 0:23:32if we were able to investigate the mineralogy of that, it might
0:23:32 > 0:23:37be something that, for example, contains clay minerals or sulphates.
0:23:37 > 0:23:40So, those are minerals that formed in water, but they're softer.
0:23:40 > 0:23:43So, part of the evidence that there was some water here or some
0:23:43 > 0:23:47dampness here is the fact that you have clay and these other things?
0:23:47 > 0:23:50That's right. In between is this unit,
0:23:50 > 0:23:54which is just composed of gravel and sand and dust.
0:23:54 > 0:23:57Those are common deposits on Mars,
0:23:57 > 0:24:01where you've got a little bit of fluvial activity.
0:24:01 > 0:24:04- That's river-like, right? Or water.- Yeah, exactly.
0:24:04 > 0:24:07So, when we look at this image, we see a landscape partly
0:24:07 > 0:24:09shaped by water.
0:24:09 > 0:24:11And the crater's 5km deep,
0:24:11 > 0:24:15so should I be imagining a big, deep lake? Was the crater full of water?
0:24:15 > 0:24:18As we've investigated this further, it seems that no,
0:24:18 > 0:24:20it probably wasn't ever filled like that.
0:24:20 > 0:24:22But, certainly, there was water here.
0:24:22 > 0:24:24There were small lakes that came
0:24:24 > 0:24:27and went at the scale of thousands of years.
0:24:27 > 0:24:30It seems like a lot to a human, but geologically, it's a snapshot.
0:24:30 > 0:24:33It's amazing to me how much you can tell from this one image,
0:24:33 > 0:24:36but, of course, that's the beauty of these images of other worlds.
0:24:36 > 0:24:41They're not just beautiful things to look at, they're data as well.
0:24:41 > 0:24:42Yeah, that's right.
0:24:42 > 0:24:45Every single image is packed with scientific information.
0:24:45 > 0:24:47- Joe, thank you very much.- Thanks.
0:24:51 > 0:24:54That brings us to our last image, which is
0:24:54 > 0:24:56a bit different to our others, because even I haven't seen it yet.
0:24:56 > 0:24:59It's only just been taken.
0:24:59 > 0:25:02Via this NASA website I can access data from a satellite called
0:25:02 > 0:25:07the Solar Dynamics Observatory, which sits 36,000km away
0:25:07 > 0:25:10from Earth staring at the sun and sending its data back.
0:25:10 > 0:25:14This is its most recent image, taken just ten minutes ago.
0:25:14 > 0:25:16It's not the view of the sun we're used to,
0:25:16 > 0:25:19it's not a featureless yellow disc.
0:25:19 > 0:25:21This is the sun in the ultraviolet.
0:25:29 > 0:25:32The Solar Dynamics Observatory captures images using
0:25:32 > 0:25:35light in ten different wavelengths.
0:25:36 > 0:25:39It reveals the sun to be a very different
0:25:39 > 0:25:43beast from the featureless, golden disc we're used to seeing.
0:25:44 > 0:25:48It shows the surface to be incredibly active,
0:25:48 > 0:25:53bursting with flares and massive explosions of super-heated plasma.
0:25:53 > 0:25:56This is the true face of our sun.
0:25:57 > 0:26:00I never get tired of seeing the sun like this.
0:26:00 > 0:26:04It's not just a boring, yellow disc, it's a dynamic and active world.
0:26:04 > 0:26:06There are wonderful features in its atmosphere
0:26:06 > 0:26:11and the disc itself is a turbulent, boiling mass of gas.
0:26:11 > 0:26:14And we can see all of that because we're looking in the ultraviolet.
0:26:14 > 0:26:17And that's one of the reasons we chose this image, it
0:26:17 > 0:26:20demonstrates that by going beyond the light that our human eyes
0:26:20 > 0:26:24are sensitive to, we can get much more information about the cosmos.
0:26:26 > 0:26:30The Solar Dynamics Observatory actually images the sun once
0:26:30 > 0:26:33every ten seconds,
0:26:33 > 0:26:36giving us a real-time view of the star that allows us
0:26:36 > 0:26:38to trace the source of its surface activity.
0:26:39 > 0:26:44In some wavelengths, we can see dark sunspots on this surface.
0:26:44 > 0:26:48But in other wavelengths, we can see that those dark spots
0:26:48 > 0:26:51are the sites for the greatest solar activity.
0:26:53 > 0:26:57Where arcs of plasma burst from the surface along the twisted
0:26:57 > 0:26:59magnetic field lines of the sun.
0:27:01 > 0:27:02And that's important,
0:27:02 > 0:27:06because activity on the sun has a tremendous affect on the Earth.
0:27:08 > 0:27:11The activity on the sun's surface creates what is known as
0:27:11 > 0:27:14space weather.
0:27:14 > 0:27:17The flares and ejections from the surface
0:27:17 > 0:27:20send streams of charged particles shooting out into space.
0:27:22 > 0:27:26If they hit the earth, they create quite an effect.
0:27:26 > 0:27:30Causing aurorae, like the Northern and Southern Lights.
0:27:30 > 0:27:34But those solar storms can also cause severe damage to the
0:27:34 > 0:27:38electrics of satellites and even interrupt power supplies on Earth.
0:27:39 > 0:27:44And that is why the Solar Dynamics Observatory images are so important.
0:27:44 > 0:27:48It is hoped that the information embedded in these brilliant images
0:27:48 > 0:27:51will give us an understanding on the causes
0:27:51 > 0:27:55and variety of solar activity, helping us to predict
0:27:55 > 0:27:57space weather and finding out when solar storms
0:27:57 > 0:28:00are heading towards Earth.
0:28:01 > 0:28:04So, that's it, our choices for the top five solar system photos.
0:28:04 > 0:28:07And if you think we've missed something or if you disagree,
0:28:07 > 0:28:09you can use Twitter to let us know.
0:28:09 > 0:28:12But whatever your favourite images, you can agree, I'm sure,
0:28:12 > 0:28:13that we've come a long way
0:28:13 > 0:28:17since this wonderful image of the moon taken almost 160 years ago.
0:28:17 > 0:28:19We really have.
0:28:21 > 0:28:24And that's all we have time for this month.
0:28:24 > 0:28:28Next month, we'll be joined by Stephen Hawking to explore
0:28:28 > 0:28:30the recent discovery of gravitational waves
0:28:30 > 0:28:33and what they can tell us about black holes.
0:28:34 > 0:28:38In the meantime, get outside and get looking up.
0:28:38 > 0:28:39Goodnight.