BBC The Sky at Night - Ice Giants [HD]

over 2.8 billion kilometers from the Sun too vast and mysterious worlds patrol the outer reaches of the solar system these are the huge icy bodies of Uranus and of Neptune and they're unlike any of the other planets tonight the sky at night asks why are these ice giants so unique [Music] welcome to the Institute of astronomy at the University of Cambridge a place that played a key role in the story of the discovery of Neptune the outermost planet of our solar system it's a perfect time of year to view Neptune and its neighbor Uranus in the night skies so tonight we're dedicating this program to them coming up we find out how the ice giants could provide clues to help us answer one of our greatest riddles Uranus and Neptune capture the very best of why we want to explore the outer solar system and that is to try and understand why our solar system is so perfect for life to exist here on planet number three dr. John Cole GOG reveals had a unique location makes the ice giants the exotic worlds they are by the time we're at the orbit of Uranus the temperature is so low that it's not just water turning into ice complex gases like methane and ammonia are forming ice as well and Pete joins award-winning astrophotographer Damien peach but tips on imaging the solar system's outermost planets first the basics since Pluto has been relegated Uranus and Neptune are the outer planets of a solar system they are a colossal distance from the Sun 19 times further than the earth or Uranus and a whopping 30 times for Neptune that distance means they take a long time to complete an orbit one year on Neptune amounts to a hundred and sixty-five earth years and it also means they're very cold parts of our atmospheres can reach temperatures as low as minus 200 degrees Celsius their most obvious feature their striking colors comes from thick atmospheres rich in methane that absorbs the red light but reflects green and blue Uranus and Neptune are clearly very different planets from the others in the solar system so why are they like that and what does it tell us about how the other planets were formed this is his temple Garg is seeking the answers all the planets in the solar system are composed of unique combinations of chemicals whilst the gas giants are made almost entirely of hydrogen and helium the same basic stuff of stars Uranus and Neptune are chock-full of methane and ammonia ice and of course these ice giants are completely different from the rocky inner planets like our own so why do we see this variety the answer to this question is all to do with heat and to understand why we have to go back in time to the birth of the solar system itself [Music] before we had planets there was a huge cloud of gas and dust known as a solar nebula it was in the heart of this nebula that our star the Sun was born but making a star didn't use up all of the gas and dust the rest of the cloud continued to spin flattening into a disk imagine this bench is our disk of stellar dust all the bits and pieces are going to go into making our brand-new solar system now in the center the Sun pushes the temperature up by over 1,700 degrees Celsius but as we move away the temperature drops and down towards the edge of this disk an incredible 9 billion miles away the temperatures dropped to a chilly - 250 degrees Celsius this temperature gradient from Inferno to freezer is critical to the way each planet is formed all elements and compounds have their own special properties their own way of responding to certain environments take water cool it till it's very cold in it or form ice but heat it up and it's going to vaporize into a gas now all matter in the universe does this and it's when it's solid rather than liquid or gas that it's most likely to become a building block for a planet which is why the temperature gradient is so important different elements change states at different temperatures now here close to the center of our primordial solar system the temperatures upwards of a thousand degrees Celsius in this searing heat only certain rocks and metals can remain solid and that's why Mercury Venus Earth and Mars are made up mostly of rocks and silicates most rocky material has an extremely high melting point of 1200 degrees Celsius so other than very close to the Sun rock is solid throughout the solar system and this explains why we find rock and metals in all planets including the ice giants as we move further out into the solar system beyond Mars we reach the snow line an imaginary line where the temperatures drop to zero degrees and water ice can form now what's really interesting about this is that ice sticks together much more easily than rocks do and this explains why gas giants Jupiter and Saturn are a bit like these balloons filled with hydrogen and helium the ice helped the cause of these giant planets to form very early and suck up vast amounts of gas from the proto planetary disk it's only when we get further out much further out double the distance from Earth to Saturn that we start to see the ingredients of the ice giants appear by the time we're at the orbit of Uranus the temperature is so low that it's not just water turning into ice complex gases like methane and ammonia are forming ice as well suddenly now that these volatile gases are locked into solid form they can start to coalesce and they seed what will become Uranus and Neptune these chemicals are what made Uranus and Neptune so iconic they gave them this striking color and drove their extraordinary weather systems and as more and more of the volatile ice clumped together and mixed with frozen water it formed a staggering 60% of the ice giants mass but none of this could have happened without the deep freeze of the outer solar system any closer to the Sun and these planets simply could not have formed and although the ice giants seemed exotic to us recent studies suggests they could be the most common type of planet in the galaxy to find out why I'm meeting dr. Helen Fraser who thinks a clue lies in one particular element within our ice giants the strange thing about Uranus and Neptune is they have 60 times more carbon in them than we see in the Sun and that's very exciting because that's more carbon than we have on earth and it's certainly more carbon 10 or 20 times more carbon than we have in Saturn or Jupiter so it's a very big sort of warning beacon to tell us that the the formation of Uranus and Neptune is somewhat different and probably it comes down to the fact that Uranus Neptune formed very close to what we call the co snowline the carbon monoxide snowline this is the point that carbon monoxide freezes and that solid ice could have become a key building block for Uranus and Neptune [Music] scientists believed that this band of icy carbon monoxide might also exist elsewhere and now there's proof 18 months ago the Alma telescope which is a very big telescope in Chile was used for the for the first time to image the carbon monoxide snow lion in a protoplanetary disc outside our solar system a different one which is just forming planets and the evidence suggests that most planetary discs would also have carbon monoxide snow lines so in each of these discs there could be vast amounts of material to build ice giant type planets it's very likely if we've got Eliseo snow lines everywhere that that kind of process that formed Uranus and Neptune is absolutely the dominating process in other solar systems in which case I guess it's very important for us to try and understand the formation of our own ice giants if we get to understand what's going on out there with what seems to be most of the planets absolutely vital and they're big targets that we should really be sending probes to in the next few years and trying to get missions to [Music] in the last few decades we've had enormous success sending probes out across the solar system to give us windows on new worlds Cassini has been orbiting Saturn since 2004 and it's returned astonishing images of the ringed planet and its dynamic moons Mars has five spacecraft orbiting it giving us an unprecedented view of its varied and complex surface and on the ground two Rovers leave no rock unturned NASA's probe Juno is on its way to Jupiter right now but the ice giants have been forgotten it's been more than 25 years since Voyager 2 visited Uranus and then Neptune but a group of scientists are trying to change that planning a mission that will take us back to the ice giants Maggie's been talking to Lee Fletcher to tell us why we should revisit these enigmatic worlds I think that we take the ice giants for granted why do you think they were of interest compared with the rest of the Savior system your Anderson Neptune capture the very best of why we want to explore the outer solar system and that is to try and understand why our solar system is so perfect for life to exist here on planet number three what makes this but the architecture of our solar system particularly special so if you do this mission what would you expect to find well one of the big questions where we're trying to address if you look at Uranus and Neptune they they formed at roughly the same sort of temperature they took about the same length of time to form you would expect them to be roughly the same they're the same sort of composition the same sort of whether they look similar colors if they have similar colors and that's because of the amount of methane that they have in their atmosphere is it methane absorbs all of the red light so what you're left with is the blue the blue to be reflected back at you but they're the similar similarities really end in fact Neptune despite being the furthest planet from the Sun it's actually one of the most dynamic places in our solar system it has these incredibly strong weather patterns and weather systems with clouds popping up and large cumulus systems developing that then gets sheared apart by all the win and jets and these can happen on an hourly basis so that Neptune really doesn't look the same each night that we look now contrast that was somewhere like Uranus Uranus when Voyager flew past in the eighties was a very sluggish very dare I say boring looking so I read about serene and calm all said and done Neptune looks like a much more powerful much more active planet than Uranus despite being much much further away at 30 astronomical units from the Sun versus 20 astronomical units recent German we think the Sun powering weather an energy input from the Sun sort of a mix of turbulence drives the weather so yet the further you're away from the Sun you think the less dynamic it would be that would be the expectation most of the giant planets if you were to look at them with infrared eyes would be glowing hot so they were missing they're emitting energy Neptune has the biggest heat source of any of the giant planets and maybe that's contributing to this really powerful weather that we see on that planet but then contrast that with somewhere like Uranus Uranus has almost no appreciable heat source that we can detect maybe all that energy is being locked away in the interior you just can't get out through the various atmospheric layers it can't convex and diffuse out to the where we can see it well maybe there's just the energy is not there anymore maybe something in its distant past removed all of the energy from Uranus which makes it a rather sluggish world today now there's evidence to support that view that something happened as something happened because one of the biggest mysteries about Uranus is why it's tilted over almost completely onto its side some sort of spins it spins that way as opposed to that way in our solar system that let's make it very strange it's the oddball in our solar system the big question is well why has that happened or how did that happen in the first place and what implications does that have for how the planet itself works one pole can spend four decades in the darkness of winter versus then four decades in summer sunshine if you like and that sets up a real difference in the amount of heating that each each hemisphere gets so maybe whatever caused that big tilts on unis whatever bowled it over deep in its distant past after formed is the same explanation for why Uranus has no appreciable heat source anymore it's all connected now going to both planets in one mission this house pretty challenging so which one would you go to that's a good question we do have to choose between the two and my my choice would be to go to Uranus and the reason for that is exactly what we've said it is the missing link and it is the oddball of our solar system there's nowhere else quite like it frankly we need to do this to complete our picture of the solar system of it the planets 1 to 6 if you like out to Saturn have now been characterized by orbital missions ok you understand Neptune has simply been forgotten about that's the next step in my opinion in the exploration of our solar system let's get to those missing links well thanks very much Lee you put it over a pretty convincing argument and good luck with the missions in the future thanks very much bill a pleasure [Music] Neptune was the last planet in our solar system to be found for good reason it is by far the faintest of the major planets [Music] to find it required an intellectual leap and an international space race we've been joined by Carolyn Crawford who's going to tell us this extraordinary story ancient peoples knew about all the planets out to Saturn but it wasn't until 1781 where William Herschel discovered the planet Uranus though there was a realization that there were new planets out there just just waiting to be found there's things we can see with our visible eyes and then beyond that then we need other methods to detect them that's right they're too far away so they're dim and they're faint and so any further progress really relied in having telescopes and Uranus was a surprise in the first place Herschel wasn't out doing a systematic search for planets yeah what a wonderful surprise it must have been to just discover the first new planet completely serendipitously when you're sweeping the sky with a telescope but after that people started observing Uranus and mapping out its orbit and how its behaving and that's where they really found a surprise because Uranus wasn't moving as you might predict if it's just responding to the gravity of the Sun and the other planets every so often it would kind of speed up and then little bit later it would slow down and so by the 1820s astronomers realized that maybe there was another planet out beyond Uranus and the gravity was exerting a tug anew on Uranus every so often and this is where the Cambridge connection comes in that's right so Neptune is peculiar in that it was the first planet whose presence was predicted but it wasn't until a Cambridge undergraduate and then a graduate called John pooch Adams came along he was the first one to tackle this problem properly and mathematically he took a potshot at where this extra planet would be what its you know how far out from the Sun where it is relative to Uranus predicted okay what gravitational target would produce in that planet and then compared that what was the scene in Uranus and the day and then obviously he didn't get it right first time because there's almost infinite variety of possible you can leave it further away you can make it bigger you can yeah yes do a lot with it so you can imagine it took him a couple of years to get to refine his calculations and by 1845 1846 he's saying okay it's in that part of the sky it seems obvious he's done three years worth of work he you'd come down to this Observatory point the telescope of that position and and see what you could see didn't quite happen that straightforwardly and in practice even though coach Adams had started on this quite early there was a French astronomer urban Lavoisier who was making the same predictions and it was until Caen midsummer 1846 when the Brits realized that there was a competing prediction that placed this new planet in the same part of the sky that they began to look for it in earnest there was a race there's a race on and so this is where this telescope came in it was used for the search for Neptune here at Cambridge and to find a new planet you've got to map that whole area of sky from one day to the next from one week to the next and he's looking for the one object that moves relative to the backdrop of the star thirty of difficulties he couldn't point directly at one spot the predictions are that precise and of course no photography it's no photography so all the observations are done by eye and the astronomer who was leading the search who was Professor James chalice wasn't entirely sure whether he had seen it known practice he had actually observed the planet he could have detected but he wasn't sure enough of his calculations and in the end he was picked to the post by the French and the German astronomers so there's one way of describing this this is the telescope that nearly discovered Nanjing but they saw it but it doesn't realize it yes it failed to find Neptune I'm afraid [Music] next up Pete's guide to finding the ice giants and then getting the most out of observing them it's an excellent time of year for the outer planets of the solar system because both Uranus and Neptune are really well placed at the moment and even from a light polluted location like a town or city they're both relatively easy to view it's just possible to see Uranus as a faint dot with the naked eye but with a bit of optical assistance it's a much easier target a small telescope really brings out the character of the planet because it has a striking emerald green color and it's worth taking the time just to look for that it's a little trickier to spot Neptune but don't let that put you off Neptune is over 29 times further away from the Sun than we are so that far out it's quite a dim planet and it certainly can't be seen with just the naked eye now with a small telescope the view of Neptune shows that it has a character all of its own compared to its neighbour Uranus it appears as a small disc and it's enchanting bluish color really helps it stand out both planets do have more to offer because with the right equipment it is possible to make out subtle detail on their discs I am meeting award-winning amateur photographer Damian peach whose captures some striking images of these exotic worlds so Damian you're well known for taking some amazing pictures of the planets including URIs and Neptune have you got any top tips for getting the best pictures firstly you need a large aperture telescope at least 10 inches an aperture to stand the chance of getting some detail okay all these planets secondly I would say another important factor is the the use of filters particularly near infrared and red light filters okay so what's the purpose of the filters now what they do is to help contrast those brighter zones and darker bands most clearly than you would otherwise seem visible light I've seen you've got some fantastic pictures on your laptop can we have a look at them yes anyway oh wow that's incredible so that's Eunice the first thing that strikes me there is you've got color in shot is that color that's been captured through the telescope or is that added on afterwards the image you have here is actually the real image taken through a near infrared filter and it's been colorized okay later to give a a more aesthetically pleasing appear and that's because it's quite tricky to get the different color components with it exactly that's right because these planets are so dim it's very difficult to obtain good color data to actually make a true color but it's work really well in the detail there is amazing so you've got these shaded bands running around the planet that's right and one of the great things is it's only in recent times that it's become possible to start recording detail on planets such as Uranus and Neptune with amateur telescopes okay well why is that do you think I think it's a combination of the development of very powerful software for processing the data right that were able to capture and then the cameras we have now are so much better yeah they were even five or six years ago because these are pretty tiny I mean in terms of how they appear in the sky that they're not dissimilar to the moons of Jupiter the mystery of two slightly smaller I mean when you're looking at something like Neptune yeah it's only very slightly larger than Jupiter's moon Ganymede an apparent size so it's a very small object you got any shots of Neptune on there we happen to eat here ah there's Neptune and it's moon Triton that's pretty amazing cuz there is detail on that planets disc isn't there there is some vague markings visible and again this was taken through a near infrared filter absolutely incredible image really is something else thank you very much thank you so no matter what your level of expertise Uranus and Neptune are definitely well worth a look so here's my guide how to find them and some other highlights happening this month Uranus is in pieces just south of the faint star Delta piss Kiev to find Delta first locate the great square of Pegasus high in the southern part of the sky around 10 p.m. extend the upper right to lower left agonal of the square about half the distance again using binoculars placed Delta at the top of the field of view Uranus is the lower of the two dimmer but similar brightness dots close to the center to find Neptune first locate the pattern of stars which looks like a three-pronged steering wheel known as the water jar asterism look for the faint star sigma aquarii eye which lies south of the water jar in binoculars Neptune is the brightest dot to the right of Sigma finally don't forget to keep a lookout for Orionid meteor which peak on the 21st of October they appear to come from a region of sky above and left of Bethel ghazan Orion another result of earth passing through the debris stream of comet Halley Uranus and Neptune don't make their slave possession across the night sky alone like many other planets they have moons Neptune's largest moon Triton is one of the most fascinating worlds in our solar system chris is speaking to guarantee aims I guess the first thing to say about it is that it's big it is yes it's the South largest moon in our solar system so it's smaller than our Moon slightly smaller than Jupiter's moon Europa but bigger than Pluto which until a few years ago was considered one of the major planets and it's just got an incredible surface so the one encounter we've had Voyager 2 in 1989 that spacecraft revealed this amazing world very young very few impact craters so it hasn't been exposed for very long it's got an atmosphere and also active geysers on the surface and that I think is the iconic tried to discovery Voyager actually saw those geezers shooting up into the sky that's right if you look around the the south polar I think we can zoom in in fact yeah there we go so these dark streaks the dark material is thought to be dust may be contaminated with methane which is darker than the other ices on the surface so they've been carried up into the atmosphere and the larger particles fall down immediately downwind of the other geysers we get an eruption and we get these almost dirty streaks follow the following yeah I know you said in a wind which means there's an atmosphere what do we know about the atmospheric Tyson well it's incredibly tenuous so it's it's predominantly nitrogen gas so it's thought that the pole that's being warmed the most by the Sun is heated up the nitrogen ice that's there sublimate so it turns from a solid straight into a gas it adds to the atmosphere that material moves over to the night side of Triton where it's really cold then it freezes out and its surface is incredibly varied there's this South Pole trend there's also this other region up towards the top right in this picture where things look very different yeah so when that was first viewed in the the Voyager images the scientists almost immediately referred to it as the cantaloupe terrain and I've got the cantaloupe melon here very good I'm glad we got to the melon sir if you look closely at the the surface of this melon you can see there's these interweaving features very similar to the the fractures we see on the surface of f triton suggest that there's liquid water layer somewhere under the surface there's movements of the icy water ice crust through those cracks you get water lava breaking through may be mixed in with ammonia to make it more runny a water lava would be sort of a sludge we nearly melted form of water that's still very cold it is extremely cold liquid water flows out to the cracks and forms of pairs of ridges on either side of these fractures and this appears to have occurred over quite a large area of the surface mapped by my Voyager 2 and if you look at some of the regions you can see the hints of ancients impact craters that have been split in two by these fractures and have been shifted around so that means it's activities more recent than the impact craters so this is the kind of thing that Triton's possibly still doing today yes from looking at the number of impact craters which show you how all the surfaces some parts may be as young as five or six million years old which is incredible young in in geological terms and may indicate that volcanism of the large-scale type might be occurring even now that's it for this month but if you want to find out more about ice giants or Pete's guide to how to find them please go to our website at BBC co uk when we come back next month we have a very special program we'll be following along as one of the most exciting missions of recent decades reaches its climax ESA's Rosetta probe will attempt to place a lander on comet Jeremy of Grass amenca the landing site has been selected the timetable is in place but it looks to be a daunting task we'll be at the heart of Mission Control for the landing itself bringing you the first ever images from the surface of a comet and hopefully some early science from the Landers instruments so join us at 9:00 p.m. on the 16th of November in the meanwhile get outside and get looking up good night we may all think the Americans won the space race with their moon landing in 69 but Russia's cosmonauts were spacewalking years before a brand new film tells their thrilling and terrifying story tomorrow night at 9:00 here on BBC four [Music] you

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Keywords: The Sky At Night (TV Program), Space, Uranus, Urano, Espaço, bbc the sky at night, neptune, neptuno, ice giants, space ice, formation of solar system, ice planets, outer planets, cosmos

Id: DEIOliMj2KE

Length: 29min 0sec (1740 seconds)

Published: Sun Jan 07 2018