good evening ladies and gentlemen how is everyone doing why stressed and not well the moon assignment is not that difficult but i told you guys not to underestimate the assignment so tomorrow you're writing our physics anaesthetist good luck with that one so in last night's lecture we ended off by with our lecture on all the terrestrial worlds we've learned about military venus earth saturn axor earth earth's moon the moons of mars but now we're going to start looking at the jovian walls meaning jupiter's saturn uranus nymphs as well as their moons okay so for this so the aim of this chapter is the four joven wolves that forms part of the outer solar system and after that anything we have to lift is the asteroid belt and the earth cloud so of you have seen jupiter through a telescope so this is one of my favorite objects i usually like to observe and you can usually see a couple of its moons as well and can you guys tell me what this feature on jupiter is it's a giant storm says the red stormwater red eye of jupiter and it's about the size of four earths and have you guys seen saturn through a telescope they're gonna surface at six but what's recording that's no problem so saturn is also a very beautiful object to observe and depending on where we are in our orbit towards around the sun and towards saturn but it is very beautiful if we can see the entire ring and then uranus so uranus also has rings so uranus and neptune are the two planets we cannot see with our naked eye because then we are reaching the limits of minus six minus seven apparent visual magnitude and then there is neptune so what do these planets have in common so what we tell guys tell me about these planets call them big so they're not that cold so all grass plants yes [Music] and they're all very big much larger than earth and then lastly i just added this for traditions sake but this is a image of pluto that's no longer a planet in the last three chapters you watched our solar system form then studied earth and other terrestrial planets as they have evolved to the present day in this chapter the jovians and jupiter-like planets will be a challenge to your imagination there are such alien worlds they would be unbelievable if you didn't have direct observational evidence to tell you what they are like in contrast pluto and other bodies in the kuiper belt are not planets intriguing remnants of the planet construction process as you think you must have planet so there is no evidence for planet mine mr melville so as you explore you will find answers to four important questions so firstly what are the properties of the jovian planets secondly what is the evidence that some moons in the outer cell system have been geologically active number three how are planetary rings formed and maintained and lastly why do pluto and the other kuiper belt objects tell us about the formation of the solar system the sulfuric acid clouds of venus may seem totally alien to you but compared with the planets of the other solar system venus is almost like home for example the four german planets has no solid surfaces the worlds of the outer solar system can be studied from earth but much of what astronomers known has been radioed back to earth from space groups the pioneer and voyager missions flew past our planets in 1970s 1980s galileo orbited jupiter in the late 1990s and the cassini orbiter and probe arrived at saturn in 2004 the new horizon squad flew past pluton 2015 and is now sailing deeper into the kuiper belt juno arrived in orbit around jupiter in 2016 for planned multi-year close-up investigation of the planets magnetosphere and gravity field throughout this discussion you will find images and data returned by these robotic explorers the outermost planets in our solar system are jupiter saturn uranus and neptune the jovian planets meaning they resemble jupiter in fact they are each individuals with sacred personalities 18.1 compares the four outer worlds to each other and to earth one striking feature is this size jupiter is the largest of the german wolves every limit times saturn is slightly smaller and uranus and neptune are quite a bit smaller than jupiter and saturn but still four times the size of earth pluto not pictured in his figure is smaller than earth's moon but was considered a planet from the time of his discovery in 1930 until 2006 when it was reclassified as a dwarf planet you learn about pluto's characteristics and a reason for that decision in this chapter so here we can see a shadow of one of jupiter's many moons on a planet we can actually see that quite regularly so earth is a greater rule compared to these planets so jupiter more than 11 times earth's diameter is the largest planet in our solar system so here we can see the cloud belts and zones on saturn are less distinct than on those of jupiter so these belts we can see with the telescope on triple that's actually beautiful to watch uranus and neptune are green and blue colored because of small amounts of methane in hydrogen-rich atmospheres and then uranus and neptune are both about four times earth's diameter the other feature you will notice immediately when you look at figure 18.1 is saturn's rings they are bright and beautiful and composed of billions of ice particles jupiter uranus and neptune also have rings but they are not easily detected from earth and are not visible in the figure nevertheless as you invited these wolves you will be able to compare contrast as four sets of planetary rings the four jovian worlds have origin rich atmospheres folds were filled with clouds on jupiter and saturn you can see that clouds form stripes and bands that circle each planet known as bald zone circulation you will find traces of these same types of features on uranus and neptune but are less distinct models based on observations indicate that atmospheres of the journey and planets are not very deep for example jupiter's atmosphere makes up only about one percent of its radius below the atmospheres jupiter and saturn are mostly liquid so the conventional term for these planets gas giant should probably be changed to liquid giants uranus and neptune are sometimes called ice giants because they contain abundant water in solid forms only near the centers to the jovian planets have caused of dense material of the composition of rock and metal none of the jovian walls has a definite solid surface on which you can walk you can't really land your spaceship on the jovian wolves but you might be able to land on one of their moons all the jovian worlds at the extensive satellite systems those moons are classified into two groups one the regular satellites which tend to be large and orbit relatively close to the apparent planet with low in inclinations to the planet's equator moving in the pro direction along with most objects in the solar system versus secondly the irregular satellites which tend to be smaller than irregular satellites sometimes have retrograde and or highly inclined orbits and are generally far from a parent planet the astronomers have evidence that the regular satellites swarm approximately where they are now as the planets formed but the irregular satellites are mostly if not all captured objects so what the scene of the jovian planet's radius is liquid i'm not too sure about that some of the jovian moons are geologically active now while others show signs of past activity of course geologically active activity depends on heat flow from the interior so you might ponder what could be eating the insides of these small objects you'll get some answers to that question later in this chapter jupiter is the largest and most massive of the jovian planets containing 71 of all the planetary matter in the solar system just as he used earth the largest of the terrestrial planets as the basis for comparison with the others you can examine jupiter and detail as a standard in your comparative study of the other jovian planets although jupiter is very large it is only 1.3 times density in water for comparison earth is more than 5.5 times denser than water as you have already learned the density of the planet is an important clue about the average composition of the planet's interior jupiter's shape also gives information about its interior ghibli and other joking planets are all slightly flattened a world with a large rocky core a mantle would not be flattened much by rotation but an all liquid planet would flatten significantly this stupidest oblateness so the fraction by which equatorial diameter exceeds the speed of diameter combined with its average density helps astronomers calculate what's insides alike models show that in theory of jupiter is mostly liquid hydrogen however if you jumped into jupiter carrying a kayak expecting an ocean you would be disappointed the base of the atmosphere is so hot and the pressure is so high that there is no sudden boundary between liquid and gas as you fell deeper and deeper through the atmosphere you would find the gas lines increasing around you until you were sinking through a liquid but you would never splash into a distant distinct liquid surface under very high pressure liquid hydrogen becomes liquid metallic hydrogen a material that is a very good conductor of electricity model calculations indicate that most of jupiter's interior is composed of this material that large mass of conducting liquid stirred by convection currents and spun by the planet's rapid rotation drives the dynamo effect and generates a powerful magnetic field jupiter's field is over 10 times stronger than earth's field a planet's magnetic field deflects the solar wind and dominates the volume of space around the planet called the magnetosphere jupiter's magnetosphere is 100 times larger than earth's if you can see it in the sky it'll be more than five times larger than a full moon just as the case of earth interactions between generous magnetic fields and a solar wind generates powerful electric currents that flow around the planet's magnetic poles these are visible ultraviolet wavelengths as rings of aurora lights that are larger diameter than earth in image a we can see jupiter's large conducting core and rapid rotation creates a powerful magnetic field that holds back the solar wind and dominates the magnetosphere cut a bloomer diagram high energy particles trapped in a magnetic field from giant radiation belts then image b aurorae and jupiter are confined to rings around the north magnetic pole and the south magnetic pole as shown in these ultraviolet images earth's array follow the same pattern the small shaped spots are caused by powerful electrical currents flowing from jupiter's moon io the strong magnetic field around jupiter traps charged particles from the solar wind in radiation belts billion times more intense than the fun iron belts that surround earth the spacecraft that have flown through these regions received over four thousand times the radiation that would have been lethal for a human at jupiter's center a so-called rocky core contains heavy elements such as iron nickel silicon and so on with a temperature four times hotter than the surface of the sun and a pressure of 50 million tons of sea level atmospheric pressure this material is unlike any rock on earth the term rocky core refers to the chemical composition not to the mechanical properties of the material careful measurements of the heat flowing out of jupiter reveal that it emits about twice as much energy as it absorbs from the sun this energy appears to be heat lift over from the formation of the planet in chapter 15 you saw that jupiter should have grown very hard when it formed and some of that heat remains inside slowly leaking into space so look back to figure 5.17b the infrared image of jupiter acquired by the sofia airborne telescope shows a white stripe where the planet's internal heat flow is prominent in 2016 the juno pro began orbiting jupiter on a path coming within 4 200 kilometers of the cloud tops making detailed measurements of the planet's magnetosphere and gravity field for insight into its internal structure it's a common misconception that jupiter is a ball of gas in fact as you have learned jupiter is almost entirely a liquid planet its atmosphere is only a thin outer skin of turbulent gases and clouds the processes you will find there are repeated in slightly different ways on the other joking so notice four important ideas firstly the atmosphere is origin rich and the clouds are confined to a shallow layer secondly the cloud layers are located at certain temperatures within atmosphere where ammonia ammonium hydrosulfide and water respectively can condense three the belt zone circulation pattern of coloured cloud bands circling the planet like stripes on charles ball is related to the high and low pressure areas found in earth's atmosphere number four the large circular or oval spots seen in jupiter's clouds are circulating storms that can remain stable for decades or even centuries photos of jupiter lead to the common misconception that the clouds are at the top of the atmosphere realize that the atmosphere of transparent origin and helium extends high above the cloud tops what you see in photos is only the cloud layers gpa has four large moons and at least 60 smaller ones so this is about this is outdated so this textbook is a couple of years old the latest stats or figures i've seen as jupiter has about 84 moons currently that has been classified so larger telescopes and modern techniques are continuously finding more small moons orbiting the german planets and each of the german planets probably has many more small underscored moons some of the small moons are probably captured asteroids in contrast the four largest moons of jupiter called the gilean moons after the discoverer galileo are clearly related to each other and almost certainly formed with jupiter so here we can see from left to right the moons are io europa ganymede and callisto so note that io is almost exactly same size as earth's view so what can you tell interesting what facts do you know about these moons is everyone still awake so europa is very interested or interesting object because we can detect water on io that might have bacterial life so that is something interesting to visit in the future the outermost gilead moons ganymede and callisto are about the size of mercury one and a half times the size of earth's moon in fact ganymede is the largest moon in the solar system galamid and cholesterol have low densities of only 1.9 and 1.8 1.8 grams per cubic centimeter respectively meaning they must consist roughly of half rock and half ice observations of the gravitational fields by the galileo spacecraft reveal that ganymede has a rocky or metallic core and lower density icy exterior so does differentiated cholesterol is apparently only partly differentiated both moons interact with jupiter's magnetic field in ways that show they probably have mineral rich layers of liquid water 100 kilometers or more below the icy crusts cholesterol surface and most of ganymede surface appear old because they are heavily crated and very dark the continuous blast of meteorites evaporate surface ice leaving behind embedded minerals to form dark skin like the grammy crust on an old snow bank this icy surfaces gets darker with age more recent impacts dig up clean eyes and leave bright craters as you can see on callisto in figure 18.3 ganymede has some younger bright groove terrain believed to be the systems of faults in a brittle crust some sets of groups grooves overlaps other sets of grooves suggesting extended episodes of geological activity so which website we use if there is cloud cover to check the position of the new from allocation you can use stellarium so i've seen this don't underestimate the moon assignment so it's starting now with your observations is cutting it so that means you don't have any room for area because it has to be in corrective 31st so you have really led this to the last moment so don't underestimate it but if you want to do yourself if you're only starting observations now the best time would be around about five a in the mornings in image a the contrast enhanced visual wavelength image of ganymede shows the frosty falls at the top and bottom the old dark terrain and a brighter groove terrain than an image b a band of bright terrain on ganymede runs from left to upper right and a collapsed area a possible caldera lies at the center of this visual wavelength image caldera is full where subsurface liquid has drained away and the bright areas contain other features associated with flooding by water the density of the next moon inward europa is three grams per cubic centimeter which means that europa is mostly rock with thin icy crust the visible surface is very clean ice contains very few craters has long cracks in the icy crust and includes complicated terrain that resembles blocks of ice in bird's arctic ocean the pattern of mountain-like faults on its surface suggests that the icy crust breaks as the moon is flexed by tides europa's gravitational influence on the galileo spacecraft reveals that a liquid water ocean perhaps 200 kilometers deep lie below the 10 to 100 kilometer thick crust the lack of craters tells you that europa is an active world where craters are quickly erased in image a the icy surface of europa is shown here in natural color many folds are visible on its surface but very few craters the bright crater google a young implicit imbian impact feature in image b this circular bull's eye is remains of a crater 140 kilometers in diameter so notice the younger cracks and folds the crust and all the feature image c like icebergs on the ocean blocks of crust on europa appear to have floated apart and rotated the blue icy surface is stained ground by mineral-rich water painting from below the crust white areas are ejected off from the impact that formed pavel crater image d the gravitational influence of europa on the passing galileo spacecraft shows that this moon has differentiated into a tin score and rocky mantle magnetic interactions with jupiter show that it has liquid water ocean below its icy crust heat produced by tidal heating could flow out with its convection in such an ocean and drive geologically activity in the icy crust images from spacecraft reveal that io the innermost of the four gillian moons has over 100 volcanic veins on its surface the active volcanoes throw sulfur-rich gas and ash high above the surface that ash falls back to bury the surface at a rate of a few millimeters a year this explains where you see no impact craters on io they are covered up as fast as they form io's density is 3.6 grams per cubic centimeter showing that it is composed of rock and metal its gravitational influence on the poor single a spacecraft reveal that it is differentiated into a large metallic core a rocky mantle and a low density crust these enhanced color images of volcanic features on io were produced by combining visual and near infrared and digitally enhancing the colors to human eyes most of io would look pale yellow and light orange so that unless i was going through the quiz we will go through the quiz in the last 10 minutes of the lecture the activity you see in the gilean moons must be driven by energy flowing outward yet these objects are too small to have remained hot from the time of their formation ios volcanism seems to be driven by tidal eating io follows a slightly elliptical orbit caused by its interactions with the other moons as ios distance from jupiter varies the planet's gravitational field fixes the moon with varying tidal force and the resulting friction its eyes interior that heat following outward causes the volcanism europa is not as active as io but it also must have heat source presumably tidal eating ganymede is no longer active but when it was younger it must have had internal heat to break the crust and produce the groove terrain so to go through the scope means now i'm also going to give you the scope at the end of this lecture in fact those three moons are linked together in orbital resonances io orbits jupiter four times while europa orbits twice and ganymede orbits once these resonances keep all three orbits slightly elliptical and drive tidal eating that makes the moons active now or made him active in a past distant callisto is not caught in this orbital resonance and appears neither to have been strongly active given the lack of surface activity it is surprising that there is evidence of a subsurface ocean within callisto as well as in europa and ganymede astronomers has known for centuries that saturn has rings but jupiter's rings was not discovered until 1979 when the voyager 1 spacecraft sent back photos less than one percent as bright as saturn's icy rings jupiter's rings are very dark and reddish showing their material as rocky rather than ice so this is a bit off topic but do you guys know anything about voyager spacecraft uh mr melville what is the character pronunciation voyager 1 and voyager 2 spacecraft are already in deep space they are indeed [Music] and so the voyager spacecraft are the furthest man-made objects from earth so i'm not exactly sure how far they are but you can google it i know at some point in the next couple of years we will lose communication with voyager 1. it's past the edge of the solar system they are in the earth cloud so yes in a couple of years we will lose contact with voyager 1 because then we need more power and transmitters and begin soon as so it becomes more difficult to pick up signals from the voyager spacecraft but yes they are still have power still operating and still moving deep and deep into space so what is the point of a spacecraft that we can't communicate with so that is a very good question so remember if we want to communicate with something in deep space you need a powerful transmitter to be able to send signals and then you need a powerful receiver to be able to pick up those signals so here on earth we can build beta and beta and beta receivers and we can also build beta transmitters to send information to voyager but the problem is voyager's transmitter is not that powerful and we cannot upgrade voyages transmitter so it comes back to one over r squared rule so the further the object is way the more difficult it is to detect and at some point even with our best radio telescopes and best receivers we won't be able to pick up wager anymore astronomers can also conclude that the ring particles are mostly microscopic photos of the ring show that it is very bright when you illuminate it from behind called forward scattering large particles do not scatter light forward a ring filled with basketball-sized particles would look dark and illuminated from behind forward scattering tells you that jupiter's rings are made of tiny grains with diameters approximately equal to the wavelengths of light less than a million of meters about the size of particles in cigarette smoke so a question says sir since there are so far is physical maintenance not possible for them yes physical maintenance is not possible because how can we that means we need to send another spacecraft to do physical maintenance on voyager so if i'm correct voyage has been launched in 1970 or 1980 run about day so say it's almost say 40 years back when it was launched so if we need to do maintenance on it we need to have a spacecraft that is moving faster than voyageur to catch it and it will take safe moving force to somewhere from 40 to 60 years to catch up with it so yes physical maintenance is therefore impossible so something interesting so does so we are careful of what we launched into space but something interesting the voyager spacecraft contains a engraved metal plate on it that shows who we are as humans and how to get to earth so it's a road map of who we are and where we are that's left on the voyager spacecraft in case the other civilization picks it up in the future in image a the main ring of jupiter illuminated from behind glows brightly in its visual image made by the galileo spacecraft what it was with intricate shadow image b digital enhancement and false colour revealed the halo of ring particles that extends above and below the main ring the island is just visible in the panel image c structure in the ring is probably caused by a gravitational influence of jupiter's inner moon the rings orbit inside the rush limit so remember we have talked about rush limits and rush loads in the previous lecture the distance from a planet within which a moon cannot hold itself together by its own gravity if a moon were to come inside the rush limit tidal forces would overcome the moon's gravity and pull the moon apart so you guys know you guys understand what i meant or what i'm trying to say with the gravitational forces and tidal forces so with this such as the earth and the moon has tidal forces on each other so does jupiter have tidal forces with its moons and moonset title forces on jupiter but the different moons also has tidal forces with each other as well so the rush limit is about 2.4 times the planet's radius depending somewhat on the relative densities of the planet and the opening material the rings of saturn uranus and neptune also lie inside restrictive rush limits for each planet now you can understand jupiter's dusty rings if dust speck gets knocked loose from a larger rock inside a rush limit the rock's gravity cannot hold the dust stick for that same reason the billions of dust specks in the rings can't pull themselves together to make a move because of tidal forces inside the rush limit thinking about a plate in the seams we could make the analogy that we have given strangers over the internet directions to our house yes i'm watching myself i say yes that is true and also think about it and that we're going to discuss all these topics in our upcoming lecture but we have been broadcasting radio waves since we [Music] discovered and invented radio television so we have been almost now 400 years been broadcasting electromagnetic radiation away from earth that's another way a civilization can know where earth is and find us you can be sure that jupiter's ring particles are not old the pressure of sunlight and the planet's powerful magnetic field can quickly alter the orbits of the particles images show faintering material extending down towards the cloud tops evidently thus specs firing towards jupiter dust is also lost from the ring as electromagnetic effects electromagnetic effects falls it out of the central plane to form aloe density allow dense to form allow density halo above and below the ring another reason the ring particles can't be old is that the continuous radiation around jupiter tends to grind the particles down to nothing in a century or so therefore the ring you see today can't be material left over in its current situation since the formation of jupiter instead the ring must be continuously resupplied with new dust observations made the galileo spacecraft provide evidence that the source of the ring material is meteorites eroding the small moons and rusty meters amathia and phoebe that orbit near or within the rings so yes you are correct mr pretorius so yes the rush limits on the planet must be quite spectacular the rings around saturn uranus and neptune are also known to be short-lived so they also must be resupplied by new material probably eroded from nearby moons aside from supplying the jovian planets rings with particles moons also act to confine the rings keep them from spreading outwards and alter their shapes you will explore these processes in detail when you study the rings of the other planets later in this chapter so legend just said i might disconnect something that's no problem at all so i'm standing shooting problem it puts all the evidence together and tell the story of jupiter creating such a logical argument of evidence and hypothesis is the ultimate goal of planetary astronomy jupiter formed far enough from the sun to incorporate large numbers of icy beneficials but it must have grown rapidly once it was about 15 times more massive than earth it could grow by gravitational collapse capturing gas directly from the cellular nebula this it grew rich in oxygen and helium from the solar nebula its present composition resembles the composition of the sun and the cellular nebula jupiter's gravity is strong enough to hold onto all its gases even hydrogen the large family of moons may be mostly captured asteroids and jupiter may still encounter wandering asteroid or comet now and then so this is interesting so is actually a shield against asteroids and comets for earth and other planets because jupiter is the largest planet in the solar system it also is the planet with largest gravitational field so it captures most asteroids and comets and it's actually protecting earth and something that you'll see so yes some country scientists call jupiter a failed star because its composition is a lot like the sun's but it stops and it doesn't continue with fusion reaction or confuse elements together so that's one of the reason it is called a failed star but some other people make a joke and say jupiter is an over achieving planet so some of these are deflected and some like comet schumacher leaving nine that struck jupiter in 1994 actually fall into the planet thus blasted of the inner moons by meteorite impact settles into the equatorial plane from jupiter's ring but no problem i completely understand like shooting the four galilean moons are large and seem to have formed like a mini solar system in a disc of gas and dust around the forming planet the innermost canadian moon io is densest and the densities of the other decrease as you move away from jupiter similar to the way the densities of the planets decrease with distance from the sun perhaps the inner moons incorporated less ice because they form close to the heat of the glowing planet you can recognize the tidal eating also has been important and intense heating of the inner moon moons could have driven off much of the isis this a combination of two processes may be responsible for the composition of the canadian moons saturn is most famous so before continuing to saturn what can you tell me about the juno probe that visited jupiter so thank you astronomers also has a bit of sense of humor so all jupiter's moons is named of these lovers and juno is jupiter's wife so they literally seemed jupiter's wife to go check up on jupiter and yes juno is still working saturn is most famous for its beautiful rings easily visible through the telescopes of modern amateur astronomers large earth-based telescopes have explored the planet for many decades the first close of these came in with voyager probes through saturn in 1918 and 1981. the cassini spacecraft went into orbit around saturn 2004 and began an extended exploration of planets its rings and its moons yes juno is still sending back later so if i'm correct your correctness is wonderful but i'm not exactly sure what happened there so as you can see in figure 18.1 certainly shows a faint belt zone circulation by voyager cassini and hubble spacecraft telescopes images confirm that belts and zones are present and that associated winds are up to three times faster than the winds on jupiter battles and zones on saturn are less visible than on jupiter because they occur deeper in saturn's colder atmosphere below a layer of methane haze image a saturn's valve zone circulation is not very distinct at visible wavelengths these images were recorded when saturn's southern hemisphere was stuck towards earth then image b because saturn is colder than jupiter the clouds form deeper in a hazy atmosphere notice that the free cloud layers on saturn form at about the same respective temperatures as to the free cloud layers on jupiter so here we can see we have ammonia ammonium hydrosulfide and water saturn is less dense than water so in theory saturn would be able to float on water suggesting like it is like jupiter region origin and helium saturn is the most ablate of the planets and this is evidence that its interior is mostly liquid with only a small core of heavy elements because its internal pressure is lower saturn has less liquid metallic origin than jupiter perhaps that is why saturn's magnetic field is 20 times weaker than jupiter's like jupiter saturn rotates more radiates more energy than it receives from the sun and models predict that it too has a very hot interior saturn has nearly 50 known moons saturn has nearly 59 moons many of which are small and all of which contain mixtures of ice and rock many are probably captured objects so planet threading of water strongers are funny sometimes that you can say again the largest of saturn's moons is titan a bit larger than a planet mercury measurements of the effect of its gravitational fields and probes passing nearby indicate that it has a rocky core under a figment of isis saitan is so cold that its gas molecules do not travel fast enough to escape it has an atmosphere composed mostly of nitrogen which trace with traces of argon and methane the ultraviolet component of sunlight converts some of the methane into complex carbon-rich molecules that collect into small particles filling the atmosphere with orange smog some of those particles evidently settle downwards and coat parts of the surface what has been described as organic goo meaning it is composed of carbon rich molecules and is probably semi-liquid so our saturn jupiter gonna shrink a bit when they reach thermal equilibrium if so you know how much they will shrink so yes i believe they will shrink as the temperature changes but i'm not sure with how much exactly as the hidden spray the stainless steel titan smoggy atmosphere is an image a in image b it photographed the surface from an altitude of eight kilometers although no liquid was present dark drainage channels led into the lowlands in an image c once the probe landed on its surface it back photos showing a level of plane and chunks of ice smoothed by moving liquid radar images from the cassini orbiter revealed lakes of liquid methane and ethane around the poles the cassini spacecraft dropped by the huygens probe a drop diagonals broken atmosphere of titan eigen is found as expected that titan's surface is composed mainly of isis of water and methane at [Music] 2180 degrees celsius images made by the descending probe show dark drainage channels suggesting that liquid methane falls as rain washes the dog go off the higher terrain and drains into lowlands such methane downpours may be rare however no evidence of liquid methane was that as the probe descended but later radar images made by the cassini orbiter have detected what appear to be lakes presumably containing liquid methane infrared images suggests that the presence of methane volcanoes that replenish the methane in the atmosphere so titan must have some internal heat source to power the activity most of the remaining moons of saturn are small and icy have no atmospheres are able to cratered and have dark ancient surfaces the moon in cadiz however shows signs of recent geological activity some parts of the surface contain a thousand times fewer craters than other regions an infrared observation showed that its south pole polar region is usually worn invincing water and ice containing organic compounds evidently a reservoir of liquid water lies just below the surface at some point in its history the moon may have been caught in a resonance with another moon and had its interior warmth by tidal heating in the right image the bright clean icy surface of incidence does not look old some areas have few craters and numerous cracks and lanes of groove terrain disable the surface of jupiter's moon ganymede enceladus is fencing water is energetic molecules from geezers near south pole the thermal infrared image reveals internal heat leaking to space from the tiger stripe cracks where the geezers are located like nearly all moons in the solar systems saturn's moons are tidally locked to the planet rotating to keep the same sight facing the planet the leading side of these moons the site facing forward in the orbit is sometimes modified by debris lipids for example has a crater trailing site about as bright as dirty snow but its leading site is as dark as fresh asphalt one hypothesis is that a dark material is carbon rich dust from anterior meteoroid impacts on phoebe the next moon outward from saturn lepidus also has a strange equatorial reach that may have been produced by representation when the moon was young the rings of saturn are perhaps the most beautiful sight in our solar system notice three important ideas plus one new term the rings are made up of billions of ice particles each in its own orbit around the planet the ring particles you observe now can't be as old as saturn the rings must be replenished by impacts on saturn's icy moons or other processes the same is true if the rings around the other jovian planets secondly the gravitational effects of small moons are called shipped satellites can confine submarines in narrow strands or keep the edges of the moon sharp moons can also produce waves in the rings that are visible as slightly round ringlets and lastly the ring particles are confined in a thin plane spread among small moons and confined by gravitational interactions with larger ones the rings of saturn and the rings of the other german worlds are created by and controlled by each planet's moons without moons there would be no rings observations made by the cassini spacecraft shows that ring particles have compositions that resemble that of saturn's distant icing phoebe a large impact on phoebe may be part of the complex history of saturn's rings tiny icy particles from jesus from the moon and clear this understood to be the main source of material for the outermost low density ring discovered by the cassini probe and named the earring within which inseglius orbits saturn formed in outer solar nebula where ice particles were stable and may have contained more trapped gases the protoplanet grew rapidly and became massive enough to attract hydrogen and helium by gravitational collapse the heavier elements sand to the middle to form a small core and oxygen formed a liquid mantle containing liquid metallic origin the output flow of heat from the interior drives convection inside a planet that helps produce its magnetic field because saturn is smaller than jupiter the internal pressure is less the planet contains less liquid metallic origin and its magnetic field is weaker the rings can't be primordial that is they can't be material left over from the formation of the planet such isis would have been vaporized and driven away by the heat of the protoplanet rather you can suppose that the rings are debris from the occasional impacts of meteoroids asteroids comets on saturn's icy moons some of saturn's moons are probably captured asteroids that wandered too close but large moons almost certainly formed with saturn many of saturn's moons have ancient surfaces but in clearness and tide then have free surfaces evident the ongoing geological activity you will see a few more examples of recent geological activity and also captured moons when you explore further from the sun now that you are familiar with the liquid giants in our solar system you will be able to appreciate how strange the ice giant uranus and neptune are uranus especially seems to be the oddball of the family uranus has only one third diameter of jupiter and only one twentieth as massive four times further from the sun in jupiter its atmosphere is almost 100 degrees colder than jupiter's uranus never grew massive enough to capture large amounts of gas from a nebula as jupiter then saturn did so there's much less hydrogen and helium each internal pressure is enough less than jupiter's but it should not contain any liquid metallic origin models of uranus based in part of its density and ablativeness suggests that it has a small core of heavy elements and a deep mantle of partly solid water although that material is referred to as ice it would not be anything like iron spice on earth and the temperatures and pressures inside uranus the mantle also probably contains rocky material plus dissolved ammonia and methane circulation in that electrically conducting mantle may generate a planet's peculiar magnetic field which is highly inclined to its axis of rotation above the mantle lies a deep hydrogen and helium atmosphere uranus rotates on its side with its equator inclined about 98 degrees to its orbit as a result the winter summer contrast is extreme with the sun passing near each of the planet's natural poles at the solstice so half of the planet is in perpetual darkness and of off and perpetual light for the 21-year long summer and winter seasons compare that with seasons on earth discuss in chapter 3 section 1 when voyager 2 flew past in 1996 the planet southpaw was pointed almost directly as sun so imagine living on a planet that is basically 21 years summer 21 years winter and also 21 years tonight 21 years day uranus rotates on axis that is stepped about 98 degrees from perpendicular to its orbit so its seasons are extreme one of its poles is pointed nearly at a sun a solstice and inhabitants of uranus would see the sun near celestial pole never rising or sitting as uranus orbits the sun the planet maintains the direction of its axis in space and thus the sun moves from pole to pole at a time of an equinox and uranus the sun would be on a celestial equator and would rise and set with each rotation of the planet compared with similar diagrams for earth and the right hand page of concept art 3a voyager 2 photos show a nearly featureless ball the atmosphere is mostly hydrogen and helium but traces of methane absorb red light and this make the atmosphere look green blue there is no belzone circulation visible in the voyager photographs although computer enhancements revealed a few clouds and bands around the south pole in a decade since voyager 2 flew past uranus spring has come to the northern hemisphere of uranus and autumn to the southern hemisphere images made by hubble space telescope and new large earth-based telescopes reveal changing clouds and cloud bands in both hemispheres in image a if you had been riding on board voyager as it passes uranus the planet would have looked like a bland green image b later ground-based contrast announced images review traces about in circulation deep in the atmosphere so here we can see that all syringes also has rings and now clouds were visible in the voyager 2 flyby until recently astronomers could see only five moons orbiting uranus voyager 2 discovered 10 more small moons in 1986 and more have been found in images recorded by powerful telescopes on earth the international astronomical union which decides definitions and naming conventions for celestial objects and surfaces features specified that moons of uranus will continue to be named of the characters in place of william shakespeare and alexander well so this is something interesting about uranus for all the other main conventions in the solar system is greek and roman mythology uranus moons are named after the plays and characters of shakespeare and alexander pope the five major means of uranus are smaller than earth and have old dark created surfaces a few have deep cracks produced perhaps when the interior frozen expanded in some cases liquid water lava appears to have erupted and smoothed regions aerial is marked by broad smoothed floored valleys that may have been cut by flowing ice evidence of geological activity under two uranian moons a ariel has an old credit surface but some regions are marked by broad shallow valleys for few craters and b the face of miranda is marked by ovoids which are believed to have formed when internal heating caused slow conviction in the eyes of moon's mantle note that a five kilometer high cliff at the lower edge of the moon miranda the innermost moon is only 14 diameter of earth's moon but its surface is marked by grooves called ovoids they may have been caused by internal heat driving convection in the icy mantle rising currents of ice have deformed the crust and created ovoids by counting craters on the ovoids astronomers conclude that the entire surface is old and the moon is no longer active perhaps it was warmed by tidal heating long ago the rings of uranus are not easily visible from earth the first thing that uranus has rings comes from occulations the passing of the planet in front of a star during which the rings will materially block the star's light observed by astronomers onboard the kuiper airborne observatory in 1977 most of what astronomers know about these rings comes from observations by the voyager 2 spacecraft the composition appears to be water ice mixed with methane that has been darkened by exposure to cellular particles trapped in the planet's magnetosphere notice three important points plus one new term the rings of uranus were discovered during an oculation when uranus crossed in front of a star secondly the rings are dark contain little dust and are confined by small moons thirdly particles orbiting in the rings around uranus and neptune cannot survive for longer periods so the rings need to be resupplied with material from impacts on wounds as is also true for the rings around jupiter and saturn when you read about neptune's rings late in this chapter you can return to this return to this art spread and see how closely the two wing systems compare in 2006 astronomers found two new very faint greens orbiting far outside the previous membranes of uranus the newly discovered satellite map appears to be the source of particles of the larger ring and the smaller of the new rings is confined between the orbits of moons portra and rosalind no yeah i know some of this stuff can be a bit weird and funny uranus never grew massive enough to capture large amounts of gas from a silly nebula as that juvederm saturn uranus is rich in water and eyes surrounding hydrogen and helium modern models of the origin of the solar system suggests that uranus and neptune formed closer to the sun than their present positions into acting interactions with massive jupiter and saturn could have gradually moved uranus and neptune outward and societal effects may have produced uranus accumulation another hypothesis is that uranus was struck by large planetesimal as it was forming and given its highly inclined rotation the highly inclined magnetic field of uranus may be produced by convection in its electrically conducting mantle with very little heat flowing out of the interior this convection must be limited now we are touching neptune through a telescope on earth neptune looks like a tiny blue dot with no visible cloud features in 1989 voyager 2 flew past and revealed most of what we know today about neptune so the international storm called union really has fun with the naming of these celestial objects yes they do almost exactly the same size as uranus neptune has a similar interior model calculations predict that a small core of heavily heavy elements lies within the slushy mantle or water isis and rocky materials below a hydrogen-rich atmosphere yet neptune looks quite different on the outside of uranus neptune is dramatically blue and has active cloud formations neptune's dark blue tint is caused by its atmospheric composition of one and a half times more methane uranus methane absorbs red photons better than blue and scatters blue photons better than red giving neptune a blue color and uranus a green blue colour something interesting that you guys know that neptune wasn't discovered through a telescope neptune was mathematically determined so when you look at rest of the cell system we start studying the gravitational influence of all the bodies in the solar system they realized in the area where neptune was because nature is not visible with the naked eye only fruit telescope something must be a certain body of a certain size to have a gravitational influence so they calculated where that is bing when they pointed the telescope to that point there was neptune and mr mavel that's why planet nine is not discovered so if you want to do the same principle then you can calculate to extreme accuracy where planet 9 should be but if you point your telescope towards it there's nothing so planet 9 does not exist atmospheric circulation on neptune is much more dramatic than on uranus when voyager 2 flew by neptune in 1989 the largest feature was the great dark spot roughly the size of earth the spot seemed to be an atmospheric circulation pattern much like jupiter great red spot smaller spots were visible in neptune's atmosphere and photons showed they were circulating like hurricanes more recently the hubble space telescope has photographed neptune and found the great dark spot is gone a new cloud formations have appeared as shown in figure 18.14 evidently where the patterns on neptune are very changeable in image a because neptune's equator is inclined in 28 degrees it is all in its orbit it experiences seasons the planet's overall period of 165 years causes each season to last more than 40 years in image b since 42 visited in 1989 spring has come to southern hemisphere and the weather has changed significantly that is surprising because sunlight on neptune is 900 times thinner than on earth the atmospheric activity on neptune is apparently driven by heat flowing from the interior plus some contribution by the sunlight 30 amuse from the sun the heat causes convection in the atmosphere where the rapid rotation of the planet converts into high speed winds high level white clouds of methane ice crystals and rotating storms visible as spots neptune may have more activity than uranus because it has more heat flowing out of its interior for reasons that are unclear like uranus neptune has a highly inclined magnetic field that must be linked to circulation in the interior in both cases astronomers suspect that ammonia dissolved in the liquid water mantle makes demands on a good electrical conductor and that convection in the water coupled with the rotation of planet drives dynamo and generates the magnetic field neptune has two moons that were discovered from earth before voyager 2 flew past in 1989. voyages covered six more very small moons since then a few more small moons have been found by astronomers using earth-based telescopes the two largest moons have peculiar orbits in a raid about a tenth the size of earth's moons follows a large elliptical orbit taking the india earth year to circle neptune once triton almost 80 percent of the size of earth's moon orbits neptune retrograde so that means backwards these odd suggest that a system was disturbed long ago in an interaction with some other body such as a massive plantation with a surface temperature of about 36 kelvin so this information is wrong uh it looks like when i copy and paste it as temperature the format screwed us up but yes it's 36 kelvin triton has atmosphere of nitrogen and may find about 10 to the power five times less dense than earth's like significant part of triton is ice in deposits of nitrogen frost are visible at a southern pole which at its own past had been turned towards sunlight for 30 years the nitrogen frost appears to be vaporizing the sunlight and is probably re-freezing in the darkness at triton's north pole visible wavelength images of neptune's means triton image a triton's southern poly cap is formed of nitrogen frost no dark smudges caused by organic compounds sprayed from hydrogen geezers an absence of craters in which we these ground basins and triton appear to have been repeatedly flooded by liquid from the interior many features on triton suggest it has had an active past it has few craters on its surface but it does not have long faults that appear to have formed when the icy crust broke some approximately round basins about 400 kilometers in diameter appear to have been flooded time after time by liquids from the interior analysis of dark smudges visible in the southern pillar cap reveals that these are deposits produced when liquid nitrogen in the crust formed by the sun erupts from winds and spews up to eight kilometers in high into the atmosphere methane in the gas is covered by solar ultraviolet radiation into dark compounds that fall back leaving black smudges but counting craters on triton planetary scientists conclude that a surface has been active as recently as a million years ago and may still be active to energy source for triton's geezer activity could come from radioactive decay the moon is two-thirds rock and although such would not be able to generate sufficient radioactive decay to keep molten rock flowing to its surface fruit triton may be the site of water volcanism big sharp water and ammonia could melt at very low temperatures and erupt to resurface parts of the moon i'm just waiting for the slide to load on my side neptune's rings are faint and very hard to detect from earth but i illustrate some interesting principles of comparative dermatology comparing the rings of neptune with those on uranus that is two additional points neptune's greens named after the astronomers involved in discovery of the planet are similar to those of uranus but gaining more small dust particles also neptune's rings show another way that moons can interact with rings one of neptune's moons is producing short arcs in outermost ring neptune's rings resemble the rings of uranus saturn and jupiter in one important way as you have already learned these rings can't be primordial that is they have they can't have lost it since the formation of the planets planetary rings are constantly being made so yes mr victorious but as you will learn in the last chapter there are other ways we can look for life and this otherwise our life can look for us neptune must have formed much as lunas did growing slowly and never becoming massive enough to track large amounts of hydrogen and helium he developed a core of heavy elements a mantle of slushie isis and rock and a deep hydrogen-rich atmosphere neptune's internal heat may be generated partly by radioactive decay in its core and partly by dense material sinking inward laboratory experiments showed that the temperatures and pressures expected deep in the atmospheres of nature and uranus methane can decompose and the released carbon might form diamond crystals perhaps as large as pebbles the tears flow of diamonds falling into planets interior which release gravitational energy and help on the planet this process may be the source of some of neptune's internal heat but the lack of internal heat and uranus remains puzzled the possibility of planet white hailstorm of diamonds serves to remind you that other worlds are actually unearthed and may hold the things you can hardly imagine the heat flowing outward towards neptune's surface can drive convection using the field and help create atmospheric circulation the moons of neptune suggest some catalyst catalyst mutant counts and long ago put narid into a long period elliptical orbit and tried them into retrograde orbit you have seen evidence of major impacts throughout the solar system so such interactions may have been fairly common certainly impacts on the satellites could provide the debris that is trapped among the smaller moons to form greens out on the edge of the solar system orbits a family of small icy worlds pluto was the first to be discovered in 1930 but modern telescopes are found more you may have learned in school that there are nine planets in our solar system but in 2006 the iau voted to remove pluto from the list of planets and reclassified as a dwarf planet pluto is a very small icy world it isn't jovian and it isn't terrestrial its orbit is highly inclined and elliptical enough that pluto actually comes closer to the sun than neptune at times to understand pluto's status you can use comparative dermatology to analyze spruto and then compare it with its neighbors so according to me pluto should have been kept the planet just to keep tradition alive and population sake but the iau has voted and that is where he is for the cd someone's gonna try to bring it up again to have it reintroduced as a planet due to just traditionally but we'll see what will happen on that so pluto is a very difficult to observe from earth as its diameter is 2 370 kilometers smaller than australia and two-thirds the diameter of earth's moon in earth-based telescopes pluto never looks like more than a faint point of light and even in hubble space telescope images it shows little detail orbiting so far from the sun pluto is cold enough to freeze most compounds you think of as gases and spectroscopic observations have found evidence of nitrogen in the vein isis on its surface pluto has a thin atmosphere of nitrogen and carbon monoxide with small amounts of methane pluto has five known moons four are quite small but sherman is relatively large with half of peter's diameter shown orbits pluto in an orbit inclined at 180 degrees to the plane of pluto's orbit around the sun which means sharon's motion is retrograde pluto and shone are tidally locked facing each other so peter's axis of rotation is inclined at the same large angle to its orbit such that its rotation is also retrograde knowing shown's overall period of 6.4 days and orbits in a major axis of 19600 kilometers allow to use skipper's third law to calculate that the total mass of the system is about 0.002 for earth masses most of that mass is splitter which has about nine times the mass of shearin then diameter is a mass of pluto and sharon allows determination that pluto data densities are respectively 1.9 and 1.7 grams per cubic centimeter that indicates that both pluto and sharon must contain about 30 to 40 percent ice and 60 to 70 rock the new horizon spacecraft flew past pluto in july 2015 radioing back impressive images and other measurements close-up pictures show mountains up to 3.5 kilometers high methane and hydrogen ice would not be strong enough to stand that tall so country scientists conclude that the mountains must be made of water ice that would be rock-hard at previous temperature the lack of craters on and near those mountains indicates that this particular landscape is very young say no older than 100 million years one of the younger surfaces observed in the solar system pluto has been active geologically recently which means that heat must be flowing outward although country scientists wonder what the internal heat source could be sherman's orbit is perfectly circled so tidal heating is not explanation radioactive decay would seem to be the only plausible alternative although that heat source should also have faded long ago one theory scientist on new rising steam remarked this may cause us to rethink what powers geological activity on many other icy worlds pluto turns out to be a world full of surprises so what defines a planet to understand why pluto is no longer considered a planet you should recall what you have already learned about the kuiper belt since 1992 astronomers has discovered more than a thousand icy bodies orbiting beyond neptune there may be as many as minimum about objects larger than one kilometer in diameter they are understood to be isotonic decimals left over from the outer cellular nebula some of the kuiper belt objects are quite large and one aries is about the same diameter splitter but is 27 percent more massive three other part about objects found so far satan and orcas are half the size of pluto or larger areas and orcas are known to have moons of their own in that way they resemble pluto and its family of moons a bit of comparative planetology shows that pluto is not related to jovian or terrestrial planets it is obviously a member of a newfound family of worlds that orbit behind neptune these bodies must have formed at about the same time as the eight classical planets of the solar system but it did not grow massive enough to clear their orbital zones of remnant planetesimals and consequently remain embedded among the swarm of our objects in the kuiper belt the the iau criteria for a full planet status is that object must be large enough that its gravity has pulled it into spherical shape and also large enough to dominate and gravitationally clear its orbital region of most or all of objects over a span of billions of years areas of pluto the largest objects found in a kuiper belt and serious largest object in the asteroid belt are too small to clear the orbital zones of other objects and therefore do not meet the standard for being called planets on other hand all three are large enough to be certifical so there are the prototypes of a new class of object defined by the iau as dwarf planets so pluto and plutinos so no the section is not about the 1950s rock band it is about the history of the outer solar system and it will take you back 4.6 billion years to watch the planets form more than a hundred of the kyber belt objects are caught with pluto in a three to two resonance with neptune that is that orbit is sun twice from neptune orbits three times the subset of kbos have been named plutinos the plutinos formed in outer ceiling nebula but how did i get caught in a resonance with neptune as you learned earlier some models of the formation of the planet suggest that uranus and neptune may have migrated outward early in the social solar system's history as neptune moved further from the sun its orbital resonance could have swept up small objects like a kind of temporary snowplow the patinas are caught in a three-to-two resonance and other type about objects caught in other reasons the evidence appeared to support those models that predicted uranus and neptune migrated outward the migration of the outer planets would have dramatically upset the motion of some of the kuiper belt objects and some could have been thrown inward where they could interact with the jovian planets some of those objects may have been captured as moons and astronomers wonder if moons such as neptune's triton could have started life as a capable object other objects may affect bodies in the inner solar system and cause the late bombardment episode especially evident on the surface of earth's moon the small frozen walls on the fringes of the solar system may hold clues to the formation of the planets 4.6 billion years ago in the subsequent history of earth so ladies and gentlemen this was our lecture on the solar system so now we have finished the solar system do you guys guess what remains so yes one of the objects so one of the lectures we still need to do is astrobiology and the other one we still need to do is comets and asteroids so we will finish up these last two lectures next week but for now let's quickly go through the memo of the second quiz so let me just find my site and open it up so i will give that right after we go through the memo can everyone see my screen yes you can calculate the diameter of the moon through your estimated angle diameter so the first question is if it takes light eight minutes to reach earth from the sun and 1.3 hours to reach second what is the distance from the sun to saturn do i have any volunteers that can perhaps explain this [Music] any volunteers how did you calculate this answer so yes you convert one to three hours two minutes so we so well we know light yeah is way too big and we know that it's from the earth to the sun is one i you does not consider logical answers you can answer it that way but you know it takes eight minutes for light to reach the sun and the sun to earth is one au one a use 150 million kilometers so you take that 150 million kilometers divide by eight then you know how far light travels in one minute can you take those 1.3 hours convert that to minutes and then you know how far light travels in one minute you know how many minutes they are and then voila you calculate how far it is away and that is 9.75 a u then secondly to determine the radius of a distance star we need to know its temperature and luminosity so those are two important concepts throughout this module if you know what the object's temperature and luminosity is you can determine the radius in question three absorption lines due to interstate media indicate that some components of interstellar medium are called and of low density because the lines are extremely narrow so remember kirchhoff's laws then question number four the full first quarter moon arises at about noon uh i can't zoom into myself they should be able to zoom in and on your side so if you've done your moon research and worked on your assignment you will realize a first quarter moon always rises at about noon the last question what is the approximate age of a star cluster if turn off point lies with spectral type g stars so now you have to learn and use your hr diagram so in the hr diagram we know the turn-off point of the specular g-type stars are about 10 million years old so that means the approximate age of that cluster will be 10 billion years old is everyone happy with this explanations okay then coming to the semester test so the semester is the scope for v semester so let me just check on my side so to make it fair for you guys the scope of the test will be half of the modules work so the scope will be chapter 1 to 10. so chapter 1 is everything from the night sky and the introduction and you will end off with the deaths of stars so chapter 1 to 10. is that fair okay cool and then i will also provide you guys with a mock test for practice for these mystics i will what is it last tuesday i will release that to you by tomorrow and then so next week monday and tuesday we will have our normal lectures but if it's fine with you guys we will i will schedule two question answer sessions so one for next week wednesday and one for next week thursday um it's not compulsory that you can i will be active and you can ask questions so what's on next week wednesday and thursday will work for you so on thursday's class i will go for the memo of the mock test so what time next week wednesday and thursday will work for you guys for recap sessions or question and answer sessions well seven to eight o'clock to i will ask on the group but i've asked you guys what will the evenings work for say for example 7 to 8 on wednesday evening next week and 7 to 8 on thursday evening next week i will ask on the whatsapp group as well then there's two classes on compulsory at all so the idea is that you study and if you have questions then you could we have an answer question answer session during those two sessions that you can um ask questions and uh we can discuss so next week thursday when are you writing next week at what time you're writing next week thursday or when do you end your semester list 5 30 to 7 30 we can even do on next week thursday we can even do that class from eight to nine if you guys are up for it just to compensate for you guys writing so it won't be compulsory but it will be open for questions and questions and answers now so do you have any interesting quants and gravity yes i have a little bit of don't know much about it about my field of expertise but yes i have no interest in it so um that's the last admin so one thing is just remember your moon assignments that is also due in about 14 days please do not underestimate it also now i will be taking plagiarism seriously so if you guys have no further questions then you are more than welcome to log off if you're writing tastes this week good luck preparation for those fists and good luck of this itself then have a wonderful evening and i will see you all next week so if you guys have no further questions i am also going to log off so have a wonderful evening guys now you are more than welcome to email me pleasure so i'm also going to log off so have a wonderful evening everyone