Worlds of Shadow and Light: The Moons of Uranus and Neptune

you [Music] it's fair to say that william lhasa was a very lucky man born on the right side of nineteenth-century england's pitiless wealth divide in his mid-20s he attained his fortune the old-fashioned way by marrying a rich widow his family had been clock and watchmakers but he decided to follow his dowry and enter his wife's late husband's business of brewing in 1825 at the age of just 26 Lhasa founded his own brewery and since the production of legal recreational drugs is an eternally lucrative profession he found that he could leave it to more experienced underlings and become a gentleman of leisure but unlike many who drift upward into the indolent classes for Lhasa Easy Street was a blank canvas on which he would paint his legacy what Lhasa intended his legacy to be can be gleaned from the name he gave his house starfield as befits a scion of clockmakers Lhasa possessed a natural mechanical ingenuity and dexterity and by the age of 21 had already constructed his own nine-inch aperture reflecting telescope in 1844 with the help of James Naismith the inventor of the steam hammer lhasa constructed a reflecting telescope with an aperture of 24 inches and a focal length of 20 feet it was the first telescope of its size to be constructed with an equatorial mount which allowed its position to be subtly moved in line with the Earth's rotation keeping the target in sight according to the account is Edward S Holden director of the Lick Observatory in California who was an acquaintance of last Louie's early the Reverend William Dawes glasses friend and fellow astronomer had sent him an urgent letter requests as he joined the hunt for the eighth planet which England was in danger of losing to the French unfortunately Lhasa was laid up with a sprained ankle and due to the carelessness of a maid never saw the letter until it was too late and so the French would ultimately locate and named the planet Neptune this story is based on hearsay and widely regarded as apocryphal but I find it too cute to exclude in the aftermath of Neptune's discovery John Herschel head of the Royal Astronomical Society and son of William Herschel who discovered Uranus wrote feverishly colossal that he and his remarkable telescope quote find satellites with all possible expedition exclamation point England may have lost Neptune but it could still raise its flag on Neptune's moon it says something about last saw standing at the head of the Royal Astronomical Society entrusted the job of finding Neptune's moon to a complete amateur whose only qualification was that he was rich enough to have his own telescope the trust however was well placed on the 10th of October 1846 just 17 days after the discovery of its parent planet Lhasa announced that he had found Neptune's moon today named Triton after the son of Poseidon the Greek Neptune in an ironic final twist to this tale of national cosmic rivalry the name was chosen by a Frenchman Camille Flammarion the following year my suspected he may have observed two ghosts Lee points around the planet Uranus but it wasn't until 1851 after Lhasa had done the obvious relocated his Observatory to Malta from the astronomically inhospitable climes of northern England that he was able to confirm but even after his discovery was confirmed Lhasa found himself the subject of not a little scorn William Herschel who discovered Uranus is two largest moons as well as the planet itself playing in a later paper to have found another - and possibly another four moons leading many to conclude that Lhasa had merely followed up on Herschel's discoveries however lhasa after observing uranus at more than a thousand times magnification found no other moons and concluded in a letter to the reverend john of Sheepshanks of the Royal Astronomical Society that quote I think it's high time that Uranus's establishments should be reduced he has been luxuriating these many years with a retinue that I really believe does not belong to him and therefore he must be cut down to four attendants until some astronomer arises rich enough to present him with some more posterity agrees with him lhasa is now considered the sole discoverer of the two moons with four moons now to deal with John Herschel decided they needed names and in another act of poetic nationalism rather than going the traditional route of Greek mythology decided to draw an English literature for inspiration each of the four moons was given the name of a fairy from a pen of an English writer titania and Oberon from Shakespeare Umbriel from Alexander Pope and Ariel from both it's actually unclear if it was Herschel or Lasell who maimed some or all of the moons but Herschel is usually given full credit the outermost planets of our solar system do not give up their secrets easily even now and it would be nearly 100 years before lasses promise successor arose contrary to lasses prediction though Gerard Peter Piper was not particularly rich in fact he owed his academic career mostly to hard graft exceptional visual acuity and shrugging off the snobbery of his wealthier classmates by the time he left his native Holland and settled in the u.s. Piper had become the most important planetary astronomer of the 20th century in fact I have made extensive reference to his achievements in previous videos and will very likely make a biography of him someday as such I do not intend to dwell on his story here suffice to say that in 1948 at the University of Texas is McDonald Observatory Piper fought past the glare of Uranus to glimpse a tiny dim inner moon smaller and closer by far than any of his siblings in the preceding decades the fairy rationale for naming Uranus's moons had been forgotten and Kuiper chose to name his petit moon Miranda after a human character from Shakespeare's The Tempest an unwitting precedent that would unleash a flood once Voyager 2 arrived only a year later Piper also discovered the second known moon of Neptune mariette which would remain Triton so no sibling until the arrival of Voyager 2 in 1989 just to give you an idea of what a phenomenal astronomer Gerard Kuiper was nary it is a broken piece of space junk about 170 kilometers across that orbits its planet in slightly less than one earth year Kuiper was able to observe that object and its movement from over four billion kilometres away for much of the space ages golden era the satellites of Uranus and Neptune remained tantalizingly inscrutable for 40 years astronomers strained against the distance to glean whatever facts they could about their diameters masses or compositions and patiently waited for Voyager 2 to date our only mission to the two outermost planets to prove them all SPECT ocularly wrong the one thing nearly everyone could agree about the moons of the outer planets was the Triton was blindingly bright while the moons of Uranus were 10 inversely dark the only question was to what degree when in 1986 Voyager 2 finally rendezvous with Uranus the scientists could say that in that regard at least their predictions were confirmed but the moons of Uranus are even darker than they had thought even the brightest of the moons Miranda is barely brighter than our own planet while the darkest umbral is almost as dark as mercury the darkest planet in the solar system they appear as blackened shadowed tomb worlds Riven with ancient fractures and cross by rolling coal black plains they were also tiny while astronomers who determine their diameters and masses fairly accurately by the time of voyagers arrival all the major moons proved substantially smaller and less massive in the flesh than they had on paper and this was strange because once we lurked the moon's densities they suggested that unlike the moons of Saturn which were worlds of water orbiting a desiccated ball of gas the moons of the solar system's first water world appeared to comprise an even mixture of ice and what astronomers call rock that is dense non-volatile materials this composition is strikingly similar to another alien visitor from the dark depths of space that was scheduled to return later that same year comet Halley in fact Holly and the uranium moons may owe their blackened tortured appearances to a similar cause before being yanked into the inner solar system by Neptune Holly was likely a bright icy object much as astronomers find daily in the region beyond the farthest planet but as Holly sped round and round the inner solar system every pass by the Sun exposed it to its radiation and magnetic field which gradually stripped the comet of its icy material leaving mostly dry carbonaceous dust similarly the moons of Uranus all lie within Uranus magnetosphere whose charge particles bombard the airless worlds and gradually strip off their lighter elements in particular hydrogen which some argue was originally present as methane ice in the moon surfaces but is present now only as bear solid carbon possibly graphite this model is complicated by the fact that no methane has yet been observed on any of Uranus t'as moons even though it has been observed on Triton and Pluto a similar process is believed to have created the carbon dioxide present in the surface of the Moon since that compound would not survive on the surface for very long with oxygen in the water combining with carbon on the surface the moons of Uranus are all roughly the same color and no those images are not black and white that's what they look like and Criss crossed with sinuous steep-sided canyons appropriately called graben after the german word for grain crop inform when land splits apart or faults causing either the sides to rise or the center to subside in the case of Uranus's moons this faulting is believed to be due to a weird property of water that I discussed in my video on Titan as it freezes water expands and if water freezes below an already frozen surface it pushes upward creating those blistering cracks so horribly familiar to ice skaters this means that the moon's interiors must at some point have been liquid and it isn't the only evidence all the larger moons of Uranus show signs of tectonic activity usually a vast lava flows obliterating earlier evidence of impacts these lava flows are believed to have been created not by liquid rock but by a viscous lava like water ammonia mixture precisely how such tiny moons could have retained inner heat long enough to produce these tectonic features is not clear they certainly are not visible on Saturn's mid-range moons such as Rhea DoD or Iapetus all of which are comparable mass and similar composition perhaps the uranium's rockier interiors allowed for radioactive decay to continue for a longer time more likely though tectonic activity was true by early changes in their orbits which saw them fall into temporary resonances with one another as Europa and Enceladus are today but no matter how extensive that tectonic activity may have once been it is gone now all of Uranus has moved show evidence of ancient crater II not unlike our own moons primordial hail which means that again much like our own moon any volcanic activity they made once demonstrated was over billions of years ago today the moons of Uranus are very much dead as it turns out the lugubrious appearances of the satellites of Uranus are even more apropos than that as current consensus among astronomers is that the moons are scars from an ancient wound Uranus as I explained in the previous video in this series orbits the Sun on its side when its moons and winged circling it like the hands of a clock the most likely culprit is a massive collision that thrashed Uranus in the chaotic era of the solar system's formation this collision is believed to have ejected a massive amount of material into orbit which eventually coalesced into the moons a similar impact is believed to have formed their own arguably the most striking feature of the largest moons of Uranus is their similarity to one another few of the moons demonstrate the individuality seen in the moons of Jupiter or Saturn of course this may be simply due to a lack of data since all we have of their surfaces are their southern hemispheres and in fact not even that since they were only half illuminated by the Sun Oberon has a distinctive pimple on its left side that may be the central peak of an impact crater if so it would be the largest in the uranium system the mostly drab moon Umbriel has a bright white feature in its top side called Wanda that gives it the appearance of a cherry bomb it is believed to be cryovolcano can origin possibly an eruption triggered by a meteorite strike the white spot in the corner called vu there may be a frozen tip of a cryovolcano for all the moon's seeming drabness and sameness there was one spectacular staggering exception an exception so bizarre it inexplicable that the poor scientists at NASA who had little more than 24 hours to come to terms with it before revealing it to the press were left speechless even before voyagers encounter it was clear that miranda was different from her siblings being both substantially smaller and less dense in fact miranda is one of the smallest objects in the solar system known to still be spherical under its own gravity it's low relative density meant that unlike its rockier neighbors if follow the satellites of Saturn in being mostly made of ice its size and bulk composition are similar to that of Saturn's timing only Venus which led the NASA team to assume that it would be similar in appearance as well a squashed icy ball riddled with craters they were wrong for all the universe Miranda resembled an ancient alien spacecraft summoned from the pages of the Necronomicon with strange geometrical cysts erupting from its ancient craters and the cleft in its side so deep it was as if some cosmic monster had torn it with its teeth by the way that bite Verona rupess is the highest vertical drop in the solar system 20 kilometers straight down in Miranda's low gravity if you jumped off the top it would take you 12 minutes to hit the surface if Miranda were scaled to the size of the earth Verona would be 320 kilometers or 200 miles deep and stretched halfway across the continental United States and yet for all that it is probably the least studied feature on Miranda I had to personally contact the planetary scientists for information about it and he graciously informed me that pretty much no one had studied it guessed it wasn't awesome enough for them if I had hazard a guess as to how it formed Verona seems tied to a series of ice fractured Robin the follow Miranda's 340 degree line of longitude called appropriately enough the three hundred and forty degree casma perhaps Verona is a mega version of the same faulting process that overtook all the major moons of Uranus but again that's just a guess the main focus of scientists attention on Miranda has been the three weirdly geometrical features called Corona the talk market surface the first and least distinguishable on the left side is called Elsinore the middle Corona which touches the South Pole is called Inverness and the far Corona on the right side is called Rd in their initial attempts to make sense of these structures monumental openness astronomers and planetary scientists went full apocalyptic Miranda had been hit by a giant planetary body that had literally torn it apart its fragments then Rico elastin to a random chaotic jumble with bits of heavier core falling downward from the surface as the fragments fell the crust contracted and the corona where the scars left behind superficially this idea is compelling Miranda's orbit around Uranus is highly inclined or tilted from Uranus's equator by as much as 10 or even a hundred times the other large moons something must have happened in its past to jacket's orbit so market but over time that melodramatic explanation fell from favour as it simply did not fit the facts the corona I of Miranda are surrounded by concentric rings of faults and scarps if the catastrophic impact hypothesis is correct those scarp should reveal signs of compression instead they show signs of having been pulled apart this is consistent with the hypothesis that the corona I formed not from a falling impact but from a rising plume from within Miranda itself today most scientists in the field support the idea that the corona formed through a process called diapered ism which while it sounds like the state of being a blood sucking baby is in fact the extrusion of a solid mass through a brittle or more malleable Rock in essence the corona a rubber ducks held under water and then let go at some point in its past when its orbit was far more eccentric than today Miranda would have entered into a three to one resonance with Hungary which like the resonances that power the volcanism on Io and Enceladus would have heated its interior pure water has too high a melting point for to have been the mechanism alone though it may have been a mixture of water and ammonia or simply saw it ice that was hot enough to convict heat much like Earth's mantle today this resonance would have jacked Miranda's orbit to its current inclination the heating of the interior created what were essentially magma plumes within Miranda analogous to the hot spots on earth the form of the Hawaiian Islands the upwelling produced the banded terrain seen on the corona particularly in Venus similar to the effects seen and similar dye pairs on earth such as salt domes even given the solutions presented here they are still merely educated guesses Miranda it's tortured surface and its fellow moons are likely to remain a mystery until such time as we see fit to send an orbiter to Uranus as no such orbiter is likely in the foreseeable future there is a mystery our children will likely not see solved while Uranus has its own retinue of fascinating oddball satellites Neptune essentially has one yes there are other neptunium moons there even fact but all of them together comprise just one-third of one percent of the mass in orbit around Neptune for all intents and purposes to speak of the moons of Neptune is to speak solely of Triton don't worry those smaller moons as well as the smaller moons of Uranus will have their day in the next episode when I discussed the planets rings before Voyager to whose arrival on Neptune astronomers could say only three things definitively about the tuna Triton first that it was bright really bright but precisely why it was so bright was still not settled objects appear bright through a telescope for three reasons first because well they're bright second because they're close and finally because they're big everyone knew where Triton was so the second option was out it was possible the Triton could simply have an inherently bright as bright as say fresh snow but a far more intoxicating idea and the one that took hold of astronomers imaginations was that it was big early estimates for its diameter were as high as six thousand kilometer which would have made it the largest moon in the solar system and almost as big as Mars the second thing everyone knew or at least was moderately certain of was the Triton had an atmosphere in 1977 Dale Cruikshank an astronomer at the University of Hawaii found strong spectrographic traces of methane and molecular nitrogen on Triton which suggested given Triton surface temperature that they might be present as gas the strength of the bands also suggested the presence of of all things liquid nitrogen on its surface which set Crookshanks mind the light with visions of nitrogen oceans dotted with methane icebergs in 1987 in the lead-up to voyagers encounter astronomers emmelda litski and WR Thompson lyrically pondered that they might glimpse quote the glint of a dis and Sun reflected off a calm nitrogen to see the final thing that everyone knew and in many ways strangest of all was the Triton giant glimmering Triton was a captured object that is rather than forming with its planet as all of the large satellites are supposed to have done Triton was a separately orbiting body that somehow got ensnared by Neptune's gravity and set into orbit around it this was insane objects as big as Triton do not get captured the next largest captured object in the solar system is Saturn's moon Phoebe a former comet 3,000 times smaller than Trekkie the reason Triton is almost certainly captured is because its orbit is retrograde in other words in orbits Neptune through the opposite direction to the planets rotation moons that form with their planets just like planets that form with their stars orbit in the same direction that their planets or stars rotate beyond this Voyager also identified carbon monoxide ice on Triton surface model suggests that carbon monoxide would not survive in the swirling photo satellite nebula around a giant planet the Triton is captured also goes some way toward explaining why Neptune's other moons are a scattered mess of pulverized rubble as so often happens in solar system exploration reality dashed the hopes of the romantics while at the same time revealing truths no one predicted Triton sadly was not 6000 kilometers across but 2700 which still made it larger than the then still planet Pluto Triton is in fact rather bright with an albedo averaging 0.76 about the same as day-old snow which is appropriate because its surface is largely composed of frozen nitrogen with little water ice mixed in this brightness actually make strike in the coldest place ever to have its temperature directly measured at just 33 degrees above absolute zero even Pluto which is usually farther from the Sun than Triton is warmer than that because it's darker surface retains more heat as for the atmosphere well it turned out the predictions had been right like Titans and ours Triton's atmospheres composed mainly of nitrogen unlike Titan in this case the pessimists were also right Triton's atmosphere has a surface pressure only 14 micro bars about 170 thousand the surface pressure on earth though it was still a billion times thicker than our own moons pathetic atmosphere and substantial enough to support wind and clouds of nitrogen ice particles like Titan's atmosphere or indeed that of its own adopted planet Triton's even managed to gain a hydrocarbon haze through fatalis of methane sadly no liquid nitrogen seas were observed but steaming nitrogen geysers were and while Voyager couldn't provide an explanation for Triton's capture events over the next few years would offer a stark change of perspective on that in the years leading up to the Voyager encounter it was noted the Triton was becoming gradually less red Voyager would reveal the reason why like Uranus Anna's moons Triton orbits the Sun on its side meaning that the moon's 42 year long seasons were extreme the South Pole which was the only Pole Voyager could see the other was still trapped in decades-long darkness was capped by a sheet of methane and nitrogen stained red with car enrich tollens created by reactions of methane ice with sunlight this cap was gigantic extending down to 35 degrees latitude on earth it would touch Oklahoma City or Tokyo and it was still evaporating meaning that had once been much larger even before Voyager it was speculated the Tritons atmosphere could freeze into solid nitrogen at the poles much as Mars as carbon dioxide atmosphere freezes at the poles during its far shorter winter it seemed likely that as the nitrogen evaporated from the cap it traveled from the sunlit pole to the darker colder equator remember Triton his sideways and froze again leaving a bright patina on the surface that obscured the darker material underneath this would mean that atmospheric density would vary greatly with season in 2010 when Triton southern hemisphere passed from spring into its long long summer astronomers at the European Southern Observatory noticed this atmosphere notice ly thickened as nitrogen evaporated from its surface since Voyager a noticeable ribboning of Triton surfaces occurred likely due to cry of volcanic deposition of dark material which has led to a decrease in Triton's albedo and a subsequent rise in temperature the most spectacular finding of the Voyager probe however was the Triton was a member of a highly exclusive club of worlds in the solar system those known beyond any doubt to be geologically active the only others to date are IO Enceladus and of course earth though that will almost certainly change in future Trek the surface is remarkably smooth down to the limits of its camera's resolution Voyager found very few impact craters this meant that triteness surface had to be strikingly young millions of years instead of billions and thus it must have been resurfaced relatively recently almost all of the features on Triton surface were endo genic that is the result of processes emerging from within tracking itself either volcanic such as icy lava flows or tectonic such as the sinuous fracture ridges of the kind seen on Europa and on Uranus as satellites all this suggested the Tritons interior was molten until very recently and likely remains so today Voyager found the region of Triton surface to be 55% nitrogen ice and 45% a mixture of water and carbon dioxide ice with the volatile nitrogen forming an upper cap and the water / carbon dioxide forming the in volatile bedrock although water ice was not initially detected it was later in subsequent spectrographic studies it was the only substance strong enough to support what few mountains were seen on the surface and so was deemed to be the moon's main construction material the inherent weakness of water as opposed to Rock meant that there was very little variation in the terrain barely a few hundred metres between the lowest and the highest elevation many smooth Plains show evidence of having been filled in by watery lava flows most likely the same water ammonia mixture hypothesized for the satellites of Uranus and even the calderas from which they erupted much of Triton was composed of so called cantaloupe terrain a field of roughly equal sized depression that had no analogue anywhere in the solar system the current favourite hypothesis for their existence is yes diaper ism the higher rims are believed to be solid lumps that have floated to the surface but this was only the start the voyager team had initially been perplexed by a series of Northwest were trending dark streaks dotted around frightened South Pole clearly they were being driven by the prevailing wind but what could they be perhaps dust devils like those seen on earth or Mars and then Voyager caught one of the most significant shots of its tour a plume of cloudy material rising from the ground an eruption Triton was volcanic ly active but with what the Voyager team noticed that all the observed eruptions were occurring near the subsolar point or the point at which the Sun shines brightest on track the surface this suggested that what was occurring was related somehow to sunlight the preferred model today is that these eruptions are not technically volcanoes but geysers solid nitrogen is translucent and as the Sun passes through it creates a more literal version of the greenhouse effect heating the material below until it vaporizes gradually building pressure until the surface cracks releasing it as an explosion of dirty nitrogen smoke which then travels eight kilometers the atmosphere whereupon it is capped by a thermal inversion and spread eastward it seemed like something out of a fantasy a vibrant living world of volcanoes geysers clouds and winds that somehow found itself adrift in space and swept up into another worlds embrace how could this have happened there had always been a problem with the notion of tritons capture something would have had to intervene to slow Triton down enough for Neptune to catch it the chances of this happening at random let alone in a space as huge as the region near Neptune are infinitesimal so whatever that something was would have had to have been tied somehow to either Neptune or Triton one thing that had become clear in the decade prior to Voyager was the Triton was strikingly similar in both size and composition to the planet 1 unquote Pluto Voyager would only strengthen this connection as well as being nearly the same size and density both worlds had surfaces covered in a combination of nitrogen ice and red stained Tolan though Pluto is far redder than Triton and thin nitrogen based atmospheres for a short time the hypothesis circulated either that Pluto was a former moon of Neptune that it had its orbit disrupted by the coming of Triton or that both Triton and Pluto were moons of Neptune that had had their orbits disrupted by a larger body except that Pluto as I noted in earlier video never actually comes anywhere near Neptune in its orbit so what could have happened in 1992 the answer finally revealed itself Pluto was just one of hundreds of thousands of similar objects in its region of space now called the Kuiper belt Triton was once another Kuiper belt object like Pluto and like Pluto probably existed as part of a binary in the early years of the solar system Neptune is believed to have been kicked into the early Kuiper belt by the gravity of Saturn and in the process likely collided with this hapless couple Triton sad Souter was sent spiraling alone into the void but not before slowing her betrothed enough to send him into the arms of the home-wrecking neptune but like all torrid relationships that between Neptune and Triton is destined to end badly Triton's orbit around Neptune is slowly decaying and in 3.5 billion years or so it will pass inside Neptune's Roche limit once that happens Triton will be torn apart granting Neptune a vast set of pretty new rings over time these rings too will fade as Neptune slowly consumes them thanks again fellow seekers for following me through this exploration of the little-known satellites of the outermost planets please join me next time when I will be exploring the rings of Uranus and Neptune and as always please like comment subscribe and follow me on social media I have links in the description see you soon [Music] [Music] [Music] [Music] [Music] [Music]

Channel: ParallaxNick

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Keywords: moons of uranus and neptune, uranus and neptune moons, uranus neptune moons, moons uranus neptune, moons of uranus, moons of neptune, satellites of uranus, satellites of Neptune, satellites of uranus and neptune, satellites uranus neptune, ariel, umbriel, miranda, Titania, Oberon, Triton, ariel moon, umbriel moon, miranda moon, titania moon, oberon moon

Id: bJ7wvaawkBo

Length: 34min 4sec (2044 seconds)

Published: Thu Aug 02 2018