Saturn, Queen of the solar system, reigns in majesty over a retinue of exotic moons and icy rings like a celestial crown. No other planet of our solar system can compete with its domain for sheer beauty: Exquisite alien vistas that boggle the mind, countless scientific wonders, material wealth beyond imagining, and the promise that some day humanity will know this cosmic work of art with our own eyes and join in its mystery. But when we do, it can only be from among its satellites, because while planet Saturn is a picture in grace from a distance, below its clouds a maelstrom rages forever. Welcome to a realm of unparalleled strangeness and visual revelation. We will be remaining here for the next dozen or so parts of this series, as we explore all the various worlds that Saturn has to offer, beginning with the planet itself.
The progress of our adventure so far (current in bold):
1. The Sun
2. Mercury
3. Venus
4. Earth (Vol. 1)
5. Earth (Vol. 2)
6. Earth (Vol. 3)
7. Earth (Vol. 4)
8. Earth (Vol. 5)
9. Earth (Vol. 6)
10. Luna
11. Mars (Vol. 1)
12. Mars (Vol. 2)
13. Mars (Vol. 3)
14. Phobos & Deimos
15. Asteroids (Vol. 1)
16. Asteroids (Vol. 2)
17. Asteroids (Vol. 3)
18. Ceres
19. Jupiter (Vol. 1)
20. Jupiter (Vol. 2)
21. Io
22. Europa (Vol. 1)
23. Europa (Vol. 2)
24. Ganymede
25. Callisto
26. Saturn (Vol. 1)
27. Saturn (Vol. 2)
28. Saturn (Vol. 3)
29. Rings of Saturn
30. Mimas
31. Enceladus
32. Tethys
33. Dione
34. Rhea
35. Titan
36. Iapetus
37. Minor Moons of Saturn
38. Uranus
39. Miranda
40. Ariel
41. Umbriel
42. Titania
43. Oberon
44. Neptune
45. Triton
46. The Kuiper Belt & Scattered Disk
47. Comets
48. The Interstellar Neighborhood
Saturn, exactly as our eyes would see it if we were there close to equinox:
6. Magnetosphere
As described in Vol. 2, the convection of the metallic hydrogen layer of Saturn's interior creates the planet's magnetic field - the fourth most intense (if we include the Sun's), being about 5% as intense as Jupiter's and slightly less intense than that of Earth. However, the total effect of the field is 580 times greater than Earth's (as measured by magnetic moment), with the lower intensity due to the fact that metallic hydrogen is not nearly as efficient at generating magnetic fields as the liquid iron of Earth's outer core. This means that the intensity of a field doesn't scale nearly as rapidly with increasing volume of a hydrogen dynamo as an iron one, allowing a relatively small planet like Earth to get more magnetic bang for its buck. Comparison charts:
The size of the magnetosphere is also much smaller than that of Jupiter, extending only between a few dozen to several hundred Saturn radii outward from the planet, whereas Jupiter's reaches out almost to Saturn's orbit in the direction opposite the Sun. Although the intensity of the field is on the same order as that of Earth, Saturn's field is much larger in size, and is the third largest in the solar system after the Sun and Jupiter. Another distinguishing characteristic is that because Saturn is farther away from the Sun, the pressure of the solar wind is much less, so the shape of the field isn't stretched as much in the radial direction pointing away from the Sun (although it still does extend somewhat). A European Space Agency (ESA) illustration of the Saturnian magnetosphere (not to scale - the planet's relative size is exaggerated):
As with Earth and Jupiter, particles from the solar wind are directed to the polar regions of Saturn by its magnetic field and interact with the atmosphere to produce aurorae surrounding both poles. However, the aurorae don't occur in visible light, so they are detectable mainly in infrared (IR) and ultraviolet (UV) spectra. The Southern aurora in IR wavelengths:
The Northern aurora in IR, which seems to have a strong correspondence to the polar hexagon:
Southern aurora in UV:
Both aurorae seen obliquely in UV:
The Southern aurora in UV superimposed on visible spectra of the same image:
Just as an aside, to reiterate from Vol. 2, you can know which hemisphere of Saturn you're looking at in a true-color photo by the fact that the South has a reddish mid-latitude band and a muddy-colored polar region while the North has a greenish mid-latitude band and a blue polar region. So you could know without being told that the image immediately above is of the Southern hemisphere, and not just because it's "pointed down," which obviously has no meaning in an astronomical context. Since there are no prominent cues in the cloud formations like the Great Red Spot is for Jupiter, the coloration of the bands is the handiest way to know the orientation of a true-color image of Saturn.
A number of moons and rings interact electrically with the magnetic field, particularly Enceladus. A large amount of icy material constantly ejected by the geysers of Enceladus (upwards of 300-600 kg per second) is ionized by the field and swept up in its rotation, creating a plasma torus of charged particles much like those of the Galilean moons around Jupiter, although far thinner and less energetic. A diagram showing the relative positions of significant moons within the magnetic field and plasma regions:
Like we saw in our exploration of Io's plasma torus, charged particles around Saturn that have been accelerated above orbital velocity by the rotation of the field eventually recapture their electrons, become neutralized, cease to be bound by the field, and are sent rocketing off into space away from the planet. Because the material in the torus is being constantly replenished by Enceladus and other moons, there is also a constant stream of neutral atoms flying away from Saturn that are detectable. A direct image of both the neutral hydrogen cloud and the plasma tori, which vaguely outline the shape of the magnetosphere:
One thing to notice about the image above is that there are more particles in the direction pointing away from the Sun, which is because of the magnetotail - the extended portion of the field stretching out in the opposite direction from the Sun due to being dragged by the solar wind. Also, the plasma tori (the bright regions) seem brighter at certain points rather than being circularly uniform only because of the perspective of the image - i.e., you're looking through a thicker region of torus along the edges to either side rather than parts that are in front of or behind the planet. Illustration of this perspective:
[Update: I just realized something else about the particle image: The bright region on the left is bigger than the one on the right because the plasma torus is rotating counterclockwise along with the magnetic field, so when ions in the torus become neutralized and are freed from the field, the ones that shoot off from the left would tend to shoot toward the probe while those on the right would be more likely to shoot off in the opposite direction.]
Saturn has significant radiation belts due to its magnetic field, but they are far more benign than those of Jupiter for three reasons, in descending order of significance:
1. As stated, the magnetosphere is both much weaker and much smaller than Jupiter's, so it can't pull as many energetic particles out of the surrounding space into the radiation belts.
2. The water ice of its moons and ring material absorbs a lot of the radiation that does occur. This absorption breaks apart water molecules into hydrogen, oxygen, and various combinations thereof, and also ionizes (strips electrons from) the resulting atoms. These ions are what comprise the plasma torus, and the atoms are the neutral cloud.
3. Saturn is farther away from the Sun, so fewer solar wind particles reach it in a given period of time.
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IV. Summary of Rings and Satellites
We will be exploring the rings and moons of Saturn in depth in subsequent entries, so this will just be a quick informational overview.
The rings of Saturn are a finely-detailed system of small orbiting debris overwhelmingly consisting of water ice flakes - a kind of "orbital snow" - as well as larger chunks of ice up to several meters in diameter. This system is about 62,280 km wide from the innermost to outermost regions of the main rings, with an outer circumference of roughly 880,000 km, and yet the ring plane is on average only a few hundred meters thick - which is why probes like the Cassini spacecraft can occasionally pass through it on inclined orbits without incident. The "surface" area of the ring plane is so vast it would cover the entire Earth more than 70 times over.
Details of the ring system are so fine that even images that show exactly what the human eye would see are often hard to distinguish from computer-generated mathematical abstractions:
Ring systems in general result from material orbiting within a body's Roche Limit - the boundary at which tidal forces would tend to rip an object apart and form rings by stretching its material all around its orbit. This occurs because objects in lower orbits move faster than those in higher orbits, so solid objects always experience a level of shear tension between the side facing a massive body and the opposite side: The near side always wants to move ahead of the far side, but outside of the Roche Limit, the gravity of the object itself will hold it together. However, there is currently no compelling reason to suspect that Saturn's rings formed from a single object being torn apart: Rather, material from the early formation of the planet may simply never have had a chance to coalesce in the first place.
A number of gaps in the ring system occur due to orbital resonances among the moons that tend to throw material out of the rings if they migrate into these regions. Also, some gaps are caused by the presence of small satellites called shepherd moons that suck up whatever material enters these regions and gravitationally stabilize adjacent rings. A few images of shepherd moons amid the rings:
Saturn has 62 known moons, but only about a dozen or so are significant in size - and of that dozen, only seven are massive enough to be spheroidal: Mimas, Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus. We will explore each of those individually in later entries. The remainder are irregularly-shaped asteroidal or comet-like objects that we will explore collectively under the heading "Minor Moons of Saturn."
Titan is by far the most important and exotic object in the Saturn system, as it not only has an atmosphere, but a thick one with surface pressure 45% greater than Earth sea level. This has made possible the other remarkable Titanian feature - the presence of liquid hydrocarbon lakes in the polar regions. Its environment is a windy, soupy, frigid hell whose atmosphere is analogous to ultra-refrigerated gasoline fumes, but the sheer complexity of the organic chemistry that has been observed - not to mention the presence of standing liquids - has raised eyebrows among scientists who study the possibility of extraterrestrial life. Since it's so cold that water is essentially a form of rock, life-as-we-know-it (LAWKI) is not possible on Titan, but chemists have speculated on ammonia-based chemistries that might give rise to exotic forms of life - though even then it would very likely be limited to simple organisms given the lack of environmental energy.
Iapetus is famous mainly for a huge equatorial ridge that makes the moon look like a walnut from certain perspectives. Tethys, Dione, and Rhea are relatively undistinguished snowballs with very similar features to each other but also some modest differences that will be explored in their individual entries. Enceladus is also a snowball, but despite being much smaller than the previous three, it is highly geologically active with constant geyser activity and cryovolcanism spewing water-ice into Saturn orbit. There is some speculation that very basic LAWKI might be possible within Enceladus due to this activity. Mimas, which is an even smaller snowball, is known as the "Death Star moon" because one face is dominated by a huge mid-latitude crater that makes it look like the Imperial battle stations from A New Hope and Return of the Jedi. A quick family photo album of the moons with worthwhile images, in order of ascending orbit:
Pan:
Atlas:
Prometheus:
Pandora:
Epimetheus:
Janus:
Mimas:
Methone (Mee-THO-nee):
Enceladus (En-sell-AH-Dus):
Tethys (TEE-this):
Telesto:
Calypso:
Dione (DIE-oh-nee / die-OH-nee)
Helene (Heh-LEE-nee):
Rhea:
Titan:
Hyperion:
Iapetus (EYE-app-eh-tus):
Phoebe (FEE-BEE):
The moons of Saturn are by far the most motley crew in the solar system, and will no doubt provide centuries of scientific fascination, epic adventure, and commercial opportunity to whatever generations of humans end up finally having the chance to meet them face to face.
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V. Past Relevance to Humanity
Saturn is named for the Roman version of the Greek primordial titan Κρόνος (Kronos), whose name entered English as the etymological root chron, signifying time - an apt association for the planet, given how eerily ancient the system is while still being highly dynamic. In fact, the word "Saturn" has its own oddly appropriate connotations via the word saturnine: An adjective describing a cold and gloomy demeanor. The word existed long before anyone knew anything about the planet Saturn other than its apparent movements in Earth's sky, and yet we find that Saturn is indeed a very saturnine planet.
Kronos/Saturn in Hellenic mythology was the titan who embodied Time, and was a child of Uranus (the Cosmos) and Gaia (the Earth). After overthrowing his father as ruler of the universe, Saturn reigned over a Golden Age of natural perfection - the Greco-Roman version of Eden, which gave rise to the Roman holiday of Saturnalia where people would ceremonially mimic how they imagined the hedonism and egalitarianism of this lost age. Aspects of Saturnalia persist today in Christmas and New Year's celebrations.
Another, darker aspect of the Saturn story is that he repeatedly devoured his own children to avoid being usurped by them, which bears some poetic symmetry with the early formation and destruction of gas giant satellites - and, of course, the "moon apocalypse" theory of Saturn ring formation is still at least considered a possibility despite being out of favor. Ironically, the legend had it that the Golden Age of Saturn ended when he himself was overthrown by his own son, Zeus - aka, Jupiter. Had the ancients known the facts about the planets they had named for the titan of Time and the king of Olympus, they would probably have believed the stories all the more, albeit with some creative editing. It's hard not to appreciate the mythic narratives suggested by these monstrous worlds of the outer solar system, larger than all that human beings have ever known or been throughout all of history combined.
But, of course, the ancients had no notion that Saturn or any other planet was a world: They were "stars" distinguished from the others purely by their motion and relative brightness, and were designated as the omen-bearers of the gods they were named for, not identified as the gods themselves. So Saturn's position in the sky and relation to the other "omen stars" indicated the mood and disposition of the god, but like the other planets was rarely if ever speculated as being physically anything more than a beacon of light fixed on to an invisible sphere rotating around the motionless Earth.
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VI. Modern Relevance to Humanity
Humanity's view of Saturn took the first step into the modern world when Galileo made the fortunately blasphemous decision to look at astronomical objects with a telescope - up to that point a tool only used as an aid for maritime navigation and warfare. What he saw were not stars or bronze beacons from Vulcan's forge, but disks - some of them with little points of light clearly orbiting them, indicating that the disks themselves were in fact globes. In the case of Saturn, his findings were more of a head-scratcher than a revelation, because the planet seemed to have big, floppy love handles on either side. His actual sketches:
Having never seen, heard of, or imagined anything like a planetary ring system before, Galileo had no frame of reference in which to make an accurate guess. His best hypothesis, which made perfect sense within the available base of knowledge, was that the "love handles" were two completely separate bodies from Saturn and that it was in fact a triple planet whose constituents were stationary relative to each other. Note that this was long before the formulation of Newton's laws of motion, so Galileo had no objective reason to think this wasn't possible: If he could look through a telescope and see things that millennia of philosophy had never even imagined, then why not three nearby planets that are fixed relative to each other? He described his observations in these terms:
The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the zodiac, and the middle one (Saturn itself) is about three times the size of the lateral ones.
With prolonged observations, it confused Galileo no end that the two sidekick planets he hypothesized seemed to periodically flatten into nothingness - when the ring-plane was seen edge-on from Earth's perspective - and then reinflate again when Earth's perspective saw the plane at an increasing angle. He was never able to come up with a sufficient explanation for these anomalies, but he had already changed the world simply by observing them.
It wasn't until half a century later, in 1655, that Christiaan Huygens turned a powerful enough telescope on Saturn to realize that the two lobes were in fact a ring surrounding the planet. However, he, like Galileo, lacked the physical foundation to rigorously hypothesize about the nature of this ring, and thought it was a single, solid object: An idea that could have been instantly ruled out had Newtonian physics existed at the time. Huygens wrote a book on the planet, Systema Saturnium (1659), with a number of other important contributions such as the discovery of Titan, the ring plane's angle of inclination, and the phases of the ring:
A contemporary of Huygens, Giovanni Cassini, discovered Iapetus, Rhea, Tethys, and Dione a few years later, and was actually able to (correctly) surmise that the surface of Iapetus was divided between a bright and a dark region. He was also the first astronomer to observe gaps in the ring in 1675, giving the first clear evidence that it was not a solid object - the largest gap, which is 4,800 km wide, is now known as the Cassini Division in his honor.
Further progress was made over a century later when Pierre-Simon Laplace applied state-of-the-art math and physics to argue that rather than being one or a few thick, solid rings, the ring system was actually countless solid rings that were each very thin. One of the failures of imagination of the early observers was that they were in love with the abstract perfection of Saturn: As many of us can remember from childhood perceptions of astronomy, the idea of a planet with solid rings just hanging there or rotating in perfect balance is mesmerizingly beautiful and mystical, and not something that formal idealists would want to abandon in favor of more dismal, materialistic explanations.
The granular, messy reality of a bunch of powder and rubble had to wait for a more reductionist era - specifically, the passage of yet another century, and James Clerk Maxwell. He argued in 1859 that any solid ring structure would be rapidly destabilized and torn apart by tidal forces, and was proven correct four decades later. This was when humanity learned that the rings had more in common with the driven snow than with some cosmic geometric Form: Saturn took a few steps down from heaven, and we took a few steps up toward it.
Evolution in our understanding of Saturn went pretty slowly for the next several decades, with incremental observations teasing out new details about the planet and its moons - e.g., that Titan has an atmosphere, which was discovered in 1944. What was known wasn't exactly common knowledge either: Outside of scientific circles, people had no notion whatsoever of what a gas giant was other than "big with a thick atmosphere." And although scientists could deduce what must be beneath the clouds of a planet like Saturn based on the broad properties of these planets like volume and mass - i.e., it must be a whole lot of hydrogen and not much else - the amount of hard data with which to test specific theories barely budged until the Space Race. Then, an explosion of revelations from robotic probes.
Pioneer 11 was the first spacecraft to visit Saturn, flying by in 1979 and giving mankind its first up-close images of a world of wonders:
Pioneer 11 also discovered several new moons, including one - Epimetheus - that it discovered just in time to barely avoid crashing into it. The next year Voyager 1 radically expanded humanity's knowledge of Saturn and its moons with shockingly beautiful, breathtaking, alien images, and then Voyager 2 built on that achievement even further the year after that. Humanity went in the span of three years from the same fuzzy, ground-based images we'd been looking at for centuries, to this...
So what more might be possible if we dared now like we dared then? The Cassini-Huygens mission has contributed virtually all of the images used in the three volumes of this Saturn exploration, and has orbited Saturn for nearly a decade collecting images worthy of actual gods and science that will some day make those worlds a part of the human landscape. But Cassini will eventually end, as it's slated to do in 2017 with a controlled descent into Saturn, and nothing - nothing - is currently planned to replace it, let alone go even farther in the exploration of this limitless wonderland.
In any case, Saturn has played a major role in science fiction due to its awesome visuals and wide diversity of exotic locations, particularly in literature. Works written before the scientific understanding of gas giant planets often set events "on" Saturn itself, but since then depictions have revolved around its moons and rings, or else in dirigible "cloud cities" floating around in the atmosphere. One of the most prominent examples is Arthur C. Clarke's 2001: A Space Odyssey which, unlike its film adaptation, sets the stargate monolith on Iapetus rather than Europa - and incorrectly predicted that Iapetus would have a totally smooth, featureless, and artificial surface. Another would be Accelerando by Charles Stross, where humans fleeing from an inner solar system now dominated by an incomprehensible post-Singularity AI ecosystem have colonized the Saturnine clouds.
However, credible TV and film science fiction often avoids setting events in the Saturn system because it's so visually exotic that it's difficult to get the look right without being vague, or else like some New Age calendar art if the the details are given too much attention to the detriment of the whole. Usually if a TV show or movie involves a Saturn setting, the images of the planet are kept very brief, and even then they tend to be generic depictions rather than trying to replicate the full impact of reality. Saturn is generally shown as a dull beige planet without much structure rather than having the multi-colored bands and intricate, swirling cloud formations that we've seen from the Cassini probe. Here is Saturn in the 2009 Star Trek movie:
Doesn't look much like the real Saturn, does it? At best it looks like the Pioneer 11 images that haven't been current in thirty years, and seems more like Venus with some rings thrown around it. Not that anyone will ever mistake the J.J. Abrams version of Star Trek for science fiction, but it is an example of a general pattern in the genre of poorly representing Saturn - a fact for which there's no longer any excuse given all the hyper-clear probe images and the ubiquity of graphics tools capable of replicating them to a reasonable degree. In fact, it seems like it would be cheaper to just literally use the probe images themselves as backgrounds, so I honestly don't understand why studios would rather pay CGI companies a bunch of money to make generic scenes like the above.
Despite these quibbles, Saturn today remains the most exciting location in robotic space exploration due to the ongoing, ultra-high-quality output of Cassini and the tremendous diversity of worlds and features to explore. The Saturn system all by itself would justify its own dedicated space program with dozens of simultaneous missions, and would be unlikely to run out of scientific excitement for the remainder of the 21st century. Given what I'm hearing from Planetary Resources - a billionaire-backed venture seeking to (among other things) develop a cheap, generalized space probe that can be deployed en masse to any given target - we may actually see this happen in the next few decades. So while the collapse of political support for large, expensive space science missions is worrisome, there are credible hopes of something even better than what went before on the horizon.
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VII. Future Relevance to Humanity
Saturn is by far the most promising location in the solar system: If humanity manages to expand beyond Earth, I have no hesitation about saying that Saturn would ultimately become the center of solar system civilization, and likely its richest and most populous location. If I were writing a future history of humanity in the solar system, Saturn would be where its Classical Age unfolds, and the foundation from which future expansions into the whole rest of the solar system and other star systems begins. Here are my reasons:
1. While the moons of Jupiter are also abundant in water ice, those of Saturn are the closest to Earth where organic hydrocarbon ices occur in abundance - and also very likely the richest concentration of these resources in the solar system.
2. Gravitationally easier to enter and leave the Saturn system than the Jovian system, and yet much closer to Earth and its earlier colonies than Uranus and Neptune, so trade would be faster and cheaper.
3. The radiation belts around Saturn are far weaker than those of Jupiter, so it's not much of a problem for exploration or colonization of the Saturn system.
4. Most of the moons of interest are within the planet's magnetosphere, so they enjoy a level of protection from solar and cosmic particles that more immediate goals like Mars and the Moon don't have, so colonization might actually get somewhat easier once we progress into the outer solar system than it will have been closer to home.
5. Once you figure out how to flourish there, the rest of the solar system beyond it is pretty much a snap, so it's very easy to imagine that Saturnine civilization would be the origin of further waves of human expansion that are much more capable and rapid than those that went before.
6. Vast concentrations of deuterium and helium-3 for potential fusion energy applications, as well as observed antimatter concentrations substantially greater than those near Earth. In other words, if we develop the technology to utilize these resources, there they are - right where they would be most useful.
7. Unspeakably beautiful and spiritually mesmerizing.
That answers the question of "Why explore Saturn?" Because eventually we want to live in the vicinity. However, the question of how to explore it rigorously - i.e., with human missions - is less obvious, and fleshes out the challenges that make it both difficult and tantalizing. Humans could explore the Saturn system with evolved versions of existing technology (specifically, nuclear fission), but it would be at mind-boggling cost of money and time to mount such expeditions unless they were being launched from existing colonies around Jupiter or the asteroid belt, so that puts a constraint on the timeline for when such exploration can happen practically. Either it has to occur as an initiative by descendents of people who already colonized some other part of the solar system, or we need major progress in both propulsion and energy to get people there and back in a reasonable amount of time. So that's probably outside the 21st century horizon.
But we know what technologies will put it within the horizon, and Saturn has the benefit of being both the nearest and most potentially rewarding frontier that would benefit from those advances: Fusion power, and either thermonuclear, nuclear electric, or antimatter propulsion. Fusion power is a necessity (at least of colonization) because energy is the only scarce resource in the Saturn system that isn't also scarce on Earth, and we need these new propulsion technologies to travel there on psychologically and materially practical timescales rather than the 7 years Cassini spent in transit.
Antimatter propulsion, for instance, has been found - at least on paper - to make a 4-month trip duration to Jupiter possible, which would correspond to less than a year to Saturn, and allow for the kind of shipboard lifestyle that would make the trip far more tolerable. Based on current developments, it seems reasonable that this would be possible by the end of the 21st century, and that practicality would be within reach a few decades later. However, that's mostly for the purposes of exploration - I don't expect that human colonization of the Saturn system would become industrially practical for several centuries, and would probably have to await intermediate steps like colonization of Mars, development of the asteroid belt, and colonization of Jovian moons.
When manned exploration does occur, conditions exist that would allow humans to directly explore the clouds of Saturn: Specifically, the range of temperatures and pressures in the cloud layer (as explored in Vol. 2) is relatively benign, with pressures of about 10 Earth atmospheres at temperatures just above freezing. This is the same pressure as being about 300 feet underwater, which unaided human divers have gone deeper than, and any submarine made today can handle. Of course, sub-freezing temperatures at lower multiples of Earth atmospheric pressure would also be an option.
Furthermore, unlike Venus, which also has the potential for atmospheric exploration, the clouds of Saturn aren't full of sulfuric acid, so that's one less environmental hazard. Also, the gravity one would experience in a floating balloon station "on" Saturn would only be 1.065 g: A barely noticeable increase from Earth, unlikely to have any negative health effects. This is very different from the clouds of Jupiter, where one would be experiencing 2.5 g. The 6.5% gravity increase would be a challenge for rocket transport to and from Saturn orbit, but I doubt a prohibitive one for a set of technologies that had gotten there in the first place. Additionally, thermonuclear propulsion like Project Orion wouldn't have any of the environmental objections that make it untenable for Earth liftoff, so transport between the cloud layer and orbit probably wouldn't be a big deal.
Ultimately there's no reason you couldn't have cloud cities and directly colonize Saturn itself. In fact, if we suppose fusion technology, it would actually be the most obvious location since it's where the raw materials for fusion are - the deuterium and helium-3 are right there in the atmosphere of the planet, so why not live right where the fuel is if it's not too inconvenient? An additional fact arguing for colonizing Saturn directly rather than exclusively on its moons is that the moons have very paltry gravity (the highest, Titan's, is only 14% of g), and colonists on them might have to deal with resulting health problems. So in terms of gravity, the clouds of Saturn would actually be the second healthiest natural environment to colonize in the entire solar system after Earth. It also has very low radiation and a trivial meteoroid impact threat, making it safer on those terms than Mars, the Moon, asteroids, space stations, Europa, Ganymede, or Callisto.
The more I think about it, the more the clouds of Saturn begin to seem like a smorgasbord of good things. Titan, by comparison, would likely be a lot messier and more dangerous: The surface is composed entirely of ice peppered with volatile organic compounds, and it would seem very challenging to create a safe, efficient way to dispose of waste heat that doesn't turn the surrounding environment into a sludge lake with potentially problematic chemical reactions occurring. But even before you addressed that issue, you would need to figure out how not to dispose of it - i.e., how to sustainably keep a habitat from having its energy rapidly sucked out of it by cryogenically cold winds in a thick atmosphere. Titan may actually prove more useful as a source of organic compounds than a location for settlement.
Some day, perhaps in the third or fourth quarter of this millennium, an unimaginably rich, populous, and advanced civilization living in vast cloud cities could look up at the faint blue star that is Earth and wonder how such a speck of rock boiling beneath the Sun in the inner solar system could have given rise to this species. But more than that, Saturn is where humanity learns how to directly colonize and utilize the resources of gas giants, since Jupiter won't be directly accessible to those who colonize its moons before Saturn is. This would represent an evolutionary leap forward in the general survival potential of the species, and put us on a path whereby in the utmost distant future, at the very limit of imagination, we are colonizing the outer shells of stars or even more exotic objects in some vast, interstellar sprawl of bizarre "post-human" civilizations. By learning how to live in the shadows of gods, we may put ourselves on a path to becoming them.
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VIII. Future of Saturn
Due to the fact that Saturn emits more than double the heat it receives from the Sun, it will continue to cool and contract over the course of its future natural evolution - excluding any sort of artificial interference, whether deliberate or a side-effect of human activity. As this happens, the proportion of helium in the upper atmosphere will continue to decline as it precipitates into lower layers of the planet, and the winds of the cloud layer will both increase in speed and become smoother and less turbulent. As a result, the cloud bands would become much thinner and more numerous, but also much less visually distinct since turbulence is the reason we see heterogeneous cloud formations at all.
Most of the planet would come to resemble the bland, yellowish equatorial zone, although there would probably still be plenty of discernable structure in the polar region - and we have no idea how permanent something like the polar hexagon would be over millions or billions of years. One contributing factor to the "blandification" of Saturn could be the expansion of the Sun exposing its upper atmosphere to more solar radiation, which we can suppose would turn more of the ammonia ice clouds into obscuring haze without much in the way of structure. Unfortunately, it also means that a lot of the ice around Saturn - e.g., its rings - would sublimate (go directly from solid to gas, as happens to water ice in vacuum above certain temperatures) and disappear into space. But that is far in the future, so nothing that we would recognize as a human being will ever look upon Saturn without its rings.
I would assume that because of conservation of angular momentum, the contraction of the planet would probably cause it to rotate more rapidly and make its shape even more oblate than it already is. Meanwhile, the end-stage expansion of the Sun would blow off quite a lot of its atmosphere, leaving behind a smaller planet that would migrate farther out into the solar system as the Sun loses mass, maybe becoming something like a more massive version of Neptune. As discoveries of exoplanets mount, we're learning how little we truly know about the diversity of possible planetary configurations, so just as Earth is radically different from what it had been in the distant past and will be in the future, Saturn may evolve into a planet we wouldn't even recognize based on what it is today.
However, one thing that is worth noting, and which at least one science fiction author I've read - Stephen Baxter - has explored, there will be an extended period of time when the Sun is large enough for Titan to become a warm, potentially habitable place. If not an abode for the Earth life that would have been swarming around the solar system for eons, then maybe this period could give rise to a native Titanian biosphere out of the vast abundance of organic compounds on its surface and in its atmosphere. Unfortunately, this period of would be relatively short-lived compared to the ones enjoyed by terrestrial life, so unless evolution occurred at an accelerated pace, such life would be eliminated by later solar developments before having a chance to become complex or even, far less likely, intelligent: A mere epilogue to the story of life in the solar system.
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IX. Catalog of Exploration
1. Past & current probes:
Pioneer 11 (USA - 1979 flyby)
Voyager 1 (USA - 1980 flyby)
Voyager 2 (USA - 1981 flyby)
Cassini-Huygens (USA and Europe - entered Saturn orbit 2004, currently operating)
2. Future probes:
(none planned)
