But the glory of the rings continually drew Bowman's eye away from the planet; in their complexity of detail, and delicacy of shading, they were a universe in themselves. In addition to the great main gap between the inner and outer rings, there were at least fifty other subdivisions or boundaries, where there were distinct changes in the brightness of the planet's gigantic halo. It was as if Saturn was surrounded by scores of concentric hoops, all touching each other, all so flat that they might have been cut from the thinnest possible paper. The system of the rings looked like some delicate work of art, or a fragile toy to be admired but never touched ....

Sometimes a star would drift behind the rings, losing only a little of its brilliancy as it did so. It would continue to shine through their translucent material -- though often it would twinkle slightly as some larger fragment of orbiting debris eclipsed it.

• 

If you’re anything like me, you might have enhanced your friends’ enjoyment of space adventure films by pointing out at great length and in fascinating detail just why the crowded asteroid belts backgrounds that appear in so many of these films are implausible and inaccurate! Our solar system asteroids are far from crowded. If you were to find yourself on the surface of a typical asteroid, you probably wouldn’t be able to see your closest rocky neighbour with a naked eye.¹

Are there situations in which these visuals wouldn’t be misleading? Can we imagine places where we could expect what appears to be an impending Kessler Syndrome on a solar scale?

At first glance Jupiter’s trojan asteroids look like they might do. For reasons gravitational, Jupiter has collected two impressive sets of asteroids in its L4 (leading) and L5 (trailing) Lagrangian points. Between them, the two populations of asteroids (one named—mostly—for Trojans, and the other named—mostly—for Greeks [even-handed treatment of both sides of the Trojan War]) may number almost half a million 2 km+ diameter asteroids, over a million 1 km+ objects, and a larger number of smaller bodies. A cloud in a limited area with millions of bodies in it sounds very promising indeed!

Unfortunately, the term “point” is somewhat misleading. The L4 and L5 communities are spread out about 2.5 AU along the orbit of Jupiter. A quick back of the envelope calculation² suggests that the separation between the 1 km rocks could be comparable to the Earth-Moon distance. This is excellent news for people hoping to found vast clouds of space habitats (not only are the rocks comparatively close but also the delta vee to get from one to another is low³) but less than excellent news for fans of crowded asteroid belts. A sky full of 1 km rocks separated by hundreds of thousands of kilometers is not the jam-packed vista beloved by skiffy fans.

(Obviously, for each 1 km object there are a number of smaller bodies but the decrease in average separation won’t result in angular width discernible to the human eye.⁴)

Somewhat farther from our sun, Saturn’s rings seem offer the very thing we want. The rings are composed of a very large number of bodies, most of them somewhere between marble and shed-sized (in total, massing about the same as a small moon). The close proximity of Saturn prevents them from aggregating into a single body; basic orbital mechanics constrains them to a surprisingly thin (10–10,000 metres) plane. If you were within the rings, your field of vision would be jam-packed with small bodies of appreciable angular diameter.

Unfortunately, their apparent size would be due to close proximity, so it’s probably a good thing most of the ring particles in a given region likely have more or less the same orbit. If that weren’t the case, the experience might be akin to having swimming pools full of gravel fired at you at supersonic speeds. As it is, maybe it’s more like being in a cement mixer filled with dice.

Moving above or below the ring plane will deny you the immediate effect of being surrounded by a myriad of objects, but replace it with a no doubt stunning vista of the rings seen from just above or just before, for as long as it takes your ring crossing orbit to pass through the rings. Bring armour or hope for low relative velocities while you traverse the rings on an orbit whose parameters are definitely different from ring particles.⁵

Another option is to find a very young stellar system, still rich in planetesimals, where giant worlds have not either absorbed them or thrown them out of the system. Not only would such a system have a more chaotic and more populous collection of small bodies, but proto-stars and very young stars offer all manner of potentially exciting behaviours not seen in boring, middle-aged suns like our own.

(This would seem to require a time machine or really good space ships. But perhaps all we need is patience enough to wait until the next time the solar system passes through a stellar nursery. A few million or billion years … no prob.)

Perhaps the easiest solution is to posit successful space industrialization combined with a lack of environmental regulation. Earth seems likely to be the main market for goods for the foreseeable future. Therefore, why not transport megatons of semi-processed raw materials to the Earth-Moon system for use in facilities in proximity to Earth? And wouldn’t compelling companies to take whatever steps are needed to prevent increasingly dense clouds of debris in said system be an onerous burden on hard-working business folk? With just a little effort, and a lot of short-sightedness, perhaps we could have entertainingly crowded skies in our own back yard. (And eventually a Kessler syndrome that would provide a one-time spectacular light show for those of us fortunate to live on the planet surface.)

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1: Assuming one’s space helmet neither assisted nor impeded vision. Obviously, if one simply doffed the helmet, the optical properties of the face plate would no longer be an issue, although painful death by vacuum that would immediately follow could be very distracting.

2: Carried out for me by a friend because, for reasons related to my CPAP machine, my brain is befogged. This is why an early draft of this essay had three footnote 1s.

3: The delta vee to send material to and from Earth isn’t horrible if you’re willing to invest the years to send the packages via Jupiter. The nice thing about using Jupiter as a central shipping point is that the scale of the system is such nobody is going to get a large spaceship jammed in a crucial shipping lane.

4: Why not simply replace the human eye with something with more resolving power? This sounds reasonable but it turns out that while removing eyes is one ice-cream scoop away, actually replacing them with something functional, let alone superior (whatever parameters you are using for superior) is a bit tricky.

5: Traditionally, people exploiting the rings do so for the abundant water. Alas, the same proximity to Saturn that keeps the rings from collapsing into a moon mean the delta vee cost of retrieving material from the main rings is not insignificant. Water is abundant in the outer solar system and there are places from which one can retrieve it at lower cost. A suggestion I ran across more than a decade ago is that a very small fraction of stranglets (https://en.wikipedia.org/wiki/Strangelet) passing through Saturn could be braked just enough for ring material to finish the job. Stranglets could have many interesting applications, and probably could not be used to destroy the world. (Note: it would be scientifically timid not to test that last assertion.)

The common objection to colonization of the Jupiter system is the intense radiation belt, especially the plasma torus around Io.

But whereas most people see this as a fatal flaw, I see it as a source of POWER ("POWER", to rhyme with "If you only knew the POWER of the Dark Side...").

As I see it, radiation is pretty much a fact of life in extra-terrestrial colonization. The only places where there isn't a lot of long term radiation exposure is inside the depths of a thick atmosphere, and generally those atmospheres are far less pleasant than just dealing with building a thick layer of radiation shielding.

Venus? Forget about it!

Floating inside a sulfiric acid gas giant atmosphere over an abyss of certain death? No thanks!

Titan? About as good as it gets outside Earth, as long as you don't mind the extreme cold and all the cyanide.

Engineering a colony to deal with being immersed in a cold atmosphere is more difficult than engineering one to deal with being immersed in a vacuum.

So wherever you set up your colonies, those colonies are going to need thick radiation shielding. Once you've commited yourself to that idea, then life inside Jupiter's radiation belts is no longer such a big deal.

On the other hand, Jupiter's intense plasma torus provides gobs and gobs of cheap electrical power. Unlike most people, I don't assume a fusion economy so the potential reserves of Helium-3 in the gas giants is of marginal interest to me. The availability of immense amounts of cheap power around Jupiter is what attracts me.

Saturn, in terms of travel times (if not Delta V) is far enough out there that it may never get utilized, unless something (akin to He3) is found that's worth the expense to ship it back.

This is based on the flawed idea that there needs to be something to ship back. I see Jupiter and the other gas giants as places worth expanding to for expansion's own sake. If there's money to be made back home, its made by offering all of the transport and equipment for the colonists at a price. The colonists earn their wages back home and save up in hopes of moving to a new place for a better life (if not necessarily for themselves, then for their children).

There's no particular need for ANYTHING to be worth exporting back home.

In both cases (Jupiter and Saturn), using solar power for anything at all is dubious - yes, you can do tether electrical currents around Io and beam power...

Yes, indeed. The thing about solar power is that it's pretty expensive, and really pretty restricted to the inner solar system where you've got a limited number of planetoids to exploit. Mercury has a lot of power, but not a lot of raw resources to exploit. The entire asteroid belt has less mass than our own Moon and its inconveniently spread out thinly. Our Moon is big enough that its gravity well is a bother, and it doesn't really have a good mix of resources.

The gas giant systems have lots of cheap tether power, as well as lots of nearby planetoids with easy gravity wells to exploit. The mix of resources is very good.

But in order to work there, you're going to need shielding capable of near constant immersion in Jupiter's Van Allen Belts, which are pretty intense.

While the level of radiation is intense, the actual thickness of shielding required isn't going to substantively differ from what's required for any other space colony.

What I somewhat doubt is that you'll get human populations large enough to form independant governments without shirtsleeve environments.

I disagree. Once you start building space colonies, there's no particular reason to stop.

Certainly, one can make the argument that long before Mars is colonized, Antarctica will have been carved up by the real estate developers, as it costs less energy and time to get there, and has a much more hospitable climate (on top of breathable air, and ready access to water!)

Antarctica is a less hospitable climate than Mars, and much less hospitable than an orbital colony. The huge enduring problem with living in Antarctica is the pervasive cold. It's hard to keep warm, when the thick atmosphere is constantly robbing you of heat. The fact that you spend six months at a time in the darkness of night doesn't exactly help either.

A Martian colony has to deal with a much thinner atmosphere and consequently much less thermal insulation is required. An orbital colony doesn't even have to deal with that.

Cultures that are much more communal in nature than Western norms may work best out there.

I think that simply cramming people together in densely populated cities has a natural tendency to give rise to more communal mindsets. Whether it's Liberal or Socialist or Communist or whatever...it ain't gonna be no Libertarian lassez faire-yland.

When you have a thousand neighbors and it seems like every little thing they do affects you and vice versa, the notion that anyone can do anything they please isn't going to have much traction. You don't need space colonies to see that effect in action.

This, of course, leads to all kinds of story fodder when the city-states of the solar system have their regime changes and the New Glorious Dictator has a different interpretation of foreign policy than the Newly Revealed Apostate...

...and this differs from Western norms in exactly what way?