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    Deep within the human soul lurks a pattern to which we respond, much as we respond to human faces, with recognition. We can't grasp it: it eludes our every effort to pin it down for study. Nonetheless, it has a name. We call it Eden. And it will have a very special meaning for us as we become a space-faring civilization: However far we may wander, whithersoever we may roam, we will never forget in the deepest part of our souls that the green hills of Earth will always mean home.

    But moving into the bleaklands of space will necessitate growth. As civilization goes interplanetary Humanity will need more people to carry out tasks that we cannot yet imagine. What will futurefolk do when Humanity has grown so numerous that few can reasonably visit Earth, much less live on it? Unless they become something other than human, they shall simply have to clone Eden.

    Huge fliederstädte and O'Neill-style annulurbs floating on orbits about Earth and then on heliocentric orbits as Humanity spreads outward will provide living and working space for vast numbers of people. Imagine a New York City with five-hundred boroughs instead of five: the Fliederstadt of High New York will provide a stage upon which a billion people can act out the human drama, but it will not have sufficient extent to offer them more than small patches of natural landscape. We won't find our Eden in the gigantopolitan society of interplanetary space, though in the construction of the cities the builders will develop and refine the construction techniques that they will need later.

    Terraforming Venus comes readily to mind as one possible project to create more of Eden. But that effort will yield little more land area than we already have. And it obliges the terraformers to spin up a planet almost as large as Earth, presumably by making the comets bringing water for the planet's new oceans strike the planet obliquely, converting linear momentum into angular momentum. Certainly they will do it, but our descendants will rightly regard it as a sideshow.

    No, future Humanity's master builders will have to do more. They will have to create a new Eden on or in an artificial world the size of a gas giant. Indeed, they may even use a gas giant as part of that artificial world's structure. Jupiter seems an obvious choice to play that role.

    Cast your imagination uptime into the vast, dense tangle of possible futures and find one in which our descendants have undertaken this particular exercise in civil engineering. Imagine riding a ship that has slid along a Hohmann trajectory from Earth and has crossed Jupiter's orbit some distance apprograde the planet. As the planet overtakes and passes your ship, high above Jupiter's starward side the ship performs its delta-vee dance to put herself into Jovicentric orbit. Gazing at the backlit planet, you see titanic flashes of lightning rip and rend the dark and briefly illuminate the clouds that shroud the planet. You also notice a band, extending beyond the planet's limbs, on which band thin, delicate webs of light glow steadily and bespeak the presence of civilization. As your ship comes around to Jupiter's sunward side that band, under the sun's light, appears as a world built on a great ring, very much like Larry Niven's Ringworld. Spanning the area of fifteen Earths, that ring rotates once every twenty-four hours, to give its inhabitants a normal day-night cycle, and a person standing on that ring's outer surface feels normal Earth gravity directed toward Jupiter. How did such a thing come to exist? How did the Builders put it together and how do they keep it from collapsing into Jupiter? Start with the simplest question: On what radius did the Builders construct the ring?

    On the ring the acceleration due to Jupiter's gravity must exceed by 9.8 meters per second per second the centripetal acceleration that the ring's components need to move in a circle around Jupiter once every twenty-four hours. Converting that statement into its algebraic equivalent produces a depressed cubic equation whose solution tells us that the ring must have a radius of 110,438 kilometers, which puts it 39,068 kilometers above the clouds at Jupiter's equator. From that datum other facts about the ring follow, such as its circumference (693,900 kilometers) and the speed of its rotation about the planet (8.029 kilometers per second). With a width of 11,000 kilometers, the ring will have over fifty-one times the area of all the land on Earth, fifteen times the entire area of Earth, enough to give each of 7.65 billion people one square kilometer (246 acres).

    At a distance of 110,438 kilometers from Jovicenter a body must move at 33.86 kilometers per second to remain on circular orbit. The ring will fall short of that speed by 25.83 km/sec. So what holds the ring up, keeps it from simply collapsing into Jupiter? No material known or anticipated has the strength for the job. Here the Builders will stop thinking only of matter as construction material and add momentum and energy as structural components. Taking a cue from Greek mythology, they will use Atlases to hold up their artificial world.

    Pondering the mass of a freight train, each Atlas will move around Jupiter faster than 33.86 kilometers per second. Clad in superconducting material, it will press spaceward against the magnetic field of its track (via the Meissner effect) and thereby draw on the ring's weight to augment the planetward pull of Jupiter's gravity to hold it on a circular orbit. Myriads of these slugs, riding on an array of orbital planes that spread them uniformly across the underside of the ring, form a vast black, swirling river whose centrifugal reaction against the ring's weight holds the ring up.

    Using a fluid structure to support the ring will give the Builders a special advantage -- stability. As Larry Niven noted in his Ringworld stories, a solid ring will not stay centered on a gravitating body. Any perturbation that shifts the ring slightly off orbit makes the gravitational force acting on the ring grow stronger on one side of the planet and weaker on the other, thereby initiating a positive feedback process that ends in the ring collapsing into the planet. The river of Atlases flowing under TerraJove protects this particular ringworld from meeting such a fate. Because each Atlas moves more or less independently of the others, it can speed up or slow down as needed to adjust the force that it exerts upon the ring. If TerraJove moves off orbit, the Atlases that move closer to the planet will speed up in accordance with Kepler's second law while the Atlases on the opposite side of the planet slow down. The consequent changes in the centrifugal forces establish a restoring force in a negative feedback process that returns the ring to its proper location.

    It began in the Asteroid Belts, in the Kuiper Belt, and in the Oort Cloud. Task groups of robots cruising those realms picked suitable bodies, swarmed over them, and transformed them. And then the task groups moved on, leaving behind what we might denote as flying brickyards, giant packages of building materials floating on their original planetoidal orbits.

    Some time later the tugs came. Like some spacefaring race of harvester ants, the tugs came to pick up their loads and carry them to Jupiter. Reaching out with what looked, to distant observers, like an array of insect-thin appendages, each tug took its load in a full, firm-but-gentle, load-bearing embrace. From points positioned around the tug's body, ultraviolet-glowing bolts of thermonuclear hellfury stabbed at the vacuum and slowly, majestically, the tugs and their loads began to dance Pierre-Simon Laplace's Ballet du Mécanique Céleste, an astroterpsichorean production in four movements as graceful and as powerful as anything Ludwig von Beethoven ever composed.

1. Hohmann's Minuet

    In grand procession the tugs and their loads floated starward from the Asteroid Belts, trading kinetic energy for potential energy as they glided sunup to Jupiter's orbit. Still other fleets of barges plunged, cometlike, sunward from the Kuiper Belt and the Oort Cloud, trading potential energy for kinetic energy as they fell sundown to Jupiter's orbit. Between 3.5 and 4.5 years for the loads coming from the Asteroid Belts and even longer for those falling from Great Cryonesia, time elapsed as the tugs and their loads drifted in cold silence toward their rendevous with the autumn-colored planet. Approaching from sunward, the warmside tugs allowed the planet to pass them as they reached its orbit, allowing it to pull slightly prograde of them so that its gravity would increase the tugs' speed enough to bind the tugs and their loads, however loosely, to the Jovian system. Likewise, the coldside tugs passed apprograde of Jupiter as they crossed its orbit so that the planet's gravity would diminish their velocities, also binding them to the Jovian system with only minimal expense of rocketpower.

2. Waltz of the Jovian Moons

    Even with thermonuclear-based rocketpower providing delta-vees to change their loads' trajectories, the tugs expended impressive quantities of propellant. Deeply committed to making most efficient use of available resources, the tugs' robotic brains did not disparage freely-available delta-vee, so with slight exertions of fiery finesse, the tugs made delicate adjustments to their motions around Jupiter, altering their trajectories to pass close to Jupiter's largest moons. On each such pass a tug would swing around its partner and transfer kinetic energy and momentum. Through such encounters the tugs used the moons' gravitational fields to reduce their orbital angular momenta relative to Jupiter and thereby sink themselves deeper into Jupiter's gravity well.

3. Glissade au Rond

    On elliptical paths that just barely kiss the TerraJovian orbit at their periJove, the tugs and their loads soared in seemingly endless procession. Moving at the slowest speeds achievable with the available resources, the tugs then had to apply direct rocketpower to transform what started as a brief kiss into a full embrace. At enginestop each tug had come close to and matched velocities with some part of the largest construction site humans had ever instigated.

4. Separation and Farewell

    Floating on orbit, at rest relative to the growing components of TerraJove, the tugs released their cargoes and retracted their spider-like arms. Freed of their burdens, the tugs turned their engines arretrograde and again, more gently than before, thermonuclear fire flared in the void. In the final movement of the great dance, the tugs boosted themselves onto trajectories that would take them back to whence they had come, to swarming Astronesia between the orbits of Mars and Jupiter or to Great Cryonesia in the shallows of the vast Interstellar Sea. Each tug would then pick up another load and then rejoin the cosmic dance.

    In circumJovian orbit a yeast of robots, of all sizes, swarmed over each of the loads as it arrived. Working primarily at the atomic level, they transformed the semi-raw material of each block into the components of a Bifrost Bridge to span the Jovian sky. Intended to form the foundation of TerraJove, these great arc-like pieces grew floating on orbit. One end of each foundation arc floated several hundred meters from the near end of its neighbor, to which it would later connect. The Builders initially kept the foundation arcs separated from each other so that they would not form an unstable ring before the robot labor force had built the world's stabilizing mechanism and put it into operation.

    Thousands of kilometers wide and tens of thousands of kilometers long, the foundation arcs grew in orbit. Huge frames of magnetic track, they might have evoked in an observer's mind an image of a three-dimensional railroad marshaling yard. Megameter upon megameter of superconducting bars and cables came together, along with giant slugs made primarily of superconducting material, the massive Atlases whose super-orbital motions hold up the world. On the side of the tracks facing away from Jupiter kilometer-scale springs and shock absorbers grew, god-sized arms and hands holding up the impermeable sheet of rigid material upon which the world would rest. Those arrays of mechanical low-pass filters convert the fluctuating forces that the Atlases exert upon the tracks into a steady force supporting the world.

    Using the repulsive force of the Meissner effect, the frame manipulates the Atlases as it actively controls the support of TerraJove. That support came into being when the Atlases accelerated to super-orbital speed and conservation of momentum decelerated the frame until the frame moved at eight kilometers per second about Jupiter. The support of TerraJove comes from the excess centrifugal force of the Atlases compensating the deficiency of centrifugal force in the frame. As part of the accelerating/decelerating process the frame's parts moved a few hundred meters closer to Jupiter and that motion closed the gaps between the arcs. Thousands of couplings engaged and locked, uniting the arcs into one continuous and now-stable circle. Stable because if TerraJove shifts off position, the Atlases on the side that moves closer to Jupiter will speed up and exert more force while the Atlases on the opposite side of TerraJove will slow down and exert less force: the net force will thus act to move TerraJove back to its proper position.

    With the frame fully assembled and the minor rings built under the main ring rotating in synchrony with Jupiter, strange roots descended into Jupiter's atmosphere. From the minor rings vast webs of polybuckminsterfullerene grew downward. Their weight distributed uniformly over the length of their ring, the webs gathered in on themselves at intervals and thousands of kilometers below the ring they formed thick cables that continued to grow into the planet's atmosphere. At their tips the cables fanned out and grew structures that absorbed gases from the atmosphere. Inside the cables' buckytubes fluctuating electromagnetic fields exert peristaltic forces that lift the gas molecules -- ammonia, methane, hydrogen, helium, and others -- to the minor ring.

    Refrigerators in their millions liquify the gases coming out of TerraJove's roots and load the liquids into tanks that resemble, for good reason, the world's Atlases. Magnetic fields grip each filled tank and lift it onto the deceleration track. As with the Atlases, the fields move the tanks, in this case decelerating them, shunting them onto tracks that take them through the spaghetti-weave of Atlas tracks and deliver them to the main ring. Megaton upon megaton of liquid then spills into the holding tanks of TerraJove's chemical manipulators while the empty transfer tanks get shunted into acceleration tracks and thereby returned to the minor rings for reloading.

    On the finished foundation the world's floor and thin-shell mountains grew. Isolated mountains and mountain ranges grew out on the world itself and a continuous, unbroken range of mountains, as high as the Himalay, grew along each of the world's edges. Those latter mountains hold in the world's air, keeping it from spilling into space. They also anchor the sky.

    That sky consists of a two-meter thick sheet of plastic that holds TerraJove's air in place from above through its weight. Dimples of thicker and heavier plastic sink deeper into the atmosphere in places: those and the sheet's attachment to TerraJove's internal mountains keep the sheet stable against fluctuations. With only vacuum on its upper side, the sheet simply floats on air. Dense networks of capillaries weave throughout the sheet, though not so densely as to compromise the sheet's transparency, and carry the microbotic blood that maintains and repairs the sheet. Initially built laid out on the ground and draping down the mountains, the sheet rose as air came into the world. At the edges, where the sheet connected to the mountains, robots took in the extra material and recycled it.

    Here and there across the world sawtooth mountains rise above the sky and open their interiors to vacuum. Into these mountains new loads of material fell from space and slid down decelerator tracks that guided them to the factories that rendered them into the things that the world needs. Here also armies of robots built the great spaceports that serve as interfaces between TerraJove and the rest of the solar system with regard to movement of freight and passengers.

    Asteroidal regolith entered the world through those tunnels. Spread over the world's floor, it made TerraJove, temporarily, a vast desert, bleaker by far than Arabia's Rub' al Khali. But then again the microbots came in their mega-swarms. They reformed the regolith, using it to cover the mountains and parts of the floor in solid rock. In other places they turned the regolith into sand, gravel, pebbles, and cobbles. And over wide swathes of land they left the regolith unaffected, a base for the soil that the new world would need. Once finished with their tasks the microbots underwent a process similar to apoptosis; they simply fell apart, leaving some parts for larger robots to recover and the rest to become part of the soil. At the end of the reforming process this new world lacked only water and warmth to become an abode of life.

    Water came from Great Cryonesia. Things that would have become comets became, instead, part of TerraJove's hydrosphere. Great gushing fountains filled the shallow seas that, like the Persian Gulf or the Bahamas, sink no deeper than thirty meters. Transformed into rain, water also filled the rivers and lakes and moistened the soil, preparing it to receive the blessing of life.

    The arrival of water clarified the landforms, which the Builders designed to offer the maximum of variety. This world will have few endless prairies, vast steppes, broad veldts, or other wide open spaces. (Ah, but think of the possible vistas on a world whose horizon lies more than seventeen times farther away from us than Earth's does.) Most of TerraJove took the form of more intimate spaces, places reminiscent of rural Japan, Switzerland, New England, or New Zealand.

    Warmth comes to TerraJove, as it does to Earth, from the sun. Floating on Jupiter's orbit 5.2 AU from the sun, TerraJove receives a flux of solar energy twenty-seven times less dense than the flux of sunlight crossing Earth's orbit. In order for life on TerraJove to enjoy Earth-like conditions, as it must do in order to live at all, something must compress the sunlight reaching Jupiter's vicinity and direct it onto the dayside of TerraJove. That something will consist of an immense swarm of Fresnel lenses floating on orbits far above Jupiter. The lenses won't so much compress the light directly as they will compress it indirectly by deflecting light that would otherwise fly past TerraJove, deflecting enough onto the world to produce the effect of a twenty-seven-fold compression. Spanning thousands of kilometers, each of those lenses will possess the chameleon-like ability to change any part of itself from transparent to reflective and back. With a simple animal intelligence, each lens will maneuver itself as a solar sail throughout the Jovian system, periodically putting itself on an unmarked line in the eternally silent emptiness that will position it to cast its share of deflected sunlight onto TerraJove. At times a ship will bring a vast army of microbots to carry out maintenance and repair on the lens. And at the right time visitors on ships approaching TerraJove may catch a glimpse of the array, like a flow of cars on an invisible freeway.

    Finally TerraJove stood ready and life-bearing ships began to arrive. Bacteria and algae had already come to this new world with the first flows of water and had spread, converting the regolith into soil suitable for planting and converting the original reducing atmosphere into the oxygen-rich atmosphere that evolved life needs. Next came the higher plants and animals, stored on the space arks in the form of seeds, eggs, and embryos, the better to protect them from the hazards of interplanetary flight. Those creatures that required parental care got it initially from robots, but eventually all life had to stand on its own abilities, succeeding only to the extent that those abilities fit the creatures' environments. Brought to maturity and spread across TerraJove under robotic care, the flora and fauna of Earth resumed the majestic pas de deux of mutation and selection that has shaped life on Earth. For TerraJove provides not only space enough, but time enough as well for evolution to occur. Indeed, as a semi-living thing TerraJove itself will evolve, though not under the pressure of natural selection: TerraJove will evolve under the guidance of true intelligent design.

    Then the people will come and take up residence in this Eden. The actors will take the stage and the human drama will continue to play out. Given such room, how will civilization grow? How will it evolve as it expands? Certainly it will seem incomprehensible to us, just as our civilization would seem incomprehensible to the Founders and the generation of the Revolution if they could see it. But familiarity will also abide here: if we could see it, we would certainly recognize it as a human civilization.

    If this still doesn't give us enough room for a Humanity large enough to expand into the Galaxy, then think of it as practice for the construction of TerraSol. With a radius of 3,676,000 kilometers, TerraSol doesn't need to rotate to have Earth normal gravity on its outer surface. If the Atlases can cross each other's paths without colliding or compromising their support of the world, we can build TerraSols that intersect each other: in time the sun may come to resemble an old-fashioned picture of an atom. Tilted out of the Ecliptic, the 100,000 kilometer-wide TerraSol will display a solar transit twice a year, blocking a maximum of 0.918 percent of the sun's light. Over an interval of slightly more than thirteen hours observers on Earth will see a thin black line slide across the face of the sun.

    We will do this again and yet again. We can do nought else. For just as our brains contain structures that automatically recognize human faces, so too they contain structures that automatically recognize environments ideal for a bipedal, naked ape, however sentient that ape may have become. As long as we remain human, then so long as we explore the bleak, dessicated graylands of other worlds and extend the human presence into the Galaxy, we will always carry that collective memory and its endless yearning for the blue skies, the scented breezes, the rivers and the meadows of the sweet green hills of Earth.

    And in some farthest future, when the bright stars all have died and only red dwarf stars continue to abide, when our far away descendants set out to rebuild and renovate the Galaxy that Humanity has filled, they will look back on TerraJove to measure Humanity's gain, just as we regard the first clusters of crude huts on the Tigris-Euphrates Plain.


Note: for the solution of the depressed cubic equation that yields TerraJove's radius see "Cardano's Solution of the Depressed Cubic Equation" under "The Platonic Dream" on this website.


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