Terraforming Ganymede with Robert A. Heinlein
Part 2

by Gregory Benford

World Making

I grew up, to the extent that I ever have, amid the farmlands of southern Alabama. Farming is hard work. Thinking of growing crops on distant worlds, as Robert A. Heinlein did in several novels, demands hard thinking.

In Heinlein’s Farmer in the Sky pioneers on Jupiter’s moon Ganymede create their "soil" from scratch by pulverizing boulders and lava flows. Tough work, but in fact it will be even harder for any future farmers there.

We now know that probably Ganymede never had volcanoes—and if so, they spouted mostly water. The Moon has approximately equal amounts of silicate rock and water ice. It is fully differentiated into layers, with an iron-rich, liquid core like Earth. There may be a saltwater ocean 200 km down, sandwiched between layers of ice. Its dark surface regions, pocked by impact craters from four billion years ago, cover about a third of the surface. More recently made lighter regions, crosscut by long, deep grooves and ridges, cover the remainder. The light terrain most likely comes from tectonic flows driven by tidal heating.

Heinlein didn’t worry about radiation, but we now know he should have. Ganymede is the largest moon in the Solar System and the only moon with a magnetosphere. Jupiter's magnetic field overshadows it and funnels high-energy protons onto its surface. Ganymede receives about 0.08 Sv (8 rem) of radiation per day. (Sv is the standard derived unit of dose equivalent.) For comparison, the average amount of radiation taken on Earth by a living organism is about 0.024 Sv per year; the highest natural radiation levels on Earth are about 0.26 Sv per year. So without an atmosphere, Ganymede is deadly.

Indeed, the levels of ionizing radiation on the inner moons Io, Europa and Ganymede are hostile to human life. Adequate protective measures are hard, short of burrowing deep under the ice and rock. Callisto is the only one of Jupiter's Galilean satellites for which human exploration is feasible without massive shields.

But with an atmosphere, matters get easier. To have an Earth atmospheric pressure would demand an atmosphere about seven times as deep as ours. How to make it? First, melt the water ice with fusion reactors, and then let UV crack the water into oxygen and hydrogen. Let the hydrogen blow off and keep the oxygen. Add other elements, especially nitrogen, as needed. Let smart biology work on the gases for a while. Then cap the growing atmosphere with a monolayer that traps the gas. That’s a genuinely grandiose project, demanding biotech to grow the filmy layer, and orbiting satellites spooling forth millions of square kilometers of it.

Heinlein’s farmers seed the pulverized dust with carefully formulated organic material. They had no bioteched organisms, apparently because no one imagined those in 1950. We also now know the satellite has a thin oxygen atmosphere that includes O, O2, and possibly O3 (ozone). I showed that later in my novel, Jupiter Project, though enhanced by considerable engineering.

Ganymede is the only moon in the Solar System known to possess a magnetosphere, likely created through convection within its liquid iron core. This meager magnetosphere is buried within Jupiter's much larger magnetic field and connected to it through open field lines. But that connection could give birth later to a major energy industry.

Jupiter is similar to a device called a unipolar generator. It generates a vast domain dominated by Jovian magnetic fields (see figures). When Jupiter rotates, its ionized upper atmosphere, the ionosphere, moves relatively to the planet's dipole magnetic field. This makes the poles negatively charged and the regions closer to the equator become positively charged. This has to get balanced, and somewhat weirdly, some of that happens by running currents between the moons and the poles, making a beautiful aurora.

Generally, the incoming solar winds makes the main ovals, which are bright and narrow (less than 1000 km in width) circular features at 16 degrees from the magnetic poles. Ganymede, Europa and Io have satellite auroral spots, the footprints of their magnetic field lines connecting their ionospheres with the ionosphere of Jupiter. It’s a marvelous electrodynamic engine.

Those glowing spots develop because the co-rotation of the plasma is slowed in the vicinity of moons. The brightest spot belongs to Io, which is the main source of the plasma in the magnetosphere. Europa's and Ganymede's spots are much dimmer, because these moons are weaker plasma sources.

Still, a million amperes flows from the top of Ganymede’s atmosphere in a narrow tube of magnetic fields. Io’s is much larger still—one could harness it and beam the energy to Ganymede on microwaves. Imagine harnessing that for the early days when you have few fusion plants -- and of course sunlight is a chilly 1/27 of Earth’s. Heinlein didn’t know of this, and I didn’t either when I wrote Jupiter Project.

With surface gravity of 0.146 g, even less than Luna’s 0.18 g, Ganymede is a light place to live. It’s cold, with a maximum temperature of 152 Kelvin (our room temperature is 300 K). Think of it as like the Arctic, with the Sun a mere small hot dot in the sky. The capped atmosphere could run temperatures up a lot, but not above water’s freezing point. After all, you’re 5.2 times further from the Sun than Earth.

But in that thick atmosphere you can also fly—with an Earth atmosphere pressure, and some extensions on your arms, you can ride updrafts with ease. Heinlein predicted such feats in a wonderful, crisp short story, “The Menace from Earth,” set on Luna--but on Ganymede it’s even easier.

Why Go?

Both Heinlein and those who followed knew that inevitably, as humanity opened the Solar System to exploration and commerce, it would be cheaper in energy to tug small asteroids in from the orbits between Mars and Jupiter than to lift them with mighty rocket engines from Earth. So I began constructing a future history that led to Farmer in the Sky and beyond. I’ll present it here, as in Part 1, as a popular historian would. There we left our colonists with some crunched gravel and grit, but had not really introduced biology. Heinlein didn’t use biotech either—this was around the 1950s, and DNA had barely been discovered. But I have the advantage of sixty years of progress, and have even started some biotech companies myself (Genescient, LifeCode). So I envision how we’ll use that to make a new world…


Any atmosphere can blunt the energy of incoming protons and screen against the still-dangerous Sun’s ultraviolet, but to be breathable, it has to be engineered. Once a tiny fraction of the ice plains were melted into vapor, a greenhouse effect began to take hold. Sunlight striking the ice no longer reflected uselessly back into space; instead, the atmosphere stopped the infrared portion, trapping the heat. Once this began, the fusion-crawlers were a secondary element in the whole big equation.

The fresh ammonia streams and methane-laced vapors were deadly to Earth-based life. A decade after the first fusion-crawler lumbered through a grooved valley, hundreds of them scooped and roared toward Ganymede’s poles, having scraped off a full hundred meters of the ice crust. They had made an atmosphere worth reckoning with. Ice tectonics adjusted to the shifting weight, forcing up mountains of sharp shards, uncovering lodes of meteorites, which in turn provided fresh manufacturing ore for yet more fusion-crawlers.

The first rains fell. A slight mist of virulent ammonia descended on the Zamyatin Settlement. It collected in a dip on the main dome, dissolving the tenuous film on it. After some hours, the acid ate through. A whoosh of lost pressure alerted the agriworkers. They got out in time, scared but unshaken. These were farsighted people: they knew one accident wasn’t reason to kill the project that gave them so much hope.

The only solution was to change the atmosphere as it was made. Further rains underlined the point – it became harder to work outside because the vapors would attack the monolayer skinsuits. The fusion plants were no help. They were hopelessly crude engines, chemically speaking, limited to regurgitating vapors that had been laid down three billion years before, when the moon formed. They could not edit their output. As they burrowed deeper into the ice fields, the situation worsened.

Io, the pizza planet, had once enjoyed a more active stage. Its volcanoes had belched forth plumes of sulfur that had escaped the moon’s gravity, forming a torus around Jupiter that included all the moons. On Ganymede, this era was represented by a layer of sulfur that now occasionally found its way into the deep-dug crawlers’ yawning scoops. The result was a harshly acidic vapor plume, condensing to fierce yellow rains that seared whatever they touched. Fifty-seven men and women died in the torrents before something was done.

The fusion-crawlers had been a fast and cheap solution because they were self-reproducing machines. The answer to bioengineering of the atmosphere lay in a tried-and-true method: self-reproducing animals. But these creatures were unlike anything seen on Earth.

The central authority on Ganymede, Hiruko Station, introduced a whole catalog of high-biotech beings that could survive in the wilds of near-vacuum and savage chemicals. Hiruko Station’s method was to take perfectly ordinary genes of Earthside animals and splice them together. This began as a program in controlled mutation but rapidly moved far beyond that. Tangling the DNA instructions together yielded beings able to survive extreme conditions. The interactions of those genes were decidedly nonlinear: when you add a pig to an eel, flavor with arachnid, and season with walrus, do not expect anything cuddly or even recognizable.

There were bulky gravel gobblers, who chewed on rocky ices heavy with rusted iron. They in turn excreted a green, oxygen-rich gas. The scooters came soon after, slurping at ammonia-laden ice. These were pale yellow, flat shapes, awkward and blind on their three malformed legs. They shat steady acrid streams of oxy-available mush. Hiruko Station said the first plant forms could live in the bile-colored scooter stools. Eventually, plants did grow there, but they weren’t the sort of thing that quickens the appetite.

Both gravel-gobblers and scooters were ugly and dumb, hooting aimlessly, waddling across the fractured ice with no grace or dignity, untouched by evolution’s smoothing hand. They roved in flocks, responding to genes that knew only two imperatives: eat and mate. They did both with a furious, single-minded energy, spreading over the ice, which was for them an endless banquet.

Hiruko Station liked the results, and introduced a new form – rockjaws – that consumed nearly anything, breathing in the ammonia-rich atmosphere, and exhaling it back as oxygen and nitrogen. Rockjaws could scavenge far more efficiently than the gravel gobbler, and even bite through meteorites. Metallic jaws were the key. The high-biotech labs had turned up a method of condensing metal in living tissues, making harder bones possible.

Rockjaws were smart enough to stay away from the Settlements (unlike the others, who constantly wandered into greenhouses or tried to eat them). At this point the long-chain DNA-tinkering of Hiruko Station ran afoul of its own hubris. The rockjaws were too smart. They were genetically programmed to think the loathsome methane ices were scrumptious, but they also saw moving around nearby even more interesting delicacies: gravel-gobblers. And they were smart enough to hunt these unforeseen prizes.

Hiruko Station later excused this miscalculation as an unfortunate side effect of the constant proton sleet, which caused fast genetic drift and unpredictable changes. Hiruko Station pointed to the big inflamed warts the creatures grew and the strange mating rituals they began to invent – none of this in the original coding. The scooter flocks were showing deformities, too. Some seemed demented (though it was hard to tell) and took to living off the excretion of the gravel-gobblers, like pigs rooting in cow manure.

First Hiruko Station tried introducing a new bioengineered animal into the equation. It was a vicious-looking thing, a spider with tiny black eyes and incisors as big as your finger. It stood three meters high and was forever hungry, fine-tuned to salivate at the sight of any mutation of the normals. This genetically ordained menu was quite specific and complexly coded, so it was the first thing to go wrong with the ugly beast. Pretty soon it would hunt down and eat anything that moved – even humans – and Hiruko Station had to get rid of it.

That led to a surprising solution to other rising societal stresses. The only way to exterminate the spiders was by hunting them down. Many men and women in the Settlements volunteered for the duty. After some grisly incidents, they had grudges to settle, and anyway it gave them a reason to get out of the domed regularity of their hothouse gardens and manicured fields. Thus was revived a subculture long missing from Earth: the Hunt, with its close bonding and reckless raw life in the alien wilderness.

These disorderly bands exterminated the spiders within a year. Hiruko Station found it was cheaper to pay the hunters a bounty to track down and destroy aberrant scooters, rockjaws and gravel-gobblers, than it was to try for a biotech fix. It was also healthier for the psyche of Ganymede’s settlers. The Settlements were tradition-steeped societies – internal discipline is essential when an open valve or clogged feed line can kill a whole community. The Hunt provided an outlet for deeply atavistic human urges and pressures, long pent and fiercer for their confinement.


The atmosphere thickened. Hiruko Station added more mutant strains of quick-breeding animals to the mix, driving the chemical conversion still faster. The biotechnicians found ways to implant microprocessors into the animals, so that they wouldn’t get out of control. That was expensive, though, so hunting continued, echoing the heritage of mankind that came down from the plains of Africa. Bounty hunters were hard to fit into the labor scheme, and the socioplanners kept trying to phase them out, largely from sheer embarrassment. But Earthside 3D programs lapped up tales of the rough ‘n’ ready bountymen and –women of the Hunt, giving what the planners felt was a “false image” of the Settlements. Mutation of the released gene-engineered animals was rapid, however, and the biosphere was never truly stabilized. The hunters became an institution. To this day, they are an unruly crew who don’t fit into planners' orderly diagrams.

Rain lost its sulfuric tang. Steam rose at morning from the canyons, casting rosy light over the Settlements. The moon’s first rivers cut fresh ravines and snaked across ice plains.

All this hung in delicate balance. Huge sodium-coated mirrors were spread in orbit nearby, to reflect unceasing light on the paths ahead of the fusion-crawlers. This speeded evaporation and was used also to hasten crops to ripeness. But Ganymede was, after all, an ice world. Too much heating and a catastrophic melting of the crust would begin. If the crust broke or even shifted, moonquakes would destroy the Settlements.

Thus it was a careful hand that started up the first Ganymede weather cycle. Solar heating at the equator made billowing, moist clouds rise. They moved toward the poles as colder air flowed below, filling spaces the warm air left. As they moved, masses of warm clouds dropped sheets of rain. This meant there was only one circulation cell per hemisphere, an easier system to predict than the several-cell scale of Earth. Rainfall and seasons were predictable; weather was boring. As many on Luna and in the asteroids had learned long before, low gravity and a breathable atmospheric pressure gave a sensational bonus: flying. Though Ganymede would always be cold and icy, people could soar over the ice ecology on wings of aluminum. Compared to the molelike existence of only a few generations before, this was freedom divine.

There came at last the moment when the air thickened enough to absorb the virulent radiation flux. Years later, a foolhardy kid stepped outside an airlock five hours before the official ceremony was to begin, and sucked in a thin, piercingly cold breath. She got back inside only moments before oxygen deprivation would have knocked her out, but she did earn the title she wanted: first to breathe the free air of Ganymede. Molecules locked up for billions of years in the ice now filled the lungs of a human. Her family was fined a month’s labor credit by her Settlement.

By this time Europa’s cracked and cratered face was also alive with the tiny ruby dots of fusion-crawlers, chewing away at that moon as well. They crept along the cracks that wrapped the entire moon, melting the wall away, hoping to open the old channels below the cracks. In spots the churning slush below burst forth, spreading stains of rich mineral wealth. Jove itself, hanging eternally at the center of the sky, was now the only face unmarked in some way by mankind.

Not to be outdone, the Republic of Ganymede hastened the heating of their air. They laid a monolayer over the top of the atmosphere, spinning it down from orbit and layering it in place, letting it fall until the pressure supported it. All the while, weaving sheets stitched themselves together and automatically locked as the smart-layers stretched. This gossamer film stopped the lighter molecules from escaping into space, feeding the chemical reactions balanced in the atmosphere and hastening the greenhouse effect. Chlorfluorocarbons, especially, did their complex work. The designers of the atmospheric cap left holes large enough to let orbital tugs slip through. With control modules fitted to the boundaries of these openings, they could be closed at will. From the Ganymede surface, Callisto, Europa and Io swam in the sky, lambent with halos of gauzy, scattered light.

Rain hammered the plains of Ganymede and evaporated within hours. But the gas density rose and water did its ancient trick of passing through phase transitions at the change of a degree or two. The first lake on Ganymede formed in a basin of dirty meteorite rock eight kilometers wide. This created a ready source of fresh water and soon elaborate homes were carved into the spongy rock overlooking the view. In insulated suits people could sail and even swim. Mirrors hung in orbit, focusing sunlight on fields that slowly turned an odd blue-green, patches spreading wherever water trickled.

Space continued to yield up mineral riches. Near-Jovian space held many useful nuggets the size of cities, both the Trojan asteroids, locked in stable resonance at Jupiter’s Lagrange points, and the wide-wandering Transjovians. At first, ready access to manufacturers made producing metal-rich products much cheaper on Ganymede, where the skilled workers and robot factories already were. This briefly cut into the asteroid commerce from the outer planets, but there were other commodities flowing both ways along that same slow route.

Interplanetary trade increased. Stations around distant Saturn drew food and other perishable supplies from Ganymede to support their key energy industries. Saturn, Uranus and Neptune were fast becoming "the Persian Gulf of the Solar System" – a phrase referring to an era centuries past, when fossil fuels in a single Earthside zone provided the major energy sources. Now the outer planets were the largest sources of deuterium and helium-3 to drive the fusion economy. Saturn was the most valuable of the three, because of its relative proximity, low radiation, and excellent system of moons. The largest of these--gloomy, ruddy Titan--was now explored and its resources identified. Some tried to make a go of it at the bottom of that chilly bowl of primordial soup. Few stayed – something in the human psyche cried out to see the skies. Robots busily labored on, untouched by such biological considerations, in murk where only people with acute claustrophila could be happy.

There were many other moons, though, some ripe for development and colonization, some just icy rocks with a number, not a name. A portion of these were set aside as preserves, where scientists and selected tourists could see how the ice worlds had once been. Some never felt the explorer’s boot, held for far-future technologies to understand. Humanity had learned from the Age of Appetite to preserve bleak wastes and allow them to become future frontiers.

As always, economics called the tune. Moons just now boiling off their ices had to find innovative ways to compete with long-established Ganymede. They quickly realized that not capping their atmospheres would make it simple to profit from the new business of slinging asteroids, using atmospheric braking effects to dissipate incoming energies.

Simple chunks — nickel, iron, differentiated silicates rich in rare ores, the usual—came arcing in on long slow ellipses. Deftly dropping their momentum with a brush through uncapped atmosphere simplified and shortened their delivery orbits. Vast fortunes were made and lost with bewildering speed in the early days of the Second Asteroid Rush. Demand continued to escalate, as the off-Earth populations increased in numbers and affluence, but transport was the key to supply. The Jovestar Conglomerate crashed when their monopoly market faltered. Their legal crews, moving quickly, had locked up mineral rights of the obvious first million Trojan asteroids, and their grip on those could not be broken. But the Transjovians were still out there for the plundering, if only they could be cheaply moved to near-Ganymede orbit. The siren song of fabulous wealth ensured that it happened sooner rather than later.

The Europa entrepreneurs jumped into the fray, taking advantage of every last commercial possibility. Since their atmosphere was open to space, they had long sent asteroids zooming through it, en route to easy orbits in Ganymede’s neighborhood. The incoming asteroids, linked to guiding tugs, also heated up Europa’s air, and properly marketed, provided a valuable tourist attraction, with their well-choreographed displays of burnt gold, electric blue, and ruby amber. As the trajectories of these rockships became more graceful and regularly scheduled, they began to carry passengers. Later, atmosphere-grazing in protected fallsuits became popular. In the freewheeling ethical climate of the time, bookings were permitted for those who signed on as suicides. Indeed, the rates were even lowered, contingent on use of long-obsolete suits. The in-fall failure of century-old systems sealed the decision for some with second thoughts.

Some time later, a large Earthside foundation proposed capping the Callisto atmosphere. They intended the largest work of art possible – a gaudy, beribboned design of loops and swirls that could be seen (properly magnified) throughout the Solar System. The glorious monolayer film would have changeable polarization and colors, so that later generations of artists could express themselves through it.

This idea was opposed by a rare coalition of environmentalists – Keep Callisto Clean – and business interests, who wanted to horn in on Europa’s atmospheric deceleration franchise. The foundation lost its zoning permit. Undeterred, they set about plans to move Pluto into a long, looping orbit, which passed through the inner Solar System. Suitably decorated, they said, Pluto would make a magnificent touring art gallery.

Ganymede, oldest and wealthiest of the Jovian colonies, was becoming relatively luxurious. A shining complex of high-end hotels and shops went up, surrounding a sybaritic waterpark that took full advantage of low gravity. Reservations to surfglide at the wave pool became the most hotly sought date in the Settlements. The songs of The Beach Boys, fallen into obscurity as Earth’s rising oceans made crashing waves a source of societal terror, became wildly popular again. Surf culture was resurrected, albeit in forms no twen-cen California Girl could have foreseen.

Soon there was talk of starting a power-generating plant on Io. Not one using the volcanoes there – those had already been tapped. This plan proposed hooking directly into the currents that ran between Io and Jupiter itself – six million amperes of electricity just waiting to be used. Work began. Soon they would harness the energy that drove the aurora.

The forward vector of humanity had by now passed beyond the Jovian moons. Near Earth, the first manned starship was abuilding, soon to depart for Alpha Centauri. Given the engineering abilities of humanity, the matter of whether an Earthlike planet circled there seemed beside the point. (As it turned out, there was no such world within 18 light years.) Humans could survive anywhere. Better, they would prevail, and learn to enjoy just about anything. Any place where sunlight and mass accumulated, mankind would find a way to form a roiling, catch-as-catch-can society – and probably make a profit doing it.

Of course, there was Jupiter itself. It and the other gas giant planets had formed the backdrop for all this drama, but that was all. Many a Ganymede native, perhaps as he lounged beside a lake in a heated skinsuit or banked and swooped through gossamer clouds, peered up at the swollen giant and idly wondered. Jupiter occupies two hundred and fifty times as much of the sky as Luna does from Earth; it was never far from the minds of the millions who lived nearby.

So it was probably inevitable. A physicist on Luna had developed a new theory of Jove’s interior, accounting for all the latest data on pressure and temperature and chemical composition. She found that there had to be stratified bands of pure hydrogen metal near the surface of Jupiter. Such hydrogen metal might be close to the outer layers of rock, shallow enough to mine.

Her theory suggested that once compressed into being by Jupiter’s huge gravitational pressure, metallic hydrogen would be a stable form. At great expense, laboratory tests synthesized a few grams of the stuff. It was incredibly strong, light and durable. It could even survive a slow transition up to low pressure. If you could go down there and mine it...

The pressures deep in that thick Jovian atmosphere were immense. Where they had even been measured at all, the conditions were brutal. The technology for handling the mines was completely undeveloped. It was an insane idea.

They said, of course, that it was impossible. They always do.


So endeth my own historical version of our possible Jovian future(s).

I wrote Against Infinity as a sequel to Jupiter Project. In it, I supposed the big agricomplexes were productive but didn’t really build a coherent culture. For this, Ganymede needed farmers who would own land, care for it painstakingly, and build communities. That’s how America was built; we know how to do it.

So in this era, Farmer in the Sky’s Bill Lerner and his family came to Ganymede to start their farm. He saw farming as a natural role as humanity rolled out from its Earthly bounds. After writing that novel, Heinlein hammered out the great “juveniles” to follow: Between Planets (1951), The Rolling Stones (1952), Starman Jones (1953), The Star Beast (1954), Tunnel In the Sky (1955), Time for the Stars (1956), Citizen of the Galaxy (1957) and finally Have Space Suit — Will Travel (1958). To my taste he improved steadily, but Farmer remains my favorite.

So I followed later with a novel set after Farmer, in 1982: Against Infinity. It is set in a terraformed Ganymede a bit before the time of Farmer. It concerns hunting a special prey on Ganymede--an unknowable alien artifact that roamed and ruled Ganymede for countless eons, its purpose unknown.

In another sense it’s about my own growing up, hunting and roving in the rural South. The great aspect of the American South is that it never truly leaves you, even if you haul off to exotic California to pursue a scientific career and write the occasional novel. I’ve gone further still since, setting several stories around Ganymede. Eventually, I’ll finish them into a novel and complete the Jupiter Trilogy, I suppose I’ll call it. This is how science fiction develops—as a continuing conversation between authors and fans and just plain readers. It’s one of our great strengths.

Others have used the Jovian system to their own ends, perhaps most famously in Arthur C. Clarke's novel 2061: Odyssey Three (1987). In that novel, Ganymede is warmed by the new sun Lucifer and contains a large equatorial lake. It becomes the center of human colonization of the Jovian system.

So the dream goes on. Jupiter swims still in our skies, beckoning.

Terraforming implies more than human survival: it is the

evolutionary extension of life from Earth beyond the Earth. I’m sure that Heinlein thought of terraforming as itself an act of nature, inevitable and ordained. We ambitious primates came out of Africa and are still on the move, a natural outcome of evolution’s unfolding mysteries.

There’s even a practical side to this, I think: we need to study, understand, and experiment, and make our mistakes on other planets first-- before we mess with the one we live on. So Heinlein’s ideas resonate even more now, as we consider grand schemes like geoengineering, to offset climate change. There are lessons to be learned on other worlds.

Farmer in the Sky is paying conceptual dividends long before a boot makes its first print on the icy plains of Ganymede, beneath the great globe of churning Jupiter.



Copyright © 2011 by Gregory Benford