Worldbuilding Cloud Cities on Venus

The idea of alien life or human colonies on Venus is one as old as scientific speculation and science fiction; the bright cloudy shroud over the surface made Venus for centuries much more mysterious than the other (relatively) Earth-like planet in the inner solar system, Mars. Mikhail Lomonosov was the first man to discover Venus had an atmosphere, by observing an arc of light surrounding the part of Venus off the Sun’s disc during a transit in 1761. It was always supposed that Venus was warmer than the Earth, since it is nearer the Sun; in 1870 Richard Proctor speculated the poles may be the only region of the planet cool enough to be habitable. By 1940, Rupert Wildt calculated the amount of carbon dioxide in the atmosphere would raise surface temperatures worldwide above the boiling point of water. His calculations were confirmed by space probes that flew by in the 1960s, that revealed a much thicker atmosphere and hotter surface than almost anyone expected.

That seemed to foreclose the possibility of Earth-like life on Venus, but much like Mars a closer look over the decades since the first flybys has revealed a more dynamic, clement, and fascinating planet than the initial shock in the 1960s suggested. If the same processes that created liquid water oceans on Earth (and probably Mars) also occurred on Venus early in its geological history, recent studies have shown water oceans would have been stable for hundreds of millions of years; a 2019 study raises the possibility of ocean survival as late as 700 million years ago, long after Mars’s oceans are thought to have evaporated. No Earth-like life could survive on the surface today, but any native life may have found a refuge in the upper reaches of Venus’s atmosphere.

Venus’s surface is famous for being the harshest environment in the inner solar system; the surface temperature is 500 degrees Celsius (over 900 degrees Fahrenheit), hot enough to melt lead, and the atmospheric pressure is 90 times the Earth’s surface, similar to the pressure found 3000 feet underwater. The surface is under perpetual cloud cover; these clouds absorb so much of the bright sunlight the surface illumination is actually dimmer than on Earth. Sulfuric acid rains these clouds produce evaporate before they even reach the surface. These conditions conspire to make Venus’s surface the hardest one to colonize of any terrestrial world in the solar system.

A Paradise among the Clouds

However, there is a silver lining to this story: that 90 bar atmosphere, like all atmospheres, grows thinner with altitude. Between the surface and outer space, there is a layer with pressure similar to Earth. In Venus’s case this is 50 kilometers above the surface, where the temperature is a hot but manageable 167 degrees Fahrenheit. 5 kilometers higher up, the temperature becomes a downright pleasant 80 degrees Fahrenheit, at the price of 0.5 instead of 1 atmosphere of pressure but still well within the shirt-sleeve range. At 60 km, the temperature drops to around freezing and the pressure is still 0.23 atmospheres; low, but well within the shirt-sleeve range. This 50-60 km altitude band is where the most habitable conditions for humans will be found. Indeed, considering that humans could walk outside without a spacesuit or even cold-weather clothing, it is probably the most Earth-like environment anywhere in the solar system outside of Earth. So much for Venus being Planet Hell, as is so often implied.

This same band of the atmosphere is where any lingering native life most likely makes its abode; unlike Earth life any Venus life would need to be perpetually airborne, but since some bacteria on Earth remain airborne for long stretches this shouldn’t be too much of an obstacle. The extremely low humidity of the atmosphere is much more challenging, unless the microbes use a more abundant substance than water as their solvent; in any case there is some water in Venus’s atmosphere, albeit only around 20 parts per million. The acidic environment is another challenge, though it is worth noting there are plenty of acidophilic microbes on Earth; the most habitable band of the atmosphere also happens to be where some of the heaviest concentrations of sulfuric acid are located. Sulfuric acid cloud cover peaks at 48 kilometers in altitude, not too far below the human-habitable band. Any native microbes or human colonies would need to contend with acidic rains on a regular basis.

None of these obstacles are formidable, especially for human colonists, and it’s worth noting the environment actually holds several advantages as a colonization site. Assuming we are using floating cities (or vehicles in earlier or smaller scale efforts) as our colonies, the lifting gas will need to be lighter than air. Since the air on Venus is 96% carbon dioxide, which is considerably denser than Earth air, Earth’s mixture of 78% nitrogen and 21% oxygen is actually a lighter-than-air lifting gas on Venus! If the interior of the colony was airy enough and made out of lightweight materials, no special envelope of lifting gas would even be needed. Even better, if there were a rip or tear in the colony no depressurization would take place, only slow diffusion, giving ample time to make repairs. The reason for this is that the pressure inside and outside is almost the same. At 50 km this would take a 1 atmosphere mix of nitrogen and oxygen, but even at 60 km a 100% oxygen 0.2 bar atmosphere could be used to achieve neutral pressure.

Sulfur from the Sky

The atmosphere at these altitudes presents another advantage: the same sulfuric acid clouds that would present a corrosion challenge to any metallic structure also make the region they form in the most hydrogen-rich part of the planet. Venus’s atmosphere is depleted of hydrogen-containing molecules, and the only real source aside from ambient water vapor is the sulfuric acid clouds. Any colony would likely fulfill at least some of its hydrogen needs domestically, by extracting hydrogen-containing substances from the air and clouds. Sulfuric acid is composed of two parts hydrogen, four parts oxygen, and one part sulfur; broken down, it efficiently makes one water molecule (two parts hydrogen, one part oxygen) with three oxygen atoms and a sulfur atom left over. Oxygen can be used as breathing gas and rocket fuel, and the leftover sulfur introduces interesting possibilities.

Elemental sulfur since antiquity has been used as a skin treatment, in the form of a cream used to treat scabies, ringworm, psoriasis, eczema, and acne, among other maladies. Interestingly, the exact mechanism of action remains unknown. This actually seems to be the primary use of elemental sulfur, and since a Venus colony may end up with more sulfur than they know what to do with sulfur creams may be a cosmetic and medical mainstay of Venusian colonists. Venus, named after the goddess of beauty, may yet live up to its namesake.

Combined with other elements, however, sulfur has many other uses, perhaps the most prominent of which is the sulfonamides, a group of antibiotics commonly used in medicine. Many other compounds used in industry and agriculture contain sulfur, suggesting that Venus’s relatively cheap and abundant supply of sulfur may give the colonies a competitive advantage in production of industrial chemicals, at least until Io, with its far greater concentrations of sulfur, is colonized.

Venus: Carbon Powerhouse

Where Venus has a real competitive advantage that will prove durable is carbon; no other place in the solar system has such an abundance of carbon dioxide in its atmosphere. Even at the 50 km level, there is one Earth atmosphere worth of carbon dioxide to extract; production of carbon dioxide on Venus will be as trivial and cheap as nitrogen or oxygen is on Earth. Raw carbon dioxide might find some use, but the real profits will be made through splitting it into carbon and oxygen; once again, oxygen serves as breathing gas and rocket fuel, but the carbon has any number of uses. Carbon fiber, among other carbon-based substances, is already widely used as a high-grade material, and will only become more widespread in the future; if graphene comes anywhere near its widely suggested potential, the demand for elemental carbon in the near future will be voracious.

All Venus’s colonists need to do to get as much carbon as they want is to extract raw air from their planet and split it into its parts, a process likely to prove far cheaper and more effective than that available to any other site in the solar system. The closest thing they will have to competition is carbon extracted from methane in the outer solar system; even in that region there is nowhere near 1 bar of methane to be found anywhere except well below the 1 bar level on Uranus and Neptune, a considerably harsher environment than Venus’s upper atmosphere. These ice giants will be further away from the inner solar system and therefore more expensive to ship from, so Venus may remain the inner solar system’s preferred carbon source indefinitely. The only development that could threaten Venus’s overall carbon hegemony is the center of human population shifting to the outer solar system, which will only occur further in the future.

The competitive advantage gained from this carbon hegemony may be so great as to render carbon extraction, and later as they move up the value chain carbon-based products, the all-dominant industry on Venus. Extracting carbon and manufacturing derived chemicals and materials for export while importing almost all other needs and wants from off-world is a very pleasant economic position to be in, reminiscent of Earth’s Persian Gulf today. Interestingly, the petroleum the Gulf states export is also carbon-based, and Venus even shares an arid climate lacking raw fresh water with these countries.

If the cloud cities of Venus continue further along the Persian Gulf’s path, some cities with more visionary leaders may invest in attempts to diversify their economies beyond carbon. Sovereign wealth funds, as in real life, would play a crucial role in this process, which will see grand and luxurious construction undertaken to attract business and tourism from across the solar system. Dubai is the most famous and most advanced instance of this phenomenon.

Science-fiction worldbuilders don’t often consider incorporating Dubai-style cloud cities on Venus into their settings, but this element is both realistic and rich in possibilities. The sovereign wealth funds alone would provide potential for almost any amount of intrigue across the solar system, let alone the social conflicts between cosmopolitan and conservative elements that would result from visionary leadership attempting to modernize their city. Venus even shares with the Persian Gulf certain strategic significance in the logistics field, as Venus is useful for gravity assists given its position, mass, and frequent launch windows due to its short orbital period; while spaceflight will be cheap enough to obviate this method for anything time-sensitive, it still will be cheaper than using propulsion, indicating extensive use for bulk cargo.

Venus may even have an advantage over the Persian Gulf; being the most habitable extraterrestrial environment in the solar system may be a major tourist draw if nothing else due to the sheer novelty of being able to roam outside in summer clothing while not being on Earth. The sulfuric acid rains will be a hazard necessitating some protective clothing, but when it’s dry you could go outside even without clothing if you wanted, so long as you brought an oxygen tank and breathing mask with you. The only other place in the solar system you could do this is the bottom of Hellas Basin on Mars (the only region where the pressure is enough for water to stay liquid) during summer afternoons; the gas giants and Titan are the other sites that have Earth-like atmospheric pressure, but require high-grade winter clothing.

Space Opera on Venus: unrealistic no more

The real advantage for science-fiction worldbuilding or futurological speculation is, as this post at Rocketpunk Manifesto and the fascinating comment thread demonstrates, the fact that inside an atmosphere like Venus all manner of space-opera and even steampunk tropes become quite realistic. Cloud cities would naturally demand lighter-than-air vehicles, opening the door for zeppelins to make a comeback, only this time in an extraterrestrial sky. Pirates using stealth technology are plausible enough even in open space, but Venus’s context dictates much closer-range swashbuckler-style attacks like those seen in classic science fiction stories. The opaque cloud cover and deep atmosphere would be pretty forgiving terrain for pirate craft.

The cloud cities may all be independent and very competitive much like the kingdoms of Europe in the Age of Sail, and carbon hegemony would engender many Spanish Main-style targets. In this “Pirates of the Cytherean” setting, small birds sitting on the Captain’s shoulder may find a practical use as a “canary in the coal mine” style detector for air leaks aboard ships frequently damaged by weapons fire. Combined with the zeppelins, this has the potential to make a very cool setting.

It has been suggested that the high delta-v may effectively isolate any exiles or dissidents sent there, perhaps making Venus a home of people with strange beliefs that may burst on the wider scene when spaceflight becomes cheaper. Since cheap spaceflight is almost a prerequisite for space colonization and would be developed rather quickly anyway, this stage of isolating exiles in gravity wells if it arises at all won’t last for long. Of course, dissidents might be attracted to building “cloud nine”-style habitats inside atmospheres (candidate planets for this are Venus, Saturn, Uranus, and Neptune) since it may prove relatively cheap compared to, say, a full-fledged O’Neill cylinder.

The actual cloud cities may be air-filled geodesic spheres similar to Buckminster Fuller’s “Cloud Nine” proposal for an airborne habitat on Earth, or may take the form of zeppelin-style gondolas positioned right under a big hydrogen balloon. Over time a kind of modular system may develop as different balloons or geodesic spheres are linked together in the same location. Given the bright sunlight in this region of Venus, both from the sun above and the highly-reflective clouds below, solar power will likely be employed considering there is a large surface area available to put panels or (more likely at this stage) film on. The predominant source of power, however, will likely be nuclear reactors. Solar will not have the power density required for all their needs, and combustible chemicals are scarce. Nuclear reactors also have the advantage of naturally generating a great amount of heat, which can be used to break down the likes of carbon dioxide and sulfuric acid for the colonists’ industrial operations.

Another convenient feature of life on Venus would be the fact that the atmosphere “super-rotates”, meaning the clouds rotate much faster than the surface. This is nice, since the surface famously has a rotational period of 243 days, longer than its orbital period of 225 days. The surface rotation is also retrograde, and due to this the solar day (sunrise to sunrise) is 118 days. The clouds rotate about once every 4 days on average; longer than an Earth day but not interminable. The strong jet streams associated with this phenomenon would assist considerably with navigation, much like Earth’s jet streams do today for our aircraft.

Jetting around Cloud Cities

Venus’s aircraft could use carbon monoxide and oxygen for fuel, as the components could easily be extracted from carbon dioxide as part of the carbon production process. This would take the form of a rocket engine, probably attached to a zeppelin; heavier-than-air craft such as airplanes are of course also possible, particularly for faster transportation. Nuclear reactors could also easily be used to power zeppelins or airplanes, in this case by the simple mechanism of using reactor heat to heat the air as it passes through the jets, thus creating thrust. This is in fact the same principle as the famous nuclear thermal rocket, except you use the ambient air as the working fluid instead of lugging around your own supply. Given the lack of ambient oxygen, the fact that the cloud cities will likely be nuclear-powered anyway, and the likely much more advanced state of nuclear technology at the time of colonization, it seems likely nuclear thermal jets will dominate transportation on Venus.

Since there is an extreme dearth of such elements in the atmosphere, fissile material and the metals needed to build a reactor (and likely the reactors themselves) will all have to be imported, introducing another point of strategic vulnerability for our Venusian colonists. Exports would of course need to be transported off-world, and Venus’s gravity well is nearly as deep as Earth’s. While the unmatched carbon reserves would most likely offset the high delta-v requirements for cloud-city-to-orbit flight, the lack of hydrogen almost rules out the most effective rocket fuel. Oxygen is abundant enough, since it’s found in the native carbon dioxide, but the other abundant elements of carbon and nitrogen don’t react with oxygen very effectively.

Oxygen, can, however, be used on its own as a working fluid for a nuclear thermal rocket, along with nitrogen (which is 3% of Venus’s atmosphere). Nuclear thermal rockets can take you from Earth to orbit but are less effective in atmospheric contexts than hydrogen-oxygen or hydrocarbon-oxygen rockets, therefore they aren’t used much; on Venus they may well be the most cost-effective option available.

Another way would be to split the native carbon dioxide into oxygen and carbon monoxide; this actually makes a feasible chemical rocket, but since it is very inefficient much larger amounts of fuel are required per pound of payload compared to hydrogen-oxygen rockets. This would have the advantage of not needing to use a valuable nuclear reactor to reach orbit, but the reactors could simply be reused by putting the nuclear thermal cloud-city-to-orbit stage in a booster and having it fly back home like SpaceX’s boosters do today. Cloud-to-orbit transportation will be no economic obstacle to Venus colonists.

Conclusion

Most of this has been much closer to speculation about the real-world solar system of the near future than science-fiction worldbuilding, but these speculations should easily awaken science-fiction fan’s imaginations. The storytelling and artistic possibilities of a setting like this, with cloud cities on Venus, already a cool enough concept on their own, harboring luxuries and feats of engineering straight out of the 21st century Persian Gulf while beset by cutthroat and even piratical political intrigue straight out of the 17th century Caribbean, are enormous.

Even better, they are seldom explored in the chronicles of science fiction writing and worldbuilding. This entire premise is relatively recent in origin; “aerostats”, or cloud cities, on Venus was first proposed by Soviet scientists in 1971, but only really took off when it was revived by Geoffrey Landis of NASA starting in the 2000s. The excellent blog posts on the subject by Rocketpunk Manifesto in 2010 and ToughSF in 2016 are actually among the earlier appearances of the concept on the Internet; even this blog post in 2020 could be counted among their number.

Given this backdrop amid the enormous potential of the premise, I strongly encourage anyone with an interest in Venus or these elements that is seeking to create artwork, stories, or worldbuilding settings to pursue these ideas further. It might just prove to be a breath of fresh air and the beginning of a new chapter in the annals of science fiction.

3 Replies to “Worldbuilding Cloud Cities on Venus”

Leave a Reply

Your email address will not be published.