Venus sure has it tough.
Before the Soviets landed their probes on Venus and found out about the hellish conditions the hard way, we thought of Venus as a tropical planet, hidden from telescopes by its clouds. Today, we know better. With Mars getting all the attention as a potential first colony location, Venus can only lurk in shame.
Some people think different, though. If the history of ideas is any guide, the conventional wisdom cannot be trusted to hold in the future. Mars may have all the hype now, but that doesn’t mean it *will* be the first planet to host an extraterrestrial colony. Despite the talk about Mars being the planet most similar to Earth, it is still quite hostile. The temperatures range from +20 degrees C (only 68 F, at noon, in summer!) to -130 C at night. Even the South Pole would be a safer place to be, and we don’t talk about colonizing Antarctica, do we?
It turns out that there is another place in the Solar System that has conditions very similar to these on Earth. Notice that I am talking about a specific place, not a planet in general. If you think only in terms of bulk planets when choosing a colony location, you may as well throw up your hands because there are NO planets anywhere in the Solar System that come close to having Earthlike conditions.
Except for one. Venus.
Wait, what, you say? Venus with the lead-melting surface conditions? Venus with the rocks that glow red-hot at night? Venus with the atmospheric pressure that could float a submarine?
It’s true that the Venusian surface is a hellish place to be. But fifty kilometers up, the picture is very different. High in the atmosphere, the pressure is the same as that at Earth’s sea level (1 bar) and the temperature hospitable (0 – 50 degrees C). At Venus’ distance from the Sun, it gets twice as much sunlight as Earth does, and the sulfuric acid clouds are very reflective so any solar panels pointing down would get nearly as much light as those facing upward. There’d be no need for thick pressure hulls and spacesuits, but protection against sulfuric acid droplets would be necessary. This is merely a matter of selecting nonreactive materials, such as glass.
So we’d need a floating structure. That may seem unsafe for a long-term colony, but once again the conventional wisdom can be deceptive. Venus’ atmosphere is 96% carbon dioxide – a heavy gas. The molar mass of CO2 is 44 g/mol, compared to 28 g/mol for N2 and 32 g/mol for O2. What we call “air” on Earth would be a lifting gas on Venus – a lifting gas that we can also breathe. If the pressure differential between inside and out is small, the lifting envelope can be made very large. Our hypothetical “cloud city” would not even need to be suspended under the lifting envelope like a traditional balloon would – it could be inside the envelope!
Because the outside atmospheric pressure would be the same as that inside, any tear in the lifting envelope would result in the gases diffusing at normal atmospheric mixing rates, giving plenty of time to repair the damage. It would take a very long time for signs of carbon-dioxide poisoning to show up in the population. Unlike a Moon or Mars colony, there is simply no risk of rapid decompression. Overall, a Venusian floating colony would require less exotic engineering than a Moon or Mars colony and be more healthy for its inhabitants due to the more Earthlike gravity and thick atmosphere that blocks out radiation.
But Why Do It?
Throughout history, people built colonies for many reasons, chief among them the desire for an economic return. This won’t be an exception. So what’s on Venus that people would pay to use somewhere else? Sulfur, either in its pure form or as sulfuric acid, would be one. Sulfuric acid has many industrial uses. Carbon is another possible export, owing to its ability to form graphene, fullerenes, and diamond. Venus would be an even better exporter of carbon and sulfur than Mars because of 3 things:
Location – Venus is closer to the Sun, so it moves faster in its orbit. This opens up more opportunities for transit from there to anywhere else in the solar system. In other words, it has a shorter synodic period with other bodies than Earth or Mars. Venus’ greater orbital velocity also acts as a catapult for spacecraft on journeys outward from the sun, making for reduced transit times.
Abundance – Venus has simply more sulfur in its different forms (sulfur dioxide, sulfuric acid) in its atmosphere than the Moon and Mars have in their soil. Atmospheric extraction is a lot easier than ground extraction and processing. For carbon dioxide, Venus has Mars beaten (95 bar vs. a puny 0.00636 bar).
Power – Venus has twice the solar insolation (2603 vs. 1370 W/m2) of Earth, and over four times that of Mars (2603 vs. 600 W/m2). The extra electrical and thermal power does away with the need for extra receiving area and makes industrial processing easier. Unlike on Mars, nuclear power will be unnecessary in a Venus aerial colony.
I don’t expect Venus to become an exporter of metals because all the available ores are located on the surface where the pressure is 95 bar and the temperature rivals that inside a self-cleaning oven. The Moon and asteroids would be better sources of metal. However, even if the carbonaceous asteroids turn out to be easier/cheaper sources of carbon and sulfur, Venus still has value as a base for asteroid mining operations.
On first sight, it may seem obvious that a Mars or Ceres base would be better for asteroid mining because well, they’re close to the belt, right? But astrodynamics is often counterintuitive. An asteroid in the belt is not necessarily close to Mars or Ceres. It could be on the other side of the Sun. Paradoxically, the more similar two orbital periods are to another, the fewer opportunities there are for a trip to occur. As I said before, Venus’ proximity to the sun gives it a faster orbital velocity, which has two effects: increasing the synodic period (more transit opportunities) and boosting the velocity of any outbound spacecraft.
Life in the Cloud City
The upper Venusian atmosphere is the only place in the solar system other than Earth where all the elements needed for life – H, N, O, C, and S – are abundant in conditions that are comfortable for humans. Oxygen gas can be created by splitting carbon dioxide. Water and hydrogen can be obtained by processing sulfuric acid – a trivial task. 3.5% of the atmosphere is nitrogen, which can simply be separated and concentrated using well-understood techniques in use on Earth. Any leakage losses in the habitat or lifting envelope could simply be replenished by processing a little more of the atmosphere.
A Venusian aerial colony would be a terrific place for agriculture. There’s plenty of sunlight, and a 24-hour day-night cycle could be achieved by placing the colony at a high latitude so the winds push it all the way across the planet in a day. Any trace metals that plants need could be dredged up from the hellish surface.
With carbon dioxide being so abundant on Venus, the production of pure carbon will result in the byproduct of massive quantities of oxygen. That oxygen will be dumped back into the atmosphere, gradually reducing the greenhouse effect that’s making Venus such a hellhole.
How It Could Happen
Obviously, the devil is in the details. As I’ve shown, a Venus colony probably won’t happen until there is enough mining of the asteroids to justify operations from Venus. It is definitely possible to package a small aerostat habitat inside an aeroshell and deploy it in the atmosphere, but a huge lifting envelope for a city-sized vessel requires some more thought.
It’s still too early to tell how much of a role Venus will play in the expansion of humanity into the solar system. I’ve only scratched the surface in this post. A more in-depth analysis would probably take a book. A serious comparison of Mars vs. Venus as a colonization target requires the use of numbers. Much effort has been spent on coming up with concepts for Martian colonization, but almost none for Venus. This needs to be changed if we are to have a conversation about the pros and cons of either planet.