A 1969 Star Trek episode features a floating sky city called Stratus, whose residents believe they are superior to people who live down on their planet’s surface, but real humans advocating for off-world colonization today may suffer from a prejudice opposite that of the fictional Stratus dwellers. I’m talking about ‘surfacism’, the idea that reaching a new world, or living there, is more meaningful if humans set down on that world’s solid surface.
Don’t think we’re surface prejudice? Then, tell me the names of the astronauts who flew to the Moon on Apollo 10, without Googling. Launched May 18, 1969, this NASA flight took Thomas Stafford, John W. Young, Eugene A. Cernan into orbit around the Moon. Stafford and Cernan then boarded the lunar excursion module (LEM) ‘Snoopy’ and descended to within 16 km of the lunar surface. They demonstrated everything that needed to be done for the landing of Neil Armstrong and Buzz Aldrin two months later, so the mission was an enormous success. It had numerous firsts. But they did not touch down, did not walk on the surface, did not plant a flag on the lunar surface.
Nearly half a century later, some of us are engaged in serious talk about establishing a human presence off the Earth –not merely a few scientists rotating onto the International Space Station (ISS) and back to Earth like scientists visiting Antarctica, but a colony. Billionaire entrepreneur Elon Musk is working to create a human settlement on Mars. His goals are shared by various human organizations, particularly the Mars Society.
When it comes to Solar System exploration by government organizations, such as NASA and the European Space Agency (ESA), the number of missions and the amount of resources devoted to Mars far outweighs programs to explore other potential homes for a human colony, such as Venus. And when it comes to culture, there is a long history of human focus on the Red Planet. A fair number of novels and films imagine human Mars missions and colonies in the future; actually, they assume it will happen. The 2015 film The Martian, for instance, presented a vision of how a human Mars mission might be carried out, a vision that was very accurate scientifically, except for one thing. In real life Mars expeditions, astronauts would be stationed far underground.
Living in an underground bunker will be a reality of life on Mars, unless humans terraform the planet, but doing so could take centuries, so generations of colonists would be living in bunker conditions. Along with radiation, there’s a gravity issue. Your weight at the Martian surface is 38 percent what it is on Earth. This causes de-conditioning of bones, the cardiovascular system, and other body systems, and we should be able to deal with it for astronauts traveling to Mars and returning to Earth. But it could make the Red Planet inappropriate for families and those wishing to become ancestors. It may or may not be possible for someone who grows up on Mars to visit Earth, and that may be a secondary issue to boot. For we don’t know yet if human fertility will be adequate and pregnancy will be normal in a 0.38 G field.
Mars has other problems. The regolith –the dirt that covers the Martian surface– contains high concentrations of perchlorate salts, which will be toxic to humans and plants if we don’t filter them out. The low gravity and the thin atmosphere advantageous as they make it easy to get spaceships up and down between the surface and space. But while the atmosphere is too thin to provide any useful air pressure on the human body, it is just thick enough to lift dust to mess up equipment and there are even dust storms.
Considering all of this, a minority of space enthusiasts have been advocating consideration of an alternative to Mars, namely Venus. Serious consideration started in 2003 when NASA’s Geoffrey Landis delivered a paper on how a colony could thrive in a certain altitude range in the Venusian atmosphere. Popular thinking is that the most Earth-like environment in the Solar System is Mars, but that’s true only if you consider planetary surfaces.
The surface of Venus is not livable. The few Russian probes that have attempted to land there have imploded due to air pressures in the area of 92 times that of Earth at sea level. Then after they imploded, they melted, because the Venusian surface temperature is like a pizza oven. Venus is even hotter than Mercury, because of its thick atmosphere consisting of mostly carbon dioxide, a greenhouse gas.
But that same carbon dioxide could allow us to build a real life Stratus, a cloud city. If you forget about solid surfaces, the most Earth-like place in the Solar System is in the Venusian atmosphere about 50-60 kilometers high. Carbon dioxide is heavier than oxygen and nitrogen that makes up our breathing air. This means that if you fill a dirigible with regular air, it will float at around 50 km altitude on Venus. That gets you out of the pizza oven while providing an air pressure nearly that of sea level Earth. It also is low enough for the atmosphere to shield against most of the space radiation, so Venus colonists would get roughly the same exposure they get on Earth.
The main problem is that the temperature at 50 km is still a little high, roughly 70 degrees C, so, to prevent having to use massive amounts of power for air conditioning, colony builders might want to add a little more buoyancy (perhaps with helium in place of some of the nitrogen) to increase altitude to 52.5 km, where temperature is a balmy 25 degrees C (~77 F). The drawback is that would increase the radiation somewhat. It also would decrease the atmospheric pressure, so the percentage of oxygen in breathing gas might need to be higher than the usual 21 percent. This would be a fire hazard if increased more than a couple of percentage points, so the altitude chosen may need to be a compromise somewhere between 50 and 52.5 km. One more problem is corrosion. The clouds where the real-life Stratus would be floating are made of sulfuric acid, so the outer skin of the colony would need to be made of specially engineered material.
Even if the travel time doesn’t shorten, Venus offers another perk. It’s closer to Earth than Mars, so even with chemical propulsion, one can get there in 100 days or so, as opposed to 150-300 days to get to Mars. Finally, being closer to the Sun, Venus would offer colonists more solar energy compared with Mars. Considering these things, our sister planet may start to look more palatable, so long as we can engineer corrosion-proof buoyant cities, work out a way for spaceships to land on such floating structures, and finally, perhaps most important, if we could just get over our ‘surfacist’ mentality.
Written by David Warmflash
David is an astrobiologist and science writer. He received his M.D. from Tel Aviv University Sackler School of Medicine, and has done post doctoral work at Brandeis University, the University of Pennsylvania, and the Johnson Space Center, where he was part of the NASA's first cohort of astrobiology training fellows. He has been involved in science outreach for more than a decade and since 2002 has collaborated with The Planetary Society on studying the effects of the space environment on small organisms.