Why We Should Build Cloud Cities on Venus
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Why We Should Build Cloud Cities on Venus

"At 50 kilometers up, Venus is remarkably Earth-like, excluding the need for any serious terraforming projects."

Geoffrey Landis, 59, of Columbus, Ohio, is a scientist and prolific science fiction writer. Last year, he was the recipient of the Robert A. Heinlein Award, given in honor of the sci-fi author; in 1992, he was awarded a Hugo, the sci-fi equivalent of the Pulitzer, and in 2011, he received a Hugo nomination for a short story entitled "The Sultan of the Clouds." A sci-fi tale with the sepia tints of Heinlein and Arthur C. Clarke, "Sultan" tells the story of a technician living on Mars named David Tinkerman as he accompanies his secret crush, the scientist Leah Hamakawa, on a mysterious voyage to the second planet from the Sun. Upon entering the atmosphere, Tinkerman describes what he sees:


           "The surface of Venus is a place of crushing pressure and hellish temperature. Rise above it, though, ​and the pressure eases, the temperature cools. Fifty kilometers above the surface, at the base of the clouds, the temperature is tropical, and the pressure the same as Earth normal. Twenty kilometers above that, the air is thin and polar cold.
           Drifting between these two levels are the ten thousand floating cities of Venus."

The first paragraph is completely accurate. The second is not, of course, but Landis, who has worked as a scientist at NASA for 26 years, has spent the last decade and a half attempting to change that.

A comparison of Earth and Venus, sometimes called "Earth's twin" for its similar size. Image: NASA

Venus's gravity is 90 percent of Earth's, and it's easier to get to than Mars, reachable in just five months as opposed to nine for Mars.

At NASA, the idea of sending humans to Mars and Venus was first proposed in the run-up to Neil Armstrong's historic moonwalk, during the Apollo program, when the space agency was giddy with exploration and rich in funds. Public support for the space agency was also on its way to heights it would never otherwise reach. It  had begun sending probes to Venus in 1961, as part of the Mariner program. For ​the human​s-to-Venus proposals, which would repurpose Apollo hardware, engineers determined that the three astronauts on board would only have time for between 45 minutes and two days for close observations. Even with nuclear engines (also theoretical) this wouldn't be enough time to make the 400-day trip worth it. Going the extra distance to Mars, meanwhile, was considered practically impossible. To explore these planets, robots would have to be enough.


Landis, who wears a beard beneath a swoop of reddish-brown hair, joined NASA two decades after Apollo, at the end of the Reagan era, and two years after the Challenger disaster rocked humanity's resolve to explore space. After receiving his Ph.D. in physics from Brown University, Landis worked as a postdoctoral researcher at NASA, as a senior scientist at the Ohio Aerospace Institute, and served as a visiting professor of Astronautics at MIT.

Landis is now a civil service scientist in the Photovoltaics and Power Technology branch at NASA Glenn, where he has worked on the teams responsible for landing both the Spirit and Opportunity rovers on Mars. He's also patented eight photovoltaic device designs, developed laser sail propulsion systems for interstellar travel, and collaborated on a project aimed at putting a submarine on Titan as part of NASA's Innovative Advanced Concepts program.

At a conference on space exploration in Albuquerque in 2001, Landis delivered a presentation that has since linked his name with a small sect of space scientists who have seriously considered the human exploration and colonization of Venus.

To begin to explore the cloud planet—nicknamed for the thick swaths of carbon dioxide and sulphuric acid that encircle it—Landis proposed a solar-powered airplane that could navigate the atmosphere and even a land-sailer that could survive the planet's extreme surface climate. He developed the concept in more detail at another conference in 2003, where he claimed that "robotic exploration of Venus could potentially lead to the development of a human mission to explore the clouds of Venus by aircraft," concluding that "ultimately we could even envision colonization of the Venus atmosphere."


Landis' early proposals for exploring the Venusian atmosphere by way of large balloons and solar powered airplanes, as implausible as they may seem, have recently inspired other researchers at NASA to explore the idea. In October, Dale Arney and Chris Jones, a pair of NASA scientists based in Langley, Virginia, completed a study for an idea they call the High Altitude Venus Operational Concept. HAVOC proposes that an ​initial manne​d mission orbit Venus for a length of 30 days, before making ​an attempt at living a​bove the hellish planet. The video that accompanied the report, viewable below, garnered over half a million views on YouTube.

The Argument for Venus

These ideas of course fly in the face of conventional wisdom, which holds that humanity's next space habitat should be on the surface of Mars or in free space—places where Earth's particular environment can be approximated for the benefit of human explorers. But the atmosphere of Venus, Arney and Jones argue, is "probably the most Earth-like environment that's out there."

Up in its clouds, temperatures are more Earth-like, and due to its size—roughly the size of Earth—the planet boasts a gravitational pull that's only 90 percent of Earth's, something which would be immensely energy-intensive and mechanically complex to simulate elsewhere. This is what earned Venus its other nickname: Earth's twin.

Venus is also easier to get to than Mars. You can travel to Venus in five months whereas Mars takes nine. If you're taking the shortest path, opportunities to travel to Venus come once every 1.6 years, whereas the optimal window for Mars comes every two years.  Moreover, while both planets boast ample amounts of volatile life-sustaining materials like hydrogen, carbon and nitrogen, only Venus's dense atmosphere would be helpful in shielding human colonists from the harsh assault of solar radiation. Mars, meanwhile, has almost no atmosphere, leaving the Red Planet in a deep freeze and putting future Martian colonists in danger of irradiation.


An image from Landis's 2003 paper

The thickness and high CO2 content of Venus's atmosphere has also transformed its surface into a veritable furnace. During daytime on Venus, temperatures normally reach over 900 degrees Fahrenheit, hot enough to melt lead. At ground level, atmospheric pressure is 92 times greater than Earth's, equivalent to pressures found at nearly 3,000 feet below Earth's oceans.

It is precisely this complex, inhospitable environment (and our relative ignorance as to how it came to be this way) that calls for closer exploration of the planet. Venus's boiling environment and carbon-rich atmosphere offers the solar system's best example of global warming in the extreme. Scientists theorize that as recently as one billion years ago, Venus used to be much cooler, a hospitable desert planet. But a number of hypothesized events, such as the halt of plate tectonics some 700 million years ago, could have contributed to a massive buildup of carbon in the atmosphere, heating Venus up to hellish temperatures and evaporating the oceans that may have once existed there.

By the late 1970s, NASA climate modeler James Hansen concluded that the CO2 combined with sulfate aerosols in the atmosphere were "responsible for the basic climatic state on Venus." This was instructive for Earth, Hansen wrote, because sulfates and CO2 were increasingly being emitted by human industry, contributing to the buildup from more natural emission sources such as volcanoes. (Hansen's would be one of the loudest and earliest voices of concern  ​ab​out the effects of atmospheric carbon dioxide on Earth's climate)


The double vortices at Venus' south pole. Image: ESA

"Certainly Venus is a prime example of a greenhouse effect planet—maybe it's the future of the Earth, but the far, far future of the Earth," said Landis. Regardless, "we learn about our planet by learning about other planets, and we learn to live on our planet by living on other planets."

The exploration of Venus began in earnest in 1961 when the Soviet Union launched Tyazhely Sputnik (otherwise known as Venera 1VA No. 1), a mission to send a fly-by probe to Venus. The rocket exploded before it even left Earth's atmosphere. In 1962, NASA's Mariner 2 revealed that heat radiation detected by telescopes was coming not from the planet's atmosphere but from its hot surface. "It was very disappointing to many people," one of the discoverers recalled, "[they] were reluctant to give up the idea of a sister planet and perhaps even the possibility of life."

In 1966, after several more failed attempts to get its program off the ground (or somewhere near Venus) the Soviets finally succeeded in putting the first man-made object on another planet, when Venera 3 crash landed on Venus. On December 15, 1970, Venera 7 touched down on the planet's surface relatively intact and became the fi​rst probe to transmit data from the Venusian surface. Given the extreme environment, it didn't last very long.

An image of the surface taken by the Soviets' Vanera 13 lander in 1981. It survived 127 minutes. 

"The surface environment of Venus is a warning," Carl Sagan wrote. "Something disastrous can happen to a planet rather like our own."


Landis traces his own pursuit of Venus to a paper published in 1961—the year that the Soviets began Venera—by another scientist and fabulist. That year, the young planetary astronomer Carl Sagan, then a doctoral student working at NASA's Jet Propulsion Laboratory, where he contributed to the first Mariner missions to Venus, published an article​ in Science entitled "The Planet Venus." In it, he put forward the first serious proposal to colonize Earth's twin.

To start, Sagan advocated bombing the upper Venusian atmosphere with genetically modified blue-green algae. The idea was to reduce the carbon-dioxide-saturated atmosphere to a level conducive to supporting terrestrial life. According to Sagan, the algae (specifically harvested from the Nostocacae family) have been known to survive immersion in liquid nitrogen and in hot springs whose temperatures sometimes exceed 80 Celsius, making them ideal candidates for weathering the extreme atmospheric conditions found on Venus. These algae are also known to be capable of photosynthesizing "evolving molecular oxygen," suggesting that they would be able to perform the crucial task of dissociating carbon dioxide into oxygen and elemental carbon, significantly lowering the planetary temperature and allowing for photosynthesis in green plants.

Sagan's lofty geoengineering proposal didn't make it very far. "It was a wonderful, radical notion for 1961, but they were only just beginning to understand Venus," said Landis. [Sagan] didn't quite understand how thick the atmosphere of Venus really was. He was one of the first to understand that Venus had a very thick carbon dioxide atmosphere," but they didn't quite understand that it was 92 times denser than the Earth's atmosphere. You just can't convert that much carbon dioxide into oxygen."


Three decades later Sagan himself declared the idea "fatally flawed." But he still thought Venus bore important lessons for Earth. In his 1980 book Cosmos, Sagan mused on the "goldilocks" quality of Earth by pointing to the effects that carbon dioxide had had on Venus's climate:

          Like Venus, the Earth also has about 90 atmospheres of carbon dioxide; but it resides in the crust as limestone and other carbonates, not in the atmosphere. If the Earth were moved only a little closer to the Sun, the temperature would increase slightly. This would drive some of the CO2 out of the surface rocks, generating a stronger greenhouse effect, which would in turn incrementally heat the surface further. A hotter surface would vaporize still more carbonates into CO2, and there would be the possibility of a runaway greenhouse effect to very high temperatures. This is just what we think happened in the early history of Venus, because of Venus' proximity to the Sun. The surface environment of Venus is a warning: something disastrous can happen to a planet rather like our own.

The Terraforming Options

As outlandish as Sagan's plans for "microbiological planetary engineering" may seem, a number of other proposals have surfaced in the five decades since, calling for a complete reverse of the planet's greenhouse effect. In his 1981 book New Earths, James Oberg proposed making Venus habitable by removing 98 percent of its atmospheric mass by displacing 10 quintillion tons of CO2 into outer space. According to his calculations, if such a project were designed to take place over a time span of 100 years, this would involve the removal of roughly 300,000 tons of gas per second. By comparison, the Amazon moves roughly 10,000 tons of water per second.


In more expansive visions, pumping Venus full of sulfur dioxide or hydrogen—or surrounding it in Sun shields—could terraform its climate into submission. 

In 2010, the Nobel prize-winning atmospheric chemist Paul Crutzen proposed releasing massive amounts of sulfur dioxide high in the Venusian atmosphere, which he argued would lower surface temperatures and slow the runaway greenhouse effect by re-creating conditions similar to a massive volcanic eruption on Earth. The idea echoed his now famous proposal for Earth: pumping gas into the atmosphere to stave off the effects of global warming—a kind of plan B for the climate that helped propel the geoengineeri​ng craze.

In the early 1990s, a scientist named Paul Birch propose​d a different terraforming approach to Venus's CO2 problem: infusing the planet's atmosphere with 40,000,000,000,000,000,000 kg of hydrogen obtained, somehow, from the gas giants Jupiter and Saturn. According to Birch, the hydrogen would react with all the excess carbon dioxide in the atmosphere in a process called a Bosch r​eaction, producing elemental carbon and incredible amounts of water—by his estimate, enough water to cover 80 percent of the Venusian surface. This process would reduce atmospheric pressure to a mere 3 bar, roughly three times that of Earth, and this nitrogen rich atmosphere would continually decrease in pressure as the nitrogen dissolved into the newly created oceans.


"The other idea Paul Birch had was to put sun shields around Venus so you freeze the atmosphere out, and that's really a wild notion," said Landis. Birch's freezing process involves massive slatted solar mirrors placed at a lagrang​ian point between Venus and the Sun. These mirrors would serve a dual purpose of generating solar power and reflecting excess sunlight away from the planet, lowering the surface temperatures there. But among gigantic visions, these are goliaths. "Paul Birch has some wonderful, far-reaching ideas on how to terraform planets—he really was a futuristic thinker," Landis told me. "But I'm thinking that Paul may be a little optimistic."

The Cloud Options

In Landis's more down-to-Earth vision, humanity's place on Venus will not be on the planet's surface but instead dozens of miles up in the planet's thick cloud cover. "My idea is, don't even try to terraform the surface, just build up from the surface," said Landis. "I don't know if biological solutions are out of the question, but I just think the sweet spot on Venus, the spot you really want to focus on, is 50-60 kilometers out—let's start with floating cities."

He conjures the poetry of something like this in "The Sultan of the Clouds," when his protagonist first pierces the planet's atmosphere:

          "A hundred and fifty million square kilometers of clouds, a billion cubic kilometers of clouds. In the ocean of clouds the floating cities of Venus are not limited, like terrestrial cities, to two dimensions only, but can float up and down at the whim of the city masters, higher into the bright cold sunlight, downward to the edges of the hot murky depths… The barque sailed over cloud-cathedrals and over cloud-mountains, edges recomplicated with cauliflower fractals. We sailed past lairs filled with cloud-monsters a kilometer tall, with arched necks of cloud stretching forward, threatening and blustering with cloud-teeth, cloud-muscled bodies with clawed feet of flickering lightning." 


At 50 kilometers up, Venus is remarkably Earth-like, excluding the need for any serious terraforming projects. The atmospheric pressure is a comfortable one bar, the gravity about 90 percent that of Earth's, and temperatures fall within a hospitable range of 0-50 degrees Celsius."

These cities would be hovering near the top of Venus' cloud layer, allowing them to reap plenty of sunlight for solar energy during a typical Venusian day, which lasts around 117 Earth days. Although humans would still have to grapple with a host of uniquely Venusian environmental factors—200 mph winds circle the planet every two days in a process known as "super rotation," whipping up clouds of sulfuric acid in their wake—finding technical solutions to these variables are relatively simple when compared with the task of trying to pump an entire planet's atmosphere out into space.

The most recent concept for floating cities over Venus, part of a "side project" at NASA's Systems Analysis and Concepts Directorate in Langley, Virginia, calls for spacecraft to enter the Venutian atmosphere and deploy smaller blimps, but it follows a similar concept to the idea outlined by Landis.

In the HAVOC proposal, 129-meter-long blimps would be deployed after entering Venus's atmosphere and later form the basis for larger floating habitats. Image: NASA

Although Landis' plans predate the Langley proposal by over a decade, he sees the two not so much as competing propositions but as two different concepts toward the same aim: placing humans on Venus. "Their work is a little more focused on the initial phases of exploration," said Landis. "We're definitely thinking along similar directions, but I can't claim credit for their work. They've done a lot of work on filling in the details for the initial concepts for early missions."


To the Langley scientists, Landis's idea was an inspirational precursor. "For a long time now, his ideas have been the source of human Venus exploration concepts," Dale Arney, who co-authored the HAVOC proposal, told me. "We read one of his papers and we decided it would be a cool idea to look into, to actually see what would be required for that type of mission to be feasible."

Landis' initial proposal for Venusian sky cities was much broader in scope than the HAVOC mission, involving the construction of massive aerostat habitats floating 30 miles above the surface of the planet. These would serve as 'forward operating bases' for surface missions and relay stations for interplanetary travel. In essence, these cities would exist in massive floating envelopes of breathable air, a mixture of oxygen and nitrogen which would act as a lifting gas in Venus' carbon dioxide atmosphere.

"You'd really have to do this for the long term exploration of space. This is where the future is. We're moving out into the solar system." —Dale Arney

What about the prospect of entire colonies plummeting dozens of miles to the surface while burning up in clouds made of sulfuric acid? Landis didn't seem too phased.

"Well of course anything humans do has some risk," he said. "But you'd want to make your cities quite robust. Obviously, the larger a balloon is the more time you have to deal with a leak. If you have a tiny balloon, a child's balloon, it pops instantly. You'd want a giant balloon with multiple different chambers in it [for these floating cities]. It'd be huge compared to any balloon we've ever had on earth. It would absolutely dwarf the Hindenburg."


The exploratory ships proposed for the HAVOC mission would be 130 meters in length, the equivalent of two Boeing 747s placed end to end, which is still only roughly half the length of the Hindenburg. Landis's vision calls for habitats orders of magnitude larger. The aerostat habitats he imagines would be comprised of multiple balloons, each up to a kilometer in diameter, capable of supporting tens of thousands of people. ​

To put this in perspective, a balloon that is one kilometer in diameter is capable of lifting about 700,000 tons, or the weight of two Empire State Buildings. Add a second balloon of the same size and the lift capacity of these two balloons increases exponentially: it's now capable of supporting nearly 6 million tons of weight. In fact, these balloons would actually be easier to keep afloat in the Venusian atmosphere than on Earth given that gravity tends to be slightly weaker on Venus.

In "Sultan of the Clouds," Tinkerman and Hamakawa watch the city of Hypatia appear through the clouds:

          "The city was a dome, or rather, a dozen glistening domes melted haphazardly together, each one faceted with a million panels of glass. The domes were huge, the smallest nearly a kilometer across, and as the barque glided across the sky the facets caught the sunlight and sparkled with reflected light. Below the domes, a slender pencil of rough black stretched down toward the cloudbase like taffy, delicate as spun glass, terminating in an absurdly tiny bulb of rock that seemed far too small to counterbalance the domes."
          'Beautiful, you think, yes? Like the wonderful jellyfishes of your blue planet's oceans. Can you believe that half a million people live there?'"


Despite the warm public reception for the HAVOC proposal and his own buoyant optimism, Landis acknowledges the chances of a manned mission to Venus in the near future are remote. Funding for U.S. moon missions petered out by 1973; NASA's overall budget shrunk from a peak of $5.9 billion in 1966 to a low of $3.2 billion in 1974. As a percentage of federal spending, it conti​nues to shrink: in 1966, NASA made up 4.4 percent of all federal spending. Now it's around 0.5 percent.

"As with all missions, money and politics are the real problems. I think we could do it, technically, although there's a lot of detailed engineering work that needs to be done. It's getting the political buy-in that is tough," said Landis. "My belief is, we need to go out and colonize the solar system but politically we can't do anything without a consensus on our direction."

Why, if Venus is so promising, does the Red Planet steal all the attention? In an ironic twist, this may have to do with the rovers Landis has already helped land there. "I think [Venus] tends to be ignored possibly because the images we're getting from Mars are so spectacular," he said. The best way to build the political and economic support needed for manned missions to Venus is simply sending more robots there to begin with.

"I think if you're going to send humans you're going to need some more robotic probes exploring the environment in great detail," Landis said. His solar plane concept could help. "I think we could do the solar plane with technology we have now. We'd need a little work in developing it, but it's definitely a do-able project and we could be looking at the Venus upper atmosphere." A rover would also help: "What we need is to put some missions onto Venus that have as much capability—and as good cameras—as the recent missions to Mars, to get people really excited."

The HAVOC team, meanwhile, has effectively disbanded.  The extra time allotted for Arney and Jones's "little side project" by Langley's Systems Analysis and Concepts Directorate has expired, and the two have returned to the directorate's Space Mission Analysis Branch, helping to design and oversee current solar system exploration.

"Currently Chris and I don't have any imminent plans to do any work in this specific area, but there certainly are plenty of opportunities to explore for robotic missions and things like that," said Arney. "A rigorous robotic campaign is needed, similar to what we've been doing with Mars for the last couple of decades. So really that would have to start picking up. Science proposals for Venus missions will have to get in the works."

So far, the HAVOC team hasn't received any sort of feedback from the current administration or from members of Congress regarding their study. "I can't really speak to the politics and how all of that is going to change, but right now Congress and the President are pretty focused on the asteroid redirect a​nd Mars missions."

In spite of the immediate bearing on our scientific understanding of climate change, Arney admits there isn't much short-term economic (or military) incentive to send a manned mission to the planet.  "It's hard to give Venus exploration a good economic rationale at the moment, I'm afraid," he said. "I think you have to do that with more long term, or even more—if I dare say it—idealistic motives. You'd really have to do this for the long term exploration of space. This is where the future is. We're moving out into the solar system."

Yet scant economic incentive isn't the same as no economic incentive. While Venus might not be a goldmine, there are fiscally compelling reasons to give colonizing the planet serious consideration, especially in the long term.  "On the surface [of Venus] there are a lot of resources but it's pretty expensive to get down there to potentially mine those resources, so we primarily focused on what you could get out of the atmosphere, like nitrogen and carbon dioxide," Arney said.

"Economically I'm not sure what kind of market there would be in the near term for those [atmospheric] resources," he added, "but if you think in the long term where humans are a multi-planet species, readily available atmospheric resources would be useful."

Notwithstanding a future market for nitrogen, Arney thinks that private companies, firms like SpaceX and Boeing, also have a role to play in developing the technology for future NASA missions to Venus.  "Traditionally robotic missions have used commercially available launch vehicles, so I could see that as a place where the private sector might be involved [in Venusian exploration]," he said.

Landis sees a wealth of work to do in the immediate future in order to pave the way for more exploration of Venus. In the meantime, he credits the Langley team for reigniting interest in the cloud planet, and laments the fact the last attempt to drop a probe into its atmosphere was made by the Soviet Union.

"You always have to start with this brainstorming and then move beyond the brainstorming into the engineering details," said Landis. "But simultaneously I think we do have to stop neglecting Venus as a target for science missions. Let's go back with modern technology—let's explore the atmosphere and this planet pole to pole and see what it's all about. I think this would help us get the same feelings for exploring Venus as we have for Mars."

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