Welcome to Cloud City: The case for going to Venus, not Mars

Welcome to Cloud City Why future generations may prefer floating above Venus to colonizing Mars by Chris Taylor NOTE FOR 2020 READERS: This is the 12th in a series of open letters to the next century, now just 80 years away. The series asks:...

Welcome to Cloud City: The case for going to Venus, not Mars

Welcome to Cloud City

Why future generations may prefer floating above Venus to colonizing Mars

by Chris Taylor

NOTE FOR 2020 READERS: This is the 12th in a series of open letters to the next century, now just 80 years away. The series asks: What will the world look like at the other end of our kids' lives?

Dear 22nd Century,

Is there life on Mars?

Human life, I mean. Or does a pioneering percentage of you have your heads in the clouds of a closer planet instead?

It’s not the sort of thing we take surveys about, because we’ve got a lot on our political plate right now. But if you were to ask the average 21st century Joe which planet we are most likely to establish permanent habitation on first, Mars would win in a landslide. It’s just a given. It’s NASA’s official plan — has been ever since the first President Bush announced we’d land on the planet by, ahem, 2019 — as well as Elon Musk’s highly theoretical plan for 2024. We’ve watched and read The Martian, cheering for deposits of ice and potatoes grown in Mars' barren soil.

We didn’t pay so much attention to the downsides of trying to settle so far from home. We ignored reports of toxic sands on the red planet that might poison human visitors, let alone our potatoes. We didn’t really consider the surface radiation problem, or the minimum 260 days of cosmic radiation that will bombard (and could really mess up) astronauts' brains on the way there. So much radiation, in fact, that it could double their risk of getting cancer over a lifetime.

But what if there were another option? What if there were a planet you could travel to in roughly half the time? One that is increasingly full of mystery —and that is, due to the weird nature of orbital dynamics and slingshot maneuvers, actually on the way to Mars? What if we didn’t set foot on this planet —avoiding all the overtones of Martian “colonization,” a word that is being widely reconsidered in a year when we’re tearing down Christopher Columbus statues — but simply floated above its cloud layer instead?

Step out of the shadows, Venus, your time has arrived. 

Over the last decade, planetary scientists have started beating the drum for more Venus missions. Partly, this is because we keep discovering more mysteries about our sister planet — strange dark spots, active volcanoes, and a three-billion year period where it had liquid water and potentially life. Partly it’s because we keep finding exoplanets in what’s known as “the Venus zone” around other stars — two more were discovered as I wrote this — and would love to know what makes them tick. (Oh yeah, and scientists may have some urgent interest in studying a planet with a greenhouse effect caused by carbon dioxide. Can’t imagine what that reason might be.)

And we are most definitely heading back there, after a long lull. India, Russia, and Europe are all looking at launching Venus orbiters in the next decade. In February 2020, just before the coronavirus pandemic hit, NASA announced that two Venus missions had been shortlisted for its next Discovery mission, to be announced in 2021. 

“I haven’t seen the Venus community this energized for years,” says Noam Izenberg, a veteran planetary scientist at John Hopkins University. “It’s a groundswell for more missions. It’s got real momentum.”

And then there’s the fact that NASA scientists, five years ago, produced a little-known plan that treats Venus “as a destination for humans to reside.” Still conceptual in our age, but a possible reality by yours, this plan requires no technology we don’t already have. Zeppelin-like balloons can float at a safe altitude, atop the clouds 50 kilometers (or 31 miles) above Venus’ surface. You wouldn’t fill them with explosive hydrogen or expensive helium, but nitrogen and oxygen. That is, regular Earth air.

Never mind wearing heavy claustrophobic astronaut gear on Mars; the temperature 50 kilometers up on Venus is balmy, and the sun here is just as bright as on Earth. Here the atmosphere protects you from solar radiation. Here the gravity feels like Earth. You can go outside — on a viewing deck, say — wearing little more than a fireman’s respirator. Never mind space tourism to our dusty old moon; Venus could be the real economic driver. We still have no idea of what amazing cloud formations it offers. Imagine vast silver cruise liner balloons chasing the sunset, on a planet that spins so slowly you can almost make it stand still. 

“It fires the imagination, it’s human adventure stuff,” enthuses Izenberg. “Picture the first Venus selfie.”

And there’s more. With the right balloon technology, you might even have a full-on, Empire Strikes Back-style Cloud City.

The 50-kilometer high layer of Venus “is in many ways the most Earthlike place in the solar system, with temperature and pressures at values close to what humans like to live at,” says Geoffrey A. Landis. He’s a NASA planetary exploration engineer, currently working on a landsailing Venus rover, as well as the author of The Sultan of the Clouds, an award-winning 2011 science fiction story set in “11,000 floating cities” above Venus, each one of them “kilometer-diameter domes [that] easily lifted a hundred thousand tons of city.”

In short, we could be on the cusp of a much-needed renaissance in Venus exploration. One that ends with you in floating habitats, as also predicted for Venus in the 22nd century by another popular science fiction franchise, The Expanse. (Although that particular prediction didn’t have a happy ending.)

Like this, but with fewer Imperial entanglements: Cloud City, Bespin.


And yet, Mars persists. The planet of the God of War has dominated our imaginations over the past 50 years, despite being smaller, lower gravity and further away. Mars missions still get the lion’s share of NASA’s space exploration budget, along with their hopscotch step of stopping on the moon first. After Bill Clinton dismissed his predecessor's plan, George W. Bush reversed course again, proposing a crewed mission to Mars in the 2020s. Barack Obama wanted one for the 2030s. That is also Donald Trump’s goal, although Trump seems a little perplexed about the first-stage mission to the Moon in 2024 that he signed off on.

What gives? Why all this focus, you may well wonder in less misogynistic times, on our brother planet at the expense of our sister? Well, on a larger timescale, what we’re seeing is the aftermath of a love affair Earth had with Venus right up until the 1960s. Until we sent probes her way without fully understanding her, and she opened the very mouth of hell.


We’d been fascinated for centuries with the brightest non-solar point in the sky, that celestial body known as both the morning star and the evening star, even after we figured out they were the same thing. She was almost always a goddess; she was Isis, she was Ishtar, she was Aphrodite, she was Venus, the Roman goddess of love. 

Almost everything we learned about her drove us crazy. She spins the wrong way compared to every other planet; if you could see it from the surface, the sun would rise in the west and set in the east. She has the most perfect circular orbit, compared to our elliptical one. She is moonless, which is unusual. From a telescope she seemed blue, with a thick cloud layer. What was she hiding? Endless rain and vast oceans? One influential Nobel prize winner certainly thought so.

Transits of Venus across the face of the sun, once we learned to predict them, were a really big deal. It was the promise of observing one that made Captain Cook sail to Tahiti. The 1874 transit was the first event humans ever turned into a movie; the first space fantasy story about Venus had been published nine years earlier. 

Edgar Rice Burroughs, HP Lovecraft, C.S. Lewis, Isaac Asimov, Robert Heinlein — all the big names in science fiction and fantasy wanted to write books set in this supposed aquatic world with its exotic, swampy life. Venus was also the preferred location of two top female science fiction writers in the pulp age, C.L. Moore and Leigh Brackett (who would go on to write the first draft of The Empire Strikes Back). 

A poster for Kurt Maetzig's 1960 science fiction film "First Spaceship On Venus"

Silver Screen Collection / Getty Images

When NASA and the Soviet space agency came to design their Venus probes in the late 1950s and early 1960s — for humanity’s excitement was such that Venus was the target of our first successful interplanetary missions, years before we could reach the moon — they designed them for water landings. Then on December 14, 1962, NASA’s Mariner 2 mission went into orbit around Venus, probed its cloud layer with microwaves and infrared, and delivered a feverish reading. The surface was 932 degrees Fahrenheit, said Mariner 2. 

That was a little high, as it turned out. Over the next decade Soviet and U.S. missions clocked an average of 863 degrees Fahrenheit, still making it the hottest planet in the solar system, hotter than the surface of Mercury, hot enough to melt lead. The pressure of its carbon dioxide atmosphere was greater than that at the bottom of Earth’s deepest ocean. 

It wasn’t a swamp. It was a nightmare.

The planetary romancers clung on for a while. One of the most notable sci-fi movies of 1965 was a U.S.-Soviet collaboration called Voyage to the Prehistoric Planet. Set in the year 2020 (!), it showed the first human visitors encountering dinosaurs on the surface of Venus. By then, any well-informed moviegoer knew this was laughable. Sci-fi writers published a telling anthology in 1968 called Farewell, Fantastic Venus! There could be no life on Venus (leaving David Bowie only the possibility of bacteria on Mars to sing about). There could never have been any life on that lava-filled hellscape. Right?


Not so fast. The Pioneer probe sent to Venus in 1978 detected traces of methane in that CO2-filled atmosphere. Methane is a rare chemical to produce without life acting as some kind of intermediary. “People tried to explain it away and they couldn’t,” says Sanjay Limaye, a planetary scientist at the University of Wisconsin–Madison, and a former chair of NASA’s Venus Exploration Analysis Group.

In 2018, Limaye co-authored a paper by an international team of scientists in the journal Astrobiology, laying out a strong case for microbial life thriving in the upper reaches of the Venutian atmosphere the way it survives in superheated, carbon dixoide-rich vents at Yellowstone. Carl Sagan made a similar speculation in the pages of Nature in 1967. If we find definitive proof, this would change our entire concept of life in the cosmos — especially considering the thousands of Venus-like planets we’ve found around other stars. One recent paper calculated that 40 percent of all yellow dwarf stars like our sun — one of the most common stars — have a planet in their Venus zones.

“If there was life, methane would be the strongest signal,” Limaye says. “We’ve been doing spectroscopy [studying the sun’s electromagnetic radiation as it hits the planet]; we haven’t been directly looking for organisms on Venus. Why not?”

A NASA model of how Venus might have looked a billion years ago.


That’s a very good question, one you may well be asking us yourself. Why did it take so long? Why did we not care more about finding proof of the life that you probably know to be living next door?

The truth is, we kind of lost interest after those 1960s and 1970s missions. There were cutbacks at space agencies around the planet. Since Venus was not going to return our love, and was going to crush our surface probes within an hour of landing, we decided to flounce off in a huff and explore the rest of the solar system instead. The last pictures we got of its land masses were via the Magellan spacecraft 26 years ago. Scientists are still forced to work from Magellan’s low-res maps today.

“We have better topographic data from Pluto than we do from Venus,” says Darby Dyer, the current chair of NASA’s Venus Exploration Advisory Group, with a frustrated chuckle. “NASA and the majority of planetary scientists have bought into the notion that Mars is the most likely place to have water and evidence of life. Overturning that paradigm is a tough battle, but we’re fighting it.”

Dyer is 62; the days when Venus was thought to be a swamp planet are within her living memory. She also remembers being in grad school at MIT in the 1980s, on the day Ronald Reagan canceled a NASA mission that was going to take an orbital radar to Venus.

“There were people crying in the corridors,” she says. “Ph.D.s whose whole theses vanished in an instant.” The Venus community gathered its energy and pushed back enough to create one final mission, planned for 1986, which was delayed by the Challenger shuttle explosion until 1989. That was Magellan.

Still, even with that Magellan data and our limited Earth-based spectroscopy, what wonders and mysteries we’ve been able to uncover. There are the strange dark patches, large enough to affect the planet’s weather, which may be where those microorganisms are hanging out. A 2020 study says that Venus’ volcanoes are still active, erupting as we speak.

And it’s only been four years since a groundbreaking study that suggested we might have been right all along about Venus being covered in liquid water; we just got the wrong era. Turns out Venus had oceans between 4 billion and 1 billion years ago — way longer than liquid water existed on Mars, and more than enough time for it to develop life.

“If you had water for 3 billion years, life probably arose on Venus before it did on Earth,” says Dyar. “Maybe they had trilobites in those oceans; maybe they got as far as whales.” 

So what happened? Why the runaway greenhouse effect? Here too, it’s embarrassing how little we know. The leading theory is that it was simply a result of our sun expanding over time, making the Venus zone uninhabitable. What happened there will start happening to Earth in another billion years, as our yellow dwarf star continues its inexorable growth into a red giant.

We may raise CO2 in the atmosphere to the point where it threatens the threads of human civilization, but only a growing sun can boil the oceans and burn the land, creating enough CO2 to dominate the atmosphere for a full-on runaway greenhouse effect.

But! It’s also possible that Venus was slammed by multiple impacts, including a possible former moon, which might explain why the whole place is spinning upside-down and so slowly. You know what would help us figure it out? More data.

Right now we don’t even know what Venus’ core is made of, or whether it has tectonic plates like Earth, or whether there’s evidence of old oceans to be found in the atmosphere, or exactly what kind of organisms have clung to it like mushrooms thriving in the radioactive ruin of Chernobyl’s old reactor.

It won’t be dinosaurs, but life on Venus may well have, uh, found a way.

The question is: How soon can we?

Tethers connect the habitats of a future Venus city.

Bob Al-greene / Mashable

There are some encouraging signs. Russia is working on its first Venus probe since 1983, the long-delayed and (to English ears) unfortunately-named Venera-D. Its goal is to study Venus’ greenhouse effect, and look at why the atmosphere rotates faster than the planet itself. Venera-D aims to deliver a lander, too; with today’s materials and technology, landers should be able to last a lot longer than a few hours on the planet’s pressurized surface.

The tentative launch date for Venera-D is 2026. By then it might also include VAMP, a proposal by aerospace companies, previously endorsed by NASA, for autonomous balloons that would probe the all-important 31-mile cloud layer, looking for signs of microbial life.

NASA is noncommittal on such things right now, possibly wary of any news that might distract attention from Trump’s favored Mars mission. There are two Venus-bound contenders for its 2021 Discovery program, which allocates around $300 million, total, per multi-year mission, mere crumbs from the $23 billion annual NASA budget. DAVINCI would be the first atmospheric probe to Venus since Magellan, and the first ever to take photos of her weird volcanic ridges. VERITAS would also focus on the surface, finally giving us better maps of our sister planet than we have of Pluto.

Which is nice and all, but these two missions were finalists for the last Discovery program too, and didn’t get picked then. You can forgive the Venus community for feeling like Charlie Brown, with NASA playing Lucy holding the football. (I hope Peanuts references have survived in your era.) They’re also frustrated that NASA administrator Jim Bridenstine hasn’t yet committed to swinging by Venus on the agency’s crewed Mars trip.

“Flying by Venus on the way to Mars minimizes delta-V, using less fuel and making the trip shorter,” planetary scientist Noam Izenberg points out. And if they’re swinging by the planet anyway, he adds, you might as well drop a couple of drone probes that the astronauts can control in real time, picking up samples: “This is value-added science you can’t do by remote probes alone.”

Not even this swing-by plan is as bold as HAVOC, the NASA crewed mission concept from Obama’s last term (which came with a nifty video, above). The five-phase proposal makes for fascinating reading: We send a robot balloon; we send a crew to orbit for 30 days; we send a crew to the 31-mile cloud layer for 30 days; we establish a permanent balloon-based habitat. I’d love to provide some quotes for posterity from the HAVOC scientists, but NASA, solicitous in many other areas, never responded to my request to speak to them.

Which leaves us with only Venus’ old friends, the science fiction writers, to imagine what that permanent habitat might look like in your century. The first book of James S.A. Corey’s Expanse series, the basis for the popular TV show, mentions a legal firm that had been involved in the “epic failure of the Venusian cloud cities” which led to a “decades-long lawsuit.” No further details are offered — and no spoilers, but this is a setup for the book’s ending, which requires that Venus be uninhabited.

The thought of cloud cities supported by balloons gives some Venus scientists the heebie-jeebies. What if they got a puncture? “The consequences of that city losing altitude would be severe,” says Stephen Kane, a planetary scientist at the University of California Riverside, who is excited about more uncrewed Venus missions that will help us understand exoplanets, but something of a HAVOC skeptic. “Would you want to build your house over a pit of sulfuric acid?”

Still, balloons would be cheap to send, and there’s nothing to stop regular resupply missions from Earth. You could provide hundreds of backup balloons as easily as we backup our data. And there would be plenty of time to transfer from one to another. “If there is a break, the gas equilibrates though the gap very slowly,” explains one character in The Sultan of the Clouds, the story by NASA engineer Landis. “Even if we had a thousand broken panels, it would take weeks for the city to sink to the irrecoverable depths.” (This is accurate so far as we know without actually testing it; it’s a case where all that air pressure on Venus is actually helpful.) In this forgiving environment, Landis imagines “cities of helical buildings and golden domes, with huge open areas and elaborate gardens” inside his vast and sturdy balloon structures.

Landis’ story suggests these vast cloud cities will be populated by all manner of refugees from Earth; those fleeing persecution, the misfits, the dreamers. In other words, the usual kind of pioneers who light out any time we find new land. Only this time, there’s no land to despoil, no ground to plant a flag on. There will be no debate of the kind that accompanies the Martian colonists in Kim Stanley Robinson’s classic book Red Mars, whether to terraform or to leave the planet’s slight, fragile ecosystem alone. We will, likely, never terraform Venus. We could cover her in cloud cities and she won’t feel a thing.

Here’s hoping you have embraced this enlightened, more buoyant alternative to our old ideas of space colonization.

Yours with our head in the clouds,


  • Story by

    Chris Taylor

  • Art by

    Bob Al-Greene

  • Edited by

    Brittany Levine Beckman

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