Overview
"It might be possible to terraform Venus some day, when our technology gets good enough. The challenges for Venus are totally different than for Mars. How will we need to fix Venus?"\(^{[1]}\)
The first serious proposal in scientific literature on terraforming other worlds in the universe was about
terraforming Venus. The planetary scientist Carl Sagan imagined seeding the Venusian skies with photosynthetic microbes capable of converting Venus's \(C0_2\)-rich atmosphere into oxygen. Other proposals involve assembling a vast system of orbital mirrors capable of blocking the Sun's light and cooling Venus until this hot and hellish world became very frigid and rained \(C0_2\) from its atmosphere. The solleta would also be capable of simulating an Earth day/night cycle. To create oceans and an active hydrosphere on Venus, we could hurl scores of icy asteroids from the Kuiper belt to Venus and, upon impacting the Venusian atmosphere, would rapidly disintegrate releasing enormous quantities of water vapor into the atmosphere which subsequently condense to form the first seas on Venus. Or perhaps Saturn's moon Enceladus—containing a colossal subsurface ocean dwarfing that of the Earth's—could be sacrificed towards the end of creating the first seas on Venus. But even if humans never terraform this hellish world, they could still live their—partially at least—by deploying thousands of blimps into the Venusian skies capable of supporting a long-term, human presence of perhaps over a million people. Venusian sky cities. But eventually, after many millennia of terraforming Venus, a rich ecosystem of life—including us—could live on Venus's surface.
Colonizing the Venusian skies
"We continue our look at colonizing the solar system by visiting Venus, and exploring both the options for vast floating habitats in the upper atmosphere as well as full terraforming of the planet."\(^{[2]}\)
Artist concept of lightning on Venus. Image credit: ESA
On the surface of Venus, temperatures are a hellish \(~875°F\) (hotter than the boiling point of lead) with an atmospheric pressure over 90 times greater than that of Earth's—this would be the equivalent of standing (and getting crushed) underneath \(1km\) of ocean water on Earth. One thing is pretty clear: Venuse's surface, at least presently, is totally uninhabitable. Even most of the Venusian sky is uninhabitable. The lower portion of Venuse's atmosphere is comprised of hurricanes and, even worse, perpetual never ending rainstorms of sulphereic acid. Higher up in Venuse's atmosphere, temperatures are very cold—which, by itself, isn't that big of a problem. But the upper-portions of Venuse's atmosphere are also unprotected by the Sun's radiation—and given how close Venus is to the Sun, the enormous amounts of materials which would be necessary to shield any potential inhabitants living up there is rather prohibitive. Fortunately for us, there is a sweet spot. At roughly \(50-55km\) above Venuse's surface, the temperature and atmospheric pressure is Earth-like and you are above the dangerous Venusian hurricanes and sulferic-acid rainstorms. Thus, if any humans were living up their, they wouldn't need to wear big, clunky, pressurized space-suits. One major perk about Venus over any other world in our solar system (besides, of course, the Earth) is it's Earth-like gravity.
"NASA Langley researchers want to get a better idea about conditions on our nearest planetary neighbor, Venus, so they have come up with HAVOC or a High Altitude Venus Operational Concept - a lighter-than-air rocket ship that would help send two astronauts on a 30-day mission to explore the planet's atmosphere."\(^{[3]}\)
Venus's surface gravity is \(92%\) as strong as that of the Earth's. Thus, anyone living on Venus wouldn't need to worry about their bodies atrophying and degrading due to the harmful effects of micro-gravity and there would be no need to build massive rotating habitats for human supplementation. (The effects of living on Mars due to Martian gravity—which is about one-third the strength of Earth's surface gravity—is much more iffy because, quite frankly, we're still unsure of the harmful, long-term side effects associated with living under Martian gravity for long amounts of time.) In fact, the first humans to live on Venus would likely live in gargantuan blimps \(~50-55km\) above Venuse's surface. The science fiction writer Geoffrey Landis in his award-winning short novel, The Sultan of the Clouds, imagined immense sky cities on Venus consisting of \(10,000\) enormous blimps inhabited by millions of people. Indeed, something like this would actually be possible. Large numbers of blimps could be tethered together (resembling something like many grapefruits all bunched together); there could be many separate grapefruit-like bunches of blimps connected by very long bridges. These bridges could be graced by walking Venusian settlers; as they peered down, they would see hurricanes and storms from above. These sky cities could also incorporate ultra-long cables dangling dozens of kilometers from the base of the sky cities and throughout the Venusian atmosphere and used to collect resources from Venus's atmosphere.
Although the first generation of Venusian explorers would be confined to living in the sky, they would maybe begin the long and posthumous process of terraforming Venus—that is, making Venus "Earth-like." Although such a project would take many millennia and possibly even over a million years to complete, it is theoretically possible according to the laws of nature. Such an endeavor, therefore, merely becomes an engineering problem—albeit, one of gargantuan and epic proportions whose energy and material requirements vastly exceed (by many orders of magnitudes) the current energy and materials production of present \(21st\)-century human civilization. But our descendants will have nuclear fusion and the entire solar system at their disposable as sources of energy and materials, respectively. For them, terraforming Venus might not be as formidable of a challenge.
Sequestering \(\textbf{C0}_{\textbf{2}}\) from Venus' atmosphere
According to the phycisist Freeman Dyson, the first step in terraforming Venus should be to cool the planet since this step would take the least amount of time (only \(\text{~200 years}\)). According to the researcher Paul Birch, this could be accomplished by constructing an enormous solleta of orbital mirrors with a diameter roughly twice that of Venus's at the Venus-Sun \(L_1\) lagrange point which is located in between Venus and the Sun at a distance of roughly one million kilometers away form Venus. The reason why Venus is so hot is twofold: first, because of its close proximity to the Sun, it receives an enormous amount of solar insolation; second, because of its thick \(C0_2\) atmosphere which traps the Sun's heat energy. The sollete could kill two birds with one stone by eliminating both of these problems. On the former, the sollete, of course, would do nothing to alter Venus's close proximity to the Sun by moving it farther away from the Sun; but it could be used to drastically reduce the amount of solar insolation reaching Venus. The sollete would be an array of slated mirrors that would reflect sunlight away from Venus causing the planet to cool. After cooling the planet for \(\text{~58 years}\), the planet's temperature would drop to the melting point of \(C0_2\) at Venusian atmosphereic pressure; this would cause \(C0_2\) to rain from the Venusian skies filling the Venusian surface with enormous oceans of liquid \(C0_2\). After \(\text{~121 years}\) of \(C0_2\) rainfall, the planet will have cooled to the freezing point of \(C0_2\). This would cause all of those seas of liquid \(C0_2\) to turn into vast ice sheets after \(~17\) years. At this stage, Venus would essentially just be a giant ball of ice (like how the primordial Snowball Earth once was). For the next \(~9\) years, the remaining atmospheric \(C0_2\) would fall from the skies in the form of snow.
The entire process eliminates the problem of Venuse's thick \(C0_2\) atmosphere. But, unfortunately, it creates a new problem. All of the frozen \(C0_2\) on Venus's surface could potentially get melted and vaporized due to Venuse's geological activity, released back into the Venusian atmosphere, and killing any surface life that was potentially living on Venus. One solution to this problem was simply just to cover the frozen \(C0_2\) ice. This likely wouldn't work and we'd have to get rid of Venus's \(~5×10^{20}kg\) of \(C0_2\) ice sheets the hard way: by exporting it out into space. The amount of energy and time necessary to do this would be enormous. This would be, by far, the most difficult and prohibitive part involved in terraforming Venus. Future generations will have to ask whether or not it is "worth it"—after all, the amount of time, energy and matter that would be needed to colonize the asteroids and to build artificial space habitats would be many orders of magnitude less than that required to fully terraform Venus. Or, perhaps, by then they will have devised a better solution all together.
Liquid water and life on Venus
"A conceptual picture I made of Venus if it were terraformed. (Credit: Daein Ballard) Notice the interesting cloud formations and that the planet has polar caps. I decided to show the planet this way after studying Venus' atmosphere. The two Hadley cells the planet has stop at 70 degrees north and south. So the polar regions are cut off from the warm air. Also the slow rotation of the planet causes the clouds to whip around the planet very fast, especially at the equator, to balance out the temperature difference between day and night sides of the planet."\(^{[5]}\) Image credit: Ittiz at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
After removing nearly all of Venus's \(C0_2\) and cooling the planet to a frozen iceball, the next stage of terraforming could be commenced: using the solleta to let in more sunlight in order to heat up Venuse's surface to Earth-like temperatures and importing enormous amounts of water to create seas of liquid water as well as a functioning hydrosphere. One proposal for accomplishing the latter would be to hurl Saturn's moon Enceladus towards Venus. As Enceladus approached Venus, it could be split into two halves and sent into orbit around the Sun. When the two halves of Enceladus intersected Venus again its orbit, each half could be disintigrated into myriand tiny icy chunks. When these ice chunks eventually collided with Venus, enormous quantities of water would be imported onto the planet. This would activate a hydrosphere on Venus and cover its surface with seas of liquid water with a mean depth of \(~140\) meters.
With seas of liquid water, and Earth-like temperatures and an Earth-like day/night cycle, the final step in terraforming Venus would be to create an Earth-like atmosphere. First, we would need to hurl asteroids rich in nitrogen from the Kuiper belt towards Venus; after allowing many such asteroids to disintegrate in Venus' atmosphere, Venus' atmosphere would become rich in nitrogen as well as in oxygen. Photosynthetic microbes could use the \(C0_2\) to generate enormous amounts of oxygen. Gradually, after microbes create arable soil, plants could be introduced into the Venusian environment which would continue oxygenating this world. And, eventually, Venus' atmosphere would have Earth-like proportions of carbon dioxide, oxygen and nitrogen; at this point, animals and humans could live on Venus' surface.
Terraforming Venus would be much more challenging than terraforming Mars and would require many millions of years and an energy budget which vastly exceeds anything like what we have today. But perhaps in the future when we have interplanetary vessels powered by nuclear fusion and we have mastered the technique of star lifting and extracting resources from the atmospheres of the Jovian planets, we would have enough energy to pull a terraforming project like this off.
This article is licensed under a CC BY-NC-SA 4.0 license.
References
1. Fraser Cain. "How Do We Terraform Venus? Turning this Hellish World Into Something Earthlike". Online video clip. YouTube. YouTube, 2 February 2014. Web. 21 October 2017.
2. Isaac Arthur. "Outward Bound: Colonizing Venus". Online video clip. YouTube. YouTube, 07 September2014. Web. 16 November 2017.
3. Oberhaus, D., & Pasternack, A. "Why We Should Build Cloud Cities on Venus." Motherboard, D. Oberhaus & A. Pasternack, Februrary 2 2015, https://motherboard.vice.com/en_us/article/539jj5/why-we-should-build-cloud-cities-on-venus
4. NASA Langley Research Center. "A way to explore Venus". Online video clip. YouTube. YouTube, 10 October 2014. Web. 21 October 2017.
5. Terraforming of Venus. (2017, November 11). In Wikipedia, The Free Encyclopedia. Retrieved 01:31, November 17, 2017, from https://en.wikipedia.org/w/index.php?title=Terraforming_of_Venus&oldid=809780250
6. Fogg, Martyn J. Terraforming: Engineering Planetary Environments. Society of Automotive Engineers, 1995.
Other Sources
European Space Agency, NASA