October 11th, 2012Top StoryShould we terraform Venus first?By George Dvorsky
Runaway greenhouse One of the more frightening scenarios presented by climate scientists is the problem of a runaway greenhouse effect.
No one knows for sure if this will be the ultimate climax of human-caused global warming, but it's a possibility that clearly needs to be taken seriously. It's a genuine existential risk. And disturbingly, there is precedent for this right here in our solar system. Scientists are quite certain that Venus went through a runaway greenhouse effect when it was young and when it still had oceans. In those early days, and as the sun got brighter, Venus's oceans began to boil and evaporate into the atmosphere, where it eventually leaked out into space. Today, and as a consequence, Venus has an absolutely massive amount of carbon dioxide in its atmosphere, the result of poor carbon recycling (which is facilitated by the presence of liquid water). A veritable hell As a result, Venus has essentially turned into hell. It features an average temperature of 467°C (872°F) — a temperature that's hot enough to melt lead. And its thick layer of carbon dioxide (CO2) bears down on the planet at a level 90 times greater than what we experience here on Earth.
Making matters worse, Venus gets about twice the sunlight than Earth, and it features a day that's 224 Earth days long (making its day longer than its year). Oh, and it doesn't have a magnetosphere to protect it against solar radiation. After considering all this, it's fairly safe to suggest that the terraforming of Venus would pose a set of problems far greater than what would await us on Mars. But that isn't necessarily a valid reason to terraform Mars first. As already noted, the insights we would glean from a Venus terraforming project could serve us well given our climate change problems here on Earth. It's even fair to say that the simple exercise of thinking about it — the brainstorming of ideas — may help us deal with — and even acknowledge — our current climate crisis. But Venus poses other advantages as well. It's closer than Mars, making it easier and quicker to travel back and forth. And like the Earth, it resides within the solar system's habitable zone. We also know it can hold an atmosphere (obviously), and it has nearly the same mass and size as Earth. Mars, on the other hand, is considerably smaller, and would pose serious health risks to humans (reduced muscle mass and bone density) on account of its low gravity. Getting rid of the CO2 Should we decide to terraform Venus, or any planet for that matter, we need to accept the fact that a project of that magnitude would take a considerable amount of time. It would be a long term, generational project that would have to be rolled out over a series of phases. Thankfully, a number of visionareis have given us a head start in thinking about how we could do this. The first step, it's fairly obvious to say, is that we'll need to get rid of the excess CO2.
More recently, NASA engineer James Oberg proposed that all the CO2 could be blown out into space. Writing in his 1981 book, New Earths, he wrote:
And in the 1990s, Paul Birch proposed a plan that would see Venus flooded with over 4x1019 kg of hydrogen. This would cause a reaction with the CO2, which would in turn produce graphite and water — a lot of water. His estimates predicted that about 80% of the surface area of Venus would eventually be covered in water (compared to Earth's 70%). Other plans describe the capture of carbonates, direct liquefaction and sequestration, advanced nanotechnology, a megascale quicklime process, or a combination of some or all of these. Temperature, rotation, and the magnetosphere Once the CO2 problem is resolved, the next phases of Venus's transformation would likely involve addressing ongoing temperature problems, irregular planetary rotation, and the lack of a magnetosphere. It's safe to assume that, by virtue of the elimination of the excess CO2, the temperature would start to get more reasonable. But it's still likely that Venus would experience temperatures much greater than what life can withstand. Meteorologist Paul Crutzen, winner of the 1995 Nobel Prize in Chemistry, suggested a number of years ago that it would be possible to artificially release massive quantities of sulfur dioxide at an altitude of 20 kilometers in order to cool down surface temperatures and offset the growing greenhouse effect. This would be similar to the effect of volcanic eruption here on Earth. Another possible solution proposed by Birch would be to place space-based mirrors at the lagrange point between Venus and the sun. Angled correctly, the mirrors would reflect the excess sunlight away from the planet, while simultaneously serving as solar power generators.
And indeed, we might also want to readjust the spin of Venus to give it a rate more comparable to Earth's. Now this would truly be an epic task, requiring an absolutely tremendous amount of energy. In all likelihood, the only way to do it would be to introduce large celestial bodies around Venus in order to accelerate its rotation up from once every 224 Earth days. And in fact, it might just be simpler to arrange a series of massive mirrors to redirect sunlight to the dark side of the planet. Finally, there's the problem of the magnetosphere — a complete deal breaker for the onset of life. It's possible that the slow rotation of Venus is to blame for this. Perhaps future technologists will devise a plan to create a virtual magnetosphere — one that can shield the planet from solar radiation and devastating solar storms. A valuable thought experiment It's clear that the terraforming of Venus will be hard. We may never get it to the point where life will be able to flourish — but it will be interesting to see the extent to which we could make it habitable for human occupation, along with synthetic life that could live under harsh conditions. Perhaps the first step in the process, aside from taking the possibility seriously and conjuring novel ways to fix the planet, would be to create simulations of all these proposals to determine which ones would work best. Moreover, these simulations would compliment similar models of what might happen to Earth given a similar set of circumstances. The quest to make Venus habitable for life, it would seem, just might ensure that Earth can continue to do the same. Images: 1:NASA | 2 | 3 | 4 | 5: J. Storrs Hall |
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