As a future terraforming species, we take it for granted that Mars will be our first megaproject. But while transforming the Red Planet into something more hospitable for life seems the most logical — if not easiest — first step towards colonizing the solar system, it may actually make more sense to tackle our sister planet first. Because some scientists warn of a runaway greenhouse effect here on Earth, it may be prudent for us to terraform Venus first — a planet that has already undergone a carbon dioxide-induced apocalypse. And by doing so, we may learn how to prevent or reverse a similar catastrophe here on Earth.
One of the more frightening scenarios presented by climate scientists is the problem of a runaway greenhouse effect.
Should carbon emissions continue to increase at the current rate, they warn, we may hit a critical tipping point after which a positive feedback loop will be created between the surface of the Earth and the increasingly thick and opaque atmosphere above it. Hypothetically, the effect would instigate a rapid and progressively escalating rise in temperature that would eventually result in the extermination of all life on the planet and the evaporation of the oceans.
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.
To say that Venus has a lot of CO2 in its atmosphere would be a gross understatement. Over 96% of its atmosphere consists of CO2, which it displays prominently through its thick layer of clouds that float 50-70 km above the surface. Above that, is has clouds and mist that are comprised of concentrated sulphuric acid and gaseous sulfur dioxide (which is derived from the sulphuric acid).
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.
Fifty years ago, Carl Sagan suggested that we use atmospheric-based GMO algae to convert the CO2 into something more benign or useful. It's not the greatest idea in the world, but give him credit — he was the first person to seriously suggest that we terraform Venus.
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:
If we wish to remove 98% of the mass of the Venusian atmosphere in a reasonable time, say, 100 years, we must haul up a mass 10 quintillion tons, or 300,000 tons per second. Compare that to the flow along the Amazon river...10,000 tons per second. The largest machines built which handle flowing water...handle 400 tons per second.
Or look at it from an energy requirement: hauling the mass of gas 100 km high, and then accelerating it by 20 km per second requires about 1025 ergs over a 100-year period. That's all the sunlight falling over the same period on an area of 10,000 square km assuming 100% efficiency...Throw in a factor of 10 for engineering reality, and the air scoopers must have an area of...three times the total area of Venus.
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%).
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.
Alternately, the reflectors could be placed in the atmosphere or on the surface of Venus. Nanotechnology expert J. Storrs Hall has devised a weather machine for Earth that could essentially perform this task. There's no reason to believe that such a system couldn't also work for Venus. And given the planet's proximity to the sun, along with its agonizingly slow rotation, a long term technological solution will likely be mandatory.