How about we terraform Venus and Mars at the same time?

Thanks to groundbreaking research by famed scientists like Carl Sagan, James Oberg, James Lovelock, Robert Haynes, and Martyn J. Fogg, several approaches have been put forth for how Venus and Mars could be ecologically engineered. According to their proposals, the result would be planets with temperate climates, breathable atmospheres, and ocean-covered surfaces.

The existence of Earth-like conditions on these planets would allow for exponential growth - economically, socially, and intellectually. With three terrestrial planets settled and sustaining life, humanity would enter an era of post-scarcity and be safe from any cataclysmic fate that affected a single world.

Unfortunately, these proposals all involve a huge commitment in time, resources, and elbow grease! They are riddled with challenges, highly theoretical, and require that many developments and innovations happen first. But given how Venus and Mars are at opposite ends of the Sun’s HZ and require opposite strategies to make them hospitable, there could be a “two birds, one stone” solution here. 

Opposite Extremes

Venus orbits close to the inner edge of the Sun’s HZ at an average distance (semi-major axis) of about 67.69 million mi (108.939 million km), or 0.728 times the distance between the Earth and the Sun (1 Astronomical Unit (AU)). Venus receives twice as much solar radiation as Earth at this distance, contributing to its extremely hot atmosphere. Venus is the hottest planet and the Solar System, with a mean temperature of 867 °F (464 °C) - hot enough to melt lead!

The atmosphere is composed mainly of carbon dioxide (96.5 percent by volume), the remainder being nitrogen and trace gases. This led to the runaway Greenhouse Effect in Venus’ atmosphere and the accumulation of sulfuric acid clouds. The surface atmospheric pressure is estimated at 93 bar, roughly 92 times the air pressure on Earth at sea level. 

Its closer proximity to the Sun means it has a shorter year, taking 224.7 days to complete an orbit of the Sun. The planet rotates in the opposite direction of most of the Solar planets (retrograde rotation) and very slowly to boot, taking over 243 days to complete a single rotation on its axis. These characteristics also mean that Venus is isothermic, experiencing virtually no temperature variation between day and night or during the year. 

At the other end of the HZ is Mars. The Red Planet orbits our Sun at an average distance of about 155.72 million mi (250.61 million km), or one and a half times the distance between the Earth and the Sun (1.5 AU). Mars receives about half as much solar radiation at this distance as Earth. Its wider orbit results in an orbital period of 686.98 days, making a year on Mars almost twice as long as one on Earth.

On the other hand, a day on Mars (a Sol) lasts about the same as a day on Earth - 24 hours, 37 minutes, and 22.7 seconds. Its axis is tilted at 25.19°, very close to Earth’s own tilt (23.4°), meaning Mars experiences seasonal changes throughout the year. It also experiences extreme variations in temperature, ranging from -166 °F (-110 °C) during the winter at the poles to 95 °F (35 °C) during summer at mid-latitudes. 

The atmosphere is incredibly thin, with a surface pressure of 6.52 millibars (mbars), or roughly 0.6 percent of Earth’s at sea level. And like Venus, it’s largely composed of carbon dioxide (95.97 percent by volume), with trace amounts of argon, nitrogen, oxygen, and water vapor. 

Two Birds…

In short, Venus is too hot, its atmosphere is too thick and toxic, and it rotates too slowly. Mars is too cold, the atmosphere is too thin and toxic, and it rotates just fine (for our purposes, anyway). Therefore, making these planets more accommodating to Earth organisms requires specific and opposing strategies. 

As we explored in a previous article, the solution to terraforming Venus comes down to three steps (with a possible bonus step thrown in for good measure). These are:

• Thin the atmosphere
• Stop the runaway Greenhouse Effect
• Convert the atmosphere
• (Bonus) Speed up the rotation

These steps are complementary, meaning progress in one will lead to progress in others. The greenhouse effect will be arrested by thinning the atmosphere and/or converting the CO2 into other gasses. This can be accomplished in several ways. Step one can be achieved by introducing calcium and magnesium particulates into the atmosphere. These will chemically bond with the carbon dioxide, creating carbonates that will then fall to the surface.

Another way is to introduce hydrogen gas (H2), which will chemically interact with CO2 to create water (H20) and elemental carbon (graphite (C)) - known in chemistry as the “Bosch reaction.” The water will then rain down on the surface, creating oceans of considerable depth, while the graphite will need to be captured and sequestered. It must be removed to prevent it from reacting with the water and re-entering the atmosphere as CO2.

Yet another way is to position orbital sun shields to block sunlight from being absorbed by the atmosphere. A sun shield positioned at the Sun-Venus L1 Lagrange Point would cause Venus’ atmosphere to cool considerably to the point that the clouds of CO2 would freeze to form “dry Ice.” This ice must then be sequestered and relocated to prevent it from melting and re-entering the atmosphere. 

And now Mars! As we explored in another previous article, terraforming Mars also comes down to three steps (and a bonus step), including:

• Melt the ice caps
• Thicken the atmosphere
• Trigger a Greenhouse Effect
• (Bonus) Introduce a magnetic field

Once again, these steps are largely complementary. By thickening the atmosphere, the planet will retain more heat. A magnetic field will ensure that the atmosphere is not slowly stripped away. And increased heating will melt the polar ice caps (which contain large amounts of dry ice), further thickening the atmosphere and creating a water cycle.

A good way to get started would be to use orbital mirrors or low-albedo materials on the surface (dark plants or dust) to melt the polar ice caps. A nuclear device will do in a pinch, though that seems a bit harsh! Thermal boreholes drilled into the surface will release heat and carbon dioxide that will thicken the atmosphere further and increase surface temperatures.

Not exactly a cakewalk, is it? Terraforming just one of these planets (let alone both) would be a herculean effort and calls for engineering on a planetary scale. The sheer cost in terms of resources, energy, and time would be extremely high. 

…0ne Stone?

To make matters worse, Mars does not have enough carbon dioxide locked away in its ice or subterranean caches to allow for terraforming. This was the conclusion of a NASA-sponsored study released in 2012 titled “Inventory of CO2 available for terraforming Mars.”

“These results suggest that there is not enough CO2 remaining on Mars to provide significant greenhouse warming were the gas to be emplaced into the atmosphere; in addition, most of the CO2 gas in these reservoirs is not accessible and thus cannot be readily mobilized. As a result, we conclude that terraforming Mars is not possible using present-day technology.”

Venus, on the other hand, has far too much carbon dioxide. What’s more, two of the aforementioned terraforming strategies lead to byproducts - dry ice and graphite - that must be dealt with. If these were transported to Mars, they could help make up the CO2 deficit. Dry ice could be transported to Mars and dropped into the atmosphere, where it would sublimate before reaching the ground, gradually thickening it.

Graphite could be spread atop the polar ice sheets to absorb solar energy (or it could be heated), helping to melt them. The graphite would dissolve in the melting ice and slowly be released into the atmosphere as CO2, triggering a greenhouse effect. 

In either case, the main issue is that of transport. Since Venus’ gravity is roughly 90 percent that of Earth, the escape velocity, at 6.44 mi/s (10.36 km/s), is close to that of Earth’s - 6.96 mi/s (11.186 km/s). This means that vehicles attempting to launch from the surface and achieve a Mars transfer orbit need considerable amounts of propellant. 

A possible solution is to leverage the “Long Rain” scenario. After bombarding Venus’ atmosphere with hydrogen, automated facilities could be deployed to the surface to collect and store the graphite. Meanwhile, other facilities would collect rainwater and convert it into liquid hydrogen and oxygen (H₂ and LOX). This would allow reusable rockets to land on the surface, refuel, be loaded with graphite, and take off for Mars. 

Alternately, some of this graphite and/or dry ice could be used to create graphene ribbons, a super-material with incredible tensile strength. These could be connected to a station in geostationary orbit (GSO), making a space elevator to lift megatons of graphite or dry ice from the surface to orbit. 

Furthermore, the orbital shields and mirrors could be assembled using carbon super-materials. These could be harvested directly from Venus’ atmosphere by floating platforms stationed 31 mi (50 km) above the surface, where the atmosphere is warm, and the atmospheric pressure is comparable to Earth at sea level (100 kPa). This way, the same mirrors that help warm Mars and cool Venus could be assembled from the same source.

Let the “Greening” Begin!

Finally, severe ecological engineering can begin once Mars and Venus have been warmed and cooled (respectively). In both cases, this means planting terrestrial organisms on the surface of both planets, gradually introducing lifeforms of greater complexity, and creating the natural cycles that ensure climate stability.

The first to go would be simple single-celled life forms (cyanobacteria), lichens, moss, and other photosynthetic organisms. These would gradually convert atmospheric CO2 into oxygen gas and organic nutrients. As water accumulates on the surface, algae, sea grasses, and kelp would help balance the acidity of the rivers, lakes, and oceans. 

Grass, plants, and trees would follow, stabilizing the soil and creating a nitrogen and water cycle. As these organisms die and break down in the soil, they further enrich it with organic nutrients, paving the way for insects, nematodes, and other terrestrial and marine invertebrates. 

Venus is already known to have active volcanoes, meaning outgassing from the interior (including carbon and sulfur dioxide) already takes place. Once water flows on the surface, this geological activity would create hydrothermal vents, essential for maintaining marine life. On Mars, some geological activity still exists, though minimally, meaning it would need to be restarted - possibly by positioning nuclear devices near the core-mantle boundary. 

The final step would be introducing complex life forms like avians, reptiles, amphibians, and mammals to both worlds. This would complete the carbon cycle and (along with the water and nitrogen cycles) would maintain habitability over time.

* * *

Granted, tackling both planets together would not make this herculean effort any less... herculean. Terraforming remains a highly-speculative enterprise and something that humanity will not be able to contemplate until many preliminary steps have been taken first. These include (but are not limited to) propulsion systems that allow for rapid transits between planets. These closed-loop systems will enable self-sustaining habitats and a lot of infrastructure extending from Low Earth Orbit (LEO) to the Moon and beyond.

These advancements would allow humanity to become an interplanetary species. But to truly expand and plant the seed of human civilization in extraterrestrial soil, we must ensure that we bring Earth's ecosystem and cycles (the things that sustain life and gave rise to our species) with us - in one form or another. In the short term, bioregenerative life support systems can accomplish this.

But in the long run, the most effective way to support life is to recreate Earth-like conditions on other planets. And while it may be a far-off prospect, terraforming could be accomplished with the right technology, know-how, and dedication. Considering the immense benefits, it is something we may find ourselves doing before long.