The Idea Factory

Here's how we'll one day live in space

There's more than one way to terraform a planet

In the words of aviator and poet John Gillespie Magee Jr., we've always wanted to slip "the surly bonds of Earth." To rise away from the dirt where we began and take to, as in Magee's case, the air, and finally the stars. But we've been naive as to how good we've had it. Sure, the Earth is terrifying: Storms, waves, solar radiation — even oxygen, vital to life, is a powerful carcinogen. But this is as good as our solar system gets, believe me.

It's for that reason that — rather than seeking an Eden on other planets — "planetary engineers" are looking to bring Earth's atmosphere to the rest of the universe. Carl Sagan, the famous physicist, called this a "Nobel" endeavour, and thought about how we could make Venus our second home. Buzz Aldrin advocates the colonisation of Mars. Ultimately, the idea is that we can extend biological life to the rest of our solar system and beyond by making the environments of other planets and moons similar to Earth's. We call this terraforming, or ecopoiesis.

The need is there. Some of the world's most renowned scientists are saying that it's too late for the Earth, that we've pushed the environment too far and only the most efficient retreats from industry can prevent a runaway destabilising of Earth's atmosphere. (By the way, there are plenty who also plead ignorance.) Plus, the Earth almost certainly has a shelf-life — in the next billion years the sun's supply of hydrogen will mean our solar systems' centre will go into a state of flux — both in terms of heat and gravitation pull — meaning Earth could fry in a Red Giant or freeze as it spins away from its current orbit.

It's better to hedge our bets with as many occupied planets as we can get our hands on, right?

So we have terraforming as an option. Terraforming is a simple idea: Making another place in space as habitable to us as Earth is — it literally means "Earth-forming." The idea that planets have different environments and so are suited to different forms of life was probably first recognised in H. G. Wells War of the Worlds, in which the Martians introduce their own flora to Earth in the hopes of making it habitable to themselves. The term was than extrapolated to terraforming on other planets by humans, and was coined in 1941 by fiction writer Jack Williamson, in his book Collision Orbit.

Carl Sagan was one of the first scientists to take the idea seriously. He thought we might be able to introduce certain bacteria to Venus to get the process started. In effect, this would a recreation of the history of Earth. What we'd now call "extremophile" micro-organisms, which live in extreme conditions like acid, salinity, or heat, settled Earth when it was just barren rock and ocean. The development of photosynthesis changed life for us: It changed the atmosphere and made it possible for larger organisms to grow.

So Sagan sought to send thermophilic bacteria to Venus — which is 450°C at its surface — to gradually redistribute elements on the planet until it was more habitable. The most suitable bacteria for this is Pyrodictium occultum, which would work wonders: Taking carbon dioxide and sulphur from the air and turning it into organic material. The only problem being that, while P. occultum loves heat, it does so only up to a point: 105°C is its best temperature, less than a quarter of the current heat it'd experience to survive on Venus.

The other problem with this idea is one of timescale. If we were to try the same thing on Mars, 100,000 years would be about right to create an oxygen atmosphere which humans could breathe. At first, we'd be looking to make Mars habitable to Earth's microbes and plants — which is a big ask, but actually achievable in the (sort-of) immediate future, 200 years or so. Photosynthesis would then do the hard work for us, creating an atmosphere around Mars which would be akin to Earth's. If we were to combine several terraforming methods we might even cut that time down to 900 years.

This is the appealing option: The sit back and relax, "nature will find a way" approach. It doesn't, however, get great airtime because it isn't the fast option — it could take hundreds of thousand to millions of years to work by itself. Before we can even think of dropping organisms onto Mars or Venus the planets have to first be made habitable for them. It's these — the most immediate options — that are attracting the gaze of short-term terraforming advocates.

Before we dip in, there is one quasi-type of terraforming not explored here, but The Kernel covered it in an earlier article on colonising Mars. This is paraterraforming — erecting insular domes elsewhere in the universe which recreate Earth's atmosphere. There's not much purpose to these settlements except as mining facilities to take resources back to Earth or to build great colonies. But at the current cost of space travel that isn't feasible. Their only purpose today would be to help terraforming, so a factory could pump CO2 into the Martian sky to create an atmosphere (which Mars lacks), or floating cities on Venus could reflect light from the overheated planet to cool it down.

But paraterraforming suffers from some severe disadvantages. For instance, on Mars there's no atmosphere, which means meteors and other space debris often don't burn up on impact. A puncture could be sci-fi levels of disastrous, although one researcher discusses the unpalatable possibility of sealing off impacted zones. Building colonies this way would also be forbiddingly expensive to establish and maintain: A start-up cost of maybe a hundred billion dollars ("in this economy?!"). The benefit of a colony over the next hundred years would be primarily for research or, frankly, to say we'd done it.

So, if we're serious about living on other planets as seems to be the case, serious terraforming would be our main concern. The ecopoesis route is the longest and most efficient route, but will rely on some more explosive, Michael Bay-type science.

The most often cited is impacts and collisions. It might surprise you, but Mars was once a temperate, wet, and relatively warm planet. Carbon sequestration — when atmospheric carbon is brought from the air into rocks or dry ice - ended that happy era and brought about Mars's current desert climate. So, it's said, what we need to do is get the carbon out of the rocks and the ice (which lies in a gargantuan sheet on Mars's south pole) and back into the air. How? By steering asteroids onto the planet's surface. A good impact would vaporise the ice and throw clouds of carbon into the air, recreating Mars's temperate atmospheric conditions.

Steering an asteroid — as you might expect — is not a simple task. But it is feasible. Asteroids and minor "satellites" have pathways like planets do, but are obviously easier to adjust due to being smaller. But adjusting these pathways — perhaps with a minor rocket collision, or by physically pushing it — the trajectory could change and be set on a course for Mars. One study suggests a good candidate could be an asteroid, 2.6km in diameter, of frozen ammonia — which would helpfully put nitrogen into the air as well. A rocket would steadily push the asteroid onto the right course for Mars. Around fifty such asteroids would be enough to make Mars temperate by these methods, as well as covering about a quarter of the planet with a layer of water 1m deep.

Why — you might ask — not just drop nuclear bombs on the planet to vaporise the water and get the carbon sealed with the rocks? Radiation and ethics: The radiation of consecutive hydrogen bombs would make Mars uninhabitable. Plus, of course, there might be life on the planet.

So there's that. There's also the building of giant aluminium mirrors.

On Venus, we'd be using the mirrors to reflect light away from the planet, to cool it down. On Mars, a giant mirror would reflect light back to the planet, most likely to melt the dry ice glaciers. Such a mirror would probably need to be, say, 125km in radius, and at that size could be more potent than an asteroid impact. Considering, however, that the 90s saw a massive drive to recycle diet coke cans due to an aluminium shortage, this may not feasible in the short term.

There's one other thing about all this, and that is that a lot of these processes have a "tipping point", during which the process will continue almost by itself. In Mars's case, once enough of the ice has melted, the heat retained by the new atmosphere will heat the rest of the ice, which in turn will make the planet warmer and so melt more ice. On Venus, as the planet cools more gases will become liquid or solid, which in turn will reduce the atmosphere and cool the planet. You've probably heard of the "tipping point" attached to Earth's melting ice caps and warming climate — the albedo, or the amount of light reflected by the polar ice, gets reduced with all the ice that's melting, further heating the planet and melting the ice.

It's a tricky business, this planet building. Never mind the cost, technology and international agreements required to launch a terraforming initiative — how are we going to divvy up a planet? — but the time scale of these projects means whoever starts them will be long dead before they're finished. In light of which, Carl Sagan seems to have had it right when he called this man's "nobel" endeavour: it'll be for our children's children, not us, that we settle a new planet. Here's hoping our offspring make a good job of conquering the galaxy.

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