Jim Baen's Universe

Nonfiction articles

Terraforming: A Bumpy Road Ahead

Written by B. B. Kristopher

Illustrated by Paul Campbell

I grew up watching Marvin the Martian and Bugs Bunny fight it out over the Illudim Pew-36 Explosive Space Modulator. Along the way, I also had a run-in with Bradbury's The Martian Chronicles, Robinson Crusoe on Mars, E. E. "Doc" Smith's Lensman series, the earlier works of Robert Heinlein and a whole host of works that depicted Mars as a vital, life bearing world. Venus often followed along side, usually as a world of swamps and tropical jungles.

Somewhere in the back of my mind, I knew it wasn't right. I'd been exposed to enough science before I started kindergarten that I knew the other worlds in the solar system were barren, lifeless places. But like any child, I didn't let a little thing like reality distract me from dreams of walking on other worlds rich and flush with life.

I'm a long way from those Marvin the Martian cartoons, but some part of me still longs for a Mars you could run across without a space suit and an oxygen tank. I follow the terraforming discussions the way some people follow their favorite football team.

What I see doesn't make me happy.

These days, most terraforming discussions center around Mars, and the discussions can get pretty heated. People argue about ethics. They scream about protecting any life forms that might exist on Mars. They go on about how easy or how hard it would be to terraform the planet. They put forth ideas and theories, some of which are even intelligent.

What I have yet to see is anyone admit just how massive an undertaking terraforming any of the bodies in our solar system would be. This is disturbing because any attempt to mount a terraforming effort that does not realistically consider all the challenges involved is ultimately doomed to failure.

Since most of the current terraforming discussions focus on Mars, let's start by taking a look at what would be involved in making Mars Earthlike.

One of the most popular suggestions is to start by bombarding the planet with large, fast-moving asteroids. This, proponents suggest, would heat the planet up. They argue that polar strikes could melt the carbon dioxide ice caps, releasing massive amounts of CO2 into the atmosphere which would result in a greenhouse effect which would trap sunlight and heat the planet. Others suggest that a large enough strike could even restart the planet's geological processes.

Using asteroid bombardment would seem to make sense. After all, an asteroid impact can deliver more force than all the nuclear weapons on Earth combined. The problem is, that's still not much energy on a planetary scale. There are two basic scenarios here. One, a single large impact at the poles would result in the entire polar region becoming molten and most of the CO2 would end up trapped in the rock as the lava cools. Alternatively, small impacts could be used to melt both polar caps, releasing millions of tons of CO2 into the atmosphere, which, if the bombardment were performed at midsummer, the CO2 would stay in the atmosphere for about eight months to a year.

The fact is, the Martian atmosphere is already ninety-five percent CO2, and every Martian winter, nearly a quarter of the atmosphere falls on the poles as snow. Even if you managed to get the CO2 in the ice caps into the atmosphere, there wouldn't be enough time before the winter arrived for the greenhouse effect to take hold, and it would all snow back out. Worse, since we're not sure how much of the ice caps are dry ice (frozen CO2) and how much is water ice, it might not even take that long, because the temperature on Mars rarely gets above the freezing point of water.

Surface bombardment to kick start the greenhouse effect would be an ineffective waste of energy at best, and at worst would result in trapping precious CO2 and water in newly formed rock from which it couldn't be released without melting the rock.

As for a heavy bombardment to restart the planet's geological cycle, the idea would have merit on another planet, but on Mars there is a reason to reject the proposal outright. In order to explain why, it's necessary to take a quick look at the history of Mars and understand how it got into the shape it's in today.

Imagine you have a glass coffee cup, a glass coffee pot and a large glass saucepan, all full of boiling water. If you leave them sitting on the counter for about half an hour, when you come back, you'd find a coffee cup full of room temperature water, a coffee pot full of warm water and a saucepan full of hot water. The reason you get this effect is that the water in the coffee cup has a higher ratio of surface area to volume. Since all the water's heat is lost at the surface, a higher percentage of the water in the coffee cup is giving off heat than the water in the coffee pot or the saucepan.

The same principal holds true for planets. They lose all of their internal heat at the surface. Since Mars is a very small planet, roughly fifteen percent of the volume of Earth but only eleven percent as massive because of differences in density, Mars lost the internal heat generated during its formation a long time ago. Hundreds of millions, perhaps even one or two billion years ago, all geological activity on Mars simple stopped. There was no more sea floor spreading, no more subduction, no more marsquakes and most importantly for the future of the planet, no more volcanoes.

Up until that point, Mars was probably incredibly Earthlike. It had vast seas, a thick atmosphere and, quite probably, life. Once that last volcano erupted though, it was all over.

When a volcano erupts, it releases three major gases -- carbon dioxide, sulfur dioxide, and water vapor. All three of these are greenhouse gases. At first, water could still enter the atmosphere through evaporation. The problem is, when water condenses and falls as rain or snow, it has a tendency to take CO2 and SO2 out of the atmosphere with it. Slowly, over thousands or even millions of years, the natural cycle of evaporation and rain leeched both gases out of the atmosphere, and as they were leeched away, the temperatures on Mars began to fall. Eventually, the planet got very cold, the rate of precipitation outstripped the rate of evaporation, and the level of water vapor, the last greenhouse gas entering the atmosphere, began to fall. The temperature sank even further. The rain turned to snow and a blizzard started. This blizzard lasted for millions of years and carried the bulk of Mars's atmosphere to the ground with it. In the end, Mars's atmosphere was nothing but a thin envelope of CO2, but the bulk of the original atmosphere and water (not all, but the bulk) is still locked up in ice sheets below the surface of Mars.

Now, if current theory is right, if all of those atmospheric gasses and all that water is trapped in the upper layers of the Martian crust, the last thing you want to do is hit Mars with enough force to restart the planet's geological processes.

To give you an idea of the force involved, let's consider the Earth for a second. At some point in the distant past, and the number varies from around four to around one point five billion years ago, depending on who you ask, an object roughly a tenth the mass of Earth struck the planet at a closing velocity of roughly thirty-five times the speed of sound. Just for reference, Mars has about eleven percent of Earth's mass. In other words, Earth got hit with an object the size of Mars traveling at mach thirty-five. Not only was it not sufficient to turn the entire planet molten, but if you believe the one point five billion year old number, which is supported by some pretty compelling evidence, it wasn't even enough to wipe out all life on Earth. What it did do was cause the eruption of almost every volcano on the planet, boiled away massive amounts of ocean and blew off a divot that we refer to today as "the Moon."

The Moon, coincidentally enough, is about one tenth the mass of Mars. That being the case, if you were to take the moon and toss it at Mars at thirty-five times the speed of sound, it wouldn't turn the planet molten. It would almost certainly turn vast tracts of the surface molten, trapping a large portion of the remnants of the Martian oceans and atmosphere in the rock that would form as the planet re-cooled. It would also blow huge chunks of the Martian surface into space where they would either escape and become a hazard to Earth and anything we put in space, or form a debris field which would make access to Mars that much more difficult. The gravity of Phobos and Deimos would likely prevent them from accreting into a new moon, so, eventually, the debris would fall back to the surface.

There is also something else to consider. When the Earth got hit, the interior was still hot. It could absorb the impact more readily that Mars will be able to, because the interior of Mars is solid. It's entirely possible an explosion large enough to make Mars molten would instead shatter the planet. And that doesn't even consider how long it would take the surface heat to dissipate. It could take thousands of years before the surface was livable again, all for no real gain.

Now, at this point, you might be asking, why bother restarting the geological processes in the first place? Well, restarting the geological processes isn't actually necessary to make the planet habitable. It's only necessary in order to keep the planet habitable. If you can reheat the interior of the planet, you get the CO2 cycle back, which means that the planet can keep itself warm again by putting CO2 back in the atmosphere through volcanism. The other major benefit is the magnetosphere. We'll come back to this in a moment.

I just said it wasn't necessary to restart the geological cycle in order to make Mars habitable, but let's take a quick look at what is necessary. There are two major steps in turning the surface of Mars into an environment that you can survive in without a space suit or some kind of sealed habitat.

The first is to warm the surface of the planet. A lot of methods have been suggested for this, everything from the asteroid bombardment I mentioned earlier, to hanging giant mirrors in orbit. Margarita Miranova, grad student at the California Institute of Technology, recently suggested dumping large quantities of octafluoropropane, a colorless, nontoxic gas with a faint sweet odor into the atmosphere. Octafluoropropane, better known as R218, is used in refrigeration and manufacturing. It's also a persistent, highly effective greenhouse gas. If we pumped enough of it into the Martian atmosphere, it would kick off a greenhouse effect which could, in theory, melt the atmosphere out of the Martian soil. It would take an awful lot of the stuff, it would be incredibly slow, and there is another problem. The latest data from the Mars Express indicates ice as far down as one point eight kilometers in places.

If you want to free all the water and atmosphere you've got to heat the ground down to about two kilometers. The greenhouse effect alone won't accomplish that. Sinking a massive network of underground pipes and running a heat carrying liquid through them could do it. The temperatures in the heat exchange system of a nuclear reactor regularly get up to several hundred degrees. If the coolant exiting the heat exchange was then pumped down into the pipes, you would get an artificial geothermal process which could heat the ground, but again, it would be a slow and expensive process.

There are other tricks that can be used as well. You can pump liquid water out of the heated ground and spray it into the atmosphere where it can be heated by microwave towers. The microwave towers can be powered by building solar towers which generate power by heating the air inside a large greenhouse and letting the resulting convection currents drive turbines. Not only does this power the microwave towers, but the heat generated by the process is dumped straight into the atmosphere. You can even build fusion reactors in orbit to serve as miniature suns. Whatever methods you employ, the process will be slow and expensive. It will also be highly labor intensive.

Once you're done cooking the atmosphere out of the ground, you get to step two, making the atmosphere breathable. There are three ways to go here, and two require the large scale introduction of anaerobic bacteria into the Martian ecosphere. The first method is to introduce a bacteria that takes in CO2 and releases O2. The problem is, unless you've restarted the geological processes, you'll be stripping your atmosphere of C02, which it needs. The second option is to introduce an organism that eats iron oxide (rust) and excretes O2 and iron. Since the entire surface of the planet is covered with iron oxide, you would get a lot of oxygen this way. You'd also get a surface covered with conductive iron dust, which is going to play all kinds of hell with your electronics. The third is to split your water into oxygen and hydrogen via electrolysis (the same method used to produce oxygen on nuclear subs). This method leaves you with a lot of surplus hydrogen that can be used for fuel, but unless you've restarted the planet's geological processes, it's not that great an idea.

Yes, we're back to restarting the geological processes, because in addition to releasing greenhouse gasses, which can be done artificially, heating the planet's core also would allow the planet to develop a magnetic field, which in turn gives the planet a magnetosphere.

The magnetosphere is an important feature of any planet you want to make habitable. The magnetosphere largely prevents the direct interaction of the planetary atmosphere and the solar wind. Without it, the solar wind would strip away the upper layers of the atmosphere. Among other nasty effects, this can lead to the breakdown of water vapor into oxygen and hydrogen and the stripping of the hydrogen from the atmosphere, preventing the reformation of the water, which can lead to some nasty chemical reactions in the atmosphere that can destroy your ecosystem. The magnetosphere also helps to protect the planet from various radiation hazards including cosmic rays. It helps shield communications hardware from solar flares and coronal mass ejections (although not perfectly, and under the right circumstances, it can actually worsen the effects). Like the volcanic out gassing of CO2 and SO2 mentioned earlier, a magnetosphere is not necessary to make