Here we go again. I'm doing NaNoWriMo this year (which is what I should be working on instead of a blog post), and because it takes place in part on Mars I've seemed to have fallen off the terraforming deep end again. I'll assume you know what terraforming means and dive right into it.
I really like the idea of terraforming other planets to make them habitable for humans. It's the most permanent solution to sustaining a larger human population. Mars and Venus are the most likely candidates, but I sometimes wonder: what if we terraformed every possible world in the Sol System?
Now, there's obviously this scenario, which is by authorial admission impossible. But there are a large number of potential terraforming candidates around. Let's go through the list and see what we think.
Mars
Sol IV is the most likely planet for terraforming (considering that it's the most similar planet to
Terra in many regards and arguably more gravitationally suited to human life) and has been subjected to the most academic treatment. I rather expect that terraforming work will have begun within one century; it wouldn't terribly surprise me if it's begun within fifty years.
I won't waste space discussing this when there's more planets to get to.
Venus
Next up is Venus. Venus is sometimes known as Terra's sister planet, because it shares many geological similarities. In the aspects most critical humans, atmosphere and rotation, it differs greatly. The atmosphere is thick, beyond boiling hot, and completely poisonous. A day is longer than a Venusian year. Altogether, it's probably the least hospitable world in the Solar System.
That said, though, it's probably one of the easiest to make fully habitable. The atmosphere of Venus is mostly carbon dioxide, which isn't that difficult to convert to a more pleasant gas, oxygen. Most discussion on terraforming Venus centers on using genetically-engineered microbes to slowly convert the CO2 in the upper atmosphere, working their way down to the surface. Without the greenhouse effect of CO2, the planet will cool off into temperatures compatible with liquid water, Terran life can be introduced, and the rest is relatively minor.
The thing most proponents of terraforming Venus overlook, of course, is the extremely slow rotation. Most handwave this with the assumption that by 2400 or whenever we get around to this, we'll have the technological know-how to angularly accelerate a planet.
I can think of a few ways to do this with near-future technologies, though. First off, evidence indicates that we'll need to introduce more water to Venus to make it truly terrestrial, and the usual tactic proposed for achieving this is by redirecting comets to skim the atmosphere, melting and imparting their water (and potentially absorbing some of the heat).
Why not kill two birds with one stone, though? If we wait on adding more water until the bulk of the atmosphere has been removed (and might I suggest using cycling scoop-ships to move CO2 to Mars, where it's actually needed?), we can use the cometary impacts to speed up the planetary rotation. Slamming the comets into the equator would impart an angular acceleration.
I haven't done the math on this, but I assume that we'd need to use a truly astronomical number of meteoroids to get the planet up to speed. However, there is another option available to us: mass drivers. The industrialization of Venus can begin long before common colonization takes place. Venus could potentially be the system's factory planet (though Mars would be a more suitable candidate, with it's lower gravity and great chemical resources. That isn't to say that Venus wouldn't be an industrial power. Exporting minerals off-world would make a fortune, especially for use in colonizing the Lagrange Points and the Inner Solar System. (Remember, Venus has a lower gravity than Terra and might be a better starting point for trajectories.)
Suppose we put a whole bunch of mass drivers on the equator, pointed against the direction of rotation (Venus rotates so slow that it wouldn't sacrifice much of the acceleration advantage). Launching huge masses of materiel off the equator would speed up rotation and slowly reduce the planet's mass, which would speed up the process even more.
Still astronomical numbers, though. Maybe we should just set off a string of h-bombs around the equator. I've got a better use for our nuclear arsenal, though.
Mercury
The big issue with terraforming or even colonizing Mercury is its proximity to Sol. To fix that, I say just move the whole planet.
This isn't as ridiculous as it seems. We've the nuclear capacity to bomb the Earth's surface several times over. If all that were concentrated in one place, and set off in fairly quick succession, it could impart the force needed to move a small planet. Now I haven't done the math, but we'd probably need orders of magnitude more megatonnage of TNT to actually accelerate Mercury so it assumes an orbit further from the sun (I'm thinking 1.25 AUs but that might be too far out when considering interactions with the other Inner Planets). We know how to make nukes, though. Maybe some of the mass lifted from Venus could be h-bombs, using Venusian uranium as the triggers.
Mercury has a natural place to use these, as well: the Caloris Basin, the biggest crater in the Solar System. I'd say we give it a once over with the existing nuclear arsenal of Terra to harden it up (not to mention nuclear disarmament), before blasting it with enough bombs to move it to another orbit. It wouldn't need to be too fast, either: if it's not going to cross the orbit of Venus, the path could take a century; even if it does, the time constraint might be several decades at the minimum.
The rest of the terraforming would be fairly simple: just dump atmosphere, water, and seed with life. It might take awhile to get to safe radiation levels, though. Maybe if we ever get "clean" nukes figured out.
That's all the planets out there (unless you count Pluto, which would melt at human-habitable temperatures). But there are other worlds we could terraform.
Europa, Ganymede, and Callisto
The idea of making some of the Jovian moons habitable goes back a long way, but I haven't come across to much serious work on the issue. We know they have water; the real issue is getting the other materials. Additionally, there's a lot of radiation coming off of Jupiter (Europa in particular orbits near a major radiation belt), and they've all got relatively low gravities.
I'm somewhat on the fence about these. There's little need to terraform them, and there's easier candidates out there. If we find intelligent life under the surface of any of them, they're out of consideration. (The same goes for any other world on this list.)
Titan
Titan is probably about as far out as we can go and still hope to terraform, at least while Sol is still a yellow dwarf. It's got all the chemicals for life: after Mars, it's the most likely place to find life in the Solar System. The big challenge would be converting the atmosphere from nitrogen to oxygen. My guess would be to leave the nitrogen alone, and just pour in oxygen (harvested from Venus, maybe?). Heating it up would also be an issue.
On this one, I'd say leave it alone. We can colonize it easily without terraforming, and use the same sort of life support techniques the rest of the Saturnian colonists will need. Bear in mind, too, that once the sun does become red giant, the increased warmth means that Titan could become a proper complex chemistry world, possibly bearing complex life.
Luna
Having a fully habitable world just three days away would be a great incentive to get people off the planet, but I'm not sure there's any way it can be spun economically. Mars is a much better terraforming candidate, and about as easy to reach (delta Vs, you know?). Most of Luna's potential utility comes from the very fact that it lacks a significant atmosphere and biosphere, which allows all sorts of industries impossible on Terra without any need for environmental oversight--all three days from home.
Without even considering the horrible aesthetic damage, it's a no from me, unless you're really desperate for places to put people.
Ceres and Vesta
The major asteroids are about as small as you can go before trailing off into ridiculousness. Sure, you could do it, but what's the point? The advantage of asteroids is that you can drill holes straight through them at reasonable costs: it'd be easier to hollow them out and pressurize the insides.
On the other hand, though, these are small enough that paraterraforming is potentially affordable and technologically doable. I'd say that, maybe within a few centuries, it might be worth considering. Start with domes for the moment, if you care about seeing starlight.
This concludes my rambling sleep-addled thoughts on terraforming.
