It's a popular Sci-fi theme to terraform Mars (or sometimes Venus), but both need a lot more than just a breathable atmosphere to be habitable, almost to the point of impracticality. Mars receives too little light, Venus too much, neither has a whole lot of water and neither has much of a magnetosphere (water and air are probably not too bad, but I imagine the magnetosphere'd be a killer). Not to mention spinning up Venus to a sensible day-night cycle.

My question is: Are there any astronomical bodies in the solar system worth terraforming? Or is it far better value to just build giant space stations and use the other planets for resources as opposed to refuge. There's a couple of centuries to play with here so no rush and the tech is based ~200 years ahead so things like decent sub-light travel (no ftl... yet), controlled fusion, off-world mining, city-sized space craft etc are common place.

(While I think it'd be cool to have a local terraformed world or two, I get the feeling that it's just not practical, not impossible, just not a worthwhile use of materials, but I thought I'd ask people more knowledgeable than myself before ruling it out altogether.)

Edit: There is a not totally unrelated question here: Order of Solar System Colonization but that seems to be primarily about colonisation, but more importantly states that "To this end, planet-wide terraforming, for example, is out of the question" as they're dealing with 2016 tech as opposed to 2216 tech, whereas I'm curios if there's any other local planets/moons etc. besides Venus and Mars that would be suited to terraforming.

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    $\begingroup$ Venus is far more viable for terraforming than any other object in our solar system. Mars doesn't come even close, largely due to the impossibility of an atmosphere and low gravity. $\endgroup$
    – Feyre
    Commented Apr 12, 2017 at 21:06
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    $\begingroup$ @Feyre: It's not impossible for Mars to have an Earthlike atmosphere, if you import it from elsewhere. (Which seems to be to be easier to do than to get rid of Venus' excess.) After all, it did have one originally. If it leaks away in a billion years or so, so what? $\endgroup$
    – jamesqf
    Commented Apr 13, 2017 at 4:48
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    $\begingroup$ Terraforming vs space station is a matter of the way your tech developed. Cheap anti meteorite shields and solar wind shields? Habitats. Cheap Lagrange point magnetic generator? Planets and moons. $\endgroup$
    – Mołot
    Commented Apr 13, 2017 at 6:39
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    $\begingroup$ @Feyre: No, a Martian atmosphere would not drift off at a fast rate. The proof of this is that it originally did have a dense atmosphere (and an ocean), and held it for a billion years or so. $\endgroup$
    – jamesqf
    Commented Apr 13, 2017 at 17:26
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    $\begingroup$ "While I think it'd be cool to have a local terraformed world or two, I get the feeling that it's just not practical, not impossible, just not a worthwhile use of materials..." The ADVANTAGE of terraforming a planet is materials. Planets are large, and made of all kinds of materials. It's so much easier to only travel a mere thousand or so miles to mine what you need, rather than astronomical distances. That's a prime selling point of planets. $\endgroup$
    – Jedediah
    Commented Oct 13, 2020 at 21:35

5 Answers 5


Venus and Mars are the best candidates available, so if you discard them from the beginning, then no. Certainly you would have to move any candidate to a better position relative to the Sun, just for starters.

It seems to me that you are somehow forgetting how big a planet is1. Changing it so radically that it becomes close enough to Earth is never going to be an easy task, unless it was very close to Earth to begin with.

In a somewhat unrelated note, AFAIK the issue with Venus is not so much distance to the Sun as the high atmospheric pressure inside it and the mix of gases causing a "greenhouse effect" of biblical proportions, which makes it way more "terraformable" than Mars.

1Useful hint: take a little walk. That thing is HUGE!


I'm going to borrow some thoughts from Kim Stanley Robinson's book 2312, which articulates my thoughts on the subject extremely well.

Terraforming Venus

...would actually not be all that difficult, just kind of slow.

You'd start with a sun-shield, preferably one covered in solar panels, at the L1 point between Venus and the sun. This would have the dual effect of lowering Venus's temperature and giving you copious energy to work with. You could also include a strong magnetic field generator in your sun shield, which would deflect the solar wind away from Venus, reducing atmospheric stripping.

Without the sun constantly heating it, Venus's atmosphere would be able to cool rapidly. I don't have the numbers on me, but certainly within a century or so the carbon dioxide would begin to precipitate out of the atmosphere - it would snow dry ice.

Your task then would just be to decide what you want to do with the CO2 ice, crash a couple of asteroids into the planet to both add water and spin it up, then you could selectively open the sun shield to re-warm the planet to a comfortable temperature.

Teraforming Mars

Mars has two problems - it's cold, and it lacks a magnetosphere to hold onto its atmosphere. Problem one is easily solved - orbital mirrors. With large solar arrays in orbit, you can focus a lot more light onto the planet's surface, increasing its temperature. Those solar arrays could also use some of the power they generate to create an artificial magnetic field. You can also do something similar to the Venusian sun-shield, and place an artificial magnetic field at L1 to deflect the solar wind.

Terraforming Asteroids

HOWEVER...asteroids are our best bet for extraterrestrial habitation. You'd select your reasonably-sized asteroid and start hollowing it out, leaving a nice thick layer of rock around the outside for hull integrity and radiation shielding. The material you remove from the inside will become raw materials to thicken the outside and build your technology.

Once you've got a nice hollow rock, you can install airlocks and add engines where needed, then spin it up. The interior is now an O'Neill cylinder, and you can build your landscape there. Robinson calls these asteroid habitats Terraria.

The best thing about basing your population in terraria is that you don't need to worry about gravity. Spinning your rock will simulate gravity very nicely, certainly well enough for humans and animals to live comfortably, while at the same time giving you easy access to microgravity.

In the long term, living on a planet is not an optimal strategy. Planets are too big for a space faring species to use them as a base - they can't dodge debris, and it's too energy-intensive to try to travel around them or to leave them. You'll want some population on planets, yes, to maintain the ecosphere and so on, but in the long term, the future is in space habitats.

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    $\begingroup$ Depends on the bacteria you use - there are species of halophilic bacteria we could use to clean the soil and the water, not to mention that once you've got running water it's going to dissolve a lot of those salts and carry them into the seas. $\endgroup$
    – Werrf
    Commented Apr 13, 2017 at 14:04
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    $\begingroup$ A lot of things depend on factors we don't have good data on yet. Such as the ratios of toxic substances (perchlorates) to non (potassium, iron). Eg, if the entire surface was 100% iron oxide, it would be worthless as a soil, bacteria and water won't help. But at the moment we think the soil is about 8.3 pH with traces of various chemical compounds helpful for supporting life. $\endgroup$ Commented Apr 13, 2017 at 14:34
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    $\begingroup$ Some recent research shows that we may not need to induce magnetic fields in Mars and Venus. Simply positioning a 1 Tesla magnetic field in the L1 point may but sufficient for shielding the atmosphere of those planets. phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html $\endgroup$
    – Jim2B
    Commented Apr 14, 2017 at 20:42
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    $\begingroup$ and I very much like and agree with your point - any planetary terraforming is going to be slow. They are projects we would start so our grandchildren (or later) might have a nice place to move to. $\endgroup$
    – Jim2B
    Commented Apr 14, 2017 at 20:43
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    $\begingroup$ asteroid proposal really is the worst, as recent asteroid missions kinda point out - u spin the thing just a little and it will fly apart. using it as source materials for a new construction yes\maybe, but hollowing it out is just no $\endgroup$
    – MolbOrg
    Commented Feb 2, 2021 at 13:05

The key to all of these sci-fi futures is the (magical) force field generator (FFG). If you can squeeze together deuterium and tritium (and keep it together) then fusion power is easy.

If your FFG is small enough to put on a rocket (or truck), then space travel is a breeze. But you still have conservation of energy and momentum. I didn't do the math, but you can calculate the amount of mass you have to remove from Venus' atmosphere, and convert that to the energy required.

You can do the same thing with the mass you'd need to drop onto Mars (but where would you get it from? Jupiter? Or some fusion process where you convert H into O?) Your question about "worth" assumes, ahem, that value is an objective property. It is not. You almost recognize that by comparing the value of a terraformed planet with the value of some city in space.

Which is worth more? Well, mama lives in Texas, so would I rather be 4 hours away or 4 months? Depends on my relationship to her. Different people will value those two choices oppositely.

Anyway. I find the idea of city sized space craft absurd. Why bother? What possible reason would we have to make such silly things? 70% of Earth's surface is water. Long before it makes sense to terraform Venus or Mars, we'll have populated not just the oceans but the skies of Earth. Think "floating" cities (thanks to force fields!).

Just think, to double the current population, we'd only need to double the size of each building (crudely speaking). I can go wildly off into ya-ya land, pretending that in some (magical) future, economics will be obsolete, and any resource can be made from hydrogen. Such a future might be possible, if only force fields could be made that were better at shielding and holding things than matter (lead, iron, etc.) is. A pretty big if, imho.

  • $\begingroup$ If you have an interplanetary civilisation, city-sized spaceships would be vastly superior to floating cities, simply because of gravity. Wet cities are still trapped deep in the gravity well of the planet, and need to expend enormous energy to get into space. City-ships can do whatever they want with their gravity, and aren't fighting an atmosphere when they want to move. $\endgroup$
    – Werrf
    Commented Apr 13, 2017 at 14:42
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    $\begingroup$ @Werrf: But why on Earth (or maybe off Earth would be better here?) would people want to live in giant spaceships? $\endgroup$
    – jamesqf
    Commented Apr 13, 2017 at 17:28
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    $\begingroup$ @jamesqf The same reasons they want to live in cities today - that's where the action is. Our way of life today is incredibly unnatural, but we're accustomed to it. $\endgroup$
    – Werrf
    Commented Apr 13, 2017 at 17:30
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    $\begingroup$ @Werrf: Very few people actually want to live in cities. They move there to make money, or they're born there because their parents did. Most of those who do manage to make sufficient money (a small fraction) eventually leave. But there really isn't anything you can do in giant spaceships that you can't do on Earth (except maybe manage terraforming projects :-)), and a host of things you can't. $\endgroup$
    – jamesqf
    Commented Apr 14, 2017 at 5:45

Right here.

The tech you develop for Mars can be proofed and applied to good effect in the Gobi desert and Antarctica.

There are places on Earth not quite to our liking. Even here in Texas we make use of air conditioning and all the lakes are artificial. Many places have water management and even back in ancient times this was the case.

So local terraforming is something we have been doing all along. We can continue spreading to more habitats on Earth even into the 21st century.


Space habitats are a better choice.

There are numerous reasons for that.

  • mobility
  • flexibility in desired results
  • speed of achieving the desired results
  • material efficiency
  • very high theoretical limits for resulting surface area for the approach
  • flexibility of clustering those constructions (ability to pack vast amount of people and surface in planet size conglomerate if one would wish so)
  • Full control over created environment.
  • Effectively no physical borders for the group, preventing their grow/extension as a social group.

Mobility is a good thing as it allows to choose locations(planets), distance to a star, distance to neighbors etc.

Flexibility in results - one can choose gravity, day/night cycles, weather, climate.
Ability to choose/create particular flora and fauna to live in. (Would like to see how it was in dino time to live - resurrect all those animals and well go test/see that)

The result can be achieved pretty fast, in a year or two(in certain cases even faster, in some cases slower 10's of years) instead of a long time for planetary situations even with proper technology it will take a long time to replicate earth like system just because it needs time for the planet to settle down after intervention and all doings.

Material efficiency - the materials which have to be spent on building a space habitat are in the range of 100-1000 tons per human(based on O'Neil project, it might be more or less it depends on the technology and result we would like to have). So a space body like the Moon would be enough for about 6-7 orders of magnitude more people than there are currently living on the planet.

If one would like or if it would be needed with proper technology all those space habitats(made from the Moon with 1016 humans) could be collected in pretty compact configuration, they can be placed in a sphere of a few thousand km in diameter, allowing them fast information and matter exchange.

Space habitats offer more flexibility and freedom of choice, where using of planets needs definitely not fewer efforts as it goes for technology and environment. A planet might demand some compromises, just because not all of its aspect might be accessible/controllable even with pretty advanced technologies - insides of a planet as an example, which affect different aspects of its behavior on the surface and it takes a long time to change things and for them to settle. Because of the pressure, certain parts of it might be not accessible at a required level of influence, when those processes could be manipulated/supported in the way they should be.

Everything has its price and a planet a pile of materials pretty much maintains itself for a long time, where a Space Habitat should be probably maintained regularly and constantly be monitored. However, maintenance task might be not that hard as it looks now it has to be, and it can be done with realistic(my opinion) means of ... hm it seems I can't avoid the word ... smart matter. I assume the option as realistic because I keep in mind particular implementation of such technology which is not that much sophisticated, definitely not a clarke-tech, and pretty much fits in +200 years theme and for it, maintenance would be not a problem.

But even without smart matter maintenance is pretty manageable subject, with a variety of different approaches(those I also keep in mind at least 2-3 of them).


I'm all for the Space habitats, they offer too much for too little, and planets are just a source matter for them.

Most importantly they offer flexible borders(because of there none of them), and freedom to devide the group which can be done easily and fast(opposite is true too). Those things they are important, and they can't be realized on a planet (or it will be not a planet in the sense we usually assume).


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