I'm looking to have a few worlds that were relatively easy to terraform as a first wave of colonies.

The first colonies in this setting were meant to be on worlds that were relatively easy to terraform with only one planet already able to sustain life. These easily terraformed planets were meant to be lifeless when discovered, no plants or significant microbial life. They were meant to take 20-50 years each to terraform, some being faster than others.

Is it possible for a planet to have an atmosphere that cannot support life that only needs one key addition (oxygen, water, etc.) to convert a world for human habitation in that 20-50 year span?

What types of planets, if any, would I be looking at that only need something that mankind with technology slightly ahead of our own could affect in such a short time span? Most of their advancements are in propulsion, limited FTL capability (requires gates on both ends) and energy production.

Are there any planets that meet these conditions in our own solar system that would be good testing grounds for these processes?

And what would the conditions of these planets likely be after terraforming?

  • $\begingroup$ Add super greenhouse gases and oxygen to Titan. The super greenhouse gases to keep it warm near the surface and there's plenty of water there that could be used to produce the needed oxygen. Could be a nice little test run for terraforming a planet. It already has the hardest part which is a thick nitrogen atmosphere. $\endgroup$
    – rclev
    Sep 7, 2017 at 23:42
  • $\begingroup$ According to the answer on my question: worldbuilding.stackexchange.com/questions/57042/… it would take about 200 years for algae to oxygenate an other wise lifeless earth like planet $\endgroup$ Sep 8, 2017 at 4:25
  • $\begingroup$ @DarcyThomas There are abiotic mechanisms that can give a lifeless planet atmospheric oxygen (for example titania exposed to near UV can generate oxygen from water), so algae would not be necessary for such a planet. Titania is among other things possibly carcinogenic, so something may have to be done there, though maybe only parts of the planet are covered with it. $\endgroup$
    – Eth
    Sep 8, 2017 at 12:56
  • $\begingroup$ Undoubtedly there are more than one way to skin a cat, or oxygenate a planet. It would need to be better than 19% efficient or cover an area larger than the ocean (see the 2nd part of the accepted answer on that question) $\endgroup$ Sep 9, 2017 at 21:07

10 Answers 10


Your ideal candidate should be in Goldilock zone and should already have all elements (hydrogen, carbon, nitrogen, oxygen) available. What would stop the planet from being habitable is unbreathable atmosphere or unsuitable climate.

Take precambrian Earth for example. The planet, as far as we know, was perfectly right, but the air was unbreathable. It took a Great Oxygenation Event to turn the Earth into an environment that can harbor animal life. In our case, oxygenation took hundreds of millions years. With advanced planetary scale technology it might be realistic to complete the process into 20-50 years.

Also, you can look at Cryogenian period, when the Earth is thought be be a cold snowball. The planet, again, is right, but the climate is wrong. You can manipulate the climate and cause "global warming", turning ice age into a more hospitable environment.

If your planet lacks necessary elements, you need somehow to provide them. If your planet is outside the goldilock zone, you have to move the planet or build planet-sized orbital structures. All of this is realistic, but less conceivable than manipulation of climate or atmospheric composition.

  • $\begingroup$ I just want to mention that even if a planet isn't in the Goldilocks Zone it can still be or become habitable depending on the composition or size of its atmosphere. $\endgroup$
    – rclev
    Sep 9, 2017 at 18:27

Venus, as dcy665 said, is crying out for a floating city. Isaac Arthur did a very good video on how it could be terraformed – https://www.youtube.com/watch?v=BI-old7YI4I&t=20s. He makes a very good case for why it is easier to terraform than Mars, too.

Venus has a very dense atmosphere of CO2 and Nitrogen. This allows to build fairly large floating structures filled with Hydrogen or Helium (even Earth air would float). We can then live in floating cities. Of course, this air along with extra Hydrogen (for water) will need to be brought in, which seems very difficult. Compare this, however, to Mars, whose need for Nitrogen (for growing crops) would be a lot more expensive. Venus already has Nitrogen in the atmosphere, which can be fixed into soil. Also keep in mind that Hydrogen is a lot commoner than Nitrogen. Thus, in terms of bringing things from outside, Venus is definitely better off than Mars.

Venus also has more resources than Mars, especially in its CO2, which can be transformed into Graphene.

Ultimately, Venus has fewer obstacles and more opportunities than Mars, which is why it is likely to be terraformed.

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    – Secespitus
    Sep 8, 2017 at 21:21

No it is not possible for a planet to be incapable of supporting life simply by removing one gas from the atmosphere to prevent it from being breathable. Earth actually used to lack oxygen, but prehistoric plants created it through photosynthesis. There are bacteria that breathe other gasses as well.

Probably in order to make it terraformable but not have life you want one of two things.

A young planet doesn't necessarily need to be inhospitable, it just needs to not have yet developed life.

Radiation problems could also prevent life, but could be blocked out with massive quantities of ozone, or other methods.

  • $\begingroup$ I had not thought about young planets, actually. That seems one possibility. $\endgroup$
    – Arvex
    Sep 7, 2017 at 22:27
  • $\begingroup$ Yeah, not having an atmosphere to protect from radiation and cause over cycles to develope will be the main problem in any terraformong that isn't a young planet. $\endgroup$
    – Necessity
    Sep 7, 2017 at 23:01
  • $\begingroup$ ...I find it funny that you said its not possible to make a planet incapable of supporting life by removing a gas and then suggest bringing in ozone to make a planet habitable(because it is a gas!). Though those circumstances where there isn't enough matterial to make ozone when all other things are fine are rare and were likely caused by those materials being stripped from those planets because of an event. $\endgroup$
    – Necessity
    Sep 7, 2017 at 23:06
  • $\begingroup$ Mars is a great example of radiation problems and needing to use other methods to fix it. Mars main fault is its weak magnetic field due to weak internal movement. NASA is looking into making something that can create a large magnetic shield so that mars can create an 'natural' atmosphere. $\endgroup$
    – Necessity
    Sep 7, 2017 at 23:12
  • $\begingroup$ @Necessity I was referring initially to making the air un-breathable by removing a gas. $\endgroup$
    – Braydon
    Sep 8, 2017 at 20:43

The current best candidates are Mars, asteroids and the Jupiter moons Ganymede and Europa.

Mars was for all what we know now very similar to Earth, it had a magnetosphere, oceans and even likely at one time oxygen.

The jupiter moons are ideal for submerged cities because they are water/ice worlds so we can build structures under the ice. We won't live on the surface anyway because Jupiter's radiation is much too high, so we will live under the protecting ice shield.

Asteroids are also possible as domed colonies, but their gravity is much too low to hold an atmosphere.

Merkur is far too hot.

Venus is quite a problem because of the thick atmosphere and hellish conditions. It may be possible to decrease and rebuilt Venus atmosphere, but it at least a much more difficult task than the other planets.

The moon is only suitable for domed colonies.

All gas planets have no surface, so no structure can be build on this planets.

  • $\begingroup$ Venus aches for a flying city. High enough to approach reasonable pressure and temperature. Rats, now I have to look for something like it. ;-) $\endgroup$
    – dcy665
    Sep 8, 2017 at 3:44

Sterilized planet

sterilized planet comic panel from http://starwars.wikia.com/wiki/Sterilization_of_Geonosis

One could have an Earthlike planet where everything has died. This might have been done on purpose by an intelligent agent, or by accident by an intelligent agent. Or it might have happened from some cosmic event; the Permian extinction occurred due to hyper volcanism and came close to wiping out Earth life. One can think of other life sterilizing scenarios - nearby supernova, solar flares, impact event.

If the reason that the sterilization happened is over, such a planet would be toothbrush ready.

Moonless planet.

Could one have a nice planet like earth that just never found a moon and settled down to make babies? Maybe.

from https://www.space.com/12464-earth-moon-unique-solar-system-universe.html

The moon has long been recognized as a significant stabilizer of Earth's orbital axis. Without it, astronomers have predicted that Earth's tilt could vary as much as 85 degrees. In such a scenario, the sun would swing from being directly over the equator to directly over the poles over the course of a few million years, a change which could result in dramatic climatic shifts.

Such shifts have the potential to impact the development of life. ... Once the violent formation period ended, the researchers' simulation showed 180 planets, almost half of which wound up with a moon. But, most of these satellites were too small to be comparable to our Earth-Moon system. Only fifteen pairs — about eight percent — resemble our unique planetary system.

Earthlike but with dramatic climatic shifts might make it tough to evolve life, but such a planet should be a chip shot to terraform. Earth has photosynthesizers that can handle dramatic climatic shifts, at least in the geological short term. A few truckloads of them should get the job done.

  • $\begingroup$ These both seem like good possibilities. $\endgroup$
    – Arvex
    Sep 9, 2017 at 15:39

I have been researching terraforming as well. Atomic Rockets has a good article about it

Science fiction Encyclopedia Terraforming

I ask a question recently specific to changing oxygen which has some links you might like.

I guess with such a short timeline you would have to have one small things off such as a couple of percentage points of oxygen. Maybe the atmosphere is okay but little water and your colonists force an asteroid (or many) of frozen water down the gravity well.

With 60 years they might be able to genetically alter the humans to live in the new planet's environment.


This answer assumes that a terraformed planet allows establishing a self-sustainable settlement on its surface without the need for special protection such as domes or special suits. In other words, once a planet is terraformed it becomes Earth ver. 2.0 with some small but insignificant changes.


With your conditions, Mars is the only option potentially suitable for terraforming:

  • it is close enough, so we do not have to spend years (or centuries) travelling to it before we can establish an FTL gate;
  • it is big enough to hold an atmosphere;
  • it has easily accessible (but frozen) water;
  • it has a continental-like crust;
  • it seems to have no life presently.

The drawbacks:

  • Mars is cold (perhaps can be fixed with an atmosphere and controlled greenhouse effect);
  • its gravity is only 38% of Earth's, which leads to not well-understood health consequences;
  • it is not clear how low gravity will affect our ability to produce food in a long run;
  • the tectonic activity is either dormant or non-existent for a very long time;
  • it has no magnetosphere (theoretically can be fixed with a big electromagnetic shield);
  • there is a remote possibility that as we revive the planet we will encounter potentially dangerous prions or primitive life.

With the current or slightly higher level of technology, your main challenges most likely would be related to transporting raw materials to Mars to create a breathable atmosphere and topsoil essential for establishing an Earth-like ecosystem.

Ecosystem itself will be an enormous undertaking, and I am not sure it is possible to achieve a somewhat balanced state in a period of several decades. You will need just the right mix of bacteria, plants, insects, and whatever else you want to be there for the system to function properly and not to collapse. Even if we have enough processing power to model an entire eco-system, we do not know enough for the model to be very accurate. Therefore, we'll be forced to resort to a combination of modelling and trial-and-error approaches. It takes time. Or we might get lucky :)

You will also need to build, man, and maintain an extensive network of observational stations that will monitor the world. They will be necessary to make sure that everything is balanced. The collected data will be invaluable for terraforming tweaks (if necessary) and early warnings.

Other Planets

From what I read no other planet, moon, or asteroid in the Solar system can be terraformed with modern or near-future technologies. (Protected settlements are possible, though.) So, they are off the list.

Planets in other star systems are just too far away and do not fit into your timeframe. They might be very much like our Earth and require minimal changes, but just travelling time to them is enormous. You might get to them faster if you wait a century for more advanced space travel technologies.


For a basic introduction look here.

However, 50 years from lifelessness to life? And that's an "easy" terraform? If transportation isn't the problem, no one would start with a lifeless planet unless there wasn't an option. They'd look for the most life-bearing planets they could find.

  • Large enough mass to hold down an atmosphere

  • Existing atmosphere

  • Goldilocks positioning from the Sun (not too hot, not too cold....)

Adding water, methane, etc. isn't that hard if you have propulsion technology. Find asteroids that are mostly ice and drop them onto the planet (tracking with the spin to minimize impact velocity, of course).

But, 50 years? That would suggest you're starting with a planet that can support saplings for almost anything but Poplars. In reality, terraforming would take centuries to get to the point of general tree growth and a well enough fixed ecology to support animal life.


Several other answers have mentioned Mars, but that planet does not meet your criterion that a slightly more advanced civilization could terraform it in 50-100 years. Every serious proposal for terraforming any planets in the solar system have had timescales of thousands of years. I think the primary problem is the quantity of oxygen that would have to be liberated to produce a breathable atmosphere. Just to give an example of how hard it is to change a planet's atmosphere, global human industry is fairly efficient at producing carbon dioxide, since it happens as a byproduct of much of what we do. But it would take us 500 years to produce the amount of CO2 to match Mars' current atmosphere, and that's working within an atmosphere with lots of existing oxygen that wants to combine with carbon. But, as I said, that's just an example of how much work it takes to produce that much gas. What is really needed is lots of oxygen, and probably even more nitrogen to make a really satisfactory atmosphere. Breaking apart oxidized compounds to get oxygen is much harder than burning fuels to get carbon dioxide.

Of course, the approach would be to use plants, but they are not fast either, and there is just not that much CO2 on Mars to be converted into oxygen. I don't know how much is locked up in the ice caps, but ice caps take a long time to evaporate, and we haven't even talked about where we would get the heat from.

But I have the impression you are talking about a hypothetical planet, perhaps in another solar system, that would need to be terraformed. That is still a very tough problem, for pretty much the reasons that apply to mars. I have some suggestions, though:

  • The planet lacks an ozone layer and is uninhabitable because of UV exposure. The idea of an artificial ozone layer has been studied.

  • The planet is unacceptably hot, but not quite at runaway-greenhouse levels. It could be cooled by the same means that have been considered as a last-ditch method to combat climate change (SO2 in the upper atmosphere to block sunlight). Perhaps also some CO2 could be scrubbed from the atmosphere.

  • The planet is too cold. We know how to add CO2! (To do that well, we need an oxygen-bearing atmosphere, which is hard to explain without the presence of life. We also need a source of carbon that is convenient for burning, which on earth would also mainly come from life. But perhaps there is life on the planet, it's just not useful to us.)

I guess that's all I can think of. I think the best approach is to think of ways we may be about to mess up Earth, and imagine reversing that.

  • $\begingroup$ carbon does not come from life... life uses it as one of the building blocks. However, the main problem for colonising another star system is travel time. There is no FTL before gates are established unless we are talking about a StarGate type universe where gates are leftovers of some old civilisation. But if this is the case, why bother with terraforming at all? Just find an already terraformed planet and colonise it. $\endgroup$
    – Olga
    Sep 8, 2017 at 4:59
  • $\begingroup$ @Olga - nothing in the OP's question suggested that FTL wasn't available. But if you're limited to, say, a hundred times the speed of light, you'd still be limited in your selection of planets. $\endgroup$
    – jdunlop
    Sep 8, 2017 at 5:06
  • 1
    $\begingroup$ @jdunlop, the OP states: "limited FTL capability (requires gates on both ends)" $\endgroup$
    – Olga
    Sep 8, 2017 at 6:59
  • $\begingroup$ @Olga - you're correct, my mistake. $\endgroup$
    – jdunlop
    Sep 8, 2017 at 14:32

If speed is your goal then the best you can get is to add at least one zero to 20-50 years and you have something possible with really advanced technology (really cheap interstellar transport). You just need to add oxygen and bacteria.

Start with a world nearly identical to the early earth, as close as possible, with only very earliest forms of life, (barely having cells). Then spread your own bacteria and algae on an industrial scale, let them liberate oxygen, and wipe out the native stuff on their own. That will get you oxygen in the atmosphere. 2-300 years is possible with enough mechanical help. Your real issue is not making oxygen it is using/filling up enough the rocks/sediment that will bind up all the free oxygen, it will be constantly sucking the oxygen out of the atmosphere. You are not making the same level of oxygen as the modern atmosphere you are making about ten times that at a minimum. If your people can import billions of tons of oxygen then can speed it up my an order of magnitude. It took at least a billion years to do this on earth, if you import huge quantities of oxygen (electrolyse a few comets) you can speed this up, kill off the native life, and probably see some really cool gigantic sized fires all at once.

Then you want to spend a few decades or so building soils using more imported bacteria, Then you can start importing plant and animal life and living on the surface, taking another few decades. All together you are talking anywhere from 3-500 years, maybe half that with really advanced technology (lots of automation and bulk interstellar travel).

People can start living on the planet right at the beginning as long as they are living in domes or other enclosed environments with greenhouses for making food. They can even use their waste products to speed up the terraforming process if the sterilize it first.

Alexander's mention of the snowball earth time period works as well, although it will be a lot harder to wipe out life that advanced, though this could provide additional material for the story with persistent pockets of the native life. Of course you will have a lot of protest about wiping out native life.


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