Let's say we are about a century in the future. The Earth's overcrowded, so natural resources fundamental to life as we know it (water, farming soil, energy, food) are not enough to meet everyone's needs (we can hypothesize we have evolved in a worldwide super-fair society, so social inequalities between different countries are non existent: we're all starving the same way).

The only way to avoid extinction is to transfer half of the world's population (let's say about 7-10 billion people, from a total of about 15-20 billion people) to another planet capable of hosting sustainable life.

It is a worldwide project: all governments, space agencies, research centers, major companies, share all of their resources in order to accomplish it and preserve humanity.

The other planets in and around the Solar System are inadequate: their gravity is either too low or too high for us to live, or can't be terraformed.

So we decide to engineer a planet like the Earth, with gravity, temperatures, atmosphere, soil chemistry and non-human life forms similar to those on Earth (and then bring all those people there).

We are in the 2100s, so the technology is quite better than the one we have in the 2010s, but nothing fundamentally different (e.g.: faster and larger spacecraft, larger and more efficient robotics, higher survival rates for serious diseases, but nothing like human teleportation or biological immortality).

Notice that, in order to transfer people efficiently, the planet must also be reasonably close to the actual Earth.

How do we do it?

If you like to think about it, more specifically:

What do we need to do it? Where do we start? Who's gonna do it (planning, design, manufacturing)? How long will it take?

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    $\begingroup$ IMO, if we had the technology to move 10 billion people to an new 'engineered' planet, we'd have the technology to not need to do so. $\endgroup$ – GrandmasterB Jun 23 '16 at 20:38
  • $\begingroup$ First, the population of the planet is not going to be that high by 2100. We are talking around 11-12 billions max. Secondly, if we started using our resources more efficiently, we could sustain that many people. But the rich countries might have to lower their consumption of some goods like fossil fuel. $\endgroup$ – Vincent Jun 23 '16 at 21:06
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    $\begingroup$ Agreed. If you have enough energy then you can easily support 20 billion people. Use intense, artificially lit vertical farms with desalination, recycling... If you don't the sending things to space is HARD. $\endgroup$ – Donald Hobson Jun 23 '16 at 21:07
  • $\begingroup$ I think this question is too broad. We know too little about the society and technology to effectively answer it. $\endgroup$ – Xandar The Zenon Jun 23 '16 at 23:11
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    $\begingroup$ Using current technology, even in sustainable form, the world could support closer to fifty billion people. Also, richer countries are already leveling off their population. Space habitats are easier to build than planets. And the biggest problem: population growth isn't a sudden issue. If the planet can't support twenty billion people, there won't be twenty billion people. If we handwave all those issues, then what are the remaining things that we can't handwave? $\endgroup$ – Brythan Jun 24 '16 at 0:33

Quite simply: We don't.

Let's hand-wave a bit.

Suppose, for sake of argument, that we were able to teleport material to the L5 Lagrangian Point, where it could coalesce into a planet. Where are we going to get this mass from? If we got the entirety of the asteroid belt, we would have a "planet" with about 4% of the mass of the moon. In order to get even close to the same scale as Earth, we'd basically have to combine as much of the solar system as possible.

But even that doesn't really work -- if we were to start with Mars and then add Mercury, the moon, the entire asteroid belt, the moons of Jupiter, and the moons of Saturn, we'd end up with a planet that has about 26.5% the mass of Earth. Not nearly enough to get a similar gravity to Earth.

All that aside, even if we were able to make a planet the size of Earth, getting seven billion people off the planet takes a looooot of energy. Without some type of significant advance in rocketry or propulsion, it's just not going to happen.

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    $\begingroup$ ...So you're saying there's a chance. $\endgroup$ – Ranger Jun 23 '16 at 20:48
  • $\begingroup$ You could borrow sum mass from sun. It will be only 0.000003003 of sun to create earth - assuming we can teleport it and contain enough to cool it. As a bonus it should give about 1.703×10^32 J. Since delta T is quite large between space and cooling earth carnot cycle should be efficient way of getting energy. Hopefully enough to transport 7 billion people. $\endgroup$ – Maciej Piechotka Jun 23 '16 at 23:48
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    $\begingroup$ The problem with taking mass from the sun is that you're getting the wrong kind of mass. To build a terrestrial planet, we need heavy elements, like iron, not gaseous elements like hydrogen and helium. $\endgroup$ – Nick2253 Jun 23 '16 at 23:58
  • $\begingroup$ I believe that your calculations about the mass of our new Earth is right, but your wolframalpha's link produced an error for me. $\endgroup$ – Victor Stafusa Jun 24 '16 at 1:39
  • $\begingroup$ @VictorStafusa I think I see what's up - WolframAlpha tries to be smart, but isn't always. By default it thinks that "Mass of Mercury" is referring to the atomic mass of the element Mercury, not the mass of the planet. Change the wording of that part (like move Planet to be in front of Mercury, that should work). $\endgroup$ – John Robinson Jun 24 '16 at 1:59

If it was our solar system (bear with me), I don't see why Earthlings would be so disinclined to terraform/populate Mars, a comparatively far more feasible task than "creating" an earth-like planet.

So on that note, if the surrounding planets are that ill-equipped, at the very least they will want to use the physical materials from said planets. The goal will then be to add or subtract mass (for suitable gravity) and terraform the bajeezus out of it.

I also think transferring 7 billion people from an earthlike planet is extremely unrealistic. BUT you may have stumbled upon an interesting potential plot point. Perhaps the public believes 7 billion people are being shipped off planet, but in actuality the powers that be are plotting to kill them off to sustain the rest. A little dark dystopian, but I think there's some potential there.

EDIT: with the added knowledge that irradiated surface matter on surrounding planets is non-arable, and your populace is deadset on planet creation I'd consider perhaps two possible scenarios:
1. dimension/space spanning teleportation of another celestial body. (e.g. an alternate dimension's uninhabited earth or a nearby solar system's inhabitable planet.)
2. matter creation through star trek energizer-esque energy-to-matter manipulation. if your earth's scientists discovered the process for this, i could see the rest falling into place.

  • $\begingroup$ Interesting plot turning indeed! But say the intrinsic radiation levels of Mars' soil are dangerous for human health (like I believe they are), and so we can't terraform it... $\endgroup$ – Electrical Architect Jun 23 '16 at 20:10
  • $\begingroup$ If you feel like the premise for the question is unclear it might be a good idea to ask about it under the question before attempting to answer. $\endgroup$ – Martine Votvik Jun 23 '16 at 20:14
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    $\begingroup$ I don't feel like the question was unclear. I found the question very interesting so I provided feedback and OP seems to have responded in kind. I appreciate your advice considering my being new to the site, but I don't appreciate the downvote. $\endgroup$ – mordecai Jun 23 '16 at 20:20
  • $\begingroup$ Upvoted. Love the plot twist! $\endgroup$ – GrandmasterB Jun 23 '16 at 20:42
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    $\begingroup$ @ElectricalArchitect Most radiation in Mars is dangerous because its thin atmosphere and weak magnetic field do not protect its surface from radiation coming from space, (mostly, the Sun), and not from the planet itself. $\endgroup$ – Victor Stafusa Jun 23 '16 at 20:59

You know what's cheaper than building that planet? Terraforming an already existing one.

Now everybody thinks and talks about Mars. Poor Venus gets no love.

Venus is the closest thing to Earth in terms of size and mass (they are practically twins). It is also the closest thing to Earth if you don't count the moon and artificial sattelites.

What makes Venus a hell to colonize is its hellish atmosphere. It's literally made of sulfuric acid (among some other dangerous materials), and at 90 times the pressure of our own at the surface, it would crush you dead.

If we could get rid of that atmosphere and replace it with a more Earth like one, and then kickstart its core to have it produce a decent magnetic field (because no one likes space radiation cooking their skin), then it could be seeded with all kinds of lifeforms and be colonized. The only problem left to solve would be the immoral amounts of sunlight you'd get, so maybe people would have to be content with living on the poles.

Alternatively, leave the atmosphere there. Most of the acid and heat is where the atmosphere is thicker. High up to where the pressure is about 1 atm, you could have floating cities. People would have to be locked inside all the time, but you could say the city is in a transparent dome so they can see the sky. Make sure the dome can filter out a lot of UV and space radiation.

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    $\begingroup$ The atmosphere filters out a lot of space radiation, And the domes could be really big, complete with vast gardens. Earth like air and water can easily be extracted from Venus atmosphere, and it has a lot of solar too. $\endgroup$ – Donald Hobson Jun 24 '16 at 18:17

Building a complete planet able to sustain half Earth's population with the 2100's technology is waaaaaaaaay off the reality. The simple reason is that it would need to be built by a large quantity of mass. Where we could get such quantity of mass? Since we want to preserve Earth, we will need to dismantle at least part of Moon, Mars, Mercury, Ceres, Venus and/or some asteroids. But there is no way that this could ever be achievable in the 2100's.

Further, if we manage to create a large planet near Earth for that, we would already be way passed the point of being able to terraform the Moon or Mars at least.

So, your best hopes is to build very large rotating spaceships and fill them with people. The rotation will provide centrifugal force.

Other possibility is creating biohabitats in the Moon, Mars, Mercury or Ceres (Venus is way harder, but possible too). Since their gravity is lower than Earth's this is not a problem (the problem would be if it was higher). However there is no way that this is achievable in the 2100's.

Another possibility is just to build underwater cities in our oceans, like Gungans. Earth is overpopulated just in the land, not in the deep seas. Large underground cities are also another possibility.

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    $\begingroup$ Hir idea might be unrealistic or illogical but saying it is impossible is simply wrong , 90 years are a lot of time for technology, Due to technological advances we still consider science fiction a lot of things we have already invented years ago. $\endgroup$ – user21718 Jun 23 '16 at 20:26
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    $\begingroup$ @Threose So, you say that we can build an entirely habitable planet with oceans and atmosphere in just 90 years? For now, we weren't even be able to land a probe into a nearby comet correctly, even with the most capable scientists and engineers working on it. If you really think that this is possible, go on and post an answer, I would really apreciate to read it. $\endgroup$ – Victor Stafusa Jun 23 '16 at 20:31
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    $\begingroup$ @Threose Over the last 50 years, we went from launching people and things into space to...well....launching people and things into space slightly more efficiently. We still have never sent a person beyond the moon, and we only just recently were able to target a probe to objects as small as a comet or asteroid. In that context, 90 years is virtually nothing to develop the tech to build a planet. $\endgroup$ – Nick2253 Jun 24 '16 at 0:02
  • $\begingroup$ Anything is possible , you just need to know ''how'' when you discover it becomes feasible. There's isn't a cycling system of how technology progresses or when people discover new things. Therefore this ''how'' could be discovered even tomorrow $\endgroup$ – user21718 Jun 24 '16 at 16:55
  • $\begingroup$ @Threose Ok, "how" could you gather an Earth mass in orbit nearby (not counting Earth itself) in only 90 years starting from today without magic, help from aliens or anything like that? What revolutionary fantastic technology do you think that might be possible for doing that without violating the mass conservation law nor the thermodynamics laws? And no, nobody will discover "how" to violate or workaround those laws of nature and much less "how" to use it to perform useful work in planetary scales in only 90 years counting from now. $\endgroup$ – Victor Stafusa Jun 24 '16 at 17:27

Not a problem. Yes, it can be done with proper tools, which we able to produce in next 50 years.

But first of all planing saves time and effort - so build O'Neill cylinders before u even touch that overcrowded problem

Second if you wish round body, then use Jupiter, Saturn etc mass to do so.

You may just use it as is, forming Planetoid from hydrogen masses, cover it protective layer add soil above. So it will be gas core and surface above.

Also you may wish to exchange mass of hydrogen for more heavier materials from sun, and by mass there much of it. Probably drain sun from them is't best idea ever, you have to figure out how much of materials it need to work property.

Gas giants alone contain plenty of more heavier materials, so you may start with them, but I have notice there materials needed for upper cover, not for planet it selfs. For cover mostly carbon is needed.

Subject and problems of doing new planet, are same as in situation of moving a planets, and dissemble of planets.

In the question How can I move a planet?

I have posted instruction how it can be done.

I strongly insist, this is technology of near future, just scale is unusual for us today. And it's more question of Do we need it, or When we need it. All parts are here, we just have to assembly them, when we will have need in them. So it's more speed of our needs.

It's just same situation, which is happened with information, compared to 100 years ago. Accessing information is easier and there much more available of it. It's so easy, that any kid, not theoretically, but practically, have easy access to it. Although understanding information, still a challenge.

As humanity, there is nothing we can't do(1).

(1) not guaranteed, consult your Physicist first, and Law of Physics

  • $\begingroup$ Since hydrogen is much less dense than Earth's rock, to match Earth's gravity, this new planet would be much larger than Earth. Which material is strong enough to be kept stable when it takes a form of a planetary cover around a mass of hydrogen that large, without rupturing and sinking towards the centre of the newly formed gas-planet nor leaking out the hydrogen in order to prevent that? And of course all of that with 2100's technology. $\endgroup$ – Victor Stafusa Jun 23 '16 at 20:50
  • $\begingroup$ Large planet is good, more peoples may live there. Cover is't question of how strong it have to be, but more question how well you can manipulate that cover. Could you manipulate metal like in terminator movie, issue it's weak will be not problem, if you have enough of it. It will be like balloon, and pressure will be compensated by gravity force, not by strength of material. Although strength helps. But mostly it answers how much you may place on top. $\endgroup$ – MolbOrg Jun 23 '16 at 21:05
  • $\begingroup$ If you release a latex helium-filled ballon out there, after it raises for some kilometers, the outwards pressure exerced by the gas makes it pop. Now takes this pressure to something as large as an entire planet pushing the protective layer outwards and see it fail catastrophically in a few nanoseconds or less. To gravity counter that, let's see that even the Earth's gravity can't hold hydrogen for long time and that even a child throwing a ball upwards is able to put enough force to counter Earth's gravity. So, your baloon-like material would need to be unrealistically strong. $\endgroup$ – Victor Stafusa Jun 23 '16 at 21:24
  • $\begingroup$ Also, if it was made of some sort of liquid, it would quickly rain down towards the planet center. $\endgroup$ – Victor Stafusa Jun 23 '16 at 21:25
  • $\begingroup$ Well, ok then. Just to let you know, it was not me who downvoted you. $\endgroup$ – Victor Stafusa Jun 23 '16 at 22:57

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