Shell Worlds Infographic

Here’s an idea we discussed in Episode #1 of the SciFi Ideas podcast.

As stated in the podcast, the Shell Worlds concept is the brain-child of engineer Ken Roy, who envisions the building of enormous air-tight spheres around small planets and moons to facilitate terraforming. Once completed, the ‘shell’ could be filled with breathable atmosphere, turning the body into an enormous biodome. Roy imagines the constructed ‘shell’ also being used as a foundation for residential and industrial facilities, with the surface being used primarily for agriculture.

The following infographic (created by illustrates the concept perfectly:


Check out the article at for more information.

Listen to Episode #1 of the SciFi Ideas podcast to hear us discuss this idea in more detail.

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  • Gabriel

    Basically, the atmospheric pressure ensures atmosphere’s altitude is even around the globe (Yes, atmosphere is a fluid, the communicating vessels principle applies here as well). So, unlike a dyson sphere around a star – which needs to be constantly stabilized – a sphere wrapping around a planet to hold-on to an atmosphere is always stable.

    I would, however, alter the design: Would it be much simpler to build a translucent sphere and all megastructures built on the planet’s surface instead? The only thing which needs to remain at the surface of the sphere is a maintenance system, designed to track and repair punctures by meteor impact on the shell. A spaceport or just a remotely-controlled space-gate is all what it needs to allow spaceships to pass through.

    • Cool. We hadn’t considered that the atmospheric pressure would keep the shell in place. Makes perfect sense.

      I think the reasons to build the cities on the sphere (rather than the surface) are:
      – Make more room for agriculture/oxygen production on the surface
      – Pump waste/polution into space
      – Easier access to spaceports

  • The idea that this would be a “shortcut” to terraforming, or in other words an easier way to terraform, highlights just how difficult terraforming a planet would really be.

  • In a world like this, there could be 3 different kids of city: shell city (on the outside), hanging city (below the shell), and surface city (on the ground).