Or, technically, a civilization near the core of a planet.

In this question I will describe some aspect of my design, and you may comment on the realism of these aspects and add improvements, or point out something I am not aware of.

The Planet

The planet will be a rocky planet, possibly tidally locked to its star so as to reduce the effect of rotation on the world within.

I am not sure what effect a major satellite would have on a civilization inside a planet, so there will be none for now.

The planet will either be too small or too old to have volcanic activities, and the layers above the level of the civilization will be solid. This also means the planet probably don't have a strong magnetic field, but this would seem trivial to a civilization living under many kilometers of rock. The core, however, is still hot enough to emit light and heat.

And just so you know, the world built here is supposed to be a bleak, end-of-time sort of place, so the "star" about which the planet revolves is probably a black-hole or something dark and useless like that.

The architecture of the civilization

This is where things get a bit crazy. See diagram below (not to scale): pictures are worth a thousand words...this question is getting long I hope the diagram is sufficiently self-explanatory. That being said, a few significant note with this design:

  1. The support structure must be made from something that has a melting point higher than the temperature of the core's surface
  2. Either the core is quite solid, so as to be able to handle the weight of the supports, or that the rocky crust is quite solid, and the support structure can anchor itself securely on the inner surface of the crust without putting too much weight on the core
  3. The idea here is that the civilization derives its power from the light and heat coming out of the core, this means that the support probably wouldn't enclose the core completely, unless it is transparent (to permit the output of light).
  4. There must be some way that the excess heat is disposed of. My idea so far is that the universe itself has gotten quite cold at this point, so the conduction of heat into the crust and its later radiation into space should suffice.

Life in this world

The social aspect of this world is trivial at this point, however, life on the "residential area" would have the following major features:

  • Gravity will be like the gravity felt around a planet the size of the core, since inside a even hollowed sphere, the spherical shell's own gravity is balanced out at every point. Also, because the planet is designed to be tidally locked, the effect of centrifugal force, or the illusion of it, will be quite small, I hope.
  • If the core is bright enough to shine like a sun, sunlight will seem to shine from beneath the floor.
  • Major building project will be difficult, because a lack of raw material (it will probably be a bad idea to excavate the rock from the crust, but what do I know?)

That concludes my design so far. At this point, I don't see any major problem beside some numbers' game balancing the melting point of the support and the temperature of the core, but if you see any, or have improvements for the design, I would really like to hear.

  • 1
    $\begingroup$ Thanks to shell theorem your supports does not need to be that strong. And I advise having only 4 of them. Sadly, this is far from a full answer. $\endgroup$
    – Mołot
    Dec 19, 2016 at 19:16
  • $\begingroup$ This sounds like a low-mass planet like Mars or possibly smaller. If was a Moon-mass body the chances of constructing a core habitat might be better. This does mean a low-gravity environment for its inhabitants. $\endgroup$
    – a4android
    Dec 20, 2016 at 7:46

4 Answers 4


No, it is not.

The crust of a planet gets pretty massive shake-ups as the tectonic plates move. Even on a planet with relatively stable plates, you're still going to experience a LOT of forces at those depths. The pressure and heat you're subjected to also grow exponentially as you descend towards the core.

Humanity has not been able to descend much further down than a kilometer or so, before the technical complications, and instability of the tunnels simply become too dangerous and/or expensive to overcome.

For you to dig down to tens of kilometers, isolate the molten core of a planet, and build a scaffold to hold the rest of the bulk of the planet up around you is simply preposterous.

If you are able to go to this length of effort simply to "keep warm", you're better off simply building a dyson sphere around your Sun, and siphoning off its energy to heat your atmosphere.

  • $\begingroup$ Well-informed answer, but here are a few objections: 1 I am not sure how much tectonic movement there will be if there are not molten magma moving underneath the plates. In fact, I wouldn't call it plates if they were parts of a solid body of rock. 2 What humanity can do today is not that important to the question, even if it's difficult to create such a structure, some hand-wave will do. 3 stars may have shorten lifespans then geothermic cores, also, there may not be suitable stars near by. $\endgroup$
    – Luna
    Dec 19, 2016 at 22:34
  • 1
    $\begingroup$ Also, you mentioned complications in digging deep on Earth, can you specify what these complications are? And just so we don't go too far off topic, the question focuses on the maintenance of the proposed structure, not its creation or the intentions behind its design $\endgroup$
    – Luna
    Dec 19, 2016 at 22:40

A major problem with your concept is thermodynamic.

If the core of the world is hot enough to glow it is going to be pretty hot.

At least >525 °C and for reference the earth's core is 3,000 - 5,400 °C, so yes it would glow.

However, the problem is that the rock layer above the hot core is going to be only slightly cooler than the core. The temperature profile would follow a gradient from hottest at the core to the lowest at surface radiating heat into space, the heat has no where else to go but up. So your Rocky crust would be just as hot as the core (and would also glow) making your habitable region between the 2 regions nearly the same temperature, which isn't very habitable.

A mega structure level refrigeration system in place to move heat out of the region above the core to the surface could possibly fix this, but it would be pretty huge and require an amazing level of technical ability. At this level of engineering you're basically replacing your planet with an artificial structure. Your civilization would likely be better off and it would be easier to just build the artificial structure (A Dyson sphere).


If you want this to be science-based, you have some pretty big problems to overcome:


The pressure near the Earth's mantle-core boundary is around 140 GPa, so your support structures need to withstand at least such pressures. However the strongest known materials have compressive strengths on the order of several hundred MPa, so you have a few orders of magnitude to overcome. Does your civilization have access to force fields?

To have more reasonable pressures you will need to have a much smaller world, probably closer to an asteroid than to a planet. But such a small world won't have much heat left in its core if it is a few billion years old. And also you will have a very low gravity.


As already mentioned in other answers, there is a thermal problem. Many miles of rock is a pretty good thermal insulator merely by being many miles thick. (Note that in the Earth's mantle heat transport happens by convection, but in your world the crust/mantle needs to be frozen solid.) So if you have a bare core thermally radiating into the excavated space, that space will quickly heat up and fry anyone living there. So you need to cover the core in thermal insulation, and have active cooling in the excavated area. For cooling I would recommend pumping water from the surface around to transport the heat outside. Assuming the planet has water or ice available on its surface.

Nuclear energy

And a third problem: Why go through all the trouble? Nuclear fission or fusion energy is much easier, and a civilization that can hollow out a planet should be advanced enough to have mastered fusion energy. Even on just fission energy there's plenty of fuel material available on an earth-like planet if you include U-238 and thorium in both the crust and seawater, and this civilization seems to be good at digging/mining. I guess you could just say that this world has barely any uranium and thorium, which AFAIK can differ quite a bit between star systems, but even then this civilization looks like they should have mastered fusion, and hydrogen is available everywhere.


Frame shift: encode thought in hot Ice XVIII in the core of Uranus or Neptune

First: unless Adamantium appears in your periodic table, there is no way you're going to make pillars of material to hold up a planet's core. The Earth's inner core is solid iron but it's not strong enough - the pressure down there is much more than you'd find in a pair of bolt cutters. (The thermodynamic issues are less trouble - they might be dealt with by an advanced technology like neutrino pair production for cooling) So can life be found in the core of a planet?

Well, consider superionic ice (Ice XVIII). Here's an introduction. It is a highly conductive form of ice because protons move freely in a matrix of O2-. It might be responsible for the strange, asymmetrical magnetic field of Uranus. This suggests such a material can be carrying flows of electricity, potentially usable for some sort of logic processing. It can also be physically altered akin to a computer chip, for example by doping the structure with nitrogen in place of oxygen. Last but not least, because it can be found at 3000 K or higher, it may be in contact with a liquid-like supercritical phase of water, creating the potential for dopant ions or robust chemicals to be moved from place to place.

Conceivably, your civilization might have encountered sentient life within an ice giant, learned how to encode information within its core structure, solved the hard problem of consciousness, and transferred its own thoughts to be stored in a similar planet.


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