# Building a Dyson sphere while preserving moons/other objects?

Humans want to build a Dyson sphere around the Sun. They have noticed that Ganymede's icy composition would be perfect for mining to get the icy resources needed to build the sphere, or Mercury could be used due to its silicate composition. However, they do not want to remove the moon itself as to avoid these scenarios:

Ganymede, aka Jupiter III, was the largest moon in the solar system, until space mining removed its existence.

Mercury was the smallest and nearest planet to the Sun, but due to space mining, Venus is now the first planet from the Sun.

Would it be possible to preserve the astronomical significance of various celestial bodies while supplying the vast amounts of resources needed to build a Dyson sphere? What alternate methods could be used?

I suppose asteroids and KBOs could be used for this as asteroids would supply the metals and the KBOs would supply ices, but the large distance of the KBOs would make construction very cost-ineffective.

• Is the reason to preserve those bodies for aesthetic reasons or something else? Commented Jan 11, 2022 at 14:54
• A moon will hardly provide enough material to put a decent balloon around the sun, let alone it could be relevant when building a Dyson sphere. I think for a Dyson sphere, we'd have to shove the entire asteroid belt our way and cannibalize the planets Mars, Jupiter and Saturn. For a hot yellow star, like our sun, it is very unlikely the entire solar system can provide for enough material. Commented Jan 11, 2022 at 16:27
• "Small amounts of resources". Nice Commented Jan 12, 2022 at 18:41

## Leave your moons in peace, harvest some nearby stars

As with all of Dyson's inventions, we'll have to hand-wave how it has to be produced anyway..

Any moon, or even planet Earth would be irrelevant, you may as well preserve it

Volume of a sphere:

V = 4/3 πr³

Volume of a hollow sphere:

V = 4/3 πrOuter³ - 4/3 πrInner³

Where rOuter-rInner = thickness of your Dyson sphere. Now suppose you'd rotate your Dyson sphere, the hull would need to provide support, not mass. In order to get a safe Dyson sphere, and a minimum of one km thickness (1000m) will do, with a density of say 3gr/cm (part is metal) you'll still need a giant amount of matter, when your Dyson sphere would be a solid construct (not "sparse")

Calculation example

Suppose you'd take the Earth orbit as a guideline for its size (less hot and more convenient would be Mars, so take Earth's orbit as a minimal radius r1) you would get

1 AE = 149 597 870 700 meters radius, which yields a total volume of 4.2e34 m³

For the Dyson hull, subtract like in above formula. You'd still need 8.43e26 m³ which is a few orders less of course, but assuming we need an average density of 3.0gr/cm³, you'd still need a mass of 2.531e+33 grams according to my calculation. To build that thing, you'd need 2.531e+30 kilograms of material.

The total Solar system including the sun has a mass of 2.1e+30 kg.

The sun itself has a mass of 1.9e+30 kg, so if you want to keep it, you're left with 0.2e30 kg of building material.

Conclusion: if you could harvest ALL MASS in the solar system except the sun, you'd have less than 10% of the material required.. so you'll have to set up some interstellar transports anyway, to import the material required !

Make the Dyson hull as thin as technologically feasible..

Say, you repeat the calculation for only 100 meters thickness, the required mass would be in the order of 10e+29 kg, still more than a million times the moon mass. But a hull weighing 10e+29 kg could (theoretically) be built by shredding our gas giants Jupiter and Saturn.

Solid or sparse, Dyson shell or Dyson swarm

A Dyson sphere harvests energy of a sun, that is its intended purpose. Inhabitable Dyson spheres are fiction.

A solid shell was first named by Dyson, but after that, he ensured his public that a solid sphere could never be constructed. The shape of the megastructure would be rather look like a swarm, like

The two differ in the way each "solar cell" would move. In the left case, everything is in orbit, only harvesting the energy. In the right case, propulsion is needed, which can be provided by the solar radiation itself. On the right, each satellite is stationary in space.

Material will be less of a problem, but you'll have to crush some moons to build it. The location - to start - could be between Mars and Jupiter, the asteroid belt, creating an Dyson ring from available material. Mars' moons Deimos and Pheibos can crushed first. Then some of Jupiter's moons.. the ring will take shape in a few centuries..

https://en.wikipedia.org/wiki/Dyson_sphere

Materials

Notice that the Wiki-topic does not mention materials or "metal". When I proposed to use gas giants and stars to gather the mass needed, I ignored the fact that material for a solid Dyson sphere should be solid, or solidified, in some way. You could hand-wave that, but this is a science based topic.

To gather the energy, you'll need metal parts

How much metal would be needed and where harvest that.. Suppose you'd like to have cables connect each spoke of the above Dyson swarm of solar cells, gathering the energy.

A radius of 1AE, circumference will be

C = 2πr = 2 * 149597870700 * 3.14 = 939 951 143 167 meters cable per spoke

..suppose you'd need a cable of 1cm in diameter, that is 0.0003 m2, you'd need

V = πr2 * C = 0.0003 * 939 951 143 167 = 281 985 342 m³ metal per spoke.

Using iron, amounting to 7873 kg/m3 times that amount when it's iron: 2 220 070 605 tons. The Earth's yearly total production of iron in 2015 was about half of that amount, let's go for it.. we can do it now.

Far future

In the (far) future to construct a true, solid inhabitable Dyson shell like Star Trek shows us, like a giant armored inhabited sphere around a sun, humans could consider to go harvest iron in a supernova.. in a certain stage of a supernova, a massive amount of iron will be produced. Maybe the supernova could be stopped just before it occurs ? You'd have a giant solar core consisting of iron.

https://futurism.com/what-happens-when-stars-produce-iron

• "less hot at Mars" - This shouldn't matter. If you build a Dyson sphere, you're capturing all the energy output of the sun, thus the temperature of the sphere will approach the temperature of the sun over long time periods. You'd need to build it large enough not to kiss the corona, but other than that, radius would be dictated by your cooling systems. Commented Jan 12, 2022 at 3:54
• True, I'd prefer a very cold star for a DS, maybe small red swarf, brown dwarf.. but that's not what this topic is about, there's a lot to find on WB about Dyson sphere temperatures, check out worldbuilding.stackexchange.com/search?q=Dyson+climate Commented Jan 12, 2022 at 7:18
• if you spread out the energy of the sun over a larger surface, you'll get a lower temperature.
– ths
Commented Jan 12, 2022 at 9:27
• "Shredding our gas giants Jupiter and Saturn": There is an issue with this solution: Dyson spheres probably would consist of silicates, while gas giants are mostly helium; you may have a few Earth masses of rock and stuff in the core, but that would be hard to extract. Commented Jan 12, 2022 at 13:41
• Why does it need to be that thick? I would have assumed most of it is just a thin layer of a solar panel, so a millimeter thickness should suffice. Maybe you can even use some foil, so you can get a few more orders of magnitude thinner. You would need some thicker structural beams in between but they cover only a tiny portion of the surface. Commented Jan 12, 2022 at 14:07

Have you ever seen what happens when an historically significant building needs to be renovated?

You demolish the inside and leave only the outside, so that the appearance of the building isn't changed.

You people can do something similar: they can leave a shell in place, to keep intact the appearance of the celestial body, and mine the inside to get all the needed material.

• Wouldn't the shell collapse in on itself because of gravity? Also most of the important resources on Ganymede, like ice, are on the surface. Commented Jan 11, 2022 at 14:53
• Ah you're going to put a hollow moon in the sky.. How American. The above is St Elisabeth's hospital in Washington. As a Dutchman I view this method as window dressing, this is NOT the way to preserve historical buildings jamesdixonarchaeology.com/2016/10/30/… Commented Jan 11, 2022 at 16:37
• The hollowing removes most of the mass of the moons which changes the gravity of the moon and therefore also changes its orbit. Commented Jan 11, 2022 at 22:55
• @GrumpyYoungMan the orbit of a moon is mostly influenced by the mass of its parent body, not by its own mass. Commented Jan 12, 2022 at 0:40
• @PaŭloEbermann Nah, actually the moon does affect the orbit, if it has enough mass relative to the planet it's orbiting. Or more precisely, the orbital behavior of the planet-moon system is affected by both their masses. If, say, Earth's moon somehow lost most of its mass without a corresponding change in the mass of Earth, I'm pretty sure there would be a pretty significant change in their orbits. On the other hand, Jupiter's moons are small enough relative to Jupiter that there probably wouldn't be. (A small change, still, but not significant.) Commented Jan 12, 2022 at 7:25

Celebrate the origin of the sphere with the sphere.

The sphere will be called the Cupid sphere. It will be asserted to be the direct descendant of Mercury - made of Mercury stuff and occupying the place of honor by the Sun. Mercury will have taken the next step in its evolution, begetting the Cupid Sphere.

Cool things about the Sphere will be placed in the context of cool things about the planet. Some pieces of the sphere will be unmodified Mercury bits as a paean to its provenance.

You all like that "paean to its provenance"? People who mourn Mercury will eat that stuff up. Because the truth is, Mercury is not much involved with day to day affairs on Earth, and people bothered by its loss are ideas people. Those people are also comforted with ideas, and so the sphere makers will meet them where they are.

• This might be overly pedantic, but how exactly would someone be able to rip out the top 100 meters of the Caloris basin, reshape it to match the curvature of the sphere without breaking it? Rock is brittle. Also it kind of is a waste of space as no energy will be produced from that region. Commented Jan 12, 2022 at 13:44
• @fasterthanlight - I think you meant this comment to be on Dutch's answer., He is the one with the hollow buildings / planets. I take a more pragmatic approach. Commented Jan 12, 2022 at 18:15
• I did intend to comment on your answer, you mentioned that "pieces of the sphere will be unmodified Mercury bits." I'd appreciate it if you could edit in how you could extract, for instance, the Caloris basin, on Mercury and put it somewhere on the sphere for its significance. Commented Jan 12, 2022 at 18:19
• @fasterthanlight - When I write bits, I mean bits. Not freaking landforms! Little bitty bits. Rocks. And not big ones. It's the principle of the thing, you understand. Commented Jan 12, 2022 at 18:54
• I see your idea, that's pretty nice. Maybe diverting some power to run a display a projection of Mercury would be cool :) Commented Jan 12, 2022 at 19:21

### Replace the mined material with something else

Nearby bodies (Jupiter resp. the Sun) have a lot of hydrogen. You'll need a nuclear fusion device to make material that's solid at those temperatures (especially in the case of Mercury), and perhaps some combustion as well, but that can probably double as a propulsion for your spacecraft.

• Good point +1.. so even shredding the gas giants won't yield anything acceptable... Commented Jan 11, 2022 at 17:37

## Import all your materials from other solar systems

As mmomtchev comments, the mass of the solar system isn't actually that much when you remove the sun from the equation.

It's hard to overstate how ridiculously massive such a structure would be!

Realistically to build a Dyson Sphere you'd need to strip the entire solar system and several of its neighbours for raw materials.

You're going to need materials from at least one other solar system anyway, so use that same technology to fetch all your materials from elsewhere and leave the planets and moons you care so much about entirely alone.

Given the obvious gravitational impact of introducing a whole solar-system's worth of material into an existing solar system, you may want to build your Dyson Sphere elsewhere too.

• your last line is very interesting. Can you (or anyone?) give a hint on what the impact would be? Commented Jan 12, 2022 at 11:38
• Well, Straight off, we're talking about putting a mass equivalent to Jupiter and Saturn combined into the solar system. Gravity isn't a point-mass, and spreading it around the surface of a sphere an AU in diameter would definitely not be the same result as dumping it into the sun, but it's fair to say I think we'd see a LOT of distortion in the orbits of planets. Also we'd need to do something about Earth because it's in the way. It would definitely crash into the sphere at some point without intervention, and with a solid sphere in the way it'd freeze over pretty quickly. So there's that too Commented Jan 12, 2022 at 12:01
• Remember that Jupiter is basically the Big Brother for the inner planets. Intercepting asteroids and comets that could threaten us. The solar system is mostly a safe place because of the gas-giants. Introducing that much mass into the inner system will distort the orbits of all the planets. Essentially expect all the planets to develop elliptical orbits that bend inwards towards the sun. Additionally, expect a lot of comets from the oort cloud to suddenly become a problem as their orbits get disturbed. The Sphere is going to get bombarded by comets pretty heavily for a bit, and so are we. Commented Jan 12, 2022 at 12:05
• This all assumes that the Sphere spontaneously pops into existence overnight of course. Realistically it'd be built over centuries, so the gravitational effects will be spread out across the full orbits of the planets. They'll probably keep their circular orbits more or less as they are, maybe a little smaller. The Oort Cloud is still a problem because their orbits take centuries and we're making our changes pretty much in the same small arc of that time-frame. Never mind that a lot of those objects are so far out that they don't really even -have- an orbit per-say. Commented Jan 12, 2022 at 12:10

What alternate methods could be used?

There are many(at leas more than one), including bulding dyson swarm, or if you like it to be a shell, then to build one which is enough and suficient for purposes of extracting energy, collecting energy for a star (it can be in form of statites as an example, or active supporting structures - some suitable approaches to make a shell of that size)

As mentiont in one of the answers, a correct feasible thing is Dyson swarm, and it has the purpose to collect energy of a star, meaning it is a tool for such collecting. Correct tool with correct purpose.

Then, if you use it that way, as a tool for energy collecting and conversion, then it does not require that much of mass of materials, 1 a.u. radius sphere, for energy collecting, with average mass of 1kg per square meter(it can be a solar panel if you have difficuties to imagine more efficient solutions, 1kg, by mass, solar panel in microgravity can be feasible with cirrent technologies) then the whole sphere requires about 5% of Venus mass for it - total. No planet dissapearing and such.

Depends on major materials for structural elements, which can't be hydrogen, lol, as it was suggested in some answer, but, gas giants and the Sun itself can be sources of heavy elements as well, where they are persent in around 1% concentrations. It is a bit more sofisticated approach and technology, but it also possible.

So one of the ways is - do not create unnecessarly problems, this way there is no need solving them.

If solid dyson sphere is an actual goal, as massive epic construction with porpose to be epic and massive, it possible to do so with active supporting structures, (watch Isaac Arthur channel for explanations what it is) then borrowing materials from other star systems and stars is the way to preserve celestial bodies of this system, but it has a problem of changing orbits of those bodies is Solar system, because of additional mass of that sphere, it can be corrected but then orbit periods will change which is end game - wall of laws of physics of this universe or more advanced technologies ....

So choosing goals in a wrong way leads to all kinds of problems. Is it impossible to squeeze water out of a rock?, eeehh not really, but yes it possible if you try hard(like converting matter and other transmutations as an example, which isnt scify, it just energy inefficient etc). So make right choices, and you will get proper results. Build Dyson Swarm it is epic and practical and useful.

It is even less than that: the solar system mass is only 1.0014 solar masses, Jupiter which is about 3/4 of the non-sun mass is at about 2*10^27 kg - so you don't need anything but Jupiter and eventually Saturn.

No point bothering with the rest.

One will have to really master ultralight materials - and their production from hydrogen - to make a solid Dyson sphere.

But such a solid Dyson sphere is not really feasible anyway as it would be impossible to maintain it in place - gravity won't be of any help once you have completely surrounded the start and the tension forces will be on a yet unknown scale - far beyond any theoretical tensile strength limits.

The only realistic project is the so-called Dyson Swarm - billions of small orbital elements with solar panels - which was the original idea of Dyson - it got extended to a solid sphere by not so-scientifically minded sci-fi authors. Dyson was an astrophysicist.

• Whilst correct, this seems to not address the main point of the question, "preserve the astronomical significance of various celestial bodies while supplying the vast amounts of resources needed to build a Dyson sphere" - a Dyson sphere is specified, and you'd need to justify how your answer does the preserving of the significance. You could have left this as a comment on the question in preference to as an answer. Commented Jan 11, 2022 at 23:15
• In fact, you need only Jupiter and Saturn - everything else does not count Commented Jan 11, 2022 at 23:39