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Assuming that some future civilization of hyper-advanced humans, or aliens for that matter, had the technology to reshape the solar system so that there were several habitable planets the rough size of Earth, complete with water and biospheres, how many be made using only materials from the solar system? Venus would need minimal changes besides water and adjusting the atmosphere, and Mars would be more difficult, given that it's only half the size, but it should be possible with such technology, especially since it has a good amount of water to start with, so that's three counting the original Earth, how many others could be constructed?

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  • $\begingroup$ Venus is indeed about the size of Earth. Mars is much smaller than Earth. It's nowhere near the rough size of Earth. $\endgroup$ – AlexP Feb 3 '18 at 0:56
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    $\begingroup$ To be clear, the hyper-advanced race doing the rearranging can move matter wherever in the solar system, but cannot transmute matter? Because the necessary energy to shuffle around the solar system would mean that it would be economically viable to make the requisite elements if you didn't have them close by. $\endgroup$ – jdunlop Feb 3 '18 at 1:25
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    $\begingroup$ This advanced race seems to be treating the solar system like a big bonsai tree or zen garden. $\endgroup$ – Giter Feb 3 '18 at 1:46
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    $\begingroup$ The composition of the gas giants is largely guesswork and it also depends on your people being able to manufacture elements from others., so a better question would be, how many planets could you have orbiting the sun in the habitable zone and have a stable solar system. $\endgroup$ – Kilisi Feb 3 '18 at 5:01
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    $\begingroup$ @Harper - I don't see how the link supports avoiding transmutation. Our mechanism for elemental transmutation is very crude - bombard an element with neutrons and get the result. Assuming that the superscience of our hypothetical race is sufficient to rearrange a solar system (effectively unlimited energy), they could also be capable of direct matter manipulation. $\endgroup$ – jdunlop Feb 5 '18 at 18:06
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My best guess is the solar system has enough solid mass for 45-95 Earths, all but two of which are from the gas giants. They can get closer to 500-600 if they can convert hydrogen and helium into material the Earth is made out of. More than 300,000 if they can convert the entire Sun. However, it's unlikely you'd get more than a few to actually have biospheres if you can't convert elements to other elements, since large amounts of iron would be needed in the core of each planet to produce a magnetic field to protect the planet.

Let's start with the rocky planets, since it's easy to estimate material from them. For the record, you are overestimating the size of Mars. According to the Wikipedia list objects in the solar system by mass, Mercury gets you 0.06 Earths, Venus 0.82, Earth 1(unsurprisingly), Mars 0.11, and scraping together all of the moons and dwarf planets gets another 0.10 if you round up generously, for a total of 2.09 Earths worth of mass. Let's round down to 2 Earths(or round up to 3, this mass is irrelevant anyway).

The gas giants are where the real planetary mass is: Jupiter alone would be more than 300 Earths worth of mass. However, unless your advanced civilization can convert the hydrogen, helium, and other gases that make up most of these gas giants mass into rocks your Earth collection will be a bit soft. So, we'll look at estimates for the solid material in these. Wikipedia provides estimates of 12-45 Earths worth of solid mass in Jupiter, 9-22 for Saturn, 9-14 for Uranus, and 10-15 for Neptune. This totals up to 40-96 Earth-masses worth of solid material in the planets.

If they can convert all of the gasses in those gas giants into the material the earth is made out of(32% iron, 30% oxygen,15% silicon, 14% magnesium, 10% assorted), then you could easily get a few hundred Earths.

However, all of this is irrelevant if they can convert gaseous elements into rocks: the sun alone would get you more than 300,000 Earths worth of mass.

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  • $\begingroup$ How many biospheres could you make if conversion was possible? $\endgroup$ – The Literary Lord Feb 3 '18 at 8:28
  • $\begingroup$ @TheLiteraryLord: Well, if conversion of was possible then the full 300,000-ish Earth-like planets are possible, you just need to convert all of the helium, hydrogen, and other elements into what the Earth is made of, spin the rocky balls so the iron core creates a magnetic field, and add some seeds. However, there's no way this many planets could stably orbit a single star, so you'd need to spread these new planets around many stars. $\endgroup$ – Giter Feb 3 '18 at 12:36
  • $\begingroup$ What about asteroids? $\endgroup$ – user673679 Feb 4 '18 at 10:24
  • $\begingroup$ Asteroids are pretty irrelevant. The 10 largest objects in the asteroid belt represent 90% of the mass, and even they are less than 0.01 Earths. I included all of that mass in the 'all of the moons and dwarf planets' part. $\endgroup$ – Giter Feb 4 '18 at 14:10
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    $\begingroup$ They're not irrelevant if you're the Millennium Falcon. $\endgroup$ – Harper - Reinstate Monica Feb 5 '18 at 19:04
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They won't.

Making entire planets is incredibly wasteful - the interiors are, for the people living on the surface, entirely useless.

So what any space faring race capable of such engineering would build is something more like IM Bank's Orbitals.

You get pseudo gravity from rotation of the ring, and you can get vast areas of land without the waste (and time) required to form a planet. Note that putting a planet together would generate enormous heat - just from gravitational compression and maybe from other processes (like colliding large lumps of matter together to form bigger masses). That heat is useless waste.

If you have the tech required to do anything on that scale, you will have the tech required to build and maintain a ring more easily.

Here's a quote from a document attributed to Bank's himself :

The attraction of Orbitals is their matter efficiency. For one planet the size of Earth (population 6 billion at the moment; mass $6\times 10^{24}$ kg), it would be possible, using the same amount of matter, to build 1,500 full orbitals, each one boasting a surface area twenty times that of Earth and eventually holding a maximum population of perhaps 50 billion people

So any society capable of engineering planets just won't do it as it's ludicrously wasteful.

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  • $\begingroup$ Not quite the answer I was looking for, but interesting anyways, thanks. $\endgroup$ – The Literary Lord Feb 3 '18 at 8:29
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    $\begingroup$ I suppose in the context I'm suggesting, actually making a complete planet from scratch might be considered an Ego Trip for the entire civilization : "look what we can do !" kinda thing. So even in this context a complete planet might be built. $\endgroup$ – StephenG Feb 3 '18 at 8:33
  • $\begingroup$ @StephenG perhaps they wanted to build a couple of zoos? $\endgroup$ – John Dvorak Feb 3 '18 at 13:52
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    $\begingroup$ Two things planets have over every other structure are robustness and simplicity. It is hard to imagine anything more robust. $\endgroup$ – Peter Wone Feb 3 '18 at 22:22
  • $\begingroup$ Also a good business model: just ask the Magratheans. $\endgroup$ – jdunlop Feb 5 '18 at 18:10
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Earth + 1 additional Earth

The limiting factor is Iron. The Earth has a lot of it, and it is molten, providing us with a magnetic field and plate tectonics. No where else in the solar system is there that much Iron.

Consider that the Mass of the Earth is 5.97e24 kg, while the combined mass of Venus, Mars, Mercury, the Moon and the asteroid belt is 5.92e24 kg. That is, the Earth is more massive than those three planets, one moon, and many asteroids combined. Much of the mass of those smaller bodies is 'crust'-like materials, carbon and silicon and oxygen and what have you. The Earth definitely has more Iron than those planets combined. Without Iron, you won't have a planet with nearly the density and gravity, much less the life-sustaining magnetic field as Earth has. Other than Iron-56, no other element in the solar system is nearly abundant enough to give a newly constructed planet the density of Earth.

On the other hand, how much Iron is in the Gas Giants? Who knows? We certainly don't. From the material available in the solar system outside of the cores of the four gas giants, there is only enough Iron to make one additional Earth. There may be enough material inside the gas giants to make a few more, but that is not known with any certainty.

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  • $\begingroup$ ...and extracting any iron from the core of a giant planet, no matter how much there may be, would be yet quite a couple orders of magnitude more infeasible than the planet-constructing idea itself. Those guys are excellent at swallowing any equipment that comes along for good... $\endgroup$ – leftaroundabout Feb 3 '18 at 23:12
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This answer is intended as a very rough, order of magnitude estimate.

My rough estimate is about 1000 Earths.

This answer also assumes that elements cannot be turned into other elements and that the Sun will be used.

The mass of the Solar System is approximately 1.992x1030 kg*. The mass of the Earth is 5.972x1024 kg (Wikipedia).

Then I found the relative abundances of elements in the Solar System** and on Earth (KnowledgeDoor, Wikipedia). I used only elements with more than 1000 PPM abundance on Earth.

Table:

$$ \left| \begin{array}{cc|c|c} &\text{Element}&\text{Solar (PPM by mass)}&\text{Earth (PPM by mass)}\\ \text{Al}&\text{Aluminum}&55&15,900\\ \text{Ca}&\text{Calcium}&69&17,100\\ \text{Cr}&\text{Chromium}&15&4,700\\ \text{Fe}&\text{Iron}&1,112&319,000\\ \text{Mg}&\text{Magnesium}&618&154,000\\ \text{Mn}&\text{Mangnese}&12&1,700\\ \text{Ni}&\text{Nickel}&676&18,220\\ \text{O}&\text{Oxygen}&8,255&297,000\\ \text{P}&\text{Phosphorus}&7&1,210\\ \text{Si}&\text{Silicon}&674&161,000\\ \text{Na}&\text{Sodium}&33&1,800\\ \text{S}&\text{Sulfur}&384&6350\\ &\text{Total}&11,914&997,980\\ \end{array} \right| $$

I then multiplied the PPM by the masses (and divided by a million) to get the approximate amount of each element present in the Solar System and on Earth in kilograms. Then I divided the amount of the element in the Solar System by the amount on Earth to get how many Earths worth of the element was present in the Solar System.

Table:

$$ \left| \begin{array}{cc|c|c} &\text{Element}&\text{Solar (Kg)}&\text{Earth (Kg)}&\text{Solar/Earth}\\ \text{Al}&\text{Aluminum}&1.10\text{e+26}&9.50\text{e+22}&1,155\\ \text{Ca}&\text{Calcium}&1.38\text{e+26}&1.02\text{e+23}&1,353\\ \text{Cr}&\text{Chromium}&3.16\text{e+25}&2.81\text{e+22}&1,125\\ \text{Fe}&\text{Iron}&2.22\text{e+27}&1.91\text{e+24}&1,163\\ \text{Mg}&\text{Magnesium}&1.23\text{e+27}&9.20\text{e+23}&1,341\\ \text{Mn}&\text{Mangnese}&2.44\text{e+25}&1.02\text{e+22}&2,406\\ \text{Ni}&\text{Nickel}&1.35\text{e+27}&1.09\text{e+23}&12,378\\ \text{O}&\text{Oxygen}&1.64\text{e+28}&1.77\text{e+24}&9,272\\ \text{P}&\text{Phosphorus}&1.42\text{e+25}&7.23\text{e+21}&1,968\\ \text{Si}&\text{Silicon}&1.34\text{e+27}&9.61\text{e+23}&1,397\\ \text{Na}&\text{Sodium}&6.60\text{e+25}&1.07\text{e+22}&6,136\\ \text{S}&\text{Sulfur}&7.66\text{e+26}&3.79\text{e+22}&20,212\\ &\text{Total}&2.37\text{e+28}&5.96\text{e+24}&3,976\\ \end{array} \right| $$

This is like a limiting reagent problem in chemistry. Chromium is the limiting factor. There is only enough chromium in the Solar System to make about 1000 Earths. As the other answers mentioned, you would run out of iron very soon after and iron is more important than chromium.

Reflection

I think only considering these elements makes sense because these elements make up 99% of Earth. The other elements are trace elements so I don't think their exact amounts matter as much. However, trace elements are important for life so I don't know what consequences having an insufficient amount of some trace elements would have on life. These elements will still be present in the new Earths, I just can't guarantee that there is enough to put as much into the new planets as there is on Earth.

There is also the problem that I think that chromium may be replaced by other elements for an Earth-like planet, but I don't know how essential that we have this specific amount of chromium.

*I could not find a number but the mass of the Sun is 99.86% of the mass of the Solar System and the Sun has a mass of 1.989x1030 kg (Wikipedia, Wikipedia). This gives us 1.992x1030 kg as the approximate mass of the Solar System.

**I had to convert from atoms per 106 Si atoms to PPM

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    $\begingroup$ Chromium does have seem to have a biological role, but we are not sure how important it really is. The same applies to aluminum which was long thought to have no biological role. $\endgroup$ – papirtiger Feb 4 '18 at 0:14
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    $\begingroup$ ncbi.nlm.nih.gov/pubmed/20684046 $\endgroup$ – papirtiger Feb 4 '18 at 0:18
  • $\begingroup$ @papirtiger Even if it was very important, I don't know how important it is to have the exact concentration of it as we do on Earth. If you could use less aluminum per planet, you may be able to squeeze a few more in. $\endgroup$ – jkd Feb 4 '18 at 5:42

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