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my question is pretty much in the title and i mean in "habitable planet" like earth, but not necessary to be same size or content.

so i was thinking rather than finding habitable planet which probably contain extraterrestrial lifeform already, and can possibly bring many problem from invasion/war,unknown space disease like from "war of the worlds movie bacteria stuff" or like the first contact with native people,political or social like living together with this extraterrestrial that require adaptation either culture or the land itself,the colonialism stuff.

and finding suitable planet to terraform is quite a gamble need thorough research and require different formula or material for the terraform.

why not just make the planet itself from accumulating compressed human excrement and just bring it to the suitable orbit or star and start terraforming, at least with this i believe the formula or material require would be the same, while also can be mass produce if human need new land, also i believe finding suitable star is more easy than suitable planet with different distance.

here some example visual spaceship from starwars (not necessary to be round shape so dont take it to literal) with my paint to point the core or the inside that contain compressed human excrement, with the outer layer can be stretch or expand to give room if it out of capacity and can be split like egg or scater into smaller ship to let it out so the ship can just focus to keep moving to their destination while the human excrement can accumulate or produced and i assume the human excrement can give methane as an extra fuel.

enter image description here

i believe maybe it can be made from accumulating asteroid too but i think it require to mine the asteroid and its a moving object so it will need the ship to follow around while full of danger from flying debris or another asteroid also i think asteroid is mismatch of many mineral wth different hardness its probably hard to compress without endangering the ship.

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    $\begingroup$ Ugh, I can almost smell it from here. Those poor colonists.... $\endgroup$
    – user535733
    Aug 7, 2019 at 11:48
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    $\begingroup$ @user535733 FWIW, the energy released by accumulating that much poop in one place would probably sterilise/boil/bake the stuff leaving you with a weird carbonaceous rocky world with a water atmosphere (for a while). It would smell of whatever superheated steam smells like. The transports on the other hand... $\endgroup$
    – Starfish Prime
    Aug 7, 2019 at 12:15
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    $\begingroup$ After 5 years of trying to amass such amount of excrement's NASA would be more than happy to announce that there is new kind of bacteria in SPAAACE. A bacteria that humans cannot deal with because it's SPAAAACE bacteria. $\endgroup$
    – SZCZERZO KŁY
    Aug 7, 2019 at 13:06
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    $\begingroup$ @user535733 the poor colonists? ;D $\endgroup$
    – Punintended
    Aug 7, 2019 at 21:09
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    $\begingroup$ Finally I understand what Sergeant Hartman was talking about when he threatened to send his Marines to a "world of shit". $\endgroup$
    – Jeremy Friesner
    Aug 7, 2019 at 21:22

2 Answers 2

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Mass of the moon: $7.4*10^{24}kg$

Average amount of poop produced an an average human in an average day, on average: $0.5kg$.

Amount of time required for a trillion people to produce that much poop: $4.05 * 10^9 \textrm{ years}$.

I'm not sure your plan is very viable.

To answer your question in a slightly different way, related to Kepotx's comment, why on earth would you do this? That's an enormous amount of very useful biological material and water, and when you form it into a planet almost all of it will be on the inside, basically inaccessible, doing nothing more useful than bending space and holding up the surface.

If you had that much poop to spread around, you'd do a much better job just dropping it onto the surface of an existing rocky world as part of the process of terraforming that, instead. Poop is better as a growth substrate for plants, bacteria and fungi than rock is. Use it where it can do you the most good.

The total biomass on earth is something like $10^{13}kg$. Poop is about 25% solids, 75% water, so with a mere $4 * 10^{13}kg$ of poop (which would take your trillion people a few days to produce) poured only a boring rocky world, you've got the makings of a nice (if slightly malodorous) desert world. You could do this many billions of times if you had a moon's worth of poop. That's how wasteful planetbuilding is.

Collecting teratonnes of human waste is left as an exercise for the reader.

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    $\begingroup$ @LiJun furthermore, you could probably terraform practically any even slightly suitable world in far, far less time than that... Mars, Venus and the Moon, just as a start. $\endgroup$
    – Starfish Prime
    Aug 7, 2019 at 11:25
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    $\begingroup$ Time is not the only problem. Shall we do this, earth would lose 7.4∗10^24 kg of fertile matter $\endgroup$
    – Kepotx
    Aug 7, 2019 at 11:26
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    $\begingroup$ My original timescale was a bit off (what's 4 orders of magnitude between friends?) but it would still take almost the same amount of time to collect that much poop as it did for earth to turn from a protoplanetary disc into a habitable world with intelligent life. So the idea is still silly. $\endgroup$
    – Starfish Prime
    Aug 7, 2019 at 12:02
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    $\begingroup$ @LiJun it remains an utterly terrible and wasteful idea regardless of the number of people involved. But it scales linearly, so it will take $~4.09 \times 10^{22}$ person-years. To do it in a hundred years, you'll only need a little over four billion worlds with a hundred billion poopers on each. That means you need to inhabit at at least one in every hundred stars in the galaxy, most of which seem to have no planets and/or are dangerously hostile to life for various reasons. Maybe you've inhabited multiple galaxies? $\endgroup$
    – Starfish Prime
    Nov 28, 2019 at 9:53
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    $\begingroup$ @LiJun also, that's 100 years to produce enough poop. Once you've smashed it all into one big blob you'll need to wait some time for it to cool down, as there will be quite a lot of energy released (the gravitational binding energy of the moon is of the order of $10^{29}$ joules). That won't take a billion years, but it'll probably take more than 100. Piling the stuff on carefully will stop it getting so hot, but will probably take much longer than 100 years, too. $\endgroup$
    – Starfish Prime
    Nov 28, 2019 at 9:57
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I would say - no.

The main reason is absence or great shortage of elements that make a rocky planet:

  • silicon (no rocks)
  • aliminium (no rocks)
  • calcuim (bones and corals)
  • other metals (no complex minerals)
  • phosphorus and chlorine

All you would get - a sort of dwarf gas gaint with diamond or ice core (depending on how exactly this planet forms)

Check this as a more authoritative opinion - moles and poop does not differ much at such scale. Seriosly - you do not need to separate humans from their excrements. Result would be the same :)

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  • $\begingroup$ Of course there's an xkcd for that... $\endgroup$
    – Yksisarvinen
    Aug 7, 2019 at 22:07

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