Consider a scenario where there is an over-populated solar system (not necessarily our solar system). Several other rocky planets and moons in this solar system are inhabited by the same humanoid race, and every planet's population is reaching its Malthusian limit. It's not too hard getting things into space (via a space elevator, or something like it). Travel between planets is also relatively easy, but travel outside of the system is not feasible. Attempts have been made, but nothing successful has come of it. Limits on reproduction are enforced, but population culling would be considered unethical and war is uncommon.

Besides over-crowding, every planet in this system has had a serious waste management problem. In order to combat this, for the past 50-ish Earth years, each planet has been shipping its garbage into space. Let's assume that this "cosmic dump" lies outside the effective reach of any nearby gravity well, and the trash itself isn't really moving through space at all.

Leaders and committees of the various planets have come up with an idea to deal with the rubbish that is filling up space and perhaps help relieve the population crisis.

The idea is this: take all the garbage that is floating around space and bring it to a massive asteroid. Using the asteroid as a core, they'll dump all the garbage onto the surface, making it somewhat larger.

For some rough Fermi estimations, let's assume we have:

  1. 50 earth years worth of trash
  2. 10 billion people on each planet
  3. 10 inhabitated planets
  4. Each person produces 2 tons of waste per year

This comes out to be about 10 trillion short tons, or 9.07185x10^15 kg of material. The largest asteroid in our solar system, Ceres, is 946x10^18 kg. Using that as a figure, and adding the waste our trash planet would be about 9.4600907x10^20 kg. Let's also assume that the contents of the waste are distributed as per http://www.epa.gov/epawaste/nonhaz/municipal/.

I'm guessing gravity would be pretty low on trash planet. Feel free to play with the numbers a bit to make it larger, if necessary. Also, please don't focus on the holes in my scenario - it can change...my main question is, could trash planet support a population? What if we added nuclear waste, let's say 1 billion kg of it? How would that change habitability? If trash planet is habitable, would the population it could support even really help reduce the strain on the other planets?

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    $\begingroup$ Reminds me of the Human Occupied Landfill, though that involved far less science... $\endgroup$ – Telastyn Feb 18 '15 at 16:43
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    $\begingroup$ I don't see the point in including the trash at all. If you add your 50 years of waste to Ceres, the trash only makes up 0.001% of the final mass. You'd be better off pulling multiple asteroids together. Adding Vesta and Palles would give you a mass of 1.4E21 which would be 149% the size of the proposed Ceres + Trash planet. $\endgroup$ – Engineer Toast Feb 18 '15 at 20:08
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    $\begingroup$ When I saw this subject line, I was expecting a futurama-esque scenario where such a planet naturally formed. $\endgroup$ – Random832 Feb 18 '15 at 21:25
  • $\begingroup$ Trash is full of useful organic and non-organic materials. Once we have decent robotics and lots of energy I imagine we will have it all mined for useful materials and there won't be any trash. $\endgroup$ – Matthew Lock Feb 18 '15 at 23:41
  • $\begingroup$ asset-b.soup.io/asset/3275/3584_b875.gif $\endgroup$ – Cort Ammon Feb 20 '15 at 17:02

Could the trashteroid support life?

Your trash planet (Well, not really a planet, since it isn't big enough to clear its orbit. We'll call it a trashteroid.) is as habitable as Ceres is. Covering Ceres in trash still leaves it as a lifeless, atmosphereless lumpy asteroid being baked by solar radiation. Ceres would be, as it is now, completely inhospitable to life. Solar and cosmic radiation would quickly bake all of the trash you dumped there into sterility, while it was simultaneously frozen and dehydrated by the icy vaccum of space.

You would not want to go there for summer vacation.

Unless, of course, you had a space station built there.

Life on the trashteroid (in a space station)

You could, of course, life there in a space station. Life on a space station on Ceres could be enjoyable, in a sense. You'd effectively be living in space, but with a tiny amount of gravity to hold you down to the floor. Ceres has a gravitational pull of $0.27 m/s^2$, which is about 1/40th that of earth.

You couldn't really enjoy jumping around in that gravitational constant all that much, since you'd be stuck inside all day, and your space station wouldn't be likely to have high ceilings. You could, of course, go outside in a space suit, but why would you want to? Everything outside is covered in trash.

How much trash would you need to make an inhabitable planet?

Let's assume that our trash is gassy enough to form an atmosphere in which a Mars-sized planet could be inhabited. Mars is about 1000 times as massive as Ceres. Ceres is about 100,000 times as massive as the trash we've already dumped there, so we'll just need to dump around 100,000,000 times as much trash to have a reasonably sized planet. (Let's assume we're using worm holes to dump the trash of every planet in the Milky Way on Ceres.)

Our new planet, based on the composition of garbage, will have a ton of carbon, and as such will probably be able to support a large, healthy biome, once it cools off. Why does it need to cool off? Well, dumping that trash onto the planet is going to release lots of kinetic energy. The first few thousand loads will go on easily, since the gravity is so low, but the more garbage we dump, the higher the gravity will be, and the more energy the trash will release as it drops from space onto the surface of the planet. That energy will turn to heat, which will be further increased by the billions of kilograms of radioactive waste you're planning on dumping as well. They planet may well liquify, but it should cool down in a few million years into a nice habitable planet. (Provided you stop dumping garbage on it!)


Yes, that planet could support population. But population would need independent life support system, aquaponics, etc, exactly as if it was build in empty space. Trash will support only gravity and nothing else (maybe some radiation pollution to boot).

But it would be rather expensive way to build a planet: lifting all that trash up the gravity well will take lots of resources. Even with space lift, lifting trash up is easy but not free. Spending rocket fuel to direct all that trash flying in space to target asteroid is not free either. Recycling trash on the planet would be much more energy efficient, and better use of planet's limited resources.

And if you want to use resources and material, you can get more livable space by building more traditional orbital space colonies, where gravity is provided by rotation. You can settle more people for ton of material spent (but that material cannot be trash)


When a civilization reaches that point, recycling all those useful atoms would be much more likely than throwing them all away.

At this point I would also expect in order to get more living space that they would start making a ring around the planet or a Dyson swarm, this would also help in catching energy from the sun. A ring around the planet could have a huge living surface at a fraction of the wasted material churning away in the center of the planets. Rolling earth out like pizza dough to a thin couple hundred feet would give plenty of living space for a much larger number of citizens.

So while you could 'make' a planet with garbage, it would be as pleasant as building your house on a land fill and actually fairly wasteful.

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    $\begingroup$ And this, here, is the answer of how it can be made viable in a story. The trash isn't just trash - it's raw materials for the ring. It'd need to be joined by an awful lot more mass - large asteroids towed in and so forth - but each planet in the system pays its dues to the future by contributing the mineral wealth of its trash towards the project, melted down and converted on-site by solar collectors (eg plastic doesn't burn so easy in space, just melts), to slowly spin the ring, like a spider its thread. The ring wouldn't be habitable for centuries, but the "spinneret" could be manned. $\endgroup$ – Dewi Morgan Feb 19 '15 at 9:03

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