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So, I've got a planet that's basically a junkyard. It's just one big junkyard. People from various space-faring societies dump all the crap there that they don't want to deal with. Derelict spaceships, obsolete tech, that sort of thing. And because the people doing this are lazy, what they basically do is just haul a big space barge close enough to the planet's gravity well, cut all the garbage loose, push it just over the edge of the well, and let it fall.

So my question is, assuming the trash isn't getting permanently trapped in orbit, and assuming both the trajectory and the exact point in space from which the garbage is released are both random, would the places the garbage falls be random too? Would there be an equal distribution over the entire planet's surface, or as the trash collects over thousands of years, would it start to pile up more in some places then others? Would it start to accumulate a whole lot around the equator, but barely any at all near the poles? Would things like mountain ranges or ocean currents influence this at all?

Update: Because everyone was asking, the reason there even is a junkyard planet is simply because humans are lazy. Various corporations and space governments figured out that they could just dump a ton of metal on a planet, and after about a hundred years, an eyeblink in space time, desperate folk would move there and begin setting up their own small-scale recycling operations, purifying the metal, lifting it back up out of the gravity well, and selling it to the companies again for a pittance. It takes a while but it's the cheapest and laziest possible way to recycle things on a massive scale.

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    $\begingroup$ Sounds like Soldier (1998). Anyway... where the incoming stuff lands depends on the where the space barges comes from. If from a polar direction, then it could land anywhere; if from an equatorial orbit, then somewhere near the equator; etc. Since it's falling from space, mountains and oceans have no impact. $\endgroup$ – RonJohn Mar 7 '18 at 19:48
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    $\begingroup$ The premise is utterly flawed, though, since metal is 100% recyclable, and the strong, lightweight alloys needed for space travel aren't cheap. Thus, you'd recycle it. And space travel itself is expensive. Much simpler (I mean much simpler) to just drop stuff that's too expensive to recycle stuff into your own star. $\endgroup$ – RonJohn Mar 7 '18 at 19:52
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    $\begingroup$ #1 free, limitless energy is impossible. #1 e=mc^2 -> m=e/c^2, which means that you need a lot of energy to make mass. LOTS. Recycling your unobtanium is a lot simpler. $\endgroup$ – RonJohn Mar 7 '18 at 21:17
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    $\begingroup$ Gotta go with RonJon here. Nearly free and nearly limitless energy is nice, but recycling, or simply disposing junk into the nearest star makes more sense in energy and time than going across the galaxy to a junk planet. $\endgroup$ – Dan Clarke Mar 7 '18 at 21:49
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    $\begingroup$ @Willk Then presumably you can just turn your waste into energy instead of carting it off to some planet. $\endgroup$ – Samuel Mar 7 '18 at 23:26
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The distribution of impact craters on the Moon is random. I believe the same can be said about Mercury, another crater-ridden body in our solar system. They got their craters from asteroids and comets that struck them randomly throughout the ages.

If the drop trajectories over your planet are really random, so will be the impact regions. If you still have doubts, a couple hours simulating this on Kerbal Space Program should solve the problem for you in a very practical manner.

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The initial falling is pretty well covered by the other answers, so this will focus on the other question in the OP.

As the trash collects over thousands of years, would it start to pile up more in some places then others?

Many of the processes would apply to trash on Junkyard the same way that they apply to dirt on Earth.

Precipitation

If you wanted there to be a variety in its distribution, you could add weather that would prevent some trash from making it to the surface, or dissolve trash, creating a climate-like distribution of trash. For example, if your planet had acidic oceans, the patterns of accelerated trash decay would form in the same way that patterns of precipitation form on Earth, with less precipitation corresponding to less disintegration, and thus more trash. The oceans themselves would only contain trash that could survive their acidity.

For example, if Junkyard had Earth's geography, trash on the Western side of the Rockies would receive a lot more acid rain than trash on the opposite side, analogous to how California receives a lot more rain than Nevada.

Geological Activity

If the Junkyard planet is geologically active, subduction zones might swallow up a lot of trash, and the areas where new crust is made would be briefly bare. Also, the way trash reacts to lava could cause areas near volcanos to have unusual concentrations of specific types of trash

Weathering from Wind

Additionally, if certain latitudes have faster wind than others (comparable to the winds around Antarctica here on Earth), that trash would erode faster (on a very slow time scale, but still), and would have a tendency to settle around the belt instead of inside of it.

Glaciers

I'm sure there are more creative ways to incorporate glacial erosion, but at the very least, if someone dropped a comet onto the planet, its chunks might move like glaciers, carving out valleys behind them.

For processes that wouldn't apply to Earth:

Tidal Locking

If the planet orbits around a star, you might want to make it tidally locked, causing trash on one side to melt, and causing trash on the other side to accumulate. Additionally, dumpers may prefer one side or the other to avoid the heat of the star, or to get its energy, depending on which side you prefer.

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It sounds like the pattern would indeed be random, if the drop-off process is as haphazard as you suggest. It's just that if the planet is used as often as you suggest, such a random set of flight patterns could get dangerous. You could have ships heading in to make a drop interfering with each other's flight paths. SOME process wold likely emerge, even if it's only getting on the radio and saying "Hey this is the USS Macawber, if we don't hear from anyone in a half hour, we'll be making a drop run around Planet Junkyard".

I wouldn't be surprised if some governing body stepped in and set up flight paths, if only to make sure that some of the trash DOESN'T end up in orbit, or missing the planet entirely and causing a flight hazard.

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Maybe, but I don't think it would be "All over the planet".

Most of it would fall along the equator, well assuming normal orbits (equatorial orbits). If you were dropping it in random orbits then it would be random. But if you drop in the plane of the planets rotation (again equatorial) then it would be concentrated at the equator.

Obviously if your orbit determines where it will de-orbit, unless you dump it with a good amount of velocity.

Anyway now that everyone is done splitting hairs about what I said, and I do stress the OP never defined an "orbit".

UPDATE (just an idea)

I think a better premise then a Junk planet is a graveyard planet. From an energy standpoint it doesn't make much sense to take the effort of flying garbage to a planet and then slowing down and dumping it, when you can just shoot it into the nearest star.

A better idea as I said is a graveyard planet, what I mean by that is something like this:

enter image description here

The US military bone yard.

For the most part we keep this place pretty clean but a whole planet used for this purpose and it wouldn't be worth the energy to clean it up. The purpose would be for things like military treaties that limit the use or number of certain ships, for example. It could also be used for deprecated/obsolite equipment. Some of this equipment even though obsolete could still be better then some factions have. And then there is always the use as a parts yard, for post production equipment. You know to keep some of the old stuff fit and running you sacrifice some of them for parts.

After a few centuries the place would start looking pretty dumpy.

And most of this stuff would have been, safe'd by having the engines or fuel removed before being place for long term storage. So it wouldn't be like you could just land there and sneak off with a star destroyer. Besides you could always have the place guarded by some orbital defense satellites and what not.

Even if you want to leave the military aspect out of it, I could see a mega corp taking a small, arid and mineral poor planet and using it for this purpose. Basically a giant Scrap/Junk yard. There may be valuable parts that take specialized manufacturing, or dangerous material that needs specialized handling and recycling facilities. So they take the only thing the planet has to offer a somewhat breathable atmosphere and gravity and use that. Being arid its no good for food production, being poor in minerals its no good for mining. The dryness of the place would be good for preventing corrosion etc. Then they import old ships and equipment, cannibalize them and export replacement parts and scrap metals.

But in this case, and if you have valuable infrastructure that you don't want destroyed, you probably wont want stuff just falling from orbit randomly over the planet. You might have a corridor that is setup for reviving bulk scrap metals. Stuff that has no salvageable parts as the energy to deorbit it "gently" would not be justified. This could be around the equator (see what I did there).

Couple this with prison/slave labor, and I would believe it was possible in some distant future.

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    $\begingroup$ #1 There's no such thing as a "normal" orbits. #2 It also assumes that stars exist only in the planet's equatorial plane. $\endgroup$ – RonJohn Mar 7 '18 at 21:19
  • $\begingroup$ it doesn't matter if there is a sun or not, it matters which way the planet rotates plane of the planets rotation there is a relationship between the orbit, tidal forces, and the planets rotation that can have a small effect on the orbiting bodies. $\endgroup$ – ArtisticPhoenix Mar 7 '18 at 21:28
  • $\begingroup$ I didn't mention the sun in my comment. All I said was "planet's equatorial plane". $\endgroup$ – RonJohn Mar 7 '18 at 21:49
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    $\begingroup$ Why would we think that you assume it? Because you wrote, "Most of it would fall along the equator, well assuming normal orbits." $\endgroup$ – RonJohn Mar 7 '18 at 23:31
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    $\begingroup$ "equatorial orbits, which are more efficient" for ground launches. Not for arriving from another star. $\endgroup$ – RonJohn Mar 7 '18 at 23:38
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Does it rotate? If so, the trash would be more likely to pile up on the plane of rotation, which for an earthlike setup is the Tropics of Cancer to Capricorn. However, I think you need to think through the whole low orbit thing. If people were being at all careless in their dumping, there would quickly be a sheath of debris orbiting this planet such that it'd be difficult to land there, and it'd be constantly bombarded with impacts. This would be a tough place to live.

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  • $\begingroup$ Trash would pile up in whatever orbit people dumped it in. You might be thinking of the fact that planets are mostly in the orbital plane, but recall that ring systems for planets depend more on the planet's rotation than its orbital plane. Uranus for example has rings that are almost perpendicular to the orbital plane because that's how Uranus rotates. And all that is only that way as a leftover from formation, not because it's a better orbit. $\endgroup$ – Samuel Mar 7 '18 at 20:56
  • $\begingroup$ You're absolutely right; rotation would trump orbit hands' down. Clarifying my post. $\endgroup$ – Carduus Mar 7 '18 at 21:07
  • $\begingroup$ Oh, still, the plane of rotation doesn't really come into it unless they're launching from the surface (as it's a cheaper orbit to get to from the surface). Being in orbit at all is assuming people dump their trash at orbital velocities. $\endgroup$ – Samuel Mar 7 '18 at 21:37
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    $\begingroup$ "If you're orbiting and dropping, the trash is going to come out in a line based on both your trajectory and the planet's rotation" - No, the planet's rotation doesn't enter into it, only the orbital parameters. A ship only needs to enter an orbit if it plans to stay. Would you agree it's feasible for a ship to approach a planet directly, drop its trash, and then make a slight course adjustment to miss the planet entirely? In that case it wouldn't even need to slow down from interplanetary speeds to orbital speeds nor waste the energy slowing its trash down in the same fashion. $\endgroup$ – Samuel Mar 8 '18 at 17:12
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    $\begingroup$ That's very true. And I suppose with the halo of trash already there, it's best to just throw it and run. $\endgroup$ – Carduus Mar 8 '18 at 17:17
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As @ArtisticPhoenix said, it will likely have a bell curve distribution centering on the equator or some other line near the equator. That is because most planets lie in their star's plane of ecliptic and have a spin that corresponds roughly with the plane of the ecliptic. Most stars are on or near the galaxy's plane of the ecliptic and their spin's correspond generally to the galaxy's plane.

This isn't 100% but the majority of the ships dumping stuff should come in with a least cost approach near the equator.

Even if ships do not come in on an equatorial plane, since the planet is spinning, their trash has a good chance of crossing the equator and will otherwise be distributed around the planet. If you have ships from different stars coming in at different angles and directions, almost all of their dumps will cross the equator. This will make the distribution higher as you approach the equator.

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    $\begingroup$ "The majority of the ships dumping stuff should come in with a least cost approach near the equator. Why? There are a whole lot of stars in the Northern Hemisphere, so what's to stop barges from coming in from a polar direction? $\endgroup$ – RonJohn Mar 7 '18 at 22:25
  • $\begingroup$ @RonJohn, first, many of the "stars" you see are actually galaxies. Also, get into an area with dark skies and look at the Milkyway or find a picture on the internet (but that's not nearly as good). Even if all of the "stars" you see are actual stars, look at how many more come from near the Milkyway's plane of the ecliptic. Also, in the second part of the question, I address the situation if they aren't in a near equatorial orbit. $\endgroup$ – ShadoCat Mar 7 '18 at 22:34
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    $\begingroup$ The Milky Way is -- from some point on the Earth at some time of year -- at every angle from almost 0° to 90°. $\endgroup$ – RonJohn Mar 7 '18 at 22:40
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    $\begingroup$ The premise is "assuming both the trajectory and the exact point in space from which the garbage is released are both random". Are you saying the premise of the question is wrong? $\endgroup$ – Samuel Mar 7 '18 at 23:23
  • $\begingroup$ A drop of trajectory would only be less costly by bwing close to the equator if the starting trajextory is already within the same plane as the equator. Even in our own solar system that is rarely true, since each planet's orbit around the sun has its own plane. $\endgroup$ – Renan Mar 8 '18 at 11:08

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