I'm creating a sci-fi world similar to ours roughly 50 years in the future. Unobtanium, a futuristic metal and fuel source, was discovered in 2020. Its broad utility led to rapid advances across all parts of industry, but especially spaceflight, which is now commonplace for government / business leaders and military operations. However, even occasional spaceflight is beyond the means of average families.

My goal is to have have a dense cloud of debris completely blanketing the Earth. The main requirements are:

  • The debris needs to not exist around present-day Earth yet be fully formed within a couple hundred years, 50 years being preferable.
  • Ideally the debris would be of varying sizes, from micrometeorites to large rocks several hundred meters in diameter. It is most important to have debris in the tens-of-meters range.
  • The average debris density is flexible, but, at its densest, flying through should be risky without planning or active piloting. It would be ideal if debris were present at every latitutde.
  • The event that causes the debris cannot radically affect human society. Things like destruction of artifical satelites or small climate change (changes to day length, tides, global temperatures, etc.) are fine, but not things like "all humans are forced to live in underground bunkers".
  • To be clear, I'm not interested in long term stability. The debris only needs to be around long enough for it to be part of "everyday life" for spacefarers.
  • Bonus points if your soultion can explain the sudden appearence of large but expendable amounts of unobtanium (~10,000,000 m^3) on Earth's surface and in the debris field in 2020.

My first approach was to have an asteroid impact Earth’s moon, which would be convenient for other plot reasons, but after looking into it, it seems an impact strong enough to create the sort of debris density I need would have lots of appocalyptic side effects for the residents of Earth down below.

Another approach I considered was having people attempt to break up an inbound asteroid before it stuck Earth, but it seems like a object of mass sufficent to cause the sort of debris field I want would be imposssible to stop without causing significant damage to the Earth.

TLDR: How can I explain the sudden appearence of a dense debris field around earth?

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    $\begingroup$ is there a reason Kessler syndrome doesn't work? $\endgroup$ – John Oct 22 '18 at 2:13
  • $\begingroup$ @John I'd like to have debris tens of meters in diameter, but I couldn't think of a good way to explain the larger bodies not breaking up under the constant collisions. $\endgroup$ – cinnamon18 Oct 22 '18 at 2:25
  • $\begingroup$ How long does the debris field need to last for? a few years or a few hundred or more? $\endgroup$ – Blade Wraith Oct 22 '18 at 9:10
  • $\begingroup$ I’d like it to exist at least 50 years before and after my story’s present day, so humanity is used to its presence but can’t simply wait for the structure to destroy itself. $\endgroup$ – cinnamon18 Oct 22 '18 at 12:53
  • $\begingroup$ Wouldn't a dense debris field affect the amount of sunlight reaching Earth, potentially creating an ice age? $\endgroup$ – Tracy Cramer Oct 22 '18 at 22:46

The problem with asteroid capture scenarios is the capture. You need to somehow massively slow down the asteroids or they fly right on by.

Instead I suggest that people started trying to create an Orbital Ring around the planet. Roughly half way through construction though something went catastrophically wrong and the ring got ripped into pieces. Those pieces then hit each other and in a chain reaction smashed each other into various sized fragments that are now a major hazard in orbit.


  • $\begingroup$ This would also explain the Unobtanium in orbit. It's all pieces of the ring, and can be salvaged. $\endgroup$ – Andon Oct 22 '18 at 23:37

Asteroid Mining

enter image description here There are currently several groups gearing up for bringing a near-Earth asteroid to orbit for mining purposes. Let's say there are 4 or 5 companies (you can even use the ones currently doing this for realism purposes), with asteroids in orbit and something causes them to collide (maybe a new one comes in and the rocket malfunctions hitting one of the other ones causing changes in orbits which then eventually strikes the others.) Some pieces will come to Earth, some will leave orbit, and some will stay in orbit.

Planetary Resources

Deep Space Industries



I mean, your question answers itself. Have a bunch of Unobtainium-rich meteors rain on the Earth. The rocky portions of the meteors burn up in orbit, but the Unobtainium crashes to Earth leaving various deposits, especially near coastlines. Have some of the meteors land in a perpetual orbit around the Earth where they are still there, but only enough to be an inconvenience. Some of the meteors crashing into each other as they fall, shattering apart into not just being rocks, but a couple clouds of dust too. This would result in a minor temperature drop, of course, but it'd be enough of a sign to make the world governments look into their new satelights.

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    $\begingroup$ It is not really possible to get a stable orbit from a transfer orbit without deceleration or an extern force. And to saturate LEO, you would need a huge amount of meteors. $\endgroup$ – DarthDonut Oct 22 '18 at 6:51
  • $\begingroup$ @DarthDonut, The OPs questions doesn't stipulate stable orbiting debris field, so this answer is valid, and several large asteroids that breakup during aero-braking from a transfer orbit could generate a significant debris field that could meet the OPs needs $\endgroup$ – Blade Wraith Oct 22 '18 at 9:16
  • $\begingroup$ @BladeWraith maybe my skills in the English language failed me, but all i wanted to say is that to even become an "inconvenience" there still has to be an enormous amount of meteorites, comets or the like. $\endgroup$ – DarthDonut Oct 22 '18 at 9:51
  • $\begingroup$ @DarthDonut, sorry i wasn't criticizing your comment, but you'd be surprised how few you'd need to generate a Kessler syndrome type effect, especially if they start out as a few 100m across to begin with $\endgroup$ – Blade Wraith Oct 22 '18 at 9:57
  • $\begingroup$ An inconvenience can be as much as it makes it hard to see, which a sufficiently large enough dust cloud could easily do since you'd have to either work around it or fly through it. A minor inconvenience is still an inconvenience. Still, I appreciate the insight. $\endgroup$ – Sora Tamashii Oct 23 '18 at 0:49

Collision of two planetesimals in Earth's vicinity

Have a couple of those little oddities meet in a perpendicular collision (for better fragment spread), close enough to the Earth - in a way that would bring the speed of most of the remainders below 11 km/s.

Their exact mass and diameter is up to you, though keep in mind you'll need a fairly large amount of material to litter up Earth's orbits to the degree you've described.

Here's something to feed your imagination with.

Asteroid size.
And who would've known, one of those bodies had a wealth of formerly unheard of element, in ores and rich deposits. Some debris remained in orbit, other pieces rained down on Earth. Even to this day, despite the blanket of fragments - sand grain to house-sized and beyond - wrapped around our planet, some daring souls venture into it to make a fortune off untapped resources.

Eventually the cloud should flatten and form some sort of ring system, but that should be noticeable over tens of thousands of years, not couple of centuries.

Now, would it spread more or less evenly in a time frame of century or two? I'm not one hundred percent positive, but it would certainly make space travel a far more dangerous affair.

Satellites, aside from geostationary and beyond, are totally screwed. You'll also have an initial, quite intense, rain of asteroid chunks - which I see as the only plausible-looking way to introduce this new metal to the Earth. As the years pass by, strikes from above will be less and less frequent. Just safe enough for humans to leave their bunkers.

Finally, if your new element was packed into a single sphere of pure unobtainium, it would have a diameter of around \begin{equation} d = 2\sqrt[3]\frac{V}{(\frac{4}{3}\pi)} = 267.3m \end{equation}

Which is a quite a sizable, but certainly not unheard of impacting body. Chicxulub asteroid or comet is thought to have been 10 to 15 km in diameter, so your asteroid - even with some added rock content - would cause an impact well below an extinction-level event. You may also split those resources between several smaller bodies hitting the planet in different spots. Here's another helpful page to help you calculate some effects of various impacts.

Don't forget your carbon fiber umbrella, we might have a mild precipitation today.

  • $\begingroup$ Do you know a good way to estimate the amount of material that would renter after such a collision? Or to explain almost all of it falling in harmless areas? (I guesstimate if ~10^13 kg of material renters, earth starts to get toasty) $\endgroup$ – cinnamon18 Oct 23 '18 at 13:40
  • $\begingroup$ The amount of fallen material may wary wildly with their incoming angles (if both are pointing right at Earth, we have a planetary scale life-wiping scattershot), as well as their speed and angle of collision, which would shape the orbits of chunks within the new cloud. There's such a large amount of possibilities that you can cherry-pick one suiting your plot and go with it. Vast amount of rock & metal may remain in orbit. What you need is 10,000,000 m^3 on Earth. If density is, say, 4g/cm^3, you would need just 4 * 10^7 kg of it. With added rock, maybe 1-2 * 10^8? Still no biggie. $\endgroup$ – tlaik Oct 23 '18 at 17:05
  • $\begingroup$ Also, about explaining it falling into unpopulated areas: Earth's surface is 71% water. Whatever falls, already has a high probability of not hitting anything important. Not sure if scuba diving for precious rocks was in your plans, though. $\endgroup$ – tlaik Oct 23 '18 at 17:09
  • $\begingroup$ I like this answer, a highly improbable scenario but theoretically it should be plausible and a fictional setting can usually get away with 1 very unlikely thing. $\endgroup$ – Tim B Oct 24 '18 at 8:49

The Kessler Syndrome is the answer.

If you've seen the movie Gravity, then you've seen what the Kessler Syndrome is: the complete or near complete destruction of everything in orbit due a cascading chain effect of destruction.

Basically: two objects in orbit collide, resulting in their destruction and the creation of a cloud of debris that scatter around. The debris hits other orbiting object, destroying them, creating even more debris that hit other objects in orbit, destroying them and so on. Rinse and repeat until tehre's nothing left in orbit but a debris of varying size, mass and speed making space flight a quite risky venture.

Basically, this: https://youtu.be/prlIhY3e04k?t=40


Giant Meteor

You can borrow from Armageddon(yes, that Michael Bay movie). Basically, big scary meteor that will cause catastrophic damage is spotted on a collision course with Earth. Earth authorities resort to any number out of several possible solutions to this threat: sending a team to plant explosives on the meteor exactly as per the movie, or maybe unveiling a prototype technology like a really large functioning railgun. Either way, the problem is dealt with but not in a perfectly clean way. The meteor is blown up closer to Earth than needed to be totally 'safe', and thus a series of relatively small fragments impact on Earth and cause minimal damage while a large portion of the resulting debris doesn't strike Earth but gets caught by its gravity well. Your meteor can be used to explain unobtanium as well.


Some official/technocrat gets overzealous with the idea of cloud seeding and takes it a step further, by attempting to create a field of particulates in orbit. Motives to do this could be an attempt to engineer the climate(whether mutually agreed or not), slow down the effects of global warming, or an act of war against certain countries. To add some variety to your field of debris, you could have some man-made satellites accidentally on purpose shredded by the new particles being introduced. Unobtanium in orbit could be explained as a hitherto undiscovered reaction between certain elements in micro-gravity, but here I'm just grasping at straws.

  • $\begingroup$ The problem with this idea is that the meteor would still have escape velocity. Either it hits the atmosphere or it flies on by... $\endgroup$ – Tim B Oct 22 '18 at 9:58
  • $\begingroup$ @TimB Having the whole meteor blown up into small chunks should alter its velocity and trajectory $\endgroup$ – nullpointer Oct 23 '18 at 1:04
  • $\begingroup$ Conservation of momentum says nope...the chunks would continue with their original trajectory. If you somehow split the meteor in half and had one half shoot off at much increased speed and one slow down drastically that might work. Rather hard to explain though. $\endgroup$ – Tim B Oct 23 '18 at 14:56
  • $\begingroup$ nullpointer, tell that to an arrow shot from a bow. $\endgroup$ – Sora Tamashii Oct 23 '18 at 19:06
  • $\begingroup$ @TimB Yeah it's pretty hard if the requirement is for the debris field to be in stable-ish low orbit. According to Physics SE(physics.stackexchange.com/questions/134819/…) the debris in Lagrange L1 or L2 can be arranged. Alternatively, splitting the meteor and slowing one half might be possible if something like a railgun is used, but I'm just speculating here. $\endgroup$ – nullpointer Oct 24 '18 at 8:36

An unobtainium meteor collides with the moon and the pieces hit the Earth.

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    $\begingroup$ A bit more detail wouldn't go amiss. In particular, how might the pieces hit Earth without causing a catastrophe? $\endgroup$ – Philip Rowlands Oct 22 '18 at 7:47
  • $\begingroup$ I don't think there would be any alternative unless aliens brought it down... it has to impact the Earth either in smaller pieces or as one piece. I think some catastrophy is going to be unavoidable. Or it could crash into the ocean in fragments. I mean the Tunguska explosion was kind of big but there were no real effects. Maybe it all comes down in periodic meteor showers. $\endgroup$ – Althaen Nov 23 '18 at 5:34

So, unobtanium is a fuel source? That should answer your question.
I expect that no later than 45 seconds after the discovery, some very large western power will start a war against the terrorists in the country the Unobtanium was found in. And rightly so, because not handing all your energy sources to them is an unacceptable affront. Or something.
You mention space flight becoming quite common, so you may expect some part of that war taking place in LEO. After all, LEO is a god place to be if you want to see your opponent, or if you want to drop things on them.
So now you have things of interest in LEO, and you have a reason to remove those same things, leading to debris, and eventually to Keppler Syndrome.

  • $\begingroup$ Well I mean ICBMs already do a good enough job of striking any location on the planet and satellites can already see everything. $\endgroup$ – Althaen Nov 23 '18 at 5:38

Self-replicating nanites gone wild.

Since the most significant problem associated with self-replicating nanotechnology is that of confinement, the initial experiments with such technology take place in orbit (e.g. on a captured asteroid) where matter — the nanites can transform — is limited, thus preventing them from taking over the entire planet in case something goes wrong (which actually happens).

The nanites could be made out of Unobtanium, while the goal of the self-replication experiments could be to turn an asteroid into pure Unobtanium, hence the large amounts of it in the debris field.


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