# Could a solar system with large amounts of dust and debris exist?

I'm working on a sci-fi/fantasy world set in a solar system with a few habital, currently-being-colonized planets. Most of the action will be taking place on the surface of one of them, but I want background detail to add to the setting and give me info for future developments.

I was wondering if a solar system could exist with massive amounts of natural debris and dust, such as asteroid belts and the like, that affected space travel in such a way that ships couldn't accelerate too fast for fear of losing maneuverability and hitting something. I'm talking dense. This would also add an element of uncertainty and surprise to space battles, as normally you would be able to see your opponent from far away using sensors, but in the dust and debris, stealth would be much more feasible.

On another note, I want a Star Trek or Mass Effect kind of ship handling, and to me, imposing this sort of speed limit will help with that. Any suggestions along that vein would be most appreciated too!

EDIT: Wow, didn't expect so many helpful responses, especially on my first post ever! You guys are making my life a lot easier. I'm leaning toward a debris disk/field right now, as that seems perfect for what I had in mind.

For additional info, the reason that there are people in this solar system is that that's where life appeared, and as they haven't developed FTL tech, they're basically stuck there. I think I'll call the system and the star Apex. The 'homeworld' colonizes a couple other planets in the system, and after a civil war between the colonies, one of them suffers orbital bombardment, plunging the few survivors into a post-apocalyptic mess hundreds of millions of kilometers from home.

• You might want to consider a gas torus, rather than dust and rocks - check out Larry Niven's Integral Trees for an example. – John Feltz Aug 25 '16 at 20:30
• We have this now. Isn't this crap exactly why the Star Trek Enterprise has a deflector dish? It's a snow plow, for space. – candied_orange Aug 25 '16 at 21:47
• Two star systems with large Oort clouds could have passed close in the (reatively) recent past. With enough cloud objects getting disturbed, it could be messy closer in, perhaps for millions of years. – user2338816 Aug 26 '16 at 5:38
• I think yiu’re confusing acceleration and velocity. Or did «accelerate too fast» mean accelerate up to a too-high velocity rather than how quickly you change your speed up to the final value? – JDługosz Aug 26 '16 at 10:03
• You could have a proto-planetary disk, but if it's proto-planetary, I doubt there would be any habitable planets. Also, spcecrafts can fly out of the plane of the disk to get around it. And if the system is full of debris, planet could receive monthly asteroids, which will make it very uneconomical to live there. – sampathsris Aug 26 '16 at 10:55

## 9 Answers

What you described looks just like very young solar system, where planetary formation is a process still in progress.

Your dust and asteroids is simply a protoplanetary disk. Planets are on the small side, still clearing their neighborhood. Probably no native life there, but easier to mine. This might be a reason to go there at all.

Can't find source, but I remember reading somewhere that thickness may be about 19% of diameter. That's quite a lot - and interesting stuff is inside. Also, you seem to care about stealth. Risk of being attacked may outweigh risk of traveling inside stealth-able environment. Or not, but you still need to get in and out.

• Invoking a protoplanetary disk is a chicken and egg problem. While the disk was present the planets would not have formed yet (or, if they were newly formed, they would likely have global magma oceans). – Sean Raymond Aug 26 '16 at 14:28

# Give it a protoplanetary disk:

Image in the public domain.

Protoplanetary disks are circumstellar disks that form early on in the life of a planetary system, from the original protoplanetary nebula around the star. They can survive for over 10-20 million years (see Mamajek et al. (2009)), meaning that life likely could not develop, but you could have loads of protoplanets and related bodies around while still retaining plenty of dust.

I would recommend a debris disk, but they're not necessarily as dense. Additionally, they won't necessarily have bodies as large as protoplanets inside them - although even asteroid-sized bodies can be hazardous to space travelers.

What will the densities actually be like? They can vary quite a lot over time. Here's a graph of surface density $$\Sigma$$ vs. radius $$R$$ from Dullemond et al.:

Initially, there are maximum surface densities in the order of 10,000 grams per square centimeter; after 3 million years, this peak has gone down to 100 grams per square centimeter. We can use Equation 5 from here to find the spatial density: $$\rho(R,Z)=\frac{\Sigma(R)}{\sqrt{2\pi} H}\exp\left(-\frac{Z^2}{2H^2}\right)$$ At an elevation of $$Z=0$$, and assuming a scale height consistent with that of Chiang & Goldreich (1997), then at a distance of about 1 AU, $$H\sim0.045$$ and at a time of about half a million years, the density is . . . quite substantial.

Sean Raymond's suggestion of a debris disk might be better than my answer, for a few reasons that he pointed out:

• Debris disks aren't so short-lived.
• They can contain large rocky planets; the debris disk I suggested only holds small planetesimals

You should strongly consider that.

• If there's a disk, what's the reason to not just fly above/below it and avoid most of the danger? – OrangeDog Aug 26 '16 at 7:57
• @OrangeDog Same reason all of our probes fly (at least initially) in the orbital plane - it takes a freakin' huge amount of energy to orbit the Sun, and if you start from a planet you get most of it for free - if you stay in the same plane. – Ordous Aug 26 '16 at 13:04
• @OrangeDog Protoplanetary disks are not thin. Even at $Z=H$, the density will still be about 0.60 times the density at $Z=0$ at the same radius - and if $H\sim.045$, then that's still over 4 million miles - about 17.5 times the distance from Earth to the Moon. So trying to escape and fly above/below it once you're at $Z=0$ (where most of the protoplanets will be) will take a lot of time and effort. It's not so simple. – HDE 226868 Aug 26 '16 at 13:50
• It's true that protoplanetary disks are not that thin, with typical aspect ratios of 5% or so. However, large planets tend to sink to the very thin mid-plane where there is the most action. That being said, as I mentioned in a comment above, this is a chicken-and-egg problem. While the protoplanetary disk is there, rocky planets do not exist yet; they are still forming. And even if they are fully-formed they cannot yet be habitable since their surfaces are likely molten. What you need is a debris disk, preferably during an instability (see answer below) – Sean Raymond Aug 26 '16 at 14:30
• @SeanRaymond Fair point. I chose 3 million years as a decent intermediate point because it would land in the very early stages of planetesimal formation; I was willing to not have there be proper planets in order to gain some small rocky bodies while retaining large amounts of dust. I also misunderstood the composition of mature debris disks; I thought the dust fraction was much smaller. I think your proposal is better, then. – HDE 226868 Aug 26 '16 at 14:45

It's not plausible to invoke a protoplanetary disk: they are too short-lived. There's a ton of dust floating around in those disks because it's where planets are forming. If your planets are already formed (with non-molten surfaces) then the disk is gone.

What you need is a "debris disk". In astronomer-speak, debris disks are belts or disks of rocky/icy leftovers of planet formation that produce enough dust that you can see them directly. Here are a couple of famous examples (note that debris is usually inferred from spectra rather than seen directly; these are prime examples):

Most debris disks are relatively cold, made of bodies on very cold (think Neptune-ish) orbits. But a few do have warmer belts closer to where terrestrial planets live. The trick is this: very dense belts don't last long.

The best way I can think of to have a super dense debris field is to make your story take place during a late heavy bombardment-type event. Like the Solar System's bombardment (https://en.wikipedia.org/wiki/Late_Heavy_Bombardment) but much heavier. This is totally plausible from an astrodynamical point of view.

• +1; I like it. I did a little bit of reading, and I've seen varied statistics for debris disk lifetimes (many on orders of magnitude greater than the lifetimes of protoplanetary disks). Out of curiosity, what would be the lifetime of a typical debris disk here? – HDE 226868 Aug 26 '16 at 14:52
• Well, debris disks -- meaning belts of comets that slowly grind to dust -- can last for billions of years. However, the instability phase, during which an instability in planets' orbits causes a massive deluge of debris throughout the planetary system, is much shorter, typically 0.1 to 10 million years long. The Solar System's late heavy bombardment was pretty wimpy compared to what is likely to have happened in many extrasolar planetary systems. – Sean Raymond Aug 26 '16 at 17:05

That solar system is just a slag pile from some Type 2 Civilization's strip mining operation. We thought it was natural when we arrived. Some kind of young solar system or a late-blooming proto-planetary disk; but its sun turned out to be too old for that. Also, most of the expected heavier metals were missing.

It was a real mystery for a while.

Then we found the first of the artifacts. No more than a thousand Earth-years ago, some very advanced miners reduced most of the system to dust and rock fragments. They left a couple planets intact. Probably used them as their mining camps.

They even took most of the primary star's mass. It didn't used to be a dwarf. They left just enough mass to keep all this junk from floating away and causing havoc out in open space.

This place would be a wasteland, except those ancient strip miners left some of their tools behind; mostly broken bits and warn-out parts. Probably junk to them, but precious artifacts and technological wonders for us. That whole solar system has become a technological boom town.

It is the center of the 24th century gold rush!

Such a system wouldn't be colonised in the first place.

In a protoplanetary disk, there's a lot of debris floating around, which is what you asked for. But that large amount of debris crossing planet orbits also means lots of impact events. These tend to do bad things to real estate values. Really bad things.

Most sensible colonists would avoid this as way too likely to get a rock dropped on you from orbit. Unless there's some reason why you can't just go to the star next door.

• Indeed. It would be next to impossible to reach one of the planets at all, for the fear of colliding into something, let alone trying to colonize some planets! – Youstay Igo Aug 26 '16 at 5:05
• @YoustayIgo nah, you just activate your pegasus cloak, and fly right through! – Benubird Aug 26 '16 at 11:16

You could make your solar system filled with a combination of frequent clouds of gas and frequent asteroid belts. This could potentially force slowness and allow stealth while still allowing for an inhabitable solar system.

• The OP already said all of this in the question. (S)he wants to know if/how such a system could actually exist. – JBentley Aug 26 '16 at 8:36
• Hi, Gen_Luke, welcome to Worldbuilding SE. Your answer can be improved by explaining how the dense gas, dust & asteroids form part of the solar system. Here we prefer facts, discussion, details & reasons why something is so. It takes time to learn the rules here. Just hang in there and you pick them up. – a4android Aug 26 '16 at 11:38

There's an example of this, a later stage star with a crap ton of debris. The suspicion is that two planets within it collided.

http://articles.latimes.com/2014/mar/08/science/la-sci-sn-beta-pictoris-star-planet-gas-collision-comets-carbon-monoxide-20140307

Even if we're pretty far away, if Mercury hit Venus, we'd have a lot of junk floating around. Not sure, how long we'd live.

You can place an ancient megastructure on this system, like a Dyson sphere.

Due to his abandonment, the structure collapsed long ago, creating numerous remains. Over time, theses remains started to collide at high speed, creating smaller remains.

At last, you obtain a system with a lot of debris on various size, from dust to country-sized part.

Any advanced civilization can easily and logically create such kind of structure.

I'm going to more or less disagree with everyone here.

I don't think the option of protoplanetary disk would work. If it's proto-planetary, planets are not yet formed or still in the stage of big ugly magma balls, incapable of hosting any life. When a planet gradually cools down and terraforms itself to be capable of hosting life, several billion years would have passed and the debris would have been cleared by the planets.

You could have another planet in the system to have collided with a rogue planet recently (i.e. few million years in the past). That will give you a nice debris field. But it would mean that planet would be frequently and heavily bombarded with asteroids. It would not be suitable for life.

If somehow you were able to have a debris field and have a thin debris free strip for the planet, the debris would not affect spacecrafts. Because they need not to fly in the planetary plane, they can fly out of it and get out of the system.

So the alternative for you is to have your planet in a debris free zone, but give some incentives for the spacecrafts to go into a dangerous zone full of debris in another part of the system.

Look at this breathtaking animation of Jupiter herding the asteroids: https://www.youtube.com/watch?v=yt1qPCiOq-8

I got an idea from this. Have a star larger/hotter than Sun, where your habitable planet is around 5-8 AU from the star. Have a gas giant closer to the star. And then have an inner planet collide with a rogue planet few 100,000 years ago.

The gas giant will herd the debris so your planet will not be affected much. And oh, the rogue planet was crossing the planetary plane, so the debris is not a disk, but a big mass ball of dust, sand, and rocks around the star.

And maybe your spacecrafts need to go near the star to recharge like Rama, or there's a valuable mineral that could be mined in the asteroid field.