
A Simulated Stable Planetary System with 416 Planets in the Habitable Zone - prostoalex
http://nautil.us/blog/-i-built-a-stable-planetary-system-with-416-planets-in-the-habitable-zone
======
odabaxok
Previous submission:
[https://news.ycombinator.com/item?id=14764125](https://news.ycombinator.com/item?id=14764125)
(91 points, 32 comments)

~~~
mihai_maruseac
It's the same article, same content, same title, but different publication
date.

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bmcusick
Although obviously ridiculous in many ways, the ability to design large stable
systems is relevant for when thinking about the question "How many O'Neil
cylinders can we build in the habitable zone?".

If we mine the asteroids, Mars, and Mercury for materials we can build
habitable surface areas that are in aggregate many times greater than Earth in
size. Each carbon fiber Bishop Ring could have an internal surface area the
size of India.

This simulation reminds us that space is really, really big, and really,
really empty. If you can fit 416 planets, just think how many space stations
you can fit.

~~~
sigstoat
> the ability to design large stable systems is relevant for when thinking
> about the question "How many O'Neil cylinders can we build in the habitable
> zone?".

pretty sure the answer is "as many as we can figure out how to get the mass
for".

absent dismantling the gas giants themselves, you're not going to do anything
very interesting do the dynamics of the solar system, regardless of what you
take apart, or how you reconstitute it.

and the man-made structures can include mechanisms for closed-loop control of
their position. which they'd need anyways, as they'd accumulate positional
error from vehicles coming and going.

~~~
elihu
I think the point of building habitats is that spherical planets are a very
inefficient use of matter from a surface-area-to-mass ratio point of view. We
could create a lot more surface area (i.e. usable land) with less material if
it were arranged in a more useful configuration.

~~~
sigstoat
those are all completely true things. i assume something i said has been
misinterpreted, but i can't imagine what or how.

~~~
elihu
Probably this line:

> absent dismantling the gas giants themselves, you're not going to do
> anything very interesting do the dynamics of the solar system, regardless of
> what you take apart, or how you reconstitute it.

I would consider reconfiguring available materials to achieve more usable
surface area to be interesting (not to mention potentially useful if we manage
to accomplish it someday).

However, what's "interesting" is highly subjective and dependent on context.
Perhaps you meant something different by "you're not going to do anything very
interesting" than the way some of us are interpreting it?

~~~
sigstoat
"you're not going to do anything very interesting..." to the dynamics of the
solar system.

the _orbital_ dynamics of the solar system. (the thing you'd be worried about
if you thought you needed to learn how to make 416-body systems stable.)

certainly packing the habitable zone full of new places to live is
interesting, on all sorts of social and technological levels. it just doesn't
raise any questions about the stability/dynamics of the n-body system that is
the solar system (until you maybe start taking apart the gas giants).

hopefully that clears that up?

~~~
elihu
Yeah, thanks.

And I agree; it turns out that planets are really heavy and have an incredible
amount of inertia; moving some asteroids around isn't going to cause the Earth
to slip on a banana peel and fall into the sun.

The original article about placing 416 Earth-sized planets in a stable orbit
does involve a quantity of mass greater than Jupiter (at 317.8 Earth masses),
but building habitats out of what we have available in and inside the asteroid
belt is a much more modest scope.

~~~
bmcusick
I love how turning the entirety of the asteroid belt, and maybe Mercury, into
livable space stations "is a much more modest scope". :-D

Not that I disagree! We also have the Hilda, Trojan, and Greek asteroids (in
Jupiter's Lagrange points) to work with. The Jovian and Saturnian moons too.
It'll be a long, long time before we need to worry about dismantling the gas
giants themselves.

On our path towards maximizing the livable land area in the Solar System, I
wonder what we will run out of first. It looks like water, iron, carbon, etc.
are all pretty abundant. We'll run out of* some rarer element (like
Phosphorous or something) before we ever approach maximum constructed land
area.

*And by "run out of", I mean even with perfect recycling, the spot market demand for the material maintains a price level where it's uneconomical to develop further, barring discovery of new supplies or more efficient usage.

~~~
jeremysmyth
This assumes that we don't create such elements as a by-product of fusion or
other processes that we develop in parallel with the technology advances
required to bring significant industry outside earth's gravity well.

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matte_black
Would like to see an artist rendition of this sky.

Someone should make a VR app that lets you simulate the surface of any kind of
planet and any kind of sky based on a solar system configuration.

~~~
bmcusick
It's real question how dark these planets would ever get. With 416 planets
reflecting light, the closest ones would be pretty bright all the time. Maybe
even visible discs from the surface, although I'm not sure. Brighter than
Venus is on Earth though, and lots of them.

You'd have to take that into account when doing your global warming models
too.

~~~
Retric
Venius is a long way from impacting earths climate. The scale is 2.512^(x-y).

Sun −26.74, Moon −12.74 (average full moon), Venus -4.89 to −3.82. So sun is
around 400,000 times as bright as the moon, and the moon is ~1500 times as
bright as the Venus which is bright largely because it's so close to the sun.

Mars is −2.91 at it's brightest. So 1/2 as much light as Venus because it's
further from the sun even if it's closer. These might be closer than Mars, but
not closer than the moon.

~~~
bmcusick
Venus all by itself is minimal. These planets would be closer and there'd be a
lot more of them. If they're supposed to be Earth-like they'd also have
clouds, making them reflect more like than airless worlds like the Moon does.
I bet there would be a measurable effect.

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amelius
Can't we see a simulation of this running?

Also, I'm wondering about tidal forces ...

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AndrewStephens
> This system is completely stable—I double-checked with computer simulations.

Until some idiot on planet 297 moves his couch from one side his living room
to the other. Then the whole system is going to slowly fall apart,

~~~
catpolice
When I read this article initially, I got the impression that here "stable"
actually means that it's not sensitive to small perturbations - the orbital
pattern is a local attactor and is thus sort of "self-correcting", at least
over some non-trivial timespan. Someone can correct me if I'm wrong about that
(in which case this whole exercise is somewhat silly).

~~~
ygaf
Yeah I think HN forgot to be charitable today.

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linuxguy2
I thought I had seen this before....

Previous discussion:
[https://news.ycombinator.com/item?id=14764125](https://news.ycombinator.com/item?id=14764125)

It even links to the same site and the blog was posted by the same guy. I
wonder why he's recycling content.

~~~
hobofan
The financial situation of Nautilus is not the best[0] which might explain why
they recycle content.

[0]: [https://nautil.us/blog/a-letter-from-the-publisher-of-
nautil...](https://nautil.us/blog/a-letter-from-the-publisher-of-nautilus)

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spacepinball
This would be like a gigantic space pinball as soon Oumuamua showed up.

Then it would just be a huge asteroid belt which would eventually form a
normalized amount of planets.

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berbec
Impressive. Pierson's Puppeteers only managed six. [1]

1:
[https://en.wikipedia.org/wiki/Pierson's_Puppeteers#Homeworld...](https://en.wikipedia.org/wiki/Pierson's_Puppeteers#Homeworld%E2%80%94The_Fleet_of_Worlds)

~~~
clort
its worth noting, that they were not orbiting a star (I don't know if that
would be a positive or negative issue, for stability .. they moved away from
the star to cool off)

~~~
logfromblammo
If I recall correctly, they were attempting to move away from the galactic
core, so that they could escape some ultimate cataclysm faster than the
destruction could catch up to them. Their major technological problem was
rejection of waste heat.

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dmytrish
It's hard to imagine natural formation of such a complex structure in real
universe. It needs a lot of precision (interplanetary engineering?) or luck to
put 416 bodies in the exact positions and velocity for the model to be stable.

Another unnatural thing about this model is that adjacent orbits rotate in
opposite directions: according to existing theories of formation of planetary
systems, it seems impossible for the gas disk to go into different directions
in layers.

Anyway, this model is definitely cool (416 bodies in stable orbits!) and might
be a useful blueprint for interplanetary engineering of the future.

~~~
jpfed
The fact that it would never occur naturally makes it even more interesting.
Imagine interplanetary civilizations rearranging star systems to send the
unambiguous signal "1\. intelligent life lives here, and 2. they are powerful
enough to arrange planets, so a peaceful posture is probably advisable.".

~~~
animal531
Probably if you're capable of capturing and moving 400+ planets into a new
sun's orbit in a decent enough amount of time, then no one is going to be
bothering you.

But it'll send a pretty impressive message.

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hateful
Could probably apply for a job on Magrathea.

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unit91
> This system is completely stable—I double-checked with computer simulations.

I would think that's a hilarious joke if the author didn't seem so serious.

~~~
d33
I assume you're alluding to N-body problem?

[https://en.wikipedia.org/wiki/N-body_problem](https://en.wikipedia.org/wiki/N-body_problem)

~~~
marcosdumay
I assume he is alluding to how a simulation of finite precision can not prove
anything about a chaotic system.

And yes, that the N-body problem is chaotic.

~~~
saalweachter
Well, that's the question - _is_ his 416-planet system chaotic? Do
perturbtions get amplified or do they get pushed back to the stable
configuration?

Of course, when you're talking about a civilization building 416 equal-mass
planets equally spaced in 8 counter-rotating orbits, worrying about _how_
stable they are is kind of silly; as long as they're "mostly" stable the
maintenance of monitoring and tweaking their orbits for a billion years would
presumably both be feasible and cheap compared to the initial construction.

~~~
marcosdumay
Orbits on a N-body system are chaotic if N > 2\. Always.

That said, the longer you simulate those orbits, the more certainty you have
that they are stable. But you will never get a mathematical proof, because
only symbolic math can ever prove things in a chaotic system, finite precision
math can only deal with statistic degrees of certainty.

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120bits
This is really nice read! I remember I visited a local Planetarium few weeks
ago. They had a game where you will need to pick like 5 planets and design the
solar system. It had the asteroid belt. Big planets and small ones. The game
will end if the EARTH collides with any other planet and if the other planet
collides you lose points. The simulation was just amazing.

~~~
dylan604
what local planetarium is this? that sounds worthy of a visit.

~~~
120bits
Downtown Salt Lake City. It had a huge screen with touch controls. You can
drag planets around run the simulation to see if the system in stable.

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wcoenen
Makes you wonder whether the remarkable density of terrestrial planets in the
TRAPPIST-1 system is the result of engineering. Maybe somebody is planning far
ahead and counting on the tiny star's long lifetime (which is in the trillions
of years) to keep their civilization going?

On the other hand, the intense star flares and tidal locking seem very
inconvenient.

~~~
avmich
> which is in the trillions of years

Is it always such a big lifetime for small stars? White dwarfs have a long
lifetime, but they have interesting stories behind them; what about other
types of small stars?

~~~
wolfram74
If I'm not mistaken, the smaller stars don't have as high a gravitational
gradient and are fully convective so the helium ash and hydrogen fuel mix
closer to uniformly, allowing them to burn through all of it. Stars on the
scale of sol slowly build up helium until it chokes out, compresses and starts
burning helium at higher temperatures, causing the rest of it to expand.

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tempodox
If only one inhabitant of any of these planets so much as sneezes too hard, it
will destabilize the whole system.
[https://en.wikipedia.org/wiki/Butterfly_effect](https://en.wikipedia.org/wiki/Butterfly_effect)

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tardo99
Couldn't you fit in more if you didn't assume all planets orbit in the same
plane?

~~~
JoeAltmaier
A planet cannonballing through the plane is generally very disruptive, giving
anything they pass near an impulse normal to their orbit and eventually making
the whole thing wobble like a plate on a circus clowns finger

~~~
0xfeba
I want to see that simulation.

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COil
That's a lot of eclipses no?

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loxs
And a lot of collisions, resulting in formation of bigger planets.

~~~
HorizonXP
Or maybe a white sky and hard rain scenario.

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sys13
Makes me think about Firefly with "dozens of planets and hundreds of moons".

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Casseres
Reading the article, I imagined what the people (?) on those planets must
think when they discover they're not alone.

Let's say we discover we are not alone. We know those aliens must not be from
our galaxy, so do we push for development of faster-than-light travel? If so,
why? Intelectual curiousity, defense, offense, trade, habitation?

As for the hypothetical galaxy with two planets of life: Are they developing
the same? If not, do they, and if so why, expand to the other? If they are,
are they afraid of each other? Do they have a "cold war"? The possibilities
are endless.

Like Firefly, there are many posibilities for great sci-fi.

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hossbeast
They're all still orbiting in a single plane. What about the z axis?

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maxxar92
Call up Isaac Arthur, I'm sure we'll have an episode on how to build this
system soon.

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Thoreandan
"Our moon is almost half the size of Earth"

What? No, it's not.

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detuur
Does this remind anyone of the "Golden Hour" from House of Suns?

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spennant
Wake the Magratheans.

~~~
jmts
I for one was expecting the author to be Slartibartfast.

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exelius
Yeah but now connect them all with space elevators.

~~~
blunte
space catapults, good aim, good timing. (and lots of pillows)

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tartuffe78
Would make for an interesting sky

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aklemm
Who can summarize why this is interesting?

~~~
_rpd
Becoming a Type II civilization on the Kardashev scale might involve
construction of a Dyson swarm. This is a thought experiment in which each of
the swarm elements is Earth sized, presumably providing near-ideal additional
habitat for a larger human population.

~~~
blackrock
Is a complete Dyson sphere even possible? Given the mineral resources
available in a solar system.

Say you are an advanced alien civilization. And you reach the point where you
haven't nuked yourself to death, so now you can expand into space. The first
thing you do is to mine all the asteroids, that hadn't coalesced into a
planet. So you spend all this energy to capture them, to smelt them, and then
you build out your Dyson sphere.

You can achieve some coverage of the star, but is it even possible to cover
the entire star with solar collecting panels, to capture all the energy output
of the star?

At best, I think you might be able to get a ring around the star. But even
this, is dubious.

~~~
_rpd
You would likely need to obtain the material via ...

[https://en.wikipedia.org/wiki/Star_lifting](https://en.wikipedia.org/wiki/Star_lifting)

and possibly large scale transmutation. Disassembling the gas giants might be
enough for some designs.

My understanding is that it isn't physically possible to construct rigid
spheres or rings in that orbit, so it would be an orbital swarm of some kind,
with the elements able to actively correct for the inevitable perturbations.

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cmurf
Easier and cheaper than a Dyson sphere?

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jlebrech
God? is this you?

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personjerry
What's the point of this if it's impossible to arrive at?

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hendersoon
I imagine this sort of thing is how HN will actually look in a hundred years,
if humanity survives that long.

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utopkara
This points to a fundamental problem in the understanding of planetary
systems. Planets do not come to being out of nothing; enourmous amounts of
matter have to come together to make up a planet. Great example of experts
ignoring "details" outside their expertise.

~~~
lalaithion
"But nature would have a tough time forming this system. If it exists, it
could only have been built by a super-advanced civilization."

