Nebular Solar System Gen for Dummies Like Me

[robject]

Here's how I generate solar systems, mostly.

(Mostly = I insert the mainworld and asteroid belts after the system is generated. So it's not a complete system. But it is fun.)

Allocate 21 "main" rows, 1-1 thru 6-6.
Assign 2d? masses to each of the 21 "main" rows.
The snowline is beyond row 2-5.

Iterate until no masses can grow or move:

1. randomly determine a row number which has a non-zero number of masses
2. steal 1d masses from both adjacent rows, if any
3. if beyond the snowline, and mass > 15, promote to GG
4. if a GG, and if adjacent to another GG, the bigger one pushes the smaller one out 1d rows, and imparts some axial tilt to it.
5. if a GG, eject 1d masses from outer adjacent row out to the next outer adjacent row, and impart a proportional amount of eccentricity to its orbit.
6. if a GG's inner adjacent row has masses, move into that row and gobble them up.

Evaluation.

Non-GG masses are planets with Size = mass/2, rounded down.
GG masses have Size = mass.
For every GG which has moved within row 3-3 (or something), inflict one action onto each world insystem. Possible actions include:

1. nothing?
2. the capture of 1d planitesimal planetoids
3. a collision event resulting in some axial tilt
4. a major collision event resulting in a sizable moon
5. potentially being violently flung 1d rows outside of the GG's own row
6. potentially reduction to an asteroid belt?

 

[FreeTrav]

Would you be so kind as to post a fully-worked example? I'm having trouble visualizing some of the steps from just the descriptions.

 

[Magnus von Thornwood]

I am with FreeTrav.

Say what?

Yeah, a bit more detail or perhaps one of those "examples" might be helpful.

What I think I understand of it seems pretty neat.

 

[Andrew M]

Well I guess this is a star system generation system in its nebula stage I like it a lot!

I don't know enough to say if this is physically realistic. You might want to get some feedback from Evil Doctor Ganymede who studies this sort of thing for a living. He can be found on the SFRPG, and possibly the Mongoose, forums.

I think I understand how it works. One rule that has been left unclear is whether material in a gas giant can be sucked into a neighbouring row. It seems pretty obvious that it shouldn't, but it's probably worth making this clear anyway. You might want to make a distinction between dust clouds and proto-planets in general. I guess that is what the mass threshold for gas giants is about. Maybe that concept could be extended to rocky planets, but have the threshold vary with distance from the sun.

Anyway I like where this is going, and I am glad that it is relatively simple at the moment.

 

[Gray Lensman]

Ditto

Would you be so kind as to post a fully-worked example? I'm having trouble visualizing some of the steps from just the descriptions.

Me too!

 

[robject]

This system needs shortcuts, and the model is relatively untested.

First, I draw up 23 slots, with a mark after slot 25 for the snowline. Next, I roll 2D for each slot.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66
----------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10

Now the iteration begins. I figure each iteration is worth 10
million years. Something like that.

Epoch 1. For each iteration, I roll a slot location with two dice.

> 5 2

Okay, I rolled a 5 and a 2. That's slot 25. Now I take 1D masses
from its neighboring orbits and add them to its total.

From slot 24:
> 1

From slot 26:
> 2

So the current state is:

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66
----------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
                         7 10   10

I'm only updating the values which have changed, to save my sanity.

Epoch 2. I roll 3 and 3.
Slot 33 takes 2 masses from slot 26 and 1 mass from slot 34:

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66
----------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
                         7 10   10
                                 8  9  9

Epoch 3. I roll 3 and 6.
Slot 36 takes 3 from 35 and 3 from 44.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66
----------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
                         7 10   10
                                 8  9  9  3 12  4

Epoch 4. Roll is slot 14, which siezes 2 and 6 masses.
Epoch 5. Slot 15, seizing 2 and 3 masses.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66
----------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
       3 11  3           7 10   10
          9  8  7                8  9  9  3 12  4

Epoch 6. Slot 15 again, seizing a whopping 5 and 4 masses.
Epoch 7. Slot 56, seizing 6 and 5 masses.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66
----------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
       3 11  3           7 10   10                       2 21* 5
          9  8  7                8  9  9  3 12  4
          4 17  2

It took a lot longer than other times, but a GG has finally coalesced
at slot 56. Since this is the promotion step, the GG acts.

First, the GG ejects 1D masses from its outward neighbor one slot
further out. I roll a 4. Since 66 is the outer slot, I create a
"fake" slot at 77 and move those masses there.

Second, there is mass in its inward neighbor, so the thing actually
moves into that slot, absorbing those masses (I think there should
be a chance of those masses becoming moons, but I'll think about
that later). I also think that there should be a chance that the GG
does NOT move inward, but there are lots of things missing in the
system so far, so I'm not ready to worry about that yet.

I'm going to skip a bit because I'm at my posting limit.

Epoch 8. Slot 35, taking 1 and 6 masses.
Epoch 9. Slot 11, taking 2 masses (only one neighbor).
Epoch 10. Slot 15, taking 5 and 5 masses.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
          9  8  7                8  9  9  3 12  4       23* -  1  4
          4 17  2                      1 10  6
          - 23  -

Note that slots 14 and 16 don't have 5 and 5 masses. So I just
empty them out, and they're pretty much out of the game. I don't
have good rules yet for near-collisions which may slingshot masses
into other orbits.

Epoch 11. Slot 45, taking 5 and 2 masses.
Epoch 12. Slot 26, taking 4 and 6 masses. This is a big one. Took
long enough...

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
          9  8  7                8  9  9  3 12  4       23* -  1  4
          4 17  2           6   18  3  1 10  6  - 13  5
          - 23  -

So another Gas Giant has formed, this time right beyond the snow line
at slot 26. On its promotion, it ejects the masses at 33 to 34, and
moves inside the snow line into orbit 25, creating a minor threat to
the proto-inner system.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
          9  8  7                8  9  9  3 12  4       23* -  1  4
          4 17  2          24*   -  -  4 10  6  - 13  5
          - 23  -

Epoch 13. Slot 36, taking 2 masses.
Epoch 14. Slot 25. The youngest GG. It doesn't take masses, it
scatters and moves. Slot 24 has mass, so the GG moves in.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
          9  8  7                8  9  9  3 12  4       23* -  1  4
          4 17  2          24*   -  -  4 10  6  - 13  5
          - 23  -       31* -             8  8

Epoch 15. Slot 12 takes 6 and 2 masses.
Epoch 16. Slot 55. The older GG moves inward.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
 3 17  1  9  8  7                8  9  9  3 12  4        -  -  1  4
          4 17  2          24*   -  -  4 10  6  - 13 28*
          - 23  -       31* -             8  8

Epoch 17. Slot 35 takes 5 and 1 masses.
Epoch 18. Slot 36 takes 4 masses.
Epoch 19. Slot 24, the young GG moves again, in a march to destroy
the inner system.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
 3 17  1  9  8  7                8  9  9  3 12  4        -  -  1  4
          4 17  2          24*   -  -  4 10  6  - 13 28*
          - 23  -       31* -          - 13  7 
                     38* -                9 11

Epoch 20. Slot 36 takes 4 masses from 35.
Epoch 21. Slot 35 takes 2 masses from 36.
Epoch 22. Slot 13 takes 1 mass from 12.
Epoch 23. Slot 12 takes 6 and 3 masses.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
 3 17  1  9  8  7                8  9  9  3 12  4        -  -  1  4
   16  2  4 17  2          24*   -  -  4 10  6  - 13 28*
 - 21  -  - 23  -       31* -          - 13  7 
                     38* -                7 13

Epoch 24. The only move left ** inside the snowline ** is for the GG
in slot 23 to move one final step inward. Slot 16 has no masses, so
the GG is effectively stopped.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
 7 11  5  3  9 10  6  7  8  7   12  6 10  6  6  7  7  7  8 10 10
 9  9  3 11  3           7 10   10                       2 21  5
 3 17  1  9  8  7                8  9  9  3 12  4        -  -  1  4
   16  2  4 17  2          24*   -  -  4 10  6  - 13 28*
 - 21  -  - 23  -       31* -          - 13  7 
                     38* -                7 13
                  44* -

Since there are no valid moves left within the snowline, the simulation
halts. Rocky planets are formed by halving their accumulated masses,
rounding down. Gas giants' mass is kept as a size rating.

Rocky worlds that are still adjacent to a GG become asteroid belts.

11 12 13 14 15 16 22 23 24 25 : 26 33 34 35 36 44 45 46 55 56 66 77
-------------------------------------------------------------------
   10       11    GG                      3  6    AB GG        0  2

So the final system has 6 rocky planets, 2 GGs, and 1 belt.

Because the inner Gas Giant occupied 5 slots adjacent to or inside the snowline, it inflicts 5 events to each world in the inner system. It's like 5 damage rolls, sort of like anti-mustering-out benefits. They will end up with interesting characteristics, including tilts, moons, scars, perhaps a retrograde orbit, etc.

 

[aramis]

Aside from the inner areas having the same mass as outer ones available, and the unexplained missing chunks in the numbering...

 

[Gray Lensman]

I understand how and why he numbered it that way (I think), and I believe I get the system as a whole. But I do have a question.

Couldn't you also generate the stellar formation itself this way?

And yes, Unless you are one of those here with problems with EDG he should see this!

 

[Sifu Blackirish]

Ummm...a question back here...

I understand the concept now. Thanks for the detailed example! It has that semi-random quality that appeals to my background gearheadedness, without the appearance that you pulled completely random numbers out of your butt.

However...

If this procedure is a simulation of gravitational mass accretion, how can a smaller mass steal material from a larger one? It's my only quibble with what looks like an elegant system.

Are you assuming that something like, oh, induced gravity waves from the central mass is disrupting everything periodically?

I know it doesn't really make a difference, since this is just a simulation, but it's my anal-retentive personality that wants to know "WHY???" even if no one else ever knows...or cares...

 

[robject]

If this procedure is a simulation of gravitational mass accretion, how can a smaller mass steal material from a larger one? It's my only quibble with what looks like an elegant system.

That's not really what's happening. At any given stage, the number you see (for non-GGs) is really a gauge of the proto-planetesimals floating around in a relatively narrow track around the primary. Only when things calm down can you assume that these things have finished congealing into a "planet". So what this does is simulate the collision and perturbations of all of these masses with each other... and in many cases the effect of Very Large Masses (gas giants) near the inner system as well.

Aside from the inner areas having the same mass as outer ones available [...]

This is actually mostly misleading, because the outsystem is the nursery for Gas Giants. Even one GG would effectively put about 99% of the system's mass in the outsystem, at least to begin with. So the outsystem's values are on a dual scale, potentially.