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Moon formation sims (Read 13283 times)
frankuitaalst
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Re: Moon formation sims
Reply #15 - 03/17/09 at 11:52:46
 
What I said about the tendency of a system to put the larger bodies at the center may become clear here :  
The plot gives the results of the above sims .  
X-axis represents the Sma in 1000 kms.  
Y-axis is the % Mass distribution of each moon .  
Smaller moons tend to be near the planet , while the bigger ones are found near the middle ...
Curious what the distribution will be if more simulations are run .
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DistributionMoonsJupiter3Sims.jpg
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Re: Moon formation sims
Reply #16 - 03/17/09 at 16:18:52
 
The thing we have to keep in mind is that this isn't the whole story - there's things like gas drag within the protosatellite disk, and more material coming in from the protoplanetary disk as well. Plus of course the lack of tidal interactions (which will be important for the innermost objects).
 
But I think this is still useful to give the right kind of idea for how regular satellite systems can form.
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Re: Moon formation sims
Reply #17 - 03/19/09 at 22:15:12
 
Run #5:
 
600 bodies (blue, tiny)
5e20 mass each
341km  radius each
0 ecc?
0 inc
random orbits
300,000 to 900,000
 
305 bodies (purple, moonlet) <-------------dense second ring of material at fixed distance within main disk.
1e21 mass each
430km  radius each
0.025 +/- 100% ecc  
0 inc
random orbits
600,000 to 650,000
 
RESULTS (4403 years)
 
4 moons:
1: 3.45e22 kg, 2797.27 km diameter, 336699.8338 km SMA, 0.071377976 ecc, tiny 318
2: 9.90e22 kg, 3975.64 km diameter, 438558.2045 km SMA, 0.040308547 ecc, tiny 401
3: 3.90e23 kg, 6281.56 km diameter, 627899.5448 km SMA, 0.020376947 ecc, moonlet 63
4: 8.30e22 kg, 3749.10 km diameter, 869612.6261 km SMA, 0.0575289 ecc, moonlet 135
 
 
COMMENTS:
- I made two belts - a main "tiny" belt containing 600 bodies at 5e20kg, from 300k-900k (I think I accidentally set their ecc to 0), and a denser "moonlet" belt within the main belt containing 305 bodies at 1e21 kg from 600k to 650k with ecc 0.00-0.05.  
- it only took 17 years to form the four satellites.
- However, the moons are listed in gravsim in a strange order - the two outer moons are listed first, then the two inner moons. I have no idea why.  
- Bizarrely there is MORE mass here than there was to start with?! I have no idea how that happened, I seem to have sprouted an extra 3 "tinies" worth of mass (6.065e23 kg total instead of 6.05e23 kg. I was sure that I had 600 tinies (3e23kg total) and 305 (3.05e23 kg total) moonlets...! I guess I must be wrong about that but... weird! Shocked
- I did however end up with a larger moon around the 600k distance, with the other three moons being about the same sort of size as in the other sims. I'm not sure if the largest moon formed first though (my collision.dat file for some reason didn't record this gsim?) - as far as I can see the last body in its neighbourhood that might have been in its neighbourhood was moonlet 97 which disappeared at year 3 (it hit either 63 or 135), then 317 and 318 merged closest to the planet at year 17 and there were four moons after that.  
- Very strange. Maybe someone else could regenerate the run from scratch and see what they get?
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« Last Edit: 03/20/09 at 00:30:12 by EDG »  

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(formerly known as Mal)
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Re: Moon formation sims
Reply #18 - 03/19/09 at 22:19:11
 
initial gsim for run #5.
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Re: Moon formation sims
Reply #19 - 03/20/09 at 09:26:32
 
Quote from Mal on 03/19/09 at 22:15:12:

- Bizarrely there is MORE mass here than there was to start with?! I have no idea how that happened, I seem to have sprouted an extra 3 "tinies" worth of mass (6.065e23 kg total instead of 6.05e23 kg. I was sure that I had 600 tinies (3e23kg total) and 305 (3.05e23 kg total) moonlets...! I guess I must be wrong about that but... weird! Shocked

I had the same experience with missing or added mass . In my 5 runs with 400 bodies each there was a loss or gain of maximum 5 body masses (395...403 ) . I didn't pay much attention to it .  
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Re: Moon formation sims
Reply #20 - 03/20/09 at 10:32:33
 
Quote from frankuitaalst on 03/20/09 at 09:26:32:
I had the same experience with missing or added mass . In my 5 runs with 400 bodies each there was a loss or gain of maximum 5 body masses (395...403 ) . I didn't pay much attention to it .

 
Missing mass could just be mass ejected from the system (it'd be nice if there was a flag for that). But if mass is being added then there must be a bug there somewhere... Tony, any ideas?
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Re: Moon formation sims
Reply #21 - 03/20/09 at 11:54:45
 
Mass should be conserved.  It could be a bug.  Can you send me before and after sims?
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Re: Moon formation sims
Reply #22 - 03/20/09 at 12:40:15
 
Quote from Tony on 03/20/09 at 11:54:45:
Mass should be conserved.  It could be a bug.  Can you send me before and after sims?

 
The "before" sim is attached to the previous post, it's the AccraMoonFormation0000r5.gsim file.  
 
Can you see what's going on with the moon sizes as well? They don't seem to increase in radius as shown in the gravsim window, though they are increasing in radius in the file itself.
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Re: Moon formation sims
Reply #23 - 03/21/09 at 03:38:42
 
Mal , for some reason your above program terminates after some seconds without warning . I don't know why . I had this with some other simulations , I think when there are some bodies merging from the start , but this isn't the case in your simulation as I can see move the timer .  
 
Hereunder is the result of 5 sims I've made with 300.000-2.000.000 km range around Jupiter ( 400 circular bodies ) .  
Black circles are the real thing .  
The distributions seem to match relatively well , except for the innermost Io which has about 3 times more mass .  
If the smaller inner moons are merged into each other the situation might correspond better to reality .  
Maybe Io really was created by merging some smaller protomoons orbiting close to Jupiter as a relict of Jupiters creation itself  ?
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DistributionJupiterMoons5Runs.jpg
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Re: Moon formation sims
Reply #24 - 03/21/09 at 15:31:39
 
I get the same problem as Frank.  I'll have to debug this.  As far as size, your objects are 860 km and your screen scale is 16 million km.  So each pixel represents 10000 km.  So one has to be larger than this before it is bumped up to 2 pixels in size.
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Re: Moon formation sims
Reply #25 - 03/21/09 at 16:37:21
 
huh. let me recreate it here and upload a new version and you can try that (I'm using the latest beta too)
 
EDIT: here's the start. I recreated it exactly as shown above, but I gave the 600 'tinies' an eccentricity of 0.025 +/- 100% (which is what I wanted to give them initially). So it's:
 
Run #5b:
 
600 bodies (blue, tiny)
5e20 mass each
341km  radius each
0.025 +/- 100% ecc  
0 inc
random orbits
300,000 to 900,000 km
 
305 bodies (purple, moonlet) <-------------dense second ring of material at fixed distance within main disk.
1e21 mass each
430km  radius each
0.025 +/- 100% ecc  
0 inc
random orbits
600,000 to 650,000 km
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Re: Moon formation sims
Reply #26 - 03/21/09 at 22:46:36
 
OK, so here are the results for 5b (left it running for 15851 years though)
 
 
RESULTS (15851 years)
 
3 moons:
1: 8.25e22 kg, 3740.64 km diameter, 350288.8325 km SMA, 0.060213114 ecc, tiny 6
2: 2.025E+23 kg, 5048.12 diameter, 803979.2898 km SMA, 0.029265853 ecc, moonlet 663
3: 3.195E+23 kg, 5877.36 km diameter, 565369.4297 km SMA, 0.023163272 ecc, moonlet 673
 
 
COMMENTS:
- this time it took much longer to form three satellites - 1127 years. Before that, there were four moons since year 94.  
- However, the moons are listed in gravsim in a strange order - the two outer moons are listed first, then the two inner moons. I have no idea why.  
- This time the total mass was 6.045e23, which is one "tiny" less than what we started with.
- Again, the largest moon is at the 600k distance, but it's not really that much bigger than the second moon...  
- This time the masses were listed in the right order in gravsim.
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Re: Moon formation sims
Reply #27 - 03/21/09 at 22:47:28
 
And here's what the run was like at the end when I stopped it.
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Re: Moon formation sims
Reply #28 - 03/22/09 at 07:33:04
 
I did the following experiment :
Took a full develloped system with 7 moons  
Added the same original system with 400 small bodies  
---> 7 moons with a lot of bodies as start of a new sim .  
Result : the 7 moons which were stable end up with 4 moons + ca. 20 original small bodies which sma increases with time .  
The result in Mass as function of Sma is shown here :  
The result is shown in red , whereas blue represents the original sim and black is the Jovian configuration .
 
Interpretation : adding smaller moonlets will reduce the number of big moons . The merging occurs very quickly in the inner region . The outer region needs more time to merge . Some moonlets will not be merged but will escape the system over longer timeperiods as their eccentricity builds up .  
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JupiterMoonsAdding.jpg
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Moon formation sims
Reply #29 - 03/22/09 at 07:37:01
 
The evolution of the individual moonlets' Sma can be seen here versus time .
The inner space is rather quickly cleared as the moonlets mere with the existing moons . Some inner moons also merge . The outer moons need more time to merge .  
Result is that the system "ends" with 4 big moons and about 20 very tiny moonlets at high eccentricity .
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