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PostPosted: Fri Jun 07, 2019 1:36 pm 
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I'm constantly puttering with an app in python to generate systems, and I'm not quite clear about how to do moons.

I get the concept of roche limit and hill sphere, but not quite sure how to calculate them. I assume that these two numbers will tell me how close in a world can be to a primary and still have moons.

Let's say for simplicity's sake it's a star and planet with the same mass/radius as the sun and the Earth. Can someone show me what the equation looks like?

Much obliged!

Or as the office manager at my previous job would say, "thanks in advanced[sic]"


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PostPosted: Fri Jun 07, 2019 7:06 pm 
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The Hill Sphere is basically where the secondary body's gravity dominates over the primary's.
https://en.wikipedia.org/wiki/Hill_sphere

Use the second equation there to calculate it. Note that actually stable prograde orbits only seem to be found within about 1/3-1/2 of the Hill Radius. Retrograde orbits can be more stable at a greater distance.


The Roche Limit is where tidal forces can tear satellites apart - it depends on the densities and materials of the planet and satellite. The full explanation is on the wiki page below but I think the best formula to use is the first formula in the Fluid Satellites section (since satellites are not purely rigid bodies and deform under stress). Don't worry about the second equation there, you don't really need to care about oblateness etc :
https://en.wikipedia.org/wiki/Roche_lim ... satellites

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PostPosted: Thu Jun 13, 2019 12:39 pm 
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Thanks!


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