Orbital simulator and non fixed orbit

[FLOUR]

Hello,
Let's consider a small 3 planet system. One of the planet's is fixed and is a lot heavier than the others. The acelleration is
mP2 * aP2 = - FP3 - FP1
From with the velocity is derived with allows to calculate the positions of the planet's in a simulator program. After running the simulation, The orbit of one of the "moving" planets isn't fixed - some variation occur after each loop.

What can cause this? The other planet (that's not fixed) has an elliptic fixed orbit.
FP = Gravitational Force of Planet
Thanks.

 

[FLOUR]

Hello,
some more data about the situation:

Planet 1 - fixed on the center of the referential
Planet 2 - initial distance = 3 AU (start_x= 3 AU, start_y = 0)
Planet 3 - initial distance = 6 AU (start_x= 6 AU, start_y=0)

So Planet 2 is on the "middle" of the system.

Planet 1 is about 1000 times "heavier" than Planet 2.
Planet 3 is about 30 times "heavier" than Planet 2.

Planet 3's orbit is fixed elliptic. Planet 2's orbit has some variation to the initial elliptic orbit.

1) I was under the impression that orbits were suposed to be fixed...
2) I'm guessing the planet in the "middle" is getting heavy interaction from the other planet's...

Thanks for your comments.

 

[kyle8921]

There are a few possible causes for the non-fixed orbit in your simulation. One possibility is that there are external forces acting on the planet, such as gravitational forces from other bodies in the system or non-uniform density distributions within the planet itself. Another possibility is that there are numerical errors or approximations in the simulation program, which can lead to small variations in the orbital path over time. It is also important to consider the initial conditions and parameters used in the simulation, as these can greatly affect the stability of the orbits. Further analysis and adjustments to these factors may help to improve the accuracy and fixedness of the orbits in your simulation.