Are you certain that your model is conserving energy?  I have worked
with many finite-difference models in the past, and from my experience
it is very possible and even probable that you are not conserving
energy.

	I don't know what scheme you are using to determine the orbits, but you
might want to consider using a different one.  Two of the simpler ones
are called

	- the velocity Verlet algorithm
	- the 4th order Runge-Kutta algorithm

Besides this, I'm sure that there are a variety of special algorithms
for planetary motion.

	Good luck.

	In Him,
	Ben
	<><

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