View Full Version : The same question but different

2004-May-28, 08:16 AM
I asked if this was possible once before and was told both of the moons would eventually collide.

I forgot to ask a follow up question. If both of these moons were the identical distance from their planet (which is the same size as the Earth) as the Moon is to the Earth and orbited at the same speed and were the same size as our moon how long would it take before they collided?


What is the chance of their orbits degrading until they collided with the planet?


PS> I know they wouldn't all look identical. I just used the same image for the picture.

2004-May-28, 08:27 PM
I was intruiged by this system, and I wanted to see what happened. I used to have an old n-body gravity simulator where you could set objects with mass, diameter, position, and velocity and set them on their happy Newtonion ways. I seemed to remember it being called the Solar System Simulator, but that's such a generic name I couldn't find it all afternoon.

Then I stumbled on what looks like an almost identical program, called Gravity6 http://www.andersson-design.com/gravity/index.shtml

I got out my handy Fundamentals of Astrodynamics book, and put together a rough simulation of two moons in orthogonal circular orbits. If you download the program, you can load the simulation I made here:

I haven't run it to see how long it would take before they would collide (space is pretty big, after all). The system does go chaotic very quickly. Eventually the moons end up in highly elliptical orbits. I'm sure it's only a matter of time before a collision.