# Thread: Distances between planetary orbits

1. Member
Join Date
Aug 2009
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12

## Distances between planetary orbits

I am working on constructing a fictional solar system, but I am determined to make it work within known laws of physics and despite a lot of research, I still have many questions...
I can calculate speed of planets on their orbit using Kepler's third law, but I have problem determining the right orbit radius for different kind of planets. I know that a radius of habitable zone (in AU) is determined as root from luminosity of a star divided by luminosity of our sun. Is there a similar formula for gas giants or ice giants for example? My star is a close binary of two Sun-like stars (G-type), so the planets have to be further away I would think.
And yet another question: how to determine distances between planetary orbits so that the orbits are stable? Is there any specific distance necessary between an asteroid belt and a planetary orbit?

And one more thing: is there any solar system creator\simulator that would let me check if my system would work?

I would appreciate any help
Thank you

2. The same rough scaling as with the habitable zone applies to the rocky planet / gas giant transition too, so just take our solar system and scale to other luminosities the same way you scale the habitable zone (gas giants appear something like 5-10 times farther than the habitable zone). As for stability, some think that "Bode's rule" has something to do with stability, others think it's just numerology, but if you used it in a putative solar system, no one could really argue with it.

3. ^
What he said.

As per simulations, the best one I've found is here, at the "Astronomy Workshop". Try the "Working with Orbits" and "Orbital Integrator" subsections:

http://janus.astro.umd.edu/AW/awtools.html#orbits

Play your cards right, and you can literally have hours of fun here.

Here's another fun one, though I think it's usefulness for realistic simulation is a little limited:

http://www.arachnoid.com/gravitation/small.html

Click on "Lines", and tamper with the data, and, once more, you can have hours of fun.

Best of luck!

4. The links as provided by 'Romanus' are excellent and, I have doodled for hours with these...and come to some conclusions:
That a Binary star system could have planets orbiting at the green zone stably. Provided that the stars give room for that... as with Alpha Cent., Its worth mentioning that a more distant orbit to encircle both stars would be rare if not impossible. Or fare to cold.

5. Orbit simulator is popular. The simulations linked to above are toys. You need to simulate millions of revolutions to be reasonably certain of stability.

6. Member
Join Date
Aug 2009
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Thank you everyone very much for help, I'll try those links right now.

Originally Posted by timb
Orbit simulator is popular. The simulations linked to above are toys. You need to simulate millions of revolutions to be reasonably certain of stability.
Timb, do you have any particular orbit simulator in mind? Maybe you have a link to a good one? I would appreciate it.

7. Originally Posted by Aite
Thank you everyone very much for help, I'll try those links right now.

Timb, do you have any particular orbit simulator in mind? Maybe you have a link to a good one? I would appreciate it.
Yes, this one. There's a better one written by an Italian professor, but I don't have the link to hand.

8. Originally Posted by timb
Yes, this one. There's a better one written by an Italian professor, but I don't have the link to hand.
You are correct, in a previous post when you say one must literally simulate millions of revolutions to have a reasonable assurance of stability.

If the Italian professor is Aldo Vitagliano, he wrote the Solex simulator seen here but I am not aware of the ability to test random solar systems. It is however, an excellent example of a numerical integrator used for ephemeris calculations, reportedly accurate for tens of thousands of years. It is a fine program.

9. Originally Posted by Veeger
You are correct, in a previous post when you say one must literally simulate millions of revolutions to have a reasonable assurance of stability.

If the Italian professor is Aldo Vitagliano, he wrote the Solex simulator seen here but I am not aware of the ability to test random solar systems. It is however, an excellent example of a numerical integrator used for ephemeris calculations, reportedly accurate for tens of thousands of years. It is a fine program.
a fictitious Solar System can easily be loaded to the program, to model the gravitational dynamics of N-body systems and to get insights on aspects such chaos

10. Banned
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Oh, it's science fiction - make up whatever you'd like!

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