I am trying to set up 2 Planets in a co-orbital configuration around a Jupiter size planet similarly to Saturn's moons Janus and Epimetheus. I'm trying to do this in Universe Sandbox 2 but when I place these planets they mess with each others orbits too much. Is it possible to have such a system and how would it be done?

Diagram showing what Epimetheus and Janus do.

  • $\begingroup$ It seems very unlikely that could happen with large bodies? Those two are only pebbles 100/200 km across. BTW I'd guess there is no chance that, Universe Sandbox 2 would be sophisticated enough to simulate such a thing. $\endgroup$
    – Fattie
    Sep 24, 2016 at 11:51
  • 1
    $\begingroup$ Pedantic, but wouldn't the 2 bodies be moons? $\endgroup$
    – CGCampbell
    Sep 24, 2016 at 14:02
  • $\begingroup$ Smaller moons should perturb each other less. $\endgroup$
    – Mike G
    Sep 24, 2016 at 20:14
  • $\begingroup$ There is a simulation of Saturn with all it's moons in the game. $\endgroup$
    – Althaen
    Sep 24, 2016 at 22:30

1 Answer 1


Because this has gone unanswered, and using this very nice answer as a reference, I can answer this part way. Source article here.

it was found that if the mass of second body becomes larger than 1/1200 of the first body, horseshoe orbits become unstable.

So Earth mass orbiting Jupiter (1/318) won't work according to the research above. You could try Mars mass objects orbiting Jupiter (1/2970) and you might get that to work for a fairly extended number of orbits. Horseshoe orbits are never stable over the long term the way trojan orbits can be, but they can be stable over numerous orbits if they are properly set up.

I tried to work out the specifics for higher mass horseshoe objects, but my attempts at calculations have just sent me in circles so far. If I make any progress I'll post an update. You'd have to move the Mars-mass moons quite far from the planet and you'd need to keep the variation in their semi-major axes quite small. Janus and Epimethius have only 50 km variation in their orbits, which is 1 part in 3000 of their orbital radius.

I'd explore variations in that range, and I'd start at the outer edge of stable region of Jupiter's hill sphere, and if you can't get it to work, decrease the mass some more, maybe lunar mass.


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