I have created a planetary system consisting of a Super Jupiter (10 Jupiter Masses) and up to 8 Earth Sized/mass Moons (on average) and now I wonder if it would be stable.

I already tried to create it in Universe Sandbox2, but US2's Game Speed drastically reduces if I would add so many bodies into one simulation, so I am not sure how long it would be stable. (I'm talking about a time span of several billion years.)

So I decided to bring this up here: The 3 innermost moons you can see have a mass of between 0.6 and 0.7 Earths. Their orbits have a distance of 290000-300000 KM to each other.

The next 3 are basically remains of a collision, so their mass is not impactfull to the systems integrity.

However, the next group of Moons consists of bodies being 0.9, 1.6 and 0.8 as massive as earth and having an orbital distance of aprox. 700'000 KM to each other.

And finally, the two last objects are two super-earth-sized moons with 11 and 16 Earth Masses. Both of these have their own subsattelites.

The Lunar System has a witdh of 850000KM to 1,0472e+9 km.(0.07 AU).

Edit: The Gas Giant has an orbit of 3.7 AU to its sunlike star.

picture of the system designed in space engine

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    – L.Dutch
    Commented Aug 17, 2018 at 12:17
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    $\begingroup$ Wouldn't a celestial orb of 10 Jupiter Masses ignite fusion at its core? I think you have a very dimly lit but traditionally structured star-and-planets. $\endgroup$ Commented Aug 17, 2018 at 12:19
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    $\begingroup$ @A.I. Breveleri Good Point, it could also be a sub-brown dwarf, but according to a german vikipedia article about brown dwarves, the Deutherium Fusion begins at 13.5 Jupiter Masses, so my candidate would actually just be a really huge gas giant still. $\endgroup$ Commented Aug 17, 2018 at 12:37
  • $\begingroup$ key question how big and how far away is the parent star? $\endgroup$
    – Slarty
    Commented Aug 17, 2018 at 12:57
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    $\begingroup$ If you wait at least 24 hours before accepting an answer you have more chances of attracting the attention of all the users we have around the globe. This is what we generally advice. $\endgroup$
    – L.Dutch
    Commented Aug 17, 2018 at 13:31

1 Answer 1


The giant planet-brown dwarf boundary is at about 13 Jupiter masses (it's a little fuzzy; see http://adsabs.harvard.edu/abs/2011ApJ...727...57S).

In terms of stability, there's no problem having a system of ~Earth-mass moons. The natural orbital spacing is logarithmic. Moons should be spaced either by a given number of mutual Hill radii (typically 10-20) or in orbital resonances (see https://wp.me/p3BSYQ-66). At 3.7 AU the planet's Hill radius is about half an AU in size, so the largest possible orbit is about 0.25 AU. If the innermost moon is at 0.01 AU, that is a dynamic range of 25 in orbital distance or 125 in orbital period. You could fit a system of 7 moons if each adjacent pair of moons is in 2:1 resonance (as for Jupiter's 3 inner Galilean moons), or 12 moons if adjacent pairs are in 3:2 resonance.

  • $\begingroup$ Hi, Sean Raymond Thanks for your answer. So you are saying that any moon within an orbit of <0.01 AU to the 10-jupiter mass object cannot exist? If so: Could he exist as a desert/volcanic world for at least a few million years or would it be crushed relatively soon after coming <1000000km close to the gas giant? Then i have another, similar sized moon on a 0.007 AU orbit and another one on 0.009 AU orbit. both of which i considered cool and stable despite some tidal effects. Wouldn't be that possible actually? edit: In order to attract more users, i unchecked again $\endgroup$ Commented Aug 17, 2018 at 14:18
  • $\begingroup$ Sure, you could have an orbit closer than 0.01 AU, I just chose that as a simple number to illustrate the spacing idea. I just looked it up and Io's orbit around Jupiter is about 0.003 AU. Planets above Jupiter's mass have about the same size as Jupiter (compression) so I supposed it's plausible to have an innermost moon at 0.003ish AU. That would give you a lot more orbital real estate (an extra factor of 5 or so in orbital period, so ~3 additional moons). Your moons at 0.007 and 0.009 AU wouldn't be a problem. $\endgroup$ Commented Aug 17, 2018 at 14:34
  • $\begingroup$ Hi again Thats great. So my system actually works out (apart from the sub satellites i guess)? Ive read about en.wikipedia.org/wiki/GQ_Lupi_b, which could be a gas giant bigger in size than jupiter, but thats not sure yet. When it comes to sub satellites, i know, none have been confirmed yet, but when it comes to super earth sized objects, i think they can exist, especially if they are in an area with an abundance of asteroids. $\endgroup$ Commented Aug 17, 2018 at 15:07
  • $\begingroup$ Sure, looks fine. Sub-satellites are iffy but plausible. $\endgroup$ Commented Aug 17, 2018 at 17:06
  • $\begingroup$ I'm not sure how to calculate this, but my understanding is moons which are not in resonance orbits will either be ejected, dropped into the central planet or "pumped" into a resonant orbit. So there may be a period of time where there is instability, until the moons are spaced "correctly". $\endgroup$
    – Thucydides
    Commented Aug 17, 2018 at 22:54

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