I once conducted a thought experiment and with some amateurish calculations based around Hill sphere and Roche limit came up with semi-major axis distances like this:

Procyon-BD:  3.6 AU
BD-Jupiter:  0.7 AU
Jupiter-SE:  0.12 AU
SE-Mars:     0.02 AU
Mars-Pluto:  0.0033 AU

Assuming respective masses of: 496 260 earths, 15 000 earths, 313 earths, 6 earths, 0.107 earths and 0.00218 earths.

Clarification: I use names of specific bodies (Procyon, Jupiter etc) but a Procyon-like star, a Jupiter-like gas giant and so on would be more precise. Think of them only as examples of bodies with such masses.

Could such a system be possible?

  • $\begingroup$ You want a system with those exact distances or a system with just those bodies present? Should they all orbit the central object (thus Procyon) or should each orbit the next bigger object? The latter would certainly not work stably. A system would also be considered bound when the orbits are outside the bigger object's hill sphere. $\endgroup$ Commented May 10, 2020 at 14:44
  • $\begingroup$ A brown dwarf orbits a Procyon-like star in the center, a Jupter-like gas giant orbits a brown dwarf, a superearth orbits a gas giant, a Mars-like planet orbits a superearth and a Pluto-like planet orbits a mars planet. So it wouldn't be stable? Why? $\endgroup$
    – z33k
    Commented May 10, 2020 at 15:01
  • $\begingroup$ For information, I have raised a question on Meta about the on-topicness of "solve my n-body system"-type questions. $\endgroup$
    – user24157
    Commented May 10, 2020 at 16:18
  • $\begingroup$ Are you just asking about the orbit stability of such a system? Or are you (also) asking if it's theoretically possible for such a system to form naturally? (My guess is that it's not stable, and that it couldn't form). $\endgroup$
    – PM 2Ring
    Commented May 11, 2020 at 0:33
  • 3
    $\begingroup$ I’m voting to close this question because it is getting into off-topic territory. The general question about the feasibility of subsatellites has already been asked, the question about details of a specific hypothetical system are more suited for Worldbuilding. $\endgroup$
    – user24157
    Commented May 18, 2020 at 17:32

1 Answer 1


Thanks to this answer linked by antispinwards I learned that such system most probably would not be stable, as I calculated it with proximity to upper limit of Hill sphere for each body.

But, if instead, I would have taken distances closer to 1/3-1/2 Hill sphere, it could be theoretically feasible.

The orbit of a satellite's satellite will be stable if it's deep enough inside the Hill sphere, within the so-called true region of stability. The limits are a bit fuzzy, but the true region of stability is typically the lower 1/3 to 1/2 of the Hill sphere.

On a personal note, if it's so, it surprises me this type of systems are not more pondered on and discussed, with maybe even some probabilities calculated. As it could have a great impact on thinking about abundance of potentially habitable worlds in the universe (imagine how great a number of earth-like satellites could live in such a system in the habitable zone of its host star (it being short-lived on cosmological time-scale notwithstanding)).

  • $\begingroup$ Probabilities of systems are calculated - from disk evolution models. Not by a-priori assumptions of what they should look like. A system like the one described here is not a likely solution by a huge margin of any reasonable models based on physical models $\endgroup$ Commented May 19, 2020 at 11:01
  • $\begingroup$ Is how reasonable these models are measured against vastness of space and multitude of systems? I know the chance is small, but faced with enormity of space, is it orders of magnitude too small? $\endgroup$
    – z33k
    Commented May 19, 2020 at 12:22
  • 1
    $\begingroup$ IMHO yes. Maybe not as unlikely as a stone jumping up and the room getting cooler, but it goes in that direction. It get's very difficult to reason wrt how planets form in a disk around a star - and it needs all the matter to form such planet within a larger portion of the disk. Given that, there never is enough material for another planet where another forms, or they would eventually collide - especially not given your cascade. The existing bigger moons generally are what roughly can form within the hill sphere, given available material, formed due to catastrophic collision or were captured. $\endgroup$ Commented May 19, 2020 at 12:58

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