As the title says. I need to have at least 3-5 habitable Earth-gravity worlds (preferably with atmosphere, nitrogen oxygen) as many smaller, lifeless moons as possible, and a planetary ring. (i.e. Saturn)

Now, when I say 'habitable' I just mean a bear minimum of being able to go outside and not melt or set on fire or get irradiated to death on 3-5 of the words orbiting this gas giant, and having roughly Earth-like gravity. The moons not being tidally locked would be great too, or at least having one or two that aren't.

Giant storms, volcanoes, meteorite strikes, etc. are fine, and actually pretty cool!

Now, as you can probably imagine I'm not very knowledgeable about how astrophysics works, so I fully expect a lot of what I'm hoping for to be downright impossible. But any scientific solutions are greatly appreciated.


  • $\begingroup$ What is the actual question here, I don't see a question. $\endgroup$
    – kingledion
    Commented Jan 23, 2018 at 20:26
  • $\begingroup$ I agree with kingledion. Looked back on it, realized how vague it was, made some changes. Original question was intended to be something like 'How many Earth-gravity worlds can I have orbiting a single gas giant that are at least marginally habitable?' edit: also changed title for clarification. $\endgroup$
    – Armok
    Commented Jan 23, 2018 at 20:31
  • $\begingroup$ Are you artificially putting moon into orbit around a gas giant? Anyways, there is no problem with a large gas giant having a dozen Earth sized moons but the chances of it naturally happening probably isn't high. $\endgroup$ Commented Jan 23, 2018 at 20:34
  • $\begingroup$ A dozen is too many - 3-5 should be fine then, I suppose. Thanks! $\endgroup$
    – Armok
    Commented Jan 23, 2018 at 21:00
  • $\begingroup$ Sounds like the system in Firefly/Serenity $\endgroup$
    – pojo-guy
    Commented Jan 24, 2018 at 6:32

1 Answer 1


What you need is a Brown Dwarf. Technically, these are not quite low mass stars, but a bit bigger than (say) Jupiter. They give off heat, although not much. Your planets would be a great deal darker than Earth, and they would have to orbit closer (radiation issues), and your system would last for less time than a main sequence star, but it's possible.

Ideally, the brown dwarf would have formed around a main sequence star at about the orbit of Saturn, allowing the main sequence star to contribute more light and heat to your system. This would mean that your planets (moons in this model, really) would have more light and heat introduced to their systems on a periodic basis, so night and day would be very confusing out there. I'd also add that unlike Earth, you'd probably WANT a great deal of greenhouse gas to trap what little heat reaches the planet into its biosphere.

Think Venus around a much heavier Saturn. (Saturn is only about 30% the mass of Jupiter, but nearly as big.)

As for the planet/moons not being tidally locked, again possible, but depends on the forces in play during creation. Tidal locking is common because it's the least energetic configuration. Put something in play that strikes the forming planet with a glancing blow or two, and you'd probably get rotation.

Ideally, you need a moon for your moon to generate a magnetic field via a spinning core; your brown dwarf is going to release most of its heat as radiation I suspect. Great for heating the surface, but pretty bad for survival rates of humans.

I must say; this is not a nice planet to live on. You'd probably need a human adapted to high CO2 levels (either that or you dump a heap of methane into the air), a form of fungus in lieu of conventional plants (low light means less photosynthesis) and good night vision.

Another option which goes against your OP would be a low mass star, but for now I think a Brown Dwarf meets the spirit of your question (just) and solves for the needs you have.

Of course, if you really want a gas giant, just move Jupiter closer to the sun (say Mars orbit) and the latent heat coming off it (in conjunction with the heat from the sun) may also provide you with a livable planet. Even though Jupiter and Saturn are 'planets' they still give off some heat. Generally though, it's not enough to turn the tide in terms of sustaining a biosphere by itself.


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