I've read a lot of posts about moons around large gas giants and I think I have fairly good idea about basics to them. I'm not super great with all the science parts myself but they give me lots of greats information reading them.

For this particular one I'm trying more to figure out how an extreme environment could effect the colonists who depend on farming and plant-life for survival.

Scenario :

  • Colony has exists for ~2000 years
  • Colony has been put together on the moon of a gas giant, that moon has a gravity slightly less than that of Earth (lets assume 80-90%)
  • One hemisphere is periodically "cooked" by the long exposure to the star. I'm hoping for a moon that never fully exposes the other hemisphere to the star, but the region that life can live in changes over the course of time. Example for 100-200 years 60%+ of moon has survivable (even if harsh conditions to humans) and then for another 40-100 years, there are times where up to 80% of the moon gets cooked, aka "Sunfall". Time periods are up for debate if something would make more sense, I'm trying to get a feeling of how forest fires act on an ecosystem.
  • The planet has formed basic life : bacteria, mosses, plants, fungus, and small insectoid/amphibious type creatures. A lot of these live underground, but the mosses and photosynthesizing plants wax and wane across the moon with the "Sunfall" periods.
  • Large cave systems


How would the extremity of this waxing/waning of life on the moon affect the ecosystem, in particular how may plant life evolve and the factors this may have for the colonists that depend on it?

Though, we're obviously basing this on earth life I'd like to try and create a realistic imagery of what type of plant life would be encountered on such a world. With the main pollinators and spreaders of it being insects or weather. Also, unsure how fertility periods may work for these plants, with soil nutrition coming from very very long burn cycle followed by long growing periods.

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    $\begingroup$ Hi and welcome to the forum! We really can help with a problem like this however we need you to break it down into single questions with distinct answers. Our help center has details for how to ask a good question, but this problem sounds like a great candidate for the sandbox. This is a place where you can refine a question to get the best answer. $\endgroup$
    – Vogon Poet
    Commented Oct 29, 2019 at 13:50
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    $\begingroup$ I recommend you narrow this down to the orbit. What would the orbit and rotation of the moon and parent planet look like to produce the outcome you want. I like the idea of Sunfall but I am struggling to wrap my head around the circumstances that would produce it. I am hoping someone will post diagrams. $\endgroup$
    – Willk
    Commented Oct 29, 2019 at 13:59
  • $\begingroup$ Ok, thanks. I'll go look there and hopefully be back soon with something a bit more concise. $\endgroup$
    – Nymn
    Commented Oct 29, 2019 at 14:02

1 Answer 1


Your moon orbits a gas giant but you say the northern hemisphere is cooked by exposure to the star. That would require a very odd orbital configuration (gas giant close to the parent star, moon in a polar orbit with the lunar north pole pointing towards the star and somehow tidally locked so that its orbit around the gas giant rotates once per planetary year so as to keep the northern hemisphere pointed at the star. An imperfect tidal lock could explain the periods of "sunfall", essentially there would always be an area affected by sunfall but it would move around the moon depending on how tight the tidal lock was.

There are moons in the solar system with pretty odd orbits and the usual theories tend to involve conventional orbits altered by collisions with other bodies in the early solar system.

As for the effect on life, I suspect you can tweak it to make it as strong or as weak as you like depending on how hot the baked side of the moon gets (and how cold the side facing away from the star gets - both poles will potentially be sterile for opposite reasons, one permanently scorched and the other permanently frozen).

  • $\begingroup$ For the southern pole facing the planet, I'd be looking at it with the assumption that it's staying heated by the combination of the atmosphere being heated on the opposite side and the reflected radiation coming from the gas giant. Perhaps it could get periodic sunlight at extreme angles, during certain seasons when the parent planet is further out, or through the extreme edges of the gas giants atmosphere. $\endgroup$
    – Nymn
    Commented Oct 29, 2019 at 15:07
  • $\begingroup$ If the south pole is always facing the planet then the moon isn't really a moon in the traditional sense - you always have star - moon - planet in a line and the only way this can work is for the "moon" to be orbiting the gas giant's L1 Lagrangian point: link That is probably harder to explain than the unusual polar orbit I described before, you might have to invoke a bit of handwavium. (...) $\endgroup$ Commented Oct 29, 2019 at 15:21
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    $\begingroup$ However either way, a thick enough atmosphere will go some way to distributing warmth but you should still allow for a perpetual winter at the south pole - think of winters on Earth and that's caused by only a 23 degree orbital inclination! $\endgroup$ Commented Oct 29, 2019 at 15:21
  • $\begingroup$ Maybe, I'm thinking of things in too complicated of a fashion. Would it perhaps work better to reduce the tilt and figure we have a cool hemisphere and periodically cooked one? Thinking further on it, I'm mostly wanting the population to have a region they never need to leave due to "survivable" climate vs a side that gets cooked and they have to flee from. $\endgroup$
    – Nymn
    Commented Oct 29, 2019 at 15:31
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    $\begingroup$ If you're willing to change the configuration slightly you could maybe do it with a binary star system. The primary star is large, luminous and very stable, and your "moon" is actually a planet tidally locked to the small secondary star which is variable: usually quiet and not very luminous but with occasional flare-ups lasting however long you want. The ambient temperature of the planet is controlled by the primary star, and from time to time the secondary flares up and cooks the sunward side of the planet, to whatever degree you want. $\endgroup$ Commented Oct 29, 2019 at 15:59

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