The world where my stories will take place is a moon oribiting a gas giant along with many other barren moons. I envisioned it to have a generally tropical/subtropical climate, with plenty of vegetation, jungles, forests and biodiversity (initially at least), with some vegetation even reaching up to the polar circles (which i envisioned to be sort of like cold australia, with an outback of ice caps and tundra and coasts of subartic forests), and I would like to know if it is consistent with it's current physical characteristics.

Here they are:

  • Rotation/Revolution(due to being tidally locked to the gas giant): 60 hours
  • Secondary mass: 0.7 Earths
  • Secondary Desnity: 5.56 g/cm3
  • Primary mass: 3 Jupiters
  • Primary diameter: 1.04 jupiters
  • Distance from primary: 2 Earth-Moon distances
  • Tilt: 30 degrees to the star (4 seasons)
  • Star mass: 1.314 Suns
  • Star age: 3.3 billiong years (life developed faster here, due to reasons that do not matter in this question)
  • Star type: F5V
  • Star distance: 2.08 Astronomical units
  • Atmosphere: Similar to earth, but with more oxygen and slightly more carbon dioxide and thus less nitrogen, but overall breathable for carbon based life forms
  • Land to water ratio: 40% land 60% water, consisting in 3 major landmsses, a handful of minor ones and many many islands

Here is what gas giant system would look like to scale:

enter image description here

Would the climate allow for lush woods and jungles over most of the surface?

  • 2
    $\begingroup$ Wouldn't your world by definition have the environment you say it has? $\endgroup$
    – sphennings
    Jul 12, 2022 at 12:11
  • $\begingroup$ What type of star is it, when in it's evolution (regardless of mass)? $\endgroup$ Jul 12, 2022 at 12:17
  • 1
    $\begingroup$ @sphennings The goal is to confirm or refute the fact that this world can lead to a more tropical climate (supposedly relatively to Earth), and using what is known in science. Might be missing some data for such a broad topic though, I don't know ^^'. $\endgroup$
    – Tortliena
    Jul 12, 2022 at 12:41
  • $\begingroup$ @AngryMuppet I added the information about the star ^^ apologies $\endgroup$ Jul 12, 2022 at 12:49

2 Answers 2


My personal opinion here is that it's your world so you can do a lot of hand-waving regarding the environment. If you get caught out then that gives you a reason to come up with some heretofore unknown mechanic which is operating on the environment, and which gives your characters additional opportunity for adventure and/or drama.

I may have done this incorrectly, but I'm calculating the distance between the primary and secondary as being closer to 1.4 Earth-Moon distances.

The oxygen to carbon dioxide ratio has a bit of a problem, maybe. Plants here on Earth, assuming a similar ecology, consume carbon dioxide in order to produce oxygen. The more carbon dioxide there is in the atmosphere the more of it they will consume until they find that balance. So, the higher level of carbon dioxide would be a good explanation for all the plant life, but I think you'd have to explain two things: 1) where is all the carbon dioxide coming from and why isn't it being displaced by plant-produced oxygen, and 2) why aren't the inhabitants of this world hacking down all that prime lumber and burning it for firewood and making sporks and things out of it?

Of course, maybe that's the answer, the elevated CO2 is from exactly that: the burning of wood.

You mention the orbital tilt with relation to the primary, but not the inclination. Presumably the orbital inclination takes it behind the planet for some period of roughly an earth day, and exposes it to solar radiation for very roughly 36 hours. I'm thinking that your world probably experiences a very immoderate winter season due to the drastic changes in how much solar radiation it receives during its orbit of the planet. Of course, if the inclination is very high then it could be behind the planet for as little as an hour or not at all, in which case the winters could very well be very moderate. You have a lot of surface water, and if it's very deep then that would serve to moderate the climate as well.

But at the end of the day the world is exactly the way you want it to be for whatever reasons you want. Don't underestimate people's desire to suspend disbelief when reading fiction -- especially science fiction. I was probably the only one in the theatre wondering if Endor's moon actually received enough reflected solar radiation to support so much forest.

This world looks fine to me. I'd read this story.


Orbital plane?

If the orbital plane of your moon around its giant is the same as the orbital plane of the giant around the star, there will be 1/2 the 60 hour day when the whole moon is in the shade of the giant (eclipsed) and it will get cold. The farther away it is the less eclipse the giant will make. That moon will get half of the irradiance that Earth does. Your moon is about the same distance from its giant as Europa is from Jupiter and Jupiter is 24x the apparent size of our moon as seen from Europa. Your giant is 3 times Jupiters mass and so might be bigger too and throw more shade.

You could have different orbital planes to side step this. That will mean day and night might get unusual because the rotation of the moon is governed by its tidal lock to the giant, not the star. For much of the year the sun might never set for half the planet and never rise for the other as it is on earths poles. Long dark winters, long bright summers.

  • $\begingroup$ About the gas giant being much bigger due to the mass, in reality the difference would be minimal, I have ran some numbers and the diameter would increase of 1.05 with a much increased density, I think it has something to do with electrons. I have also run a simulation in universe sandbox and eclipses would only happen during spring and summer for a few hours each day at most. $\endgroup$ Jul 13, 2022 at 17:52
  • $\begingroup$ Please post screenshots from Universe Sandbox! $\endgroup$
    – Willk
    Jul 13, 2022 at 18:10
  • $\begingroup$ Done as asked, image added $\endgroup$ Jul 13, 2022 at 18:17

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