Okay, I have this tropical moon that orbits a gas giant, and is suitable for human life. It has a radius of .9 Earth radii, a mass of .8704 Earth masses, a density of 6585 kg/m3, and a surface gravity of 1.07 g. Its atmospheric pressure at sea level is 1 atm, its mean temperature is 308 K, its minimum temperature is 264 K, and its maximum temperature is 336 K. The moon’s albedo is about 25%, and it orbits a gas giant with an radius of 11.2 Earth radii, a mass of 320 Earth masses, and a albedo of 81%.

The moon orbits the gas giant at an orbital radius of .00351 AU, and completes an orbit once every 2.45 Earth days. It’s tidally locked to the gas giant, which orbits a star of a similar mass to the Sun at an orbital radius of 1 AU, taking .999 Earth years to do so. The moon’s atmosphere is breathable, and humans can go outside without any protection. Is the moon I described realistic? Why or why not?

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    $\begingroup$ not posting actual answer due to hard-science.. The main issue is with that 2.45 day long solar cycle you will experience. Nights will be nasty, especially for the far side of the planet that gets no love from the gasgiant's presence. Nearside will have interesting weather when the giant eclipses them every single cycle, for several hours. $\endgroup$
    – PcMan
    Apr 25, 2021 at 20:54
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    $\begingroup$ Realistic in terms of existing (I don't see why not) or habitability by humans? $\endgroup$ Apr 25, 2021 at 22:57

2 Answers 2


One way to find out how habitable an exomoon might be is to look up scientific discussions of of hyopthetical exomoon habitability.

I suggest that you read my answer to the question:


It cites a number of scientific articles discussing habitability of hyptothetical giant exomoons.

For example, there is the concept of a "habitable edge" around a gas giant, where any exomoon orbiting closer to the planet than the habitable edge would be heated by reflected light and tidal heating so much it would suffer a runway greenhouse effect and become uninhabitable.

One article suggests that an exomoon would have to orbit outside the habitable edge, but also close enough to the planet to be protected from the stellar wind by the planet's magnetic field. And the article said that for a Jupiter like planet the safe distances for a habitable exomoon would be 5 to 20 times the radius of the gas giant planet.

And I believe that your exomoon is orbiting within the reqired distance range from the planet.

And that is one example of the factors which are discussed in the various scientific articles cited in my answer.


If it's tidally locked to the gas giant, that surely means that one side of the moon is continuously exposed to the heat and light from the gas giant, even if it does have a day night variation due to the star of the system. Given that, I don't think tropical plants would easily exist on the facing side, I think the one side of the moon, fixed to the gas giant, would be a desert? Exposed as it is to both the "day" of the star the continual heat and light of the gas giant itself. The "dark" side would be viable, if it gets a day cycle (even if dimly) from the star of the system.

  • $\begingroup$ Yeah, I was thinking that the near side would be cool, dark, and barren. $\endgroup$ Apr 26, 2021 at 15:11

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