Planet sized moon in orbit around a gas giant--potentially inhabitable?

[scifiwriterguy]

Assume a Neptune sized gas giant in orbit around a star, in an orbit somewhat approximate to Earth's. Assume a moon roughly the size of Mars in orbit around said gas giant. The moon is made of dense materials capable of holding an atmosphere. The surface is virtually all water.

Theoretically, could such a moon be inhabitable?

Factors to consider:

The moon would receive heat from the star through roughly half of its orbit.
The water would help stabilize temperatures.
The atmosphere could potentially be quite thick.

Another question:

The moon itself would have two cycles of light and dark, correct? An extended "night" period when hidden from the star by the mass of the gas giant, and then a period of "days and nights" during which it rotates on its axis while also being exposed to the light of the star. So maybe something like 70-90 hours of darkness followed by 70-90 hours of light / dark "days." Amy I missing anything here?

Any comments, questions, or answers to the above would be very much appreciated!

[Darvince]

On your second question, it would depend on if the moon is in the solar system's ecliptic or not. If it isn't, then dark periods when it is behind the planet would be very rare, like say once every 22nd orbit or something. The darkness would also only be like 1-5 hours, depending on how far away the moon is from the planet and how large the planet is.

If it's not tidally locked there will be four light periods, one is the star with pretty high brightness, one is the star and planet which is really bright, there is the planet which depending on how close the moon is could be anywhere from indoor lighting to only a bit brighter than the moon, and no illuminating bodies (like a new moon night). Although the amount of different light periods increases with the amount of moons, but this is assuming there is only this habitable moon.

[scifiwriterguy]

Darvince,

Thanks for the quick reply. So essentially part of the moon would always be lighted, except for the very brief period when the moon is totally blocked from light sources (like a new moon on Earth). It would have a light cycle like the northern and southern tip of earth, except the light periods would have shifting intensity and the dark period would be only hours long, not days.

Have I got that right?

I've started a YA science fiction series and care to get my details right as much as possible. It's more "soft" sci-fi than hard, but if I can get more towards a five or six on the hardness scale by researching things like this, that would make me very happy.

I appreciate your reply.

[Darvince]

No, if the moon is not tidally locked to the planet then it will have these light periods:
sun (like day on earth)
planet (like indoor lighting or dimmer)
nothing/other moons (like a night on earth)
Planet lighting will be much dimmer than the sun, like evening or so. Other than this, it will be exactly like day/night cycles on Earth. When it reaches directly behind the planet, however, it will be like a solar eclipse and the planet's shadow will darken the planet for several hours.

[karakris]

Hmmmm - similar to the Gamma System.

This has a Jupiter sized Planet - made of Rock.
This is in an orbit in the Habitable Zone.

In orbit around this, there are a number of Planets - a few of which are Habitable.
The smaller ones will not have an Atmosphere.
There are a lot of these Planets - and the most distant start to merge with the gigantic Asteroid Belt, which is also in orbit in the Habitable Zone.

This is Gamma System - which is now The Dominion of New Byzantium -
One of the Dominions of The Phoenix Confederation - in my Sci Fi Wargame.