Hey Guys, Very new to this forum - signed up as it seemed it might be possible to get some answers and advice as I'm designing a world (actually two worlds - two exomoons) and want to try and pay at least some attention to the constraints and realities of physics, as much as possible! My knowledge of physics is limited to a very basic understanding of the major concepts - that's where I'm hoping some of you much more learned members might be able to offer a bit of advice if you have the time! Broadly speaking, I'm creating a Fantasy World which I imagine would consist of a solar system with around 4-6 planets (the precise number isn't really an issue) orbiting a star or orbiting binary star system in a circumbinary fashion. One of those planets would be a gas giant, orbiting in the habitable zone. I'm setting the world across two separate moons, both of which are orbiting this gas giant (although I appreciate there would likely be many more moons in this gas giant's system). Now, I don't necessarily need everything to be 100% accurate in a physics sense (I appreciate that's probably impossible anyway), but I'd at least like to try and keep things sensible and create a fairly realistic, feasible system so that the idea doesn't become outlandish or ridiculous from a scientific point of view. I guess it's easiest to post my "criteria" in terms of how I'm hoping my world will look and then if you learned guys have any major red flags or thoughts I'd love to hear them and it would really help the overall development of my World: A solar system (single star or binary) of between 3-6 planets (doesn't really matter but I'd like to have a firm idea of the total number of planets and keep it fairly small if possible). A gas giant somewhere in the inhabitable zone (approximately 1AU). At least two moons orbiting that gas giant - I presume there would be a lot more but two habitable moons "next" to each other and the other moons can be fairly arbitrary. Both moons to be around Earth size (I presume from a physics point of view they could not be smaller and habitable). I presume both would be tidally locked so I'd be hopefully looking for them to have orbits that give them a "day" similar to Earth - around 24-36 hours. This, I'm presuming, may be tricky, but ideally they can't have the issue of having light/dark periods on the far side being days at a time. I'm trying to keep the basics of the moons fairly similar to Earth so that a humanoid style life could realistically have evolved there. I guess my questions are - are there any major physics problems that make that kind of scenario ridiculous and, if not, what might be the idiosyncrasies of those particular moons? I know there could be issues such as tidal heating but I'm hoping that it would ultimately be realistic to have two fairly Earth-like moons in orbit around a gas giant. I also know that due to tidal locking one half of the moon would see a much more irregular day/night pattern and be subject to shine from the planet, which is fine so long as the other half can experience a relatively normal day/night pattern if possible. I'm just not experienced enough in astrophysics to be able to begin working out issues related to axis, distance from the gas giant etc. and how they will impact on the overall system. Broadly speaking, I know what I want, and I just want to make sure it's at least partially feasible and how it might affect things like seasons, earthquakes/volcanoes, day cycles, weather etc. as best as possible. The whole thing doesn't have to be completely watertight when it comes to the physics. I fully imagine there will always be a little bit of license, but I'd like to think I at least did some research and put some thought into it all before creating any arbitrary system that made no sense. Any input, thoughts, critique, random observations from those who know a lot more about this would be very interesting and greatly appreciate! Thank you.