# Conditions for human life in a Jupiter-like system

I was wondering about a setting where a moon orbiting a gas giant can sustain human life on its surface, i.e. with nearly identical conditions compared to Earth (e.g. size, gravity, mean temperature, oceans covering at least 70% of the planetary surface, same atmosphere composition, etc.).

The gas giant orbits a star in the habitable zone, so the moon is in the habitable zone too. Also, the moon would be most likely tidally locked to the gas giant, with an orbiting period of nearly 24h in order to have an Earth-like day/night cycle.

Due to this small orbiting period, I guess the moon would be very close to the gas giant, most likely the innermost natural satellite in this system. Additionally, I'm assuming a (nearly) 0° orbital inclination. Because of this, some conditions would be like those of Jupiter's moon Io:

• Stronger tidal forces resulting in intense volcanic activity;
• Stronger magnetic effects, maybe resulting in intense auroras around all the globe;

Additionally, the moon's side facing the gas giant would receive far less light from the sun because of a daily eclipse that would last at least several hours each time. How can this affect life forms development? Could the reflected light from the gas giant replace to some extent the direct sunlight, in order for photosynthesis to work?

Are there any other effects I should account for? If these effects can prevent an Earth-like environment capable of sustaining (human) life, what additional conditions must be met in order to counter them?

Should the gas giant itself have some particular features? I guess that it must be at least comparable to Jupiter in terms of both size and mass, in order to guarantee a stable orbit to its moons.

• I don't think a Jovian can exist within the habitable zone. The star would strip it apart into something far smaller. Apr 7, 2017 at 16:24
• Jovian worlds have massive magnetic fields, which protect them from the solar wind. Apr 7, 2017 at 16:26
• Once formed, but they can't form that close to the star. Apr 7, 2017 at 16:54
• @Mormacil Solar system formation is very dynamic, and we're fairly certain that planets don't always stay where they're formed. So it's entirely possible that the gas giant forms further out and migrates inwards. In fact, we've found many "hot Jupiters" - gas giants that are orbiting extremely close to their star. Apr 7, 2017 at 19:49
• @Mormacil Hot Jupiters can range up to 11 $M_{Jup}$, and can orbit as close as 0.05 AU. Most of them have strangely low densities, and there's a lot we don't understand about them, but they definitely exist. Apr 7, 2017 at 20:36