[Space] How much does a Gas Giant heat it's moons?

[Anthony]

Originally Posted by Flyndaran

Does all that mean that double planets would be warmer than initially assumed because they reflect light and heat onto each other?

They also occasionally block sunlight from the other, so it's likely a wash, and in any case most of the time the effect is negligible.

[Flyndaran]

Originally Posted by Anthony

They also occasionally block sunlight from the other, so it's likely a wash, and in any case most of the time the effect is negligible.

Cool, thanks. I was afraid my double planet system had even one more hassle than those I already knew about.

[scc]

So if I've got a moon of .56 Earth diameters (.23 radius) orbiting 61.07 Earth diameters from a Gas Giant the Blackbody temperature of the moon is increased by 4% of the Gas Giant's temperature? Is that correct? And how do I calculate the temperature of the gas giant?

[Anthony]

Originally Posted by scc

So if I've got a moon of .56 Earth diameters (.23 radius) orbiting 61.07 Earth diameters from a Gas Giant the Blackbody temperature of the moon is increased by 4% of the Gas Giant's temperature? Is that correct?

No, for several reasons. First, we need the radius of the gas giant. Second, you actually add T^4 from all sources and then take the 4th root, so if the secondary heat gave a temperature of 4% of the primary, the actual increase is (1 + .04 ^ 4)^1/4 - 1, or 0.000064%

[Daigoro]

Originally Posted by Anthony

They also occasionally block sunlight from the other, so it's likely a wash, and in any case most of the time the effect is negligible.

Not so often though, unless they're orbiting perfectly flatly in the equatorial plane. Look at how uncommon eclipses are for the Earth and moon to block sunlight from each other.

For a moon around a gas giant, however, it is more likely. You'd have to figure out the axial tilt of the gas giant and then the semi-major axis and eccentricity inclination of the moon's orbit to see how long it spends under occultation.