Why are Saturn's moons so bright?

[Amaterasu21]

TL;DR Summary

Ganymede and Callisto are dark due to meteoritic dust, so why are Saturn's moons not?

Hi all,

In the Jovian system, Callisto is extremely dark (albedo 0.22) because its ancient surface is covered with meteoritic dust. Ganymede is brighter (albedo 0.43) as its surface has been resurfaced more recently and hasn't had as much time to accumulate dust; that's confirmed by the younger grooved areas being brighter than the older heavily cratered areas. Finally Europa (albedo 0.67) is the brightest and most recently resurfaced of the icy Galileans. This all makes sense to me.

When we get to Saturn though the albedo of all the moons is much higher - Enceladus obviously being a special case due to its high activity but even ancient, cratered surfaces like those of Mimas, Dione, Rhea and half of Iapetus are very bright. Why are these moons so much shinier than their Jovian counterparts? Is it because Jupiter is closer to the asteroid belt and therefore gets more bombardment from e.g. C-type asteroids and carbonaceous chondrites, as well as Jupiter's stronger gravity pulling in more surface-darkening impactors, while Saturn's moons haven't been hit with as much dark meteoritic dust as Jupiter's have since they were last active?

That makes sense... until we get out to Uranus and the moons are dark again! Is this perhaps due to methane ice photodissociating and forming carbon deposits on their surfaces, something Jupiter and Saturn are too warm for?

 

[Drakkith]

Saturn's moons are mostly made of ice (at least the ones you mentioned are), about 75% or more, whereas Jupiter's moons have much more rock. Ganymede and Callisto are about half ice while Io and Europa are mostly rock and iron.

I suspect the greater ice content of Saturn's moons is due to its greater distance from the Sun compared to Jupiter.

 

[Vanadium 50]

To expand on @Drakkith :

First you're comparing apples and oranges. Saturn has only one moon like the Gallilean moons, Titan. And it looks like the other large moons in the outer solar system.

Then Saturn has a bunch of icy moons about 1000 km across, like Dione, Rhea and Tethys, Because they are made of ice, they are bright. Jupiter has none of these.

As to why Jupiter doesn't have any of these objects, one can only theorize. Formation history, tidal heating, luck...