- #1
Amaterasu21
- 64
- 17
- 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?
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?