Jupiter moon colours

[GavStar]

I've been thinking about the views I had of Jupiter last night compared to recent years. Previously I hadn't been very interested in the moons apart from shadow transits and I mainly focused on Jupiter's surface (GRS, cloud bands etc).

However last night, the moons stood out (3 of them anyway, I think Io was hiding behind Jupiter). As I mentioned in my previous post the moons were very disc like but in addition they were very different colours. In particular I think Callisto stood out as reddish brown. I've not noticed this before - maybe it's the extra aperture (140mm to 100mm)? Another aspect for me to look at more in the coming weeks. 

Has anyone seen any surface detail on the moons - I guess this would take some serious magnification?

[John]

I can't claim to have seen any surface detail on the moons but I have noticed slight variations in their tints from time to time and the difference in their apparent diameters is quite obvious even though they are only 1 arc second or so. It's quite fun to have a go at working out which moon is which just from observing them relative to one another. Then you can check later to see if you got it right

I believe surface details have been glimpsed on Ganymede through amateur scopes under superb conditions and at very high powers.

[Size9Hex]

I think the moons are great targets. I haven't spent any time with them since last year, but if I recall correctly, in the 10" scope Ganymede was brown/grey, Io very pale subtle yellow, Europa colourless and Callisto a deeper brown. The colours changed to my eye as the moons transit in front of the planet - Io becoming more richly ochre coloured for example. A bit of extra aperture can sometimes brighten a faint point source target enough that it starts to register in colour, so this may have been what made the difference for you. My 10" shows more colour in faint double stars than my 4". I've looked for detail on Ganymede but not seen any although I've read a report of a monster scope used in great seeing that picked up some variation on the surface. Last year, as Europa emerged from eclipse, I briefly (30 seconds or so) had the impression that it was off-round - taller than it was wide - keen to recheck this when I get the chance!