Which Galilean moon is differentiated into a rock/ice blend and is notable for retaining the oldest, most heavily cratered surface?

Answer

Callisto

Callisto is the outermost moon, minimally differentiated, appears homogeneously mixed, and lacks current tidal heating, allowing it to retain the most ancient, heavily cratered surface.

Which Galilean moon is differentiated into a rock/ice blend and is notable for retaining the oldest, most heavily cratered surface?
astronomyJupitersolar systemformationmoons