- TL;DNR In icy moons, wouldn't you not be able to tell the age because of lack of a substantial atmosphere?
Main Question or Discussion Point
I've learned that the surfaces of places like the moon and the surfaces on Mars corresponding to the Noachian period signify relatively old surfaces because weathering and erosion tend to make those cratered surfaces smooth. However, I heard a professor mention that this is also true for icy bodies like Callisto and Ganymede that do not have a substantial atmosphere. Why is that the case? If these bodies are mostly icy without a substantial atmosphere to cause erosion/weathering, then wouldn't it be the case that you could never tell whether a surface is old or young?