which have gaseous atmospheres through which the crust can be seen).

The rather misleading term has caught on because planetary scientists typically use rock, gas, and ice as shorthands for classes of elements and compounds commonly found as planetary constituents, irrespective of the matter's phase. In the outer Solar System, hydrogen and helium are referred to as gas; water, methane, and ammonia as ice; and silicates and metals as rock. When deep planetary interiors are considered, it may not