Major Type of Terrestrial Class of planet. This type of world consists of a rocky core and thick ice mantle and crust. They may be a layer of slush or even a deep ocean of liquid water under the thick ice crust. Some Europan type planets support life.
In essence, these are LithicGelidian worlds with a remarkable consequence of their tidal stretching. The surfaces of these worlds are relatively smooth, the crust being made up of ice that ranges from less than a kilometer to several tens of kilometers in thickness. The surface smoothness is a result of that crust constantly being moved and resurfaced by the underlying geology, which produces an oceanic layer of liquid water ranging from just a few to hundreds of kilometers in thickness.
The depth of the ocean is directly responsible for the thickness of the crust, and worlds that are relatively heavily cratered, even though they still show surface plate movement, typically have very thin water layers, sometimes to the point of being little more than a "slush" layer only a kilometer or less in depth. The most extreme of these worlds are constantly experiencing breaks in the surface crust, exposing the ice to the vacuum of space. Some of these worlds may develop atmospheres if they are massive enough, but most remain barren of any sort of atmosphere.
EuEuropan Subtype - Text by John M. Dollan Major sub-type of Europan Type planet. Distinguished by a rocky core with an ice mantle. A subsurface ocean 10 to 100 kilometers in depth is almost always present, due to tidal stretching of the world. Surface movement is constant, and obliterates all impact scars in a short amount of geologic time. Life may be present, but is likely to be primitive, if it is even beyond the microbial stage. Atmospheres are transient.
Poseidonal Subtype - Text by John M. Dollan in his Planet Classification List Europan Type planet or moon. If the world is massive enough and experiences severe enough tidal stressing, the icy surface and mantle may be melted to a depth of hundreds of kilometers, and the world will be enveloped in a thick atmosphere. Surface ice will be present, but spotty, giant icebergs adrift on a global ocean. Life is almost always present, but rarely very advanced.