Found a really cool paper by way of Astrobiology Magazine on a hypothesis for a new kind of planet called an "Ocean-Planet". From the paper's abstract: "A new family of planets is considered which is in between rocky terrestrial planets and gaseous giant ones: “Ocean-Planets”. We present the possible formation, composition and internal models of these putative planets, including that of their ocean, as well as their possible Exobiology interest. These planets should be detectable by planet detection missions as Eddington and Kepler, and possibly COROT (launch scheduled in 2006)."