Quote (smjjames)
Exactly. It's the same with super-earths which range right into the realm of Neptunes or ice giants. Really, the only difference between a big super-earth and a sub-neptune might be how thick it's atmosphere is and other properties that define an ice giant. Heck, a planet that has the properties of a small neptune might appear like a super-earth when it's closer to it's host star.
Ice giants are supposed to be composed mostly of ices (water, ammonia, methane, etc), i.e. volatiles. On the other hand, it is possible to find a rocky super-earth planet with a mass of 10 Earth-masses and with an extremely thick atmosphere, even with hydrogen and helium. Such a planet should not be named "ice giant". I prefer a class-name "neptune" instead of "ice giant" because of that. Of course, such planets should be pretty rare - it is hard to form such a huge rocky core without accreting a lot of volatiles. That may be the core of evaporated hot giant, a result of collision and merging of a few Venus-like worlds.
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