Super-Neptune

A super-Neptune is a planet that is more massive than the planet Neptune. These planets are generally described as being around 5–7 times as large as Earth with estimated masses of 20–80 ; beyond this they are generally referred to as gas giants. A planet falling within this mass range may also be referred to as a sub-Saturn.

There have been relatively few discoveries of planets of this kind. The mass gap between Neptune-like and Jupiter-like planets is thought to exist because of "runaway accretion" occurring for protoplanets of more than —once this mass threshold is crossed, they accumulate much additional mass (due to gravity increasing with mass and the presence of material in an accretion disk) and grow into planets the size of Jupiter or even larger.

Known examples include Kepler-101b, HAT-P-11b, and K2-33b.

Mass-radius relationship
Through modelling, and analysis of discovered exoplanets, the relationship between mass and radius has given a much higher upper limit for the transition boundary between Neptune and Jupiter worlds than had been previously defined empirically from observing the planets within our solar system, for example Chen & Kipping (2017) defined the transition point between Neptunian and Jovian worlds at around 130. In studies looking into this relationship between mass-radius, Saturn, though never defined as an ice giant, is however found to sit just within the mass-radius limits for a Neptunian world, close to the transition point between super-Neptune and Jupiter world.