He thinks the name is unfortunate, that they are more like mini-Neptunes than like super-Earths:
So why are super-Earths likely not habitable? In our own solar system, Ethan Siegel reminds us, we find small clearly distinct rocky planets and gas giants. However, our most successful planet-hunting missions are mostly coming up with planets that are in between…
He thinks that the term “super-Earth” is unfortunate because it creates the impression that these planets are like Earth, only bigger. But if the mass of the planet is much greater than that of Earth, some dire changes — from the perspective of habitability — may be expected:
“… most planets will remain rocky so long as their mass remains below a certain value. Raise their mass beyond a particular threshold, and they’ll be able to start holding onto volatiles: very light gases like hydrogen and helium. Gather enough total mass together in one place, and that planet will start growing much more rapidly than the others around it, like a cosmic vacuum cleaner clearing out the material from anywhere in proximity to its orbit. With so much mass in one place, the very atoms inside that planet will start to compress; this gravitational self-compression should create a new population of gas giant planets”
News, “We are warned: Don’t try to colonize super-Earths” at Mind Matters News
Two surprises here: Siegel thinks that a rocky planet of more than 30% greater radius than Earth stands a good change of becoming a gas giant in consequence of its size.
Also, our solar system is unusual in having no super-Earths, whose atmosphere would trap volatile gases, unsuited to life. Earth is the right size to avoid that. It is hardly the mediocre planet celebrity atheist scientists have sometimes claimed.
Neptune: