Remember how we told you a few months back that super-Earths were possibly the rocky cores of mini-Neptunes that lost their outer gas covering? Well, that hypothesis is being challenged in a new paper in The Astrophysical Journal, where researchers used a simulation and thermodynamic calculations to understand the evolution of this family of planets.

The results of these calculations suggest that super-Earths are not the remnants of mini-Neptunes, at least, not all of them. Co-author Eve Lee explains: Contrary to previous theories, our study shows that some exoplanets can never build gaseous atmospheres, to begin with. Some of the rocks grew gas shells, while others emerged and remained rocky super-Earths.

Basically, the distinction between these smaller super-Earths and larger mini-Neptunes is that one had the ability to grow and retain a gas shell. Pretty obvious, yes, but different from the other hypothesis. We’re sure someone will change it next month. Add this paper to the ever-growing list of evidence that we really don’t understand planetary formation or solar system evolution.

More Information

McGill University press release

“Primordial Radius Gap and Potentially Broad Core Mass Distributions of Super-Earths and Sub-Neptunes,” Eve J. Lee and Nicholas J. Connors, 2021 February 10, The Astrophysical Journal