http://www.newsweek.com/mini-neptunes-transforming-super-earths-exoplanet-mystery-1676675

Astronomers have spotted two mini-Neptune exoplanets that are losing their puffy atmospheres, in the process possibly transforming into super-Earths. Radiation from the planets' parent stars is stripping their atmospheres by boiling away gas, causing it to escape like steam from a boiling pan.

The findings could solve the mystery of why there is a size gap in the planets found outside the solar system between these two types of worlds. The results could give scientists a better picture of how worlds like these evolve.