The mystery of the missing super-Earths and mini-Neptunes may finally be solved 

 Our universe's lack of super-Earths or mini-Neptunes could be caused by some planets migrating toward the hearts of their systems early on in their lives. 

https://cdn.mos.cms.futurecdn.net/zeWe6KV5AArUGfSZZLeRXJ.png

https://www.space.com/mystery-missing-super-earths-mini-neptunes-solved