Strange, newly theorized "eggshell planets" may possess super-thin outer layers with ultra-smooth surfaces unlike those seen on any world to date, a new study reports.

Citations D. Athanasiadou et al. Nanostructure, osteopontin, and mechanical properties of calcitic avian eggshell. Science Advances. Published online March 30, 2018. doi:1126/sciadv.aar3219.