2025ApJ...980L..40L

Short-period planets provide ideal laboratories for testing star-planet interaction. Planets that are smaller than ∼2R_⊕ are considered to be largely rocky, either having been stripped of or never having acquired the gaseous envelope. Zooming in on this short-period rocky planet population, clear edges appear in the mass-period and radius-period space. Over ∼0.2-20 days and 0.09-1.42M_⊙, the maximum mass of the rocky planets stays below ∼10 M_⊕ with a hint of decrease toward ≲1 day, ≳4 days, and ≲0.45M_⊙. In radius-period space, there is a relative deficit of ≲2R_⊕ planets inside ∼1 day. We demonstrate how the edges in the mass-period space can be explained by a combination of tidal decay and photoevaporation, whereas the rocky planet desert in the radius-period space is a signature of magnetic drag on the planet as it orbits within the stellar magnetic field. Currently observed catastrophically evaporating planets may have started their death spiral from ∼1 day with planets of mass up to ∼0.3M_⊕ under the magnetic drag. More discoveries and characterization of small planets around mid- to late M and A stars would be welcome to better constrain the stellar parameters critical in shaping the edges of rocky planet population, including their UV radiation history, tidal effects, and magnetic properties.