Neptunian desert

[1] This zone receives strong irradiation from the star, meaning the planets cannot retain their gaseous atmospheres: they evaporate, leaving just a rocky core.

[1] The physical mechanisms that result in the observed Neptunian desert are currently unknown, but have been suggested to be due to a different formation mechanism for short-period super-Earth and Jovian exoplanets, similar to the reasons for the brown-dwarf desert.

[1] The exoplanet NGTS-4b, with mass of 20 ME, and a radius 20% smaller than Neptune, was found to still have an atmosphere while orbiting every 1.3 days within the Neptunian desert of NGTS-4, a K-dwarf star located 922 light-years from Earth.

[2] The atmosphere may have survived due to the planet's unusually high core mass, or it might have migrated to its current close-in orbit after this epoch of maximum stellar activity.

The equilbrium temperature of the planet is a white-hot 3,250 K (2,980 °C; 5,390 °F) assuming a Bond albedo of 0.25, which, if confirmed, would make it the second-hottest exoplanet after KELT-9b.