Neptunian desert
Stellar region without planets equivalent to or above Neptune
From Wikipedia, the free encyclopedia
The Neptunian desert or sub-Jovian desert is broadly defined as the region close to a star (period < 2–4 days) where no Neptune-sized (> 0.1 MJ) exoplanets are found.[1] This zone receives strong irradiation from the star, meaning the planets cannot retain their gaseous atmospheres: they evaporate, leaving just a rocky core.[2]
Neptune-sized planets should be easier to find in short-period orbits, and many sufficiently massive planets have been discovered with longer orbits from surveys such as CoRoT and Kepler.[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]
Confirmed exoplanets within the Neptunian desert
NGTS-4b
LTT 9779 b
LTT 9779 b is an ultra-hot Neptune in the Neptunian desert. It has an unusually high albedo of 0.8, and likely has a metal-rich atmosphere.[3]
Candidates
Vega b
Vega b, reported in 2021, is a candidate ultra-hot Neptune with a mass of ≥21.9 M🜨 that revolves around Vega every 2.43 days, a mere 0.04555 AU (6,814,000 km) from its luminous host star. The equilibrium 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.[4]