Distribution of mass versus orbital period for planets with a measured mass. Black lines represent the Neptunian desert. NGTS-4b is shown as a red cross.

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]

Candidates

NGTS-4b

The exoplanet NGTS-4b, with mass of 20 MEarth, 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.[1]

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]

See also

Notes

  1. 1 2 3 4 Watson, Christopher A.; Walker, Simon R.; Udry, Stéphane; Thompson, Samantha J.; Sohy, Sandrine; Rauer, Heike; et al. (11 July 2019). "NGTS-4b: A sub-Neptune transiting in the desert". Monthly Notices of the Royal Astronomical Society. 486 (4): 5094–5103. arXiv:1809.00678. Bibcode:2019MNRAS.486.5094W. doi:10.1093/mnras/stz1084. ISSN 0035-8711.
  2. 1 2 "The 'Forbidden' planet has been found in the 'Neptunian Desert'". Phys.org. University of Warwick. 29 May 2019. Retrieved 29 May 2019.
  3. ↑ Jenkins, James S.; Díaz, Matías R.; et al. (September 2020). "An Ultra-Hot Neptune in the Neptune desert". Nature Astronomy. 4 (12): 1148–1157. arXiv:2009.12832. Bibcode:2020NatAs...4.1148J. doi:10.1038/s41550-020-1142-z. S2CID 256707813.
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