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 exoplanet NGTS-4b, with mass of 20 M Earth, 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. 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. 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. This zone receives strong irradiation from the star, meaning the planets cannot retain their gaseous atmospheres: They evaporate, leaving just a rocky core. The Neptunian Desert or sub-Jovian desert is broadly defined as the region close to a star ( period 0.1 M J) exoplanets are found. Black lines represent the Neptunian desert. We estimated the amount of mass this planet might have lost at a young age, and we find that while the mass loss could have been significant, the planet had not changed in terms of character: it was born as a small volatile-rich planet, and it remains one at present.Stellar region without planets equivalent to or above Neptuneĭistribution of mass versus orbital period for planets with a measured mass. HD 56414 b is what astronomers call a warm Neptune located just outside the zone around a star in which a planet would be violently stripped of its atmosphere. Planetary interior structure models of TOI-2196 b are consistent with a H/He atmosphere mass fraction between 0.4 % and 3 %, with a mean value of 0.7 % on top of a rocky interior. LTT9779 b is around the size of the solar system ice giant Neptune, which, coupled with its roasting temperature, class it as an ultra-hot Neptune.
More planets in this parameter space are needed to further investigate this finding. These planets suggest that the hot Neptune desert may be divided in two parts for planets with equilibrium temperatures of > 1800 K: a hot sub-Neptune desert devoid of planets with radii of 1.8-3 Rearth and a sub-Jovian desert for radii of 5-12 Rearth. This places the planet in the hot Neptune desert, joining a group of very few planets in this parameter space discovered in recent years. The short period of planet b implies a high equilibrium temperature of 1860 +/- 20 K, for zero albedo and isotropic emission.
Crossfield and his co-authors used a technique called phase curve analysis to parse the exoplanet ’s atmospheric makeup. A significant trend in the HARPS radial velocities points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 Mjup, respectively, assuming zero eccentricity. Hot Neptune LTT 9779b was discovered just last year, becoming one of the first Neptune-sized planets discovered by NASA’s all-sky TESS planet-hunting mission. Hence, the radius implies that this planet is a sub-Neptune, although the density is twice than that of Neptune. The radius of TOI-2196 b is 3.51 +/- 0.15 Rearth, which, combined with the mass of 26.0 +/- 1.3 Mearth, results in a bulk density of 3.31+0.51-0.43 g/cm3.
We collected 42 radial velocity measurements with the HARPS spectrograph to determine the mass. Here, we report on the intermediate-sized planet TOI-2196 on a 1.2 day orbit around a G-type star discovered by TESS in sector 27. Highly irradiated planets in the hot Neptune desert are usually either small (R 1 Rjup.
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