KELT-9b is a relatively large giant planet at about 2.8 times the mass of Jupiter; however, given that its radius is nearly twice that of Jupiter, its density is less than half that of Jupiter. Like many hot Jupiters, KELT-9b is tidally locked with its host star. The outer boundary of its atmosphere nearly reaches its Roche lobe, implying that the planet is experiencing rapid atmospheric escape driven by the extreme amount of radiation it receives from its host star. In 2020, atmosphere loss rate was measured to be equal to 18 - 68 Earth masses per billion years. As of January 2020, KELT-9b is one of the hottest known exoplanets, with dayside temperatures approaching 4,600 K, warmer than many low-mass stars Molecules on the day side are broken into their component atoms, such that normally sequestered refractory elements can exist as atomic species, including neutral and singly ionized atomic iron (Fe and Fe+) and singly ionized titanium (Ti+),only to temporarily reform once they reach the cooler night side. Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in planetary atmosphere, although higher resolution spectra taken in 2021 have not found any molecular emissions from planetary dayside. Thermosphere layer of KELT-9b is expected to heat up to 10000-11000 K, driven by ionization of heavy metals atoms like iron.
P.S Kelt 9b Is the hottest hot Jupiter but cooler than Kepler 70 b and please like and star :) Also this is outdated.
