KELT-9b

The host star, KELT-9, also designated HD 195689, is 2.3 times larger and 2.4 times more massive than the sun. The surface temperature is , unusually hot for a star with a transiting planet. Prior to the discovery of KELT-9b, only six A-type stars were known to have planets, of which the warmest, WASP-33, is significantly cooler at ; no B-type stars were previously known to host planets. KELT-9, classified as B9.5-A0 == Physical properties ==

KELT-9b is a relatively large giant planet at about 2.2 times the mass of Jupiter; however given that its radius is nearly twice that of Jupiter, its density is less than half that of it. 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 The planet's elemental abundances remain largely unknown as of 2022, but a low carbon-to-oxygen ratio is strongly suspected. , KELT-9b is the hottest known exoplanet, with dayside temperatures approaching — warmer than some K-type stars. neutral and singly ionized atomic iron (Fe and Fe+) and singly ionized titanium (Ti+), Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere, although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside. The thermosphere layer of KELT-9b is expected to heat up to , driven by ionization of heavy metals atoms like iron. == See also ==