KELT-9b
Hot Jovian exoplanet orbiting KELT-9
From Wikipedia, the free encyclopedia
KELT-9b, also designated HD 195689 b, is an exoplanet and ultra-hot Jupiter in a polar orbit around the late B-type/early A-type star KELT-9,[6] located about 670 light-years from Earth.[6] Detected using the Kilodegree Extremely Little Telescope, the discovery of KELT-9b was announced in 2016.[2][1] As of June 2017, it is the hottest known exoplanet.[7]
June 2017 (published)
Artist's impression of KELT-9b and its parent star | |
| Discovery[1] | |
|---|---|
| Discovered by | B. Scott Gaudi, et al. |
| Discovery site | KELT-North, Arizona |
| Discovery date | May 2016 (announced)[2] June 2017 (published) |
| Transit | |
| Designations | |
| HD 195689 b | |
| Orbital characteristics[3] | |
| 0.03368±0.00078 AU | |
| Eccentricity | 0 |
| 1.4811235±0.0000011 d | |
| Inclination | 86.79°±0.25° |
| Semi-amplitude | 293±32 m/s |
| Star | HD 195689 A |
| Physical characteristics | |
| 1.82±0.03[4] RJ | |
| Mass | 2.22±0.58[4] MJ |
Mean density | 0.491+0.072 −0.066 g/cm3[3] |
| Albedo | <0.14[5] |
| Temperature | 4,579±120[4] K (dayside) 2,400+400 −300 K[4] (nightside) |
Host star
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 10,170 K (9,897 °C; 17,846 °F), 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 7,430 K (7,157 °C; 12,914 °F); no B-type stars were previously known to host planets. KELT-9, classified as B9.5-A0[1][8] could be the first B-type star known to have a planet. KELT-9b occupies a circular but strongly inclined orbit a mere 0.03462 AU from KELT-9 with an orbital period of less than 1.5 days.[9][10]
Physical properties
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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.[10] The outer boundary of its atmosphere nearly reaches its Roche lobe, implying that the planet is experiencing rapid atmospheric escape[11] driven by the extreme amount of radiation it receives from its host star.[10][9] In 2020, atmospheric loss rate was measured to be equal to 18 - 68 Earth masses per billion years.[12]
The planet's elemental abundances remain largely unknown as of 2022, but a low carbon-to-oxygen ratio is strongly suspected.[13]
As of 2022[update], KELT-9b is the hottest known exoplanet, with dayside temperatures approaching 4,600 K (4,327 °C; 7,820 °F) — warmer than some K-type stars.[1][6] Molecules on the day side are broken into their component atoms, so that normally sequestered refractory elements can exist as atomic species, including neutral oxygen,[14] neutral and singly ionized atomic iron[15] (Fe and Fe+) and singly ionized titanium (Ti+),[16] only to temporarily reform once they reach the cooler night side,[6] which is indirectly confirmed by measured enhanced heat transfer efficiency of 0.3 between dayside and nightside, likely driven by the latent heat of dissociation and recombination of the molecular hydrogen.[5] Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere,[17] although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside.[18]
The thermosphere layer of KELT-9b is expected to heat up to 10,000–11,000 K (9,727–10,727 °C; 17,540–19,340 °F), driven by ionization of heavy metals atoms like iron.[19]
In June 2026 scientists found a self-absorption phenomena of Hα in the upper atmosphere KELT-9b. Due to this, it is suspected that the planet is losing 1013 grams per second and has a vertical outflow wind speed of ~5 km/s.[20]
| Jupiter | KELT-9b |
|---|---|
 |
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See also
- 51 Pegasi b, the first-discovered Hot Jupiter
- List of hottest exoplanets
