![]() Artist's impression of KELT-9b and its parent star | |
Orbital characteristics | |
---|---|
0.03462+0.00110 −0.00093 AU | |
1.4811235±0.0000011 [1] d | |
Inclination | 86.79±0.25 [1] |
Star | HD 195689 |
Physical characteristics | |
1.891+0.061 −0.053 [1] RJ | |
Mass | 2.17±0.56 [2] MJ |
Mean
density | 530±0.15 kg m−3 |
Albedo | <0.007 [3] |
Temperature | 4050±180 [1] K |
KELT-9b is an exoplanet and ultra-hot Jupiter that orbits the late B-type/early A-type star KELT-9, [4] located about 670 light-years from Earth. [4] Detected using the Kilodegree Extremely Little Telescope, the discovery of KELT-9b was announced in 2016. [5] [1] As of June 2017, it is the hottest known exoplanet. [6]
The host star, KELT-9, is 2 to 3 times larger and 2 to 3 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] [7] 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. [8] [9]
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 it. Like many hot Jupiters, KELT-9b is tidally locked with its host star. [9] The outer boundary of its atmosphere nearly reaches its Roche lobe, implying that the planet is experiencing rapid atmospheric escape [10] driven by the extreme amount of radiation it receives from its host star. [9] [8] In 2020, atmospheric loss rate was measured to be equal to 18 - 68 Earth masses per billion years. [11]
The planet's elemental abundances remain largely unknown as of 2022, but a low carbon-to-oxygen ratio is strongly suspected. [12]
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] [4] 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, [13] neutral and singly ionized atomic iron [14] (Fe and Fe+) and singly ionized titanium (Ti+), [15] only to temporarily reform once they reach the cooler night side, [4] which is indirectly confirmed by measured enhanced heat transfer efficiency of 0.3 between dayside and nightside, likely diven by the latent heat of dissociation and recombination of the molecular hydrogen. [3] Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere, [16] although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside. [17]
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. [18]
Jupiter | KELT-9b |
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![]() Artist's impression of KELT-9b and its parent star | |
Orbital characteristics | |
---|---|
0.03462+0.00110 −0.00093 AU | |
1.4811235±0.0000011 [1] d | |
Inclination | 86.79±0.25 [1] |
Star | HD 195689 |
Physical characteristics | |
1.891+0.061 −0.053 [1] RJ | |
Mass | 2.17±0.56 [2] MJ |
Mean
density | 530±0.15 kg m−3 |
Albedo | <0.007 [3] |
Temperature | 4050±180 [1] K |
KELT-9b is an exoplanet and ultra-hot Jupiter that orbits the late B-type/early A-type star KELT-9, [4] located about 670 light-years from Earth. [4] Detected using the Kilodegree Extremely Little Telescope, the discovery of KELT-9b was announced in 2016. [5] [1] As of June 2017, it is the hottest known exoplanet. [6]
The host star, KELT-9, is 2 to 3 times larger and 2 to 3 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] [7] 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. [8] [9]
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 it. Like many hot Jupiters, KELT-9b is tidally locked with its host star. [9] The outer boundary of its atmosphere nearly reaches its Roche lobe, implying that the planet is experiencing rapid atmospheric escape [10] driven by the extreme amount of radiation it receives from its host star. [9] [8] In 2020, atmospheric loss rate was measured to be equal to 18 - 68 Earth masses per billion years. [11]
The planet's elemental abundances remain largely unknown as of 2022, but a low carbon-to-oxygen ratio is strongly suspected. [12]
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] [4] 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, [13] neutral and singly ionized atomic iron [14] (Fe and Fe+) and singly ionized titanium (Ti+), [15] only to temporarily reform once they reach the cooler night side, [4] which is indirectly confirmed by measured enhanced heat transfer efficiency of 0.3 between dayside and nightside, likely diven by the latent heat of dissociation and recombination of the molecular hydrogen. [3] Surprisingly, spectra taken in 2021 have unambiguously indicated a presence of metal oxides and hydrides in the planetary atmosphere, [16] although higher resolution spectra taken in 2021 have not found any molecular emissions from the planetary dayside. [17]
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. [18]
Jupiter | KELT-9b |
---|---|
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