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KELT-9b
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
Inclination86.79±0.25 [1]
Star HD 195689
Physical characteristics
Mean radius
1.891+0.061
−0.053 [1] RJ
Mass2.17±0.56 [2] MJ
Mean density
530±0.15 kg m−3
Albedo<0.007 [3]
Temperature4050±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]

Host star

The host star, KELT-9, is 2 to 3 times larger and 2 to 5 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]

Physical properties

Exoplanet KELT-9b orbits host star KELT-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]

This graph shows the average temperature and mass relative to Jupiter (Mj) of known exoplanets as of 2022

As of 2022, KELT-9b is the hottest known exoplanet, with a 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]

Size comparison
Jupiter KELT-9b
Jupiter Exoplanet

See also

References

  1. ^ a b c d e f g Gaudi, B. Scott; et al. (5 June 2017). "A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host" (pdf). Nature. 546 (7659): 514–518. arXiv: 1706.06723. Bibcode: 2017Natur.546..514G. doi: 10.1038/nature22392. ISSN  1476-4687. PMID  28582774. S2CID  205256410. Retrieved 2017-06-06.
  2. ^ Asnodkar, Anusha Pai; et al. (4 January 2022). "KELT-9 as an Eclipsing Double-lined Spectroscopic Binary: A Unique and Self-consistent Solution to the System". The Astronomical Journal. 163 (2). 40. arXiv: 2110.15275. Bibcode: 2022AJ....163...40P. doi: 10.3847/1538-3881/ac32c7.
  3. ^ a b Jones, K.; et al. (2022), "The stable climate of KELT-9b", Astronomy & Astrophysics, 666: A118, arXiv: 2208.04818, Bibcode: 2022A&A...666A.118J, doi: 10.1051/0004-6361/202243823, S2CID  251442580
  4. ^ a b c d Brennan, Pat; Cofield, Calia (24 January 2020). "For Hottest Planet, a Major Meltdown, Study Shows". NASA. Retrieved 24 January 2020.
  5. ^ Collins, Karen A.; Stassun, Keivan; Gaudi, B. Scott; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D.; Siverd, Robert; Crepp, Justin R.; Pepper, Joshua (2016). "KELT-9b: A Case Study in Dynamical Planet Ingestion by a Hot Host Star". American Astronomical Society. 47: 204.03. Bibcode: 2016DDA....4720403C.
  6. ^ Tribur, Melissa (2017-06-05). "Meet KELT-9b, the Hottest Exoplanet Ever Discovered". Eos. Retrieved 2022-10-28.
  7. ^ Jensen, K. S. (1981). "Spectral Classification in the MK System of 167 Northern HD Stars". Astronomy and Astrophysics Supplement. 45: 455. Bibcode: 1981A&AS...45..455J.
  8. ^ a b KELT-9 b Exoplanet Exploration Program 2017
  9. ^ a b c NASA JPL, Pasadena CA (5 June 2017) Astronomers Find Planet Hotter Than Most Stars
  10. ^ Yan, Fei; Henning, Thomas (2 July 2018). "An extended hydrogen envelope of the extremely hot giant exoplanet KELT-9b". Nature Astronomy. 2 (9): 714–718. arXiv: 1807.00869. Bibcode: 2018NatAs...2..714Y. doi: 10.1038/s41550-018-0503-3. ISSN  2397-3366. S2CID  119405172. Retrieved 18 August 2018.
  11. ^ Wyttenbach, A.; Mollière, P.; Ehrenreich, D.; Cegla, H. M.; Bourrier, V.; Lovis, C.; Pino, L.; Allart, R.; Seidel, J. V.; Hoeijmakers, H. J.; Nielsen, L. D.; Lavie, B.; Pepe, F.; Bonfils, X.; Snellen, I. A. G. (2020). "Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series". Astronomy & Astrophysics. 638: A87. arXiv: 2004.13733. Bibcode: 2020A&A...638A..87W. doi: 10.1051/0004-6361/201937316. S2CID  216641961.
  12. ^ Jacobs, Bob; Désert, Jean-Michel; Pino, Lorenzo; Line, Michael R.; Bean, Jacob L.; Khorshid, Niloofar; Schlawin, Everett; Arcangeli, Jacob; Barat, Saugata; Jens Hoeijmakers, H.; Komacek, Thaddeus D.; Mansfield, Megan; Parmentier, Vivien; Thorngren, Daniel (2022), "A strong H− opacity signal in the near-infrared emission spectrum of the ultra-hot Jupiter KELT-9b", Astronomy & Astrophysics, 668: L1, arXiv: 2211.10297, Bibcode: 2022A&A...668L...1J, doi: 10.1051/0004-6361/202244533, S2CID  253708097
  13. ^ Borsa, Francesco; Fossati, Luca; Koskinen, Tommi; Young, Mitchell E.; Shulyak, Denis (2022), "High-resolution detection of neutral oxygen and non-LTE effects in the atmosphere of KELT-9b", Nature Astronomy, 6 (2): 226–231, arXiv: 2112.12059, doi: 10.1038/s41550-021-01544-4, S2CID  245385802
  14. ^ Pino, L.; Désert, J. M.; Brogi, M.; Malavolta, L.; Wyttenbach, A.; Line, M.; Hoeijmakers, J.; Fossati, L.; Bonomo, A. S.; Nascimbeni, V.; Panwar, V.; Affer, L.; Benatti, S.; Biazzo, K.; Bignamini, A.; Borsa, F.; Carleo, I.; Claudi, R.; Cosentino, R.; Covino, E.; Damasso, M.; Desidera, S.; Giacobbe, P.; Harutyunyan, A.; Lanza, A. F.; Leto, G.; Maggio, A.; Maldonado, J.; Mancini, L.; et al. (2020). "Neutral Iron Emission Lines from the Day-side of KELT-9b -- the GAPS Programme with HARPS-N at TNG XX". The Astrophysical Journal. 894 (2): L27. arXiv: 2004.11335. Bibcode: 2020ApJ...894L..27P. doi: 10.3847/2041-8213/ab8c44. S2CID  216080480.
  15. ^ Hoeijmakers, H. Jens; Ehrenreich, David; Heng, Kevin; Kitzmann, Daniel; Grimm, Simon L.; Allart, Romain; Deitrick, Russell; Wyttenbach, Aurélien; Oreshenko, Maria; Pino, Lorenzo; Rimmer, Paul B.; Molinari, Emilio; Di Fabrizio, Luca (15 August 2018). "Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b". Nature. 560 (7719): 453–455. arXiv: 1808.05653. Bibcode: 2018Natur.560..453H. doi: 10.1038/s41586-018-0401-y. ISSN  1476-4687. PMC  6322651. PMID  30111838.
  16. ^ Changeat, Quentin; Edwards, Billy (2021), "The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b", The Astrophysical Journal Letters, 907 (1): L22, arXiv: 2101.00469, Bibcode: 2021ApJ...907L..22C, doi: 10.3847/2041-8213/abd84f, S2CID  230435556
  17. ^ Kasper, David; Bean, Jacob L.; Line, Michael R.; Seifahrt, Andreas; Stürmer, Julian; Pino, Lorenzo; Désert, Jean-Michel; Brogi, Matteo (2021), "Confirmation of Iron Emission Lines and Nondetection of TiO on the Dayside of KELT-9b with MAROON-X", The Astrophysical Journal Letters, 921 (1): L18, arXiv: 2108.08389, Bibcode: 2021ApJ...921L..18K, doi: 10.3847/2041-8213/ac30e1, S2CID  239024467
  18. ^ Fossati, L.; Shulyak, D.; Sreejith, A. G.; Koskinen, T.; Young, M. E.; Cubillos, P. E.; Lara, L. M.; France, K.; Rengel, M.; Cauley, P. W.; Turner, J. D.; Wyttenbach, A.; Yan, F. (2020), "A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b", Astronomy & Astrophysics, 643: A131, arXiv: 2010.00997, Bibcode: 2020A&A...643A.131F, doi: 10.1051/0004-6361/202039061, S2CID  225127226

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