Astronomy:KELT-9b

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KELT-9b
Artist's impression of KELT-9b and its parent star
Discovery[2]
Discovered byB. Scott Gaudi, et al.
Discovery siteKELT-North, Arizona
Discovery dateMay 2016 (announced)[1]
June 2017 (published)
Transit
Designations
HD 195689 b
Orbital characteristics[3]
0.03368±0.00078 astronomical unit|AU
Eccentricity0
Orbital period1.4811235±0.0000011 d
Inclination86.79°±0.25°
Semi-amplitude293±32 m/s
StarHD 195689 A
Physical characteristics
Mean radius1.82±0.03[4] |♃|J}}}}}}
Mass2.22±0.58[4] |♃|J}}}}}}
Mean density0.491+0.072
−0.066 g/cm3[3]
Albedo<0.14[5]
Physics4,579±120[4] K (dayside)
2,400+400
−300 K[4] (nightside)


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.[1][2] As of June 2017, it is the hottest known exoplanet.[7]

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[2][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

Exoplanet KELT-9b orbits host star KELT-9

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]

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 dayside temperatures approaching 4,600 K (4,327 °C; 7,820 °F) — warmer than some K-type stars.[2][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]

Size comparison
Jupiter KELT-9b
Jupiter Exoplanet

See also

References

  1. ↑ 1.0 1.1 Collins, Karen A.; Stassun, Keivan; Gaudi, B. Scott; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D. et al. (2016). "KELT-9b: A Case Study in Dynamical Planet Ingestion by a Hot Host Star". American Astronomical Society 47: 204.03. Bibcode: 2016DDA....4720403C. 
  2. ↑ 2.0 2.1 2.2 2.3 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. doi:10.1038/nature22392. ISSN 1476-4687. PMID 28582774. Bibcode: 2017Natur.546..514G. http://works.swarthmore.edu/cgi/viewcontent.cgi?article=1317&context=fac-physics. Retrieved 2017-06-06. 
  3. ↑ 3.0 3.1 Borsa, F.; Rainer, M. et al. (November 2019). "The GAPS Programme with HARPS-N at TNG: XIX. Atmospheric Rossiter-McLaughlin effect and improved parameters of KELT-9b". Astronomy & Astrophysics 631: A34. doi:10.1051/0004-6361/201935718. ISSN 0004-6361. Bibcode: 2019A&A...631A..34B. 
  4. ↑ 4.0 4.1 4.2 4.3 Zhang, Yapeng; Wardenier, Joost P.; Householder, Aaron; Komacek, Thaddeus D.; Kesseli, Aurora; Dai, Fei; Howard, Andrew W.; Inglis, Julie et al. (2026-02-01). "Extreme winds on the emerging dayside of an ultrahot Jupiter". The Astrophysical Journal Letters 997 (2): L40. doi:10.3847/2041-8213/ae36a1. ISSN 2041-8205. Bibcode: 2026ApJ...997L..40Z. 
  5. ↑ 5.0 5.1 Jones, K. et al. (2022), "The stable climate of KELT-9b", Astronomy & Astrophysics 666: A118, doi:10.1051/0004-6361/202243823, Bibcode: 2022A&A...666A.118J 
  6. ↑ 6.0 6.1 6.2 6.3 Brennan, Pat; Cofield, Calia (24 January 2020). "For Hottest Planet, a Major Meltdown, Study Shows". NASA. https://www.jpl.nasa.gov/news/news.php?feature=7583. 
  7. ↑ Tribur, Melissa (2017-06-05). "Meet KELT-9b, the Hottest Exoplanet Ever Discovered" (in en-US). http://eos.org/articles/meet-kelt-9b-the-hottest-exoplanet-ever-discovered. 
  8. ↑ 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. 
  9. ↑ 9.0 9.1 KELT-9 b Exoplanet Exploration Program 2017
  10. ↑ 10.0 10.1 10.2 NASA JPL, Pasadena CA (5 June 2017) Astronomers Find Planet Hotter Than Most Stars
  11. ↑ Yan, Fei; Henning, Thomas (2 July 2018). "An extended hydrogen envelope of the extremely hot giant exoplanet KELT-9b" (in En). Nature Astronomy 2 (9): 714–718. doi:10.1038/s41550-018-0503-3. ISSN 2397-3366. Bibcode: 2018NatAs...2..714Y. https://www.researchgate.net/publication/326129899. Retrieved 18 August 2018. 
  12. ↑ Wyttenbach, A.; Mollière, P.; Ehrenreich, D.; Cegla, H. M.; Bourrier, V.; Lovis, C.; Pino, L.; Allart, R. et al. (2020). "Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series". Astronomy & Astrophysics 638: A87. doi:10.1051/0004-6361/201937316. Bibcode: 2020A&A...638A..87W. 
  13. ↑ Jacobs, Bob; Désert, Jean-Michel; Pino, Lorenzo; Line, Michael R.; Bean, Jacob L.; Khorshid, Niloofar; Schlawin, Everett; Arcangeli, Jacob et al. (2022), "A strong H− opacity signal in the near-infrared emission spectrum of the ultra-hot Jupiter KELT-9b", Astronomy & Astrophysics 668: L1, doi:10.1051/0004-6361/202244533, Bibcode: 2022A&A...668L...1J 
  14. ↑ 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, doi:10.1038/s41550-021-01544-4 
  15. ↑ Pino, L.; Désert, J. M.; Brogi, M.; Malavolta, L.; Wyttenbach, A.; Line, M.; Hoeijmakers, J.; Fossati, 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. doi:10.3847/2041-8213/ab8c44. Bibcode: 2020ApJ...894L..27P. 
  16. ↑ Hoeijmakers, H. Jens; Ehrenreich, David; Heng, Kevin; Kitzmann, Daniel; Grimm, Simon L.; Allart, Romain; Deitrick, Russell; Wyttenbach, Aurélien et al. (15 August 2018). "Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b". Nature 560 (7719): 453–455. doi:10.1038/s41586-018-0401-y. ISSN 1476-4687. PMID 30111838. Bibcode: 2018Natur.560..453H. 
  17. ↑ Changeat, Quentin; Edwards, Billy (2021), "The Hubble WFC3 Emission Spectrum of the Extremely Hot Jupiter KELT-9b", The Astrophysical Journal Letters 907 (1): L22, doi:10.3847/2041-8213/abd84f, Bibcode: 2021ApJ...907L..22C 
  18. ↑ 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, doi:10.3847/2041-8213/ac30e1, Bibcode: 2021ApJ...921L..18K 
  19. ↑ Fossati, L.; Shulyak, D.; Sreejith, A. G.; Koskinen, T.; Young, M. E.; Cubillos, P. E.; Lara, L. M.; France, K. et al. (2020), "A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b", Astronomy & Astrophysics 643: A131, doi:10.1051/0004-6361/202039061, Bibcode: 2020A&A...643A.131F 
  20. ↑ Zhang, Yapeng (June 24, 2026). "Hydrogen Airglow from an Escaping Ultrahot Jupiter Atmosphere". The Astrophysical Journal Letters 1005 (1): L29. doi:10.3847/2041-8213/ae7be6. Bibcode: 2026ApJ..1005L..29Z. 



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