KELT-9b

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KELT-9b
Artist's impression of KELT-9b orbiting KELT-9.jpg
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
Mean radius
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]

    Contents

    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 PIA21472 - Hottest Hot Jupiter Animation (Artist's Concept).gif
    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 Temperature vs Mass of known exoplanets.png
    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
    JupiterKELT-9b
    Small Jupiter.jpg Exoplanet sphere.jpg

    See also

    Related Research Articles

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    References

    1. 1 2 3 4 5 6 7 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. 1 2 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. 1 2 3 4 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. 1 2 KELT-9 b Exoplanet Exploration Program 2017
    9. 1 2 3 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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