WASP-18b

WASP-18b is an extrasolar planet that is notable for having an orbital period of less than one day. It has a mass equal to 10 Jupiter masses,[1] just below the boundary line between planets and brown dwarfs (about 13 Jupiter masses). In 2023, the James Webb Space Telescope discovered traces of water in the planet.[5] Due to tidal deceleration, it is expected to spiral toward and eventually merge with its host star, WASP-18, in less than a million years.[1] The planet is approximately 3.1 million km (1.9 million mi; 0.021 AU) from its star, which is about 410 light-years (130 parsecs) from Earth. A team led by Coel Hellier, a professor of astrophysics at Keele University in England, discovered the exoplanet.[1]

WASP-18b
Size comparison of WASP-18b with Jupiter.
Discovery
Discovered byHellier et al. (SuperWASP)[1]
Discovery dateAugust 27, 2009[1]
Transit[1] (including secondary eclipses)
Orbital characteristics
Apastron0.02045 AU (3,059,000 km)
Periastron0.02007 AU (3,002,000 km)
0.02026 ± 0.00068 AU (3,031,000 ± 102,000 km)[2]
Eccentricity0.0092 ± 0.0028[2]
0.94145455+0.00000087
−0.00000132[3] d
22.59487 h
Inclination86 ± 2.5[2]
96 ± 10[2]
StarWASP-18
Physical characteristics
Mean radius
1.106+0.072
−0.054[2] RJ
Mass10.3 ± 0.69[2] MJ
Temperature2500±200[4]

    Scientists at Keele and at the University of Maryland are working to understand whether the discovery of this planet so shortly before its expected demise (with less than 0.1% of its lifetime remaining) was fortuitous, or whether tidal dissipation by WASP-18 is actually much less efficient than astrophysicists typically assume.[1][6] Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying.[7]

    The closest example of a similar situation in the Solar System is Mars' moon Phobos. Phobos orbits Mars at a distance of only about 9,000 km (5,600 mi), 40 times closer than the Moon is to the Earth[8] and is expected to be destroyed in about eleven million years.[9]

    Dayside temperature measured in 2020 is 3,029 ± 50 K (2,755.8 ± 50.0 °C; 4,992.5 ± 90.0 °F).[10]

    The study in 2012, utilizing a Rossiter–McLaughlin effect, has determined the planetary orbit is well aligned with the equatorial plane of the star, misalignment equal to 13±7°.[11]

    Exoplanet WASP-18b − high carbon monoxide levels detected in stratosphere (artist concept)[12]

    See also

    References
    1. Hellier, Coel; et al. (2009). "An orbital period of 0.94days for the hot-Jupiter planet WASP-18b" (PDF). Nature. 460 (7259): 1098–1100. Bibcode:2009Natur.460.1098H. doi:10.1038/nature08245. hdl:2268/28276. PMID 19713926. S2CID 205217669.
    2. "Notes for planet WASP-18b". The Extrasolar Planets Encyclopaedia. Retrieved 2009-09-15.
    3. McDonald, I.; Kerins, E. (2018). "Pre-discovery transits of the exoplanets WASP-18b and WASP-33b from Hipparcos". Monthly Notices of the Royal Astronomical Society: Letters. 477 (1): L21–L24. arXiv:1803.06187. Bibcode:2018MNRAS.477L..21M. doi:10.1093/mnrasl/sly045.
    4. Zhou, G.; Bayliss, D. D. R.; Kedziora-Chudczer, L.; Tinney, C. G.; Bailey, J.; Salter, G.; Rodriguez, J. (2015). "Secondary eclipse observations for seven hot-Jupiters from the Anglo-Australian Telescope". Monthly Notices of the Royal Astronomical Society. 454 (3): 3002–3019. arXiv:1509.04147. Bibcode:2015MNRAS.454.3002Z. doi:10.1093/mnras/stv2138.
    5. "Webb telescope discovers traces of water in atmosphere of exoplanet with mass of 10 Jupiters". www.cbsnews.com. 2023-06-01. Retrieved 2023-06-12.
    6. Hamilton, Douglas P. (2009-08-27). "Extrasolar planets: Secrets that only tides will tell". Nature. Nature Publishing Group. 460 (7259): 1086–1087. Bibcode:2009Natur.460.1086H. doi:10.1038/4601086a. PMID 19713920. S2CID 6247145.
    7. Thompson, Andrea (2009-08-26). "Newfound Planet Might Be Near Death". Space.Com. Imaginova. Retrieved 2009-08-28.
    8. Johnson, John Jr.; Astrophysicists puzzle over planet that's too close to its sun, Los Angeles Times (August 27, 2009).
    9. Sharma, Bijay Kumar (2008-05-10). "Theoretical Formulation of the Phobos, moon of Mars, rate of altitudinal loss". arXiv:0805.1454 [astro-ph].
    10. Wong, Ian; Shporer, Avi; Daylan, Tansu; Benneke, Björn; Fetherolf, Tara; Kane, Stephen R.; Ricker, George R.; Vanderspek, Roland; Latham, David W.; Winn, Joshua N.; Jenkins, Jon M.; Boyd, Patricia T.; Glidden, Ana; Goeke, Robert F.; Sha, Lizhou; Ting, Eric B.; Yahalomi, Daniel (2020), "Systematic Phase Curve Study of Known Transiting Systems from Year One of the TESS Mission", The Astronomical Journal, 160 (4): 155, arXiv:2003.06407, Bibcode:2020AJ....160..155W, doi:10.3847/1538-3881/ababad, S2CID 212717799
    11. Albrecht, Simon; Winn, Joshua N.; Johnson, John A.; Howard, Andrew W.; Marcy, Geoffrey W.; Butler, R. Paul; Arriagada, Pamela; Crane, Jeffrey D.; Shectman, Stephen A.; Thompson, Ian B.; Hirano, Teruyuki; Bakos, Gaspar; Hartman, Joel D. (2012), "Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments", The Astrophysical Journal, 757 (1): 18, arXiv:1206.6105, Bibcode:2012ApJ...757...18A, doi:10.1088/0004-637X/757/1/18, S2CID 17174530
    12. Landau, Elizabeth; Zubritsky, Elizabeth (29 November 2017). "Exoplanet Has Smothering Stratosphere Without Water". NASA. Retrieved 29 November 2017.
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