WASP-18b

Last updated
WASP-18b
Exoplanet Comparison WASP-18 b.png
Size comparison of WASP-18b with Jupiter.
Discovery [1]
Discovered by Hellier et al. (SuperWASP)
Discovery dateAugust 27, 2009
Transit (including secondary eclipses)
Orbital characteristics [2]
0.02041+0.00015
−0.00014  au
(3,053,000 km)
Eccentricity 0.0051+0.0070
−0.0037 [3]
0.941452379(16) days
(22.6 hours)
Inclination 84.08°±0.17°
−85°+72°
−96° [3]
Semi-amplitude 1,814+23
−24  m/s [3]
Star WASP-18
Physical characteristics
1.1926±0.0077  RJ [2]
Mass 10.20±0.35  MJ [3]
Mean density
6.6+1.2
−1.1  g/cm3 [3]
Albedo Geometric: 0.027±0.011 [2]
Temperature 3,061 ± 29 K (2,787.8 ± 29.0 °C; 5,050.1 ± 52.2 °F) [2]

    WASP-18b is an exoplanet 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). 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 400 light-years (120 parsecs ) from Earth. A team led by Coel Hellier, a professor of astrophysics at Keele University in England, discovered the exoplanet in 2009. [1]

    Contents

    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] [4] Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying. [5] 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 [6] and is expected to be destroyed in about eleven million years. [7]

    A study in 2012, utilizing the Rossiter–McLaughlin effect, determined that the planetary orbit is well aligned with the equatorial plane of the star, with a misalignment equal to 13±7°. [8]

    Temperature

    The planet's dayside temperature, as measured in 2020, is 3,029 ± 50  K (2,755.8 ± 50.0  °C ; 4,992.5 ± 90.0  °F ). [9] A 2023 study found an average dayside temperature of 2,781+25
    −13     K     (2,508 °C; 4,546 °F). [10] Its been theorized that highly irradiated ultrahit Jupiter’s just as WASP-18b have large variations in atmospheric temperature and chemistry as a function of longitude, latitude and altitude. WASP-18b was observed with the Near Infrared Imager and Slitless Spectrograph instruments on JWST creating a resolved atmosphere in multiple dimensions. Mapping confirmed theoretical models revealing a weaker longitudinal temperature gradient. It also indicated the importance of hydrogen dissociation and/or nightside clouds role in shaping thermal emission on the global scale. [7]

    Atmosphere

    A 2017 study detected carbon monoxide in the planet's atmosphere, without signs of water vapor. [11] [12] However, in 2023, the James Webb Space Telescope detected water vapor in the planet's atmosphere. [10] [13]

    There are two thermally distinct identified regions on the planets atmosphere. The first is the “hotspot” surrounding the substellar point. near the dayside limbs. The hotspot region shows a strongly inverted thermal structure due to the presence of optical absorbers and a water abundance marginally lower than average. The second region is a “ring” near the dayside limb. This region shows colder temperatures and poorly constrained chemical abundances. [7]

    Exoplanet WASP-18b - high carbon monoxide levels detected in stratosphere (artist concept) PIA22087-Exoplanet-Wasp18b-COinStratosphere-20171129.jpg
    Exoplanet WASP-18b − high carbon monoxide levels detected in stratosphere (artist concept)

    See also

    References

    1. 1 2 3 4 5 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. 1 2 3 4 Deline, A.; et al. (2025). "Dark skies of the slightly eccentric WASP-18 b from its optical-to-infrared dayside emission". Astronomy & Astrophysics. 699: A150. arXiv: 2505.01544 . Bibcode:2025A&A...699A.150D. doi:10.1051/0004-6361/202450939.
    3. 1 2 3 4 5 Cortés-Zuleta, Pía; Rojo, Patricio; et al. (April 2020). "TraMoS. V. Updated ephemeris and multi-epoch monitoring of the hot Jupiters WASP-18Ab, WASP-19b, and WASP-77Ab". Astronomy & Astrophysics . 636: A98. arXiv: 2001.11112 . Bibcode:2020A&A...636A..98C. doi:10.1051/0004-6361/201936279. S2CID   241596186.
    4. ↑ Hamilton, Douglas P. (2009-08-27). "Extrasolar planets: Secrets that only tides will tell". Nature . 460 (7259). Nature Publishing Group: 1086–1087. Bibcode:2009Natur.460.1086H. doi:10.1038/4601086a. PMID   19713920. S2CID   6247145.
    5. ↑ Thompson, Andrea (2009-08-26). "Newfound Planet Might Be Near Death". Space.Com. Imaginova . Retrieved 2009-08-28.
    6. ↑ Johnson, John Jr.; Astrophysicists puzzle over planet that's too close to its sun, Los Angeles Times (August 27, 2009).
    7. 1 2 3 Sharma, Bijay Kumar (2008-05-10). "Theoretical Formulation of the Phobos, moon of Mars, rate of altitudinal loss". arXiv: 0805.1454 [astro-ph].
    8. ↑ 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
    9. ↑ 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
    10. 1 2 Coulombe, Louis-Philippe; Benneke, Björn; et al. (August 2023). "A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b". Nature . 620 (7973): 292–298. arXiv: 2301.08192 . Bibcode:2023Natur.620..292C. doi:10.1038/s41586-023-06230-1. PMC   10412449 . PMID   37257843.
    11. ↑ Sheppard, Kyle B.; Mandell, Avi M.; et al. (December 2017). "Evidence for a Dayside Thermal Inversion and High Metallicity for the Hot Jupiter WASP-18b". The Astrophysical Journal Letters . 850 (2): L32. arXiv: 1711.10491 . Bibcode:2017ApJ...850L..32S. doi: 10.3847/2041-8213/aa9ae9 .
    12. 1 2 Landau, Elizabeth; Zubritsky, Elizabeth (29 November 2017). "Exoplanet Has Smothering Stratosphere Without Water". NASA . Retrieved 29 November 2017.
    13. ↑ "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.

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