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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). 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]
Detection method
Transit[1] (including secondary eclipses)
Orbital characteristics
Apastron0.02045 AU (3,059,000 km)
Periastron0.02007 AU (3,002,000 km)
Semi-major axis
0.02026 ± 0.00068 AU (3,031,000 ± 102,000 km)[2]
Eccentricity0.0092 ± 0.0028[2]
Orbital period (sidereal)
0.94145455+0.00000087
−0.00000132[3] d
22.59487 h
Inclination86 ± 2.5[2]
Argument of periastron
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][5] Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying.[6]

    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[7] and is expected to be destroyed in about eleven million years.[8]

    Dayside temperature measured in 2020 is 3,029 ± 50 K (2,755.8 ± 50.0 °C; 4,992.5 ± 90.0 °F).[9]

    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°.[10]

    Exoplanet WASP-18b − high carbon monoxide levels detected in stratosphere (artist concept)[11]
    Exoplanet WASP-18b − high carbon monoxide levels detected in stratosphere (artist concept)[11]

    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. PMID 19713926.
    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. 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.
    6. Thompson, Andrea (2009-08-26). "Newfound Planet Might Be Near Death". Space.Com. Imaginova. Retrieved 2009-08-28.
    7. Johnson, John Jr.; Astrophysicists puzzle over planet that's too close to its sun, Los Angeles Times (August 27, 2009).
    8. Sharma, Bijay Kumar (2008-05-10). "Theoretical Formulation of the Phobos, moon of Mars, rate of altitudinal loss". arXiv:0805.1454 [astro-ph].
    9. Systematic phase curve study of known transiting systems from year one of the TESS mission, 2020, arXiv:2003.06407
    10. Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments, 2012, arXiv:1206.6105
    11. Landau, Elizabeth; Zubritsky, Elizabeth (29 November 2017). "Exoplanet Has Smothering Stratosphere Without Water". NASA. Retrieved 29 November 2017.


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    На других языках

    [de] WASP-18 b

    WASP-18 b (auch „WASP-18b“ geschrieben) ist ein extrasolarer Planet, der den Stern WASP-18 umkreist. Seine Umlaufzeit beträgt dabei weniger als ein Tag. Man nimmt an, dass es in etwa einer Million Jahren zu einer Kollision zwischen dem Planeten und seinem Zentralgestirn kommen wird.
    - [en] WASP-18b

    [es] WASP-18b

    WASP-18b es un planeta extrasolar, de los llamados Júpiteres calientes, conocido por las extrañas características de su órbita. Su período orbital es de menos de un día, siendo un planeta 10 veces más grande que Júpiter. Su posición con respecto a la estrella es altamente inestable, por lo que se barajan dos hipótesis: que termine precipitándose a su estrella en un plazo relativamente breve (menos de un millón de años) o que exista algún otro factor aún desconocido que haya permitido el mantenimiento de esa órbita. El planeta se encuentra a unos 3 millones de km de su estrella (como comparación, Mercurio está a unos 58 millones de km del Sol) y ambos, a unos 325 años luz de la Tierra.[5]

    [it] WASP-18 b

    WASP-18 b è un pianeta extra-solare ed è noto poiché possiede un periodo di rivoluzione attorno alla sua stella molto breve, circa 24 ore. Ha una massa equivalente a 10 volte quella di Giove, appena sotto la linea di divisione tra pianeti e nane brune, circa 13 masse gioviane. Dovuto alla decelerazione delle maree, si pensa che il pianeta verrà inghiottito dalla stella, WASP-18, in meno di un milione di anni.[1] Il pianeta si trova a circa 1.9 milioni di miglia (circa 3057100 km) dalla stella, lontana circa 325 anni luce dalla Terra. La scoperta di questo pianeta si deve a Coel Hellier, professore di astrofisica alla Keele University in Inghilterra.[2]

    [ru] WASP-18 b

    WASP-18 b — экзопланета у звезды WASP-18 в созвездии Феникса. Находится на расстоянии ок. 330 св. лет от Солнца.


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