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]
 Size comparison of WASP-18b with Jupiter. | |
| Discovery[1] | |
|---|---|
| Discovered by | Hellier et al. (SuperWASP) |
| Discovery date | August 27, 2009 |
| Transit (including secondary eclipses) | |
| Orbital characteristics[2] | |
| 0.02024 ± 0.00030 AU (3,028,000 ± 45,000 km) | |
| Eccentricity | 0.0051+0.0070 −0.0037 |
| 0.94145223(24) d 22.59485352 h | |
| Inclination | 83.5°+2.0° −1.6° |
| −85°+72° −96° | |
| Semi-amplitude | 1814+23 −24 m/s |
| Star | WASP-18 |
| Physical characteristics[2] | |
| 1.240±0.079 RJ | |
| Mass | 10.20±0.35 MJ |
Mean density | 6.6+1.2 −1.1 g/cm3 |
| Temperature | 3,029±50 K (2,756 °C; 4,993 °F)[3] 2,781+25 −13 K (2,508 °C; 4,546 °F)[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]
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).[3] A 2023 study found an average dayside temperature of 2,781+25
−13 K (2,508 °C; 4,546 °F).[4]
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°.[9]
A 2017 study detected carbon monoxide in the planet's atmosphere, without signs of water vapor.[10][11] However, in 2023, the James Webb Space Telescope detected water vapor in the planet's atmosphere.[4][12]
See also
editReferences
edit- ^ a b c d e 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.
- ^ a b 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.
- ^ a b 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
- ^ a b c 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.
- ^ 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.
- ^ Thompson, Andrea (2009-08-26). "Newfound Planet Might Be Near Death". Space.Com. Imaginova. Retrieved 2009-08-28.
- ^ Johnson, John Jr.; Astrophysicists puzzle over planet that's too close to its sun, Los Angeles Times (August 27, 2009).
- ^ Sharma, Bijay Kumar (2008-05-10). "Theoretical Formulation of the Phobos, moon of Mars, rate of altitudinal loss". arXiv:0805.1454 [astro-ph].
- ^ 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
- ^ 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.
- ^ a b Landau, Elizabeth; Zubritsky, Elizabeth (29 November 2017). "Exoplanet Has Smothering Stratosphere Without Water". NASA. Retrieved 29 November 2017.
- ^ "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.
External links
edit
Media related to WASP-18b at Wikimedia Commons