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WASP-4 is a G-type main-sequence star approximately 891 light-years away in the constellation of Phoenix.[1][2][4] Despite its advanced age, the star is rotating rapidly, being spun up by the tides raised by a giant planet on a close orbit.[8]

Planetary system

In 2007 the exoplanet WASP-4b was discovered orbiting this star. With an orbital period of just 1.3 days, it is classified as a hot Jupiter.[4] The planet’s orbital period appears to be decreasing at a rate of 7.33±0.71 milliseconds per year, suggesting that its orbit is decaying, with a decay timescale of 15.77±1.57 million years.[9] Another superjovian planet in the system has been suspected.[9] A 2025 study further supported orbital decay for WASP-4b,[5] but another same-year study discounted this, attributing all evidence for orbital decay to the light travel time effect of an outer planet.[10] Although the previous candidate has not been addressed, this planet has nearly the same orbital elements and thus both should be the same object.[10]

The WASP-4 planetary system
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination
(°) 		Radius
b[5] 1.200+0.032
−0.030 MJ 		0.02294+0.00028
−0.00026 		1.338230994(84) 0.0013+0.0005
−0.0009 		88.05+0.85
−0.53 		1.349+0.011
−0.012 RJ
c[10] ≥6.93+1.10
−0.47 MJ 		7.96+0.72
−0.32 		8,650+1,200
−510 		— — —

See also

References

  1. ^ a b Roman, Nancy G. (1987). “Identification of a constellation from a position”. Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP…99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. ^ a b c d e f g Vallenari, A.; et al. (Gaia collaboration) (2023). “Gaia Data Release 3. Summary of the content and survey properties”. Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A…674A…1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. ^ a b c Henden, A. A.; et al. (2016). “VizieR Online Data Catalog: AAVSO Photometric All Sky Survey (APASS) DR9 (Henden+, 2016)”. VizieR On-line Data Catalog: II/336. Originally Published in: 2015AAS…22533616H. 2336. Bibcode:2016yCat.2336….0H. Vizier catalog entry Archived 2018-09-23 at the Wayback Machine
  4. ^ a b c d Wilson, D. M.; et al. (2008). “WASP-4b: A 12th Magnitude Transiting Hot Jupiter in the Southern Hemisphere”. The Astrophysical Journal Letters. 675 (2): L113–L116. arXiv:0801.1509. Bibcode:2008ApJ…675L.113W. doi:10.1086/586735. S2CID 10823235.
  5. ^ a b c d e f Baştürk, Ö; Kutluay, A. C.; Barker, A.; Yalçınkaya, S.; Southworth, J.; Barkaoui, K.; Wünsche, A.; Burgdorf, M. J.; Timmermans, M. (2025-06-17). “The Orbit of WASP-4 b is in Decay”. Monthly Notices of the Royal Astronomical Society. 541 (2): 714–730. arXiv:2506.15022. doi:10.1093/mnras/staf1009.
  6. ^ a b c d Bonomo, A. S.; Desidera, S.; et al. (June 2017). “The GAPS Programme with HARPS-N at TNG. XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets”. Astronomy & Astrophysics. 602: A107. arXiv:1704.00373. Bibcode:2017A&A…602A.107B. doi:10.1051/0004-6361/201629882.
  7. ^ “WASP-4”. SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-09-22.
  8. ^ Maxted, P. F. L.; Serenelli, A. M.; Southworth, J. (2015), “A comparison of gyrochronological and isochronal age estimates for transiting exoplanet host stars”, Astronomy & Astrophysics, 577: A90, arXiv:1503.09111, Bibcode:2015A&A…577A..90M, doi:10.1051/0004-6361/201525774, S2CID 53324330
  9. ^ a b Turner, Jake D.; Flagg, Laura; Ridden-Harper, Andrew; Jayawardhana, Ray (2022), “Characterizing the WASP-4 System with TESS and Radial Velocity Data: Constraints on the Cause of the Hot Jupiter’s Changing Orbit and Evidence of an Outer Planet”, The Astronomical Journal, 163 (6): 281, arXiv:2112.09621, Bibcode:2022AJ….163..281T, doi:10.3847/1538-3881/ac686f, S2CID 245329747
  10. ^ a b c Winn, Joshua N.; Stefánsson, Guđmundur (2025-12-01). “Orbital Decay Candidates Reconsidered: WASP-4 b Is Not Decaying and Kepler-1658 b Is Not a Planet”. The Planetary Science Journal. 6 (12): 300. arXiv:2510.05229. doi:10.3847/PSJ/ae21db. ISSN 2632-3338.