WASP-4b

---

title: "WASP-4b" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["exoplanets-discovered-by-wasp", "exoplanets-discovered-in-2007", "giant-planets", "hot-jupiters", "transiting-exoplanets", "phoenix-(constellation)"] description: "Extrasolar planet in the constellation Phoenix" topic_path: "general/exoplanets-discovered-by-wasp" source: "https://en.wikipedia.org/wiki/WASP-4b" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Extrasolar planet in the constellation Phoenix ::

::data[format=table title="Infobox planet"]

Field	Value
name	WASP-4b
image	Exoplanet Comparison WASP-4 b.png
caption	Size comparison of WASP-4b with Jupiter.
discovery_ref
discoverer	Wide Angle Search for Planets
discovery_site	South African Astronomical Observatory
discovered	October 31, 2007
discovery_method	Transit photometry
orbit_ref
apsis	astron
semimajor
eccentricity
period
inclination
semi-amplitude
star	WASP-4
physical_ref
mean_radius
mass
density
single_temperature	(1957 K)
::

| name = WASP-4b | image = Exoplanet Comparison WASP-4 b.png | caption = Size comparison of WASP-4b with Jupiter. | discovery_ref = | discoverer = Wide Angle Search for Planets | discovery_site = South African Astronomical Observatory | discovered = October 31, 2007 | discovery_method = Transit photometry | orbit_ref = | apsis = astron | semimajor = | eccentricity = | period = | inclination = | semi-amplitude = | star = WASP-4 | physical_ref = | mean_radius = | mass = | density = | single_temperature = (1957 K) WASP-4b is an exoplanet, specifically a hot Jupiter, approximately 891 light-years away in the constellation of Phoenix.

Discovery

The planet was the discovered by the Wide Angle Search for Planets team using images taken with the SuperWASP-South project's eight wide-angle cameras located at the South African Astronomical Observatory. Analysis of over 4000 images taken between May and November 2006 resulted in the detection of a transit occurring every 1.3 days. Follow-up radial velocity observations using the Swiss 1.2-metre Leonhard Euler Telescope confirmed that the transiting object was a planet.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/5/5d/WASP-4_b_rv.pdf" caption="The radial velocity trend of WASP-4, caused by the presence of WASP-4 b." alt=""] ::

Characteristics

The planetary equilibrium temperature would be 1650 K, but the measured dayside temperature is higher, with a 2015 study finding 1900 K and a 2020 study finding 1957 K.

A study in 2012, utilizing the Rossiter–McLaughlin effect, determined the planetary orbit is probably aligned with the equatorial plane of the star, with misalignment equal to -1°.

The planet's orbital period appeared to be decreasing at a rate of 7.33 milliseconds per year, suggesting that its orbit is decaying with a decay timescale of 15.77 million years. The anomalously high rate of orbital decay of WASP-4b was poorly understood as of 2021. However, in late 2025 it was determined that WASP-4b is not undergoing any orbital decay; all the data used to support it is instead explained by the light travel time effect of the wider-orbit planet WASP-4c.

References

References

1. (2025-06-17). "The Orbit of WASP-4 b is in Decay". [[Monthly Notices of the Royal Astronomical Society]].
2. . (2007-10-31). ["Astronomer discovers new planets"](http://news.bbc.co.uk/2/hi/uk_news/scotland/edinburgh_and_east/7070887.stm). *BBC News*.
3. {{Cite Gaia DR3. 6535499658122055552
4. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific.
5. Sherriff, Lucy. (2007-10-31). "UK boffins ID three new exo-planets". The Register.
6. (2008). "WASP-4b: A 12th Magnitude Transiting Hot Jupiter in the Southern Hemisphere". The Astrophysical Journal Letters.
7. (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.
8. Table 3, Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b, M. Gillon et al., ''Astronomy and Astrophysics'' '''496''', #1 (2009), pp. 259–267, {{doi. 10.1051/0004-6361:200810929, {{Bibcode. 2009A&A...496..259G.
9. (2012). "Obliquities of Hot Jupiter Host Stars: Evidence for Tidal Interactions and Primordial Misalignments". The Astrophysical Journal.
10. (2015). "Secondary eclipse observations for seven hot-Jupiters from the Anglo-Australian Telescope". Monthly Notices of the Royal Astronomical Society.
11. (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]].
12. (2020). "Systematic Phase Curve Study of Known Transiting Systems from Year One of the TESS Mission". The Astronomical Journal.
13. (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.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::