WASP-4b
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.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. The orbital decay thought to be primarily driven by tidal interactions between the planet and its host star. 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.