WASP-4

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

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. The planet's orbital period appears to be decreasing at a rate of milliseconds per year, suggesting that its orbit is decaying, with a decay timescale of 15.77 million years. Another superjovian planet in the system has been suspected. A 2025 study further supported orbital decay for WASP-4b, but another same-year study discounted this, attributing all evidence for orbital decay to the light travel time effect of an outer planet. Although the previous candidate has not been addressed, this planet has nearly the same orbital elements and thus both should be the same object.