WASP-121

WASP-121, also known as CD-38 3220, is a magnitude 10.4 star located approximately 858 ly away in the constellation Puppis. WASP-121 has a mass and radius similar to the Sun's. It hosts one known exoplanet.

The star, although metal-rich in terms of overall contents of heavy elements, is depleted of carbon. The carbon to oxygen molar ratio of 0.23$38.25$ for WASP-121 is well below the solar ratio of 0.55.

Nomenclature
The designation WASP-121 indicates that this was the 121st star found to have a planet by the Wide Angle Search for Planets.

In August 2022, this planetary system was included among 20 systems to be named by the third NameExoWorlds project. The approved names, proposed by a team from Bahrain, were announced in June 2023. WASP-121 is named Dilmun after the ancient civilization, and its planet is named Tylos after the ancient Greek name for Bahrain.

Planetary system
In 2015, the exoplanet WASP-121b was discovered orbiting WASP-121 by the transit method. WASP-121b is a hot Jupiter with a mass about 1.18 times that of Jupiter and a radius about 1.81 times that of Jupiter. The exoplanet orbits WASP-121, its host star, every 1.27 days. Hot water molecules have been found in the stratosphere of WASP-121b (i.e., the atmospheric layer in which temperatures increase as the altitude increases).