WASP-121, also known as CD-38 3220 and formally named Dilmun,[1] is a magnitude 10.4 star located approximately 858lk=onNaNlk=on 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 for WASP-121 is well below the solar ratio of 0.55.
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.[2] 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.
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).[3]