WASP-121b is an exoplanet located about 850 light-years away in the constellation Phoenix. It is classified as a hot Jupiter, meaning it is a gas giant similar in size to Jupiter but orbits very close to its star, resulting in extremely high temperatures. The planet has a unique atmosphere that contains elements like sodium and potassium, which can be detected during transits. WASP-121b is notable for its unusual properties, including a potential for atmospheric escape due to its intense heat, making it a subject of interest for astronomers studying planetary atmospheres.