Astronomers detected an atmosphere on the exoplanet WD 1856 b, which orbits a white dwarf star, using the James Webb Space Telescope. A study detailing these observations was published in the journal Nature in July 2026. This marks the first time an atmosphere has been observed on a planet transiting a dead star.

The telescope's spectrum detected signatures of small cloud particles and hydrocarbons, likely methane, in the atmosphere of WD 1856 b. Victoria Boehm, a graduate student in the astronomy department at Cornell University and a co-author of the study, stated, "Vimos las firmas reveladoras de pequeñas partículas de nubes e hidrocarburos, muy probablemente metano, lo que marca la primera vez que vemos una atmósfera en un planeta que transita una estrella muerta." She added, "Para hacerlo aún más difícil, el tránsito del planeta solo dura 8 minutos, así que es literalmente parpadeas y te lo pierdes." Boehm also noted, "Captar suficiente luz para ver el espectro de WD 1856 b, y al mismo tiempo hacerlo con la rapidez necesaria para no perder el tránsito, es algo que solo el Webb puede hacer."

WD 1856 b, located 80 light-years from Earth, was first detected in 2020. The planet is seven times larger than its host star, which is approximately the size of Earth. WD 1856 b completes an orbit around its host star every 34 hours and is less than 3 million kilometers from it. Christopher O'Connor, a postdoctoral researcher at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University and a co-author of the study, commented, "Este es uno de los sistemas planetarios más extraños que conocemos."

The research team determined that WD 1856 b has a mass between four and 11 times that of Jupiter. Infrared light emitted by the planet suggests it has a temperature of approximately 127 °C, which is 133 °C higher than it would be if heated only by its host star. Researchers concluded that WD 1856 b originally orbited its star at a greater distance and heated up while migrating inward after its host star died. O'Connor stated that this finding put the researchers "en la pista de reconstruir la historia del planeta a partir de nuestros datos." The team's data indicates that the heating of WD 1856 b occurred approximately 1 billion years ago. The abundance of methane suggests the planet did not undergo engulfment during the red giant phase of its star. The amount of methane detected was higher than predicted.

Caroline Morley, an associate professor in the astronomy department at the University of Texas at Austin, expressed skepticism. She said, "Hay razones para ser escépticos respecto del resultado de que el planeta fue 'recalentado' durante la evolución estelar." She added, "Sí creo que la detección tentativa de metano parece plausible, y la detección de nubes y/o brumas es sólida." Morley further commented, "A esta temperatura, la mejor primera suposición sobre qué 'aerosoles' están presentes son nubes de agua, que se forman y se vuelven bastante espesas a estas temperaturas."