The CHEOPS space telescope, with its scientific operations centre based at the University of Geneva, is providing new insights into the mysterious exoplanet WASP-76b. This ultra-hot giant planet exhibits an asymmetry in the amount of light observed on its eastern and western terminators, possibly due to a phenomenon known as a glory, similar to a rainbow. If confirmed, this would be the first detection of a glory outside our solar system. The study, conducted in collaboration with the European Space Agency and the University of Bern, has been published in Astronomy & Astrophysics.
WASP-76b is an ultra-hot giant planet orbiting its host star at a distance twelve times closer than Mercury orbits the Sun, receiving over 4,000 times the radiation Earth receives from the Sun. Due to the intense radiation, WASP-76b is inflated and almost twice the size of Jupiter, despite being 10% less massive. This peculiar planet has one side always facing its star, reaching temperatures of 2,400 degrees Celsius, where elements melt and evaporate before condensing on the cooler night side, creating iron clouds and molten iron rain.
Astronomers have been closely studying WASP-76b since its discovery in 2013, revealing a harsh environment where extreme conditions prevail. One of the most perplexing observations is the asymmetry between the planet’s eastern and western terminators, with the former showing a higher level of luminosity. To investigate this phenomenon, astronomers utilized the CHEOPS space telescope for twenty-three observations spread over three years, in addition to data from other telescopes. Their hypothesis suggests that a glory, a localized and anisotropic reflection, could be responsible for the excess luminous flux on the eastern side of the planet.
Glories are common phenomena on Earth, and have also been observed on Venus, occurring when light is reflected by clouds made up of uniform droplets. While the nature of these droplets on WASP-76b remains unknown, the detection of a glory on this exoplanet would be the first of its kind outside our solar system. This phenomenon requires specific conditions, such as perfectly spherical and stable atmospheric particles illuminated by the planet’s host star. Confirmation of the glory would provide insight into the presence of stable clouds on WASP-76b and the stability of its atmosphere over time.
Further data will be necessary to confirm whether the excess light observed on the eastern terminator of WASP-76b is indeed a glory, indicating the presence of stable, spherical droplets in the planet’s atmosphere. Detecting such minute phenomena from a great distance opens up opportunities for scientists and engineers to identify other crucial phenomena, such as the reflection of starlight off liquid lakes and oceans, which could be vital for assessing habitability. The study of WASP-76b and its unique features offers valuable insights into the diversity of exoplanets and the potential for finding habitable environments beyond our solar system.
