CHEOPS identifies phenomenal 'Glory' on distant exoplanet WASP-76b

WASP-76b, an ultra-hot giant planet located considerably closer to its star than Mercury is to the Sun, endures over 4,000 times the solar radiation Earth receives. "Despite being less massive than Jupiter, the intense stellar radiation inflates WASP-76b to nearly double Jupiter's size," explained Monika Lendl, an assistant professor at UNIGE's Department of Astronomy and study co-author.

Since its discovery in 2013, WASP-76b has intrigued scientists with its extreme conditions. The planet's day side faces its star permanently, heating up to 2,400 degrees Celsius-hot enough to vaporize metals. These metals then condense on the cooler night side, leading to phenomena like molten iron rain.

Investigating the Asymmetry and Luminous 'Glory'
The latest observations by CHEOPS have focused on the stark differences in light emitted from the planet's two terminators-the boundaries between its day and night sides. Notably, the eastern terminator shines brighter than its western counterpart, an anomaly that puzzled researchers.

To unravel this mystery, CHEOPS conducted twenty-three detailed observations over three years, including studies during secondary eclipses when the planet passes behind its star. These observations were complemented by data from other telescopes, such as TESS, Hubble, and Spitzer.

"The unusual brightness observed on the eastern side of WASP-76b may stem from a 'glory,' a phenomenon involving highly directional reflection of light by uniform atmospheric particles," said Olivier Demangeon, a researcher at Portugal's Instituto de Astrofisica e Ciencias do Espaco and the study's lead author.

Unprecedented Discovery and Future Prospects
Glories, typically seen on Earth and Venus, require light reflection by clouds composed of uniformly sized droplets. On Earth, these are water droplets, but on WASP-76b, they might be metallic, given the planet's scorching atmospheric conditions. Confirming the presence of such a glory on WASP-76b would be a first for exoplanetary science, necessitating further investigation to verify the persistence and composition of these atmospheric features.

"For a glory to be observed, the atmospheric particles must be almost perfectly spherical and stable enough to be seen over extended periods. Additionally, the observational alignment must be just right," Demangeon elaborated.

Further research is essential to confirm this phenomenon conclusively. If verified, it would not only confirm the presence of spherical droplet clouds but also suggest a stable atmospheric temperature over time, providing a deeper understanding of the dynamic processes on WASP-76b.

The detection of such minute atmospheric features at vast distances underscores the advanced capabilities of current astronomical technology and may pave the way for discovering similar crucial phenomena. These could include reflections from potential liquid bodies, which are vital indicators of habitability on other planets.

Research Report:"Asymmetry in the upper atmosphere of the ultra-hot Jupiter WASP-76 b"