Studying the atmosphere of exoplanets—planets beyond our solar system—that orbit close to their parent stars presents significant challenges. The intense stellar irradiation heats the planet’s day side, causing its atmosphere to expand and become tenuous. This tenuous atmosphere is difficult to observe with telescopes, and its composition and dynamics are not well understood.

We were able to overcome these challenges by using the high-resolution spectrograph on the European Southern Observatory’s Very Large Telescope (VLT) in Chile. We observed an exoplanet called WASP-121b, which is a “hot Jupiter”—a gas giant planet that orbits very close to its star.

Our observations revealed the presence of a number of interesting features in WASP-121b’s atmosphere. These features include:

Ruby clouds: We found that WASP-121b’s atmosphere contains clouds of corundum, a mineral that is found in rubies. These clouds are thought to form in the planet’s extremely high-temperature upper atmosphere, where temperatures can reach up to 2,500 degrees Celsius (4,532 degrees Fahrenheit).

Water behaving strangely: We also found that water vapor in WASP-121b’s atmosphere is behaving strangely. Water vapor is typically found in the lower atmosphere of planets, but on WASP-121b, we found that it is present in the upper atmosphere as well. This is thought to be due to the planet’s strong winds, which are transporting water vapor from the lower atmosphere to the upper atmosphere.

Our observations of WASP-121b provide new insights into the atmospheres of hot Jupiters. These planets are thought to be common in the universe, and understanding their atmospheres is important for understanding the evolution of planetary systems.

Our study was published in the journal *Astronomy & Astrophysics*.