“With this observation, we’re really getting a global view of an exoplanet’s meteorology,” Mikal-Evans says.

Astronomers at MIT have obtained the clearest view of the dark side of an exoplanet that is known to be “tidally-locked” with its star. Their observations, which include measurements of the planet’s permanent day-side, provide scientists a clear view of the planet’s atmosphere.

The planet that is currently being studied is the exoplanet that appears in Nature Astronomy, which is known as the planet “WASP-121b”, a massive gas planet that is about twice the size of Jupiter. The planet is a very hot version of Jupiter and was discovered in 2015 orbiting a star that is about 850 light-years from Earth. WASP-121b has one of the shortest orbits detected up to date, with a full period of 30 hours. It is also tidally locked, which means that the star-facing side, known as the “day” side, is permanently being roasted, while its “night” side is turned forever towards outer space.

Previously, astronomers detected water vapor on the planet and studied how the atmospheric temperature changes with differences in altitude on the planet’s day side. The new study gives more insight into atmospheric conditions. The study has captured the dramatic temperature changes from the day to the night side and measured the temperature difference with different altitudes. They also tracked the presence of water in the atmosphere, to show, for the very first time, how water cycles from the day and night side. 

On Earth, the water first evaporates, condenses, then rains down. However, on WASP-121b, the water cycle is far more intense. On the day side, the atoms that make up water are ripped apart by extremely high temperatures that exceed 3000 degrees, Kelvin. The atoms are blown around to the night side, where the temperature is colder and the atoms recombine into the water, which then goes back to the day side, and the cycle repeats. The team calculated that the planet’s water cycle is sustained by winds that blow the atoms around the planet at speeds up to 5 kilometers per second, which is more than 11000 miles per hour.

Cite: https://news.mit.edu/2022/hot-jupiter-dark-side-0221