The atmosphere of the gas giant planet HAT-P-7 b changes irregularly over time, reports a study published online in Nature Astronomy this week. Such weather-like changes have not been previously observed on a giant planet outside our Solar System.

Observations of exoplanetary atmospheres, while still difficult to perform, have become more common in recent years. Detecting any changes in their atmospheres, however, is significantly more complicated, as currently available instruments do not usually have the required sensitivity. Such observations are nevertheless invaluable for our understanding of how exoplanets work.

David Armstrong and colleagues analysed four years of light intensity fluctuation measurements that the Kepler spacecraft made of HAT-P-7 b, a gas giant exoplanet with a surface temperature of approximately 2,200 K (1,927 °C; 3,500 °F) that rotates approximately every two days around its star. They found that the position of the peak brightness changed with time, due to variations in atmospheric wind speed. This dynamic caused, in turn, variations in the cloud coverage of the planet.

The authors note that their discovery opens the prospect of monitoring weather changes on exoplanets in the future, and that planned space missions such as JWST, CHEOPS or PLATO, which feature higher sensitivity instruments, will be able to rapidly increase the number of such studies.