Study of hot Jupiter WASP-121B expands ideas about exoplanet weather Observations with the Hubble telescope and computer models have allowed researchers to study the weather of exoplanet WASP-121B in more detail. This hot gas planet lies 880 light-years from Earth and has attracted the interest of astronomers due to its extreme conditions and proximity to its star.

WASP-121B has a mass 16% more than Jupiter and is only 3.88 million kilometers from its parent star (just 2.6% of the distance between Earth and the Sun). The planet orbits the star in just 1.27 days. That is, her year on Earth lasts only 1.27 days on Earth. A unique feature of WASP-121B is that it always rotates on the same side of the star. On the side that is constantly illuminated, the planet’s surface becomes very hot, reaching 2329 degrees Celsius. As a result, the atmosphere expands, increasing the radius of the planet by 75% compared to Jupiter. WASP-121B is a perfect example for observation due to its size. Astronomers examined WASP-121B four times with the Hubble telescope: in June and November 2016, in March 2018, and in February 2019. In each case, the planet was in a different position, passing in front of or behind the star. This allowed a team of astronomers led by Caltech’s Jack Skinner to determine how the brightness of his WASP-121B changes at different viewing angles and phases. Using this data and computer models, the astronomer was able to predict the weather with his WASP-121B.

Observations by Hubbra showed that WASP-121B’s atmosphere is dynamic and changeable. The temperature gradient between a planet that is always illuminated and a planet that is always in shadow causes storms, hurricanes, and even cold and warm fronts. These weather phenomena on Earth change in about 5 days. “We used information from these observations to determine WASP-121B’s chemical composition, temperature, and cloud-free atmosphere at various points in time. This gives us insight into how Earth changes over time. “We were able to see in great detail what the researchers thought was going on,” said co-author Quentin Change. This isn’t the first time astronomers have studied the weather on an exoplanet. For example, in 2009 we used the Spitzer Space Telescope to observe another hot Jupiter, HD 80606B. This Jupiter moves in an elongated orbit around the star, similar to the orbit of a comet, leading to intense heating and the formation of huge storms. They exist in the atmosphere and disappear as the planet moves away from the star. However, WASP-121B meteorologists made significant progress in studying exoplanet weather. “The data set collected covers a significant portion of the observation time for the same planet and is currently the only data set that is consistent across such repeated observations,” Change said.

Meteorological research on WASP-121B is important for expanding knowledge in planetary meteorology and exoplanet research. The data obtained will help us better understand processes in the atmospheres of planets outside our solar system and determine how and how accurately we can predict exoplanet weather.