Free Astronomy Magazine September-October 2024

SEPTEMBER-OCTOBER 2024 circles, one from the evening, and the other from the morning. Data reveals the evening as signifi- cantly hotter, a searing 1,450 de- grees Fahrenheit (800 degrees Cel- sius), and the morning a relatively cooler 1,150 degrees Fahrenheit (600 degrees Celsius). “It’s really stunning that we are able to parse this small difference out, and it’s only possible due Webb’s sensitivity across near-infrared wave- lengths and its extremely stable pho- tometric sensors,” said Espinoza. “Any tiny movement in the instrument or with the observatory while collecting data would have severely limited our ability to make this detection. It must be extraordinarily precise, and Webb is just that.” Extensive modeling of the data ob- tained also allows researchers to in- vestigate the structure of WASP-39 b’s atmosphere, the cloud cover, and why the evening is hotter. While future work by the team will study how the cloud cover may af- fect temperature, and vice versa, as- tronomers confirmed gas circulation around the planet as the main cul- prit of the temperature difference T his transmission spectrum, captured using Webb’s NIRSpec (Near-Infrared Spectrograph) PRISM bright object-time series mode, shows the amounts of near-infrared starlight blocked by the atmosphere of hot gas giant exoplanet WASP-39 b. The spectrum shows clear evidence for water and carbon dioxide, and a variation in temperature between the morning and evening on the exo- planet. The blue and yellow lines are a best-fit model that takes into account the data, the known properties of WASP-39 b and its star (e.g., size, mass, tem- perature), and assumed characteristics of the atmosphere. [NASA, ESA, CSA, Ralf Crawford (STScI)] on WASP-39 b. On a highly irradi- ated exoplanet like WASP-39 b that orbits relatively close to its star, re- searchers generally expect the gas to be moving as the planet rotates around its star: Hotter gas from the dayside should move through the evening to the nightside via a pow- erful equatorial jet stream. Since the temperature difference is so ex- treme, the air pressure difference would also be significant, which in turn would cause high wind speeds. Using General Circulation Models, 3- dimensional models similar to the ones used to predict weather pat- terns on Earth, researchers found that on WASP-39 b the prevailing winds are likely moving from the night side across the morning termi- nator, around the dayside, across the evening terminator and then around the nightside. As a result, the morning side of the terminator is cooler than the evening side. In other words, the morning side gets slammed with winds of air that have been cooled on the nightside, while the evening is hit by winds of air heated on the dayside. Research sug- gests the wind speeds on WASP-39 b can reach thousands of miles an hour! “This analysis is also particu- larly interesting because you’re get- ting 3D information on the planet that you weren’t getting before,” added Espinoza. “Because we can tell that the evening edge is hotter, that means it’s a little puffier. So, theoretically, there is a small swell at the terminator approaching the nightside of the planet.” !