Free Astronomy Magazine July-August 2024

19 JULY-AUGUST 2024 ASTRO PUBLISHING mid-infrared light given off by an object depends largely on how hot it is, the brightness data captured by Webb can then be used to calculate the planet’s temperature. The team used Webb’s MIRI (Mid-Infrared In- strument) to measure light from the WASP-43 system every 10 seconds for more than 24 hours. “By observing over an entire orbit, we were able to calculate the tem- perature of different sides of the planet as they rotate into view,” ex- plained Bell. “From that, we could construct a rough map of tempera- ture across the planet.” The measurements show that the dayside has an average temperature of nearly 2,300 degrees Fahrenheit (1,250 degrees Celsius) – hot enough to forge iron. Meanwhile, the night- side is significantly cooler at 1,100 degrees Fahrenheit (600 degrees Celsius). The data also helps locate the hottest spot on the planet (the “hotspot”), which is shifted slightly eastward from the point that re- ceives the most stellar radiation, where the star is highest in the planet’s sky. This shift occurs because of supersonic winds, which move heated air eastward. T his set of maps shows the temperature of the visible side of the hot gas-giant exoplanet WASP-43 b, as the planet orbits its star. The temperatures were calculated based on more than 8,000 brightness measurements of 5- to 12-mi- cron mid-infrared light detected from the star-planet system by MIRI (the Mid- Infrared Instrument) on NASA’s James Webb Space Telescope. In general, the hotter an object is, the more mid-infrared light it gives off. [Illustration: NASA, ESA, CSA, Ralf Crawford (STScI). Science: Taylor Bell (BAERI), Joanna Barstow (The Open University), Michael Roman (University of Leicester)]