Global temperature map of the hot gas-giant exoplanet WASP-43 b. This map was made based on the brightness of 5- to 12-micron mid-infrared light detected from the planet 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. Although the planet is far too close to the blinding light of its star to see on its own, it is possible to calculate its brightness by measuring the brightness of the star-planet system as a whole, and then subtracting the amount of light coming from the star (measured when the planet is behind the star). Webb was able to measure each side of the planet by observing over an entire 19.5-hour orbit. The planet is tidally locked, which means that its rotation rate is the same as its orbital period, so different sides rotate into view as the planet moves around the star. WASP-43 b has an average temperature of about 2,280°F (1,250°C) on the dayside and 1,115°F (600°C) on the nightside. The temperature map also shows that the nightside is probably covered in thick, high clouds. Clouds prevent some of the infrared energy from escaping to space, making the nightside appear cooler than it would if there were no clouds.
