Free Astronomy Magazine July-August 2024

18 JULY-AUGUST 2024 ASTRO PUBLISHING detect atmospheric gases trillions of miles away. WASP-43 b is a “hot Jupiter” type of exoplanet: similar in size to Jupiter, made primarily of hydrogen and helium, and much hotter than any of the giant planets in our own solar system. Although its star is smaller and cooler than the Sun, WASP-43 b orbits at a distance of just 1.3 million miles – less than 1/25 th the distance between Mercury and the Sun. With such a tight orbit, the planet is tidally locked, with one side contin- uously illuminated and the other in permanent darkness. Although the nightside never receives any direct radiation from the star, strong east- ward winds transport heat around from the dayside. Since its discovery in 2011, WASP-43 b has been observed with numerous telescopes, including NASA’s Hubble and now-retired Spitzer space tele- scopes. “With Hubble, we could clearly see that there is water vapor on the dayside. Both Hubble and Spitzer suggested there might be clouds on the nightside,” explained Taylor Bell, researcher from the Bay Area Environmental Research Insti- tute and lead author of a study pub- lished in Nature Astronomy . “But we needed more precise measure- ments from Webb to really begin mapping the temperature, cloud cover, winds, and more detailed at- mospheric composition all the way around the planet.” Although WASP-43 b is too small, dim, and close to its star for a tele- scope to see directly, its short orbital period of just 19.5 hours makes it ideal for phase curve spectroscopy, a technique that involves measuring tiny changes in brightness of the star-planet system as the planet or- bits the star. Since the amount of Webb maps weather on WASP-43 b A n international team of re- searchers has successfully used NASA’s James Webb Space Telescope to map the weather on the hot gas-giant exoplanet WASP-43 b. Precise brightness meas- urements over a broad spectrum of mid-infrared light, combined with 3D climate models and previous ob- servations from other telescopes, suggest the presence of thick, high clouds covering the nightside, clear skies on the dayside, and equatorial winds upwards of 5,000 miles per hour mixing atmospheric gases around the planet. The investigation is just the latest demonstration of the exoplanet science now possible with Webb’s extraordinary ability to measure temperature variations and T he background artist’s concept shows what the hot gas-giant exoplanet WASP-43 b could look like. WASP-43 b is a Jupiter-sized planet circling a star roughly 280 light-years away, in the constellation Sextans. The planet orbits at a distance of about 1.3 million miles (0.014 astronomical units, or AU), completing one circuit in about 19.5 hours. Because it is so close to its star, WASP-43 b is probably tidally locked: its rotation rate and orbital period are the same, such that one side faces the star at all times. [NASA, ESA, CSA, Ralf Crawford (STScI)] by NASA/ESA/CSA Margaret W. Carruthers & Christine Pulliam