WASP-17 b, also called Ditsö̀, is a hot gas giant that orbits its star at a distance of just 0.051 AU (about 4.75 million miles, or one-eighth the distance between Mercury and the Sun), completing one full circuit in about 3.7 Earth-days. The system lies within the Milky Way, about 1,300 light-years from Earth, in the constellation Scorpius. With a volume more than seven times that of Jupiter and a mass less than one-half of Jupiter, WASP-17 b is an extremely puffy planet. Its short orbital period, large size, and thick, extended atmosphere make it ideal for observation using transmission spectroscopy, which involves measuring the effects of the planet’s atmosphere on the starlight filtering through it. WASP-17 b’s atmosphere is composed primarily of hydrogen and helium, along with small amounts of water vapor and hints of carbon dioxide and other molecules. Observations of 5- to 12-micron infrared light from Webb's MIRI (Mid-Infrared Instrument) show that WASP-17 b’s atmosphere also contains clouds made of nanocrystals of quartz (SiO2). WASP-17 b is tidally locked and has a retrograde orbit. Its temperature ranges from about 1,000 kelvins (1,350 degrees F or 725 degrees C) on the cooler nightside to nearly 2,000 kelvins (3,150 degrees F or 1,725 degrees C) on the side in permanent daylight. The star, WASP-17 (also called Diwö), is an F-type star: slightly larger, more massive, hotter, and whiter than the Sun. This artist’s concept is based on new data gathered by MIRI as well as previous observations from other ground- and space-based telescopes, including NASA’s Hubble and retired Spitzer space telescopes. Webb has not captured any images of the planet.