James Webb Space Telescope Discovery

Webb Maps and Finds Traces of Water in an Ultra-hot Gas Giant's Atmosphere

Hot exoplanet summer! Webb analyzed the atmosphere of an ultrahot gas giant and mapped its temperatures. Despite scorching heat (nearly 5000 F or 2700 C), WASP-18 b has small amounts of atmospheric water — precisely measured due to Webb's sensitivity. WASP-18b zips around its star so fast that its year is only 23 hours long. It is also tidally locked, meaning one side of it always faces its star. Credit: NASA/JPL-Caltech (R. Hurt/IPAC) The team obtained the thermal emission spectrum of WASP-18 b by measuring the amount of light it emits over NASA’s James Webb Space Telescope’s NIRISS SOSS 0.85-2.8 um wavelength range, capturing 65% of the total energy emitted by the planet. WASP-18 b is so hot on the day side of this tidally-locked planet (the same side always faces its star, as the Moon to Earth) that water vapor molecules would break apart. The Webb Telescope directly observed water vapor on the planet in even relatively small amounts, indicating the sensitivity of the observatory. WASP-18 b, seen in an artist concept, is a gas giant exoplanet 10 times more massive than Jupiter that orbits its star in just 23 hours. Researchers used NASA’s James Webb Space Telescope to study the planet as it moved behind its star. Temperatures there reach 5,000 degrees Fahrenheit (2,700 C).