The team of researchers 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.