Caption
A transmission spectrum captured by NASA’s James Webb Space Telescope reveals the presence of water (H2O) and the possible presence of sulfur dioxide (SO2) and carbon monoxide (CO), but no signs of carbon dioxide (CO2) or methane (CH4), in the atmosphere of the hot sub-Neptune exoplanet TOI-421 b. The observations support the hypothesis that planets this hot (TOI-421 b is about 1,340°F) have clear atmospheres that are not obscured by clouds and haze.
The spectrum was made by measuring the decrease in apparent brightness of different wavelengths (colors) of starlight as the planet transited, or moved across the face of the star. During a transit, some wavelengths of starlight are transmitted through the planet’s atmosphere, while others are partially blocked. Because each molecule absorbs a unique combination of wavelengths, the transmission spectrum can be used to identify gases in the atmosphere.
This spectrum was made by combining data captured in 2023 by Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph).
