This transmission spectrum, captured using Webb’s NIRSpec (Near-Infrared Spectrograph) PRISM bright object-time series mode, shows the amounts of near-infrared starlight blocked by the atmosphere of hot gas giant exoplanet WASP-39 b. The spectrum shows clear evidence for water and carbon dioxide, and a variation in temperature between the morning and evening on the exoplanet.
New analysis of the transmission spectrum of WASP-39 b builds two different spectra from the stationary day/night boundary on the exoplanet, essentially splitting this terminator region into two semicircles, one from the evening, and the other from the morning. Data reveals the evening as significantly hotter, a searing 1,450 degrees Fahrenheit (800 degrees Celsius), and the morning a relatively cooler 1,150 degrees Fahrenheit (600 degrees Celsius).
The blue and yellow lines are a best-fit model that takes into account the data, the known properties of WASP-39 b and its star (e.g., size, mass, temperature), and assumed characteristics of the atmosphere.
