Hot gas giant exoplanet WASP-39 b (artist’s concept)

Hot gas giant exoplanet WASP-39 b transmission spectrum (NIRSpec)

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 800 degrees Celsius, and the morning a relatively cooler 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.

[Image description: Graphic titled “Hot Gas-Giant Exoplanet WASP-39 b Transmission Spectrum: Morning Terminator vs. Evening Terminator” showing two sets of data points with error bars and a best-fit model for on a graph of Amount of Light Blocked by atmosphere on the y-axis versus Wavelength of Light in microns on the x-axis. In the background is an illustration of a pink-orange planet with wispy white clouds.]