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

Hot gas giant exoplanet WASP-39 b transit light curve (NIRSpec)

A light curve from the NASA/ESA/CSA James Webb Space Telescope’s NIRSpec (Near-Infrared Spectrograph) shows the change in brightness from the WASP-39 star system over time as the planet transited the star. This observation was made using NIRSpec’s bright object time-series mode, which uses a grating to spread out light from a single bright object (like the host star of WASP-39 b) and measure the brightness of each wavelength of light at set intervals of time.

The background illustration of WASP-39 b and its star is based on current understanding of the planet from Webb spectroscopy and previous ground- and space-based observations. Webb has not captured a direct image of the planet or its atmosphere.

The artist’s concept displays the terminator of the exoplanet, the boundary that separates the planet’s dayside and nightside. By analysing a transmission spectrum of WASP-39 b from Webb’s NIRSpec, astronomers confirmed a temperature difference between the morning and evening, with the evening appearing hotter by about 200 Celsius degrees. They also found evidence for different cloud cover, with the morning being likely cloudier than the evening.

[Image description: The graphic has two parts. At the top is a diagram showing a planet transiting (moving in front of) its star. Below the diagram is a graph showing the change in relative brightness of the star-planet system over time. The diagram and graph are aligned vertically to show the relationship between the geometry of the star-planet system as the planet orbits, and the measurements on the graph.]