Illustration (Artist’s Impression) of WASP-39 b and Its Star

This is an illustration (artist’s impression) showing what the exoplanet WASP-39 b could look like, based on current understanding of the planet.

WASP-39 b is a hot, puffy gas giant planet with a mass 0.28 times that of Jupiter (0.94 times that of Saturn) and a diameter 1.3 times that of Jupiter, orbiting just 0.0486 astronomical units (4 520 000 miles) from its host star. The star, WASP-39, is fractionally smaller and less massive than the Sun. Because it is so close to its star, WASP-39 b is very hot and is likely to be tidally locked, meaning that one side faces the star at all times.

Data collected by Webb’s Near-Infrared Spectrograph (NIRSpec) show unambiguous evidence for carbon dioxide in the atmosphere, while previous observations from Hubble, Spitzer, and other telescopes indicate the presence of water vapour, sodium, and potassium, as well. The planet probably has clouds and some form of weather, but may not have atmospheric bands like those of Jupiter and Saturn.

This illustration is based on indirect transit observations from Webb as well as other space and ground-based telescopes. Webb has not captured a direct image of this planet.

NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Centre providing its detector and micro-shutter subsystems.

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