WASP-39b is turning out to be one of the more important WASP discoveries, being observed with the Hubble Space Telescope, the Spitzer Space Telescope and large ground-based telescopes such as the VLT. This is because, as a Saturn-mass planet with a bloated radius, it has a low surface gravity and so is ideal for atmospheric characterisation. Further, it has relatively clear skies showing spectral features.

Now a team led by Hannah Wakeford from Exeter University have put the different data-sets together to produce the widest-coverage spectrum of the planet so far:

The dominant spectral features are due to water vapour, while there are narrower lines due to sodium (Na) and potassium (K) and a Rayleigh-scattering slope at the blue end.

The main finding from fitting the water features is that the atmospheric metallicity must be at least 100 times that of the sun. This high value shows the diversity of exoplanets. The authors conclude that “WASP-39b is an ideal target for follow-up studies with the James Webb Space Telescope”.