Early Release Science of the exoplanet WASP-39b with JWST NIRISS

Feinstein, Adina D.; Radica, Michael; Welbanks, Luis; Murray, Catriona Anne; Ohno, Kazumasa; Coulombe, Louis-Philippe; Espinoza, Néstor; Bean, Jacob L.; Teske, Johanna K.; Benneke, Björn; Line, Michael R.; Rustamkulov, Zafar; Saba, Arianna; Tsiaras, Angelos; Barstow, Joanna K.; Fortney, Jonathan J.; Gao, Peter; Knutson, Heather A.; MacDonald, Ryan J.; Mikal-Evans, Thomas; Rackham, Benjamin V.; Taylor, Jake; Parmentier, Vivien; Batalha, Natalie M.; Berta-Thompson, Zachory K.; Carter, Aarynn L.; Changeat, Quentin; dos Santos, Leonardo A.; Gibson, Neale P.; Goyal, Jayesh M.; Kreidberg, Laura; López-Morales, Mercedes; Lothringer, Joshua D.; Miguel, Yamila; Molaverdikhani, Karan; Moran, Sarah E.; Morello, Giuseppe; Mukherjee, Sagnick; Sing, David K.; Stevenson, Kevin B.; Wakeford, Hannah R.; Ahrer, Eva-Maria; Alam, Munazza K.; Alderson, Lili; Allen, Natalie H.; Batalha, Natasha E.; Bell, Taylor J.; Blecic, Jasmina; Brande, Jonathan; Caceres, Claudio; Casewell, S. L.; Chubb, Katy L.; Crossfield, Ian J. M.; Crouzet, Nicolas; Cubillos, Patricio E.; Decin, Leen; Désert, Jean-Michel; Harrington, Joseph; Heng, Kevin; Henning, Thomas; Iro, Nicolas; Kempton, Eliza M. -R.; Kendrew, Sarah; Kirk, James; Krick, Jessica; Lagage, Pierre-Olivier; Lendl, Monika; Mancini, Luigi; Mansfield, Megan; May, E. M.; Mayne, N. J.; Nikolov, Nikolay K.; Palle, Enric; Petit dit de la Roche, Dominique J. M.; Piaulet, Caroline; Powell, Diana; Redfield, Seth; Rogers, Laura K.; Roman, Michael T.; Roy, Pierre-Alexis; Nixon, Matthew C.; Schlawin, Everett; Tan, Xianyu; Tremblin, P.; Turner, Jake D.; Venot, Olivia; Waalkes, William C.; Wheatley, Peter J.; Zhang, Xi
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The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy1-4. However, these efforts have been hampered by modelling degeneracies between composition and cloud properties that are caused by limited data quality5-9. Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6-2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and signatures of clouds. The precision and broad wavelength coverage of NIRISS/SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favouring a heavy-element enhancement (`metallicity') of about 10-30 times the solar value, a sub-solar carbon-to-oxygen (C/O) ratio and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet's terminator.