Early Release Science of the exoplanet WASP-39b with JWST NIRCam
Authors: Ahrer Eva-Maria , Stevenson Kevin B. , Mansfield Megan , Moran Sarah E. , Brande Jonathan , Morello Giuseppe , Murray Catriona A. , Nikolov Nikolay K. , Petit dit de la Roche Dominique J. M. , Schlawin Everett , Wheatley Peter J. , Zieba Sebastian , Batalha Natasha E. , Damiano Mario , Goyal Jayesh M. , Lendl Monika , Lothringer Joshua D. , Mukherjee Sagnick , Ohno Kazumasa , Batalha Natalie M. , Battley Matthew P. , Bean Jacob L. , Beatty Thomas G. , Benneke Björn , Berta-Thompson Zachory K. , Carter Aarynn L. , Cubillos Patricio E. , Daylan Tansu , Espinoza Néstor , Gao Peter , Gibson Neale P. , Gill Samuel , Harrington Joseph , Hu Renyu , Kreidberg Laura , Lewis Nikole K. , Line Michael R. , López-Morales Mercedes , Parmentier Vivien , Powell Diana K. , Sing David K. , Tsai Shang-Min , Wakeford Hannah R. , Welbanks Luis , Alam Munazza K. , Alderson Lili , Allen Natalie H. , Anderson David R. , Barstow Joanna K. , Bayliss Daniel , Bell Taylor J. , Blecic Jasmina , Bryant Edward M. , Burleigh Matthew R. , Carone Ludmila , Casewell S. L. , Changeat Quentin , Chubb Katy L. , Crossfield Ian J. M. , Crouzet Nicolas , Decin Leen , Désert Jean-Michel , Feinstein Adina D. , Flagg Laura , Fortney Jonathan J. , Gizis John E. , Heng Kevin , Iro Nicolas , Kempton Eliza M.-R. , Kendrew Sarah , Kirk James , Knutson Heather A. , Komacek Thaddeus D. , Lagage Pierre-Olivier , Leconte Jérémy , Lustig-Yaeger Jacob , MacDonald Ryan J. , Mancini Luigi , May E. M. , Mayne N. J. , Miguel Yamila , Mikal-Evans Thomas , Molaverdikhani Karan , Palle Enric , Piaulet Caroline , Rackham Benjamin V. , Redfield Seth , Rogers Laura K. , Roy Pierre-Alexis , Rustamkulov Zafar , Shkolnik Evgenya L. , Sotzen Kristin S. , Taylor Jake , Tremblin P. , Tucker Gregory S. , Turner Jake D. , de Val-Borro Miguel , Venot Olivia , Zhang Xi 
Published: January 2023

Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy (for example, refs.1,2) provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution and high precision, which, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST’s Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0–4.0 micrometres, exhibit minimal systematics and reveal well defined molecular absorption features in the planet’s spectrum. Specifically, we detect gaseous water in the atmosphere and place an upper limit on the abundance of methane. The otherwise prominent carbon dioxide feature at 2.8 micrometres is largely masked by water. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1–100-times solar (that is, an enrichment of elements heavier than helium relative to the Sun) and a substellar C/O ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation (for example, refs.3,4,) or disequilibrium processes in the upper atmosphere (for example, refs.5,6).