Products and Models for "Early Release Science of the Exoplanet WASP-39b with JWST NIRCam"

Associated Publication: https://www.nature.com/articles/s41586-022-05590-4

OVERVIEW: 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 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 that, 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 µm, exhibit minimal systematics, and reveal well-defined molecular absorption features in the planet’s spectrum. Specifically, we detect gaseous H₂O in the atmosphere and place an upper limit on the abundance of CH₄. The otherwise prominent CO₂ feature at 2.8 µm is largely masked by H₂O. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1–100× solar (i.e., an enrichment of elements heavier than helium relative to the Sun) and a sub-stellar carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere.