Fig. 4: Impact of the C/O ratio and metallicity on the JWST-NIRISS spectrum of WASP-39b.
From: Early Release Science of the exoplanet WASP-39b with JWST NIRISS
a, Variation of the C/O ratio in the best-fit reference model while keeping the metallicity, redistribution and K/O ratio parameters from the reference model the same and fitting for the cloud parameters and scaled planetary radius to best explain the observations. Under these equilibrium conditions, increasing the C/O ratio results in less H2O and more CH4, the latter having spectroscopic signatures incompatible with the observations. To mute these incompatible CH4 features at high C/O ratios, the model requires a higher degree of cloudiness that also mutes any remaining H2O features in the spectrum. b, The same as for panel a but instead we vary the metallicity parameter. The metallicity constraint is driven by the λ > 2 μm data; the high-metallicity models (M/H > 2) expect larger transit depths than that seen in the data. The same reference model is plotted as a thick black line in both panels. We define our errors as the 1σ uncertainties extracted from the 16th and 84th percentiles of the transit depths fit from each pipeline. (https://github.com/afeinstein20/wasp39b_niriss_paper/blob/main/scripts/figure4.py).
