James Webb Space Telescope Feed Post

Arxiv: VIRA: An Exoplanet Atmospheric Retrieval Framework for JWST Transmission Spectroscopy Published: 3/7/2024 9:00:00 PM Updated: 3/7/2024 9:00:00 PM

Paper abstract: JWST observations are leading to important new insights into exoplanetaryatmospheres through transmission spectroscopy. In order to harness the fullpotential of the broad spectral range and high sensitivity of JWST, atmosphericretrievals of exoplanets require a high level of robustness and accuracy in theunderlying models. We present the VIRA retrieval framework which implements arange of modelling and inference capabilities motivated by early JWSTobservations of exoplanet transmission spectra. This includes threecomplementary approaches to modelling atmospheric composition, threeatmospheric aerosol models, including a physically-motivated Mie scatteringapproach, and consideration of correlated noise. VIRA enables a cascadingretrieval architecture involving a sequence of retrievals with increasingsophistication. We demonstrate VIRA using a JWST transmission spectrum of thehot Saturn WASP-39 b in the ~1-5 \mum range. In addition to confirmingprior chemical inferences, we retrieve molecular abundances for H_2O, CO,CO_2, SO_2 and H_2S, resulting in super-solar elemental abundances oflog(O/H)=-2.0\pm0.2, log(C/H)=-2.1\pm0.2 and log(S/H)=-3.6\pm0.2, alongwith C/O and S/O ratios of 0.83^{+0.05}_{-0.07} and0.029^{+0.012}_{-0.009}, respectively, in the free chemistry case. Theabundances correspond to 20.1^{+10.5}_{-8.1}\times,28.2^{+16.3}_{-12.1}\times and 20.8^{+10.3}_{-7.5}\times solar values forO/H, C/H and S/H, respectively, compared to C/H = 8.67\pm0.35 \times solarfor Saturn. Our results demonstrate how JWST transmission spectroscopy combinedwith retrieval frameworks like VIRA can measure multi-elemental abundances forgiant exoplanets and enable comparative characterisation with solar systemplanets.