Revisiting a Classic: A Comprehensive Reanalysis of the Transmission Spectrum of the Archetypal Hot Jupiter WASP-17b

WASP-17b is an archetypal hot Jupiter, marked by its frequent inclusion in theoretical and atmospheric retrieval studies, and in JWST Cycle 1 observations. Its inflated radius and long transit make it one of the very best targets for atmospheric characterisation, and as such, transmission spectroscopy of the planet has been performed both from the ground and with space-based telescopes. However, the existing space-based observations, upon which many of these studies critically rely, occurred before many of the now widely used high precision observing modes and analysis techniques were developed.

In this talk, I will present analysis of new high precision WFC3 IR observations, along with a consistent reanalysis of the Hubble and Spitzer data previously presented in Sing et al. 2016. Our updated 0.3-5 μm transmission spectrum achieves a markedly improved average precision of 272 ppm, taking advantage of recent significant advances in exoplanet data reduction and analysis techniques. I will also discuss our comprehensive atmospheric retrieval analysis of the transmission spectrum, through which we detect H₂O absorption at >7σ, and find evidence of CO₂ absorption at >3σ. These retrievals also uncovered complexities that highlight both the importance of using robust statistics for model selection and the need for high precision panchromatic observations, as we transition to a new era of atmospheric characterisation with JWST.