A comprehensive analysis of WASP-17b’s transmission spectrum from space-based observations

Due to its 1770 K equilibrium temperature, WASP-17b, a 1.99 $R_\mathrm{Jup}$, 0.486 $M_\mathrm{Jup}$ exoplanet, sits at the critical juncture between hot and ultra-hot Jupiters. We present 0.3-5 $\mu m$ transmission spectrum, with newly obtained Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) measurements, and, taking advantage of improved analysis techniques, reanalysed HST Imaging Spectrograph (STIS) Spitzer Infrared Array (IRAC) observations. achieve median precision 132 ppm, mean 272 ppm across whole spectrum. additionally make use Transiting Exoplanet Survey Satellite (TESS) ground-based transit observations refine orbital period WASP-17b. To interpret observed atmosphere, we free chemistry retrievals using POSEIDON ATMO retrieval codes respectively. detect absorption due H$_2$O $>7 \sigma$, find evidence CO$_2$ $>3 \sigma$. see no previously detected Na absorption. Across an extensive suite configurations, data favours bimodal solution high or low metallicity modes as result poor constraints in optical, demonstrate importance multiple statistics for model selection. Future James Webb (JWST) GTO observations, combined presented will enable precise on WASP-17b's atmosphere.