16450

With atmospheres hotter than 2000 K comma ultra-hot Jupiters provide the unique opportunity to measure both refractory atomic metals and volatile molecules like H2O in their cloud-free transmission spectrum. The recently observed UV-optical (0.2-0.8 micron) transmission spectrum of ultra-hot Jupiter WASP-178b indicates strong absorption at short-wavelengths by atomic metals comma consistent with refractory abundances between 1 and 4 times solar. Here comma we propose to complete WASP-178b.s UV-IR transit spectrum (0.2-1.7 micron) with WFC3-IR-G102 and G141 comma enabling the measurement of volatile abundances through H2O. With a measurement of refractory abundances at short wavelength and volatile abundances in the IR comma we can determine the planet.s rock-to-ice ratio comma providing insight into WASP-178b.s formation and migration history. With the addition of WASP-178b.s IR spectrum comma we can better compare the planet to the broader ultra-hot Jupiter population comma including whether the planet has TiO and VO in its atmosphere.