Water and methane in a juvenile transiting exoplanet

Water and methane in a juvenile transiting exoplanet Water and methane in a juvenile transiting exoplanet We propose to observe the transit spectrum of recently discovered young warm Jupiter V1298 Tau b using the HST/WFC3 instrument near 1.4 microns. We will measure the atmospheric properties of this likely inflated gas giant (~23Myr, 0.9 Jupiter radii, likely <90 Earth masses, 24 day period). At equilibrium temperature (650K), we expect the presence of methane in the atmosphere of this object, and we will have the precision to measure it. This will allow us to evaluate the equilibrium chemistry and temperature of the planet's atmosphere. We will place constraints on its metallicity and the clouds/hazes present. We will compare our results to the atmospheric properties of young directly imaged planets to evaluate the influence of the location within the disk and the stellar irradiation on planetary compositions. This observation represents an opportunity for HST to yet again open a new chapter of exoplanet characterization of a completely unexplored class of planets. Our observations will inform and enable future studies with JWST.