Program: GS-2016B-Q-42

Titanium Oxide (TiO) has long been thought to be a key constituent in hot Jupiter atmospheres, leading to temperature inversions due to strong optical absorption of incoming stellar radiation. Until now, it has eluded detection despite enormous efforts. Recently, using HST, we have uncovered strong (but indirect) evidence for its presence in the very hot Jupiter WASP-121b. Here we propose to observe two transits of WASP-121b using GMOS in order to finally confirm the presence of TiO in a hot Jupiter. Differential spectro-photometry with GMOS has already proven extremely successful, reaching precision of 0.1mmag. The TiO signal of WASP-121b is 0.8mmag, therefore easily within reach of GMOS. Our observations will be the first unambiguous detection of TiO, which is key to understanding basic atmospheric physics in the hottest exoplanets.