They haven't yet done spectroscopy on it. It's mentioned as a future possibility, but right now it's not feasible to do spectroscopy on an exoplanetary atmosphe

They haven't yet done spectroscopy on it. It's mentioned as a future possibility, but right now it's not feasible to do spectroscopy on an exoplanetary atmosphere -- the signal-to-noise you get when you try to measure something as tiny as the effect of a transiting planet's atmosphere on the spectrum of a star is too damn small to be measured with today's instruments. (I just happen to have heard a talk on this very subject a few weeks ago). Maybe in a few decades, though.