Absolutely right. Here is a recent paper on exoplanet atmosphere characterization by JWST: https://arxiv.org/abs/1511.05528 https://arxiv.org/abs/1511.05528 --

Absolutely right. Here is a recent paper on exoplanet atmosphere characterization by JWST: https://arxiv.org/abs/1511.05528 https://arxiv.org/abs/1511.05528 -- the overview is at https://jwst.nasa.gov/origins.html https://jwst.nasa.gov/origins.html As you say, the contrast between seeing (star + planet) during a transit, versus star alone, is enough to identify absorption of infrared light by some chemical species. The simulations in the above paper basically show they can infer some chemical abundances (carbon, oxygen) and some atmospheric parameters (inversion layers) for Neptunes and Jupiters. But probably not for Earths, so not for the system in the OP. Even for big, thick atmospheres, these spectroscopic characterizations take a lot of observation time (like, days). The race is indeed on to develop instruments and algorithms for this problem -- e.g., detecting CH4 or CO2 in an exo-Earth atmosphere. There's feverish activity in the Astronomy community around this, and post-JWST missions are being formulated to tackle the problem.