Astronomy Tea Talk
Close-in exoplanet and exomoon systems orbiting within << 10 R_Sun of their host stars are expected to experience extreme evaporation. At present, it would appear that thermal outgassing and photoevaporation drive planetary evolution from sub-Neptunes to super-Earths for Sun-like stars, as observed by the California-Kepler survey, valley. This is due to evaporation rates >> 10^6 kg/s (~0.42 M_moon/Gyr) corresponding to factor of two changes in transit radii due to the low-density nature of a H/He envelope. In the absence of a hydrogenated envelope, escape begins to erode a significant quantity of metals from a rocky surface itself, viewable by the technique of evaporative transmission spectroscopy. We describe how NaD2/D1 in particular can begin to geophysically characterize several transiting systems today.