FIG. 1.

Comparison of the effect of refraction on (A) an exoplanet around an M dwarf and (B) a planet around a Sun-like star with both planets receiving the same total flux. The dashed circles are the planetary atmospheres. The solid lines represent different refracted paths through the atmosphere, and the dashed lines are the hypothetical paths to a distant observer observing the planet in transit transmission. Only paths that lie exactly on that dashed line will be observed. For the M dwarf case, there will be a path connecting the star to the observer through the atmosphere at this particular tangent height. However, there is no path in the Sun-like star case. This means that a transit transmission spectrum of the planet around the M dwarf can theoretically probe higher pressures of the atmosphere than in the Sun-like star case.