S/N of the atmospheric signatures in the J band as a function of the planetary mass for exoplanets orbiting M-type stars with masses between 8 and 14 Earth mass. The S/Ns have been normalized to a reference S/N of 100 for the planet AU Mic b. In the considered mass range, the best S/Ns are obtained for the exoplanets GJ1214 b and GJ3470 b, with S/Ns of about half the one of AU Mic b.