Probability distributions (color scale) normalized to one at maximum as functions of the fractional mass depth, log q = log[1 − m(r)/M_⋆], obtained, from top to bottom, for the mass fraction of hydrogen, helium, carbon, and oxygen inside TIC 278659026. The red areas indicate the values, as functions of log q, corresponding to the best-matching seismic models. These distributions are derived from the evaluation of 1 555 425 stellar models calculated during exploration of parameter space.