We investigated the irradiation of H2O-CO2 ice mixtures with energetic electrons in an ultrahigh vacuum chamber. Our laboratory studies confirm that - besides carbon monoxide-carbonic acid (H2CO3) is the dominant reaction product of these irradiation processes. We present the kinetics and dynamics of its formation and elucidate on the temperature-dependence (10-60 K) of the formation processes. Our experimental results indicate that carbonic acid might be present in the solar system ices that contain both water (H2O) and carbon dioxide (CO2) and are exposed by radiation from the solar wind and planetary magnetospheres. Published by Elsevier B.V.