Are ultrahigh energy cosmic rays heavy nuclei?

A new approach to estimate the composition of cosmic rays is proposed. It is found that the zenith angle distributions and muon components of extensive air showers observed by the Yakutsk and AGASA arrays for energies E>1019 eV and E>4×1019 eV differ from each other. It is suggested that the primary cosmic rays at E>4×1019eV are heavier than those at E∼1019 eV. In our method we selected one variant to estimate the shower energy from two variants, as suggested by physicists of the SUGAR array. According to the “Hillas-E” model, the SUGAR array has detected 8 showers with energy E>1020 eV.