Refractory elements in the gas phase for comet 67P/Churyumov-Gerasimenko. Possible release of atomic Na, Si, and Fe from nanograins

Context. Gas-phase sodium, silicon, potassium, and calcium were previously identified in mass spectra recorded the coma of comet 67P/Churyumov-Gerasimenko, target European Space Agency’s Rosetta mission. The major release process for these atoms was as sputtering by solar wind. More recently, remote observations numerous comets over a range heliocentric distances revealed presence metal iron nickel that had been released either from nucleus or distributed source with short scale length. Sputtering, however, has dismissed due to attenuation wind comae some observed targets.