Concentrations of radionuclides in rocky planet mantles may be critical for the habitability of Earth-like planets as such planets with higher abundances likely lack a persistent dynamo for a significant fraction of their lifetimes and those with lower concentrations may often be geologically inert. Planetary dynamos create strong magnetic fields which may often be necessary for life to develop or persist as they shield planets from solar winds and cosmic radiation. The electromagnetic emission spectra of stars could be used to identify those which are more likely to host habitable Earth-like planets. As of 2020 radionuclides are thought to be produced by rare stellar processes such as neutron star mergers. Additional geological characteristics may be essential or major factors in the habitability of natural celestial bodies – including some that may shape the body's heat and magnetic field. Some of these are unknown or not well understood and being investigated by planetary scientists, geochemists and others.