Cosmic dust in modern ferromanganese nodules

Resumo

This work is about the identification of modern cosmic dust that had survived heating during its high-velocity passage through the Earth’s atmosphere from ³He isotope concentrations in marine (Gulf of Finland) ferromanganese nodules (FMNs). The measured bulk composition of helium includes components of various origins, enabling the determination of the age (1800 years) of the shallow-water Baltic FMNs and the average time of exposure (8 × 10⁷ years) of cosmic dust particles during their existence in space. The concentration of cosmic dust per gram of FMN material is found to be 0.036 μg. The contribution of solar-wind helium to the Earth’s atmospheric helium is found to be small. The experiments are conducted by the stepheating method in vacuo with the subsequent mass-spectrometric analysis of the helium released from the samples.