The magnetic effects of the Tunguska events in 1908

In the paper a new explanation for the magnetic effect registered by magnetographs of the Irkutsk Observatory during the Tunguska catastrophe in 1908 is presented. The effect was due to a local perturbation of the geomagnetic field, which began two and a half minutes after the main explosion at the epicenter of the Tunguska event in the basin of the Podkamennaya Tunguska River in Krasnoyarsk Region. The disturbance lasted for 6 hours and had a non-monotonic behavior. By now, several hypotheses have been proposed to explain this effect. But the most part of them is not consistent with other data, and the others have been not yet confirmed by quantitative parameters or model computations. The present explanation is based on the established fact of the sputtering of microparticles and submicron inclusions of iron and its oxides in the atmosphere as a result of the ablation and the explosion of the main part of the Tunguska cosmic body and its other fragments. These microparticles and inclusions, when cooling below a certain temperature (called the Curie point) in the Earth's magnetic field due to the well-studied effect of termomagnetization, received a significant unit magnetic moment. After that they moved with regard to the interaction with the Earth’s magnetic field, mainly along the magnetic field lines. In consequence of the deposition, they formed zones of high magnetization and high magnetic susceptibility of soils in the Tunguska catastrophe area. These zones were carefully marked out by A. P. Boyarkina and S. D. Sidoras during the paleomagnetic studies of friable sediments in the Tunguska catastrophe area. Moreover, they differ significantly from the areas of increased deposition of other, non-magnetic materials. Furthermore, the geometrical analysis of deposition areas of magnetic materials admits estimating the trajectory slope of the main cosmic body. This estimation in combination with other data gives a quite large entrance angle of the Tunguska cosmic body to the surface of the Earth about 76º This angle magnitude is in agreement with the results of the modern mathematical modeling of the explosion height of the main part of the Tunguska cosmic body.