I. V. Nemchinov

Ionospheric and magnetospheric disturbances caused by impacts of small comets and asteriods

Disturbances in the Earths’s ionosphere and magnetosphere caused by impacts of small comets and asteroids (with diameters from 50–60 m to 1–2 km) are analyzed. Two-dimensional hydrodynamical computations of the passage of a cosmic body through the atmosphere with allowance for deceleration and destruction due to aerodynamic loading and formation of the wake behind the body are performed. The tenuous wake facilitates an upward ejection of the plume (heated air and ablation products of the cosmic body). Numerical simulations of the motion of the plume and of its interaction with the geomagnetic field are performed. It is shown that part of the plume moves at higher than escape velocity. The rising plume operates as an MHD generator. Field-aligned currents heat the ionosphere and change its conductivity. The estimated magnetic variations are on the order of those of typical magnetic storms (for bodies with sizes comparable to the Tunguska meteorite) and are even higher for cosmic bodies with diameters of 200–400 m. Excitation of MHD waves is demonstrated. These disturbances are capable of triggering precipitation of particles from radiation belts and exciting intense electromagnetic noise. Strong oscillations of conducting ionospheric layers propagate radially from the place of impact of the low-velocity part of the plume to large distances from the impact point. For a 1-km body the energy of the high-velocity plume is comparable to that of the Earths’s magnetic field. This causes extremely intense magnetospheric disturbances. However, even 200-to 400-m bodies whose high-velocity part of the plume has energies exceeding 0.4–3 Mt TNT—i.e., much lower than the initial kinetic energy of the intruding body—produce global ionospheric and magnetospheric disturbances.

Bolides in the Earth Atmosphere

The incremental influx of cosmic material on the Earth shows few maxima in the depen- dence on the size of falling meteoroids (Ceplecha 1992). The largest one corresponds to the impact of asteroid-sized bodies—about 3 km in size and mass of about 10 14 kg. The second maximum reaches almost the same value and corresponds to the bodies with masses of 10 4 -10 6 kg (i.e., with diameters about 1-10 m). The information about these meteoroids is scarce. These bodies create the appearance of very bright meteors in the Earths atmosphere (bolides and superbolides). Sizes of these bodies are one to two orders of magnitude smaller than the sizes of meteoroids, which create asteroid hazards. It is possible to observe bolides and superbolides on a regular basis.

Evaluation of Light Flashes Caused by Impacts of Small Comets on the Surface of the Moon

Images of the dayglow of the Earths atmosphere in the ultraviolet wavelength region obtained by the photometer of the spacecraft Dynamics Explorer revealed dark spots of the order of 50 km in diameter. These “atmospheric holes” were interpreted by the American physicist Frank as concentrations of water vapor formed as a result of the disintegration and vaporization of so-called small comets at high altitudes. An analysis of the same images showed that their explanation requires a frequency of comet collisions with the Earth as high as 20 events a minute! This sensational hypothesis evoked a heated scientific debate. The paper below contains an analysis of the possibility of observing Franks hypothetical comets during their collisions with the Moon. By solving a two-dimensional radiative–gasdynamic problem, the authors demonstrate that the flashes occurring during such impacts can be observed from the Earth with ordinary telescopes.