Vol 52, No 3 (2018)

Numerical simulation of the destruction, evaporation, deceleration, and emission of the Chelyabinsk superbolide has been carried out. The model assumes that the main energy is radiated in the stage when the asteroid is already completely destroyed and does not have solidity (quasi-liquid approximation). The radiation transfer during the motion is taken into account in the approximation of radiative heat conductivity and volumetric emission. The distributions of temperatures and densities are obtained at the moments when the bolide is at different altitudes. The intensity of radiation at the Earth’s surface is calculated at certain times by solving the radiative transfer equation along the rays passing through the luminous region using the air and LL-chondrite vapor absorption coefficients. The features of superbolide radiation, the contribution of air and vapor to radiation, the size of the luminous region, and the radiation spectrum have been considered. The calculated efficiency of radiation—17% of the kinetic energy of a cosmic body—agrees with the results of observations. It is shown that due to anisotropy of the superbolide radiation, the determination of luminous efficiency from measurements can depend on the observation point. For estimations, the pointsource approximation can be used, but in general, the source luminous efficiency is unknown, and its location is determined with some error; therefore, numerical simulation is required to reliably estimate the consequences of space body falls.

In this work we study in a general view slow rotating planets as Venus or Titan which present superrotating winds in their atmospheres. We are interested in understanding what mechanisms are candidates to be sources of net angular momentum to generate this kind of dynamics. In particular, in the case of Venus, in its atmosphere around an altitude of 100 km relative to the surface, there exists winds that perform a full rotation around the planet in four terrestrial days, whereas the venusian day is equivalent to 243 terrestrial ones. This phenomenon called superrotation is known since many decades. However, its origin and behaviour is not completely understood. In this article we analise and ponderate the importance of different effects to generate this dynamics.

The four-planet problem is solved by constructing an averaged semi-analytical theory of secondorder motion by planetary masses. A discussion is given of the results obtained by numerical integration of the averaged equations of motion for the Sun–Jupiter–Saturn–Uranus–Neptune system over a time interval of 10 Gyr. The integration is based on high-order Runge–Kutta and Everhart methods. The motion of the planets is almost periodic in nature. The eccentricities and inclinations of the planetary orbits remain small. Short-period perturbations remain small over the entire interval of integration. Conclusions are drawn about the resonant properties of the motion. Estimates are given for the accuracy of the numerical integration.

We consider the estimates of the main forces acting on dust particles near a cometary nucleus. On the basis of these estimates, the motion of dust particles of different structure and mass is analyzed. We consider the following forces: (1) the cometary nucleus gravity, (2) the solar radiation pressure, and (3) the drag on dust particles by a flow of gas produced in the sublimation of cometary ice. These forces are important for modeling the motion of dust particles relative to the cometary nucleus and may substantially influence the dust transfer over its surface. In the simulations, solid silicate spheres and homogeneous ballistic aggregates are used as model particles. Moreover, we propose a technique to build hierarchic aggregates—a new model of quasi-spherical porous particles. A hierarchic type of aggregates makes it possible to model rather large dust particles, up to a millimeter in size and larger, while no important requirements for computer resources are imposed. We have shown that the properties of such particles differ from those of classical porous ballistic aggregates, which are usually considered in the cometary physics problems, and considering the microscopic structure of particles is of crucial significance for the analysis of the observational data. With the described models, we study the dust dynamics near the nucleus of comet 67P/Churyumov–Gerasimenko at an early stage of the Rosetta probe observations when the comet was approximately at 3.2 AU from the Sun. The interrelations between the main forces acting on dust aggregates at difference distances from the nucleus have been obtained. The dependence of the velocity of dust aggregates on their mass has been found. The numerical modeling results and the data of spaceborne observations with the Grain Impact Analyzer and Dust Accumulator (GIADA) and the Cometary Secondary Ion Mass Analyzer (COSIMA) onboard the Rosetta probe are compared at a quantitative level.