M. Ya. Marov

Astronomical and physical aspects of the Chelyabinsk event (February 15, 2013)

Various observational data including infrasound, seismic, optical (onboard) monitoring, ground video and photo records, and evidence from witnesses of the Chelyabinsk event on February 15, 2013, have been analyzed. The extensive material gathered has provided a base for investigations of the physical properties of the object, the results of which are discussed. A bolide light curve is constructed, which shows a multiplicity of flashes. Estimations of the energy of the meteoroid explosion, which took place in the atmosphere at an altitude of about 23 km, show evidence of the formation of a high-power shock wave equivalent to 300–500 kilotons of TNT. The object diameter corresponding to this energy falls within the range 16–19 m. The trajectory of the meteor is outlined. It is preliminarily concluded that the Chelyabinsk meteorite was a representative the Apollo asteroid family.

Modification of the jeans instability criterion for fractal-structure astrophysical objects in the framework of nonextensive statistics

Unlike classical studies in which the gravitational instability criterion for astrophysical disks is derived in the framework of traditional kinetics or hydrodynamics, we propose to consider the totality of fluffy dust clusters of various astrophysical objects, in particular, protoplanetary subdisks, as a special type of continuous medium, i.e., fractal medium for which there are points and areas not filled with its components. Within the deformed Tsallis statistics formalism, which is intended to describe the behavior of anomalous systems with strong gravitational interaction and fractal nature of phase space, we derive, on the basis of the modified kinetic equation (with the collision integral in the Bhatnagar-Gross-Krook form), the generalized hydrodynamic Euler equations for a medium with the fractal mass dimension. Considering the linearization of the q-hydrodynamics equations, we investigate the instability of an infinitely homogeneous medium to obtain a simplified version of the modified gravitational instability criterion for an astrophysical disk with fractal structure.

Modeling of aggregation of fractal dust clusters in a laminar protoplanetary disk

The evolutionary hydrodynamic model for the formation and growth of loose dust aggregates in the aerodisperse medium of a laminar disk, which was originally comprised of the gas and solid (sub)micrometer particles, is considered as applied to the problem of the formation of planetesimals in the Solar protoplanetary cloud. The model takes into account the fractal properties of dust clusters. It is shown that the clusters partly merge in the process of cluster-cluster coagulation, giving rise to the formation of large fractal aggregates that are the basic structure-forming elements of loose protoplanetesimals arising as a result of physicochemical and hydrodynamic processes similar to the processes of growth of the fractal clusters. Earlier, the modeling was conventionally performed in an “ordinary” continuous medium without considering the multifractional structure of the dust component of the protoplanetary cloud and the fractal nature of the dust clusters being formed during its evolution. Instead, we propose to consider a complex of loose dust aggregates as a special type of continuous medium, namely, the fractal medium for which there exist points and regions that are not filled with its particles. We suggest performing the hydrodynamic modeling of this medium, which has a noninteger mass dimensionality, in a fractional integral model (its differential form) that takes the fractality into account using fractional integrals whose order is determined by a fractal dimensionality of the disk medium.

Chelyabinsk event as an astronomical phenomenon

The fall of a meteorite near the town of Chelyabinsk is considered from the viewpoint of astronomy, and the major witness facts and entry characteristics (including the measured entry velocity and the height of the explosion) are analyzed. The aerodynamic phenomena that accompanied the entry of the meteorite in the atmosphere at an ultrasonic velocity and the origin of a shock wave that induced damage on the Earth’s surface are analyzed. The paper also reports the estimated frequency of the falls of celestial bodies depending on their size, and consequences of collisions of these bodies with the Earth. It is emphasized that studies of small bodies in the Solar System can provide insight into the origin of the protoplanetary disk and the processes that produced the planets. The studies of small bodies, such as the Chelyabinsk meteorite, are directly related to the problem of asteroid and comet impact hazard (ACIH). The paper reports the sizes of potentially hazardous celestial bodies whose monitoring requires the deployment of a network of specialized telescopes on the Earth to mitigate ACH and a system of space-based systems for the identification and monitoring of such bodies in near space.

Thermodynamic Model of MHD Turbulence and Some of Its Applications to Accretion Disks

Within the framework of the main problem of cosmogony related to the reconstruction of the evolution of the protoplanetary gas-dust cloud that surrounded the proto-Sun at an early stage of its existence, we have derived a closed system of magnetohydrodynamic equations for the scale of mean motion in the approximation of single-fluid magnetohydrodynamics designed to model the shear and convective turbulent flows of electrically conducting media in the presence of a magnetic field. These equations are designed for schematized formulations and the numerical solution of special problems to interconsistently model intense turbulent flows of cosmic plasma in accretion disks and associated coronas, in which the magnetic field noticeably affects the dynamics of astrophysical processes. In developing the model of a conducting turbulized medium, apart from the conventional probability-theoretical averaging of the MHD equations, we systematically use the weighted Favre averaging. The latter allows us to considerably simplify the writing of the averaged equations of motion for a compressible fluid and the analysis of the mechanisms of macroscopic field amplification by turbulent flows. To clearly interpret the individual components of the plasma and field-energy balance, we derive various energy equations that allow us to trace the possible energy conversions from one form into another, in particular, to understand the transfer mechanisms of the gravitational and kinetic energies of the mean motion into magnetic energy. Special emphasis is placed on the method for obtaining the closure relations for the total (with allowance made for the magnetic field) kinetic turbulent stress tensor in an electrically conducting medium and the turbulent electromotive force (or the so-called magnetic Reynolds tensor). This method also makes it possible to analyze the constraints imposed on the turbulent transport coefficients by the entropy growth condition. As applied to the problem of numerically simulating the structure and evolution of a protoplanetary accretion disk differentially rotating around the proto-Sun, we suggest a technique for modeling the turbulent transport coefficients, in particular, the coefficient of kinematic turbulent viscosity that allows us to take into account the magnetic field effect and the inverse effect of the heat transfer on the development of turbulence in a rotating electrically conducting disk. Our study is ultimately aimed at improving several representative hydrodynamic models of natural cosmic turbulized media, including the birth of stars from the diffuse medium of gas-dust clouds, the formation of accretion disks, and the subsequent accumulation of planetary systems. It is a continuation of the stochastic-thermodynamic approach to the synergetic description of the turbulence of astrophysical and geophysical systems that we have developed in a series of papers (Kolesnichenko, 2003; 2004; 2005; Kolesnichenko and Marov, 2006; 2007; Marov and Kolesnichenko, 2002; 2006).

The thermophob experiment: Direct investigations of the thermophysical properties of the regolith of phobos

The methodology and the main features of the Thermophob experiment developed for the direct analysis of the thermophysical properties of the surface of the Martian satellite Phobos from the Phobos-Grunt lander are considered. The methodical and engineering aspects of the measurements are discussed, and the design of the instrument and the potential of the interpretation of the measurement results with accounting for the theoretical estimates and the data of the laboratory tests are discussed.

Magnetohydrodynamic simulation of the protoplanetary disk of the Sun

In the framework of the basic cosmogony problem related with the reconstruction of the solar protoplanetary disk at the early stages of its existence, a closed system of magnetohydrodynamic equations with the scale of average motion is formulated in the approximation of single-fluid magnetic hydrodynamics; this system is designated for setting and numerically solving various problems on the self-consistent simulation of the structure and evolution of the disk and related corona. The influence of both the axially symmetric magnetic field of the proto-Sun and the large-scale field generated by the turbulent dynamo mechanism on the disk structure formation is analyzed. A new approach to the simulation of the turbulent transport coefficient in the weakly ionized disk is developed. This approach provides an account of the effects of the influence of the generated magnetic field and the processes of convective heat transport on turbulence development in the stratified layer with finite thickness and, thus, rejects the Shakura-Sunyaev α formalism widely used in astrophysical literature. The mathematical model of a thin (but optically thick) non-Keplerian disk taking into account the turbulence dissipation due to kinematical and magnetic viscosity, medium opacity, accretion from ambient space, the action of a turbulent αω dynamo on the magnetic field generation, the magnetic force and energy interaction between the disk and its corona, etc., is discussed. This study is the continuation of the stochastic-thermodynamic approach to the description of turbulence of astro-geophysical systems developed by us in a number of papers [Kolesnichenko 2000, 2001, 2003, 2004, 2005; Kolesnichenko, Marov 2006, 2007, 2008; Marov, Kolesnichenko 2002, 2006].

The nature of terrains of different types on the surface of Venus and selection of potential landing sites for a descent probe of the Venera-D Mission

We discuss a change in the resurfacing regimes of Venus and probable ways of forming the terrain types that make up the surface of the planet. The interpretation of the nature of the terrain types and their morphologic features allows us to characterize their scientific priority and the risk of landing on their surface to be estimated. From the scientific point of view, two terrain types are of special interest and represent easily achievable targets: the lower unit of regional plains and the smooth plains associated with impact craters. Regional plains are probably a melting from the upper fertile mantle. The material of smooth plains of impact origin is a well-mixed and representative sample of the Venusian crust. The lower unit of regional plains is the most widespread one on the surface of Venus, and it occurs within the boundaries of all of the precalculated approach trajectories of the lander. Smooth plains of impact origin are crossed by the approach trajectories precalculated for 2018 and 2026.

Modification of the Jeans and Toomre Instability Criteria for Astrophysical Fractal Objects Within Nonextensive Statistics

Within the formalism of Tsallis nonextensive statistics designed to describe the behavior of anomalous systems, systems with a strong gravitational interaction between their individual parts and the fractal nature of phase space, we have obtained linearized equations for the oscillations of a rigidly rotating disk by taking into account dissipative effects and give a derivation of the dispersion equation in the WKB approximation. Based on the previously derived modified Navier—Stokes hydrodynamic equations (the so-called equations of q-hydrodynamics), we have analyzed the axisymmetric oscillations of an astrophysical, differentially rotating gas—dust cosmic object and obtained modified Jeans and Toomre gravitational instability criteria for disks with a fractal phase-space structure.

Phobos-Soil space project: A new stage of the Russian planetary program

The Phobos-Soil project, based on a new generation of spacecraft, is aimed at the study of Phobos, one of the Martian moons. The main goal of the project is to bring soil samples from the surface of Phobos to the Earth for a scrutinized analysis of the relic matter collected on one of the Solar System’s minor bodies. The project is considered to be a step in the long-scale extensive quest for data on planets, comets, asteroids, and solving a vast number of other theoretical and applied problems.