Solar System Research最新文献

Abstract—In this paper, in relation to the problem of reconstructing the evolution of a preplanetary gas and dust cloud, an attempt is made to develop a model of a turbulent heterogeneous medium and to construct on this basis a new class of mathematical models of space media that take into how the character and development of turbulence are influenced by the inertial properties of a polydisperse mixture of dust particles, processes of heat and mass transfer and coagulation, phase transitions, chemical reactions, and radiation. This can significantly expand the capabilities of numerical modeling of various physical phenomena in complex space media such as accretion gas and dust disks formed in stars of various classes during their differential rotation around the center of gravity, to study their structure, physicochemical and hydrodynamic properties, and time evolution.

Abstract

In the framework of the basic problem of cosmogony, which is associated with the reconstruction of the protoplanetary solar disk at the very early stages of its existence, a closed system of MHD equations on the mean flow scale is formulated. This system is intended for numerical solution of problems on interconsistent simulation of the structure and evolution of the accretion protoplanetary disk and its corona. The model of a thin (but optically thick) disk is considered, in which turbulence dissipation due to kinematic and magnetic viscosity, opaqueness of the medium, accretion from the surrounding space, and the action of turbulent αω dynamo on the generation of magnetic field, as well as the magnetic force and energy interaction between the disk and its corona are taken into account.

Abstract

The paper presents a closed system of three-dimensional hydrodynamic equations of averaged motion, intended for modeling spiral turbulence in a rotating astrophysical disk. Diffusion equations for the averaged vortex and an equation for the transport of the integral vortex helicity are derived. A general concept of the emergence of energy-intensive mesoscale coherent vortex structures in a thermodynamically open turbulent chaos subsystem, associated with the realization of a reverse cascade of kinetic energy in mirror-asymmetrical disk turbulence, is formulated. It is shown that negative viscosity in a rotating three-dimensional disk system is apparently a manifestation of cascade processes in helical turbulence, when reverse energy transfer from small vortices to larger ones takes place. It is also shown that the relatively long decay of turbulence in the disk is associated with the lack of mirror symmetry of the anisotropic field of turbulent velocities about its equatorial plane. The work comprises a review aimed at improving new models of astrophysical nonmagnetic disks, for which the effects of helical turbulence play a decisive role.

Abstract

The paper discusses priority scientific tasks related to the study of small bodies in the Solar System, identifies the most promising objects for investigation from a spacecraft on a flyby trajectory and the sample return mission, and develops proposals for the preliminary composition of scientific instruments for remote asteroid research methods. A long-term and phased Russian scientific program for studying small Solar System bodies using spacecraft with electric propulsion has been proposed. The project is designed in such a way as to explore the largest number of scientifically interesting asteroids using a smaller number of spacecraft. A design concept for a small spacecraft to investigate near-Earth asteroids on a flyby trajectory and a main spacecraft for studying metallic asteroids in the Main Belt and sample sample return has been developed. A ballistic analysis of the flyby of five near-Earth asteroids and three metallic asteroids in the Main Belt is presented, as well as a ballistic analysis of the sample return mission from a Main Belt asteroid. The option of sample return using the nuclear tug Zevs is also considered.

Abstract

Predicting the motion of near-Earth asteroids (NEAs) is a complex task that requires the use of sophisticated technology, various techniques, and significant computational resources. In recent decades, significant progress has been achieved in this area, but many problems still await their solution. In this paper, we consider the main methods used for predicting the motion of NEAs at various stages, starting from observations and ending with the study of motion specifics such as close encounters and planetary collisions, orbital and secular resonances, as well as chaoticity and predictability of motion. The article is based on a report presented at the scientific-practical conference with international participation “Near-Earth Astronomy-2022” (April 18–21, 2022, Moscow).

Abstract

The problem of self-gravitational instability of an astrophysical rotating plasma in a strong magnetic field with an anisotropic pressure tensor is studied on the basis of the Chew–Goldberger–Low (CGL) quasi-hydrodynamic equations modified by generalized polytropic laws. Using the general form of a dispersion relation obtained by the normal-mode perturbation method, a discussion is provided of the propagation of small-amplitude perturbation waves in an infinite homogeneous plasma medium for transverse, longitudinal, and oblique directions with respect to the magnetic field vector. It is shown that different polytropic indices and anisotropic pressures not only change the classical Jeans instability condition but also cause the appearance of new unstable regions. Modified Jeans instability criteria are obtained for isotropic MHD equations and anisotropic CGL equations owing to the influence of the polytropic indices on gravitational and firehose instabilities for astrophysical plasma. It is shown that in the case of a longitudinal mode of perturbation wave propagation, the Jeans instability criterion does not depend on uniform rotation. In the case of the transverse propagation regime, the presence of rotation reduces the critical wave number and exerts a stabilizing effect on the growth rate of the unstable regime.

An Erratum to this paper has been published: https://doi.org/10.1134/S0038094623340014

Abstract

Cometary nuclei located in the Oort cloud accumulate high concentration of radicals in surface layers under cosmic ray irradiation at low temperatures. Recombination of radicals induced by an increase in the surface temperature of a comet by a close passing star, O/B stars, or nearby supernovae leads to the heating of the ice layer with the releasing of volatiles from the amorphous ice. When high gas pressure builds up beneath the cometary surface, dust and gas are ejected. The resulting jet of gas and dust can change the comet’s orbit in the Oort cloud. The studied non-gravitational mechanism can effectively expel comets with a radius of ≤1 km from the Oort cloud into the inner part of the Solar system. The total effect of cometary outbursts on the stability of cometary orbits during the evolution of Solar system can result in a decrease in the number of long-period small-radius comets.