Solar System Research最新文献

The aim of this article is to acquaint the reader to the rapidly developing stochastic-thermodynamic theory of irreversible processes using as an example the modeling of structured turbulence. Here, we consider a synergetic approach to the development of a phenomenological model of extremely developed turbulence in a compressible homogeneous fluid, taking into account the nonlinear cooperative processes in it. Inclusion in the model of a set of random variables as internal parameters of the turbulent chaos subsystem, associated with its microstructure, makes it possible in this case to derive, using thermodynamic methods, the Fokker–Planck–Kolmogorov (FPK) kinetic equations in configuration space. Stabilization of the chaos subsystem near the next stationary nonequilibrium state in configuration space corresponds to the transition of the turbulent system to a new state, adequate to the emergence of complex spatiotemporal CSs in a turbulent flow.

In this article, the possibility of influence of the hydrodynamic helicity appearing in a rotating disk on synergetic structuring of cosmic substance and on the emergence of the negative turbulent viscosity effect in it is investigated. It is shown that prolonged turbulence damping in a disk can be partly associated with the absence of reflection symmetry of the anisotropic field of turbulent velocities relative to its equatorial plane. It is shown that negative viscosity in the rotating disk system is apparently a manifestation of cascade processes in helical turbulence, when the inverse energy transfer from small to larger vortices occurs.

Abstract—In this article, a closed system of magnetohydrodynamic (MHD) equations on the mean flow scales, which is intended for simulating turbulent flows of electroconductive media in the presence of an electromagnetic field, is derived in the single-fluid MHD approximation.

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.

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.

In contrast to several classical studies, in which gravitational instability criteria for astrophysical disks are derived within traditional hydrodynamics or kinetics, it is proposed to consider the set of loose gas–dust clusters of an accretion protoplanetary disk as a special type of continuous medium, i.e., a fractal medium whose phase velocity space contains points and areas not filled by its components. Within the Tsallis formalism of nonadditive statistics (thermodynamics), intended to describe the behavior of anomalous systems, i.e., systems with a strong gravitational interaction of its individual parts and the fractal nature of the phase space, linearized equations are obtained for oscillations of a solid-state rotating disk on the basis of modified Navier–Stokes hydrodynamic equations (the so-called q-hydrodynamics equations) and in view of dissipative effects, and a derivation is given of the dispersion equation in the WKB approximation. An analysis is conducted of axisymmetric oscillations of a differentially rotating astrophysical gas–dust space object to obtain modified Jeans and Toomre gravitational instability criteria for disks with a fractal structure.

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.

Optical observations of the occultation of the star TYC 5254-00839-1 by Neptune’s satellite Triton were carried out on October 6, 2022, using the Zeiss-1000 telescope at the Sanglokh Observatory (MPC code 193). As a result of photometric processing of images, a light curve of the star was constructed and it was revealed that the areas of decline and rise in brightness had a finite duration from 15 to 24 s. This is apparently due to the presence of an atmosphere around Triton. In addition, in the resulting light curve of this phenomenon, according to our and other observations, a “step” is revealed, which may indicate the possible presence of a close, faint object near the occulted star. As a result of astrometric processing, high-precision coordinates of Triton were determined at the average moment of occultation, which, within the limits of measurement errors, coincided with its ephemeris position.

The paper presents new detailed radar maps and polarimetric data covering the southern polar region of the near side of the Moon measuring 400 × 800 km with a spatial resolution of about 75 m. The data were obtained using the 64-meter antenna (TNA-1500) of the Satellite Communications Center Bear Lakes of the Special Design Bureau of the Moscow Power Engineering Institute and the 13.2-meter radio telescope (RT-13) of the Svetloe Observatory of the Institute of Applied Astronomy, Russian Academy of Sciences, at a wavelength of 4.2 cm. At this wavelength, radar signals penetrate the lunar regolith to depths of up to 1 m and are sensitive to surface and suspended rocks larger than 1 cm. The maps show 39% of the area of permanently shadowed regions not observable by optical Earth-based instruments, which may hide water ice deposits. Analysis of radar maps did not reveal any relationship between the polarization properties of the surface in these regions and the presence of solar illumination. The data obtained as a result of this work can be used to study the surface and subsurface regolith features of the lunar south polar region, including searching for ice deposits in permanently shadowed regions, as well as for planning future lunar missions.

The degassing of Murchison carbonaceous chondrite (CM2 type) was studied using a setup specially designed for this purpose. The experiments involved stepwise heating (without gas accumulation) and isothermal annealing of meteorite samples with the composition of released gases determined through gas chromatography methods in the temperature range from 200 to 800°C. To account for sorbed water, degassing at 50 and 110°C was additionally analyzed. The IR spectra of the Murchison meteorite were obtained after annealing at different temperatures and used to trace the thermal degradation. The comparison with the degassing of the ordinary chondrite Chelyabinsk (type LL5) revealed a significant increase in the release of carbonaceous gases for the Murchison meteorite.