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Vol 57, No 2 (2023)

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Articles

Electromagnetic Phenomena Accompanying the Passage of an Iron Meteorite Through the Earth’s Atmosphere

Filonenko A.D.

Abstract

Based on observational facts, the author proposes a model for the formation of an electric charge in iron meteorites in the lower layers of the atmosphere through photoelectron emission when exposed to high-temperature plasma radiation on its surface. It is shown that at high Mach numbers, the explosive destruction of an iron meteorite can be caused not only by inertial, but also by electrostatic forces. The sub sequent charging of the fragments greatly increases their total charge, and the movement with acceleration causes electromagnetic radiation in the low frequency range. The electrostatic and electromagnetic fields accompanying the movement of meteoroids in the atmosphere can be the cause of the observed effects on the Earth’s surface, i.e., radio interference, electric shock to a person, and St. Elmo’s fire, among others.

Astronomičeskij vestnik. 2023;57(2):103-112
pages 103-112 views

Spatial and Genetic Relations of Coronae, Lobate Plains, and Rift Zones of Venus

Guseva E.N., Ivanov M.A.

Abstract

Based on the photogeological and stratigraphic analysis of Venusian coronae, we have found that (1) late manifestations of volcanic activity on Venus, lobate plains, are weakly related to the formation of coronae. The small number of coronae–sources of lobate plains (~17% of the total population of coronae) indicates that the volcanic activity of the coronae ceased mainly in the pre-Atlian time. Thus, the coronae associated with manifestations of late volcanism in the form of lobate plains are either long-lived volcano tectonic complexes or structures of the final phases of volcanic activity; their locations mark the regions of long-term volcanism; (2) the small number of coronae formed by rift structures (~14% of the total popula tion) indicates that rifting in the Atlian period did not lead to mass formation of coronae. The majority of Venusian coronae was probably formed in the Fortunian–Guineverian periods of the geological history of Venus. A sharp decrease in the number of coronae formed in the Atlian period may be associated with an increase in the thickness of the lithosphere and an increase in its role as a rheological barrier.

Astronomičeskij vestnik. 2023;57(2):113-123
pages 113-123 views

Estimation of Ejecta Thickness from Impact Craters in the South Polar Region of the Moon

Krasilnikov A.S., Krasilnikov S.S., Ivanov M.A., Head J.W.

Abstract

The paper presents the results of model calculations of impact craters ejecta thickness variations in the south polar region of the Moon from the south pole to 70° S for craters of Nectarian, Imbrian, Eratos thenian, and Copernican ages. This work does not consider pre-Nectarian craters since younger deposits often hide the boundaries of their ejecta. Housen, Sharpton and Fassett models were chosen to estimate the power. The first was used for craters larger than 45 km in diameter, the second for smaller craters (from 3 to 45 km), and the third for the Mare Orientale basin. During estimation, the mixing factor of ejecta with the underlying regolith (factor μ) was considered. As a result, maps of ejecta thicknesses were produced for the Moon’s south polar region. They provide an opportunity for quantitative estimation of the various aged impact events’ contribution to the formation of polar regolith and, accordingly, to determine the dominant source (sources) of material in a particular area, not least in the proposed landing sites.

Astronomičeskij vestnik. 2023;57(2):124-135
pages 124-135 views

Features of Foreshock Transients at Planetary Bow Shocks

Shuvalov S.D.

Abstract

In front of the bow shock with a quasi-parallel configuration of the interplanetary magnetic field, there exists a region called a foreshock, in which many nonstationary processes take place, the largest of which are collectively named “foreshock transients.” The size of these formations can reach tens of Earth radii, which significantly influences the nature of the solar wind interaction with the magnetosphere. Some types of foreshock transients are also observed at other planets, including those without their own global mag netic field, which indicates the universality of these phenomena. This article lists the most well-known non stationary processes occurring in the foreshock, as well as provides current ideas about the formation mech anisms of the largest foreshock transient.

Astronomičeskij vestnik. 2023;57(2):136-146
pages 136-146 views

Negative Polarization of Celestial Bodies: Review and Computer Simulation

Petrov D.V., Kiselev N.N., Savushkin A.A., Zhuzhulina E.A.

Abstract

A brief review of the main causes of a negative degree of linear polarization of radiation scattered by regolith surfaces of atmosphereless cosmic bodies and ensembles of particles in the opposition region is presented. The results of computer simulation are provided, which made it  possible to calculate the polariza tion degree of light scattered by pairs of irregular particles. The distance between the particles changed, which made it possible to obtain a visual representation of the total effect of the nature of negative polarization in the case of two-particle scattering (scattering in which two particles participate). Previously, a similar study was carried out for the case of two spherical particles, and showed that two-particle scattering by spheres only changes the degree of linear polarization in absolute value. We showed that two-particle scattering by irregular particles has a variable effect on the degree of linear polarization, both increasing and decreasing it. We also demonstrated that two-particle scattering by irregular particles can form a negative polarization even if the light scattered by a single particle is positively polarized. Therefore, in theoretical studies of the appearance of negative polarization, it is important to take into account two-particle scattering.

Astronomičeskij vestnik. 2023;57(2):147-165
pages 147-165 views

On the Prospects for Estimating the Properties of Particles in an Active Asteroid Exosphere by Features in the UV and Visible Reflectance Spectra

Petrova E.V., Busarev V.V.

Abstract

The reflectance spectra of active asteroids (AAs) measured in the visible and near-UV ranges exhibit unusual features, which are apparently caused by the light scattering in an exosphere formed under active processes on an asteroid. To estimate the prospects for a quantitative interpretation of these features, we numerically simulated reflectance spectra of an AA enveloped by an exosphere composed of aggregate submicron particles of various composition and morphology, as well as homogeneous submicron particles. We assumed that the sizes of aggregates’ constituents correspond to those of grains in agglomerates of come tary and interplanetary dust. It has been shown that the scattering on aggregates of submicron grains produces interference features at wavelengths shorter than 0.6 μm, and the positions of these features are determined by both the sizes of these grains (rather than the aggregates themselves) and the real part of their refractive index. The structure of an aggregate and variations (up to ±20%) in the sizes of constituents weakly influence the position of these features. The shape of the spectrum at longer wavelengths also depends on the sizes of grains in the aggregates and serve as an additional criterion for estimating this parameter. Calculations per formed for aggregate particles absorbing in a short-wavelength range (which is typical of many materials that one may expect to find on AAs) show that the absorption significantly weakens the interference details appeared in this range. Hence, the attempts to detect strongly absorbing particles in the exosphere and to esti mate their properties by these spectral features cannot yield reliable results, as opposed to the simulations for weakly absorbing particles. The presence of homogeneous weakly absorbing submicron particles in the exo sphere of an AA results in a steady growth of the intensity at wavelengths shorter than 0.4−0.5 μm. Spectral measurements at the wavelengths shorter than 0.35 μm may help to estimate more reliably the properties of weakly absorbing particles, both aggregate and homogeneous, in the exospheres of AAs.

Astronomičeskij vestnik. 2023;57(2):166-180
pages 166-180 views

Selected Problems of Classical and Modern Celestial Mechanics and Stellar Dynamics: II–Modern Studies

Shevchenko I.I., Melnikov A.V., Titov V.B., Baluev R.V., Veselova A.V., Krivov A.V., Mikryukov D.V., Milanov D.V., Mülläri A.A., Nikiforov I.I., Pit’ev N.P., Polyakhova E.N., Sokolov L.L., Shaidulin V.S.

Abstract

A review is given, in the modern context of applications, of the major important scientific results obtained by the scientists and graduates of St. Petersburg State University in the field of celestial mechanics and stellar dynamics. The second part of the review covers the following topics: estimates and calculation of the MOID parameter, problems of asteroid–comet hazard, dust complexes in the Solar System, rotational dynamics of planetary satellites, circumbinary dynamics, and methods for the discovery and determination of orbits of exoplanets.

Astronomičeskij vestnik. 2023;57(2):181-196
pages 181-196 views

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