Vol 50, No 2 (2016)

Through the example of comparison of the natural features of two regions in the northern part of Mare Imbrium, that were directly investigated in detail with remotely controlled rovers on the lunar surface, the capabilities of combining orbital remote measurements of the physical and mechanical properties and the chemical composition of the lunar soil with their direct measurements have been shown. From the remotely determined spectropolarimetric and gamma-spectrometric characteristics of the regolith surface layer, the exposure age (the maturity), the mean effective size of particles of the fine fraction, the absolute age of the formations, and the iron content in the soil were estimated. To compare the characteristics of the considered regions, the results of the investigations carried out directly on the lunar surface by the Lunokhod-1 rover and the analogous vehicle Yutu were used.

An analysis is presented for the photometric data on comet C/2013 A1 (Siding Spring) from observations at a large heliocentric distance (~4.1 AU). Comet C/2013 A1 (Siding Spring) displays intense activity despite the relatively large heliocentric distance. The morphology of the comet’s coma is analyzed. The following parameters are measured: the color indices V-R, the normalized spectral gradient of the reflectivity of the comet’s dust S', and the dust production rate Afρ. A numerical simulation is performed for the evolution of the comet’s orbit after a close encounter with Mars. The most probable values are obtained for the Keplerian orbital elements of the comet over a hundred-year period. The comet’s orbit remains nearly parabolic after passing the orbits of all the Solar System planets.

Regular optical observations of small-sized space debris on a geosynchronous orbit are carried out at the Terskol Peak Observatory (Kabardino-Balkaria). The aim of these observations is to gather data on technogenic pollution of near-Earth space; discover small-sized space debris, determine their parameters, and catalogue them; and maintain an updated catalogue of orbits. The results obtained by processing topocentric measurements of positions of one such object are presented. This object is distinctive in that it is a small-sized fragment of the Fengyun 2D satellite (international designator 2006-053A) and moves about a Lagrangian point at 75° E with a small amplitude. The observational material was accumulated in 12 twoweek sessions within a 6-year interval from 2009 to 2014. The variability of the ratio of the maximum cross section area to the object mass is revealed, and a model of variations of this parameter is proposed. The basic period of variations is 392 days. The validity of the model was verified in a series of independent observations in March, 2015.

The results of modeling of the distribution of dust in the circumsolar zone are presented. The dust distribution was retrieved from observations of the line-of-sight velocities in the F-corona to the distances of 7–11 solar radii during the total eclipses of the Sun in different years: on July 31, 1981; August 11, 1991; March 29, 2006; and August 1, 2008. Comparison of the results has shown that the dust composition varies from year to year and the dust is dynamically nonuniform. In addition to the dust related to the zodiacal cloud and concentrating to the ecliptic plane, the dust of retrograde motion and the ejections and accretion in the polar regions are observed. From the results of observations of eclipses on July 31, 1981, August 11, 1991, and August 1, 2008, the east–west asymmetry in a sign of the line-of-sight velocities was detected: they are negative to the east of the Sun and positive to the west. Such distribution of the velocities is indicative of the nearecliptic orbital dust motion, whose direction coincides with that of the motion of the planets. In the course of the eclipse of March 29, 2006, almost no dynamical connection with the zodiacal cloud was found. At the same time, the direction, where the observed velocities are largest in value and opposite in sign on opposite sides of the Sun, was determined, which provides evidence of the orbital motion deviating from the ecliptic plane. The results of observations in 2006 reveal a clear genetic connection of the observed orbital motion of dust with the parent comets of the Kreutz family found near the Sun close to the eclipse date. The velocities observed near the symmetry line in the plane of the sky grow by absolute value with increasing the elongation, which may take place, if the line of sight croßses an empty zone that is free of dust. The modeling of the data of observations near the symmetry plane allowed the parameters of the dust distribution near the sublimation zone to be obtained. In 2006, the “black” cometary dust with a low albedo (A = 0.05) was observed; it showed high values of the power-law exponents in the distance distribution of the dust concentration (V = 2.2 > 1) and in the size distribution of grains (γ = 5.2 > 4.0) and a strong radiation pressure (β = 0.70–0.74). We estimated the mean radius of grains as ≈0.8–0.9 µm and the radius of the dust-free zone as ≈9.1–9.2 solar radii. The latter corresponds to the distances, where the low-melt components of olivines and pyroxenes disintegrate. In 2008, the observed zodiacal dust concentrating to the ecliptic plane demonstrated the canonical parameters: A = 0.1–0.2, V ≈ 1, ß ≈ 0, γ = 4.0, the mean radii of grains were 0.9–1.2 µm, and the radius of the dust-free zone was 7.0–7.6 solar radii.

The isotopic composition of carbon dioxide in the Martian atmosphere from the measurements of Mars Science Laboratory have been used to estimate the relative abundances of CO₂ isotopologues in the Martian atmosphere. Concurrently, this study has revealed long-standing errors in the amounts of some of low-abundance CO₂ isotopologues in the Earth’s atmosphere in the databases of spectroscopic parameters of gases (HITRAN, etc.).