Solar System Research最新文献

A theoretical model is presented that describes the settling regime of plasma-dust clouds in the mesosphere of Mars. The values of the characteristic sizes of cloud dust particles predicted by the model are calculated. It is shown that an important factor influencing the formation of plasma-dust structures in the Martian atmosphere is the Rayleigh–Taylor instability, which limits (from above) the permissible sizes of dust particles in the cloud.

Celestial bodies which have orbital and physical characteristics typical of asteroids, but episodically exhibit the signs of cometary activity are of particular interest, because the knowledge of the nature of these bodies is necessary to understand the processes of how the Solar System formed and how water was delivered to the terrestrial planets. In the estimation of the properties of an exosphere of an active asteroid (AA) from remote-sensing data, polarimetry can play a prominent role, since the polarization of scattered light is sensitive to the properties of particles in the medium. Numerical simulations of the light scattering by particles in the exosphere around an AA have shown that, depending on the wavelength of the scattered light, the refractive index of particles, and their morphology, the light scattering in the exosphere may both weaken the polarization of light reflected by the surface and enhance it. At the same time, the spectral gradient of polarization may change both towards larger positive values and towards negative ones. At phase angles less than 30°, which are typical of observations of the Main-belt asteroids, the changes in the polarization induced by scattering in the exosphere are small and vary only slightly for particles of different properties. Nevertheless, if the polarizations of light reflected by an asteroid changes relative to the canonical values, this may indicate the presence of the exosphere. At larger phase angles, the influence of scattering in the exosphere on the polarization of an AA is more noticeable, which makes the use of polarimetry promising for studying activity of near-Earth asteroids. This effect should also be taken into account when estimating the albedo of an asteroid by the polarization maximum (according to the Umov law), if a manifestation of activity in this particular asteroid can be expected.

One of the main features that distinguishes dusty plasma from ordinary (not containing charged dust particles) plasma is anomalous dissipation associated with the process of charging dust particles, leading to new physical phenomena, effects and mechanisms. The process of anomalous dissipation is considered in the context of describing the dynamics of dust particles in the dusty plasma of atmosphereless bodies of the Solar System. A description of the oscillations of a dust particle over the surfaces of Mercury, the Moon, and the Martian satellites Phobos and Deimos is presented, the attenuation of which is determined by the charging frequency of the dust particles, which characterizes anomalous dissipation. The possibility of using an approach that takes into account anomalous dissipation to describe plasma-dust processes in the vicinity of comets is discussed. It is shown that anomalous dissipation plays a significant role in determining the possibility of using the model of levitating dust particles in describing dusty plasma over the surfaces of atmosphereless bodies of the Solar System. The results of numerical calculations are presented, confirming the possibility of using this model for a number of atmospherelesso cosmic bodies.

Using numerical modeling of the rotational dynamics of asteroid (99942) Apophis, the disturbances that occur in the rotational motion of asteroids during their close approaches to the Earth were studied. Such events can lead to significant changes in the speed of the asteroid’s own rotation and the orientation of its rotation axis in space. Assuming that the figure of Apophis is approximated by a triaxial ellipsoid, the dependences of changes in the rotation period of an asteroid on the parameters of the orbit and its rotational state before approaching the Earth were studied. It has been established that the rotation period of Apophis, which is currently about 30 h, may change due to the next approach to Earth in 2029 very significantly—to 10–15 h; in numerical experiments, both acceleration and deceleration of the asteroid’s rotation were observed. Perturbations in the rotational motion of the asteroid noticeably affect its further orbital dynamics as a result of changes in the magnitude of the Yarkovsky effect. It was concluded that as a result of close approach, the average rate of change of the semimajor axis of Apophis’s orbit caused by the Yarkovsky effect, which is currently about 200 m/year, may decrease to 160 m/year or increase to 300 m/year.

The propagation of linear acoustic disturbances in an infinite, homogeneous, gray radiating plasma, initially in mechanical and radiation equilibrium, is considered. An exact governing equation for radiation acoustics in a radiating gray gas is derived, taking into account the influence of the transverse magnetic field. Radiation magnetohydrodynamics (MHD) is described by three hydrodynamic equations and two radiative momentum equations, making extensive use of the formalism of radiation thermodynamics. With the aim of more reliably describing the evolution of radiation magnetic–acoustic disturbance waves with scattering and attenuation, the conditions of radiation-thermal dissipation, the force of radiation resistance, as well as magnetic force and Joule heat are introduced into these equations. In this case, the Eddington approximation is used, which allows one to study the modes of radiation magnetohydrodynamic waves in two asymptotic cases—optically thin and thick gas. The exact control equation derived in the work made it possible, using the heuristic Whitham method, to obtain a set of approximate control equations of the lowest order, each of which is part of a reliable approximation to the exact equation in a certain region of the independent time variable. The relatively simple form of such equations made it possible to study the physical processes occurring in each radiation magnetic–acoustic wave without a formal solution to the full problem.

The article describes simulation experiments of interaction of lunar dust with the surface of solar panels. The experiments are based on the creation of a dusty plasma cloud, when the radiation of a powerful pulsed gyrotron is exposed to a substance that simulates lunar dust. This approach was tested using a lunar regolith simulator. The analysis of the results of deposition of charged regolith particles on solar panels of different types and changes in their efficiency is presented.

Series of consecutive UV (365 nm) images of Venus cloud coverage provide a way to investigate dynamics of the mesosphere. An unprecedented series of such images was obtained by the VMC/Venus Express (ESA) and UVI/Akatsuki (JAXA) cameras from 2006 to 2022. At 10°S long-term variations in the mean zonal and meridional wind speed are observed with a period of 12.5 ± 0.5 years. Analysis of the of the mean zonal wind behavior around noon (12 ± 1 h) at phase angles of 60°–90° in limited observation time intervals shows that near the minimum of the long-term dependence the deceleration of the horizontal flow is observed above the highest part of Aphrodite Terra, Ovda Regio, for both VMC and UVI. Conversely, acceleration is observed above the Ovda Regio near the maximum of the long-term dependence. The considered longitudinal variations of the zonal wind speed extend from the equator to middle latitudes (0°–40°). The meridional wind speed shows longitudinal variations associated with the topography of the underlying surface, regardless of whether the horizontal flow is slowing down or accelerating above the highlands of Aphrodite Terra.

The article provides a description of the crater in the marginal zone of the southern polar region of the Moon with the coordinates of the center 126.59° W, 64.32° S The diameter of the crater is 34 km. It has a fractured bottom, which is considered a sign of magma intrusion into the subcrater space. The absolute age of formation of the crater under study was estimated to be ~3.85 billion years based on the spatial density of small craters superimposed on its rim. In the vicinity of the studied crater, low-iron anorthosite material is predominant. It can be argued that the basin of the crater under study is very dry compared to its surroundings. A significant loss of hydrogen/water and its redistribution from the bottom of the crater to the area around the crater could be caused by reworking of the surface due to the intrusion of magma under the crater, traces of which can be traced by the presence of cracks on the bottom of the crater.

The work used data on Saturn’s satellite Hyperion obtained from the flight results of the Cassini spacecraft due to their completeness, resolution, and image quality. They pointed out the chaotic nature of Hyperion’s rotation, as a result of which there was an ambiguity in determining its coordinate system associated with the body. The dimensions of the approximating ellipsoid and the parameters of the transition from the coordinate system, initially adopted under the assumption of uniform rotation of Hyperion around Saturn, to a coordinate system whose axes coincide with the axes of the found ellipsoid were obtained. A digital model of the Hyperion surface was also created, on the basis of which geodetic heights were calculated relative to a triaxial ellipsoid with certain parameters. The method for calculating heights is based on the combined use of the equation of the normal to the surface passing through a given point and the equation of the surface itself. As a result of the research, a map of Hyperion was compiled in the projection of the triaxial ellipsoid with horizontal lines constructed on the basis of calculated geodetic heights. An original method for studying the nature of Hyperion’s rotation is presented using the projection of Saturn’s position onto the surface of Hyperion for all known moments in time in an object-centric coordinate system. The implementation of this technique allowed us to assume that Hyperion’s own rotation axis precesses relative to the largest axis of the body in a counterclockwise direction.

The evolution of the orbits of bodies ejected from the Earth has been studied at the stage of its accumulation and early evolution after impacts of large planetesimals. In the considered variants of calculations of the motion of bodies ejected from the Earth, most of the bodies left the Hill sphere of the Earth and moved in heliocentric orbits. Their dynamical lifetime reached several hundred million years. At higher ejection velocities v_ej the probabilities of collisions of bodies with the Earth and Moon were generally lower. Over the entire considered time interval at the ejection velocity v_ej, equal to 11.5, 12 and 14 km/s, the values of the probability of a collision of a body with the Earth were approximately 0.3, 0.2 and 0.15–0.2, respectively. At ejection velocities v_ej ≤ 11.25 km/s, i.e., slightly exceeding a parabolic velocity, most of the ejected bodies fell back to the Earth. The probability of a collision of a body ejected from the Earth with the Moon moving in its present orbit was approximately 15–35 times less than that with the Earth at v_ej ≥ 11.5 km/s. The probability of a collision of such bodies with the Moon was mainly about 0.004–0.008 at ejection velocities of at least 14 km/s and about 0.006–0.01 at v_ej = 12 km/s. It was larger at lower ejection velocities and was in the range of 0.01–0.02 at v_ej = 11.3 km/s. The Moon may contain material ejected from the Earth during the accumulation of the Earth and during the late heavy bombardment. At the same time, as obtained in our calculations, the bodies ejected from the Earth and falling on the Moon embryo would not be enough for the Moon to grow to its present mass from a small embryo moving along the present orbit of the Moon. This result argues in favor of the formation of a lunar embryo and its further growth to most of the present mass of the Moon near the Earth. It seems more likely to us that the initial embryo of the Moon with a mass of no more than 0.1 of the mass of the Moon was formed simultaneously with the embryo of the Earth from a common rarefied condensation. For more efficient growth of the Moon embryo, it is desirable that during some collisions of impactor bodies with the Earth, the ejected bodies do not simply fly out of the crater, but some of the matter goes into orbits around the Earth, as in the multi-impact model. The average velocity of collisions of ejected bodies with the Earth is greater at a greater ejection velocity. The values of these collision velocities were about 13, 14–15, 14–16, 14–20, 14–25 km/s with ejection velocities equal to 11.3, 11.5, 12, 14 and 16.4 km/s, respectively. The velocities of collisions of bodies with the Moon were also higher at high ejection velocities and were mainly in the range of 7–8, 10–12, 10–16 and 11–20 km/s at v_ej, equal to 11.3, 12, 14 and 16.4 km/s, respectively.