Solar System Research最新文献

Kappa distributions, which make it possible to effectively model the observed distributions of particles in cosmic and astrophysical plasma media throughout the heliosphere, are now widely used. In this paper we discuss the physical foundations and theoretical justification of kappa distributions naturally appearing within the Tsallis nonextensive statistical mechanics. These distributions provide an adequate description of rarefied plasma configurations in stationary states that are out of thermal equilibrium. The main formulas for theoretical kappa distributions are presented, and their application to studies of decaying fine-scale turbulence in cosmic plasma is briefly overviewed. It has been shown that these distributions, which follow from the Tsallis entropy functional in nonextensive statistical mechanics, provide the missing link between the empirical Vasyliunas kappa distributions and theoretical power-law models of the suprathermal characteristics of astrophysical plasma media.

By calculating the Lyapunov characteristic exponents in the hierarchical three-body problem (star–planet–planet’s satellite), an analysis of the applicability of a number of criteria for estimating the maximum possible value of the semimajor axis a_crit of a satellite’s orbit was carried out, corresponding to its long-term stable orbital dynamics. It has been shown that the empirical criterion from the work (Domingos et al., 2006), which is often used to determine potential orbits of exomoons (satellites of exoplanets), significantly overestimates the value of a_crit. In a planar problem for a prograde orbit (the directions of orbital motion of the planet and satellite coincide) of an exomoon, when estimating a_crit the criterion proposed by Rosario-Franco et al. (2020) works better, for the retrograde orbit of the exomoon, the criterion from the work (Quarles et al., 2021) works better. If the angle between the orbital planes of the planet and the satellite can be significant (>30°), a reliable estimate for a_crit can be obtained by numerical modeling of the long-term orbital dynamics of the exomoon and using rigorous methods of motion stability analysis (calculation of Lyapunov characteristic exponents, the MEGNO parameter, etc.).

The mass distributions of unevaporated fragments of meteoroids and asteroids disrupted in the atmosphere, as well as the mass distributions of fragments of bodies disrupted in impact experiments modeling the fragmentation of asteroids at collisions in outer space, are considered. Analytical description of these distributions is carried out using the method (Brykina and Egorova, 2021), which expresses the cumulative number of fragments depending on the fragment mass, the total mass of fragments, the mass and number of maximum fragments and a free parameter—the power index. We described the results of impact experiments on the disruption of the Allende, Mbale, NWA 620, MOR 001 meteorite samples and Mauna Loa basalt samples available in the literature. We constructed and described the distributions of the Bruderheim, Villalbeto de la Peña, St-Robert, and Motopi Pan meteorites, recovered after observed passages of cosmic bodies through the atmosphere, as well as the distributions of meteorites whose falls occurred thousands of years ago: the Gold Basin, Jiddat al Harasis 073, Whitecourt, Campo del Cielo, and Canyon Diablo. The results of the description of experimental distributions confirm the previously proposed analytical dependence of the power index on the specific impact energy. Based on the description of fragment mass distributions for 22 meteorite falls, the dependence of the power index on the number of fragments in a meteorite collection is analyzed. The features of various distributions are pointed out.

Using data on Mercury’s magnetic equatorial plane crossings by the MESSENGER spacecraft, we refine the position of Mercury’s planetary dipole. Magnetic equatorial plane crossings provide precise dipole offsets for each orbit. Using data on the interplanetary magnetic field (IMF) magnitude and direction during MESSENGER flybys, we determine the influence of the IMF on the equatorial plane crossing position and refine the previously determined dipole offset for orbits with insignificant IMF contributions.

The paper proposes an approach to constructing orbits in the vicinity of a Sun–Earth libration point, which ensures the approach of a spacecraft to asteroids flying nearby. The use of halo orbits near collinear L₁ and L₂ libration points, which are located at a distance of one and a half million kilometers from Earth, for the purpose of studying asteroids has three important advantages compared to previously implemented missions. Firstly, the trajectories of potentially hazardous asteroids approaching the Earth may pass by these libration points. Obtaining new scientific information about celestial bodies of this type is the most preferable in the context of the problem of asteroid–comet hazard. Secondly, the asteroid’s approach to both Earth and the spacecraft occurs at close moments in time, which could ensure the latter’s flight at a minimal distance from the surface of the celestial body and lead to the acquisition of fundamentally new data about the object of study. Thirdly, after approaching the asteroid, the spacecraft continues to operate near the libration point and can be used to solve other scientific problems. Using the example of the flight to the asteroids Apophis, 2001 WN₅ and 1997 XF₁₁, the results of calculations of such orbits for spacecraft that are already operating near the L₂ Sun–Earth libration point are presented (James Webb Space Telescope, Euclid and Spectrum-Roentgen-Gamma). The values of the characteristic velocity required to perform a maneuver of this type demonstrate the potential of the proposed concept.

To study the surface, dielectric properties and structure of the lunar ground, the radar complex RLK-L is being installed on the Luna-26 orbiter. The complex consists of two radars operating in different frequency ranges. In this paper, we present the main parameters of the radar equipment and discuss the design and methods for processing scientific data.

Active energy-release processes with uncertain energy sources have been observed on various icy bodies in the Solar System. In this paper, we consider a spontaneous recombination of radicals accumulated in water ice as a potential energy source, which could lead to liquid water formation beneath an icy body’s surface. We simulated the propagation of the recombination process through a small, 1-km-radius icy body with an initial temperature of 10 K consisting of amorphous ice, dust, and volatile gases trapped in the amorphous ice. Our results show that the recombination front rapidly propagates throughout the body, outrunning all other processes, including gas diffusion. If a sufficient concentration of radicals accumulates, the temperature and the pressure behind the recombination front could be sufficient to the formation of liquid water inside the icy body. The time during which these conditions can be maintained inside the body is determined by the diffusion of the gases released from the amorphous ice. For a 1-km body with a porosity of 0.65 and a dust-to-ice mass ratio of 1, this time is approximately 50 years. The recombination process weakly depends on the initial temperature of the icy body and can occur at very large heliocentric distances, including comets in the Oort cloud.

Traditional manual analysis of graphical data reflecting the behavior of critical arguments of orbital resonances is a very labor-intensive process. To address this problem, an attempt was made to apply convolutional neural networks (CNNs) to automatically classify orbital resonances based on graphical representations of critical arguments. It is shown that the model trained on the resonance argument plots obtained for objects from the 1 : 2 orbital resonance region demonstrated high accuracy on test data from this resonance region but showed a significant decrease in performance when applied to other resonance regions of 2 : 1 and 3 : 1 due to the presence of previously unseen graphical examples. After retraining the model on a more diverse dataset including all three resonance regions investigated, a more accurate model was developed, achieving an average classification accuracy of 98%. The study not only confirmed the high effectiveness of CNN for automating resonance classification but also highlighted the critical importance of using a diverse training dataset to build a highly accurate classification model.

The paper provides an overview of the phenomenon of “fusion crust of chondrites.” The processes of crust formation, ablation, emission and registration of radiation spectra, the phase and structural composition of the fusion crust substance in comparison with the internal substance, and experiments with a plasma torch to model ablation processes are considered. It was shown that preliminary characterization of meteorite matter is possible based on the recorded spectrum of their bolides. Information is provided on the transformation of the composition of meteorite matter as a result of ablation and confirmation of the possibility of accumulation of elements heavier than Ni and Co in the fusion crust of ordinary chondrites. The decrease in the content of iron-containing phases in the fusion crust and changes in the composition of silicates are consistent with the spectral data of experimental ablation and the spectra of fireballs.

The stresses in the interior of Venus beneath the Atla and Beta regions were calculated. We presented the distribution of non-hydrostatic stresses in the interior of Venus based on a joint interpretation of topography data and the nonequilibrium part of the gravitational field. A system of elastic equilibrium equations for a self-gravitating planet using topography and gravitational field data is solved on a grid with a resolution of 1° × 1° in latitude and longitude. Tensile stresses reach 20–30 MPa to the north and east of Beta region and to the northwest and south of Atla region, while shear stresses exceed 30 MPa in the central parts of the uplifts.