Solar System Research最新文献

The article presents preliminary results of polarimetric monitoring of near-Earth asteroids (NEA), carried out with 2.6-meter telescope of the Crimean Astrophysical Observatory and the 2-meter telescope of the Terskol Peak Observatory. As part of the observations, 19 phase dependences of NEA polarization were obtained, and for such data were obtained for the first time for 17 asteroids, which significantly supplemented the existing polarimetric database. Near-Earth asteroids can be observed at large phase angles, which allows us to significantly expand our knowledge of the phase dependences of asteroids of different spectral classes—S, C and E. An asteroid with an extremely high degree of polarization, 25 330 (1999 KV4), has been discovered, reaching 38.5% at a phase angle of 75.7°, which suggests the presence of sublimation-dust activity. In addition, asteroids 52768 and 159402 exhibited similar orbital parameters and polarization values, suggesting that they are parts of the same parent body.

An algorithm for finding a solution to determine a preliminary orbit with a very small inclination to the ecliptic plane is proposed. The method proposed by the author is based on solving a system of transcendental equations for three variables. Solutions to the system are found by searching for the minima of the objective function using the Nelder–Mead method for a simplex. As an example, the results of determining the orbit of asteroid 255 447 (2005 YN24) are given.

In the future, cislunar space will become a hot spot for human space science research. Precise orbit determination of cislunar space probes can provide a guarantee for the implementation of exploration missions and space debris early warning. Currently traditional two-way range-rate observation are dominant tracking mode for the cislunar space probes. High-precision laser ranging is a potentially important tool to carry out orbit determination in cislunar space. By designing simulation schemes using only two-way range-rate and the combination of two-way range-rate and laser ranging, the orbit determination accuracies of the circumlunar orbits and the Earth–Moon libration points’ orbits are compared and analyzed, the results show that the incorporation of laser ranging data obviously improves the orbit determination accuracy. The laser ranging data enhances the precision of orbit determination for both the circumlunar circular and large eccentricity elliptical orbits, achieving accuracy within tens of centimeters. Similarly, it refines the accuracy of the distant retrograde orbit (DRO) and orbits around the Earth–Moon libration points to within tens of meters. The more laser ranging data we collect, the more significant the improvement in accuracy will be. It can be considered that laser ranging has an important application value in the precise orbit determination of cislunar space probes.

A review of scientific publications devoted to the mathematical problem of transition from distributions of minimum masses of exoplanets discovered by the radial velocity method to their distribution by physical masses is presented. The methods for solving this problem, both analytical and numerical, are described, and the results obtained are discussed. In conclusion, some unresolved issues requiring further discussion are described.

This paper investigates the accuracy of probabilistic estimates of asteroid impacts with the Earth obtained by mapping over time the initial orbital uncertainty modeled by linear stochastic methods based on observational material. The accuracy of the estimated probabilities is established in comparison with the probabilities obtained using nonlinear stochastic methods. The example of test asteroids shows how linear methods can be inadequate under certain observational circumstances when applied for probabilistic assessment if the nonlinearity is extremely strong. The discrepancy between linear and nonlinear probability estimates sometimes reaches one or two orders of magnitude. In addition, nonlinear probability estimates may be zero even with very significant linear estimates; in other words, in the real absence of the risk of an asteroid colliding with the Earth, linear estimates will falsely indicate the danger of a catastrophe.

Many exoplanets have been discovered very close to their parent stars. The radius of their orbits relative to the Alfvén radius and the characteristics of the parent star determine the mode of flow of the stellar wind around these planets: sub-Alfvénic or super-Alfvénic. The distance from the center of the star at which the kinetic and magnetic energy densities are equal is called the Alfvén radius. If a magnetic exoplanet is located beyond this distance, a comet-like magnetosphere with a bow shock in front of it forms around it. If the exoplanet is located inside the Alfvén radius, the magnetosphere turns into Alfvén wings. Here we will consider how the transition from a comet-like magnetosphere to Alfvén wings occurs due to the growth of the magnetic field of the stellar wind with the most efficient orientation for reconnection and how, due to this process, the bundle of open field lines in interplanetary space is transformed, compressed into a narrow tube.

Observations indicate that active energy-release processes occur within many icy bodies in the Solar System at large heliocentric distances. The energy source supporting such an activity remains uncertain. We propose the spontaneous recombination of accumulated radicals as the energy source. In our model, these radicals accumulate in water ice at low temperatures due to radioactive decay of long-lived radionuclides. We modeled the propagation of this recombination process for icy bodies of varying composition and radius, considering different initial concentrations of radicals and initial temperatures ranging from 5 to 50 K. Our results identify conditions under which this process can raise the temperature up to 273 K and demonstrate that such a temperature can be maintained within a body with a radius of 250 km for over 100 million years. We also show that the process is weakly temperature-dependent and can occur at very large heliocentric distances, including comets in the Oort Cloud.

Electric charging of the surfaces of airless cosmic bodies is caused by the action of the solar wind plasma and the solar UV radiation. In the present paper it is investigated how the dielectric permittivity of the surface layer of small cosmic bodies (asteroids, dwarf planets) influences their surface charging (and hence charging of dust grains on the surface). We show theoretically that this dielectric permittivity in some regions provides significantly stronger charging of the surface than it was estimated earlier. In relation with this it is investigated how the layer with the frozen water under the surface influences charging of dust grains.

The paper presents a review of photometric and spectrophotometric observations of the asteroid Vesta (one of the largest asteroids in the Solar System) carried out by Kazakhstani astronomers in 1986–1988. As a result, these observations yielded important results, including the final confirmation of the actual rotation period of Vesta and the reliable recording of variations in the intensity of the core of the first absorption band of pyroxene in the spectrum of Vesta’s surface. An analysis of individual spectra obtained by us at different phases of Vesta’s rotation shows a tendency for the center of the first band to shift to the long-wave region of the spectrum with an increase in the depth of the band. These features can be interpreted as the presence of significant unevenness in the distribution of pyroxene over the surface of the asteroid, or as a result of the influence of the degree of maturity (age), or the fragmentation of the pyroxene-containing substance of a certain area on the asteroid as a result of impact. Estimates of the position of the “spot” or crater indicate that on the surface of the asteroid, the pyroxene spot is located in the southern hemisphere of Vesta and has a diameter of about 40° in the planetographic coordinate system and may have a higher Ca content. Peculiarities in the distribution of the mineral pyroxene on the asteroid’s surface suggested the presence of a large impact crater. This was confirmed by the discovery of such a crater in much later years through observations from the Dawn spacecraft (in 2011). Our results are also consistent with and complemented by other studies of Vesta in recent decades.

The solar wind speed perturbation before the fronts of shock waves is theoretically investigated. It is shown that there is a small, but quite detectable deceleration in front of the Earth’s bow shock in the Earth-bound frame of reference. The perturbation is caused by the ponderomotive Abraham force. The Abraham force results from the excitation of fast magnetosonic waves in the foreshock region. The theoretical estimate of the solar wind deceleration by ~10 km/s agrees with measurements of the directional plasma flow velocity on the spacecraft in the foreshock region of the Earth’s bow shock. The use of the velocity addition theorem for interplanetary foreshocks with a structure similar to Earth’s foreshock allows to predict acceleration rather than deceleration of the solar wind in front of interplanetary shocks in the Earth-bound reference frame. The main conclusion is that the theory of ponderomotive plasma modification is of undoubted interest for the interpretation of in situ measurements in the interplanetary environment.