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In the characterization of the space debris environment, the computation of the orbit of the debris objects is usually conducted by considering the association of short sequences of observations called tracklets. In case the orbits can be already determined with sufficient accuracy from single tracklets, it is necessary to define a criterion to decide if two calculated orbits correspond to the same object. One possibility is to introduce a definition of distance between orbits and to consider a threshold below which the two orbits are considered to be originating from the same object. The concept of distance is quite general and leaves room to different definitions. There are different ways to describe and to parameterize the space of the possible orbits. In this article, new metrics are proposed which extend distance definitions suggested in previous works. In these metrics in addition to orbital plane and orbital shape, also the position of the object along the orbit is taken into account. The obtained distances are scaled according to the orbit covariance. This has the advantage that the distance between orbits with different accuracy can be evaluated. The proposed metrics are then compared with existing common metrics to assess their applicability. [ABSTRACT FROM AUTHOR]

Modern ideas about objects approaching the Earth are discussed. This population includes near-Earth asteroids (NEAs), including potentially hazardous asteroids, short-period comets, meteoroid streams, and large sporadic meteoroids. An overview is given of the currently available information on the dynamic and physical properties of NEAs and comets. Almost 5% of the currently known NEAs are extinct cometary nuclei or their fragments. Being outwardly similar with true asteroids, they differ markedly in their dynamic and physical properties. In order to distinguish between these groups of objects, it is necessary to study both their dynamic and physical parameters. Some of the known meteoroid streams are shown to contain, along with the countless small meteoroids, also large extinct fragments of cometary nuclei, which are classified as NEAs. A meteoroid stream and such bodies belonging to it form together an asteroid–meteoroid complex. Observational and theoretical data are presented to confirm the modern understanding of near-Earth objects. [ABSTRACT FROM AUTHOR]

The paper presents a method for processing positional observations of near-Earth objects using a numerical model of satellite motion developed at the Research Institute of Applied Mathematics and Mechanics of Tomsk State University (NII PMM TSU). The root-mean-square error of orbit improvement without rejection of observations for such objects does not exceed 0.3″ over a seven-day time interval. The results of the presentation of observations for the next occurrence of the object are obtained, which makes it possible to find the object in a time interval of five months. The orbit has been refined in the joint processing of measurements on several occurrences of the object over a six-month time interval. All results were obtained from observations made on the equipment of the Terskol Observatory Shared Use Center. [ABSTRACT FROM AUTHOR]

The risk of global catastrophe from natural sources may be significantly larger than previous analyses have found. In the study of global catastrophic risk (GCR), one line of thinking posits that deep human history renders natural GCRs insignificant. Essentially, the fact that natural hazards did not cause human extinction at any previous time makes it unlikely that they would do so now. This paper finds flaws in this argument, refines the theory of natural GCR, analyzes the space of natural GCRs, and presents implications for decision-making and research. The paper analyzes natural climate change, natural pandemics, near-Earth objects (asteroids, comets, and meteors), space weather (coronal mass ejections, solar flares, and solar particle events), stellar explosions (gamma-ray bursts and supernovae), and volcanic eruptions. Almost all natural GCR scenarios involve important interactions between the natural hazard and human civilization. Several natural GCR scenarios may have high ongoing probability. Deep human history provides little information about the resilience of modern global civilization to natural global catastrophes. The natural GCRs should not be dismissed on grounds of deep human history. Work on natural GCRs should account for their important human dimensions. A case can even be made for abandoning the distinction between natural and anthropogenic GCR. [ABSTRACT FROM AUTHOR]

The results are presented of a numerical simulation for the motion of a group of geosynchronous objects from positional observations obtained with the unique Zeiss-2000 research facility at the Terskol Observatory, Institute of Astronomy, Russian Academy of Sciences. A description is given of improved high-precision mathematical software designed to work with positional observations of satellites. The results are discussed of testing the software for observations of near-Earth objects obtained with the above-mentioned Zeiss-2000 facility. The modified software helps determine the dynamic state vector of a near-Earth object and its windage parameter. The testing has used observations of geosynchronous objects 90008, 90031, 90214, and 97149 (the object numbers are given in accordance with the numbering in the dynamic database of space objects maintained by the Keldysh Institute of Applied Mathematics, Russian Academy of Sciences). The resulting parameters are used to study the long-term orbital evolution of the objects. It is shown that three objects (90008, 90031, and 90214) are captured in a 1 : 1 resonance with the Earth's rotation velocity and have a stable motion in a rotating coordinate system close to a harmonic oscillator over a 10-year time interval. Object 97149 is not resonant, but its motion remains regular over a time interval of 10 years. [ABSTRACT FROM AUTHOR]

Proper elements are quasi-integrals of motion of a dynamical system, meaning that they can be considered constant over a certain timespan, and they permit to describe the long-term evolution of the system with a few parameters. Near-Earth objects (NEOs) generally have a large eccentricity, and therefore they can cross the orbits of the planets. Moreover, some of them are known to be currently in a mean-motion resonance with a planet. Thus, the methods previously used for the computation of main-belt asteroid proper elements are not appropriate for such objects. In this paper, we introduce a technique for the computation of proper elements of planet-crossing asteroids that are in a mean-motion resonance with a planet. First, we numerically average the Hamiltonian over the fast angles while keeping all the resonant terms, and we describe how to continue a solution beyond orbit-crossing singularities. Proper elements are then extracted by a frequency analysis of the averaged orbit-crossing solutions. We give proper elements of some known resonant NEOs and provide comparisons with non-resonant models. These examples show that it is necessary to take into account the effect of the resonance for the computation of accurate proper elements. [ABSTRACT FROM AUTHOR]

We present a description of the application "SDVEApp" designed to conduct research on the dynamic evolution of near-Earth space objects, namely, for calculation and visualization of the near-Earth object characteristics frequently used in research. In addition, the application makes it easier to work with a number of well-known catalogs of space objects. We demonstrate the results of application of the developed software to a set of objects from the NORAD and ESA "Classification of geosynchronous objects" catalogs, as well as objects, data on which were obtained from observations made by the employees of the Department of Celestial Mechanics and Astrometry of the Research Institute of PMM TSU. [ABSTRACT FROM AUTHOR]

Near-Earth object (NEO) impact is one of the examples of high impact and low probability (HILP) event, same as the Covid-19 pandemic the world faces since the beginning of 2020. The 7th Planetary Defense Conference held by the International Academy of Astronautics (IAA) in April 2021 included an exercise on a hypothetical NEO impact event, allowing the planetary defense community to discuss potential responses. Over the span of the 4-day conference this exercise connected disaster response and management professionals to participate in a series of panels, providing feedback and perspective on the unfolding crisis scenario. The hypothetical but realistic asteroid threat scenario illustrated how such a short-warning threat might evolve. The scenario utilized during the conference indicates a need to prepare now for what might come in the future, because even with advance notice, preparation time might be minimal. This scenario chose Europe for the impact, which may likely cope with such a disaster, through the Union Civil Protection Mechanism (UCPM) and other solidarity and support mechanisms within the European Union (EU), as well as with potential support from international partners. This short article raises concern about other areas in the world on how they may access NEO impact information and cope with such disasters. It also provides an idea on vast scale of such disaster vis-à-vis the current capacity of response systems to cope with a larger event in Europe or elsewhere. This scenario showed that planetary defense is a global endeavor. Constant engagement of the planetary defense and disaster response communities is essential in order to keep the world safe from potential disasters caused by NEO impacts. [ABSTRACT FROM AUTHOR]

A new version of the numerical model of artificial Earth satellites (AES) motion is presented, which consists of four program blocks intended for 1) predicting the AES motion, 2) studying the chaotic condition in motion of near-Earth space objects, 3) determining the AES motion parameters from the measurement data, and 4) studying the resonance dynamics of near-Earth objects. The main feature of the new version is the use of a new more efficient integrator, which is a further development of the well-known Everhart integrator. It is shown that with the same accuracy, the new integrator has much higher performance. The version intended for use in the parallel computing environment and called the "Numerical model of motion of AES systems" has undergone additional changes related to the optimization of the computation parallelization process. The estimates show that with the new method of parallelization, the integration accuracy is more stable and the integration speed increases several times. [ABSTRACT FROM AUTHOR]

Spacecraft propagation tools describe the motion of near-Earth objects and interplanetary probes using Newton's theory of gravity supplemented with the approximate general relativistic n-body Einstein–Infeld–Hoffmann equations of motion. With respect to the general theory of relativity and the long-standing recommendations of the International Astronomical Union for astrometry, celestial mechanics and metrology, we believe modern orbitography software is now reaching its limits in terms of complexity. In this paper, we present the first results of a prototype software titled General Relativistic Accelerometer-based Propagation Environment (GRAPE). We describe the motion of interplanetary probes and spacecraft using extended general relativistic equations of motion which account for non-gravitational forces using end-user supplied accelerometer data or approximate dynamical models. We exploit the unique general relativistic quadratic invariant associated with the orthogonality between four-velocity and acceleration and simulate the perturbed orbits for Molniya, Parker Solar Probe and Mercury Planetary Orbiter-like test particles subject to a radiation-like four-force. The accuracy of the numerical procedure is maintained using a 5-stage, 10 th -order structure-preserving Gauss collocation symplectic integration scheme. GRAPE preserves the norm of the tangent vector to the test particle worldline at the order of 10 - 32 . [ABSTRACT FROM AUTHOR]

A method for assessing the probability of collision of two observed space objects in near-earth space is proposed. The solution is based on the method of statistical modeling, which made it possible to take into account the shape and orientation of approaching objects. The developed method provides for the automatic stop of calculations when the required accuracy and reliability of the solution is achieved. An analysis of existing approaches to assessing the probability of collision is given. A calculation was made for the real approach of the vehicles CHINASAT-20 and SHIJIAN-17. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the dynamic structure of near-Earth orbital space in the regions of orbital resonances 1 : 4, 1 : 6, and 1 : 8 with the speed of the Earth's rotation and studying the orbital evolution of objects moving in these regions. The action zones of five components for each of the listed orbital resonances, apsidal–nodal secular resonances and resonances with the mean motion of the third body (the Moon and the Sun) in the indicated regions of near-Earth orbital space are revealed. Distribution maps of the revealed resonances are presented. The dynamic maps of the studied areas obtained using the MEGNO indicator are presented. Areas of randomness corresponding to the overlap of resonances of different types are revealed. [ABSTRACT FROM AUTHOR]

Taxonomies are useful for providing structure when categorizing large numbers of near-Earth space objects by the types of maneuvers they perform. In particular, lateral thrusting, longitudinal thrusting, and drifting may be directly linked to detectable changes in the orbital elements that affect object location and orientation. The purpose of this work is to develop a fully-automated taxonomy of the geosynchronous objects based on dynamical principles. Groups of objects are found using clustering methods, and two clustering methods are compared for constructing the taxonomy. The first is an adaptive k-means algorithm that does not require a priori information. It is compared to an agglomerative clustering algorithm that utilizes limits on cluster sizes to form distinct clusters. The effectiveness of the automated taxonomy is determined by comparison with the European Space Agency's DISCOS database and clusters from the Geosynchronous yearly report. [ABSTRACT FROM AUTHOR]

The paper presents the results of identifying secular resonances that act on objects moving in the LEO–MEO regions. The results were obtained from the processing of data of an extensive numerical experiment on the study of the orbital evolution of objects moving in the range of the semi-major axes from 8000 km to the operation zone of the GLONASS navigation systems (25 500 km), with inclinations from 0° to 180° outside the zones of orbital resonances. The distribution maps of the identified secular resonances are given. The analysis of the orbital evolution of the objects is presented. [ABSTRACT FROM AUTHOR]

Carbonaceous chondrite compositions could be an order of magnitude more abundant in comets than in asteroids; future observations of comets will calibrate this proportion. Even adopting the full reduction factor of HT ht associated with the value of I N i from Desch et al.[1], a cometary Chicxulub impactor would be up to HT ht times more likely than an asteroid Chicxulub impactor[2]. A cometary Chicxulub impactor remains more likely than an asteroid Chicxulub impactor if the fraction of CC-like comets is HT ht . [Extracted from the article]

Terrestrial accelerator facilities can generate ion beams which enable the testing of the resistance of materials and thin film coatings to be used in the space environment. In this work, a TiO 2 /Al bi-layer coating has been irradiated with a He + beam at three different energies. The same flux and dose have been used in order to investigate the damage dependence on the energy. The energies were selected to be in the range 4–100 keV, in order to consider those associated to the quiet solar wind and to the particles present in the near-Earth space environment. The optical, morphological and structural modifications have been investigated by using various techniques. Surprisingly, the most damaged sample is the one irradiated at the intermediate energy, which, on the other hand, corresponds to the case in which the interface between the two layers is more stressed. Results demonstrate that ion energies for irradiation tests must be carefully selected to properly qualify space components. [ABSTRACT FROM AUTHOR]

This study is focused on the relationships between the κ-Cygnid meteor shower and different groups of asteroids crossing the Earth's orbit (the so-called near-Earth objects (NEOs)). The analysis is based on the visible structure of the meteor shower and a comprehensive strategy for estimating the proximity of orbits of two bodies. The κ-Cygnid meteor shower (abbreviated as KCG) is observed from August 3 to August 25 every year; it is classified as a minor shower, and the size of its mean orbit is around 3.2 AU, while the geocentric velocity is 20.9 km/s. No parent body (PB) of the shower has been found among comets so far. Relationships between the shower and asteroids, as potential PBs of the shower, are under active examination; some hypotheses on this subject can be found on the website of the Meteor Data Center (MDC) of the International Astronomical Union (IAU). [ABSTRACT FROM AUTHOR]

We compare the number of lunar craters larger than 15 km across and younger than 1.1 Ga to the estimates of the number of craters that could have been formed for 1.1 Ga if the number of near-Earth objects and their orbital elements during that time were close to the corresponding current values. The comparison was performed for craters over the entire lunar surface and in the region of the Oceanus Procellarum and maria on the near side of the Moon. In these estimates, we used the values of collision probabilities of near-Earth objects with the Moon and the dependences of the crater diameters on the impactor sizes. According to the estimates made by different authors, the number density of known Copernican craters with diameters D ≥ 15 km in mare regions is at least double the corresponding number for the remaining lunar surface. Our estimates do not contradict the growth in the number of near-Earth objects after probable catastrophic fragmentations of large main-belt asteroids, which may have occurred over the recent 300 Ma; however, they do not prove this increase. Particularly, they do not conflict with the inference made by Mazrouei et al. (2019) that 290 Ma ago the frequency of collisions of near-Earth asteroids with the Moon increased by 2.6 times. The number of Copernican lunar craters with diameters not smaller than 15 km is probably higher than that reported by Mazrouei et al. (2019). For a probability of a collision of an Earth-crossing object (ECO) with the Earth in a year equaled to 10–8 , our estimates of the number of craters agree with the model, according to which the number densities of the 15-km Copernican craters for the whole lunar surface would have been the same as that for mare regions if the data by Losiak et al. (2015) for D < 30 km were as complete as those for D > 30 km. With this collision probability of ECOs with the Earth and for this model, the cratering rate may have been constant over the recent 1.1 Ga. [ABSTRACT FROM AUTHOR]

The first experience in application of artificial neural networks to a study of the dynamic structure of a selected region of the near-Earth orbital space is described. An analysis of time series describing the evolution of the resonant characteristics of the dynamic structure of the region is usually performed manually. However, a study of the dynamic structure of a large region of the orbital space requires consideration of several tens of thousands of such time series. As an alternative approach, technologies of deep learning can be used, namely, design of architecture of one-dimensional convolutional neural network for supervised learning. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study of the dynamic structure of near-Earth orbital space in the 1 : 2 resonance region with Earth's rotation speed. The results of an extensive numerical-analytical experiment to study the orbital evolution of objects moving in the semimajor axis range from 26 550 to 26 570 km, with inclinations from 0° to 180°. In this region, the zones of action of the five components of the orbital resonance and aspidal–nodal secular resonances of low orders are revealed. The distribution maps of the revealed resonances are constructed. The dynamic structure of the orbital space was also investigated using the fast Lyapunov characteristic of MEGNO and represented by a MEGNO map of the region in the section by the plane (inclination of the orbit, major axis). It is shown that a feature of the dynamic evolution of most of the studied orbits is randomness arising under the influence of overlapping resonances of various types. [ABSTRACT FROM AUTHOR]

A modified method for identifying and studying secular resonances in the dynamics of near-Earth objects is described. Unlike the traditionally used approach based on approximate analytical formulas for calculating secular frequencies that are valid only for small eccentricities, the proposed method uses exact values obtained in the process of numerical simulation of the motion from the Newton–Euler equations. This technique can be used to analyze the dynamics of objects with any arbitrary eccentricities of the orbits, but its application to the study of the motion along orbits with large or rapidly growing eccentricities is most interesting. Testing is carried out on the example of research of the Lidov–Kozai resonances in the dynamics of near-Earth objects. [ABSTRACT FROM AUTHOR]

Every year near-Earth object (NEO) surveys discover hundreds of new asteroids, including the potentially hazardous asteroids (PHA). The possibility of impact with the Earth is one of the main motivations to track and study these objects. This paper presents a tether assisted methodology to deflect a PHA by connecting a smaller asteroid, altering the center of mass of the system, and consequently, moving the PHA to a safer orbit. Some of the advantages of this method are that it does not result in fragmentation, which could lead to another problem, and also the flexibility to change the configuration of the system to optimize the deflection according to the warning time. The dynamics of the PHA-tether-asteroid system is analyzed, and the amount of orbit change is determined for several initial conditions. Only motion in the plane of the orbit of the PHA around the Sun is considered, thus the PHA chosen for the simulations has low orbit inclination. Analysis of the dynamics of the system shows that the method is feasible for planetary defense. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the possible disruption of a prolate ellipsoidal small body by the Earth's tidal forces during a close flyby. An exact expression for the stress tensor under the action of gravity, rotation, and tidal forces is obtained using the analytical solution of the elastic problem. Constraints for the critical distance are derived taking into account the size, shape, density, mechanical properties (material strength and Poisson ratio), rotation, and two variants of the body orientation. Asteroid 433 Eros is considered as a case study. The results are important for methods for assessing the asteroid hazard of near-Earth objects (NEO) and the evolution of terrestrial planets. [ABSTRACT FROM AUTHOR]

Asteroids and other Small Solar System Bodies (SSSBs) are of high general and scientific interest in many aspects. The origin, formation, and evolution of our Solar System (and other planetary systems) can be better understood by analysing the constitution and physical properties of small bodies in the Solar System. Currently, two space missions (Hayabusa2, OSIRIS-REx) have recently arrived at their respective targets and will bring a sample of the asteroids back to Earth. Other small body missions have also been selected by, or proposed to, space agencies. The threat posed to our planet by near-Earth objects (NEOs) is also considered at the international level, and this has prompted dedicated research on possible mitigation techniques. The DART mission, for example, will test the kinetic impact technique. Even ideas for industrial exploitation have risen during the last years. Lastly, the origin of water and life on Earth appears to be connected to asteroids. Hence, future space mission projects will undoubtedly target some asteroids or other SSSBs. In all these cases and research topics, specific knowledge of the structure and mechanical behaviour of the surface as well as the bulk of those celestial bodies is crucial. In contrast to large telluric planets and dwarf planets, a large proportion of such small bodies is believed to consist of gravitational aggregates ('rubble piles') with no—or low—internal cohesion, with varying macro-porosity and surface properties (from smooth regolith covered terrain, to very rough collection of boulders), and varying topography (craters, depressions, ridges). Bodies with such structure can sustain some plastic deformation without being disrupted in contrast to the classical visco-elastic models that are generally valid for planets, dwarf planets, and large satellites. These SSSBs are hence better described through granular mechanics theories, which have been a subject of intense theoretical, experimental, and numerical research over the last four decades. This being the case, it has been necessary to use the theoretical, numerical and experimental tools developed within soil mechanics, granular dynamics, celestial mechanics, chemistry, condensed matter physics, planetary and computer sciences, to name the main ones, in order to understand the data collected and analysed by observational astronomy (visible, thermal, and radio), and different space missions. In this paper, we present a review of the multi-disciplinary research carried out by these different scientific communities in an effort to study SSSBs. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S0038094623340014 [ABSTRACT FROM AUTHOR]

The paper presents the results of the study of the dynamic structure of near-Earth orbital space in the region of the 1 : 3 resonance with the Earth's rotation. The results of an extensive numerical-analytical experiment to study the orbital evolution of objects moving in the range of semimajor axes from 20 250 to 20 280 km, with inclinations from 0 to 90 degrees, are presented. The zones of action of five components of orbital resonance and apsidal-nodal secular resonances of low orders are revealed. Maps of the distribution of identified resonances are given. The analysis of the dynamic structure of the orbital space using the fast Lyapunov characteristic (MEGNO) is presented, and the MEGNO map of the region in the plane section (orbit inclination, semimajor axis) is given. It has been shown that the dynamic evolution of most of the orbits is chaotic, which is due to the superposition of different types of resonances. [ABSTRACT FROM AUTHOR]

Modern star trackers are based on photodetector arrays such as CCD or CMOS arrays. The accuracy of commercially available devices is ~1-3 arcseconds. However, the development of the space industry calls for higher orientation accuracies, which are needed in laser space communications, monitoring of near-Earth space and space debris, high-precision global mapping, and remote sensing of the Earth. The problems associated with enhancing the accuracy of modern star trackers are discussed. [ABSTRACT FROM AUTHOR]

Asteroids, comets and moons are leftovers of planet formation. Studying them and their samples, including meteorites, can help us to learn how the Earth was made and acquired the ingredients for life, to obtain practical information for deflecting near-Earth objects (NEOs), and to access resources that would enable space habitats and voyages. Answers are hidden beneath their complex and evolving exteriors. [ABSTRACT FROM AUTHOR]

The results of an analysis of changes in resonant orbital dynamics of near-Earth objects, which are caused by light pressure, are presented. We describe features of the orbital evolution of the objects subjected to the combined effect of secular resonances and light pressure. It was shown that the transfer of objects to highly elliptical and hyperbolic orbits is possible when the object’s area-to-mass ratio is large. [ABSTRACT FROM AUTHOR]

Joint influence of secular resonances and light pressure on the long-term orbital evolution of objects in the near-earth space bounded by the semi-major axes of orbits from 15000 to 45000 km is considered. The orbital evolution of each object is considered for three area-to-mass ratios: 0.001, 1, and 10 m/kg. Special attention is given to a search for resonances whose influence increases the eccentricities of near-earth space object orbits and to their joint analysis with the influence of the light pressure force on the object dynamics. [ABSTRACT FROM AUTHOR]

The Institute of Applied Astronomy of the Russian Academy of Sciences and the Goldstone Deep Space Communications Complex regularly conduct intercontinental radar observations of near-Earth objects using a 70-m DSS-14 antenna as a transmitter and the 32-m RT-32 radio telescopes of the Quasar VLBI network as receivers. To carry out the observations, the existing complex for reception, conversion, and recording of signals from the RT-32 radio telescopes has been adapted and special software for scheduling observations and processing echo signals has been developed. Since 2015, echoes from the 2011 UW158, 2003 TL4, 2003 YT1, 2003 BD44, and 2014 JO25 asteroids have been recorded. The power spectra of the echoes from these asteroids have been obtained and analyzed. [ABSTRACT FROM AUTHOR]

We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL ~ −1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 R were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another field-aligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet. [ABSTRACT FROM AUTHOR]

In recent years, following the Chelyabinsk event of February 15, 2013, the lower size limit for presumably dangerous near-Earth objects has been decreased manyfold (essentially, from 140 m to ~10 m). This has drawn an increased attention to the properties of the population of decameter-sized bodies, in particular, the bodies that approach the Earth from the sunward side (daytime sky). The current paper is concerned with various properties of this population. The properties of the ensemble are analyzed using both observational data from other authors and theoretical estimates obtained by cloning virtual bodies. This question is of great practical importance, as the means for detecting such bodies (for example, the SODA project) need to be developed with consideration for the requirements imposed by the population properties. We have shown that the average rate of entering near-Earth space (NES), i.e., at distances less than ~1 million km from the Earth, for decameter-sized and larger bodies from the daytime sky (elongation values of entry points less than 90°) is approximately 620 objects per year for elongation angles of the detection point <90° and approximately 220 objects per year for elongation angles of the detection point <45°. [ABSTRACT FROM AUTHOR]

As follows from dynamical studies, in the course of evolution, most near-Earth objects reach orbits with small perihelion distances. Changes of the asteroids in the vicinity of the Sun should play a key role in forming the physical properties, size distribution, and dynamical features of the near-Earth objects. Only seven of the discovered asteroids are currently moving along orbits with perihelion distances q < 0.1 AU. However, due to the Kozai-Lidov secular perturbations, the asteroids, having recently passed near the Sun, could by now have moved to orbits farther from the Sun. In this study, we found asteroids that have been recently orbiting with perihelion distances q < 0.1 AU. Asteroids may be on such orbits for hundreds to tens of thousands of years. To carry out astrophysical observations of such objects is a high priority. [ABSTRACT FROM AUTHOR]

Among 11 673 of near-Earth objects (NEOs), 52 asteroids are identified, which, together with the Eccentrids meteor system, comprise a single population of small bodies of the Solar System with the smallest orbits of high eccentricity. Some features of this unique system of bodies are discussed in this paper. The distribution of perihelion longitudes is studied for the given group of asteroids and compared to that of the Aten asteroids, which are the most similar to the Eccentrids. The dependence is obtained of the character of perihelion longitude distribution on the eccentricities of the NEO orbits. Eight asteroid stream of the Eccentrids are found. The Eccentrids asteroids approaching the Earth's orbit along its whole length in their aphelia can pose a certain hazard for the Earth. [ABSTRACT FROM AUTHOR]

The problem of detecting dangerous (in the sense of a collision with the Earth) celestial bodies of natural origin and the modern concept of building a system of detection of such bodies are discussed. The concept includes two items: remote detection of large (>50 m) hazardous objects providing warning time of several tens of days, which is sufficient to allow the active counteraction and detection of hazardous bodies larger than 10 m in near-Earth space providing warning time of few hours, which is sufficient to issue a warning and to carry out mitigation activities. Some examples of this approach and prospects of the international cooperation are discussed. [ABSTRACT FROM AUTHOR]

We present the first large statistical study of extreme geomagnetic storms based on historical data from the time period 1868 - 2010. This article is the first of two companion papers. Here we describe how the storms were selected and focus on their near-Earth characteristics. The second article presents our investigation of the corresponding solar events and their characteristics. The storms were selected based on their intensity in the aa index, which constitutes the longest existing continuous series of geomagnetic activity. They are analyzed statistically in the context of more well-known geomagnetic indices, such as the Kp and Dcx/Dst index. This reveals that neither Kp nor Dcx/Dst provide a comprehensive geomagnetic measure of the extreme storms. We rank the storms by including long series of single magnetic observatory data. The top storms on the rank list are the New York Railroad storm occurring in May 1921 and the Quebec storm from March 1989. We identify key characteristics of the storms by combining several different available data sources, lists of storm sudden commencements (SSCs) signifying occurrence of interplanetary shocks, solar wind in-situ measurements, neutron monitor data, and associated identifications of Forbush decreases as well as satellite measurements of energetic proton fluxes in the near-Earth space environment. From this we find, among other results, that the extreme storms are very strongly correlated with the occurrence of interplanetary shocks (91 - 100 %), Forbush decreases (100 %), and energetic solar proton events (70 %). A quantitative comparison of these associations relative to less intense storms is also presented. Most notably, we find that most often the extreme storms are characterized by a complexity that is associated with multiple, often interacting, solar wind disturbances and that they frequently occur when the geomagnetic activity is already elevated. We also investigate the semiannual variation in storm occurrence and confirm previous findings that geomagnetic storms tend to occur less frequently near solstices and that this tendency increases with storm intensity. However, we find that the semiannual variation depends on both the solar wind source and the storm level. Storms associated with weak SSC do not show any semiannual variation, in contrast to weak storms without SSC. [ABSTRACT FROM AUTHOR]

The search for asteroids that maintain stable motion in the zone between the Earth and Mars has been performed. The near-Earth object 2013 RB6, which has avoided close encounters with the planets for a long period of time, has been found. Integration of the equations of motion of the object shows that its dynamical lifetime in the zone between the Earth and Mars significantly exceeds 100 Myr. 2013 RB6 moves away from orbital resonances with the planets, but is in the secular resonance v5. Solving the question of its origin requires further observations. [ABSTRACT FROM AUTHOR]

We discuss the dynamical features of near-Earth objects moving in dangerous proximity to Earth. We report the computation results for the motions of all observed near-Earth objects over a 600-year-long time period: 300 years in the past and 300 years in the future. We analyze the dynamical features of Earth-approaching objects. In particular, we established that the observed distribution of geocentric velocities of dangerous objects depends on their size. No bodies with geocentric velocities smaller that 5 kms have been found among hazardous objects with absolute magnitudes H <18, whereas 9% of observed objects with H <27 pass near Earth moving at such velocities. On the other hand, we found a tendency for geocentric velocities to increase at H >29. We estimated the distribution of absolute magnitudes of hazardous objects based on our analysis of the data for the asteroids that have passed close to Earth. We inferred the Earth-impact frequencies for objects of different sizes. Impacts of objects with H <18 with Earth occur on average once every 0.53 Myr, and impacts of objects with H <27-once every 130-240 years. We show that currently about 0.1% of all near-Earth objects with diameters greater than 10 m have been discovered. We point out the discrepancies between the estimates of impact rates of Chelyabinsk-type objects, determined from fireball observations and from the data of telescopic asteroid tracking surveys. These estimates can be reconciled assuming that Chelyabinsk-sized asteroids have very low albedos (about 0.02 on average). [ABSTRACT FROM AUTHOR]

For a long time, the generation mechanism of simultaneous sound with passing of large meteors was a research edge until a reasonable mechanism was proposed for that. This mechanism is based on the existence of ELF/VLF radio signals. This research that aims for detection of these signals archives an improvement over previous works. The signal was found on the extremely low frequency (ELF) band which could not be generated by other sources like lightning, has a frequency range between several Hertz to 500 Hz, and so could be missed with noises produce by electrical machines. The new signal is presented at this work has a good correlation with synchronized visual data that were collected on the peak of Geminids 2011 meteor shower. [ABSTRACT FROM AUTHOR]

In this study, equilibrium points and periodic orbits in the potential field of asteroids are investigated. We present the linearized equations of motion relative to the equilibrium points and characteristic equations. We find that the distribution of characteristic multipliers of periodic orbits around the equilibrium point and the distribution of eigenvalues of the equilibrium point correspond to each other. The distribution of eigenvalues of the equilibrium point confirms the topology and the stability of periodic orbits around the equilibrium point. [ABSTRACT FROM AUTHOR]

The variation in the IMF direction distribution during the 22-year solar magnetic cycle has been studied. Data obtained in near-Earth orbits and measurements in the heliospheric regions located far from the Earth, performed with the Helios and Ulysses spacecraft devices, have been analyzed. It has been found that the correlation between the azimuth and magnetic field fluctuations is statistically significant in the low-latitude heliospheric region at heliocentric distances of 0.3-5.4 AU, and the sign of this correlation reverses at a change in the polar solar magnetic field orientation. In the polar zones of the heliosphere outside the latitudinal extension of the heliospheric current sheet, the angle correlation coefficient rapidly decreases with increasing heliographic latitude. The angle correlation sign reversal during the 22-year cycle is accompanied by a change of the asymmetry sign of the magnetic field inclination distribution. [ABSTRACT FROM AUTHOR]

Near-Earth space is analyzed as a specific object for global monitoring. The structure and specific features of near-Earth space are considered. It is shown that this zone includes almost all the terrestrial fields and the regions where space is actively explored by man. [ABSTRACT FROM AUTHOR]

The formation of space debris as an accumulation of small heavenly bodies in near-Earth space is considered. How debris can arise in near-Earth space is described. The accumulation of debris is shown to have a ring structure. The formation and spatial distribution of debris are statistically analyzed. A hypothesis for the formation of debris rings in near-Earth space is proposed. [ABSTRACT FROM AUTHOR]

In this paper, a method to capture near-Earth objects (NEOs) incorporating low-thrust propulsion into the invariant manifolds technique is investigated. Assuming that a tugboat-spacecraft is in a rendez-vous condition with the candidate asteroid, the aim is to take the joint spacecraft-asteroid system to a selected periodic orbit of the Sun-Earth restricted three-body system: the orbit can be either a libration point periodic orbit (LPO) or a distant prograde periodic orbit (DPO) around the Earth. In detail, low-thrust propulsion is used to bring the joint spacecraft-asteroid system from the initial condition to a point belonging to the stable manifold associated to the final periodic orbit: from here onward, thanks to the intrinsic dynamics of the physical model adopted, the flight is purely ballistic. Dedicated guided and capture sets are introduced to exploit the combined use of low-thrust propulsion with stable manifolds trajectories, aiming at defining feasible first guess solutions. Then, an optimal control problem is formulated to refine and improve them. This approach enables a new class of missions, whose solutions are not obtainable neither through the patched-conics method nor through the classic invariant manifolds technique. [ABSTRACT FROM AUTHOR]

Results are presented of a study of the effect of secular resonances on the dynamic evolution of objects moving along polar orbits with eccentricities changing over a wide range and semi-major axes from 8 000 to 55 000 km. It is shown that motion of polar objects with semi-major axes in the range 50 000-55 000 km is most complicated in the examined altitude range. [ABSTRACT FROM AUTHOR]

We analyzed spectra, trajectories, orbits, light curves, and decelerations of eight Draconid meteors observed from Northern Italy on October 8, 2011. Meteor morphologies of two of the meteors are also presented, one of them obtained with a high resolution camera. Meteor radiants agree with theoretical predictions, with a hint that some meteors may belong to the pre-1900 meteoroid trails. The spectra confirm that Draconids have normal chondritic composition of main elements (Mg, Fe, Na). There are, nevertheless, differences in the temporal evolution of Na line emission. The differences are correlated with the shapes of the light curves and the deceleration rates. Our data confirm that Draconids are porous conglomerates of grains, nevertheless, significant differences in the atmospheric fragmentation of cm-sized Draconids were found. Various textures with various resistance to fragmentation exist among Draconid meteoroids and even within single meteoroids. [ABSTRACT FROM AUTHOR]

In this work we summarize the initial results of a targeted effort of the ESA NEO Coordination Centre to obtain additional observational data in order to eliminate or reduce the impact probability estimate of a subset of the known near-Earth objects representing the highest fraction of the total known impact risk, as measured by the Palermo Scale. [ABSTRACT FROM AUTHOR]

The Chelyabinsk asteroid impact is the second largest asteroid airburst in our recorded history. To prepare for a potential threat from asteroid impacts, it is important to understand the nature and formational history of Near-Earth Objects (NEOs) like Chelyabinsk asteroid. In orbital evolution of an asteroid, collision with other asteroids is a key process. Here, we show the existence of a high-pressure mineral jadeite in shock-melt veins of Chelyabinsk meteorite. Based on the mineral assemblage and calculated solidification time of the shock-melt veins, the equilibrium shock pressure and its duration were estimated to be at least 3- 12 GPa and longer than 70 ms, respectively. This suggests that an impactor larger than 0.15-0.19 km in diameter collided with the Chelyabinsk parent body at a speed of at least 0.4-1.5 km/s. This impact might have separated the Chelyabinsk asteroid from its parent body and delivered it to the Earth. [ABSTRACT FROM AUTHOR]

This study continues our previous works on searching for the main source of the nuclei of Jupiter family comets (JFCs). Angular orbit element distributions are analyzed for comets and asteroids of different groups. The distributions of JFCs by argument of perihelion ω and longitude of perihelion π are studied. The distributions are shown not to have been formed during the evolution of JFCs in their current orbits. Similar distributions N(ω) and N(π) are not observed in bodies that have come into the JFC orbits from external sources. At the same time, the distributions of JFCs by all angular orbit elements are very similar to those of the Trojans. It is concluded that the latter are likely to be the main source of the JFC nuclei. [ABSTRACT FROM AUTHOR]