On the dynamics of the exoplanetary system Kepler-413

This study is concerned with the stability of motion of the circumbinary exoplanet Kepler-413b. The analysis is performed within the framework of a flat restricted three-body problem. The stability diagram is plotted in the plane of initial conditions “pericentric distance—eccentricity” using mass calculations of Lyapunov exponents. According to the diagram, the Kepler-413b planet is located in a stable resonance cell, confined by the mean-motion resonances 6: 1 and 7: 1 with a central binary star, which agrees with the conclusions of Kostov et al. (2014) based on calculations of the MEGNO parameter. It is shown that the value of the critical semimajor axis acquired from the empirical formula of Holman and Wiegert (1999) almost coincides with the value obtained directly from the stability diagram; at low and moderate eccentricities of the planetary orbit, the position of the calculated boundary of the chaos zone is in close agreement with the boundary predicted by Shevchenko’s theory (2015). If the planet were in the instability zone, its characteristic Lyapunov time would be only ~1 year. In accordance with the conclusions of Kostov et al. (2014), it has been shown that the planet Kepler-413b is outside the habitability zone of the system.     

On the definition of asteroid magnitudes

The problem of a sharp definition of two photometric parameters for asteroids in the presence of empirical phase functions is discussed. In a rational magnitude system advantage should be taken of the nearly linear phase curve.     

The Tucson revised index of asteroid data

Attention is called to the availability of the TRIAD computer file, a compilation of all reliable physical parameters for minor planets.     

On the asteroid belt's orbital and size distribution

For absolute magnitudes greater than the current completeness limit of H-magnitude ∼15 the main asteroid belt's size distribution is imperfectly known. We have acquired good-quality orbital and absolute H-magnitude determinations for a sample of small main-belt asteroids in order to study the orbital and size distribution beyond H=15, down to sub-kilometer sizes (H>18). Based on six observing nights over a 11-night baseline we have detected, measured photometry for, and linked observations of 1087 asteroids which have one-week time baselines or more. The linkages allow the computation of full heliocentric orbits (as opposed to statistical distances determined by some past surveys). Judged by known asteroids in the field the typical uncertainty in the (a/e/i) orbital elements is less than 0.03 AU/0.03/0.5°. The distances to the objects are sufficiently well known that photometric uncertainties (of 0.3 magnitudes or better) dominate the error budget of their derived H-magnitudes. The detected asteroids range from HR=12-22 and provide a set of objects down to sizes below 1 km in diameter. We find an on-sky surface density of 210 asteroids per square degree in the ecliptic with opposition magnitudes brighter than mR=23, with the cumulative number of asteroids increasing by a factor of 10^0.27/mag from mR=18 down to the mR?23.5 limit of our survey. In terms of absolute H magnitudes, we find that beyond H=15 the belt exhibits a constant power-law slope with the number increasing proportional to ¹⁰0.30H from H?15 to 18, after which incompleteness begins in the survey. Examining only the subset of detections inside 2.5 AU, we find weak evidence for a mildly shallower slope for H=15-19.5. We provide the information necessary such that anyone wishing to model the main asteroid belt can compare a detailed model to our detected sample.     

Search of exoplanetary radio signals in the presence of strong interference: enhancing sensitivity by data accumulation

We develop a statistical approach aimed at the detection of weak sporadic pulses on the noise background. The results are applied to modeling the observational time series where pulsed radio emissions have to be recognized against the sky background fluctuations. The proposed methodology demonstrates the efficiency of using the statistics of peak values (integrated tail of probability distribution function of the intensity) for the purpose of signal detection. It is established that the highest sensitivity is reached with this method at low values of the filling factor (duty cycle) of the pulsed signals. If in addition the pulses have sufficiently high intensity, the discussed approach performs better than simple integration over the observational time. Then we discuss the possibility of detecting radio pulses from exoplanetary magnetospheres, especially from known “hot Jupiters” found by radial velocity measurements in the visible and we report our results from extensive observations of several candidate exoplanets with the world largest decameter telescope UTR-2. Although no detection of pulsed emission from exoplanets has been found to date, the analysis demonstrates the feasibility of detection with more stable receivers and longer observational time.     

On the transport of bodies within and from the asteroid belt

Abstract— This paper explores two processes, sweeping secular resonance (Ward, 1981) and gas drag (Lecar and Franklin, 1997), at work during the dispersal of the solar nebula. we have two aims not previously considered for the two mechanisms: (1) to explain the likely depletion, by a factor of 1000 or so, of the rocky material in the inner belt (2.0 < a < 3.2 AU); (2) to introduce a means for providing—or contributing to—the dispersion in semimajor axis of the various asteroidal taxonomic classes. We suggest that large asteroids with birthplaces separated by an astronomical unit or more can be finally deposited, owing to drag, at the same semimajor axis. For example, we find that bodies with radii up to 100 km can be transferred by gas drag from the outer belt (a > 3.3 AU) well into the inner one, and that an object already in the inner belt as large or even larger than Vesta (r = 250 km)—thought to be the parent body of many meteorites—can be inwardly displaced by as much as an astronomical unit if the nebula dispersal times lie close to 10⁵ years. For such times, a large fraction of the inner belt's primordial mass can be ejected, with most of it passing into the inner solar system.     

Positive branch of asteroid polarization: Observational data and computer modeling

Observations of near-Earth asteroids at large phase angles made it possible to obtain a more complete (for ground-based observations) phase dependence of the polarization of the E-type asteroids’ radiation including the maximum of the positive branch of the linear polarization degree. It is shown that the position of the polarization maximum of high-albedo asteroids is noticeably shifted to the decrease of phase angles compared with S-type asteroids. Model calculations of polarimetric properties of random Gaussian particles that simulate dust particles on the regolith surface are carried out. Model calculations show a qualitatively similar behavior pattern of parameters of the positive polarization branch. The influence of the refractive index of individual scattering particles on the size and position of the maximum of the positive branch of the linear polarization degree is investigated within the considered model.     

On the bulk density of the M-type asteroid 16 Psyche

Recent estimates of the bulk density of the largest M-type asteroid 16 Psyche (1.4 and 1.8 g/cm³) seem to be too low for asteroids of this type. The interpretation of such low densities for the asteroid 16 Psyche with its increased metal content led to estimates of its macroporosity of 70%. In the present paper, it has been shown that the extremely low density estimates are caused primarily by the usage of a very high value of the IRAS diameter of the asteroid (D = 264 km, which corresponds to an IRAS albedo of 0.10). The application of the more accurate polarimetric albedo (0.170) and diameter (213 km) of Psyche results in a bulk density of the asteroid of 3.3 ± 0.7 g/cm³. For a moderate asteroid macroporosity of 30–40%, this density even agrees with the 50% metal content and, therefore, removes both the contradiction with the radar data and the problems of the very low density and unlikely high porosity of the asteroid 16 Psyche.     

On the stability of the satellites of asteroid 87 Sylvia

The triple asteroidal system (87) Sylvia is composed of a 280-km primary and two small moonlets named Romulus and Remus ( Marchis et al. 2005b ). Sylvia is located in the main asteroid belt, with semi-major axis of about 3.49 au, eccentricity of 0.08 and 11° of orbital inclination. The satellites are in nearly equatorial circular orbits around the primary, with orbital radius of about 1360 km (Romulus) and 710 km (Remus). In this work, we study the stability of the satellites Romulus and Remus. In order to identify the effects and the contribution of each perturber, we performed numerical simulations considering a set of different systems. The results from the three-body problem, Sylvia–Romulus–Remus, show no significant variation of their orbital elements. However, the inclinations of the satellites present a long-period evolution with amplitude of about 20° when the Sun is included in the system. Such amplitude is amplified to more than 50° when Jupiter is included. These evolutions are very similar for both satellites. An analysis of these results shows that Romulus and Remus are librating in a secular resonance and their longitude of the nodes are locked to each other. Further simulations show that the amplitude of oscillation of the satellites' inclination can reach higher values depending on the initial values of their longitude of pericentre. In those cases, the satellites get caught in an evection resonance with Jupiter, their eccentricities grow and they eventually collide with Sylvia. However, the orbital evolutions of the satellites became completely stable when the oblateness of Sylvia is included in the simulations. The value of Sylvia's J ₂ is about 0.17, which is very high. However, even just 0.1 per cent of this value is enough to keep the satellite's orbital elements with no significant variation.     

On possible binarity of Leatitia asteroid 39

The 39 Laetitia asteroid was observed by the digital television complex at the Crimean Astrophysical Observatory in 2000 in three spectral bands close to B, V and R simultaneously. An analysis of the variations in the absolute magnitude shows that there is a known period of rotation P = 0.^d214093. In variations of color indices B-V and V-R, this period is absent. Frequency analysis of color indices B-V and V-R makes it possible to reveal the true periods of rotation for components as follows: P ₁ = 0.^d237 and P ₂ = 0.^d177. The theoretical and observed period of librations agrees in value. Based on the two detected periods of rotation for asteroid components according to color indices B-V and V-R, a period of the libration of the satellite according to integral magnitude, we conclude that this asteroid is a binary one.     

On quasi-satellite periodic motion in asteroid and planetary dynamics

Applying the method of analytical continuation of periodic orbits, we study quasi-satellite motion in the framework of the three-body problem. In the simplest, yet not trivial model, namely the planar circular restricted problem, it is known that quasi-satellite motion is associated with a family of periodic solutions, called family f, which consists of 1:1 resonant retrograde orbits. In our study, we determine the critical orbits of family f that are continued both in the elliptic and in the spatial models and compute the corresponding families that are generated and consist the backbone of the quasi-satellite regime in the restricted model. Then, we show the continuation of these families in the general three-body problem, we verify and explain previous computations and show the existence of a new family of spatial orbits. The linear stability of periodic orbits is also studied. Stable periodic orbits unravel regimes of regular motion in phase space where 1:1 resonant angles librate. Such regimes, which exist even for high eccentricities and inclinations, may consist dynamical regions where long-lived asteroids or co-orbital exoplanets can be found.     

On the cometary nature of near-Earth asteroid 2003 EH1

Differential evolution of the orbits of near-Earth asteroid (NEA) 2003 EH1 and comet 96P/Machholz 1 under perturbing action of planets was investigated for the time interval of 28000 years. The similarity of the orbits was analyzed with the Southworth–Hawkins criterion D _SH. It has been shown that both the comet and the asteroid can be fragments of a nucleus of the same larger comet being a progenitor of the Quadrantid complex. A break-up of the parent comet apparently occurred approximately 9500 years ago. NEA 2003 EH1 is actually a dormant fragment of a nucleus of the parent comet. It was concluded that comet 96P/Machholz 1, NEA (186256) 2003 EH1 of the Amore group, and the Quadrantid meteorite swarm form a family of related objects.     

On the residuals in asteroid catalogs and a possible nongravitational effect

Based on numerical calculations of the evolution of asteroid orbits, we concluded in one of our previous papers that a nongravitational effect causing the spatial separation of asteroids with different albedos and with sizes of tens of kilometers could act in the Solar system. To find new arguments, we have analyzed the residuals in the catalogs of asteroid orbits for 1996 and 2006. The dependences pointing to the possibility of a nongravitational effect for orbits with larger residuals have been found to be more distinct than those for orbits with smaller residuals. This result may be considered as an indirect confirmation of the above nongravitational effect.     

SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450?C900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5?C10?AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (??2 Earth radii, ??10 M_??) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.     

On three types of fragmentation processes observed in the asteroid belt

From comparison of the mass ratio and velocity dispersion between the asteroid family members, we find that the fragmentation processes in the asteroid belt could be generally classified into three types: (a) surface cratering; (b) spallation; and (c) complete breakup as observed in the laboratory hypervelocity impact experiments. Whether there is ongoing accretion for large bodies like Ceres, as an additional type of collision process, is still an open question to be answered by further study.     

On the applicability of lunar breccias for paleomagnetic interpretations

Many of the breccias returned by the Apollo missions are capable of acquiring a substantial viscous remanent magnetization (VRM) which is of two forms. The first one has an upper limit to the relaxation times of about 100 to 1000min which corresponds to a grain diameter of about 145 Å. This suggests that the maximum relaxation time is determined by the transition from superparamagnetic to stable single domain particles. The second form of VRM follows the classical logt dependence typical for multidomain grains with a wide distribution of relaxation times. Hysteresis loop measurements yield the same kind of grain size distributions. In addition the analysis shows a fivefold enrichment of native iron in the breccias and soils as compared to the igneous rocks. In spite of a large VRM some breccias contain a stable remanent magnetization. Its intensity is typically 10^–6emu/gm, the same value found for igneous rocks. It is possible, therefore, to use some of the breccias to reconstruct the history of the lunar magnetic field.     

On the prevention of a possible collision of asteroid Apophis with the Earth

Currently, there is some positive probability of a collision of the asteroid Apophis with the Earth in 2036. In this study, the problem of preventing the collision by correcting the asteroid’s orbit is examined. The characteristics of the impulsive correction are investigated, as well as the ways of its implementation by kinetic and nuclear impacts. Impulsive and weak effects are compared. Weak effects leading to slow changes in the asteroid’s orbit are considered to be more usable because of the potentially higher accuracy of this correction. The characteristics of the gravitational effect of the asteroid by a special spacecraft (SC) kept by its control jet engines at a certain point near the asteroid and gravitationally perturbing the motion of Apophis are analyzed. The change in the perigee radius of the Apophis orbit in 2036 and the SC mass consumption are examined as functions of the effect duration, the SC mass, its distance to the asteroid, the start time of the correction, and the velocity of the SC engine exhaust jet.     

On the concept of the russian information and analytical center for asteroid and comet hazards

The concept is presented of the Russian information and analytical center for asteroid and comet hazards (IAC ACH) as a part of the national IAC for space threats. An overview is given of the center’s goals and objectives, as well as the requirements for the center, its structure, and the possible cooperation between the institutes of the Russian Academy of Sciences and other organizations in the creation of the center.