Showing papers in "Solar System Research in 2002"

Numerical Modeling of Marine Target Impacts

Abstract: The principles of the numerical modeling of marine impacts of large cosmic bodies are described. Three underwater impact structures, MjOlnir, Lockne, and Eltanin, are considered with the aim of studying the characteristics of the crater formation at varying sea depths; the distinctions between the underwater and continental craters are discussed. The mechanisms for tsunami-wave generation are studied at different ratios of sea depth to impactor size. The calculation results are compared to the experimental data obtained during underwater nuclear explosions.

Observations and Theoretical Analysis of Lightcurves of Natural Satellites of Planets

Abstract: We present the results of photometric observations of Saturn's seventh satellite Hyperion and four other planetary satellites: Saturn's moon Phoebe and three Jovian satellites Himalia, Elara, and Pasiphae. The observations have been conducted from September, 1999 to March, 2000, and during September–October, 2000. Analysis of periodic variations in Hyperion's lightcurve was performed. The lightcurve was modeled using the software package developed for calculating the rotational dynamics of a satellite. Our data generally indicate that over the period of observations Hyperion was in the chaotic mode of rotation.

Geology of the Venera and Vega Landing-Site Regions

Abstract: Using Magellan radar images of the Venera and Vega landing-site regions, we carried out a photogeologic analysis and mapping of these regions, the soil composition of which was earlier analyzed by the spacecraft of these series. All these landing-site regions are shown to possess a similar set of geologic situations, which are typical of the planet as a whole, and a similar sequence of geologic evolution. Judging by the results of mapping, a geochemically advanced material analyzed at the Venera-8 landing site appears to be a complex of shield plains (Psh). Tholeiitic compositions obtained by Venera-9/10 and Vega-1/2 probably represent the unit of plains with wrinkle ridges (Pwr), which is most common on Venus. The material of tholeiitic composition analyzed by Venera-14 is likely to be the unit of relatively young lobate plains (Pl).

Hydrated Silicates on M-, S-, and E-Type Asteroids as Possible Traces of Collisions with Bodies from the Jupiter Growth Zone

Abstract: Absorption bands near 0.43 and 0.60–0.80 μm, with a relative intensity of approximately 5–10%, were discovered in the reflectance spectra of five M asteroids (21, 75, 161, 201, and 497) and two S asteroids (11 and 198). It is highly probable that these absorption bands are related to oxidized and/or hydrated silicates that incorporate OH structural groups. Absorbed water in the surface material of about 24% of the known M asteroids and three E asteroids has been identified by a group of astronomers at the University of Arizona (Rivkin et al., 1995; Rivkin, 1997; Rivkin et al., 2000) on the basis of the characteristic 3-μm absorption band. In addition to this, four of the six E-type asteroids observed spectrally in the visible region quite recently were found to have an absorption band at 0.5 μm (Burbine et al., 1998; Fornasier and Lazzarin, 2001), which could likewise be associated with the presence of hydrated silicates in their material. The above data contradict the generally accepted viewpoint on the nature of M, S, and E asteroids, which is based on their common observed characteristics as bodies that arose at high temperatures (in the 1000–2000°C range). This contradiction, however, can be eliminated if use is made of the cosmogonic model developed by V.S. Safronov and co- workers. According to this model, the initial evolution of the main-belt asteroids was directly influenced by the process of the growth of Jupiter and was later controlled by its gravitational field.

On the Moment Method for the Modeling of Cloud Microphysics in Rarefied Turbulent Atmospheres: I. Condensation and Mixing

Abstract: A compact and efficient method for the description of microphysics and dynamics of condensational clouds in planetary atmospheres is proposed. It is based on the representation of the aerosol size distribution in terms of its moments. The method is justified, and different ways for closing the chain of moment equations and constructing numerical schemes are discussed. Simulations performed with the method of moments are compared to grid simulations. In a wide range of parameters, the accuracy of the method of moments is on the order of or better than 15–20%, which is comparable to or better than the accuracy of grid methods at low resolution. The method was successfully applied to the modeling of global circulation in the Martian atmosphere.

Multiple Scattering of Light in Regolith-like Media: Geometric Optics Approximation

Abstract: We present a numerical model that allows us to calculate the contribution of a specified scattering order in the geometric optics approximation for media composed of large particles with an arbitrary phase function It has been demonstrated that the correlated propagation of the incident and emergent rays, which is disregarded in the classical radiative-transfer theory, markedly affects the contributions of different orders of scattering, especially the first-order scattering If the theory describing the photometric properties of regolith-like media ignores the shadowing effect, the errors of its application may reach several tens of percent even for bright surfaces The packing density of a medium essentially influences the phase dependence of the first-order scattering, although its effect on the value and the phase curve of the higher scattering orders is relatively weak The backscattering peaks calculated on the basis of the Hapke theory are narrower than those obtained from the numerical simulations, because the Hapke theory is an approximate approach

Solar Occultation Measurements of the Martian Atmosphere on the Phobos Spacecraft: Water Vapor Profile, Aerosol Parameters, and Other Results

Abstract: The Auguste experiment onboard the Phobos spacecraft was devoted to solar occultation spectroscopy of the Martian atmosphere in the ultraviolet through infrared wavelength region Despite the short duration of the space mission and problems associated largely with a fault in the solar pointing system, data have been obtained on the chemical composition and aerosol content in the atmosphere of Mars at sunset early in the summer at equatorial latitudes (in the northern hemisphere) This paper presents a somewhat detailed review of the experiment performed, the data obtained, and their interpretation, and compares these data with new results Ozone traces were detected at altitudes of 40–60 km, and, in one case, an ozone profile was obtained Nine profiles of water vapor content at altitudes between 12 and 50 km were obtained from absorption data in the 187-μm band At altitudes of 23–25 km, the mean H2O concentration profile falls steeply to the value of ∼3 ppm, but at lower altitudes the relative H2O content is approximately constant (∼130 ppm) The overall content of water vapor is estimated as 83+25 -15 μm of settled water The temperature profile for the saturated atmosphere yields a cooling rate of 2 ± 1 K/km at altitudes from 25 to 35 km The atmospheric extinction profiles were measured at altitudes from 10 to 50 km at the wavelengths 19 and 37 μm The atmosphere is transparent up to 25–33 km; below this level radiation is attenuated by dust; it is also possible that a layer of water ice clouds is present at altitudes of 20–25 km High-altitude transparent (τ ≈ 003) clouds consisting supposedly of water ice were observed in 5 of 38 cases at altitudes z ≈ 50 km The optical depth τ0 of the atmosphere was estimated to be 02 ± 01, and constraints on the form of the size distribution of dust particles were established Spectral features in the 37 μm range have been previously attributed to formaldehyde; its content is substantially higher than the limits deduced from new ground-based observations The spectrum in the 37 μm range is discussed and other unsettled problems are pointed out

A Simple Method for Numerical Calculations of the Evolution of Orbits of Near-Earth Asteroids

Abstract: A simple method for numerical integration of the equations of motion of small bodies of the Solar System is proposed, which is especially efficient in studying the orbits with small perihelion distances. The evolution of orbits of 121 numbered asteroids with perihelion distances q < 1.2 AU is investigated over the time interval of years 2000–2100 with allowance made for the gravitational influence of nine planets and three largest asteroids. The circumstances of close encounters of asteroids with the Earth and other terrestrial planets are presented.

Asteroid 1620 Geographos: I. Rotation

Abstract: This study is part of a wide investigation, the goal of which is to find out whether meteor streams genetically related to asteroid 1620 Geographos exist and when and how they were formed. One of the possible mechanisms of the particles' removal from the asteroid's surface is their throw-off caused by rotational forces. The asteroid-rotation parameters were defined using the sidereal rotation period and another period of 0.8 days, which was obtained from observations and identified as nutational. Small oscillations of the asteroid's rotation axis were revealed. It was also found that the rotary acceleration does not exceed the gravitational one for all possible modes of the asteroid's rotation. The gravitational-force moment caused by the Sun's attraction and the light-pressure torque have a weak influence on the rotational motion; they have not essentially changed the rotation-pole position over the past 30 orbital periods.

The Expansion of the Hamiltonian of the Two-Planetary Problem into a Poisson Series in All Elements: Estimation and Direct Calculation of Coefficients

Abstract: This is the second paper in a series of articles devoted to one of the basic problems of celestial mechanics: the evolution of solar-type planetary systems. In the first paper (Kholshevnikov et al., 2001), we reviewed the history and the current state of the issue, outlined the scheme of the study, introduced Jacobi coordinates and related osculating elements, and indicated the form of the Hamiltonian expansion into a Poisson series in all elements. In this paper, the expansion coefficients are found according to a simple algorithm that is reduced to the calculation of multiple integrals of elementary functions. At the first stage, we restricted our analysis to the two-planetary problem (Sun–Jupiter–Saturn). The general case will be investigated in a forthcoming paper.

The Effect of the Shape of Dust Aerosol Particles in the Martian Atmosphere on the Particle Parameters

Abstract: The influence of the shape of dust aerosol particles in the Martian atmosphere on the imaginary part of the refractive index ni as derived from photometric observations during the period of the highest activity of the dust storm in 1971 was studied and exemplified for particles of spherical and oblate spheroidal shape. A similar analysis was performed for mean particle radii r0 and optical thicknesses τ0 of the dust layer estimated from polarization observations for periods of high atmospheric transparency. It was demonstrated that the values obtained for these optical parameters are affected by the adopted aerosol shape. Namely, the values of ni, r0, and τ0 found for spheroidal particles proved to be nearly twice as large as those for spheres. However, they are still much less than the available estimates of these parameters inferred, in particular, from interpreting space experiments. The reason for this difference needs further investigation.

A new Martian meteorite: the Dhofar 019 Shergottite with an exposure age of 20 million years

Abstract: The isotopic composition of the noble gases of the new Martian meteorite, the Dhofar 019 shergottite, found in the desert in the territory of the Sultanate of Oman on January 24, 2001, was investigated. Stepwise thermal annealing with isotopic analysis of each of the noble-gas temperature fractions was employed to determine the component composition. The concentration of the trapped noble gases in the new Martian meteorite Dhofar 019 is relatively high, although it lies within the range of concentrations in known SNC meteorites. A characteristic feature of all the trapped noble gases is the presence of two main components: a low-temperature, probably terrestrial atmospheric, component, trapped during the weathering of the meteorite on Earth, and a high-temperature trapped Martian component. Owing to the different ratios of the quantities of the two components, the trapped neon, argon, krypton, and xenon differ markedly in the kinetics of their release. The isotopic composition of the noble gases varies accordingly. The trapped xenon was found to contain two Martian components. One of them, with typical ratios of 129Xe/132Xe and 132Xe/84Kr, is representative of xenon and krypton of the Martian atmosphere; the other, of gases of the Martian mantle. Variations of the isotopic compositions of helium, neon, and argon (and also, to a lesser extent, of krypton and xenon) during the thermal annealing of the Dhofar 019 meteorite clearly point to a large proportion of cosmogenic as well as trapped components. The concentration of cosmogenic neon and argon in the meteorite is unusually high. This corresponds to a maximum exposure age among other SNC meteorites: 20 million years. Estimates of the potassium–argon age (gas-retention age) yielded the figure of 560 million years, which is within the range of values obtained for SNC meteorites by other authors, who used the rubidium–strontium and the potassium–argon technique.

The nature of volatiles in the lunar regolith

Abstract: Layer-by-layer analysis of the fine fraction of Luna-16 sample L1635 by X-ray photoelectron spectroscopy (XPS) revealed a zonal structure of its constituent particles. The outer zone, to a depth of 1200 A, is enriched with Si and Fe and depleted in refractory elements Mg, Ca, and Al as compared to the bulk composition of the sample. The second zone, in the depth range from 1200 to 4500 A, is of very unusual composition: it is enriched with carbon (up to 60 at. %) and zinc (up to 4 at. %) and contains some other volatiles. The lower zone, at depths from 4500 to 7000 A, is composed of a silicate material; however, the concentrations of refractory elements are noticeably higher than those in the near-surface layer. There is a difference in structural and chemical characteristics of most of the elements between different zones. These findings point to the exogenous origin of the enrichment of the studied sample with volatiles and are related to the fall of a volatile-rich body (comet or carbonaceous chondrite) on the Moon. The hypothesis of the cometary (carbonaceous-chondrite) impact explains the main patterns of the volatile distribution in the lunar regolith, including the formation of green and orange glasses from Apollo 15 and 17 collections.

High-Resolution Imaging of Mercury Using Earth-based Facilities

Abstract: With a view to the further development of the short exposure method with a CCD detector, new observations of the planet Mercury were carried out at the Abastumany Astrophysical Observatory, Republic of Georgia, from October 30 to November 8, 2001. Comparison with the previous data, as well as the results of data processing based on newly developed algorithms, points to considerable progress achieved in the technique for observing Mercury. In some cases, under very favorable atmospheric conditions, the resolution attained is close to the diffraction limit of the astronomic instrument used. For the first time, topographic features on Mercury's surface were reliably resolved. Features with linear sizes as small as 120 km are successfully identified in the disk center.

Solar and heliospheric causes of geomagnetic perturbations during the growth phase of solar cycle 23

Abstract: A database is compiled for the study of solar and heliospheric causes of geomagnetic perturbations with the daily average index Aр > 20 that were observed in the period 1997–2000. The number of such events (more than 200) progressively increased and fluctuated as the current solar cycle developed. It is established that geomagnetic storms are generated by dynamical processes and structures near the center of the solar disk in a zone of several tens of degrees, and these processes are responsible for the appearance in the Earth's region, within several tens of hours, of quasistationary and transient solar wind streams with a sufficiently strong southward component of the heliospheric magnetic field. These streams lasted more than a few hours. The following structures can serve as morphological indicators for the prediction of the appearance of such streams: (1) active and disappearing filaments derived from synoptic Нα-maps of the Sun, (2) solar flares, (3) coronal holes and evolving active regions, and (4) the heliospheric current sheet. The geometry of coronal mass ejections needs further observational study.

Turbulent Heat Fluxes in the Atmosphere of Venus

Abstract: A thermal regime of the troposphere of Venus is mainly determined by the greenhouse effect. A closeness of the real temperature gradient to the adiabatic one indicates that turbulent heat fluxes are also essential. Additional problems arise as only about 11% of the solar radiation absorbed by the planet reaches the surface, and most of it is taken up in the clouds at altitudes of 60–70 km. The present study summarizes experimental data on atmospheric parameters related to turbulence and estimates turbulent fluxes and turbulence characteristics. These data confirm the author's hypothesis of an anomalous downward turbulent heat flux in the free atmosphere. A normal upward turbulent heat flux exists in the planetary boundary layer.

Mars Express Mission and Astrobiology

Abstract: A short description of the ESA Mars Express mission planned for 2003 is given. The main goal of the mission is to look for traces of life with direct (in situ) or indirect (from orbit) measurements. The Isidis Planitia area was preliminary selected to be the landing site of Beagle-2, a small lander module for geologic, meteorologic, and exobiologic studies. In particular, one instrument on Beagle-2 will measure the carbon ratio 12C/13C, which should indicate the existence of extinct life. Over a period of one Martian year, the Mars Express orbiter will perform global high-resolution (10 m) imaging and global IR mineralogical mapping. Close international cooperation, including scientific data exchange and analysis, is foreseen.

A Synergetic Approach to the Description of Advanced Turbulence

Abstract: An attempt is made to construct a phenomenological model of turbulence as a self-organization process in an open system. The representation of a turbulized continuum in the form of a thermodynamic complex consisting of two subsystems—the subsystem of averaged motion and the subsystem of turbulent chaos, which is considered, in turn, as a conglomerate of vortex structures of different space–time scales—made it possible to obtain, by methods of nonequilibrium thermodynamics, the defining relationships for the turbulent fluxes and forces that describe most comprehensively the transport and structurization processes in such a continuum. Using two interpretations of the Kolmogorov parameter (as a quantity that describes the rate of dissipation of energy into heat and as the rate of transfer of turbulent energy in the eddy cascade), the defining relationships were found for this quantity, thereby making the thermodynamic approach self-sufficient. An introduction into the model of internal parameters of the medium, which characterize the excitation of macroscopic degrees of freedom, made it possible to describe thermodynamically the Kolmogorov cascade process and to obtain a variety of kinetic equations (of the Fokker–Planck type in the configuration space) for the functions of distribution of small-scale turbulence characteristics, including the unsteady kinetic equation for the distribution of probability of dissipation of turbulent energy. As an example, a detailed derivation of such relationships is given for the case of stationary turbulence, when a tendency toward local isotropy is observed. In view of the wide occurrence of this phenomenon in nature, one might expect that the developed approach to the problem of modeling strong turbulence will find its use in astrophysical and geophysical applications.

How Many Convective Zones Are There in the Atmosphere of Venus

Abstract: The qualitative characteristics of the vertical structure of the atmospheres of Venus and the Earth essentially differ. For instance, there are at least two, instead of one, zones with normal (thermal) convection on Venus. The first one is near the surface (a boundary layer); the second is at the altitudes of the lower part of the main cloud layer between 49 and 55 km. Contrary to the hypotheses proposed by Izakov (2001, 2002), the upper convective zone prevents energy transfer from the upper clouds to the subcloud atmosphere by “anomalous turbulent heat conductivity.” It is possible, however, that the anomalous turbulent heat conductivity takes part in the redistribution of the heat fluxes within the lower (subcloud) atmosphere.

Modeling Technogenous Contamination of the Near-Earth Space

Abstract: In analyzing the technogenous contamination of the near-earth space (NES), the following issues have usually been considered: the estimation of the current level of NES contamination by objects of various size; the modeling of technogenous contamination evolution; the estimation of the probability of spacecraft collisions with space objects (SOs) of various size and the possible implications of hazardous collisions; the determination of characteristics of the flux of SOs of various size through the observation zones of ground-based and onboard means of measurement. The main difficulty in solving the aforementioned problems lies in the deficiency of the experimental data. The available measurement information was obtained in relatively small domains of multidimensional space: the altitude of a point–the latitude of a point–the SO size–the time. As a consequence, additional (a priori) information is invoked for determining the technogenous contamination characteristics at various points of the region mentioned above. The efficient use of experimental data and a priori information constitutes the basic problem of space debris modeling. This paper briefly outlines the data on three space debris (SD) models: ORDEM2000 (Orbital Debris Engineering Model, 2000), MASTER'99 (Meteoroid and Space Debris Terrestrial Environment Reference Model, 2000) and SDPA (Nazarenko, 1997, 2000; Nazarenko and Menshikov, 2001). The features of modeling techniques and the comparative characteristics of technogenous contamination are discussed in the paper.

Quasi-Biennial Oscillations of Global Solar-Activity Indices

Abstract: Quasi-biennial oscillations of solar activity are investigated using several global indices. The Singular Spectrum Analysis is used to separate out and study quasi-biennial oscillations; this method is one of the modifications of the main components method. The principal components of the solar cycle are stable 11-year, secular, and quasi-biennial variations. The periods and shapes of individual variations in each quasi-biennial train depend on the length and power of the particular 11-year cycle.

Polarization of Light Scattered by Surfaces with Complex Microstructure at Phase Angles 0.1°–3.5°

Abstract: We present laboratory measurements of the phase dependences of linear polarization for surfaces with a complex microstructure in the range of phase angles 0.1°–3.5° A sample of freshly fallen snow (with particle sizes of about 50 × 500 μm) exhibits a nearly zero polarization. Surfaces with submicron structure show a narrow branch of negative polarization at small phase angles, irrespective of whether the surface is powderlike or solid with microcrystalline structure. This polarization is similar to that exhibited by Jupiter's satellites. The negative polarization branch becomes deeper with decreasing porosity of light dielectric surfaces. At the phase angles between 0.5° and 3.0°, the polarization for quartz powder with 10-μm particles is almost constant. The polarization for light dielectric surfaces depends on the geometry of illumination and observation. An inclination of the surface in the scattering plane produces a parallel shift of the negative polarization branch toward large values of the polarization modulus. The same inclination in a perpendicular direction produces the same shift toward positive degrees of polarization.

Asteroid 1620 Geographos: II. Associated Meteor Streams

Abstract: This study attempts to answer the following questions. Are there meteor streams genetically related to asteroid 1620 Geographos? When and how were they generated? Can we find any of them in the catalogs of orbits of meteors that have been observed? Numerous model streams, varying in particle-ejection scheme and in the moment of generation, have been considered. It has been found that the meteor streams observed from the Earth were most likely produced as a result of a collision with a small body. However, the generation of the meteor stream under the combined effect of rotation and tidal forces during the asteroid's close approach to the Earth cannot also be ruled out. Meteoroid streams formed at high ejection velocities (up to 1 km/s) can approach the Earth's orbit twice per orbital period: once before perihelion (in February–March) and once after perihelion (in August). The 44 orbits close to the model ones were found in the catalogs of meteoroid orbits. A taxonomic structure has been built for them. The distribution of ejection velocities for the models of Earth-approaching meteoroids points to the impact of an overtaking body, but the moment of collision remains unknown. Thus, it is quite possible that asteroid Geographos is the parent body for twin meteor showers observed at the Earth: Spring and Autumn Geographids.

Mass Transfer in the Near-Surface Layer of a Cometary Nucleus: A Gas-Kinetic Approach

Abstract: A self-consistent model of the kinetically nonequilibrium near-surface layer of a cometary nucleus is developed on the basis of the gas-kinetic approach. The weight method of direct statistical simulation is used to model numerically the two-dimensional gas outflow from an ice sample subjected to radiative heating. The effective coefficient of water ice sublimation is estimated. Mass transfer in a porous ice and mineral (scattering) nonisothermal medium is investigated by the method of test particles, and the effective gas release is evaluated taking into account the proper rotation of the cometary nucleus for various model parameters. In these calculations, allowance is made for the kinetic character of the flow and volume sublimation and condensation of the volatile constituents of the material of the cometary nucleus.

Morphology and Size-Frequency Distribution of Kilometer-Scale Impact Craters on Callisto and Ganymede Derived from Galileo Data

Abstract: Using high-resolution Galileo images, we counted the number of craters (larger than 1 km) on two of Jupiter's satellites—Callisto (outside and inside the Asgard impact basin) and Ganymede (in the dark cratered Galileo region)—and classified these craters morphologically. Based on the degree of preservation of crater rims, three morphological classes, A, B, and C (from the most preserved to the most degraded), have been identified. The A : B : C ratios, equal, respectively, to 1 : 3 : 5, 1 : 3 : 7, and 1 : 2.5 : 6.5 for fragments of the territory outside and inside the Asgard basin and within Galileo Regio, indicate that these crater populations reached a considerably high degree of maturity. The degradation of kilometer-scale craters on Callisto proceeds by the narrowing of their rims and their disintegration into chains of knobs, probably due to the sublimation of ice that composes the rim material. Comparing the density of craters of different classes in the regions inside and outside Asgard shows that class A craters on the territories examined were formed after the event that formed this impact basin. Kilometer-scale craters on Ganymede degrade through the expansion and smoothing of their rims and the dissection of them by radial furrows. This implies the involvement in the crater destruction of a downslope movement triggered by the seismic activity that accompanied the formation of tectonic grooves. It is possible that ice sublimation also took part in the destruction of craters on Ganymede, but its effect was less prominent than the effect of downslope movements.

Reversal of Heliospheric Magnetic Field Polarity: Theoretical Model

Abstract: A simple analytical model of the reversal of the heliospheric magnetic field is suggested. The shape of the heliospheric current sheet is found for each instant of time using a kinematic approximation. Calculation results are illustratively presented in graphic and animated forms, showing a 3-D dynamic picture of the reversal of the heliospheric magnetic field throughout a 22-year solar cycle.

Evaluating Cometary Delivery of Organics to the Early Earth

Abstract: An approximate calculation of the amount of organic material (OM) delivered to the Earth by comets during the first 700 million years of the planet's existence has been carried out. Approximation formulas based on lunar-crater data have been used for the flux of bodies colliding with the Earth. The calculations of impact velocities have been performed with allowance made for dragging and ablation of bodies in the atmosphere. Semianalytical models used in these calculations take into account the increase in the cross-sectional area of a disrupted meteoroid due to aerodynamic forces, as well as specific features of radiative heat transfer at large optical depths. Particular attention has been given to oblique trajectories that correspond to the perigee distances of cometary orbits close to the Earth's radius. Kilometer-sized comets, which arrived at the surface with low velocities, contributed largely to the mean OM flux under conditions of a dense early terrestrial atmosphere. For the atmosphere with a near-surface pressure of 10 bars, this flux comprises (1–40) × 107 kg per year. As will be shown below, rare but highly probable events of atmospheric entry of large (∼10 km) comets along oblique trajectories may have produced high local concentrations of organic molecules.

The Structure of the Surface of Mercury's Regolith from Remote Sensing Data

Abstract: Long experience of ground-based and cosmic studies of the Moon has shown that space-weathering processes play a key role in the formation of the surface layers of atmosphereless bodies. Undoubtedly, the surface of Mercury, which is subjected to the same processes, is covered by a mantle of shattered rocks—the regolith. The structure of the reflecting layer determines the photometric and polarization characteristics of the surface of a planetary body. Despite the general similarity of the integral optical properties of the surfaces of Mercury and the Moon, specific characteristics of the media of these celestial bodies manifest themselves as certain differences in the details of the measured parameters. Moreover, the similarity to the Moon permits in-depth interpretation of the results of remote observations of Mercury, such as integral polarimetry and integral spectropolarimetry. The data obtained suggest that the general structure of the surface layer of the Mercurian regolith is very similar to the structure of the lunar soil, although it is somewhat smoother and probably has a greater amount of the fine-grained fraction. The soil maturity matches the content of about 80% of the secondary particles. At the same time, the exposure age of the soil, which has the same degree of maturity, is less than the age of the soil formed under lunar conditions.

Atmospheric Disturbances and Radiation Impulses Caused by Large-Meteoroid Impacts on the Surface of Mars. II. Radiation Impulse Characteristics and Parameters of the Warm Layer

Abstract: This paper presents the results of the calculation of spectral and angular characteristics of radiation emitted by the disturbed region after the vertical impacts on the Martian surface of stony meteoroids with radii R0 from 1 to 100 m at speeds of 11–20 km/s. The time dependences are given for the density of the radiation flux incident on horizontal surface areas located at different distances from the impact point. For small impactors (R0= 1 m), the heating of the surface and surrounding gas by the radiation impulse from the hot region formed after the impact is insignificant even at the crater edge. However, the radiation impulse that heats up the surface is also emitted during the meteoroid flight through the atmosphere. Although this heating is insufficient to initiate evaporation, heat transfer by turbulent diffusion leads to the formation of a layer with temperatures that substantially exceed the initial temperature of the atmosphere. For large impactors (R0 = 100 m), the total specific impulse of the plume radiation gives rise to the emergence of the heated layer with a thickness on the order of several meters within several kilometers of the impact point. The formation of this “warm” layer may lead to the formation of a high-speed jet moving along the Martian surface as well as eddies at the front of the precursor with a subsequent intense rise of dust.

Convective Zones in the Atmosphere of Venus and the Anomalous Heat Flux (in Response to Criticism)

Abstract: Additional arguments have been put forward for the significant contribution of the anomalous turbulent heat flux to the thermal regime of the troposphere of Venus.