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The Surface Dust Analyser (SUDA) is a mass spectrometer onboard the Europa Clipper mission for investigating the surface composition of the Galilean moon Europa. Atmosphereless planetary moons such as the Galilean satellites are wrapped into a ballistic dust exosphere populated by tiny samples from the moon's surface produced by impacts of fast micrometeoroids. SUDA will measure the composition of such surface ejecta during close flybys of Europa to obtain key chemical signatures for revealing the satellite's composition such as organic molecules and salts, history, and geological evolution. Because of their ballistic orbits, detected ejecta can be traced back to the surface with a spatial resolution roughly equal to the instantaneous altitude of the spacecraft. SUDA is a Time-Of-Flight (TOF), reflectron-type impact mass spectrometer, optimized for a high mass resolution which only weakly depends on the impact location. The instrument will measure the mass, speed, charge, elemental, molecular, and isotopic composition of impacting grains. The instrument's small size of 268 mm × 250 mm × 171 mm , radiation-hard design, and rather large sensitive area of 220 cm2 matches well the challenging demands of the Clipper mission. [ABSTRACT FROM AUTHOR]

The paper briefly discusses hypotheses about the nature of a centuries-old mysterious phenomenon, for which there is still no clear explanation. Its essence is that an observer, usually located at a distance of 50–100 km from a flying meteor body, sometimes hears sound simultaneously with its radiation. It seems that sound travels at the speed of light. Historically, the situation was such that it was only no more than sixty years ago that attempts to instrumentally study this unusual phenomenon began. The difficulty of these searches is also due to the fact that only a few percent of the total number of observed meteoroids have this property. About forty years ago it was discovered that meteoroids can emit electromagnetic pulses of varying duration and frequency composition. However, it turned out that this fact does not always have an unambiguous relationship to electrophonic phenomena. This paper provides a brief overview of the most meaningful hypotheses and experiments of past years. It is possible that this phenomenon is of a fundamental nature and its study can introduce previously unknown information into science. [ABSTRACT FROM AUTHOR]

A brief review of theoretical studies of circumlunar dusty plasma, the important factors in the formation of which are electrostatic processes and impacts of micrometeoroids on the lunar surface, is given. Observation data of dust particles in the vicinity of the Moon, obtained within the "Luna-25" mission, are described for the first time. It is shown that there is at least one reliable observation of a dust particle either of lunar origin or associated with the high-speed Perseid stream. The need to improve the Lunar Dust Monitor device on the "Luna-27" lander is discussed. The improvement is associated with the need to install a rod for placing electrostatic sensors at a sufficient distance from the device, which is desirable to reduce disturbances of the surrounding plasma and the near-surface electrostatic field because of the influence of the lander. [ABSTRACT FROM AUTHOR]

The problem of modeling the entry of a meteoroid into the atmosphere and its interaction with it is considered. The motion, ablation, and energy deposition of a meteoroid or its fragments moving as a single body are modeled within the framework of meteor physics equations. The main parameter of these equations is the ablation parameter, equal to the ratio of the heat transfer coefficient to the effective heat of mass loss. Due to the lack of data from theoretical and experimental studies on the determination of the effective heat of ablation at high meteor velocities, its constant value is usually used in the literature. In this paper, it is proposed to use the effective heat of ablation variable along the trajectory, interpolating its value between the heat of evaporation and the heat of melting (or spallation), depending on the flight velocity. By numerically solving the meteor physics equations, we study the influence of the way of setting the effective heat of ablation and its uncertainty on the simulated characteristics: the meteoroid velocity, as well as the change in its mass and energy deposition along the trajectory and on the trajectory itself; and the inaccuracy in determining these characteristics is evaluated. [ABSTRACT FROM AUTHOR]

Space weathering is a primary factor in altering the composition and spectral characteristics of surface materials on airless planets. However, current research on space weathering focuses mainly on the Moon and certain types of asteroids. In particular, the impacts of meteoroids and micrometeoroids, radiation from solar wind/solar flares/cosmic rays, and thermal fatigue due to temperature variations are being studied. Space weathering produces various transformation products such as melted glass, amorphous layers, iron particles, vesicles, and solar wind water. These in turn lead to soil maturation, changes in visible and near-infrared reflectance spectra (weakening of characteristic absorption peaks, decreased reflectance, increased near-infrared slope), and alterations in magnetism (related to small iron particles), collectively termed the "lunar model" of space weathering transformation. Compared to the Moon and asteroids, Mercury has unique spatial environmental characteristics, including more intense meteoroid impacts and solar thermal radiation, as well as a weaker particle radiation environment due to the global distribution of its magnetic field. Therefore, the lunar model of space weathering may not apply to Mercury. Previous studies have extensively explored the effects of micrometeoroid impacts. Hence, this work focuses on the effects of solar-wind particle radiation in global magnetic-field distribution and on the weathering transformation of surface materials on Mercury under prolonged intense solar irradiation. Through the utilization of high-valence state, heavy ion implantation, and vacuum heating simulation experiments, this paper primarily investigates the weathering transformation characteristics of the major mineral components such as anorthite, pyroxene, and olivine on Mercury's surface and compares them to the weathering transformation model of the Moon. The experimental results indicate that ion implantation at room temperature is insufficient to generate np-Fe0 directly but can facilitate its formation, while prolonged exposure to solar thermal radiation on Mercury's surface can lead directly to the formation of np-Fe0. Therefore, intense solar thermal radiation is a crucial component of the unique space weathering transformation process on Mercury's surface. [ABSTRACT FROM AUTHOR]

The ion-acoustic instability in the tails of meteoroids as a result of their passage through the Earth's atmosphere is studied and the conditions under which it develops are given. The development of this instability occurs as a result of the relative motion of the plasma of meteoroid tails and the dusty plasma of the Earth's ionosphere. Dust, in turn, creates conditions when this instability can develop in a situation of approximately equal ion and electron temperatures, which is observed in the plasma–dust system under consideration. The mechanism of the excitation of ion-sound waves as a result of the development of the ion-acoustic instability in meteoroid tails is shown. The growth rates of the ion-acoustic instability and the characteristic times of its development are found. It is shown that the instability has time to develop during the time of passage of a meteoroid body in the Earth's atmosphere and the formation of a meteoroid trail, which has values much greater than the time of development of ion-acoustic instability in the system under consideration. The wave vectors and velocities of meteoric bodies, at which the development of the ion-acoustic instability is expected, are found. It is noted that the instability can reach a nonlinear regime at possible large wave amplitudes. [ABSTRACT FROM AUTHOR]

Statistical dependences of orbit parameters in four groups of sungrazing comets are studied. It is shown that the perihelia of comets of the Kreutz family are clustered around two planes (great circles of the celestial sphere). Numerical data on the observed bifurcation of perihelion distribution are provided. One of the planes basically coincides with the plane obtained by averaging orbit parameters Ω and i. The second plane with parameters Ωp = 77.7° and ip = 266.1° has an inclination of approximately 64° relative to the first plane. The distant nodes of cometary orbits relative to this plane are clustered at a distance of approximately 2 a.u. On the basis of the above, one of the authors hypothesizes that the comet group originates from the collision of a large comet with a meteoroid stream. This study examines some counterarguments expressed regarding this hypothesis. It is shown, based on a particular case, that the assumptions about the concentration of comet perihelia near one point and along two circles of the celestial sphere are quite compatible. The distribution of orbit inclinations relative to this plane is analyzed and a sharp maximum near 90° is noted. The maximum indicates that the parent body experienced lateral impacts of meteoroid bodies in all probability, which caused defragmentation of the former. New confirmations of the suggested hypothesis about the presence of another group of sungrazers have been found. It is assumed that the correlation dependence between the values of the perihelion parameters and ascending nodes of cometary orbits is of an evolutionary nature and is related to the group formation process. New relationships that concern the Meyer, Kracht, and Marsden groups are introduced. In particular, the authors have calculated the planes near which the cometary perihelia of these groups are concentrated. The example of the Meyer group illustrates the bifurcation of perihelia. [ABSTRACT FROM AUTHOR]

The theoretical and experimental study of the geomagnetic effect of cosmic bodies remains an urgent problem. This is especially true for meter-sized meteoroids, for which the very existence of the magnetic effect remains in question. The purpose of this article is to present the results of the analysis of temporal variations of the X-, Y-, and Z-components of the geomagnetic field detected by the International Real-time Magnetic Observatory Network (INTERMAGNET) on the day of the Kyiv meteoroid fall and on reference days. The analysis of temporal variations has shown that the levels of these components on the day of the cosmic body explosion and on reference days were significantly different. The level of X-component with a 6 min delay decreased by 2...5 nT, which lasted approximately 60 min. With a delay of 25 min and a duration of 25 min, a quasi-periodic disturbance was observed with a variable period within 4...12 min and an amplitude increasing from 0.3...0.4 to 1.2...1.5 nT. The first disturbance, which had a speed of approximately 300 m/s, could have been caused by a blast wave. The second disturbance was most likely associated with the generation and oblique propagation of an atmospheric gravity wave with a speed of hundreds of meters per second. Within the ionosphere, the disturbance propagated at a speed of approximately 660 km/s by means of magnetohydrodynamic waves. The temporal variations of the Y- and Z-components on the day of the explosion fluctuated for 60 min and decreased by 5...10 nT. The mechanism of long-lasting disturbances of these components remains unknown. It is likely that it could be related to the diamagnetic effect. There are reasons to believe that meter-sized cosmic bodies can cause the detected magnetic effect. [ABSTRACT FROM AUTHOR]

Micrometeoroids and Orbital Debris (MMOD) travelling at extremely high velocities in space are a threat to the structural integrity of spacecrafts in the Low Earth Orbit. Whipple shield, consisting of a Bumper and a Rear Wall, with a stand-off distance in between, is widely used to protect spacecrafts from hypervelocity MMOD impacts. In this paper, we present numerical simulations of a set of well-known hypervelocity impact (HVI) experiments on aluminium-based Whipple shields reported in the literature. These simulations are conducted using the three-dimensional Lagrangian Finite Element Method in ABAQUS/Explicit software. In six out of the seven tests reported in the literature, the Whipple shield failed due to a detached spall from the back surface of the Rear Wall, while in the seventh test, the spall was not detached. The present work successfully replicates and favourably compares the failure mechanisms observed in these Whipple shields to the corresponding experimental results. Various critical aspects of the Whipple shield's failure mechanics and mechanisms are investigated. These include impact pressure on the projectile, Bumper and Rear Wall, Bumper hole diameter, temperature rise, and residual velocity of debris particles and spalled fragments. The predicted ballistic limit of the Whipple shield falls between 2.54 mm and 3.18 mm of Rear Wall thickness in excellent agreement with the experimental results reported in the literature. The present work provides valuable insights into Whipple shield performance. The developed methodology could be employed to optimize shield design through predictive simulations, thereby improving spacecraft protection. [ABSTRACT FROM AUTHOR]

This study addresses the complexity and importance of developing a method of calibrating digital observations of meteor spectra with all-sky cameras. It aims to present novel approaches to spectral sensitivity, atmospheric extinction and flat-field corrections. Images of a known line emission spectrum were captured at various positions within the field of view using a camera with a fish-eye lens and plastic holographic grating. The flat-field correction was separated into a wavelength-independent and wavelength-dependent component, both dependent on the position of the spectral line in the field of view (FoV). Total profile intensities of spectra obtained from the images were compared throughout the spectral range at different positions in the FoV. The flat-field was constructed by fitting those dependencies with high-degree polynomial functions. Using a simplified atmospheric model, a novel approach was constructed to determine the atmospheric extinction curve throughout the spectral range, allowing it to be separately considered from the spectral sensitivity which was previously not the case. A comparison of the newly developed and previously used methodology was tested on several meteor spectra of the same meteor captured from different stations of the European Fireball Network. It revealed a significantly improved correspondence of the analysed spectra in the part of the spectral range unaffected by the limitations imposed by the newly developed methodology. Failing to follow the correct calibration methodology precisely may introduce varying degrees of uncertainty in computations of elemental abundances and other physical properties, depending on the equipment’s specific effect magnitude. [ABSTRACT FROM AUTHOR]

Comprehensive simulation of a number of main processes induced in all geospheres by the fall and explosion of the Kyiv meteoroid on April 19, 2023, have been conducted. Magnetic, electrical, electromagnetic, ionospheric, and seismic effects and the effects of acoustic gravity waves have been assessed. The magnetic effect of the ionospheric currents and the current in the wake of the meteoroid could be considerably large (approximately 0.4–0.7 nT). Owing to the capture of electrons in the atmospheric gravity wave field, the magnetic effect can reach the levels of 0.6–6 nT. Under the influence of an external electric field, a transient current pulse with a current strength of up to approximately 102–103 A can arise. The electrostatic effect can be accompanied by the accumulation of an electric charge of approximately 1–6 mC, which produces the electric field strength of approximately 10 MV/m. The flow of the electric current in the meteoroid wake can give rise to generation of an electromagnetic pulse in the 10–100 kHz band with an electric field strength in the range of 1–10 V/m. The electromagnetic effect of infrasound could be substantial (approximately 0.6–6 V/m and approximately 2–20 nT). The absorption of the shock wave at the ionospheric dynamo region altitudes (approximately 100–150 km) can generate secondary atmospheric gravity waves with a relative amplitude of approximately 0.1%. The fall of the meteoroid produced a plasma wake not only in the lower atmosphere but also in the upper atmosphere at altitudes of not less than 1000 km. The possibility of the appearance of an electrophonic effect is unlikely. The possibilities of generating the ion and magnetic sound by infrasound and generating gradient drift and drift dissipative instabilities seem to be unlikely as well. The magnetic, electrical, and electromagnetic effects dealt with in this study partially fill up gaps in the theory of physical effects produced by meteoroids in the Earth–atmosphere–ionosphere–magnetosphere system. The magnitudes of magnetic, electrical, electromagnetic, ionospheric, and acoustic effects are significant. The magnitude of the earthquake caused by the meteoroid explosion did not exceed one. The mean rate of recurrence of the fall of celestial bodies similar to the Kyiv meteoroid equals 32.3 yr–1, i.e., one event in 11 days. [ABSTRACT FROM AUTHOR]

The entry of a meteoroid into the atmosphere and interaction between them are considered. The motion, ablation, and energy deposition of a meteoroid or its fragments moving as a single body are modeled by numerical solution of the meteor physics equations. The main parameter in these equations is the ablation parameter, which is equal to the ratio of the heat transfer coefficient to the effective enthalpy of mass loss. Therefore, the setting of the heat transfer coefficient is of crucial importance in modeling the interaction of a meteoroid with the atmosphere. For the heat transfer coefficient, a correlation is used, which depends on the velocity of the body, its radius, and the atmospheric density. This correlation is an approximation of the published numerical calculations; the convective heat flux is also taken into account. The results of radiative heating simulations in the meteor range of parameters involve some uncertainty since many factors are not taken into account in the computations or are not known. Therefore, an uncertainty parameter is introduced in the formula for the heat transfer coefficient. This parameter is varied to examine the influence of the inaccuracy of setting the ablation parameter on the meteoroid velocity, mass loss, trajectory, and energy deposition along the trajectory. [ABSTRACT FROM AUTHOR]

In an effort to map our meteor showers, a total of 76,765 meteoroids were triangulated by the United Arab Emirates Astronomical Camera Network between 01 January 2017 and 31 December 2021 as part of the global Cameras for Allsky Meteor Surveillance network. The calculated meteoroid orbits were analyzed by a newly developed user-friendly software to identify potential new meteor showers. The software is designed to run in three different modes that assign orbits to either a known shower, to any of the previously reported meteor showers listed in the IAU Working List of Meteor Showers, while the remainder of orbits are linked to find newly defined meteor showers using one of three Discriminant-criterion methods. 12 new meteors showers were identified and added to the IAU Working List, most of which identify the hitherto unknown debris streams of Jupiter-family comets. [ABSTRACT FROM AUTHOR]

Comprehensive modeling studies of the thermal, turbulent, and plasma processes induced in all geospheres by the passage and explosion of the Kyiv meteoroid on April 19, 2023, were performed. Thermodynamic and plasma effects, as well as the effects and turbulence, accompanying the passage of the Kyiv meteoroid were estimated. It has been shown that the passage of the celestial body led to the formation of a gas-dust plume. The heated trail of the meteoroid cooled for several seconds. A simplified one-dimensional model of plume motion in the vertical direction is considered. The acceleration and speed of the plume are estimated. It has been shown that the initial acceleration of the plume initially reached a maximum value of 117 m/s2 and lasted ~1 ms. Its speed increased from 0 to ~1 m/s, then gradually decreased to 0 m/s. At this speed, the height of the plume's ascent hardly increased. The products of the explosion contained in the thermal, specks of dust and aerosols, further took part in the following three processes: a slow precipitation to the surface of the Earth, turbulent mixing with the ambient air, and transport by the predominant winds around the globe. The effect of turbulence in the trail has been shown to be well-pronounced, while the effect of magnetic turbulence has been shown to be absent. The following basic parameters of the plasma in the trail have been estimated: the height dependences of the electron densities per unit length and per unit volume, their relaxation times, the particle collision frequencies, the plasma specific conductivities, and the electron temperature relaxation time. At the initial moment, the linear and volume electron densities in the trail have been shown to be equal to approximately 1017–1023 and 1017–1022 m–3, respectively, and the plasma specific conductivity to be equal to ~103 Ohm–1 m–1. The role of the dusty plasma component was insignificant. [ABSTRACT FROM AUTHOR]

A sensor of micrometeoroids and space debris particles based on the detection of reflected and scattered laser radiation, when a particle passes through an optical barrier, is described. A design of the primary transducer of the sensor is proposed, a theoretical analysis of its resolution is performed, and its circuit implementation is described. The ray tracing method was used to simulate its operation using specialized software. [ABSTRACT FROM AUTHOR]

On March 5, 2022, a 12 kg meteoroid crossed the sky above Central Italy and was observed by three different observational systems: the PRISMA all-sky camera network (10 stations), the Italian national seismic network (61 stations), and a 4-element infrasound array. The corresponding datasets, each with its own resolution, provided three independent assessments of the trajectory, size and speed of the meteoroid. The bolide traveled across central Italy with an azimuth of 102 degrees, becoming visible at about 91 km above sea level with a velocity of about 15.4 km/s. Its visible trajectory lasted about 15 s. Reasonably, the residual portion of the ablated bolide terminated its path in the Adriatic Sea and could not be recovered. Seismic and infrasound data well match optical observations detecting the bolide Mach cone at 68 km above sea level with a back azimuth of 25 degrees with respect to the array. By comparing results from the three different systems, discrepancies are within the estimated uncertainties, thus confirming the mutual consistency of the adopted methodologies. Therefore, this study shows that different approaches can be integrated to improve the detection capability for bolide crossing the sky in monitored regions. [ABSTRACT FROM AUTHOR]

This study is aimed at comprehensively analyzing and estimating the effects in gas dynamics, as well as mechanical and optical effects, from the Kyiv meteoroid that entered the terrestrial atmosphere and exploded over Bila Tserkva raion, Kyiv oblast (Ukraine). According to the International Meteor Organization (IMO), the apparent magnitude of the meteoroid was –18. According to our estimates, the luminous power was 215 GW with an effective duration of 2.4 ± 0.2 s, the total luminous energy was 25.2 ± 2.5 GJ, and the initial kinetic energy was 0.09 ± 0.01 kt of TNT or 375 ± 35 GJ. The initial mass of the cosmic body was estimated to be 0.89 ± 0.09 t, the volume was 0.250 ± 0.025 m3, and the size was 79 ± 3 cm. The initial velocity of the meteoroid reached 29 km/s. The inclination angle, i.e., the angle that the trajectory makes with the horizontal plane, was 32°. The explosion altitude equal to 38 km and the inclination angle equal to 32° give an estimate of 3.5 t/m3 for the material density, which is close to the rock density. The energy of the processes, the gas dynamics effects, and the mechanical and optical effects from the celestial body have been analyzed. The main release of energy associated with the deceleration of the fragments of the celestial body, which was defragmented under a dynamical pressure of approximately 2.5 MPa, took place in the region with a length of 2 km at an altitude of approximately 38 km. A quasi-continuous defragmentation is suggested to produce a mass distribution that follows a power law. The main parameters of the ballistic and explosive shock waves have been estimated. For the Mach number of 97, the radius of the ballistic shock wave is estimated to be approximately 77 m, and the fundamental period to be 0.7 s, which showed a dispersive increase from 3.7 to 11.5 s with the propagation path length increasing from 50 to 5000 km. The radii of cylindrical and spherical wavefront shock waves were approximately 0.28 and 0.34 km, and their fundamental periods were approximately 2.6 and 3.2 s, respectively. These periods increased from 9.5 to 30.0 s and from 11.1 to 35.1 s with an increase in the propagation path length from 50 to 5000 km. In the vicinity of the meteoroid's explosion height, the relative excess pressure was a maximum. It decreased with a decrease in the altitude and increased with an increase in the altitude up to approximately 120–150 km, at which it attained values of approximately 6–7% and then further decreased down to a few percent. The absolute value of the excess pressure is estimated to be near the altitude of the explosion; subsequently it decreased with a decrease in the altitude down to 20–25 km and then increased further again. At the epicenter of the explosion, it is estimated to be approximately 94 Pa for the cylindrical wavefront and approximately 99 Pa for the spherical wavefront, which is not enough to damage objects on the ground. The excess pressure decreased with an increase in the altitude from 8–15 Pa to a few micropascals. Given an estimate of 2.4 s for the average duration of the effective light flash, the maximum power of the fireball is estimated to be 21 GW, and the power flux near the fireball (or more precisely, the cone 0.5 km in length and 2.4 m in diameter), is estimated to be 5.1 MW/m2. At the same time, the temperature is estimated to be approximately 3100 K, and the Wien wavelength is estimated to be 9.4 × 10–7 m. [ABSTRACT FROM AUTHOR]

The paper presents numerical models of mean-motion resonances detected in the Quadrantid meteoroid stream consisting of particles of mass 0.003 to 0.03 g, which helps to prove the presence of the following mean-motion resonances: the 1:9 resonance with Venus, 1:5 resonance with Earth, 1:3 and 3:8 resonances with Mars, and 2:1,7:3, 9:4 resonances with Jupiter. Resonance particles create dust trails far from the Earth's orbit. Indeed, there is no observational support for resonant effects in the observed Quadrantid meteoroid stream. [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]

This work examines the formation and evolution of meteoroid streams formed during collisions of near-Earth asteroids (NEAs) with objects in the Main Asteroid Belt (MAB). This collision scenario is considered more likely compared to collisions between NEAs, since many NEAs, by virtue of their origin, intersect the MAB region, in which the density of objects is significant compared to the inner regions of the Solar System. The resulting meteoroid streams have a number of differences from streams of cometary origin, both in terms of the formation of the stream and during further dynamic evolution. In this paper, estimates are obtained for the rate of meteoroid formation as a result of collisions of NEAs with MAB asteroids. Based on high-speed collision models and data from the DART experiment, possible particle size and velocity distributions are obtained. Numerical modeling of the dynamics of the resulting meteoroid stream was carried out, considering gravitational disturbances and radiation forces, and the influence of the initial emission velocity on the evolution of the stream was studied. An analysis of the rate of dust production was carried out considering the distribution of the current NEA population, and it was concluded that the rate of influx of meteoroids of asteroid and comet origin (in mass terms) can be quite comparable. [ABSTRACT FROM AUTHOR]

Surface-bounded exospheres result from complex interactions between the planetary environment and the rocky body's surface. Different drivers including photons, ion, electrons, and the meteoroid populations impacting the surfaces of different bodies must be considered when investigating the generation of such an exosphere. Exospheric observations of different kinds of species, i.e., volatiles or refractories, alkali metals, or water group species, provide clues to the processes at work, to the drivers, to the surface properties, and to the release efficiencies. This information allows the investigation on how the bodies evolved and will evolve; moreover, it allows us to infer which processes are dominating in different environments. In this review we focus on unanswered questions and measurements needed to gain insights into surface release processes, drivers, and exosphere characterizations. Future opportunities offered by upcoming space missions, ground-based observations, and new directions for modelling are also discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a modified effective length method for calculating heat fluxes in complex geometries in a three-dimensional formulation when moving in the atmosphere at high speeds and describes its software implementation. The method, on the one hand, does not require huge computational costs to obtain results, and on the other, demonstrates stable operation in complex geometries. [ABSTRACT FROM AUTHOR]

The problem of modeling the motion, ablation, and energy deposition of a meteoroid or its fragments moving as a single body is considered. A computer program for calculating the system of meteor physics equations by the Runge–Kutta method is created and tested. The equations take into account the curvilinearity of the trajectory of the meteor body, gravity, and a change in the heat-transfer coefficient along the trajectory. Test calculations are performed for meteor bodies of various sizes moving in the atmosphere. A change in the trajectory angle with respect to the horizon depending on the initial parameters of entry into the atmosphere is shown. The effect of taking into account the variability of the trajectory angle on a change in the velocity, mass loss, kinetic energy, and trajectory of the meteoroid is estimated. [ABSTRACT FROM AUTHOR]

This work presents a new method for estimating the population index of meteor showers using the entire distribution of meteors, thus avoiding the arbitrary choice of a threshold magnitude. This method was used to estimate the monthly population indices of 9771 sporadic meteors observed by the Brazilian Meteor Observation Network (BRAMON) between 2014 Aug. and 2021 Feb. The magnitude threshold was derived from the parameters of a Tsallis'q-exponential distribution proposed by Betzler & Borges (2015) and fitted to the observed distribution of apparent magnitudes. Population indices show temporal variation between May and September relative to the average monthly index ( 3.63 ± 0.01 ). The primary sources between May and September have a λ ⊙ solar longitude associated with helion and antihelion sources. A secondary source has a time-varying solar longitudes and a larger number of meteors than the helion source between July and November. The secondary source has solar longitudes probably related to sporadic meteors in the north toroid. The helion and antihelion sources have average λ ⊙ = 352 and 215 degrees and radii of 8 and 4 degrees, respectively. [ABSTRACT FROM AUTHOR]

A comprehensive modeling of the processes in all geospheres caused by the fall and explosion of the Yushu meteoroid in the Qinghai Province (People's Republic of China) on December 22, 2020, was performed. Thermodynamic and plasma effects, as well as the effects of the plume and turbulence, accompanying the passage of the Yushu meteoroid were estimated. It is shown that the passage of the celestial body led to the formation of a gas and dust plume. The heated meteoroid wake cooled down for several hours. Four stages of cooling of the meteoroid wake are considered. The first of them lasted approximately 0.2 s, and the temperature of the wake decreased by half due to radiation. During the second stage (~3 s), cooling continued due to radiation and expansion of the wake, and the temperature decreased by 20%. During the third stage, which lasted 6 s, the explosion products and heated gas (thermal column) with an acceleration of approximately 30 m/s2 rose at a speed of 140 m/s, and the temperature decreased by 10%. The fourth stage lasted approximately 50 s, the thermal column intensively absorbed cold air, gradually cooled, and slowed down. The maximum height of the thermal column reached 7–8 km. The explosion products (dust particles and aerosols) that were part of the thermal column were subsequently involved in three processes: slow settling to the Earth's surface, turbulent mixing with the surrounding air, and transportation by prevailing winds around the planet. It is shown that the effect of turbulence in the meteoroid's wake was well expressed, while magnetic turbulence had hardly any effect. The main parameters of the plasma in the wake are estimated: height dependences of the linear and volume electron densities, values of their relaxation times, particle collision frequencies, plasma specific conductivity, and relaxation times of the electron temperature. It is shown that the linear and volume electron densities in the wake at the initial moment were 1019–4 × 1022 m–1 and 1017–1021 m–3 and the plasma specific conductivity was of the order of 103 Ω–1m–1. The role of the dust component of the plasma is discussed. [ABSTRACT FROM AUTHOR]

A comprehensive modeling of the processes in all geospheres caused by the fall and explosion of the Yushu meteoroid in the Qinghai Province (People's Republic of China) on December 22, 2020, was performed. The magnetic, electrical, electromagnetic, ionospheric, and seismic effects, as well as the effects of acoustic-gravity waves, were estimated. It is shown that the magnetic effect of turbulence was insignificant. The magnetic effect of the ionospheric currents and the current in the meteoroid's wake could be significant (~1 nT). Due to the capture of electrons in the field of the atmospheric gravity wave, the magnetic effect could reach the order of 1 nT. The effect of the external electric field could lead to a short-term current pulse of up to 104 A. The electrostatic effect could be accompanied by the accumulation of a charge of 1–10 mC with an electric field strength of approximately 1 MV/m. The flow of electric current in the wake could lead to the emission of an electromagnetic pulse in the frequency range of approximately 10 kHz with a strength of 3–30 V/m. It was found that the electromagnetic effect of infrasound could be significant (approximately 3–20 V/m and 10–60 nT). Absorption of the shock wave at the heights of the dynamo region of the ionosphere (100–150 km) could be accompanied by the generation of secondary atmospheric gravity waves with a relative amplitude of 0.1–1. The passage of the meteoroid led to the formation of a plasma wake and to a noticeable disturbance of not only the lower but also the upper atmosphere at distances of at least 1000 km. The occurrence of an electrophonic effect seems unlikely. The possibilities of generating ion and magnetic sound by infrasound as well as gradient-drift and drift-dissipative instabilities are discussed. The magnetic, electrical, and electromagnetic effects discussed in this article partially fill in the gaps in the theory of the physical effects of meteoroids in the Earth–atmosphere–ionosphere–magnetosphere system. The magnitude of the earthquake caused by the meteoroid explosion did not exceed 2.5. The average fall rate of celestial bodies similar to the Yushu meteoroid is 0.49 year–1. [ABSTRACT FROM AUTHOR]

The kinematic reorganization of plate boundaries in the southeastern Antarctic part of the South Atlantic, expressed in the jump of the spreading axis of the Agulhas Ridge, led to a restructuring of the region's structural plan. This resulted in the formation of the southern segment of the Mid-Atlantic Ridge (MAR), extinction of the previously active Agulhas spreading ridge, and formation of the Meteor and Islas Orcadas rises, marking the location of the MAR and located symmetrically about its axis. Based on the research results, the conditions for the jump in the spreading axis were identified and an experimental model was constructed for the formation of accompanying structures, in which an important role was played by the accretion of oceanic crust on the Agulhas Ridge and westward migration of the Falkland Plateau. This resulted in southward movement of the southern segment of the MAR, formation of the Malvinas microplate, and a jump in the axis of the Agulhas spreading ridge, which led to cessation of spreading on this ridge. An important role in this kinematic restructuring was played by activity of the Shona hotspot. [ABSTRACT FROM AUTHOR]

It has been recently reported that, at late times, the total luminosity of a star freely falling in black holes decays exponentially with time, and one or two series of flashes with decreasing intensity are seen by a specific observer, depending on the number of photon spheres. In this paper, we examine observational appearances of an infalling star in a reflection-asymmetric wormhole, which has two photon spheres, one on each side of the wormhole. We find that the late-time total luminosity measured by distant observers gradually decays with time or remains roughly constant due to the absence of the event horizon. Moreover, a specific observer would detect a couple of light flashes in a bright background at late times. These observations would offer a new tool to distinguish wormholes from black holes, even those with multiple photon spheres. [ABSTRACT FROM AUTHOR]

Based on observational facts, the author proposes a model for the formation of an electric charge in iron meteorites in the lower layers of the atmosphere through photoelectron emission when exposed to high-temperature plasma radiation on its surface. It is shown that at high Mach numbers, the explosive destruction of an iron meteorite can be caused not only by inertial, but also by electrostatic forces. The subsequent charging of the fragments greatly increases their total charge, and the movement with acceleration causes electromagnetic radiation in the low frequency range. The electrostatic and electromagnetic fields accompanying the movement of meteoroids in the atmosphere can be the cause of the observed effects on the Earth's surface, i.e., radio interference, electric shock to a person, and St. Elmo's fire, among others. [ABSTRACT FROM AUTHOR]

The interaction of meteoroids with Earth's atmosphere is studied. Based on the physical theory of meteors, a mathematical model of the trajectories of celestial bodies that have invaded Earth's atmosphere has been constructed. This model considers rarely observed cases of a change in the mode of the descending movement of meteoric bodies to ascending with their possible return back into outer space. The kinematic conditions and physical characteristics that these bodies must satisfy in order to achieve such extraordinary behavior are determined. [ABSTRACT FROM AUTHOR]

An algorithm is presented for solving conjugate aerodynamic and ballistic problems, which is based on the simulation method with the use of a grid system and allows consideration of a flight for a system of bodies taking into account deceleration, relative motion of the bodies, and rotation. The algorithm is used to study the separation of two identical bodies of rectangular shape with different values of the initial moment of inertia. Rotation leads to the fact that the bodies fly apart not only under the action of a repulsive aerodynamic force, but also due to a lifting force appearing because of body tilt. Additional lateral speed is acquired after the part of the flight of the bodies with significant interference. When rotation is taken into account, the separation velocity of two meteoroid fragments of rectangular shape may increase up to three times in comparison with the situation when it is assumed that the bodies do not rotate. The study is carried out with the aim of assessing the influence of various factors on the speed of separation of meteoroid fragments in order to help with constructing the possible trajectories of meteorites that have fallen onto Earth's surface. [ABSTRACT FROM AUTHOR]

Various approaches are developed for modeling the destruction of cosmic bodies in the atmosphere into a large number of fragments. It is assumed that, at first, they move with a common shock wave as a single body deformed under the action of pressure forces. Four models of meteoroid fragmentation into a cloud of fragments are considered: two developed by us and two that are generally accepted. The main distinctions between the models are revealed. These models are used to obtain numerical solutions of the equations of meteor physics taking into account ablation to calculate the interaction of the Chelyabinsk meteoroid with the atmosphere. Solutions for different models are compared with each other and with observational data. After the fragments diverge over a large distance, their independent motion is considered. For the probabilistic and cumulative mass distribution of fragments, formulas are obtained using the results of experiments on the destruction of bodies under high-speed impact. The cumulative distribution is compared with the experimental data and with the mass distributions of recovered meteorites in the cases of a significant number of found fragments. The mass of the fragmented meteoroid and the luminosity are found by integrating over all fragments using their probabilistic mass distribution as the initial one. The mass and velocity of each fragment are determined from the equations of meteor physics. [ABSTRACT FROM AUTHOR]

The most important event in astronomy and celestial physics in the early 21st century is the fall of the Chelyabinsk meteoroid with a kinetic energy of nearly 440 kt TNT. Such an event occurs once every 65 years on average. The effects of this celestial body are considered in more than 200 scientific papers. At the same time, less than 25 papers are devoted to the fall of another large meteoroid called the Kamchatka meteoroid on December 18, 2018, at 23:48:20 UT (Universal time). Meanwhile, the parameters of this meteoroid are quite unique. The velocity components are vx = 6.3, vy = –3, and vz = –31.2 km/s, and the velocity magnitude was 32 km/s. The total optical radiated energy was Er = 1.3 × 1014 J (31 kt of TNT), the fireball explosion altitude was zr = 26 km, and the coordinates are 56.9° N, 172.4° E. The angle of entry into the atmosphere with respect to the horizon was close to 68.6°. The meteoroid had the initial kinetic energy of 173 kt of TNT, the mass of 1.41 kt, and the size of nearly 9.4 m. The fall of such bodies occurs at a frequency of once every 30 years. It is of interest to perform the further study of its ionospheric effects and compare the results measured by ground-based and satellite methods with each other. The objective of this study is to analyze the results of GPS observations for the ionospheric effects to compare them with the results measured by the method of ground-based oblique incidence sounding of the ionosphere. To observe the ionospheric disturbances following the fall of the Kamchatka meteoroid, an AC60 receiving station (geographic coordinates, 53° N, 173° E) located at a distance of 450 km from the Kamchatka meteoroid explosion site and six GPS satellites (PRN02, PRN05, PRN07, PRN09, PRN29, and PRN30) were used. The principal results of these studies are the following. GPS technologies were used to estimate the delay times of ionospheric response to the Kamchatka meteoroid explosion, the horizontal propagation velocities of disturbances (504–520 m/s) and their periods (11–18 min), durations (22–35 min), wavelengths (333–530 km), and the relative amplitudes of electron density disturbances (3–4%). The estimate obtained for the relative amplitudes of wave disturbances in the electron density by the ground-based and satellite methods have proven to be close to each other (3–4%). Their periods also have close values (10–15 min). The ground-based and satellite methods also revealed the wave disturbances associated with both atmospheric gravity and seismic waves. [ABSTRACT FROM AUTHOR]

On the contrary, in the latter case the exosphere is directly connected to the surface, thus, it is called surface-bounded exosphere, since the surface release processes are also the exospheric filling ones and atoms and molecules collide with the surface far more frequently than collisions with each other. In the Grava et al. paper ( I Volatiles and refractories in surface-bounded exospheres in the inner Solar System i ) the exospheres of extreme volatile species, like noble gas, and those constituted by refractory elements or refractory bearing molecules are considered in a comparative way. The Leblanc et al. paper ( I Comparative Na and K Mercury and Moon exospheres i ) treats in a comparative way the alkali exospheres at Mercury and Moon. [Extracted from the article]

A large meteoroid entered the terrestrial atmosphere and exploded at an altitude of 26 km between the Kamchatka Peninsula and Alaska (geographic coordinates 56.9° N, 172.4° E) over the Bering Sea at 23:48:20 UT on December 18, 2018. The meteoroid has been named the Kamchatka (or Bering Sea) meteoroid. Its basic parameters are as follows: calculated total impact energy 173 kt of TNT, total optical radiated energy 1.3 × 1014 J, mass 1.41 kt, speed 32 km/s, size 9.4 m, and the trajectory directed at an angle of 68.6° with respect to the horizon. The entry of the Kamchatka meteoroid into the atmosphere was accompanied by the generation of a transient resonance electromagnetic signal in the 25–35 mHz band observable in the vicinity of the meteoroid explosion and in the magnetically conjugate region. Oscillations with amplitudes of 0.2–0.8 nT were observed over a 7-min interval. This study is aimed at analyzing the observations of the resonance electromagnetic effect from the Kamchatka meteoroid and discussing a mechanism for this effect. The resonance effect in the Earth's magnetic field is analyzed using data with a time resolution of 1 s and an amplitude resolution of 1 nT from the database collected by the Intermagnet magnetometer network of magnetic observatories. The distance between the site of the meteoroid explosion and the magnetic observatories ranges from 1000 to 5000 km in the Northern Hemisphere and from 9010 to 12 425 km in the Southern Hemisphere. It is established that the only feasible mechanism is associated with the magnetic field displacement in the magnetosphere by the explosive impact of the celestial body, whereas only a negligibly small part of the meteoroid's energy is spent on the generation of magnetic field perturbations. The meteoroid's energy losses are similar to the losses in the reactive components of the radio frequency circuits, i.e., they return into the system. The oscillations cease after the meteoroid flies by, and the system returns into the initial state. The main results are summarized as follows. The resonance electromagnetic oscillations arose at 13 and 3 min prior to the Kamchatka meteoroid explosion. The duration of each observed perturbation is close to 7 min. The parameters of the quasi-periodic perturbations are similar to the parameters of magnetic Pc3 pulsations; however, they occured in the Y component of the magnetic field rather than in the X component of the magnetic field. Their observed periods are in the range of 33–36 s, and the amplitudes are in the range of 0.4–0.9 nT. Similar resonance oscillations were also recorded in the magnetically conjugate region. A mechanism for generating the resonance oscillations is proposed. The essence of the mechanism is that the meteoroid explosively impacts the magnetosphere and deforms the magnetic field lines that begin to oscillate at their eigenfrequencies. Depending on the McIlwain L-shell, the calculated period of oscillations is 19–169 s. For example, a period of 28–34 s is obtained with setting L≈ 3–3.2, which is close to the observed period of 30 s. The generation of the resonance oscillations consumes approximately 10–4 parts of the meteoroid kinetic energy. [ABSTRACT FROM AUTHOR]

Space dust and dusty (complex) plasma are one of the most common manifestations of matter in space. Non-atmospheric bodies of the Solar System, such as the Moon, asteroids, comets, some satellites of the planets, are directly affected by external factors of outer space—solar electromagnetic radiation, interplanetary plasma flows, cosmic rays, micrometeors. Under the influence of these factors, regolith is formed on the surface of bodies during geological epochs. Under the influence of impacts of high-speed micrometeors, dust particles of regolith scatter at different speeds. Most of them return to the surface, but some form dust clouds or lose their gravitational connection with the parent body. Under the action of solar radiation, the surface acquires an electric charge, and dust particles under certain conditions can break away from the regolith surface and levitate. Observational evidence of such dynamic phenomena has been recorded on the Moon and on some asteroids. The study of the physical processes responsible for the activation of dust particles and their dynamics is of great interest for fundamental science and practical purposes. The article discusses the main processes occurring under the influence of outer space factors on regolith, as a result of which dust particles move and a near-surface plasma-dust exosphere is formed. Unresolved issues are discussed. Methods and means of laboratory modeling in studying the activation and dynamics of dust particles are considered. [ABSTRACT FROM AUTHOR]

On Mars, structural loads and the low tensile strength of in-place Martian binders make existing solutions for Martian structures uneconomical because they are based on the terrestrial sources like inflatable units. Here we address this issue by introducing and analyzing three innovative structural forms in accordance with the structural engineering point of view using symmetric optimum parabolic rotated arch shapes and in-place waterless sulfur-based concrete. These forms minimize the tensile stresses under Martian structural loads. Probable Martian structural loads, including gravity, wind, marsquakes, asteroid and meteoroid impact loads and their effects have been investigated and calculated. The proposed models were analyzed under Martian structural loads using the implicit finite element method and the results were compared to two concrete structural forms from previous studies. The proposed models could tolerate Martian structural loads with complete elastic behavior and would significantly decrease the Martian colonization cost due to using Martian resources and reduce element importing from Earth. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of determining the aerosol optical depth above the sea surface using the data of short-wavelength channels of the multizone low-resolution scanning instrument of the Meteor-M No. 2 satellite. The algorithm is based on the use of an optical model, which is a six-dimensional lookup table containing information about spectral brightness coefficients of satellite instrument channels for various atmospheric conditions and observation geometry. The results are validated, showing an 80% correlation with the reference data of the AERONET measurement network. [ABSTRACT FROM AUTHOR]

A method is proposed for a quantitative assessment of protective properties of a spacecraft shielding structure at hypervelocity impact. The method uses a multilayer recording target, which is placed outside the shield. An experimental study has been conducted of mesh shield resistance to micrometeoroid/orbital debris damage, which has confirmed an enhancement of protective properties for a cascade arrangement of meshes (first a coarse mesh, then a fine one) and in the case of substituting a corrugated mesh for a flat one. [ABSTRACT FROM AUTHOR]

Impacts by small solar system bodies (meteoroids, asteroids, comets and transitional objects) are characterized by a combination of energy dynamics and chemical modification on both terrestrial and small solar system bodies. In this context, the discovery of glycine amino acid in meteorites and comets has led to a hypothesis that impacts by astronomical bodies could contribute to delivery and polymerization of amino acids in the early Earth to generate proteins as essential molecules for life. Besides the possibility of abiotic polymerization of glycine, its decomposition by impacts could generate reactive groups to form other essential organic biomolecules. In this study, the high-pressure torsion (HPT) method, as a new platform for simulation of impacts by small solar system bodies, was applied to glycine. In comparison with high-pressure shock experiments, the HPT method simultaneously introduces high pressure and deformation strain. It was found that glycine was not polymerized in the experimental condition assayed, but partially decomposed to ethanol under pressures of 1 and 6 GPa and shear strains of < 120 m/m. The detection of ethanol implies the inherent availability of remaining nitrogen-containing groups, which can incorporate to the formation of other organic molecules at the impact site. In addition, this finding highlights a possibility of the origin of ethanol previously detected in comets. [ABSTRACT FROM AUTHOR]

An important characteristic of the disruption of cosmic bodies (asteroids at their collision in outer space, meteoroids and asteroids entering the Earth's atmosphere) is the mass distribution of their fragments. The cumulative mass distribution of fragments, obtained using the power law for mass distribution in differential form, depends on the dimensionless fragment mass normalized to the total mass (body mass before destruction), on the mass fraction of the largest fragment and on the power index. The distribution gives a nonlinear dependence of the cumulative number of fragments on the mass in logarithmic coordinates, in contrast to the linear dependence used in the literature. The formula for the cumulative number of fragments is tested by comparison with the results of impact experiments performed to model the fragmentation of asteroids at the collision in outer space. The comparison is carried out for bodies of different shapes, masses and compositions, with different strengths, in a wide range of impact velocities. The values of the power index, which is a free parameter adjusted for the best fit of the theoretical distribution to the empirical one, are estimated. The applicability of the power law fragment mass distribution to the description of experimental results for various types of destruction is discussed. [ABSTRACT FROM AUTHOR]

Abstract—The mechanism of modulational interaction of Langmuir waves in meteoroid trails, which leaves to generation of magnetic fields, is discussed. Estimates of these fields are given. It is shown that the value of the fields agrees with the observed variations of magnetic fields in Earth's atmosphere during the passage of meteoroids. The mechanism of appearance of low-frequency electromagnetic waves as a result of the modulational interaction of Langmuir waves, which can result in electrophonic noises during the passage of meteoroids, is described. [ABSTRACT FROM AUTHOR]

The study is focused on the nature of impacts causing cometary outbursts. Specifically, we analyze an issue on whether comets may pass through known swarms of meteoroids. We consider 116 comets, which exhibit outbursts, from the list of Andrienko and Vashchenko (1981) and 102 meteor streams, the orbital elements of which are reliably known. The epochs of outbursts and passages of comets in the vicinity of meteoroid swarms are compared. For 24 comets these epochs differ only by ten days, if the swarms' zones are assumed to be within a distance smaller than 0.05 AU between the nodes of comets and the swarms' orbits. We also consider the other possibilities to check whether the type of impact may produce outbursts. In particular, the minimal orbit intersection distances (MOID) between the swarms and the corresponding comets were calculated. For 294 comets, these values are less than 0.01 AU; and, for 14 comets, they do not reach even 0.001 AU. As an additional data source, we used the most recent data for 34 comets and considered a more rigid critical distance (0.01 AU). The results of calculations suggest that the impact mechanism may be regarded as one of the main causes of outburst events in comets. In this light, the data on comet 17P are analyzed. [ABSTRACT FROM AUTHOR]

The possibility of generation of lower hybrid waves in meteoroid wakes upon their interaction with the Earth's ionosphere is analyzed. The lower hybrid waves are driven as a result of development of the Buneman-type instability due to motion of meteoroid-wake plasma relative to the Earth's magnetic field. Magneto-modulational processes that are induced by existence of the lower hybrid waves in plasma and leading to generation of quasi-stationary perturbations of magnetic field are discussed. It is demonstrated that these perturbations are of the same order of magnitude as magnetic fields induced by meteoroids passing through the Earth's atmosphere. [ABSTRACT FROM AUTHOR]

We carried out a detailed study of a bright meteor detected over the Khamar-Daban mountain range on August 12, 2020 at 14:37:35 UT by two automatic video monitoring stations functioning on the territory of the Tunka Valley (Republic of Buryatia) as part of the SkyLine project. The astro- and photometric parameters of the event were determined, its belonging to a specific meteor stream was established, and the spatial parameters of the trajectory with a projection onto the terrain were recovered. The data on the main physical characteristics of the meteor particle were obtained, including the geocentric velocity and orbital parameters. The chemical composition of the meteoroid was analyzed from the spectral data of the track. The potential possibility of using meteor phenomena as a tool to study the upper layers of the atmosphere was considered. [ABSTRACT FROM AUTHOR]

The purpose of this article was to evaluate the mechanical, optical, and gasdynamic effects that accompanied the passage and explosion of the Yushu meteoroid. The explosion occurred over a sparsely populated area, Qinghai Province (Tibetan Plateau, People's Republic of China). According to NASA, the initial kinetic energy of the celestial body was approximately 9.5 kt TNT or 40 TJ. Approximately 4.9 TJ, i.e., 12.25% of the initial kinetic energy of the body, was converted into the energy of the light flash. The projections of the velocity of the meteoroid are as follows: vx = –2.6 km/s, vy = 5.9 km/s, and vz = –12.1 km/s. They are used to estimate the angle of inclination of the trajectory to the horizon, which is approximately 5°. Using the explosion height of 35.5 km and the inclination angle, the density of the matter is estimated to be close to that of an ordinary chondrite (approximately 3.5 t/m3). Knowledge of the kinetic energy and velocity allows us to calculate the mass of the meteoroid (432 t) and its characteristic size (6.2 m). The energy of the processes, as well as mechanical, optical, and gasdynamic effects of the celestial body, are analyzed. The main release of energy accompanying the deceleration of fragments of the body destroyed at a dynamic pressure of ~1 MPa took place in a 17.2 km long area at a height of approximately 35 km. A quasi-continuous fragmentation and a power law of the distribution of the mass of the fragments are assumed. The main parameters of ballistic and explosive shock waves are estimated. With a Mach number of 45, the radius of the ballistic shock wave was approximately 280 m, and the fundamental period was 2.6 s, which increased from 9.5 to 30.1 s due to dispersion as the distance traveled by the wave increased from 50 to 5000 km. The radius of the cylindrical and spherical explosion waves was approximately 0.8 and 2 km, respectively, and the fundamental period was 7.5 and 18.8 s. This period increased from 21.1 to 66.7 s as the distance increased from 50 to 5000 km. Near the meteoroid terminal point, the relative overpressure was maximal. It decreased with decreasing height, and increased with increasing height until approximately 120–150 km, where it reached ~10–20 percent and then decreased to a few percent. The absolute value of the overpressure for the spherical wave was maximal near the explosion height, then it decreased as the height decreased to 15 km, then increased again. At the epicenter of the explosion, it was approximately 310 Pa for a cylindrical wave or ~48.5 Pa for a spherical wave, which is insufficient to damage ground objects. With increasing height, the overpressure decreased from many tens of pascals to micropascals. The average power of a light flash with a duration of approximately 1.26 s was 3.9 TW, the power flux density near the fireball, more precisely, a 3.4 km long cone with a diameter of 18.6 m, was 19.5 MW/m2. The surface temperature was close to 4300 K and the Wien wavelength was 6.7 × 10–7 m. [ABSTRACT FROM AUTHOR]

An impact of a meteoroid on the lunar surface at speeds exceeding several kilometers per second generates a light flash generally less than 0.1 s in duration. We made a simple spectral video camera for observing the lunar impact flashes and monitored the waxing crescent Moon's non-sunlit surface from Oct. 2016 to May 2017. We detected ten flash candidates though there was no report of simultaneous detections by other observers. We obtained low-dispersion spectra in visible wavelengths for nine of them. Six of them show spectra similar to those of the flashes observed during the Geminids meteor activity in Dec. 2018 by the same camera. The spectra are continuous and red. Blackbody spectra fitted to them show temperatures around 3000 K. On the other hand, three of them show continuous blue spectra. Blackbody spectra fitted to them show temperatures of more than 6000 K. Specular reflection of sunlight by space debris might lead to these flashes. However, the impact of a low-density meteoroid not against the fine lunar regolith but solid lunar rocks could cause blue flashes. In this paper, we give full details of the camera and the analytical procedures of the videos. We also discuss recommendations for future spectral observations. [ABSTRACT FROM AUTHOR]

In this review we discuss all the relevant solar/stellar radiation and plasma parameters and processes that act together in the formation and modification of atmospheres and exospheres that consist of surface-related minerals. Magma ocean degassed silicate atmospheres or thin gaseous envelopes from planetary building blocks, airless bodies in the inner Solar System, and close-in magmatic rocky exoplanets such as CoRot-7b, HD 219134 b and 55 Cnc e are addressed. The depletion and fractionation of elements from planetary embryos, which act as the building blocks for proto-planets are also discussed. In this context the formation processes of the Moon and Mercury are briefly reviewed. The Lunar surface modification since its origin by micrometeoroids, plasma sputtering, plasma impingement as well as chemical surface alteration and the search of particles from the early Earth's atmosphere that were collected by the Moon on its surface are also discussed. Finally, we address important questions on what can be learned from the study of Mercury's environment and its solar wind interaction by MESSENGER and BepiColombo in comparison with the expected observations at exo-Mercurys by future space-observatories such as the JWST or ARIEL and ground-based telescopes and instruments like SPHERE and ESPRESSO on the VLT, and vice versa. [ABSTRACT FROM AUTHOR]

The Moon and Mercury are airless bodies, thus they are directly exposed to the ambient plasma (ions and electrons), to photons mostly from the Sun from infrared range all the way to X-rays, and to meteoroid fluxes. Direct exposure to these exogenic sources has important consequences for the formation and evolution of planetary surfaces, including altering their chemical makeup and optical properties, and generating neutral gas exosphere. The formation of a thin atmosphere, more specifically a surface bound exosphere, the relevant physical processes for the particle release, particle loss, and the drivers behind these processes are discussed in this review. [ABSTRACT FROM AUTHOR]

Returning humans to the Moon presents an unprecedented opportunity to determine the origin of volatiles stored in the permanently shaded regions (PSRs), which trace the history of lunar volcanic activity, solar wind surface chemistry, and volatile delivery to the Earth and Moon through impacts of comets, asteroids, and micrometeoroids. So far, the source of the volatiles sampled by the Lunar Crater Observation and Sensing Satellite (LCROSS) plume has remained undetermined. We show here that the source could not be volcanic outgassing and the composition is best explained by cometary impacts. Ruling out a volcanic source means that volatiles in the top 1-3 meters of the Cabeus PSR regolith may be younger than the latest volcanic outgassing event (~1 billion years ago; Gya). The water and other volatiles observed in the LCROSS impact plume contained too much nitrogen to have originated from volcanic outgassing. These volatiles, stored in the top 1-3 meters of the Cabeus permanently shaded region, were delivered by comet impacts. [ABSTRACT FROM AUTHOR]