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Observations of proto-planetary disks, as well as theoretical modeling, suggest that in the late stages of accretion leading up to the formation of planetesimals, particles grew to pebbles the size of 1-mm to tens of cm, depending on the location and ambient conditions in the disk. That is the same size range that dominates the present-day comet and primitive asteroid mass loss. Meteoroids that size cause visible meteors on Earth. Here, we hypothesize that the size distribution and the physical and chemical properties of young meteoroid streams still contain information about the conditions in the solar nebula during these late stages of accretion towards planetesimal formation. If so, they constrain where long-period (Oort Cloud) comets, Jupiter-family (Scattered Disk Kuiper Belt) comets, and primitive asteroids (Asteroid Belt) formed. From video and visual observations of 47 young meteor showers, we find that freshly ejected meteoroids from long-period comets tend to have low bulk density and are distributed with equal surface area per log-mass interval (magnitude distribution index χ ∼ 1.85), suggesting gentle accretion conditions. Jupiter-family comets, on the other hand, mostly produce meteoroids twice as dense and distributed with a steeper χ ∼ 2.15 or even χ ∼ 2.5, which implies that those pebbles grew from particles fragmenting in a collisional cascade or by catastrophic collisions, respectively. Some primitive asteroids show χ > 2.5, with most mass in small particles, indicating an even more aggressive fragmentation by processes other than mutual collisions. Both comet populations contain an admixture of compact materials that are sometimes sodium-poor, but Jupiter-family comets show a higher percentage (∼8% on average) than long-period comet showers (∼4%) and a wider range of percentages among comets. While there are exceptions in both groups, the implication is that most long-period comets formed under gentle particle growth conditions, possibly near the 30 AU edge of the Trans Neptunian Disk, while most Jupiter family comets formed closer to the Sun where pebbles reached or passed the fragmentation barrier, and primitive asteroids formed in the region where the cores of the giant planets formed. This is possible if the Scattered Disk represents all objects scattered by Neptune during its migration, while the present-day outer Oort cloud formed only during and after the time of the planet instability, well after the Sun had moved away from sibling stars. • Meteoroids are the size of the pebbles that collapsed to planetesimals. • Long-period (Oort Cloud) comets often crumble into sizes indicative of gentle accretion. • Pebbles that grew to Jupiter-family comets reached or passed the fragmentation barrier. • Primitive asteroid pebbles aggressively fragmented with most mass at small sizes. • The Oort Cloud was populated later than the Scattered Disk of the Kuiper Belt. [ABSTRACT FROM AUTHOR]

Meteor and bolide phenomena caused by the atmospheric ablation of incoming meteoroids are predicted to occur at the planet Venus. Their systematic observation would allow to measure and compare the sub-mm to m meteoroid flux at different locations in the solar system. Using a physical model of atmospheric ablation, we demonstrate that Venus meteors would be brighter, shorter-lived, and appear higher in the atmosphere than Earth meteors. To investigate the feasibility of meteor detection at Venus from an orbiter, we apply the SWARMS survey simulator tool to sets of plausible meteoroid population parameters, atmospheric models and instrument designs suited to the task, such as the Mini-EUSO camera operational on the ISS since 2019. We find that such instrumentation would detect meteors at Venus with a 1.5 × to 2.5 × higher rate than at Earth. The estimated Venus–Earth detection ratio remains insensitive to variations in the chosen observation orbit and detector characteristics, implying that a meteor survey from Venus orbit is feasible, though contingent on the availability of suitable algorithms and methods for efficient on-board processing and downlinking of the meteor data to Earth. We further show that a hypothetical camera onboard the upcoming EnVision mission to Venus similar to the ISS instrument should detect many times more meteors than needed for an initial characterisation of the large meteoroid population at 0.7 au from the Sun. • We use physics-based modelling to understand the properties of meteors in the upper atmosphere of Venus and to compare meteor survey efficiency from Earth orbit and from Venus orbit. • Venus meteors would be brighter and shorter-lived than Earth meteors, due to different atmospheric density scale heights. • Assuming similar meteoroid populations at the two planets, orbital meteor surveys would detect 1.5 × –2.5 × more meteors per hour at Venus than at Earth. [ABSTRACT FROM AUTHOR]

We have estimated the largest meteoroids present in major meteor showers from observations conducted between 2019-2022 by the Geostationary Lightning Mapper (GLM) instrument on the GOES-R satellites. Our integrated time area products for the Leonids, Perseids and eta Aquariids are of order 5 × 1010 km 2 hours. We compute photometric masses for shower fireballs using the approach of Vojáček et al. (2022) to correct from narrow-band GLM luminosity to bolometric luminosity and apply the luminous efficiency relation of Ceplecha & McCrosky (1976) at high speeds. Between 2019 and 2022, the showers definitely observed by GLM were the Leonids, Perseids, and eta Aquariids, with probable detections of the Orionids and Taurids. We find the largest meteoroids to be of order 7 kg for the Leonids, 3 kg for the Perseids, and 3 kg for the eta Aquariids, corresponding to meteoroids of ≈ 0.2 m diameter. The Orionids and Taurids had maximum meteoroid masses of 4 kg and 150 kg respectively. The Leonids and eta Aquariids are well fit by a single power-law with differential mass exponent, s, of 2.08 ± 0.08 and 2.00 ± 0.09 over the mass range 10−7 < m < 1 kg. All showers had maximum meteoroid masses compatible with Whipple gas-drag ejection, with the exception of the Perseids which have much larger meteoroids than expected a result also consistent with observations from ground based instruments. This may reflect preferential ejection in narrow jets or possibly some form of mantle erosion/release in the past for the parent comet, 109P/Swift-Tuttle. • GLM has the unique ability to detect fireballs from a space-based perspective. • This is a new observational method to complement existing observation techniques. • From the data of a fireball event, a photometric mass estimate can be computed. • Provides mass information for the larger shower-related fireballs. • Flux estimations using GLM compared to existing fits agreed well. [ABSTRACT FROM AUTHOR]

The nucleus of comet 109P/Swift-Tuttle is the source of meteoroids which frequently impact the Earth as the well-known, most powerful meteor shower Perseids, # 7. In addition, the stream splits into several other filaments corresponding to few other meteor showers. In this work, we investigated, if the meteoroids of 109P's stream also impact the other three terrestrial planets. It appeared that there are meteor showers at Venus and Mars, two with the radiants in the northern and one in the southern ecliptic hemisphere of sky. Interestingly, the positions of the radiant areas of 109P's showers are almost the same at all three planets, Venus, Earth, and Mars. Any shower being so active as the Perseids was predicted neither at Venus nor at Mars, however. Some meteoroids of one filament of the 109P's stream also impacts the surface of Mercury, but the corresponding shower is predicted so low in number that it can scarcely be detected. • Meteoroid stream originating in 109P/Swift-Tuttle at Mercury, Venus, and Mars studied. • Two northern and one southern showers predicted at both Venus and Mars. • One low-numerous filament of the stream predicted to impact the Mercury. • A similar structure of the radiant areas of 109P's showers at Venus, Earth, and Mars found. [ABSTRACT FROM AUTHOR]

While comets eject mass mostly at cm-sizes and larger, that size range of particles is mostly absent from the interplanetary medium. Such particles are thought to be lost from the solar system by grain-grain collisions. Here, we investigate the lifetime of cm-sized meteoroids from their abundance in meteoroid streams of different age. For 487 streams, we measured the orbital element dispersions, the magnitude size distribution index, the ratio of fluffy and dense materials in the stream and their bulk densities, and the meteor light curve shape-parameter. We find that older long-period comet meteoroid streams tend to be more dispersed and evolve towards smaller semi-major axis, higher magnitude size distribution index, and contain relatively more high-density material. Meteoroids that approach the Sun closer than 0.2–0.3 AU are mostly young and composed of denser materials poor in sodium. We compare the observed properties of the streams to age estimates from the literature and to a set of new age estimates for long-period comet streams based on observed dispersions. We find that streams broaden with age inversely proportional to the perihelion distance (q). By selecting narrow ranges of age, we find that their magnitude distribution index changes proportional to 1/√q, less steep than expected from meteoroid destruction by collisions. Instead, this shallow dependence suggests a lifetime inversely proportional to the peak grain temperature along its orbit, with the lifetime limited by thermal stresses if 0.3 < q < 1.02 AU and by sublimation if q < 0.2 AU. • Long-period comet streams disperse with inverse perihelion distance and linear in time. • Meteoroid streams lose cm-sized grains faster than mm-sized grains. • Streams contain both low- and high-density materials, dense materials survive longer. • Streams with q < 0.2 AU are young and their meteoroids are often physically altered. • Peak grain temperature limits the lifetime of cm-sized grains in orbits with q < 1.02 AU. • Thermal stresses are important for 0.3 < q < 1.02 AU, while sublimation is for q < 0.2 AU. [ABSTRACT FROM AUTHOR]

Meteors are most often observed from the ground in the visible, most often at a distance of at least 80–100 km between the phenomenon and the observer. Such constraints lead to rough assumptions of the meteoroid's physical parameters for the data analysis. Wind tunnel experiments allow the scientists to fully characterize artificial meteors by means of a well known, controlled and calibrated environment. Here we present the first observation and full characterization of a 11.7 km/s equivalent meteor in M-IR band (3– 5 μ m). Real meteorites of different types were used in order to reproduce natural meteors in the laboratory environment. The measurements were taken with both an M-IR imaging camera and an M-IR spectrometer. We found that the overall aspect of the meteorite sample in the wind tunnel is similar in M-IR and visible bands. The M-IR spectrum shows a continuum (Planck's law), but no distinct emission lines of atoms or molecules. The derived temperatures lie in the range [ 1800 – 2500 ] K, regardless of the meteorite type. Discussions regarding the comparison with other experiments are presented. • First M-IR measurements of artificial meteors. • Black body radiation only (no emission line). • Measured temperature of 1800 – 2500 K regardless of the type of meteorite. • Light curve in M-IR seems to lag behind the visible one by 0.1 s or less. [ABSTRACT FROM AUTHOR]

In this work, we present an optical survey of mm-sized meteoroids using the Canadian Automated Meteor Observatory's (CAMO) mirror tracking system. The system tracks meteors to magnitude +7.5 through an image-intensified telescopic system which has a spatial accuracy of ∼ 1 m and a temporal resolution of 10 ms. We analyse 41 meteors from 13 showers with known parent bodies, recorded between 2016 and 2022. We fit a numerical ablation and fragmentation model to our data which models meteoroid fragmentation as erosion into 10 µm to 500 µm constituent grains and used the observed wake as a hard constraint on the model parameters. We measure average bulk meteoroid densities which are consistent with in situ measurements: 602 ± 155 kg m−3 for Jupiter-family and 345 ± 48 kg m−3 for Halley-type showers. The Geminids had the highest measured bulk density of 1387 ± 240 kg m−3, consistent with carbonaceous material. We fail to reproduce the high bulk density (> 3000 kg m−3) for Jupiter-family meteoroids previously reported in the literature derived using fragmentation models on data sets with fewer observational constraints. We also provide estimates of the meteoroid grain sizes, grain mass distributions, and energy necessary to trigger the erosion for meteoroids in the analysed showers. • The erosion model was used to investigate CAMO recorded shower meteors. • Wake was used as an additional constraint on the model to estimate grain sizes. • Bulk densities were determined, agreeing with the lower end of previous estimates. • Grain mass distribution and erosion energy were also determined for shower meteors. • Literature review of meteor shower/parent comet physical properties was presented. [ABSTRACT FROM AUTHOR]

Ground testing meteorite samples offer in-situ measurements of known materials in conditions that occur during entry into Earth's atmosphere. 22 meteorite samples with a wide range of origins and classifications were tested in the plasma wind tunnel facility PWK1 at the Institute of Space Systems in Stuttgart. These tests recreate the flow condition of a meteoroid during entry into earth's atmosphere at an altitude of 78.8 km altitude and a velocity of 11.7 km s-1. Four optical diagnostic techniques were used to measure the surface temperature above 1000 K. 2-D methods showed that the surface temperature is evenly distributed over the sample surface, while time-resolved analyses show that the samples reach a steady state temperature within 0.5 s. The steady-state temperature for chondritic samples was consistent but varied significantly for achondrites and iron meteorite samples. The composition data showed a strong dependency of the surface temperature on the silicon content. The surface temperatures were shown to be dependent on the material and a database of temperatures was set up. The Planck fit methodology could be directly adapted to spectral meteor observation systems. A comparison of the method to established methods showed an offset between the methods. This data could be applied to thermal models to better understand the energy transfer processes during meteor flight. • Ground testing of meteorites in plasma wind tunnels. • Meteorite temperature measurement with four methods. • Surface temperature distribution measurements. • Bulk composition compared to surface temperature. [ABSTRACT FROM AUTHOR]

The observation of interstellar objects 1I/'Oumuamua and 2I/Borisov suggests the existence of a larger population of smaller projectiles that impact our planet with unbound orbits. We analyze an asteroidal grazing meteor (FH1) recorded by the Finnish Fireball Network on October 23, 2022. FH1 displayed a likely hyperbolic orbit lying on the ecliptic plane with an estimated velocity excess of ∼ 0.7 km s−1 at impact. FH1 may either be an interstellar object, indicating a high-strength bias in this population, or an Oort cloud object, which would reinforce migration-based solar system models. Furthermore, under the calculated uncertainties, FH1 could potentially be associated with the passage of Scholz's binary star system. Statistical evaluation of uncertainties in the CNEOS database and study of its hyperbolic fireballs reveals an anisotropic geocentric radiant distribution and low orbital inclinations, challenging the assumption of a randomly incoming interstellar population. Orbital integrations suggest that the event on March 9, 2017 (IM2) from CNEOS may have experienced gravitational perturbation during the Scholz fly-by, contingent upon velocity overestimation within the expected range. These findings suggest that apparent interstellar meteors may, in fact, be the result of accelerated meteoroid impacts caused by close encounters with massive objects within or passing through our solar system. • Analyzed FH1, the first hyperbolic meteor detected by the Finnish Fireball Network. • FH1 was a fast, height grazing meteor with an almost ecliptic orbit. • Considered FH1 as possibly interstellar or a centimeter asteroid-like body from the Oort cloud. • CNEOS hyperbolic fireballs are statistically unlikely to be of interstellar origin. • FH1 and the so-called IM2 may be consistent with having undergone gravitational perturbation during Scholz's passage. [ABSTRACT FROM AUTHOR]

18 mm-sized Orionid meteoroids were captured in 2019 and 2020 by the Canadian Automated Observatory's mirror tracking system. Meteor position measurements were made to an accuracy of ∼ 1 m and the meteors were tracked to a limiting magnitude of about + 7. 5 at the faintest point. The trajectory estimation shows the intrinsic physical dispersion of the Orionid radiant is 0. 400 ° ± 0. 062 °. An erosion-based entry model was fit to the observations to reproduce ablation and fragmentation for each meteor, simultaneously reproducing the light curve, the dynamics, and the wake. Wake observations were found to directly inform the grain mass distribution released in the modelled erosion. A new luminous efficiency model was derived from simultaneous radar and optical observations and applied in the modelling to improve its accuracy. The results show that the apparent strength of Orionids varies with radiant location and time of appearance during the period of shower activity. The average differential grain mass distribution index was 2.15, higher than found from in-situ estimates, possibly due to the evolution of the physical properties of meteoroids since ejection. All Orionids showed leading fragment morphology which was best explained by stopping the erosion at the peak of the light curve, leaving a non-fragmenting meteoroid with ∼ 10 % of the original mass. The inverted Orionid meteoroid average bulk density of ∼ 300 kg m −3 , corresponding to porosities of ∼ 90 % , is consistent with in-situ measurements of larger dust particles by Vega-2 at 1P/Halley and Rosetta at 67P. • Captured 18 Orionid meteoroids using the Canadian Automated Observatory's mirror-tracking system. • Determined Orionid radiant intrinsic physical dispersion: 0. 400 ° ± 0. 062 °. • Introduced a new luminous efficiency model derived from radar and optical observations. • Utilized an erosion-based entry model to simulate meteor ablation, fragmentation, and light curve. • Orionid meteoroid bulk density: ∼ 300 kg/m 3 , aligning with in-situ measurements from Vega-2. [ABSTRACT FROM AUTHOR]

A relationship is developed for evaluating the initial meteoroid diameter based on the measured absolute visual magnitude prior to fragmentation. This approach provides an alternative to the luminous efficiency approach for evaluating the size of a meteoroid from a measured lightcurve. The developed relationship, which is valid for asteroidal meteoroids with entry velocities below 30 km/s and initial diameters greater than 10 cm, is written as D = 0. 0556 × 1 0 − 0. 182 M 60 k m − 0. 0562 V 60 k m , where D is the initial meteoroid diameter in m, M 60 k m is the absolute visual magnitude measured at an altitude of 60 km, and V 60 k m is the velocity in km/s at 60 km altitude. This relationship is enabled by the insights provided by recent computational fluid dynamics and radiation simulations, which show that for an unfragmented meteoroid, the M 60 k m value is a much stronger function of meteoroid diameter than the meteor ablation rate or meteoroid composition. This relationship is also enabled by the recent increase in the number of meteor events with calibrated lightcurves and recovered meteorites. In addition to providing the meteorite density, which enables a more accurate conversion between meteoroid mass and size, the recovered meteorites enable a diameter based on radionuclide or noble gas analyses. This provides an alternative to the dynamic mass and infrasound-based diameters, which results in three different meteor diameter assessments that are independent of the luminous efficiency. These three approaches are used to develop the present relationship between the meteor diameter and M 60 k m. The altitude of 60 km is chosen for developing this relationship because it is high enough to minimize the potential for fragmentation and low enough for ablation to have reached a steady-state. This altitude is also low enough to avoid significant measurement noise in the lightcurve, which may be present at higher altitudes due to weaker emission and a longer measurement distance. • Method developed for determining a meteoroid diameter from the measured lightcurve • Method enabled by recent lightcurve measurements and new meteor simulation approach • Simulations show weak dependencies of lightcurve on numerous parameters • Method correlates meteor brightness at 60 km altitude with diameter and velocity [ABSTRACT FROM AUTHOR]

The paper reports the determination of luminous efficiency values from ground testing of a comprehensive set of meteorite samples. The ground testing data is translated with commonly used ground to flight extrapolation analogies from atmospheric entry maneuver's engineering into values of a night observation. This results in a meteor at an altitude of 80 km with a flight speed of 11.7 km/s of a 34.8 mm diameter spherical meteoroid. A method is developed to determine the total luminous efficiency τ in the bands U, B, V, R, and I from the radiance data and the measured mass loss. For the first time, a measurement of luminous efficiency became possible for known materials. The values itself are in the range of 0.01% to ∼ 1%, which is in the range of previous studies from meteor measurements. • Ground testing of meteorite samples. • Determination of Luminous Efficiency. • Meteor observation. [ABSTRACT FROM AUTHOR]

Observation missions of meteoroids entering the Earth's atmosphere are conducted regularly. Meanwhile a method to replicate the flight in a ground test facilities has been established. However, numerical simulations with subsequent comparison of the spectroscopic data, on the other hand, are not yet widely used in this field. This is mainly due to the complex flow environment, which includes not only non-equilibrium radiation, but also the outgassing of species from the meteoroid that do not enter the shock since they have only the thermal velocity of the wall without macroscopic flow and therefore cannot heat up as much as the other species. This paper presents a numerical approach to replicate experimental measurements. The Direct Simulation Monte Carlo (DSMC) method is used and bi-directionally coupled with a radiation solver to simulate the atmospheric entry in 80 km of an iron meteorite with a diameter of 38 mm. The paper provides information and references on the numerical models used, the challenges encountered, and the simulation results. The study shows that the simulation models are well-suited to handle the non-equilibrium effects of meteorite entry and show good agreement with the experimental measurements. • Complete non-equilibrium simulation of a meteoroid with a gas kinetic solver. • First coupled radiative flow simulation of a meteoroid. • First successful numerical reproduction of a measured meteor spectrum by simulation. [ABSTRACT FROM AUTHOR]

Melting experiments attempting to reproduce some of the processes affecting asteroidal and cometary material during atmospheric entry have been performed in a high enthalpy facility. For the first time with the specific experimental setup, the resulting material has been recovered, studied, and compared with natural analogues, focusing on the thermal and redox reactions triggered by interaction between the melt and the atmospheric gases under high temperature and low pressure conditions. Experimental conditions were tested across a range of parameters, such as heat flux, experiment duration, and pressure, using two types of sample holders materials, namely cork and graphite. A basalt served as asteroidal analog and to calibrate the experiments, before melting a H5 ordinary chondrite meteorite. The quenched melt recovered after the experiments has been analyzed by μ-XRF, EDS-SEM, EMPA, LA-ICP-MS, and XANES spectroscopy. The glass formed from the basalt is fairly homogeneous, depleted in highly volatile elements (e.g., Na, K), relatively enriched in moderately siderophile elements (e.g., Co, Ni), and has reached an equilibrium redox state with a lower Fe3+/Fe tot ratio than that in the starting material. Spherical objects, enriched in SiO 2 , Na 2 O and K 2 O, were observed, inferring condensation from the vaporized material. Despite instantaneous quenching, the melt formed from the ordinary chondrite shows extensive crystallization of mostly olivine and magnetite, the latter indicative of oxygen fugacity compatible with presence of both Fe2+ and Fe3+. Similar features have been observed in natural meteorite fusion crusts and in micrometeorites, implying that, at least in terms of maximum temperature reached and chemical reactions, the experiments have successfully reproduced the conditions likely encountered by extraterrestrial material following atmospheric entry. • Atmospheric entry of asteroidal material reproduced in high enthalpy experiments. • The glass produced by melting basalt and an ordinary chondrite was recovered. • Characteristic features of natural meteorite fusion crusts were reproduced. • Alkali metals are vaporized, the glass is enriched in moderately siderophile elements. • Redox equilibrium independent from original oxidation state [ABSTRACT FROM AUTHOR]

A methodology is introduced to optimize and extend the inference of pre-entry size, density, strength, and mass of asteroids based on observed light curves. In this development study, a genetic algorithm (GA) approach is coupled with the fragment-cloud model (FCM) to efficiently evaluate entry and breakup for numerous potential asteroid property combinations and determine which case best matches the observed data. FCM produces energy deposition curves based on assumed pre-entry conditions, and the GA finds values for these inputs that minimize an objective function characterizing the difference between the FCM curve and a target curve. We present an overview of the GA approach, and then demonstrate its capability to infer pre-entry properties for three well-characterized events: Chelyabinsk, Lost City, and Benešov. In all cases, our initial mass and size estimates were within the range of published values. • A new approach for automatically inferring meteoroid parameters is presented. • Objective function and tuning parameters for the genetic algorithm are identified. • The method reproduces diverse meteor curves with distinct fragmentation features. • Matches for the Chelyabinsk, Lost City, and Benešov meteors are presented. • Initial mass and diameter inferences are within the previously published estimates. [ABSTRACT FROM AUTHOR]

In this paper we present the results of numerical modeling of the Chelyabinsk dust train during the first 3 min after the meteoroid entry which are in qualitative agreement with observations. Then we analyze the possibility of plume formation after impacts of small cosmic bodies and make some calculations for the Tunguska event which, unfortunately, cannot be compared directly with observations. We also estimate long-lasting disturbances in the upper atmosphere caused by the plume formation. [ABSTRACT FROM AUTHOR]

Abstract The atmosphere of Jupiter is mainly hydrogen and methane, with a large number of hydrocarbons calculated to be produced by photodissociation and subsequent reactions. It is assumed that oxygen is added by meteoroids. Recent studies have found that photochemistry does not explain the measured ratios of water to carbon monoxide, if it is assumed that water is the major constituent of meteoroids and vapourises. A possible explanation is that processes that occur during or soon after the meteoroid's passage change the proportions of the oxygen-bearing constituents. In this paper, the processes considered are dissociation, ionization of the original molecules and ionization of dissociated products. The difference between applying these processes in the bulk atmosphere and in the meteor trail itself is investigated, as is the possibility of methane being dissociated in a shock wave produced by the meteoroid. In all cases, there was no significant change to the predicted density of water at the height of a measurement. However, the density of hydroxyl relative to water differed depending on the assumed process, thus presenting the possibility that measurements of electron-driven emissions from hydroxyl could be used for remote sensing of the actual processes occurring. Highlights • Densities of H 2 O, CO, CO 2 and OH, produced by meteoritic input, are calculated for the atmosphere of Jupiter. • Dissociation, ionization, and enhanced reaction rates in the meteor trails do not influence the densities at the height of a measurement. • The OH:H 2 O density ratio shows potential for remote sensing using electron-driven emissions. [ABSTRACT FROM AUTHOR]

Abstract Meteoroid modelling of fireball data typically uses a one dimensional model along a straight line triangulated trajectory. The assumption of a straight line trajectory has been considered an acceptable simplification for fireballs, but it has not been rigorously tested. The unique capability of the Desert Fireball Network (DFN) to triangulate discrete observation times gives the opportunity to investigate the deviation of a meteoroid's position to different model fits. Here we assess the viability of a straight line assumption for fireball data in two meteorite-dropping test cases observed by the Desert Fireball Network (DFN) in Australia – one over 21 s (DN151212_03), one under 5 seconds (DN160410_03). We show that a straight line is not valid for these two meteorite dropping events and propose a three dimensional particle filter to model meteoroid positions without any straight line constraints. The single body equations in three dimensions, along with the luminosity equation, are applied to the particle filter methodology described by Sansom et al. (2017). Modelling fireball camera network data in three dimensions has not previously been attempted. This allows the raw astrometric, line-of-sight observations to be incorporated directly. In analysing these two DFN events, the triangulated positions based on a straight line assumption result in the modelled meteoroid positions diverging up to 3.09 km from the calculated observed point (for DN151212_03). Even for the more typical fireball event, DN160410_03 , we see a divergence of up to 360 m. As DFN observations are typically precise to < 100 m, it is apparent that the assumption of a straight line is an oversimplification that will affect orbit calculations and meteorite search regions for a significant fraction of events. [ABSTRACT FROM AUTHOR]

Highlights • Model of time-of-day-dependent lunar OH column density. • Consistency with observations across broad range of H diffusivity pre-factors. • Major importance of OH photolysis for time-of-day-dependent OH variations. • Minor importance of micrometeoroid-delivered OH/H 2 O for 3 µm band depth. • Probable presence of region-specific temporally constant stable OH component. Abstract In this study we determine the depth of the absorption band around 3 µm wavelength, which indicates the presence of OH/H 2 O in a thin surficial layer of the lunar regolith, for 18 lunar highland regions observed by the Moon Mineralogy Mapper (M3) instrument at 4–8 different local times of day. For removing the thermal emission component, a physically motivated thermal equilibrium based method is used, which also takes into account the roughness of the regolith surface. We propose a continuity equation based model of the time-of-day-dependent column densities of surficial atomic hydrogen (H) and hydroxyl (OH). The considered source processes for H are implantation of solar wind protons and photolysis of OH, and for OH the reaction H + O → OH. Sink processes are diffusive loss for H and OH, and photolysis for OH. Sputtering of H and OH is found to be negligible in comparison to the other sink processes. Additionally, we suggest a similar differential equation based model to describe the time-of-day-dependent behavior of micrometeoroid-delivered OH and H 2 O. The observed 3 µm band depth values indicate that the surficial OH/H 2 O does not vanish even at local midday at low latitudes, while the model predicts nearly complete removal of surficial OH/H 2 O at midday. This apparent contradiction between model and observations is reconciled by adding to the model a region-specific "offset" OH component which is assumed to be stable against diffusive loss and photolysis and is therefore interpreted as a strongly bounded OH component. Meteoroid bombardment is found to be negligible in comparison with the solar wind source of OH. Fitting the model to the observed 3 µm band depth values allows for estimating the H activation energy, the OH photolysis time, region-specific values of the offset OH component, and the proportionality factor between OH column density and 3 µm band depth. The observed time-of-day-dependent behavior of the 3 µm band depth at low and high latitudes can be explained convincingly by the modeled source and sink processes. The best-fit OH photolysis time is much shorter than the lunar day and corresponds to 1–3 times the gas-phase value, which indicates that photolysis is a mechanism of high relevance for the behavior of solar wind induced surficial OH. The surface roughness assumed in the M3 data analysis does not have a major influence on the modeling results. The strongly bounded OH component is nearly latitude-independent for low latitudes but decreases sharply for high latitudes. As a possible mode of origin, we suggest slow diffusion of solar wind induced OH to depths inaccessible for ultraviolet photons and into binding states of higher energy, counteracted by sputtering. [ABSTRACT FROM AUTHOR]

After the prediction of meteor showers in the Earth's atmosphere caused by the particles originating in the nucleus of comet 21P/Giacobini-Zinner, we went on with the prediction of showers on the other three terrestrial planets. Based on our modeling of theoretical stream of the parent comet, we predicted several related impacted meteoroid (on Mercury) or meteor (on Venus and Mars) showers. There occurred the filaments, in the stream, with the particles coming to each planet from a similar direction. We found that this is a consequence of the specific distribution of argument of perihelion (peaked close to the value of 180 °) and longitude of ascending node of the stream, and that the particles collide with each planet in an arc of their orbits being close to perihelion. • Approaches of the particles in the meteoroid stream of comet 21P/Giacobini-Zinner to Mercury, Venus, and Mars studied. • Several showers on each planet predicted. • Similar incoming direction of meteoroids to each planet. • Collisions with each planet happen mostly near the perihelia of meteoroids. [ABSTRACT FROM AUTHOR]

Highlights • The fragment-cloud model is extended to represent atmospheric breakup of meteoroids with varied structures. • The model provides excellent matches to energy deposition estimates for observed meteors. • Matches for the Chelyabinsk, Benešov, Košice, and Tagish Lake meteors are presented. • Results enable inference about pre-entry asteroid structures, breakup behavior, and potential model refinements. Abstract Asteroids populations are highly diverse, ranging from coherent monoliths to loosely bound rubble piles, with a broad range of material and compositional properties. These different structures and properties could significantly affect how an asteroid breaks up and deposits energy in the atmosphere, and how much ground damage may occur from resulting blast waves. We have previously developed a fragment-cloud model (FCM) for assessing the atmospheric breakup and energy deposition of asteroids striking Earth. The approach represents ranges of breakup characteristics by combining progressive fragmentation with releases of variable fractions of debris and larger discrete fragments. In this work, we have extended the FCM to also represent asteroids with varied initial structures, such as rubble piles or fractured bodies. We have used the extended FCM to model the Chelyabinsk, Benešov, Košice, and Tagish Lake meteors, and have obtained excellent matches to energy deposition profiles derived from their light curves. These matches provide validation for the FCM approach, help guide further model refinements, and enable inferences about pre-entry structure and breakup behavior. Results highlight differences in the amount of small debris vs. discrete fragments in matching the various flare characteristics of each meteor. The Chelyabinsk flares were best represented using relatively high debris fractions, while Košice and Benešov cases were more notably driven by their discrete fragmentation characteristics, perhaps indicating more cohesive initial structures. Tagish Lake exhibited a combination of these characteristics, with lower-debris fragmentation at high altitudes followed by sudden disintegration into small debris in the lower flares. Results from all cases also suggest that lower ablation coefficients and debris spread rates may be more appropriate for the way in which debris clouds are represented in FCM, offering an avenue for future model refinement. [ABSTRACT FROM AUTHOR]

Hightlights • An exhaustive review of the written sources from Medieval Europe (V-XV centuries) has been made searching for new records of meteors and meteor showers. • Using the new records, the distribution and evolution of meteor showers throughout the mentioned period has been studied. • The inconsistencies that appeared in previous studies that used European sources have been reduced. Abstract The distribution of meteors streams throughout a year from the 5th to the 15th century is investigated, based on a new compilation of meteor records in the diverse European Medieval sources. The records of meteor showers and storms in the chronicles of Korea, Japan, China and Arab have also been considered, and compare their appearance dates with those of showers obtained above, as well as with modern observations. We found that the three sets of data are in agreement with each other, the Perseids, Leonids, and Lyrids being best represented. [ABSTRACT FROM AUTHOR]

Current models allow to reliably simulate mechanical and thermal phenomena associated with a micrometeor passage through the Earth’s atmosphere. However, these models have rarely been applied to materials other than those most common in meteorites, such as silicates and metals. A particular case that deserves attention is the one of micrograins made of minerals, in particular carbonates, which have been associated, in meteorites, with organic molecules. Carbonates are known for their decomposition in vacuum at moderate temperatures, and they might contribute to the thermal protection of organic matter. In this work, a model with non isothermal atmosphere, power balance, evaporation, ablation, radiation losses and stoichiometry, is proposed. This paper includes the very first calculations for meteoroids with a mixed carbonate composition. Results show that the carbonate fraction of these objects always go to zero at high altitudes except for grazing entries, where the reached temperature is lower and some carbonate remains unreacted. For all entry conditions, peculiar temperature curves are obtained due to the decomposition process. Furthermore, a significant impact of decomposition cooling on the temperature peak is observed for some grazing entry cases. Although specific solutions used in these calculations can be improved, this work sets a definite model and a basis for future research on sub-mm grains of relatively volatile minerals entering the Earth’s atmosphere. [ABSTRACT FROM AUTHOR]

A high-fidelity approach for simulating the aerothermodynamic environments of meteor entries was developed, which allows the commonly assumed heat transfer coefficient of 0.1 to be assessed. This model uses chemically reacting computational fluid dynamics (CFD), coupled with radiation transport and surface ablation. Coupled radiation accounts for the impact of radiation on the flowfield energy equations, while coupled ablation explicitly models the injection of ablation products within the flowfield and radiation simulations. For a meteoroid with a velocity of 20 km/s, coupled radiation is shown to reduce the stagnation point radiative heating by over 60%. The impact of coupled ablation (with coupled radiation) is shown to provide at least a 70% reduction in the radiative heating relative to cases with only coupled radiation. This large reduction is partially the result of the low ionization energies of meteoric ablation products relative to air species. The low ionization energies of ablation products, such as Mg and Ca, provide strong photoionization and atomic line absorption in regions of the spectrum that air species do not. MgO and CaO are also shown to provide significant absorption. Turbulence is shown to impact the distribution of ablation products through the shock-layer, which results in up to a 100% increase in the radiative heating downstream of the stagnation point. To create a database of heat transfer coefficients, the developed model was applied to a range of cases. This database considered velocities ranging from 14 to 20 km/s, altitudes ranging from 20 to 50 km, and nose radii ranging from 1 to 100 m. The heat transfer coefficients from these simulations are below 0.045 for the range of cases, for both laminar and turbulent, which is significantly lower than the canonical value of 0.1. When the new heat transfer model is applied to a Tunguska-like 15 Mt entry, the effect of the new model is to lower the height of burst by up to 2 km, depending on assumed entry angle. This, in turn, results in a significantly larger ground damage footprint than when the canonical heating assumption is used. [ABSTRACT FROM AUTHOR]

Results from a meteor head echo shower survey using the quasi continuous meteor observations of the high power large aperture radar MAARSY, located in northern Norway (69.30° N , 16.04° E ) are presented. The data set comprises 760 000 head echoes detected during two and half years sensitive to an effective limiting masses below 10 − 8 kg. Using a wavelet shower search algorithm, we identified 33 meteor showers in the data set all of which are found in the IAU meteor shower catalog. We find  ∼ 1% of all measured head echoes at these masses are associated with meteor showers. Comparison of shower radiants from this survey with the observation of the Canadian Meteor Orbit radar (CMOR) transverse scattering radar system shows generally good agreement, although there are large differences in the measured durations of some meteor showers. Differential mass indices ( s ) of  ∼ 1.5–1.6 are measured for the Perseids (PER), Geminids (GEM) and Quadrantids (QUA) showers. The Orionids (ORI) show a much steeper mass index of 2.0, in agreement with other observations at small particle sizes, suggesting the Halleyid showers, in particular, are rich in very small meteoroids. [ABSTRACT FROM AUTHOR]

The implication of small amounts of cohesion within relatively small rubble pile asteroids is investigated with regard to their evolution under the persistent presence of the YORP effect. We find that below a characteristic size, which is a function of cohesive strength, density and other properties, rubble pile asteroids can enter a “disaggregation phase” in which they are subject to repeated fissions after which the formation of a stabilizing binary system is not possible. Once this threshold is passed rubble pile asteroids may be disaggregated into their constituent components within a finite time span. These constituent components will have their own spin limits – albeit potentially at a much higher spin rate due to the greater strength of a monolithic body. The implications of this prediction are discussed and include modification of size distributions, prevalence of monolithic bodies among meteoroids and the lifetime of small rubble pile bodies in the solar system. The theory is then used to place constraints on the strength of binary asteroids characterized as a function of their type. [ABSTRACT FROM AUTHOR]

In this work we model the dynamical evolution of meteoroid streams of comet 96P/Machholz, and the largest member of the Marsden sunskirters, comet P/1999 J6. We simultaneously fit the characteristics of eight meteor showers which have been proposed to be linked to the complex, using observations from a range of techniques - visual, video, TV and radar. The aim is to obtain a self-consistent scenario of past capture of a large comet into a short-period orbit, and its subsequent fragmentation history. Moreover, we also aim to constrain the dominant parent of these showers. The fit of our simulated shower characteristics to observations is consistent with the scenario of a capture of a proto-comet 96P/Machholz by Jupiter circa 20000 BCE, and a subsequent major breakup around 100–950 CE which resulted in the formation of the Marsden group of comets. We find that the Marsden group of comets are not the immediate parents of the daytime Arietids and Northern and Southern δ -Aquariids, as previously suggested. In fact, the hypothesis that the Northern δ -Aquariids are related to the Marsden group of comets is not supported by this study. The bulk of the observational characteristics of all eight showers can be explained by meteoroid ejection primarily from comet 96P/Machholz between 10000 BCE and 20000 BCE. Assuming the Marsden group of comets originated between 100 CE–950 CE, we conclude that sunskirting comets contribute mainly to the meteoroid stream near the time of the peak of the daytime Arietids, Southern δ -Aquariids, κ -Velids. Finally, we find that the meteor showers identified by Babadzhanov and Obrubov (1992) as the α -Cetids, the Ursids and Carinids correspond to the daytime λ -Taurids, the November ι -Draconids or December α -Draconids and the θ -Carinids. [ABSTRACT FROM AUTHOR]

Based on the equilibrium thermochemical approach and quenching theory, formation of molecules and dust grains in impact-produced clouds formed after collisions between meteoroids and Mercury is considered. Based on observations of Al, Fe, and Mn atoms in the exosphere of Mercury and new results of studies of the elemental composition of the surface of Mercury, quenching temperatures and pressures of main chemical reactions and condensation of dust particles were estimated. The behavior of the main Na-, K-, Ca-, Fe-, Al-, Mn-, Mg-, Si-, Ti, Ni-, Cr-, Co, Zn-, O-, H-, S-, C-, Cl-, N-, and P-containing species delivered to the Hermean exosphere during meteoroid impacts was studied. The importance of meteoroid bombardment as a source of Na, K, Ca, Fe, Al, Mn, Mg, and O atoms in the exosphere of Mercury is discussed. [ABSTRACT FROM AUTHOR]

Space weathering is one of the most common surface process occurring on atmosphere-free bodies such as asteroids and the Moon. It is caused mainly by solar wind irradiation and the impact of micrometeoroids. In order to simulate space weathering effects, in particular those produced by hypervelocity impacts, we produced microcraters via ultra-short (∼100 fs) laser irradiation of crystallographically oriented slices of forsterite-rich (Fo 94.7 ) olivine. The main advantages of the application of a femtosecond laser radiation to reproduce the space weathering effects are (1) the high peak irradiance (10 15  W cm −2 ), which generates the propagation of the shock wave at the nanosecond timescale (i.e., timescale of the micrometeoroid impacts); (2) the rapid transfer of energy to the target material, which avoids the interaction of laser light with the developing vapor plume; (3) a small laser beam, which allows the effects of a single impact to be simulated. The results of our spectroscopic and electron microscopic investigation validate this approach: the samples show strong darkening and reddening of the reflectance spectra and structural damages similar to the natural microcraters found on regolith grains of the Moon and asteroid 25143 Itokawa. Detailed investigations of several microcrater cross-sections by transmission electron microscopy allowed the detection of shock-induced defect microstructures. From the top to the bottom of the grain, the shock wave causes evaporation, melting, solid-state recrystallization, misorientation, fracturing, and the propagation of dislocations with Burgers vectors parallel to [001]. The formation of a short-lived vapor plume causes the kinetic fractionation of the gas and the preferential loss of lighter elements, mostly magnesium and oxygen. The high temperatures within the melt layer and the kinetic loss of oxygen promote the thermal reduction of iron and nickel, which leads to the formation of metallic nanoparticles (npFe 0 ). The final stage of the microcrater formation is the cooling of the melt layer that results in its partial crystallization and the formation of olivine crystals with a palisade-like texture. [ABSTRACT FROM AUTHOR]

The Earth's cumulative meteoroid flux, as found by Halliday et al. (1996), may have a shallower slope for meteoroid masses in the range 0.1–2.5 kg compared to those with masses greater than 2.5 kg when plotted on a log flux vs. log mass graph. This would indicate a lack of low-mass objects. While others such as Ceplecha (1992) find no shallow slope, there may be a reason for a lack of 0.1–2.5 kg meteoroids which supports Halliday et al.’s finding. Simple models show that a few centimeters of space erosion in stony meteoroids can reproduce the bend in Halliday et al.’s curve at ∼2.5 kg and give the shallower slope. [ABSTRACT FROM AUTHOR]

The study of the micro-meteoroid environment is relevant to planetary science and space weathering of airless bodies, as the Moon or Mercury. In fact, the meteoroids hit directly the surfaces producing impact debris and vapor, thus contributing to shape the exosphere of the planet. This work is focused on the study and modelling of the Mercury's Ca exosphere formation through the process of Micro-Meteoroids Impact Vaporization (MMIV). The MESSENGER/NASA mission provided measurements of Mercury's Ca exosphere, allowing the study of its configuration and its seasonal variations. The observed Ca exhibited very high energies, with a scale height consistent with a temperature > 50,000 K, originated mainly on the dawn-side of the planet. It was suggested that the originating process is due to MMIV, but previous estimations were not able to justify the observed intensity and energy. We investigate the possible pathways to produce the high energy observed in the Ca exosphere and discuss about the generating mechanism. The most likely origin may be a combination of different processes involving the release of atomic and molecular surface particles. We use the exospheric Monte Carlo model by Mura et al. (2007) to simulate the 3-D spatial distribution of the Ca-bearing molecule and atomic Ca exospheres generated through the MMIV process, and we show that their morphology and intensity are consistent with the available MESSENGER observations if we consider a cloud quenching temperature < 3750 K. The results presented in this paper can be useful in the exospheric studies and in the interpretation of active surface release processes, as well as in the exosphere observations planning for the ESA-JAXA BepiColombo mission that will start its nominal mission phase in 2026. • Study and modelling of the Mercury's Ca exosphere formation through the process of Micro-Meteoroid Impact Vaporization (MMIV) • Main exospheric component at high altitudes is the energetic Ca from the shock-induced dissociative ionization and neutralization of Ca+ • Photo-dissociated Ca-bearing molecules provide non-negligible Ca contribution at low energies in the low-altitudes post-dawn region. • Simulated Ca exosphere along the planet orbit agrees with the MESSENGER/MASCS observations, when the plume temperature < 3750 K. [ABSTRACT FROM AUTHOR]

A latitudinal and radial study of the lunar sodium exosphere has been performed utilizing observations made from two different methods: (1) observations made at targeted altitudes using a Fabry-Perot Spectrometer (FPS) and (2) observations made from a coronagraph. The FPS observations made from the National Solar Observatory McMath-Pierce Solar Telescope, Kitt Peak, Arizona and the coronagraph observations were made at the Winer Observatory, Sonoita, Arizona. A small subset of the high resolution FPS observations were made concurrently with coronagraph measurements. Measured linewidths and linewidth-derived temperatures from FPS observations were compared to temperatures derived from the coronagraphic intensity altitude profiles, with FPS linewidth-derived temperatures shown to be consistently lower. We suggest that the coronagraph method samples a velocity distribution perpendicular to the FPS's LOS, while the FPS samples a velocity distribution tangential to the lunar limb (i.e., along the FPS LOS). We also suggest that the coronagraph measurements may be more sensitive to the escaping population of atoms as the population close to the surface is not observed. The concurrent FPS measurements sit below the occulting disk of the coronagraph and measure the atoms closer to the surface. Furthermore, both the FPS linewidth-derived temperatures and the coronagraph scale heights show an increase towards high latitudes, an effect which is attributed to particle transport and/or contributions from a source like meteoroid impact vaporization. FPS linewidths decrease as a function of altitude, a result confirmed through a simulation of velocity distributions from nonthermal source mechanisms. And, finally, Linewidths are largest when looking over the dawn/dusk terminator. These results will enable improved characterization of the sources for the lunar sodium exosphere. • Lunar exospheric measurements from two different instruments and methods are compared. • Concurrent linewidth-derived temperatures and coronagraph scale heights increase towards high latitudes. • Observed linewidths decrease as a function of altitude. • 1-D velocity distributions simulated near local noon predict linewidths that decrease monotonically with altitude. • Near sunrise, an increase in linewidth is occasionally observed at ∼1500 km, perhaps indicating a transition to a more energetic source process. [ABSTRACT FROM AUTHOR]

The Cassini spacecraft provided key measurements during its more than twelve year mission that constrain the absolute age of Saturn's rings. These include the extrinsic micrometeoroid flux at Saturn, the volume fraction of non-icy pollutants in the rings, and a measurement of the ring mass. These observations taken together limit the ring exposure age to be ≲ a few 100 Myr if the flux was persistent over that time (Kempf et al., 2022). In addition, Cassini observations during the Grand Finale further indicate the rings are losing mass (Hsu et al., 2018; Waite et al., 2018) suggesting the rings are ephemeral as well. In a companion paper (Durisen and Estrada, 2022), we show that the effects of micrometeoroid bombardment and ballistic transport of their impact ejecta can account for these loss rates for reasonable parameter choices. In this paper, we conduct numerical simulations of an evolving ring in a systematic way in order to determine initial conditions that are consistent with these observations. We begin by revisiting the ancient massive ring scenario of Salmon et al. (2010). Here, we model not just the viscous evolution, but we subject the ring to pollution by micrometeoroid bombardment over the age of the Solar System. We find that regardless of initial mass, the ring always ends up with more pollutant than is currently observed, because the ring spends the majority of its lifetime at relatively low mass where it is most susceptible to darkening. We then show that models with initial disk masses of ∼ 1 – 3 Mimas masses reach volume fractions of pollutant consistent with the observed volume fractions of non-icy material in the A and B rings within a time scale of ∼ a few 100 Myr. Finally, we use the analysis of Durisen and Estrada (2022) to add the dynamical effects of meteoroid bombardment into the evolution equations, namely, mass loading and ballistic transport. The treatment of mass loading is exact, while ballistic transport is handled in an approximate way. Simulations show that: (1) mass loading and ballistic transport applied to an initially high optical depth annulus inevitably produce a lower density C ring analog interior to the annulus; and (2) high density rings subject to persistent micrometeoroid bombardment do not have an asymptotic mass but instead have an asymptotic lifetime much shorter than the age of the Solar System. This is because micrometeoroid bombardment and ballistic transport drive the dynamical evolution of the ring once viscosity weakens, indicating that the exposure age of the rings and their dynamical age are connected. • Viscously evolving rings over the age of the SS always end up darker than observed. • 1-3 Mimas mass viscously evolving icy rings reach observed darkening in ≲ few × 100 Myr. • Rings have an asymptotic lifetime when micrometeoroid bombardment is included. • A low optical depth, C ring-like structure can form from an initial massive annulus. • Ring age and lifetime consistent with initial 1-3 Mimas ring mass, ∼ 100 Myr ago. [ABSTRACT FROM AUTHOR]

The Cassini mission provided key measurements needed to determine the absolute age of Saturn's rings, including the extrinsic micrometeoroid flux at Saturn, the volume fraction of non-icy pollutants in the rings, and the total ring mass. These three factors constrain the ring age to be no more than a few 100 Myr (Kempf et al., 2022). Observations during the Cassini Grand Finale also showed that the rings are losing mass to the planet at a prodigious rate. Some of the mass flux falls as "ring rain" at high latitudes. However, the influx in ring rain is considerably less than the total measured mass influx of 4800 to 45000 kg s−1 at lower latitudes (Waite et al., 2018). In addition to polluting the rings, micrometeoroid impacts lead to ballistic transport , the mass and angular momentum transport due to net exchanges of meteoroid impact ejecta. Because the ejecta are predominantly prograde, they carry net angular momentum outward. As a result, ring material drifts inward toward the planet. Here, for the first time, we use a simple model to quantify this radial mass inflow rate for dense rings and find that, for plausible choices of parameters, ballistic transport and mass loading by meteoroids can produce a total inward flux of material in the inner B ring and in the C ring that is on the order of a few ⋅ 1 0 3 to a few ⋅ 1 0 4 kg s−1, in agreement with measurements during the Cassini Grand Finale. From these mass inflow rates, we estimate that the remaining ring lifetime is ∼ 15 to 400 Myr. Combining this with a revised pollution age of ∼ 120 Myr , we conclude that Saturn's rings are not only young but ephemeral and probably started their evolution on a similar timescale to their pollution age with an initial mass of one to a few Mimas masses. In addition to showing that meteoroid impacts can produce a large sustained mass inflow through the B and C rings, this paper addresses various uncertainties and considers possible contributions by additional transport mechanisms and by external torques. We also map out a set of future research projects, including global simulations. • Meteoroid bombardment can account for the observed ring mass inflow into Saturn. • The remaining life time of the rings derived from this process is 15–400 Myr. • The rings appear to be no more than a few 100 Myr old. • Mass loss rate suggests rings were initially one to a few Mimas masses when formed. • The C ring may have formed naturally from an initial dense ring annulus of material. [ABSTRACT FROM AUTHOR]

Context. Generating a synthetic dataset of meteoroid orbits is a crucial step in analysing the probabilities of random grouping of meteoroid orbits in automated meteor shower surveys. Recent works have shown the importance of choosing a low similarity threshold value of meteoroid orbits, some pointing out that the recent meteor shower surveys produced false positives due to similarity thresholds which were too high. On the other hand, the methods of synthetic meteoroid orbit generation introduce additional biases into the data, thus making the final decision on an appropriate threshold value uncertain. Aims. As a part of the ongoing effort to determine the nature of meteor showers and improve automated methods, it was decided to tackle the problem of synthetic meteoroid orbit generation, the main goal being to reproduce the underlying structure and the statistics of the observed data in the synthetic orbits. Methods. A new method of generating synthetic meteoroid orbits using the Kernel Density Estimation method is presented. Several types of approaches are recommended, depending on whether one strives to preserve the data structure, the data statistics or to have a compromise between the two. Results. The improvements over the existing methods of synthetic orbit generation are demonstrated. The comparison between the previous and newly developed methods are given, as well as the visualization tools one can use to estimate the influence of different input parameters on the final data. [ABSTRACT FROM AUTHOR]

Saturn's rings are composed primarily of water ice with a small fraction of non-icy constituents that are likely both intrinsic and extrinsic in origin. The intrinsic material is thought to be characteristic of the ring progenitor, while the extrinsic material is derived from the continual stream of hypervelocity impacting micrometeoroids that pollute the rings over time. Thus constraining these relative volume fractions and their radial distribution provides a powerful tool by which one can reveal clues about the rings’ ultimate origin and age. In this companion to our first paper for the C ring ( Zhang et al., 2017 ), we present new measurements of the non-icy material fraction in Saturn's B ring, Cassini Division and A ring as determined from microwave radiometry observations acquired by the Cassini spacecraft. We investigate the near-zero azimuthal angle observations and demonstrate a radially varying scattering phase function for B ring particles which transitions from half-Mie-half-isotropic in the inner and outer B ring to purely isotropic in the middle B ring. This variation follows the trend of the optical depth in that as the optical depth increases, more particles scatter isotropically. In the A ring radially inward of the Encke gap, we find that the phase function can vary from purely isotropic for 55% porous particles to a combination of 30% Mie/70% isotropic for porosities of 90%, while outwards of the Encke gap particles are most likely 90% porous and scatter light isotropically. We derive the non-icy material fractions, assuming silicate as the non-icy material, and show that there is a significant dependence on the assumed porosity in the B ring, but the radial distribution follows the same trend as the optical depth. Owing to the B ring's high opacity (i.e. high optical depth but low surface density), the particles there are likely to have 85%–90% porosity, with corresponding non-icy volume fractions of ∼0.3%–0.5% in the inner and outer B ring, and ∼0.1%–0.2% in the middle regions. For the A ring interior to the Encke gap, the derived non-icy material volume fraction is ∼0.2%–0.3% everywhere for porosities ranging from 55%–90%. Finally, our results for the Cassini Division indicate a non-icy material fraction of ∼1%–2% similar to most regions in the C ring, except that the Cassini Division particles are more likely to have a porosity ≳ 90% due to the high opacity there. We find that the overall pollution exposure time for the A and B rings and the Cassini Division ranges from ∼30–150 Myr, which is in line with the ∼15–90 Myr we previously derived for most regions in the C ring. These exposure times assume an initially nearly pure-ice ring that has been continuously contaminated by in-falling micrometeoroids since its formation, using the currently accepted value of the micrometeoroid flux (Grün et al., 1985; Cuzzi and Estrada, 1998; Kempf et al., 2013; Altobelli et al., 2015). Our results here, taken together with our previous findings for the C ring, further support the idea that Saturn's rings may be ≲150 Myr old suggesting an origin scenario in which the rings are derived from the relatively recent breakup of an icy moon. [ABSTRACT FROM AUTHOR]

Collisions with dust particles in retrograde orbits cause space erosion on stony meteoroids in addition to the particle drag which causes drift toward resonances. The spacing between resonances determines the maximum drift time and sets upper limits on the neon-21 cosmic ray exposure (CRE) ages for meteoroids less than ∼1 m in radius, while space erosion controls the limit for radii greater than ∼1 m; the limits accord well with the measured CRE ages of stony meteorites. [ABSTRACT FROM AUTHOR]

Without a significant atmosphere or global magnetic field, the lunar surface is exposed to micrometeoroid bombardment, ultraviolet (UV) radiation, and the solar wind. Micrometeoroid bombardment grinds the surface into a regolith comprised of dust grains ranging in size from 10 nm to 1 mm (Grün et al., 2011). Incident UV radiation and solar wind electrons and ions electrically charge the surface forming a plasma sheath whose structure is dependent on both the plasma and surface properties (Campanell, 2013; Guernsey and Fu, 1970; Poppe and Horányi, 2010; Nitter et al., 1998). Dust grains that are liberated from the surface can collect additional charge and interact with the plasma sheath. These interactions have been suggested to explain a variety of phenomena observed on airless bodies including horizon glow and dust ponding (Colwell et al., 2005; Hughes et al., 2008; Poppe et al., 2012; Wang et al., 2009). The effect of surface topography on the plasma environment and ensuing dust dynamics is poorly understood and serves as the focus of this paper. We present the results of a three-dimensional particle-in-cell (PIC) code used to model the dayside near-surface lunar plasma environment at a variety of solar zenith angles (SZA) for two different topographies. Using the results of the PIC code, we model the effects on dust dynamics and bulk transport. The simulations also address dust transport on smaller bodies such as asteroid 433 Eros and comet 67P/Churyumov-Gerasimenko to identify effects of reduced gravity. [ABSTRACT FROM AUTHOR]

Over a million individually measured meteoroid orbits were collected with the Southern Argentina Agile MEteor Radar (SAAMER) between 2012–2015. This provides a robust statistical database to perform an initial orbital survey of meteor showers in the Southern Hemisphere via the application of a 3D wavelet transform. The method results in a composite year from all 4 years of data, enabling us to obtain an undisturbed year of meteor activity with more than one thousand meteors per day. Our automated meteor shower search methodology identified 58 showers. Of these showers, 24 were associated with previously reported showers from the IAU catalogue while 34 showers are new and not listed in the catalogue. Our searching method combined with our large data sample provides unprecedented accuracy in measuring meteor shower activity and description of shower characteristics in the Southern Hemisphere. Using simple modeling and clustering methods we also propose potential parent bodies for the newly discovered showers. [ABSTRACT FROM AUTHOR]

Methone and Anthe are two tiny moons (with diameter < 3 km) in the inner part of Saturn’s E ring. Both moons are embedded in arcs of dust particles. To understand the amount of micron-sized dust in these arcs and their spatial distributions, we model the source, dynamical evolution, and sinks of the dust in the arc. We assume hypervelocity impacts of micrometeoroids on the moons produces these dust ( Hedman et al., 2009 ), via the so called impact-ejecta process ( Krivov et al., 2003; Spahn et al., 2006 ). After ejecting and escaping from the moons, these micron-sized particles are subject to several perturbing forces, including gravitational perturbation from Mimas, oblateness of Saturn, Lorentz force, solar radiation pressure, and plasma drag. Particles can be either confined in the arcs due to corotational resonance with Mimas, like their source moons ( Cooper et al., 2008; El Moutamid et al., 2014; Hedman et al., 2009; Spitale et al., 2006 ), or pushed outward by plasma drag. Particle sinks are recollisions with the source moon, collisions with other moons, or migration out of the zone of interest. The erosion of particles due to plasma sputtering is also considered ( Johnson et al., 2008 ), although its timescale is much larger than other sinks. Our simulation results show that ejecta from both moons can form maximal number densities between 10 − 4 and 10 − 3 m − 3 . In comparison with the observations of Anthe arc, the peak value in simulations is about an order of magnitude smaller. Plausible explanations for the difference include millimeter-sized particles as additional source and the uncertainties of impactor flux F imp and the yields Y . The longitudinal extension of the Methone/Anthe arc in our simulation is 10.8°/15°, consistent with observations and theory ( Hedman et al., 2009 ). Our results also show the lifetime distributions of particles and the heliotropic behavior of dust introduced by solar radiation pressure ( Hedman et al., 2010a ). The lifetimes of arc particles, defined by the time particles stay in the semi-major axes close to the source moons, are also related to particle size. Smaller ones (< 5 μm) do not stay in the arc and instead migrate outward under the influence of plasma drag. Larger grains can stay in arc in the timescale of 100 years until they leave the arcs or collide with the source moons. [ABSTRACT FROM AUTHOR]

We investigate the density and spatial distribution of the H 2 exosphere of the Moon assuming various source mechanisms. Owing to its low mass, escape is non-negligible for H 2 . For high-energy source mechanisms, a high percentage of the released molecules escape lunar gravity. Thus, the H 2 spatial distribution for high-energy release processes reflects the spatial distribution of the source. For low energy release mechanisms, the escape rate decreases and the H 2 redistributes itself predominantly to reflect a thermally accommodated exosphere. However, a small dependence on the spatial distribution of the source is superimposed on the thermally accommodated distribution in model simulations, where density is locally enhanced near regions of higher source rate. For an exosphere accommodated to the local surface temperature, a source rate of 2.2 g s −1 is required to produce a steady state density at high latitude of 1200 cm −3 . Greater source rates are required to produce the same density for more energetic release mechanisms. Physical sputtering by solar wind and direct delivery of H 2 through micrometeoroid bombardment can be ruled out as mechanisms for producing and liberating H 2 into the lunar exosphere. Chemical sputtering by the solar wind is the most plausible as a source mechanism and would require 10–50% of the solar wind H + inventory to be converted to H 2 to account for the observations. [ABSTRACT FROM AUTHOR]

Despite considerable study, Saturn's rings continue to challenge current theories for their provenance. Water ice comprises the bulk of Saturn's rings, yet it is the small fraction of non-icy material that is arguably more valuable in revealing clues about the system's origin and age. Herein, we present new measurements of the non-icy material fraction in Saturn's C ring, determined from microwave radiometry observations acquired by the Cassini spacecraft. Our observations show an exceptionally high brightness at near-zero azimuthal angles, suggesting a high porosity of 70–75% for the C ring particles. Furthermore, our results show that most regions in the C ring contain about 1–2% silicates. These results are consistent with an initially nearly pure-ice ring system that has been continuously contaminated by in-falling micrometeoroids over ∼15–90 million years, using the currently accepted value of the micrometeoroid flux at infinity of ∼4.5 × 10 −17 g cm −2 s −1 , and assuming that the C ring optical depth and surface density has not changed significantly during that time. This absolute time scale is inversely proportional not only to the flux at infinity, but also to the amount of gravitational focusing by Saturn the micrometeoroids experience before encountering the rings. We also find an enhanced abundance of non-icy material concentrated in the middle C ring. When assumed to be mixed volumetrically (“intramixed”) with water ice, this enhanced contamination reaches a maximum concentration of 6–11% silicates by volume around a ring radius of 83,000 km, depending on the volume mixing model used. This is significantly higher than the inner and outer C ring. As opposed to an intramixing model, we also consider a silicate-core, icy-mantle model to address the fact that silicates may be present in chunks instead of fine powder in the ring particles. Such a model naturally helps to account for the observed opacity distribution. We propose several models to explain the radially varied non-icy material contamination. Our preferred model is that the C ring has been continuously polluted by meteoroid bombardment since it first formed, while the middle C ring was further contaminated by an incoming Centaur, a rocky object torn apart by tides and ultimately broken into pieces that currently reside in the middle C ring. If correct, the spatial extent of the enhanced non-icy material fraction suggests that the Centaur was likely to be captured and integrated into the rings perhaps as recently as ∼10–20 million years ago. [ABSTRACT FROM AUTHOR]

Water ice in permanently shadowed regions on the Moon is exposed to galactic cosmic rays (GCRs) and solar energetic particles (SEPs). Because this radiation alters the chemistry of the ice, constraining the total radiation dose is important for understanding both the origin and evolution of the ice. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) onboard the Lunar Reconnaissance Orbiter (LRO) has measured the energetic charged particle dose rate for more than a solar cycle, providing the longest continuous dataset of radiation in the lunar environment. CRaTER's unique design enables us to measure the dose rates behind three amounts of mass shielding and thus constrain the GCR and SEP dose rates as a function of depth in the regolith. In a further improvement on prior studies, we combine these dose rates with a model for how impact gardening affects the exposure time of the regolith. We can thus calculate the total dose received by water ice in gardened regolith and find that impact-gardened ice has received a dose of ∼ 0. 1 – 1 eV molecule−1 over the past 1 Gyr. This dose is one to two orders of magnitude lower than the doses calculated in studies that do not incorporate the effects of gardening. Relatively undisturbed ice may have received a higher dose, but no more than ∼ 10 eV molecule−1 in the top centimeter. This result provides a valuable constraint for researchers studying radiation processing of lunar water ice. • Water ice on the Moon is exposed to energetic charged particle radiation. • We use LRO/CRaTER to measure the dose rate over a full solar cycle. • We model how impact gardening affects the exposure time of the regolith. • After ∼ 1 Gyr, impact-gardened water ice has received a dose of ∼ 0.1–1 eV/molecule. [ABSTRACT FROM AUTHOR]

An observing campaign was conducted in the Southern Hemisphere using low-light video camera triangulation to measure the trajectories and orbits of meteoroids with a possible origin at asteroid Bennu. New CAMS (Camera for Allsky Meteor Surveillance) video camera networks were established in Australia, Chile, and Namibia, and networks in New Zealand and South Africa were expanded. During observing periods in September 2019, 2020, and 2021, we measured 7672, 4936, and 5890 orbits, respectively. Based on the non-detection of predicted meteoroid trail encounters, Bennu's meteoroid production rate was <1.5 kg/s during 1500–1800 CE. Indeed, the current production rate is many orders of magnitude lower. Bennu may have an associated annual meteoroid stream of much older ejecta at a particle flux density of ≤1.3 × 10−6 km−2 h−1, based on seven Bennu-like orbits detected during the first three years of observations. • A search was conducted for possible meteors at Earth from debris ejected by asteroid Bennu in the past. • New networks of low-light video cameras were established in the southern hemisphere to measure meteoroid orbits from the predicted radiant in late September. • Only a handful of meteoroids in orbits similar to asteroid Bennu were detected, consistent with the low flux density expected form the present rate of meteoroid ejection. [ABSTRACT FROM AUTHOR]

We investigated the dynamical evolution of the meteoroid stream originating in the nucleus of comet 21P/Giacobini-Zinner. We created 20 partial models, in each assuming 10,000 test particles, and fixed values for the evolutionary time and the strength of the Poynting–Robertson effect. These models provided a "mosaic" with which to map the entire stream. We confirmed that the orbit of the parent comet and the orbits of the test particles, representing the meteoroids, evolved rapidly. This fast evolution resulted in a relatively short duration (up to approx. 1000 years) of the orbital concentrations of the meteoroids that could be identified as the meteor showers. We confirmed the relationship between comet 21P and the October Draconid meteor shower, #9. In addition to this shower, we predicted another five showers related to the comet. Four of these showers were also identified with their real counterparts. Some identifications were multiple. Specifically, we further found an association, or indication of association of 21P, with the ι -Cygnids, #525, August β -Aquariids, #474, June ξ 1-Sagittariids, #861, ξ 2-Capricornids, #623, Northern σ -Sagittariids, #167, α -Capricornids, #1, Daytime Capricornids-Sagittariids, #115, and ν -Draconids, #220. • Dynamics of the meteoroid stream of comet 21P/Giacobini-Zinner studied. • Fast evolution of orbits, implying a short age of related meteor showers, confirmed. • The association of the October Draconids, #9, with the 21P confirmed. • The association with other eight showers found or indicated. [ABSTRACT FROM AUTHOR]

The Lunar Meteoroid Impacts Observer (LUMIO) is a CubeSat mission to observe, quantify, and characterize the meteoroid impacts by detecting their flashes on the lunar farside. It complements lunar nearside observations performed by ground-based observatories to yield global information synthesis on the lunar meteoroid environment. Predicting LUMIO's scientific outcome involves devising a methodology to model the meteoroid environment. We propose a method where numerous known meteoroid streams, as well as sporadic collisions with the lunar surface, are modeled. Impacts are generated with a stochastic approach based on experimental observations of fireballs, impact flashes, and meteors. A catalog collecting data of both meteoroid streams and sporadic background is made available to the community. Sample scenarios are reproduced to show the capabilities of our method. A synthesis of the statistical analysis performed on the collision dynamics is presented. Results show that a typical scenario counts almost 2 million impacts with impact kinetic energy larger than 1 0 − 7 kton TNT Equivalent, out of which approximately 200.000 fall in the energy range of interest for the LUMIO mission. For that subset, the equivalent black body temperature is estimated to range in 1510 -2290 K, the average impact flash duration is expected to be approximately 15 ms, and the average plume area is predicted to be roughly 70 m2. • Comprehensive stochastic model and catalog of the lunar meteoroid environment. • Validation of the model against results reported in the literature. • Space observation of the Moon is instrumental to predict collisions with the Earth. • The equivalent black body temperature is estimated to range in 1510–2290 K. • The average impact flash duration is expected to be approximately 15 ms. [ABSTRACT FROM AUTHOR]

The Lunar Meteoroid Impacts Observer (LUMIO) is a CubeSat mission to observe, quantify, and characterize the meteoroid impacts on the lunar farside by detecting their flashes. This complements the knowledge gathered by Earth-based observations of the lunar nearside, thus synthesizing global information on the lunar meteoroid environment and contributing to the lunar situational awareness. The goal of LUMIO is to advance our current knowledge of meteoroid models in the solar system. In this work, we present the methodology devised to predict the scientific contribution of LUMIO. Our approach relies on combined modeling and simulation of payload, orbit, and environment. The analyses carried out have been used to drive the design of the LUMIO mission and its payload, the LUMIO-Cam. A payload radiometric model is derived and exploited to assess the quality of the scientific measurements. A dedicated study about straylight rejection is carried out to assess how straylight noise affects LUMIO-Cam measurements. Our results indicate that a 150 mm baffle grants good performance when the Sun angle is between 20° and 90°. Furthermore, the present-day LUMIO mission has the potential to detect more than 6000 impact flashes during the activity peak of the Geminids in 2024 in the range of the equivalent impact kinetic energy at Earth of [ 1 0 − 6 , 1 0 − 1 ] kton TNT Equivalent. Compared to previous programmes, LUMIO could refine information and fill the knowledge gap about the meteoroid population in the ranges of the equivalent impact kinetic energy at Earth of [ 1 0 − 6 , 1 0 − 4 ] kton TNT Equivalent and [ 1 0 − 4 , 1 0 − 1 ] kton TNT Equivalent , respectively. • LUMIO is a CubeSat mission to observe meteoroid impacts on the lunar farside. • LUMIO can fill the gap in the current knowledge of meteoroid flux models. • Combined modeling and simulation of payload, orbit, and meteoroid environment. • A 150 mm baffle rejects straylight noise for Sun angles larger than 20 deg. • LUMIO has the potential to detect more than 6000 impact flashes during Geminids. [ABSTRACT FROM AUTHOR]

We analyzed molecular radiation in the spectra of the very bright Benešov bolide. The Benešov bolide appeared over the Czech Republic on May 7, 1991 and reached an absolute magnitude of –19.5. It was caused by a meteoroid larger than 1 m. Small meteorites of various mineralogical types were recovered recently (Spurný et al. [2014] Astron. Astrophys., 570, A39, 14 p.). The spectrum of the bolide, recorded on two photographic plates, is probably the richest meteor spectrum ever obtained. It contains hundreds of atomic emission lines, continuous radiation and molecular bands, and covers the whole bolide trajectory from the altitude of 90–20 km. In this paper we focus on identification and analysis of molecular bands. The identification of FeO, CaO, AlO, and MgO, reported earlier (Borovička and Spurný [1996] Icarus, 121, 484–510) was confirmed. In addition, radiation of N 2 was probably detected. The oxides were best seen in the wake and in the radiating cloud left at the position of the bolide flare at the altitude of 24.5 km. Trace of N 2 was seen only in the meteor at lower altitudes. FeO bands are present in the spectra from the highest altitudes. We suppose that FeO was ablated directly in molecular form at high altitudes. CaO was first detected just below 50 km and its intensity, relatively to FeO, strongly increased toward lower altitudes. AlO, which is similarly refractive as CaO, behaved as FeO rather than CaO at lower altitudes. MgO was observed only in the radiating cloud. The spectrum of the cloud is unique because it contains almost no atomic lines. We compared the data with theoretical calculations of the presence of molecules in the mixture of meteoric vapors and air at various altitudes and temperatures. CN and TiO were not found. The upper limit of CN is in agreement with theory for ordinary chondrite meteoroid. Most of carbon should be in fact present in the form of CO, but CO bands are too weak to be detected. The non-detection of TiO can be explained by the fact that temperature in the wake and the cloud was lower than needed for the presence of TiO bands. However, AlO was found to be about 40 times more abundant than MgO, although comparable abundances are expected. The explanation may be that the abundances are in fact comparable but there are non-equilibrium conditions in the radiating cloud with the excitation temperature of MgO lower than that of AlO. The difference may be caused by higher ablation temperature of Al. Another non-equilibrium effect is the observed difference between the rotational (∼1000 K) and vibrational (∼3000 K) temperature of AlO molecules. This can be explained by short hydrodynamic timescale and the fact that vibrational relaxation time is significantly longer than rotational relaxation time. The vibrational temperature therefore could not decrease so quickly during the cooling and expansion of the cloud because of insufficient number of collisions. FeO and CaO could not be analyzed in detail, because their molecular constants, especially transition probabilities, are not well known. The increase of the CaO/FeO ratio with decreasing altitude could be, nevertheless, explained in scope of equilibrium chemistry. [ABSTRACT FROM AUTHOR]