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Context. Space weathering alters the surfaces of airless celestial bodies, thereby modifying their spectra significantly. Olivine plays a crucial role in responding to space weathering on silicate planets. However, the spectral variations that occur in olivine with varying iron content as a result of space weathering conditions remain unclear. Aims. We aim to systematically characterize the spectral variability of surface iron-rich olivine in the space weathering environments of Phobos and the Moon. Methods. We conducted nanosecond pulsed laser irradiation experiments on a set of synthetic Fe-rich olivine (Fa29, Fa50, Fa71, and Fa100). The energy levels were simulated for Phobos and the Moon. We analyzed the available near-infrared (NIR) spectroscopy. Results. We find that olivine with higher Fe content undergoes stronger weathering under the same irradiation energy, shifting absorption centers around 1.08 µm and 1.35 µm to longer wavelengths. When comparing the high energy and low frequency, spectral changes are more pronounced at low energy and high frequency. The olivine with the same iron content exhibits a more noticeable shift around 1.08 µm under various irradiation levels, while the band center around 1.35 µm remains stable. Conclusions. When the same amount of radiation energy is received, changes in the spectrum are more noticeable at low energy and high impact frequency than at high energy and low impact frequency. The absorption position at ~1.35 µm is a good indicator of the Mg# value of space-weathered olivine. [ABSTRACT FROM AUTHOR]

Context. 46P/Wirtanen is a near-Earth comet (NEC) and several previous modeling works had predicted it would produce a meteor shower for the first time on December 12, 2023. Aims. We report the most comprehensive meteor radar observations of the λ-Sculptorid meteor shower produced by comet 46P/Wirtanen. These measurements are critical to constrain the mass distribution of the particles released by the comet as radars generally detect the smaller particle population of the shower. Methods. We utilized observations with the Southern Argentina Agile Meteor Radar-Orbital System (SAAMER-OS) ideally located in the southern hemisphere to detect this shower. Since the shower was predicted to produce very slow meteors, we used the same methodology applied for the Arid meteor shower. Results. As predicted, the shower peak was observed by SAAMER-OS on December 12, 2023 (λ0 = 259.73°) at 0900 UTC, with a Zenithal Hourly Rate (ZHR) peak value of ~2.5 m h−1. Most of the activity of the shower was observed during 2 h between 0730-0930 UTC. The observed mean radiant of the shower in Sun-centered ecliptic coordinates is located at λ − λ0 = 88.9° and β = −36.6°. Our results suggest that the particles detected by SAAMER-OS are in general larger than those for which thermal equilibrium can be assumed (>3 mg) in agreement with the conclusions of previous reports using video observations. [ABSTRACT FROM AUTHOR]

Context. Jupiter-family comets (JFCs), which originate from the Kuiper belt and scattered disk, exhibit low-inclination and chaotic trajectories due to close encounters with Jupiter. Despite their typically short incursions into the inner solar system, a notable number of them are on Earth-crossing orbits, with fireball networks detecting many objects on "JFC-like" (2 < TJ < 3) orbits. Aims. This investigation aims to examine the orbital dynamics of JFCs and comet-like fireballs over 104 yr timescales, focusing on the trajectories and stability of these objects in the context of gravitational interactions within the solar system. Methods. We employed an extensive fireball dataset from Desert Fireball Network (DFN), European Fireball Network (EFN), Fireball Recovery and InterPlanetary Observation Network (FRIPON), and Meteorite Observation and Recovery Project (MORP), alongside telescopically observed cometary ephemeris from the NASA HORIZONS database. The study integrates 646 fireball orbits with 661 JFC orbits for a comparative analysis of their orbital stability and evolution. Results. The analysis confirms frequent Jupiter encounters among most JFCs, inducing chaotic orbital behavior with limited predictability and short Lyapunov lifetimes (~120 yr), underscoring Jupiter's significant dynamical influence. In contrast, "JFC-like" meteoroids detected by fireball networks largely exhibit dynamics divergent from genuine JFCs, with 79–92% on "JFC-like" orbits shown not to be prone to frequent Jupiter encounters; in particular, only 1–5% of all fireballs detected by the four networks exhibit dynamics similar to that of actual JFCs. In addition, 22% (16 of 72) of near-Earth JFCs are on highly stable orbits, suggesting a potential main belt origin for some of the bodies. Conclusions. This extensive study delineates the stark dynamical contrast between JFCs and JFC-like meteoroids detected by global fireball networks. The majority of centimeter- and meter-scale meteoroids on JFC-like orbits exhibit remarkably stable trajectories, which starkly differ from the chaotic paths of their km-scale counterparts. Our findings suggest that the JFC-like objects observed by fireball networks predominantly originate from the outer main belt, with only a minor fraction being directly attributable to traditional JFCs. [ABSTRACT FROM AUTHOR]

We present results of the Near-Earth objects Lunar Impacts and Optical TrAnsients (NELIOTA) campaign for lunar impact flashes observed with the 1.2 m Kryoneri telescope. From August 2019 to August 2023, we report 113 validated and 70 suspected flashes. For the validated flashes, we calculate the physical parameters (masses, radii) of the corresponding projectiles, the temperatures developed during the impacts, and the expected crater sizes. For the multiframe flashes, we present light curves and thermal evolution plots. Using the whole sample of NELIOTA that encompasses 192 validated flashes in total from 2017, the statistics of the physical parameters of the meteoroids, the peak temperatures of the impacts, and the expected crater sizes has been updated. Using this large sample, empirical relations correlating the luminous energies per photometric band were derived and used to roughly estimate the parameters of 92 suspected flashes of the NELIOTA archive. For a typical value of the luminous efficiency, we found that the majority (>75%) of the impacting meteoroids have masses between 1 and 200 g, radii between 0.5 and 3 cm and produced craters up to 3.5 m. 85% of the peak temperatures of the impacts range between 2000 and 4500 K. Statistics regarding the magnitude decline and the cooling rates of the multiframe flashes are also presented. The recalculation of the appearance frequency of meteoroids (lying within the aforementioned ranges of physical parameters) on the Moon yields that the total lunar surface is bombarded with 7.4 sporadic meteoroids per hour and up to 12.6 meteoroids per hour when the Earth-Moon system passes through a strong meteoroid stream. By extrapolating these rates on Earth, the respective rates for various distances from its surface are calculated and used to estimate the probability of an impact of a meteoroid with a hypothetical infrastructure on the Moon, or with a satellite orbiting Earth for various impact surfaces and duration times of the missions. [ABSTRACT FROM AUTHOR]

Context. Observations of meteors in the Earth's atmosphere offer a unique tool for determining the flux of meteoroids that are too small to be detected by direct telescopic observations. Although these objects are routinely observed from ground-based facilities, such as meteor and fireball networks, space-based instruments come with notable advantages and have the potential to achieve a broad and uniform exposure. Aims. In this paper, we describe the first observations of meteor events with Mini-EUSO, a very wide field-of-view telescope launched in August 2019 from the Baikonur cosmodrome and installed on board the Russian Zvezda module of the International Space Station. Mini-EUSO can map the night-time Earth in the near-UV range (290-130 nm) with a field of view equal to 44° × 44° and a spatial resolution of about 4.7 km at an altitude of 100 km from the ground. The detector saves triggered transient phenomena with a sampling frequency of 2.5 µs and 320 µs, as well as a continuous acquisition at 40.96 ms scale that is suitable for meteor observations. Methods. We designed two dedicated and complementary trigger methods, together with an analysis pipeline able to estimate the main physical parameters of the observed population of meteors, such as the duration, horizontal speed, azimuth, and absolute magnitude. To compute the absolute flux of meteors from Mini-EUSO observations, we implemented a simulation framework able to estimate the detection efficiency as a function of the meteor magnitude and the background illumination conditions. Results. The instrument detected 24 thousand meteors within the first 40 data-taking sessions from November 2019 to August 2021, for a total observation time of approximately 6 days with a limiting absolute magnitude of +6. Our estimation of the absolute flux density of meteoroids in the range of mass between 10−5 kg to 10−1 kg was found to be comparable to other results available in the literature. Conclusions. The results of this work prove the potential for space-based observations to increase the statistics of meteor observations achievable with instruments operating on the ground. The slope of the mass distribution of meteoroids sampled with Mini-EUSO suggests a mass index of either s = 2.09 ± 0.02 or s = 2.31 ± 0.03, according to two different methodologies for the computation of the pre-atmospheric mass starting from the luminosity of each event. [ABSTRACT FROM AUTHOR]

Aims. Impacts between differentiated planetesimals are ubiquitous in protoplanetary discs and may mix materials from the core, mantle, and crust of planetesimals, thus forming stony-iron meteorites. The surface composition of the asteroid (16) Psyche represents a mixture of metal and non-metal components. However, the velocities, angles, and outcome regimes of impacts that mixed metal and silicate from different layers of planetesimals are debated. Our aim is to investigate the impacts between planetesimals that can mix large amounts of metal and silicate, and the mechanism of stony-iron meteorite formation. Methods. We used smooth particle hydrodynamics to simulate the impacts between differentiated planetesimals with various initial conditions that span different outcome regimes. In our simulations, the material strength was included and the effects of the states of planetesimal cores were studied. Using a statistical approach, we quantitatively analysed the distributions of metal and silicate after impacts. Results. Our simulations modelled the mass, depth, and sources of the metal–silicate mixture in different impact conditions. Our results suggest that the molten cores in planetesimals could facilitate mixing of metal and silicate. Large amounts of the metal–silicate mixture could be produced by low-energy accretional impacts and high-energy erosive impacts in the largest impact remnant, and by hit-and-run and erosive impacts in the second-largest impact remnant. After impact, most of the metal-silicate mixture was buried at depth, consistent with the low cooling rates of stony-iron meteorites. Our results indicate that mesosiderites potentially formed in an erosive impact, while pallasites potentially formed in an accretional or hit-and-run impact. The mixing of metal and non-metal components on Psyche may also be the result of impacts. [ABSTRACT FROM AUTHOR]

During protoplanetary disk formation, dust grains located in the outer disk retain their pristine icy composition, while solids in the inner stellar-heated disk undergo volatile loss. This process may have left a fossil record in Solar System material, showing different nucleosynthetic imprints that have been attributed to different degrees of thermal processing. However, it remains unclear how a large mass fraction of thermally processed inner-disk pebbles is produced and how these grains are subsequently transported throughout the disk. In this work, we numerically investigate the evolution in time of a two-component pebble disk consisting of both pristine pebbles and those that underwent ice sublimation. We find that stellar outbursts exceeding 1000 times the solar luminosity are efficient in thermally altering, through ice sublimation, a large mass fraction of pebbles (around 80%). After the establishment of this initial radial dust composition gradient throughout the disk, the subsequent mixing and inward drift of pristine outer-disk pebbles alter the inner disk bulk composition from processed to more unprocessed in time. Therefore, if processed pebbles without ice mantles have an isotopic composition similar to ureilite meteorites from the inner Solar System, inner-disk minor bodies forming from the early pebble flux (<1 Myr) will be isotopically ureilite-like, while later-formed bodies will be increasingly admixed with the signature of the lateincoming, CI chondrite-like unprocessed pebbles. This appears to be largely consistent with the trend seen between the accretion age of different meteoric classes and their different stable isotope composition anomalies (in μ54Cr, μ48Ca, μ30Si, and μ58Ni), but further work may be needed to explain the role of isotopically anomalous refractory inclusions and anomaly trends in other elements. Our findings further support an early thermal processing of ice mantles via stellar outbursts that are common around young Sun-like stars. [ABSTRACT FROM AUTHOR]

Context. The meteor shower database of the IAU Meteor Data Center (MDC) is used by the whole community of meteor astronomers. Observers submit both new and known meteor shower parameters to the MDC. Two types of problems may arise during the submission process: If a new observation of an already-known meteor shower is submitted as the discovery of a new shower, a duplicate shower will appear in the MDC. If the submission of a new set of parameters for an existing shower is incorrect, a false duplicate of a known meteor shower will appear in the MDC. The MDC database contains such duplicates and false duplicates, so it is desirable to detect them among the streams already in the database and those delivered to the database as new streams. Aims. We aim to develop a method for objective detection of duplicates among meteor showers and to apply it to the MDC. The method will also enable us to verify whether various sets of parameters of the same shower are compatible and thus reveal the false duplicates. Methods. We suggest two methods based on cluster analyses and two similarity functions among geocentric and heliocentric shower parameters collected in the MDC. Results. We obtained a number of results of varying significance. Seven new showers represented by two or more parameter sets were discovered, revealing the duplicates we searched for. We found full agreement between our results and those reported in the MDC database for 30 showers. The multiple sets of parameters defining these showers are correct since they were identified as duplicates. For 20 showers, the same duplicates as given in the MDC were found only by one method. We found 27 showers for which the number of parameter sets found by both methods is close to the corresponding number in the MDC database. However, we found 56 showers listed in the MDC by more than one set of parameters for which no duplicates were found by either of the applied methods. These showers have false duplicates among their sets of parameters. Conclusions. The obtained results confirm the effectiveness of the proposed approach of identifying duplicates. We have shown that in order to detect and verify duplicate meteor showers, it is possible to apply the objective proposal instead of the subjective approach used so far. We consider the identification of 83 problematic cases in the MDC database, among which at least some duplicates were misclassified, to be a particularly important result. The correction of these cases will significantly improve the content of the MDC database. [ABSTRACT FROM AUTHOR]

Aims. We investigate the optical characteristics of flashes caused by the impact of metre- to decametre-sized outer Solar System objects on Jupiter, and the contributions of reflected light from surface clouds at visible wavelengths, in order to estimate more accurate bulk parameters, such as the luminous energy of the flash, the kinetic energy, the mass, and the size of the impact object. Methods. Using the results of recent reflectivity studies of the Jovian surface, we developed a cloud reflection model that calculates the contribution of the reflected light relative to that directly from the flash. We compared the apparent luminous energy of the previously reported flashes with the expected cloud reflection contributions to obtain their revised bulk parameters. Results. We find that cloud reflection contributions can make up to 200% of the flux directly from the flash, and thus can be the most significant uncertainty in the measurement of the bulk parameters. The reflection contributions strongly depend on wavelength. With our cloud reflection correction, we obtained revised bulk parameters for the previously reported flashes. Conclusions. Our cloud reflection correction enables us to better understand the properties of objects impacting Jupiter and is crucial for ongoing detailed investigations using high-sensitivity and multi-wavelength observation systems, such as PONCOTS. It will also be useful for understanding other optical transients in Jupiter's upper atmosphere, such as the recently discovered sprite-like events. [ABSTRACT FROM AUTHOR]

Context. Andesitic meteorites are among the oldest achondrites known to date. They record volcanic events and crust formation episodes in primordial planetesimals that took place about 4.565 Myr ago. However, no analogue for these meteorites has been found in the asteroid population to date. Aims. We searched for spectroscopic analogues of the andesitic meteorite Erg Chech 002 in the asteroid population using the Gaia DR3 spectral dataset. Methods. In order to identify which asteroids have the most similar spectrum to Erg Chech 002, we first determined the spectral parameters of Gaia DR3 asteroids (spectral slope and Band I depth) and compared them to the spectral parameters of different samples of the meteorite. In addition, we performed a spectral curve matching between Erg Chech 002 and Gaia DR3 asteroid data, and we compared the results of both methods. Results. We found that 51 main-belt asteroids have a visible spectrum similar to the one of Erg Chech 002, and 91 have a spectrum similar to the space-weathered spectra of the meteorite, corresponding to 0.08% and 0.15% of the whole Gaia DR3 dataset of asteroids with spectra, respectively. The asteroids that best match the laboratory samples of the meteorite are mostly located in the inner main belt, while the objects matching the space-weathered meteorite models show slightly more scattering across the belt. Conclusions. Despite the fact that we find asteroids that potentially match Erg Chech 002, these asteroids are extremely rare. Moreover, a visible spectrum alone is not completely diagnostic of an Erg Chech 002-like composition. Near-infrared spectra will be important to confirm (or rule out) the spectral matches between Erg Chech 002 and the candidate asteroid population. [ABSTRACT FROM AUTHOR]

Context. E-type asteroids have been linked to aubrites, while M-type asteroids have been linked to enstatite chondrites (ECs) and iron meteorites (IMs). However, as ECs and IMs generally lack absorption characteristics, distinguishing their parent bodies by spectroscopy generally poses a challenge. Aims. We aim to develop a method to distinguish two kinds of M-type asteroids, the parent bodies of ECs and IMs, and to infer their composition. Methods. We measured the visible to near-infrared (VIS-NIR) reflectance spectra of aubrite, ECs, and IMs. Then we analyzed and compared their spectral parameters, such as the reflectance at 0.55 µm (R0.55), absorption bands, and spectral slopes. We also compared the geometric albedo and spectral slopes of a total of 13 E-type and 14 M-type asteroids. Furthermore, combining the collected radar albedo and density data of M-type asteroids, we discuss their potential composition at different depths. Results. We find that for most meteorites, with the exception of very weak absorption in an aubrite and an EH7 chondrite, ECs and IMs do not show any absorption characteristics. Aubrite shows extremely high reflectance and a negative near-infrared slope (NIRS) and ECs show relatively low reflectance and moderately positive NIRS, while IMs show relatively moderate reflectance and the steepest positive NIRS. Two diagrams plotting with R0.55 and NIRS calculated in the 1.1–1.2 µm and 1.1–1.4 µm bands were subsequently shown to perform optimally at distinguishing aubrite, ECs, and IMs. In addition, M-type asteroids have a wide range of NIRS and diverse radar albedo and densities, whereby 16 Psyche shows high NIRS, radar albedo, and density, while 21 Lutetia is dominated by low values for these parameters. Conclusions. We demonstrate that NIRS is correlated with metal content and increases with metal content. In particular, the NIRS calculated in the 1.1–1.4 µm band is a potentially useful parameter for inferring the surface metal content of E- and M-type asteroids. Based on our results, we suggest that the featureless M-type asteroids ought to be divided into two subtypes: Mm- (e.g., 16 Psyche) and Me-type (e.g., 21 Lutetia) in the aim of characterizing the sources of IMs and ECs, respectively. [ABSTRACT FROM AUTHOR]

Context. Meteoroids are pieces of asteroids and comets. They serve as unique probes to the physical and chemical properties of their parent bodies. We can derive some of these properties when meteoroids collide with the atmosphere of Earth and become a meteor or a bolide. Even more information can be obtained when meteoroids are mechanically strong and slow enough to drop meteorites. Aims. Through physical modeling of bright meteors, we describe their fragmentation in the atmosphere. We also derive their mechanical strength and the mass distribution of the fragments, some of which may hit the ground as meteorites. Methods. We developed a semi-automatic program for meteoroid fragmentation modeling using parallel genetic algorithms. This allowed us to determine the most probable fragmentation cascade of the meteoroid, and also to specify its initial mass and velocity. These parameters can be used in turn to derive the heliocentric orbit of the meteoroid and to place constraints on its likely age as a separate object. Results. The program offers plausible solutions for the majority of fireballs we tested, and the quality of the solutions is comparable to that of manual solutions. The two solutions are not the same in detail, but the derived quantities, such as the fragment masses of the larger fragments and the proxy for their mechanical strength, are very similar. With this method, we would like to describe the mechanical properties and structure of both meteoroids belonging to major meteor showers and those that cause exceptional fireballs. [ABSTRACT FROM AUTHOR]

Context. The Shower Database (SD) of the Meteor Data Center (MDC) has been operating for 15 yr and is used by the entire community of meteor astronomers. It contains meteor showers categorised in individual lists on the basis of their status. Since the inception of the SD, no objective rules for moving showers between individual lists have been established. The content of the SD has not yet been checked for the correctness of the meteor data contained therein. Aims. Our aims are (1) to formulate criteria for nominating meteor showers for established status, (2) to improve the rules for the removal of showers, (3) to verify and enhance the content of the SD, and (4) to improve the user area of the MDC SD. Methods. The criteria for moving showers from the Working list to the Lists of established or removed showers were generated using an empirical evaluation of their impact on the registered showers. The correctness of the parameters of each stream included in the SD was checked by comparing them with the values given in the source publications. Results. We developed a set of criteria for nominating showers to be established. We objectified rules for the temporary and permanent removal of meteor showers from the Working list. Both of our proposed new procedures were approved by a vote of the commission F1 of the IAU in July 2022. We verified more than 1350 data records of the MDC SD and introduced ~1700 corrections. We included new parameters for shower characterisation. As a result of our verification procedure, 117 showers have been moved to the List of removed showers. As of October 2022, the SD contains 923 showers, 110 of which are in the List of established showers and 813 are in the Working list. We also improved the user area of the SD and added a simple tool to allow a quick check of the similarity of a new shower to those in the database. [ABSTRACT FROM AUTHOR]

Context. The current period is conducive to exploring our Solar System's origins with recent and future space sample return missions, which provide invaluable information from known Solar System asteroids and comets The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) recently brought back samples from the surface of the Ryugu carbonaceous asteroid. Aims. We aim to identify the different forms of chemical composition of organic matter and minerals that constitute these Solar System primitive objects, to shed light on the Solar System's origins. Methods. In this work, we recorded infrared (IR) hyper-spectral maps of whole-rock Ryugu asteroid samples at the highest achievable spatial resolution with a synchrotron in the mid-IR (MIR). Additional global far-IR (FIR) spectra of each sample were also acquired. Results. The hyper-spectral maps reveal the variability of the functional groups at small scales and the intimate association of phyl-losilicates with the aliphatic components of the organic matter present in Ryugu. The relative proportion of column densities of the identified IR functional groups (aliphatics, hydroxyl + interlayer and/or physisorbed water, carbonyl, carbonates, and silicates) giving access to the composition of the Ryugu samples is estimated from these IR hyper-spectral maps. Phyllosilicate spectra reveal the presence of mixtures of serpentine and saponite. We do not detect anhydrous silicates in the samples analysed, at the scales probed. The carbonates are dominated by dolomite. Aliphatics organics are distributed over the whole samples at the micron scale probed with the synchrotron, and intimately mixed with the phyllosilicates. The aromatic C=C contribution could not be safely deconvolved from OH in most spectra, due to the ubiquitous presence of hydrated minerals. The peak intensity ratios of the organics methylene to methyl (CH2/CH3) of the Ryugu samples vary between about 1.5 and 2.5, and are compared to the ratios in chondrites from types 1 to 3. Overall, the mineralogical and organic characteristics of the Ryugu samples show similarities with those of CI chondrites, although with a noticeably higher CH2/CH3 in Ryugu than generally measured in C1 chondrites collected on Earth, and possibly a higher carbonate content. [ABSTRACT FROM AUTHOR]

Volatile molecules containing hydrogen, carbon, and nitrogen are key components of planetary atmospheres. In the pebble accretion model for rocky planet formation, these volatile species are accreted during the main planetary formation phase. For this study, we modelled the partitioning of volatiles within a growing planet and the outgassing to the surface. The core stores more than 90% of the hydrogen and carbon budgets of Earth for realistic values of the partition coefficients of H and C between metal and silicate melts. The magma oceans of Earth and Venus are sufficiently deep to undergo oxidation of ferrous Fe2+ to ferric Fe3+. This increased oxidation state leads to the outgassing of primarily CO2 and H2O from the magma ocean of Earth. In contrast, the oxidation state of Mars' mantle remains low and the main outgassed hydrogen carrier is H2. This hydrogen easily escapes the atmosphere due to the irradiation from the young Sun in XUV wavelengths, dragging with it the majority of the CO, CO2, H2O, and N2 contents of the atmosphere. A small amount of surface water is maintained on Mars, in agreement with proposed ancient ocean shorelines, for moderately low values of the mantle oxidation. Nitrogen partitions relatively evenly between the core and the atmosphere due to its extremely low solubility in magma; the burial of large reservoirs of nitrogen in the core is thus not possible. The overall low N contents of Earth disagree with the high abundance of N in all chondrite classes and favours a volatile delivery by pebble snow. Our model of rapid rocky planet formation by pebble accretion displays broad consistency with the volatile contents of the Sun's terrestrial planets. The diversity of the terrestrial planets can therefore be used as benchmark cases to calibrate models of extrasolar rocky planets and their atmospheres. [ABSTRACT FROM AUTHOR]

We explore the heating and differentiation of rocky planets that grow by rapid pebble accretion. Our terrestrial planets grow outside of the ice line and initially accrete 28% water ice by mass. The accretion of water stops after the protoplanet reaches a mass of 0.01 ME where the gas envelope becomes hot enough to sublimate the ice and transport the vapour back to the protoplanetary disc by recycling flows. The energy released by the decay of 26Al melts the accreted ice to form clay (phyllosilicates), oxidized iron (FeO), and a water surface layer with ten times the mass of Earth's modern oceans. The ocean–atmosphere system undergoes a run-away greenhouse effect after the effective accretion temperature crosses a threshold of around 300 K. The run-away greenhouse process vaporizes the water layer, thereby trapping the accretion heat and heating the surface to more than 6000 K. This causes the upper part of the mantle to melt and form a global magma ocean. Metal melt separates from silicate melt and sediments towards the bottom of the magma ocean; the gravitational energy released by the sedimentation leads to positive feedback where the beginning differentiation of the planet causes the whole mantle to melt and differentiate. All rocky planets thus naturally experience a magma ocean stage. We demonstrate that Earth's small excess of 182W (the decay product of 182Hf) relative to the chondrites is consistent with such rapid core formation within 5 Myr followed by equilibration of the W reservoir in Earth's mantle with 182W-poor material from the core of a planetary-mass impactor, provided that the equilibration degree is at least 25–50%, depending on the initial Hf/W ratio. The planetary collision must have occurred at least 35 Myr after the main accretion phase of the terrestrial planets. [ABSTRACT FROM AUTHOR]

We present a series of papers dedicated to modelling the accretion and differentiation of rocky planets that form by pebble accretion within the lifetime of the protoplanetary disc. In this first paper, we focus on how the accreted ice determines the distribution of iron between the mantle (oxidized FeO and FeO1.5) and the core (metallic Fe and FeS). We find that an initial primitive composition of ice-rich material leads, upon heating by the decay of 26Al, to extensive water flow and the formation of clay minerals inside planetesimals. Metallic iron dissolves in liquid water and precipitates as oxidized magnetite Fe3O4. Further heating by 26Al destabilizes the clay at a temperature of around 900 K. The released supercritical water ejects the entire water content from the planetesimal. Upon reaching the silicate melting temperature of 1700 K, planetesimals further differentiate into a core (made mainly of iron sulfide FeS) and a mantle with a high fraction of oxidized iron. We propose that the asteroid Vesta's significant FeO fraction in the mantle is a testimony of its original ice content. We consider Vesta to be a surviving member of the population of protoplanets from which Mars, Earth, and Venus grew by pebble accretion. We show that the increase in the core mass fraction and decrease in FeO contents with increasing planetary mass (in the sequence Vesta – Mars – Earth) is naturally explained by the growth of terrestrial planets outside of the water ice line through accretion of pebbles containing iron that was dominantly in metallic form with an intrinsically low oxidation degree. [ABSTRACT FROM AUTHOR]

Context. Cometary meteoroid trails exist in the vicinity of comets, forming a fine structure of the interplanetary dust cloud. The trails consist predominantly of the largest cometary particles (with sizes of approximately 0.1 mm–1 cm), which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. In the 1970s, two Helios spacecraft were launched towards the inner Solar System. The spacecraft were equipped with in situ dust sensors which measured the distribution of interplanetary dust in the inner Solar System for the first time. Recently, when re-analysing the Helios data, a clustering of seven impacts was found, detected by Helios in a very narrow region of space at a true anomaly angle of 135 ± 1°, which the authors considered as potential cometary trail particles. However, at the time, this hypothesis could not be studied further. Aims. We re-analyse these candidate cometary trail particles in the Helios dust data to investigate the possibility that some or all of them indeed originate from cometary trails and we constrain their source comets. Methods. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new and recently published universal model for cometary meteoroid streams in the inner Solar System. We use IMEX to study the traverses of cometary trails made by Helios. Results. During ten revolutions around the Sun, the Helios spacecraft intersected 13 cometary trails. For the majority of these traverses the predicted dust fluxes are very low. In the narrow region of space where Helios detected the candidate dust particles, the spacecraft repeatedly traversed the trails of comets 45P/Honda-Mrkos-Pajdušáková and 72P/Denning-Fujikawa with relatively high predicted dust fluxes. The analysis of the detection times and particle impact directions shows that four detected particles are compatible with an origin from these two comets. By combining measurements and simulations we find a dust spatial density in these trails of approximately 10−8–10−7 m−3. Conclusions. The identification of potential cometary trail particles in the Helios data greatly benefited from the clustering of trail traverses in a rather narrow region of space. The in situ detection and analysis of meteoroid trail particles which can be traced back to their source bodies by spacecraft-based dust analysers provides a new opportunity for remote compositional analysis of comets and asteroids without the necessity to fly a spacecraft to or even land on those celestial bodies. This provides new science opportunities for future missions like DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science), Europa Clipper, and the Interstellar Mapping and Acceleration Probe. [ABSTRACT FROM AUTHOR]

Context. We present a new numerical model of the η-Aquariid and Orionid meteor showers. Aims. The model investigates the origin, variability, and age of the η-Aquariid and Orionid apparitions from 1985 to the present day in order to forecast their activity over the next several decades. Methods. Through the numerical integration of millions of simulated meteoroids and a custom-made particle weighting scheme, we model the characteristics of every η-Aquariid and Orionid apparition between 1985 and 2050. The modeled showers are calibrated using 35 yr of meteor observations, including the shower activity profiles and interannual variability. Results. Our model reproduces the general characteristics of the present-day η-Aquariids and part of the Orionid activity. Simulations suggest that the age of the η-Aquariids somewhat exceeds 5000 yr, while a greater fraction of the Orionids is composed of older material. The 1:6 mean motion resonance with Jupiter plays a major role in generating some (but not all) Halleyid stream outbursts. We find consistent evidence for a periodicity of 11.8 yr in both the observations and modeled maximum meteor rates for the Orionids. Weaker evidence of a 10.7 yr period in the peak activity for the η-Aquariids needs to be investigated with future meteor observations. The extension of our model to future years predicts no significant Orionid outbursts through 2050 and four significant η-Aquariid outbursts, in 2023, 2024, 2045, and 2046. [ABSTRACT FROM AUTHOR]

Context. Composition, mass, and trajectory parameters of meteors can be derived by combining observations with the meteor physics equations. The fidelity of these equations, which rely on heuristic coefficients, significantly affects the accuracy of the properties inferred. Aims. Our objective is to present a methodology that can be used to compute the luminosity of meteor entry based on detailed flow simulations in the continuum regime. Methods. The methodology consists in solving the Navier-Stokes equations using state-of-the-art physico-chemical models for hypersonic flows. It includes accurate boundary conditions to simulate the surface evaporation of the molten material and coupled flow-radiation effects. Such detailed simulations allow for the calculation of heat-transfer coefficients and luminous efficiency, which can be incorporated into the meteor physics equations. Finally, we integrate the radiative transfer equation over a line of sight from the ground to the meteor to derive the luminosity magnitude. Results. We use the developed methodology to simulate the Lost City bolide and to derive the luminosity magnitude, obtaining good agreement between numerical results and observations. The computed color index is more prominent than the observations. This is attributed to a lack of refractory elements such as Ca in the modeled flow that might originate from the vaporization of droplets in the trail, a phenomenon currently not included in the model. [ABSTRACT FROM AUTHOR]

Context. Several authors predicted an outburst of the Draconid meteor shower in 2018, but with an uncertain level of activity. Aims. Optical meteor observations were used to derive the population and mass indices, flux, and radiant positions of Draconid meteors. Methods. We performed 90min of multi-station observations after the predicted peak of activity using highly sensitive Electron Multiplying Charge Coupled Device cameras. The data calibration is discussed in detail. A novel maximum likelihood estimation method was developed to compute the population and mass index with robust error estimation. We applied the method to observed Draconids and used the values to derive the flux. Meteor trajectories were computed and compared to predicted radiant positions from meteoroid ejection models. Results. We find a mass index of 1:74 ± 0:18 in the 30 min bin after the predicted peak, and 2:32 ± 0:27 in the subsequent 60 min. The location and the dispersion of the radiant are a good match to modeled values, but there is an offset of 0:4° in solar longitude. [ABSTRACT FROM AUTHOR]

Context. Findings by the Helios and STEREO mission have indicated the presence of a resonant circumsolar ring of dust associated with Venus. Attempts to model this phenomenon as an analogue to the resonant ring of Earth - as a result of migrating dust trapped in external mean-motion resonances (MMRs) - have so far been unable to reproduce the observed dust feature. Other theories of origin have recently been put forward. However, the reason for the low trapping efficiency of Venus's external MMRs remains unclear. Aims. Here we look into the nature of the dust trapping resonant phenomena that arise from the multi-planet configuration of the inner Solar System, aiming to add to the existent understanding of resonant dust rings in single planet systems. Methods. We numerically modelled resonant dust features associated with the inner planets and specifically looked into the dependency of these structures and the trapping efficiency of particular resonances on the configuration of planets. Results. Besides Mercury showing no resonant interaction with the migrating dust cloud, we find Venus, Earth, and Mars to considerably interfere with each other's resonances, influencing their ability to form circumsolar rings. We find that the single most important reason for the weakness of Venus's external MMR ring is the perturbing influence of its outer neighbour - Earth. In addition, we find Mercury and Mars to produce crescent-shaped density features, caused by a directed apsidal precession occurring in particles traversing their orbital region. [ABSTRACT FROM AUTHOR]

Aims. We study the meteoroid stream of the long-period comet C/1963 A1 (Ikeya) to predict the meteor showers originating in this comet. We also aim to identify the predicted showers with their real counterparts. Methods. We modeled 23 parts of a theoretical meteoroid stream of the parent comet considered. Each of our models is characterized by a single value of the evolutionary time and a single value of the strength of the Poynting–Robertson effect. The evolutionary time is defined as the time before the present when the stream is modeled and when we start to follow its dynamical evolution. This period ranges from 10 000 to 80 000 yr. In each model, we considered a stream consisting of 10 000 test particles that dynamically evolve, and their dynamics is followed via a numerical integration up to the present. At the end of the integration, we analyzed the mean orbital characteristics of particles in the orbits approaching Earth's orbit, which thus enabled us to predict a shower related to the parent comet. We attempted to identify each predicted shower with a shower recorded in the International Astronomical Union Meteor Data Center list of all showers. In addition, we tried to separate, often successfully, a real counterpart of each predicted shower from the databases of real meteors. Results. Many modeled parts of the stream of comet C/1963 A1 are identified with the corresponding real showers in three video-meteor databases. No real counterpart is found in the IAU MDC photographic or radio-meteor data. Specifically, we predict five showers related to C/1963 A1. Two predicted showers are identified with π-Hydrids #101 and δ-Corvids #729. The third predicted shower is only vaguely similar to November α-Sextantids #483, when its mean orbit is compared with the mean orbit of the November α-Sextantids in the IAU MDC list of all showers. However, the prediction is very consistent with the corresponding showers newly separated from three video databases. Another predicted shower has no counterpart in the IAU MDC list, but there is a good match of the prediction and a shower that we separated from the Cameras for Allsky Meteor Surveillance video data. We name this new shower ϑ-Leonids. The last of the predicted showers should be relatively low in number and, hence, no real counterparts were either found in the IAU MDC list or separated from any considered database. [ABSTRACT FROM AUTHOR]

Aims. We investigate the spectra, material properties, and orbital distribution of millimeter- to decimeter-sized meteoroids. Our study aims to distinguish the characteristics of populations of differently sized meteoroids and reveal the heterogeneity of identified meteoroid streams. We verify the surprisingly large ratio of pure iron meteoroids on asteroidal orbits detected among mm-sized bodies. Methods. Emission spectra and multi-station meteor trajectories were collected within the AMOS network observations. The sample is based on 202 meteors of −1 to −14 magnitude, corresponding to meteoroids of mm to dm sizes. Meteoroid composition is studied by spectral classification based on relative intensity ratios of Na, Mg, and Fe and corresponding monochromatic light curves. Heliocentric orbits, trajectory parameters, and material strengths inferred from empirical KB and PE parameters were determined for 146 meteoroids. Results. An overall increase of Na content compared to the population of mm-sized meteoroids was detected, reflecting weaker effects of space weathering processes on larger meteoroids. The preservation of volatiles in larger meteoroids is directly observed. We report a very low ratio of pure iron meteoroids and the discovery of a new spectral group of Fe-rich meteors. The majority of meteoroids on asteroidal orbits were found to be chondritic. Thermal processes causing Na depletion and physical processes resulting in Na-rich spectra are described and linked to characteristically increased material strengths. Numerous major and minor shower meteors were identified in our sample, revealing various degrees of heterogeneity within Halley-type, ecliptical, and sungrazing meteoroid streams. Our results imply a scattered composition of the fragments of comet 2P/Encke and 109P/Swift-Tuttle. The largest disparities were detected within α-Capricornids of the inactive comet 169P/NEAT and δ-Aquarids of the sungrazing 96P/Machholz. We also find a spectral similarity between κ-Cygnids and Taurids, which could imply a similar composition of the parent objects of the two streams. [ABSTRACT FROM AUTHOR]

We present 25 photographic fireballs belonging to the September epsilon Perseid (SPE, IAU #208) meteor shower observed by the Czech part of the European Fireball Network in 2013–2017. Exceptional high activity of bright photographic fireballs was observed in 2013, while a lower activity, but still higher than in other years, was observed in the period of 2015–2017. Physical properties of these SPE fireballs were studied and compared to other meteor showers. Perseids are found to be the closest analog to SPE. Corrected geocentric radiant of the 2013 outburst fireballs was determined for solar longitude 167.20° and has right ascension 47.67 ± 0.04° and declination 39.493 ± 0.013° (J2000.0). On the basis of determined heliocentric orbits the parent body of the shower is an unknown long-period comet on retrograde orbit with an orbital period of the order of a thousand years. [ABSTRACT FROM AUTHOR]

Context. Comets undergo resurfacing due to solar radiation, while their primordial interiors remain unchanged. Multi-epoch observations of comets enable us to characterize a change in sublimation pattern as a function of heliocentric distance, which in turn provides information on the dust environments of comets. Aims. We aim to constrain the size and porosity of ejected dust particles from comet 252P/LINEAR and their evolution near perihelion via near-infrared (NIR) multiband polarimetry. A close approach of the comet to the Earth in March 2016 (~0.036 au) provided a rare opportunity for the sampling of the comet at high spatial resolution. Methods. We made NIR JHKS-band (1.25–2.25 μm) polarimetric observations of the comet for 12 days near perihelion, interspersed between broadband optical (0.48–0.80 μm) imaging observations over four months. In addition, a dynamical simulation of the comet was performed 1000 yr backward in time. Results. We detected two discontinuous brightness enhancements of 252P/LINEAR. Before the first enhancement, the NIR polarization degrees of the comet were far lower than those of ordinary comets at a given phase angle. Soon after the activation, however, they increased by ~13% at most, showing unusual blue polarimetric color over the J and H bands (−2.55% μm−1 on average) and bluing of the dust color in both J−H and H−KS. Throughout the event, the polarization vector was marginally aligned perpendicular to the scattering plane (i.e., θr = 4.6°–10.9°). The subsequent postperihelion reactivation of the comet lasted for approximately 1.5 months, with a factor of ~30 times pre-activation dust mass-loss rates in the RC band. Conclusions. The marked increase in the polarization degree with blue NIR polarimetric color is reminiscent of the behavior of a fragmenting comet D/1999 S4 (LINEAR). The most plausible scenario for the observed polarimetric properties of 252P/LINEAR is an ejection of predominantly large (well within the geometrical optics regime) and compact dust particles from the desiccated surface layer. We conjecture that the more intense solar heating that the comet has received in the near-Earth orbit would cause the paucity of small fluffy dust particles around the nucleus of the comet. [ABSTRACT FROM AUTHOR]

Aims. Asteroids have been exposed to impacts since their formation, and as a consequence their surfaces are covered by small particles, pebbles, and boulders. The Japanese JAXA/ISAS Hayabusa mission collected micron-sized particles from the regolith of asteroid 25143 Itokawa. The study in terrestrial laboratories of these particles provides a scientific opportunity as their physical properties can be compared with those characteristic of chondritic meteorites that are often considered proxies of the building materials of potentially hazardous asteroids (PHAs). Methods. Here we present the results from a study of the mechanical properties of three of these particles using a precise technique called nanoindentation. The derived results are compared with those obtained via a methodology similar to that used for the Chelyabinsk meteorite. Results. The reduced Young's modulus values obtained for the Itokawa samples are higher than those measured for the Chelyabinsk chondrite, so these specific particles of asteroid regolith are more compacted than the minerals forming the particular LL chondrite associated with PHAs. This might be a natural consequence of particles surviving long exposure times on the surface of a (near-Earth asteroid) NEA. The Double Asteroid Redirection Test (DART) mission plans to excavate a crater in the surface of the (65803) Didymos satellite. Our results suggest that excavating a crater with a kinetic impactor in an area of significant fine-grained regolith will increase the momentum transfer. As this will facilitate the release of particles carrying target mass in the opposite direction to the movement of the projectile, there is no need to grind up the target during the mechanical excavation phase. [ABSTRACT FROM AUTHOR]

Aims. We study the meteoroid stream of the long-period comet C/1975 T2 (Suzuki-Saigusa-Mori). This comet was suggested as the parent body of the established λ-Ursae Majorid meteor shower, No. 524. Methods. We modeled 32 parts of a theoretical meteoroid stream of the parent comet considered. Each of our models is characterized with a single value of the evolutionary time and a single value of the strength of Poynting-Robertson effect. The evolutionary time ranges from 10 000 to 80 000 yr. It is the period during which the evolution of the stream part is followed. In each model, the dynamical evolution of 10 000 test particles was then followed, via a numerical integration, from the time of the modeling up to the present. At the end of the integration, we analyzed the mean orbital characteristics of particles in the orbits that approach the Earth's orbit, which thus enabled us to predict a shower related to the parent comet. The predicted shower was subsequently compared with its observed counterparts. We separated the latter from the databases of real meteors. As well, we attempted to identify the predicted shower to a shower recorded in the International Astronomical Union Meteor Data Center (IAU MDC) list of all showers. Results. Almost all modeled parts of the stream of comet C/1975 T2 are identified with the corresponding real shower in three video-meteor databases. No real counterpart is found in the IAU MDC photographic or radio-meteor data. In the IAU MDC list of showers and in our current study, this shower is identified with the established λ-Ursae Majorid shower, No. 524. Hence, our modeling confirms the results of previous authors. At the same time we exclude an existence of other meteor shower associated with C/1975 T2. [ABSTRACT FROM AUTHOR]

Context. Micrometeorites represent, at timescales shorter than a few million years, the dominant source of extraterrestrial matter at the surface of the Earth. Analyses of ultracarbonaceous micrometeorites recovered from Antarctica, known as UCAMMs reveal an exceptionally N-rich organic matter associated with spatially extended high D enrichments. Experiments show that this specific organic matter might have been formed in the outer solar system by energetic irradiation of N-rich icy surfaces. Aims. We experimentally investigate the hydrogen isotopic fractionation resulting from irradiation of normal and D-rich N2-CH4 ices by high energy ions, simulating the exposition to Galactic cosmic rays of icy bodies surfaces orbiting at large heliocentric distances. Methods. Films of N2-CH4 ices and a N2-CH4/CD4/N2-CH4 "sandwich" ice were exposed to 129Xe13+ ion beams at 92 and 88 MeV. The chemical evolution of the samples was monitored using in situ Fourier transform infrared spectroscopy. After irradiation, targets were annealed to room temperature. The solid residues of the whole process left after ice sublimation were characterized in situ by infrared spectroscopy, and the hydrogen isotopic composition measured ex situ by imaging secondary ion mass spectrometry at the sub-micron scale (NanoSIMS). Results. Irradiation leads to the formation of new molecules and radicals. After annealing, the resulting poly-HCN-like macro-molecular residue exhibits an infrared spectrum close to that of UCAMMs. The residue resulting from irradiation of N2-CH4 ices does not exhibit a significant deuterium enrichment comparable to that found in extraterrestrial organic matter. The residue formed by irradiation of D-rich ices shows the formation of isotopic heterogeneities with localised hotspots and an extended contribution likely due to the diffusion of the radiolytic products from the D-rich layer. Conclusions. These results show that high-energy cosmic ray irradiation does not induce the large hydrogen isotopic fractionation observed at small spatial scale in interplanetary organics. By contrast, large D/H ratio heterogeneities at the sub-micron spatial scale in extraterrestrial organic matter can result from isotopically heterogeneous ices mixtures (i.e. condensed with different D/H ratios), which were transformed into refractory organic matter upon irradiation. [ABSTRACT FROM AUTHOR]

Context. Several fireball networks deploy all-sky cameras for the observation of bright meteors and bolides. Because the field is heavily distorted, a dedicated astrometric reduction is needed. A precise computation of the astrometric solution is essential to determine reliable orbital elements of the parent body and to recover possible fragments on ground. Aims. The purpose of this article is to assess the astrometric performances of this type of instruments, which is characterized by a wide field of view and small apertures. The currently available parametric models show a high level of complexity and generally suffer from parameter crosstalk and local minimum confinement if the initial estimates are not precisely provided. We address these issues here and propose a solution by adopting a new explicit parametrisation. Methods. The mismatch between the optical axis and the local zenith direction requires a geometric description that includes two centres of symmetry that lie very close to each other on the focal plane, causing an unreliable estimate of the related parameters. The introduction of new physical coordinates overcomes these issues, allowing a direct and independent estimation. We assessed the performances of different centroiding algorithms in the experimental conditions of an undersampled point spread function of reference stars and saturated bolides on video records. We implemented the algorithm for an automatic identification of bright sources on calibration frames and subsequent correlation with catalogue positions using astrometric projections of increasing complexity. Results. The algorithm and the new parametrisation of the astrometric solution are tested against real data from the PRISMA Italian fireball network and ensure good convergence properties for all cameras we tested so far. By processing astrometric data with a few months' statistics, we can achieve a random projection indeterminacy of the order of 10 arcsec, which is negligible with respect to single measurement errors on the bolide position. [ABSTRACT FROM AUTHOR]

We have characterised the Perseid meteoroid stream from data acquired in a series of observing campaigns between 2010 and 2016. The data presented in this work were obtained by the Smart Panoramic Optical Sensor Head (SPOSH), an all-sky camera system designed to image faint transient noctilucent phenomena on dark planetary hemispheres. For the data reduction, a sophisticated software package was developed that utilises the high geometric and photometric quality of images obtained by the camera system. We identify 934 meteors as Perseids, observed over a long period between late July (~124°) and mid-to-late August (~147°). The maximum meteor activity contributing to the annual shower was found at λ⊙ = 140°.08 ± 0°.07. The radiant of the shower was estimated at RA = 47°.2 and Dec = 57°.5 with a median error of 0°.6 and 0°.2, respectively. The mean population index of the shower between solar longitudes of 120°.68 and 145°.19 was r = 2.36 ± 0.05, showing strong temporal variation. A predicted outburst in shower activity for the night of August 11–12, 2016 was confirmed, with a peak observed 12.75 hr before the annual maximum at 23:30 ± 15′ UT. We measure a peak flux of 6.1 × 10−4 km−2 hr−1 for meteoroids of mass 1.6 × 10−2 g or more, appearing in the time period between 23:00 and 00:00 UT. We estimate the measured flux of the outburst meteoroids to be approximately twice as high as the annual meteoroid flux of the same mass. The population index of r = 2.19 ± 0.08, computed from the outburst Perseids in 2016, is higher than the value of r = 1.92 ± 0.06 derived from meteors observed in 2015 belonging to the annual Perseid shower which was active near the time of the outburst. A dust trail with an unusually high population index of r = 3.58 ± 0.24 was encountered in 2013 between solar longitudes 136°.261 and 137°.442. The relatively high r-value implies an encounter with a dust trail rich in low-mass particles. [ABSTRACT FROM AUTHOR]

Context. In the early 1990s, contemporary interstellar dust penetrating deep into the heliosphere was identified with the in situ dust detector on board the Ulysses spacecraft. Later on, interstellar dust was also identified in the data sets measured with dust instruments on board Galileo, Cassini, and Helios. Ulysses monitored the interstellar dust stream at high ecliptic latitudes for about 16 yr. The three other spacecraft data sets were obtained in the ecliptic plane and cover much shorter time intervals. Aims. To test the reliability of the model predictions, we compare previously published in situ interstellar dust measurements, obtained with these four spacecraft, with predictions of an advanced model for the dynamics of interstellar dust in the inner solar system (Interplanetary Meteoroid environment for EXploration; IMEX). Methods. Micrometer and sub-micrometer-sized dust particles are subject to solar gravity, radiation pressure and the Lorentz force on a charged dust particle moving through the interplanetary magnetic field. These forces lead to a complex size-dependent flow pattern of interstellar dust in the planetary system. The IMEX model was calibrated with the Ulysses interstellar dust measurements and includes these relevant forces. We study the time-resolved flux and mass distribution of interstellar dust in the solar system. Results. The IMEX model agrees with the spacecraft measurements within a factor of 2–3, including time intervals and spatial regions not covered by the original model calibration with the Ulysses data set. The model usually underestimates the dust fluxes measured by the space missions which were not used for the model calibration, i.e. Galileo, Cassini, and Helios. Conclusions. A unique time-dependent model, IMEX is designed to predict the interstellar dust fluxes and mass distributions for the inner and outer solar system. The model is suited to study dust detection conditions for past and future space missions. [ABSTRACT FROM AUTHOR]

Context. A significant fraction of small meteors are produced by iron meteoroids. Their origin and the interaction with the atmosphere have not been well explained up to now. Aims. The goals of the study are to observe faint, slow, low altitude meteors, to identify candidates for iron meteoroids among them, to model their ablation and light curves, and to determine their properties. Methods. Double station video observations were used for the determination of atmospheric trajectories, heliocentric orbits, light curves, and spectra of meteors. Meteors with iron spectra or of suspected iron composition based on beginning heights and light curves were modeled. The immediate removal of liquid iron from the surface as a cloud of droplets with Nukiyama–Tanasawa size distribution and their subsequent vaporization was assumed as the main ablation process on the basis of our previous work. The numerical model has only five parameters: meteoroid initial velocity v∞, zenith distance z, initial mass m∞, mean drop size Ddr, and luminous efficiency τ. The theoretical light curves were compared with the observed ones. Results. The model is able to explain the majority of the selected light curves, and meteoroid parameters that are not directly observable – m∞, Ddr, and τ – are determined. Unlike in most meteor studies, the mass and luminous efficiency are determined independently. Luminous efficiency ranges from 0.08 to 5.8%; it weakly decreases with increasing initial meteoroid mass. No simple dependency on initial velocity was found. The mean size of iron drops depends on the meteoroid velocity. Slower meteoroids can produce drops with a wide range of mean sizes, whereas faster ones are better matched with larger drops with a smaller dispersion of sizes. [ABSTRACT FROM AUTHOR]

Aims. We present a study of the meteor complex of the short-period comet 2P/Encke. Methods. For five perihelion passages of the parent comet in the past, we modeled the associated theoretical stream. Specifically, each of our models corresponds to a part of the stream characterized with a single value of the evolutionary time and a single value of the strength of the Poynting–Robertson effect. In each model, we follow the dynamical evolution of 10 000 test particles via a numerical integration. The integration was performed from the time when the set of test particles was assumed to be ejected from the comet's nucleus up to the present. At the end of the integration, we analyzed the mean orbital characteristics of those particles that approached the Earth's orbit, and thus created a meteor shower or showers. Using the mean characteristics of the predicted shower, we attempted to select its real counterpart from each of five considered databases (one photographic, three video, and one radio-meteor). If at least one attempt was successful, the quality of the prediction was evaluated. Results. The modeled stream of 2P approaches the Earth's orbit in several filaments with the radiant areas grouped in four cardinal directions of ecliptical showers. These groups of radiant areas are situated symmetrically with respect to the apex of the Earth's motion around the Sun. Specifically, we found that showers #2, #17, #156, #172, #173, #215, #485, #624, #626, #628, #629, #632, #634, #635, #636, and #726 in the IAU-MDC list of all showers are dynamically related to 2P. In addition, we found five new 2P-related showers in the meteor databases considered. [ABSTRACT FROM AUTHOR]

Context. Several new meteor showers are added to the International Astronomical Union (IAU) list of meteor showers every year. Given the multiplication of video meteor measurements new parent bodies are to be found in addition to new showers. Such an endeavor is usually performed by comparing orbital elements, using a high threshold single-linking Dsh-criterion. However, questions remain about the accuracy of the method and the veracity of the newly associated parent bodies. Aims. Our goal is to find the presence of new parent bodies in a statistical meaningful way. Methods. A search for parent bodies was performed among SonotaCo and EDMOND databases. The association of asteroids with meteors was based on different methods, discussed and compared below. In addition, a thorough statistical test was performed in order to investigate the possible random associations. Results. A list of potential new parent bodies associated with at least 50 meteors is found. A statistical test was used to show whether the group of meteor orbits and the asteroid is a random coincidence or not. Out of 54 potential new parent bodies, only three new parent bodies are not excluded by the statistical test: 2014 BN14, 2015 TX24 and 2015 QT3, with a probability of chance occurrence of 37, 10 and 13%, respectively. This shows the need for rigorous method when searching for the existence of meteor showers and parent bodies. Conclusions. Ideally, such a test (or even better, tests) should be conducted in order to confirm (or not) the current IAU list of meteor showers. Similarly, all meteor orbit data in our databases should ideally be revisited using the latest methods providing a better estimate of the real uncertainty and accuracy of the derived orbits. [ABSTRACT FROM AUTHOR]

Context. The discovery and tracking of 2018 LA marks only the third instance in history that the parent body of a fireball has been identified before its eventual disintegration in our atmosphere. The subsequent recovery of meteorites from 2018 LA was only the second time materials from outer space that reached the ground could be linked with certitude to a particular minor body. However, meteoroids like 2018 LA and its forerunners, 2008 TC3 and 2014 AA, are perhaps fragments of larger members of the near-Earth object (NEO) population. As the processes leading to the production of such fragments are unlikely to spawn just one meteoroid per event, it is important to identify putative siblings and plausible candidates from which the observed meteoroids might have originated. Aims. Here, we study the pre-impact orbital evolution of 2018 LA to place this meteoroid within the dynamical context of other NEOs that follow similar trajectories. Methods. Our statistical analyses are based on the results of direct N-body calculations that use the latest orbit determinations and include perturbations by the eight major planets, the Moon, the barycentre of the Pluto–Charon system, and the three largest asteroids. A state-of-the-art NEO orbit model was used to interpret our findings and a randomization test was applied to estimate their statistical significance. Results. We find a statistically significant excess of NEOs in 2018 LA-like orbits; among these objects, we find one impactor, 2018 LA, and the fourth closest known passer-by, 2018 UA. A possible connection with the χ-Scorpiids meteor shower is also discussed. The largest known NEO with an orbit similar to that of 2018 LA is the potentially hazardous asteroid (454100) 2013 BO73 and we speculate that they both originate from a common precursor via a collisional cascade. Conclusions. Future spectroscopic observations of 454100 and other NEOs in similar orbits may confirm or deny a possible physical relationship with 2018 LA. [ABSTRACT FROM AUTHOR]

Aims. The complex study of millimetre-sized meteoroids can reveal more about the structure and origin of population of these meteoroids. Methods. Double-station video observations, paired with spectroscopic video observations, were used to study small meteoroids. In total 152 sporadic and shower meteors of maximum brightness between magnitude −5 and +3 were analysed. Spectral classification was based on time-integrated intensities of lines of Na, Mg, and Fe. Meteor light curves and deceleration were fitted by the grain erosion model. Heliocentric orbits of all meteors were computed. Monochromatic light curves were constructed in order to study differential ablation. The length of meteor wakes was evaluated as well. Results. The variety of properties among millimetre-sized meteoroids proved different sources and histories of this material. Meteoroids that contain small grains tend to release their sodium early. For given grain sizes, the sodium in Na-poor meteoroids is released earlier than in meteors without sodium depletion. Overall, meteoroids with sodium depletion are revealed to have different structures: they have stronger material without very small grains and they do not show very bright wakes. Two iron meteoroids on Halley-type orbits were observed, thereby supporting the idea of large-scale mixing of material in the early solar system. The distribution of grain sizes of Jupiter-family members was in good agreement with results from the COSIMA instrument on the ROSETTA probe. [ABSTRACT FROM AUTHOR]

Aims. We aim to obtain an approximate analytical solution to the equations of meteoroid dynamics within the frames of the suggested mechanism of ablation due to meteoroid melt spraying. Methods. We have described the droplet breakaway of the melt in terms of hydrodynamic instability theory for the case of a shallow angle of meteoroid entry. The differential equation of meteoroid spraying was derived, together with the equation for the distribution function of sprayed particles by sizes. The latter was obtained considering two different frameworks for meteoroid motion law: empirical and theoretical. Results. The trinal problem of an ablating meteoroid is solved analytically. The approximate solution is found for the system of equations of motion, ablation and number of sprayed droplets. The latter yields the equation for the distribution function of breakaway droplets by sizes, for which the approximate solution is obtained by providing the intermediate and final number distributions. The meteoroid ablation–deceleration balance remains in the regime of dynamic ablation, when the meteoroid velocity deficit due to aerodynamic drag is negligible until the instant of almost total meteoroid destruction. The responsible "h"-criterion is found, which depends only on the physical properties of the media, so that for melts of materials with lower viscosity such as iron the balance is closer to dynamic ablation than for the stony melt. The differential equation for meteoroid spraying is derived and integrated, showing a near-linear decrease of the meteoroid radius with time. Conclusions. The proposed spraying model allows us to obtain approximate laws of meteoroid dynamics, which can serve as a base of a comprehensive study of meteor formation and evolution. The model provides intermediate and final number distributions of the breakaway droplets by sizes through direct numerical integration of the governing equations, or, alternatively, in the form of approximate relationships. The theory can be extended to the general case of a molten meteoroid entering atmosphere at an arbitrary angle. [ABSTRACT FROM AUTHOR]

Context. Both Pluto and Triton possess thin, N2-dominated atmospheres controlled by sublimation of surface ices. Aims. We aim to constrain the influx and ablation of interplanetary dust grains into the atmospheres of both Pluto and Triton in order to estimate the rate at which oxygen-bearing species are introduced into both atmospheres. Methods. We use (i) an interplanetary dust dynamics model to calculate the flux and velocity distributions of interplanetary dust grains relevant for both Pluto and Triton and (ii) a model for the ablation of interplanetary dust grains in the atmospheres of both Pluto and Triton. We sum the individual ablation profiles over the incoming mass and velocity distributions of interplanetary dust grains in order to determine the vertical structure and net deposition of water to both atmospheres. Results. Our results show that <2% of silicate grains ablate at either Pluto or Triton while approximately 75% and >99% of water ice grains ablate at Pluto and Triton, respectively. From ice grains, we calculate net water influxes to Pluto and Triton of ~3.8 kg day−1 (8.5 × 103 H2O cm−2 s−1) and ~370 kg day−1 (6.2 × 105 H2O cm−2 s−1), respectively. The significant difference in total water deposition between Pluto and Triton is due to the presence of Triton within Neptune's gravity well, which both enhances interplanetary dust particle (IDP) fluxes due to gravitational focusing and accelerates grains before entry into Triton's atmosphere, thereby causing more efficient ablation. Conclusions. We conclude that water deposition from dust ablation plays only a minor role at Pluto due to its relatively low flux. At Triton, water deposition from IDPs is more significant and may play a role in the alteration of atmospheric and ionospheric chemistry. We also suggest that meteoric smoke and smaller, unablated grains may serve as condensation nuclei for the formation of hazes at both worlds. [ABSTRACT FROM AUTHOR]

Context. Video observations of Jupiter obtained by amateur astronomers over the past 8 years have shown five flashes of light with durations of 1–2 s, each observed by at least two observers that were geographically separated. The first three of these events occurred on 3 June 2010, 20 August 2010, and 10 September 2012. Previous analyses of their light curves showed that they were caused by the impact of objects of 5–20 m in diameter, depending on their density, with a released energy comparable to superbolides on Earth of the class of the Chelyabinsk airburst. The most recent two flashes on Jupiter were detected on 17 March 2016 and 26 May 2017 and are analyzed here. Aims. We characterize the energy involved together with the masses and sizes of the objects that produced these flashes. The rate of similar impacts on Jupiter provides improved constraints on the total flux of impacts on the planet, which can be compared to the amount of exogenic species detected in the upper atmosphere of Jupiter. Methods. We extracted light curves of the flashes and calculated the masses and sizes of the impacting objects after calibrating each video observation. We also present results from a systematic search of impacts on >72 000 video amateur observations with a customized software that is based on differential photometry of the images. An examination of the number of amateur observations of Jupiter as a function of time over the past years allows us to interpret the statistics of these impact detections. Results. The cumulative flux of small objects (5–20 m or larger) that impact Jupiter is predicted to be low (10–65 impacts per year), and only a fraction of them are potentially observable from Earth (4–25 observable impacts per year in a perfect survey). These numbers imply that many observers are required to efficiently discover Jupiter impacts. Conclusions. We predict that more impacts will be found in the next years, with Jupiter opposition displaced toward summer in the northern hemisphere where most amateur astronomers observe. Objects of this size contribute negligibly to the abundance of exogenous species and dust in the stratosphere of Jupiter when compared with the continuous flux from interplanetary dust particles punctuated by giant impacts. Flashes of a high enough brightness (comparable at their peak to a +3.3 magnitude star) could produce an observable debris field on the planet. We estimate that a continuous search for these impacts might find these events once every 0.4–2.6 yr. [ABSTRACT FROM AUTHOR]

Context. Understanding the compaction and differentiation of the planetesimals that formed during the initial phases of our solar system and the protoplanets from the asteroid belt and the terrestrial planet region of the solar system requires a reliable modelling of their internal thermal evolution. An important ingredient for this is a detailed knowledge of the heat conductivity, K, of the chondritic mixture of materials from which planetesimals are formed. The dependence of K on the composition and structure of the material was studied in the previous study of this series. For the second important aspect, the dependence of K on temperature, laboratory investigations on a number of meteorites exist concerning the temperature variation of K, but no explanation for the observed variation has been given yet. Aims. We evaluate the temperature dependence of the heat conductivity of the solid chondritic material from the properties of its mixture components from a theoretical model. This allows us to predict the temperature-dependent heat conductivity for the full range of observed meteoritic compositions and also for possible other compositions. Methods. Published results on the temperature dependence of the heat conductivity of the mineral components found in chondritic material are fitted to the model of Callaway for heat conductivity in solids by phonons. For the Ni, Fe-alloy, published laboratory data are used. The heat conductivity of chondritic material then is calculated by means of mixing rules. The role of micro-cracks is studied, which increase the importance of wall scattering for phonon-based heat conductivity. Results. Our model is applied to published data on the heat conductivity of individual chondrites. The general trends for the dependency of K on temperature found in laboratory experiments can largely be reproduced for the set of meteorites if the heat conductivity is calculated for a given composition from the properties of its constituents. It is found that micro-cracks have a significant impact on the temperature dependence of K because of their reduction of phonon scattering length [ABSTRACT FROM AUTHOR]