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A meteor outburst consisting of at least 22 meteors above the Baltic sea and southern Scandinavia that occurred on 30 October 2022 was recorded using multiple cameras. A bright fireball was followed by fainter meteors over a 10 second period. All the meteors were travelling on parallel trajectories. The goal of this study is to determine the atmospheric trajectories and photometric masses of meteors and to use these data to determine the specifics of the progenitor meteoroid break-up and cluster formation. Double and triple-station observations using video cameras were used for the calculation of the atmospheric trajectories and photometric masses of the meteors. Their relative positions and mass distribution were then used to determine the time and cause of the meteoroid fragmentation. The relative position of the cluster particles in the atmosphere and the distribution of their masses best correspond to the separation of the smaller fragments from the mass-dominant fragment 10.6$\pm$1.7 days before the collision with Earth, assuming a meteoroid bulk density of 1000 kg.m$^{-3}$. The ejection velocities are in the range 0.16-0.61 m.s$^{-1}$. The directions of the ejection velocities are bounded by a cone with an apex angle of $43^\circ$. The axis of this cone has ecliptic coordinates of $l=154^\circ$ and $b=26^\circ$ and is $66^\circ$ away from the direction to the Sun. Thermal stresses appear to be the most likely cause of such meteor cluster formation., Comment: 10 pages, 5 figures

We follow our previous work about the September epsilon Perseid (SPE) meteoroid cluster from 2016. We assumed that the mass-dominated meteoroid is the parent body of the cluster and that the observed positions of meteoroids are controlled by the ejection velocities and the action of solar radiation pressure. A formula for the dependence of meteoroid ejection velocities on the mutual positions, masses, and cluster age was derived. Knowing values and directions of ejection velocities together with meteoroid masses then allowed us to determine the most likely process of cluster formation. The meteoroids occupy a volume of 66$\times$67$\times$50 km and are shifted in the antisolar direction by 27 km relative to the parent meteoroid. The age of the cluster is 2.28$\pm$0.44 days. The ejection velocities range from 0.13$\pm$0.05 m/s to 0.77$\pm$0.34 m/s with a mean value of 0.35 m/s. The ejection velocity directions are inside the cone with an apex angle of 101$\pm$5$^\circ$. The axis of the cone is $\sim$45$^\circ$ away from the solar direction and $\sim$34$^\circ$ away from the mean direction of the flux of small meteoroids' incident on the parent meteoroid. Formation due to the separation of part of the surface due to very fast rotation is the least likely thing to occur. We estimate the rotation frequency to be about 2 Hz and the corresponding stress is several orders of magnitude lower than the predicted strength limit. It is also difficult to explain the formation of the cluster by an impact of a small meteoroid on the parent body. However, this possibility, although not very likely, cannot be completely ruled out. The most probable process is the exfoliation due to thermal stresses. Their estimated magnitude is sufficient and the derived ejection velocities are consistent with this process of formation., Comment: 11 pages, 5 figures, 2 tables. Accepted in Astronomy and Astrophysics

The question of the existence of pairs and groups among the meteor showers is opened for a long time. The double station video observation of the 2006 Geminid meteor shower, one of the most active annual showers, is used for the search of such events. The atmospheric trajectories of the observed meteors, photometric masses, and both time and spatial distances of meteoroids in the atmosphere were determined using a double station video observation. Time gaps among them were analysed statistically. The Monte Carlo simulation was used for the determination of the probability of random pairings. Higher than expected number of candidates for pairs was found among 2006 Geminids. Evaluation of Poisson distribution shows that a significant fraction of them may be real cases. However, the Monte Carlo simulation did not confirm this result and provided a different view. Analysis of geometrical positions of candidate pairs also did not support the presence of real pairs and groups. Although we cannot exclude that some of them may be physically connected pairs, all the observed cases can be explained as the coincidental appearance of unrelated meteors., Comment: 8 pages, 7 figures, 3 tables, accepted for publication in A&A

Bulk and grain density, porosity, and magnetic susceptibility of 67 individuals of Ko\v{s}ice H chondrite fall were measured. The mean bulk and grain densities were determined to be 3.43 g/cm$^\text{3}$ with standard deviation (s.d.) of 0.11 g/cm$^\text{3}$ and 3.79 g/cm$^\text{3}$ with s.d. 0.07 g/cm$^\text{3}$, respectively. Porosity is in the range from 4.2 to 16.1%. The logarithm of the apparent magnetic susceptibility (in 10$^\text{-9}$ m$^\text{3}$/kg) shows narrow distribution from 5.17 to 5.49 with mean value at 5.35 with s.d. 0.08. These results indicate that all studied Ko\v{s}ice meteorites are of the same composition down to ~g scale without presence of foreign (non-H) clasts and are similar to other H chondrites. Ko\v{s}ice is thus a homogeneous meteorite fall derived from a homogeneous meteoroid.

The aim of this study is to estimate the rotational characteristics of meteoroids after their release from a comet during normal activity. The results can serve as initial conditions for further analyses of subsequent evolution of rotation in the interplanetary space. A sophisticated numerical model was applied to meteoroids ejected from 2P/Encke comet. The meteoroid shapes were approximated by polyhedrons with several thousands of surface elements, which have been determined by 3D laser scanning method of 36 terrestrial rock samples. These samples came from three distinct sets with different origin and shape characteristics. Two types of gas-meteoroid interactions (diffuse and specular reflection of gas molecules from the surface of meteoroid) and three gas ejection models (leading to very different ejection velocities) were assumed. The rotational characteristics of ejected meteoroid population were obtained by numerical integration of equations of motion with random initial conditions and random shape selection. It was proved, that the results do not depend on specific set of shape models and that they are applicable to (unknown) shapes of real meteoroids. A simple relationship between median of meteoroid spin frequencies $\bar{f}$ (Hz), ejection velocities $v_{\rm ej}$ (m s$^{-1}$) and sizes $D$ (m) was determined. For diffuse reflection of gas molecules from meteoroid's surface it is: $\bar{f}\simeq 2\times 10^{-3} v_{\rm ej} D^{-0.88}$, and for specular reflection of gas molecules from meteoroid's surface it is: $\bar{f}\simeq 5\times 10^{-3} v_{\rm ej} D^{-0.88}$. The distribution of spin frequencies is relatively wide; $2\sigma$-interval can be described as $\sim(0.1, 10)\times \bar{f}$. The results were determined for 2P/Encke comet, but it was shown that their validity is general.