Fragmentation pair of meteors in the early morning of May 9, 2025

In the early morning hours of 9 May 2025 (01:55:58 and 01:56:00 UT), two meteors were captured by stations of the CEMeNt ( Central European Meteor Network ) network, appearing just two seconds apart. Both meteors belonged to the Eta Aquarid meteor stream. This type of event—when several meteors appear within a very short time interval and from the same stream—is called a meteor cluster. It is an important phenomenon that may indicate fragmentation of individual particles in the atmosphere or in orbit, or a dense structure within a filament of the meteor stream.

A meteor cluster is a group of meteors that appear within a very short time interval (typically < 10 s), share the same or very similar radiant, and have very similar orbits. A cluster can form by fragmentation of a larger particle just before atmospheric entry or in the upper atmosphere (an atmospheric cluster), or it can be an orbital cluster where fragments follow similar orbits and enter the atmosphere simultaneously due to a higher particle density in a meteor filament. The minimum number of meteors considered a cluster is not strictly defined; it depends on context (observations, statistical analysis, physical interpretation).

In general, for meteor streams or substructures (e.g., filaments), a cluster is defined as a group of at least 3 meteors with very similar orbital elements (e.g., D-criteria < 0.05–0.10) that are close in time and space (radiant, time of passage, etc.). A physical interpretation (e.g., meteoroid fragmentation) may also be possible. If the meteors originated by fragmentation during flight in the upper atmosphere or just before entering it, then a cluster is understood as a group of at least 2 or 3 meteors that pass very close together in time (often within 1 s), have parallel trajectories, and have similar heights and velocities.

Meteor CM20250509_015558 crossed the sky over central Slovakia on 9 May 2025 at 01h55m58.4 ± 0.1 s UT, i.e., shortly before 4 a.m. Central European Summer Time (CEST). Within the CEMeNt network, the meteor was recorded directly on five wide-angle cameras (Fig. 1–5). The flight record is available from the stations Valašské Meziříčí SE (CZ, Valašské Meziříčí Observatory), Maruška SE (CZ, Jakub Koukal), Ždánice E (Ždánice Observatory), Vsetín E (Vsetín Observatory), and Jablonec N (SK, Jakub Kapuš). The meteor’s brightness was not sufficient for its spectrum to be recorded by spectrographs at the Valašské Meziříčí Observatory.

Meteor CM20250509_015600 crossed the sky over central Slovakia on 9 May 2025 at 01h56m00.6 ± 0.1 s UT, i.e., shortly before 4 a.m. CEST. Within the CEMeNt network, the meteor was recorded directly on five wide-angle cameras (Fig. 1–5). The flight record is available from the stations Valašské Meziříčí SE (CZ, Valašské Meziříčí Observatory), Maruška SE (CZ, Jakub Koukal), Ždánice E (Ždánice Observatory), Vsetín E (Vsetín Observatory), and Jablonec N (SK, Jakub Kapuš). The meteor’s brightness was not sufficient for its spectrum to be recorded by spectrographs at the Valašské Meziříčí Observatory.

Atmospheric trajectory, radiant, and heliocentric orbit of the fireball

All recordings were used to compute the atmospheric trajectories of meteors CM20250509_015558 and CM20250509_015600 and the meteoroid orbits in the Solar System. Recording at these stations was done with UFO Capture HD, processing in UFO Analyzer v4.32, and computation of the atmospheric and heliocentric orbits in UFO Orbit v2.63.

The initial height of the ablation path of meteor CM20250509_015558 was 122.1 km above Earth’s surface; the body entered the atmosphere at a speed of 67.20 km/s. The end of the ablation path was at an altitude of 91.5 km (Fig. 6, 7). The meteor reached an absolute magnitude of −3.48 ^m and covered a distance of 103.1 km in Earth’s atmosphere during 1.56 s of flight. The body, with an initial mass of 0.65 g, entered Earth’s atmosphere at a shallow angle of 17.05°, it was a fast meteor; the geocentric speed of the meteoroid was 65.99 km/s. The body belonged to the Eta Aquarid meteor stream and, prior to atmospheric entry, moved on an elongated retrograde orbit (Fig. 8, Tab. 1) with high eccentricity e = 0.9501, low inclination to the ecliptic i = 163.186°, and perihelion distance q = 0.6113 AU. The body was of cometary origin and belonged to the HT (LPC) group, i.e., meteoroids with cometary origin and long-period parent bodies (the 1P/Halley comet group); in this case the parent body was directly comet 1P/Halley.

The initial height of the ablation path of meteor CM20250509_015600 was 117.2 km above Earth’s surface; the body entered the atmosphere at a speed of 67.31 km/s. The end of the ablation path was at an altitude of 99.1 km (Fig. 6, 7). The meteor reached an absolute magnitude of −0.71 ^m and covered a distance of 62.9 km in Earth’s atmosphere during 0.95 s of flight. The body, with an initial mass of 0.04 g, entered Earth’s atmosphere at a shallow angle of 16.79°, it was a fast meteor; the geocentric speed of the meteoroid was 66.24 km/s. The body belonged to the Eta Aquarid meteor stream and, prior to atmospheric entry, moved on an elongated retrograde orbit (Fig. 8, Tab. 1) with high eccentricity e = 0.9588, low inclination to the ecliptic i = 163.625°, and perihelion distance q = 0.6037 AU. The body was of cometary origin and belonged to the HT (LPC) group, i.e., meteoroids with cometary origin and long-period parent bodies (the 1P/Halley comet group); in this case the parent body was directly comet 1P/Halley.

Conclusion

The first criterion evaluated was the probability of random occurrence of the event. Using a Monte Carlo simulation, we calculated the probability that under the given conditions (meteor occurrence rate, camera field of view, total observation time, the ratio of Eta Aquarid meteors to sporadic meteors in the time range considered) two meteor events with a time separation ≤ 2.2 seconds could occur in a random distribution of a total of 12 meteors during one hour of observation time, with both belonging to the Eta Aquarid meteor stream. The number of simulation runs was set to 10,000 and the resulting probability of the defined event was 1.6%. The second criterion evaluated was the similarity of the meteors’ heliocentric orbits; we used the Drummond (D _D ) and Southworth–Hawkins (D _SH ) orbital similarity criteria. The value of Drummond’s criterion was 0.008 and for Southworth–Hawkins it was 0.018. The commonly used limits for fragments originating from a single body by atmospheric fragmentation are D _D < 0.01 and D _SH < 0.02. These values confirm a very close relationship between the two fragments. Based on the low probability of random occurrence, agreement in flight direction, extremely similar orbits, and very low mechanical strength of both particles, it can be said with high probability that this is a real fragmentation pair—likely fragments of a single meteoroid that broke up before entering the atmosphere.

Acknowledgements

Thanks go to the companies DEZA , a.s., and CS CABOT , s.r.o., which contributed to the acquisition of equipment for FHD stations located at the Valašské Meziříčí Observatory and within the CEMeNt network. We also thank all partner observatories (Ždánice, Vsetín, Rokycany, Plzeň, Karlovy Vary, Partizánske, Kysucké Nové Mesto) and private station owners (Milan Čermák, Richard Kačerek, Jakub Kapuš, Tibor Csorgei, Vladimír Bahýl) for supporting the activities and growth of the network. Further thanks go to all involved institutions for supporting the network’s activities and growth. The RPOS project (Development of a cross-border observation network) was co-financed by the Small Project Fund of the Interreg V-A Slovakia–Czech Republic 2014–2020 programme, call code 5/FMP/11b, reg. no. CZ/FMP/11b/05/058. The projects KOSOAP (Cooperating Network in the Field of Astronomical Professional-Observational Programmes) and RPKS (Development of a Cross-Border Cooperating Network for Professional Work and Education) were implemented by the Valašské Meziříčí Observatory (CZ) and Kysucké Nové Mesto (SK) in cooperation with the SMPH (Society for Interplanetary Matter). The projects were co-financed by the Microprojects Fund of the Cross-Border Cooperation Operational Programme Slovakia–Czech Republic 2007–2013. The project for the purchase and operation of high-resolution spectroscopic cameras is partially funded by the Programme for Regional Cooperation of the Czech Academy of Sciences, reg. no. R200402101.