Atmospheric entry and fragmentation of small asteroid 2024 BX1: Bolide trajectory, orbit, dynamics, light curve, and spectrum

Asteroid 2024 BX1 was the eighth asteroid discovered shortly before colliding with the Earth.The associated bolide was recorded by dedicated instruments of the European Fireball Network and the AllSky7 network on January 21, 2024 at 0:32:38-44 UT. Here we report a comprehensive analysis of this instrumentally observed meteorite fall, which occurred as predicted west of Berlin, Germany. The atmospheric trajectory was quite steep with an average slope to the Earth's surface 75.6 degrees. The entry speed was 15.20 km/s. The heliocentric orbit calculated from the bolide data agrees very well with the asteroid data. However, the bolide was fainter than expected for a reportedly meter-sized asteroid. The absolute magnitude reached -14.4 and the entry mass was estimated to 140 kg. The recorded bolide spectrum was low in iron from what an enstatite-rich meteorite was expected. Indeed, the recovered meteorites, called Ribbeck, were classified as aubrites. The high albedo of enstatite (E-type) asteroids can explain the size discrepancy. The asteroid was likely smaller than 0.5 meter and should be rather called a meteoroid. During the atmospheric entry, the meteoroid severely fragmented into much smaller pieces already at a height of 55 km under the aerodynamic pressure of 0.12 MPa. The primary fragments were then breaking-up again, most frequently at heights 39-29 km (0.9-2.2 MPa). Numerous small meteorites and up to four stones larger than 100g were expected to land. Within a few days of publishing the strewn field dozens of meteorites were found in the area we predicted.