Slightly before 10.50 pm Central European Time (slightly before 9.50 pm GMT) on Saturday 20 January 2024, asteroid hunter Krisztián Sárneczky at the Piszkesteto Mountain Station of the Hungarian Konkoly Observatory observed a previously unknown asteroid on a potentially Earth-impacting trajectory. This observation was reported to the Minor Planet Center, leading other astronomers and automated tracking systems around the world to begin tracking the object, and it quickly became clear that the object was going to impact the Earth, less than two hours after its original discovery, approximately 60 km to the east of Berlin, Germany.
Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. It is possible on this occasion the object is known to have produced meteorites that reached the surface (an object visible in the sky is a meteor, a rock that falls from the sky and can be physically held and examined is a meteorite).
The asteroid is estimated to have been about a metre in diameter, and as will have exploded in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) more than 40 km above the ground. owever, this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating). These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.
On this occasion the advanced detection of the asteroid enabled accurate prediction of the area where the meteorite fragments fell, allowed meteorite hunters to narrow the search area to a few hundred meters, and a number of fragments were located in the days after the asteroid entered the atmosphere. These lacked a distinctive dark fusion crust, something seen on most but not all meteorites. On this occasion the fragments appear to be achondritic, with a light grey colour, a brecciated texture, and large white crystals which may be enstatite, a high magnesium pyroxene silicate mineral frequently found in igneous and metamorphic rocks, as well as some types of meteorite.
The asteroid was given the name 2024 BX1, which implies that it was the 48th asteroid (asteroid X1 - in numbering asteroids the letters A-Z, excluding I, are assigned numbers from 1 to 25, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 26, A2 = 51, etc., which means that X1 = (25 x 1) + 23 = 48) discovered in the second half of January 2024 (period 2024 B - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).
Asteroid 2024 BX1 is calculated to have had a 564 day (1.55 year) orbital period, with an elliptical orbit tilted at an angle of 7.29° to the plain of the Solar System which took in to 0.83 AU from the Sun (83% of the distance at which the Earth orbits the Sun) and out to 1.83 AU (1.83 times the distance at which the Earth orbits the Sun, somewhat more than the distance at which the planet Mars orbits). It is therefore classed as having been an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). Asteroid 2024 BX1 is calculated to have had 21 close encounters with the Earth before finally impacting, with the first in January 1930, and the most recent in June 2010.
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