The asteroid 2023 BU came as close to Earth as it can get in the night of 26 to 27 January without hitting it. At an altitude of only about 3600 kilometres, the Brocken passed the southern tip of South America at half past two o'clock in the morning German time – this is only about a tenth of the distance to weather and communication satellites on geosynchronous orbits. According to an analysis by NASA's "Scout" system to assess the danger posed by near-Earth asteroids, however, there was no danger that 2023 BU would actually hit Earth. And even if it did, the rock would be harmless – with its estimated diameter of 3.5 to 8.5 meters, it would have burned up almost completely in the atmosphere.
Because the good piece is so small, the Asteroid 2023 BU was only discovered shortly before his flight. On January 21, the Russian amateur astronomer Gennadi Borisow felt him in the sky, in the following days by other observatories also observed him, so that his track could be determined exactly enough to exclude an impact on Earth. Borisow is known as the discovery of the somewhat more spectacular object 2i/Borisov, an interlocking comet that appeared in the solar system in 2019. In contrast, his new discovery should attract little attention.
Conversely, however, the close encounter with Earth had dramatic consequences for BU 2023. The planet's gravity changed its orbit significantly – the asteroid performed an involuntary swing-by maneuver. So far, the asteroid orbited the Sun in 359 days on an almost circular, Earth-like orbit. After the encounter, according to calculations by NASA experts, it will orbit on an elliptical orbit whose furthest point from the Sun is about halfway between the orbits of Earth and Mars. One orbit will then last 425 days.
