2023 BU

Lore & Background

2023 BU was first imaged by Gennadiy Borisov at Nauchnyi, Crimea, on 21 January 2023, about five days before its closest approach. It passed at an altitude above low Earth orbit (2,000 km) and below geostationary orbit (36,000 km). The asteroid approached Earth from the night sky. Its relatively low Earth encounter speed of 9.3 km/s is a result of a low eccentricity and Earth-like orbit. The gravitational effect of the approach increased its orbital period from 359 days to an estimated 425 days and lifted its perihelion and aphelion distances. The asteroid came to perihelion four hours after closest approach with Earth.

Reader's Guide

2023 BU is significant as one of the closest known non-impacting approaches to Earth, ranking fifth after 2025 UC11, 2020 VT4, 2020 QG, and 2021 UA1. Its passage at an altitude between low Earth orbit and geostationary orbit highlights the frequency of small near-Earth objects passing within the satellite belt. The asteroid's size range of 3–8 meters means that even at the larger estimate, it would have broken up around 30 km above the ground if it had entered the atmosphere, posing only minimal threat. Its 1 in 17 million chance of impacting Earth on 20 January 2110 underscores the rarity of such events. The encounter altered its orbit, demonstrating how close passes can reshape the trajectories of small asteroids. The discovery by Gennadiy Borisov, who also discovered the interstellar comet 2I/Borisov, adds to the object's legacy as a well-observed near-Earth object.

Did You Know?

• 2023 BU passed about 3,589 km from Earth's surface over the southern tip of South America.
• The asteroid's orbital period increased from 359 days to 425 days due to the Earth encounter.
• If it had entered the atmosphere at 8 meters diameter, it would have broken up around 30 km altitude.