# 2023 BU

2023 BU is a near-Earth object that passed 9,967 ± 1 km (6,193.21 ± 0.62 mi) from the centerpoint of Earth around 27 January 2023 00:29 UT. Since Earth's radius is about 6,378 km (3,963 mi), it was expected to pass approximately 3,589 ± 1 km (2,230.10 ± 0.62 mi) from the surface of Earth over the southern tip of South America. It passed at an altitude above low Earth orbit which is 2,000 km (1,200 mi) and below geostationary orbit which is 36,000 km (22,000 mi). The asteroid is about 3–8 meters in diameter and approached Earth from the night sky. It is the fourth closest non-impacting approach known to Earth (excluding Earthgrazers) after 2020 VT4, 2020 QG, and 2021 UA1.

## Orbital details

The asteroid came to perihelion (closest approach to the Sun) on 27 January 2023, four hours after closest approach with Earth. 2023 BU was first imaged by Gennadiy Borisov at Nauchnyi, Crimea, on 21 January 2023 23:53 UT, about five days before closest approach. It was last observed on 31 January 2023.
2023 BU closest Earth approach on 2023-Jan-27 00:29 UT :
| Date and time of closest approach | Earth distance (AU) | Sun distance (AU) | Velocity wrt Earth (km/s) | Velocity wrt Sun (km/s) | Uncertainty region (3-sigma) | Reference |
| 2023-01-27 00:29 | 0.000067 AU (10,000 km; 0.0261 LD) | 0.985 AU (147.4 million km; 383 LD) | 9.3 | 35.2 | ± <1 km | Horizons |
The gravitational effect of the 2023 Earth approach will increase the orbital period from 359 days to an estimated 425 days. It will lift the perihelion and aphelion distances. The relatively low Earth encounter speed of 9.3 km/s (21,000 mph) is a result of a low eccentricity and Earth-like orbit.
Orbital elements :
| Parameter | Epoch | Period (p) | Aphelion (Q) | Perihelion (q) | Semi-major axis (a) | Eccentricity (e) | Inclination (i) |
| Units | | (days) | AU | AU | AU | | (°) |
| Pre-flyby | 2022-Oct-25 | 358.9 | 1.05 | 0.926 | 0.988 | 0.063 | 2.35° |
| Post-flyby | 2023-Feb-25 | 425.4 | 1.23 | 0.984 | 1.11 | 0.111 | 3.75° |

## Impact assessment

There was no risk of an Earth impact during the 2023 Earth approach. Assuming the asteroid is at the larger size estimate of 8 meters in diameter, if it had entered the atmosphere it would not have reached the ground intact and would breakup around 30 km above the ground, thus representing only minimal threat to life.
Impacts by objects 8 meters (26 ft) in diameter occur, on average, every 5 years; impacts by objects 4 meters (13 ft) in diameter happen, on average, once every year. 2023 BU has a 1 in 17 million chance of impacting Earth on 20 January 2110.
History of 2023 BU closest approach uncertainties for the 3500–3600 km pass of Earth's surface :
| JPL SBDB solution | Observation arc | Date and time of closest approach | Uncertainty region (3-sigma) |
| JPL 1 | 1 day (25 obs) | 2023-01-26 21:17 ± 02:22 | ± 2,600 km |
| JPL 2 | 2 days (30 obs) | 2023-01-27 00:17 ± 01:05 | ± 1,700 km |
| JPL 3 | 3 days (42 obs) | 2023-01-27 00:28 ± 00:10 | ± 262 km |
| JPL 4 | 3 days (39 obs) | 2023-01-27 00:26 ± 00:10 | ± 260 km |
| JPL 5 | 4 days (65 obs) | 2023-01-27 00:28 ± 00:02 | ± 29 km |
| JPL 6 | 4 days (61 obs) | 2023-01-27 00:28 ± 00:02 | ± 27 km |
| JPL 9 | 5 days (121 obs) | 2023-01-27 00:29 ± <00:01 | ± 5 km |
| JPL 11 | 5 days (143 obs) | 2023-01-27 00:29 ± <00:01 | ± 2 km |
| JPL 12 | 6 days (166 obs) | 2023-01-27 00:29 ± <00:01 | ± 0.3 km |
| JPL 13 | 6 days (191 obs) | 2023-01-27 00:29 ± <00:01 | ± 0.2 km |
| JPL 14 | 6 days (194 obs) | 2023-01-27 00:29 ± <00:01 | ± 0.19 km |
| JPL 15 | 6 days (199 obs) | 2023-01-27 00:29 ± <00:01 | ± 0.18 km |
| JPL 19 | 10 days (231 obs) | 2023-01-27 00:29 ± <00:01 | ± 0.15 km |
| JPL 21 | 10 days (238 obs) | 2023-01-27 00:29 ± <00:01 | ± 0.13 km |
Closest non-impacting asteroids to Earth, except Earth-grazing fireballs (using JPL SBDB numbers and Earth radius of 6,378 km) :
| Asteroid | Date | Distance from surface of Earth | Uncertainty in approach distance | Observation arc | Reference |
| 2020 VT4 | 2020-11-13 17:21 | 368 km | ±11 km | 5 days (34 obs) | data |
| 2020 QG | 2020-08-16 04:09 | 2939 km | ±11 km | 2 days (35 obs) | data |
| 2021 UA1 | 2021-10-25 03:07 | 3049 km | ±10 km | 1 day (22 obs) | data |
| 2023 BU | 2023-01-27 00:29 | 3589 km | ±<1 km | 10 days (231 obs) | data |
| 2011 CQ1 | 2011-02-04 19:39 | 5474 km | ±5 km | 1 day (35 obs) | data |
| 2019 UN13 | 2019-10-31 14:45 | 6235 km | ±189 km | 1 day (16 obs) | data |
| 2008 TS26 | 2008-10-09 03:30 | 6260 km | ±970 km | 1 day (19 obs) | data |
| 2004 FU162 | 2004-03-31 15:35 | 6535 km | ±13000 km | 1 day (4 obs) | data |