A box-truck-sized asteroid has made one of the closest approaches by a near-Earth object ever recorded, brushing past our home world at a distance of a couple of thousand miles on Thursday.

Codenamed 2023 BU, the space rock is estimated to be between 11.5 and 28 feet (3.5 to 8.5 metres) across. Although it's fairly sizable, most of the asteroid would burn up in our atmosphere, with any larger surviving parts falling as meteorites, if it were to barrel head-first into Earth.

The asteroid thus didn't and doesn't pose any danger. NASA earlier confirmed 2023 BU will not hit Earth. Astronomers observed the object and calculated the risk using the Scout impact hazard assessment system, which takes into account various factors including an asteroid's trajectory, size, and speed.

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"Scout quickly ruled out 2023 BU as an impactor, but despite the very few observations, it was nonetheless able to predict that the asteroid would make an extraordinarily close approach with Earth," Davide Farnocchia, a navigation engineer at NASA's Jet Propulsion Laboratory, who developed Scout, [2]said earlier this week.

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"In fact, this is one of the closest approaches by a known near-Earth object ever recorded."

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2023 BU was expected to fly over the southern tip of South America at about 1627 PST on January 26 (0027, January 27 UTC), coming as close as 2,200 miles (3,500 kilometres) above Earth's surface at a distance well within that of geosynchronous satellites in low-Earth orbit. Despite its startlingly close proximity, the cosmic boulder was only just discovered by amateur astronomer Gennadiy Borisov.

Borisov spotted the speeding space rock on January 21 from the MARGO observatory in Crimea, Ukraine. His findings were later [9]confirmed by the Minor Planet Center and other astronomers around the world. Borisov is no stranger to discovering strange new objects: he found the [10]comet 2I/Borisov, a rogue interstellar visitor that likely came from outside the Solar System, in 2019.

To be fair to boffins, asteroids are difficult to spot; they are often small and dark. Emitting no light of their own, astronomers find it hard to clock them and the rocks are often obscured by the glare of our Sun. The best chance of seeing one is during twilight hours when sunlight is dimmer.

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All asteroids' orbits are warped slightly when they come close to Earth due to its gravitational influence. Since 2023 BU was expected to fly incredibly close to our planet, scientists predicted its orbit will stretch from a circular one to a more elongated oval shape, and be pushed slightly out halfway between Earth and Mars' orbits. The asteroid takes about 359 days to circle the Sun, and that will increase to 425 days after its encounter with our planet. ®

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[2] https://www.jpl.nasa.gov/news/nasa-system-predicts-small-asteroid-to-pass-close-by-earth-this-week

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[5] https://www.theregister.com/2023/01/25/space_dust_asteroid/

[6] https://www.theregister.com/2022/06/29/asteroid_earth_impact_esa/

[7] https://www.theregister.com/2022/02/02/second_earth_trojan_asteroid_confirmed/

[8] https://www.theregister.com/2022/10/12/dart_spacecraft_asteroid_deflection/

[9] https://www.minorplanetcenter.net/mpec/K23/K23B72.html

[10] https://www.jpl.nasa.gov/news/newly-discovered-comet-is-likely-interstellar-visitor

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