There are hundreds of millions of asteroids in our Solar System, which means new asteroids are discovered quite frequently. It also means close encounters between asteroids and Earth are fairly common.

Some of these close encounters end up with the asteroid impacting Earth, occasionally with severe consequences.

A recently discovered asteroid, named 2023 BU, has made the news because today it passed very close to Earth. Discovered on Saturday January 21 by amateur astronomer Gennadiy Borisov in Crimea, 2023 BU passed only about 3,600km from the surface of Earth (near the southern tip of South America) six days later on January 27.

That distance is just slightly farther than the distance between Perth and Sydney and is only about 1% the distance between Earth and our Moon.

The asteroid also passed through the region of space that contains a significant proportion of the human-made satellites orbiting Earth.

All this makes 2023 BU the fourth-closest known asteroid encounter with Earth, ignoring those that have actually impacted the planet or our atmosphere.

source theconversation.com