There are hundreds of millions of asteroids in our solar system, which means that new asteroids are discovered quite often. It also means that encounters between asteroids and Earth are quite common. Some of these encounters end with the asteroid impacting the Earth, sometimes with dire consequences.
A recently discovered asteroid, called 2023 BU, made headlines for passing very close to Earth today.
Discovered Jan. 21 by amateur astronomer Gennadiy Borisov in Crimea, 2023 BU passed only about 3,600 km from Earth’s surface (near the southernmost tip of South America) six days later, on Jan. 27.
That distance is just a little further than the distance between Perth and Sydney and is only about 1 percent of the distance between Earth and our moon.
The asteroid also passed through the region of space that contains a significant portion of man-made satellites in orbit.
All this makes 2023 BU the fourth-closest known asteroid encounter to Earth, ignoring events that have affected the planet or our atmosphere.
How does BU rate 2023 as an asteroid and a threat? 2023 BU is unremarkable, except that it came so close to Earth. The diameter of the asteroid is estimated to be only 4-8 m, which is on the small side of the asteroid size range.
There are probably hundreds of millions of such objects in our solar system, and BU 2023 may have come close to Earth many times before in the past millennia. Until now we have not been aware of this.
In this context, an asteroid with a diameter of 4 meters will impact the Earth every year on average, and an asteroid with a diameter of 8 meters approximately every five years. the atmosphere. They produce spectacular fireballs and some asteroids can crash to the ground as meteorites.
Now that 2023 BU has been discovered, its orbit around the sun can be estimated and future visits to Earth can be predicted. It is estimated that there is a 1 in 10,000 chance that 2023 BU will hit Earth sometime between 2077 and 2123.
So we have little to fear from 2023 BU or any of the many millions of similar objects in the solar system.
Asteroids must be larger than 25 meters in diameter to pose a significant risk to life upon impact with Earth; to challenge the existence of civilization, they would have to be at least a kilometer in diameter.
It is estimated that there are fewer than 1,000 such asteroids in the solar system and they could impact Earth every 5,00,000 years. We know more than 95 percent of these objects.
Will there be more nearby asteroid passes? 2023 BU was the fourth closest pass of an asteroid ever recorded. The three smaller passes were made by very small asteroids discovered in 2020 and 2021 (2021 UA, 2020 QG, and 2020 VT).
Asteroid 2023 BU and countless other asteroids have been very close to Earth during the nearly five billion years of the solar system’s existence, and this situation will continue into the future.
What has changed in recent years is our ability to detect asteroids of this size so that any threats can be characterized. That an object about 5 meters in size can be detected many thousands of kilometers away by a highly dedicated amateur astronomer shows that the technology for making important astronomical discoveries is within the reach of the general public. This is very exciting.
Amateurs and professionals can continue to discover and categorize objects together, so that threat analyzes can be done. Another very exciting recent development came last year, through the Double Asteroid Redirection Test (DART) mission, which successfully collided a spacecraft with an asteroid and reversed direction.
DART makes plausible the concept of diverting an asteroid away from a collision course with Earth if a threat assessment identifies a serious risk with sufficient warning.